United States Office of Water EP A-822-B00-001 Environmental Protection Office of Science and T echnologyApril 2000 AgencyWashington, DC 20460 www .epa.gov 

# Nutrient Criteria T echnical Guidance Manual
Lakes and Reservoirs

First Edition

# Nutrient Criteria Technical Guidance Manual Lakes and Reservoirs

Written by George Gibson, U.S. Environmental Protection Agency Robert Carlson, Kent State University

Jonathan Simpson, Tetra Tech, Inc. Eric Smeltzer, Vermont Department of Environmental Conservation Jeroen Gerritson, Tetra Tech Inc. Steven Chapra, University of Colorado Steven Heiskary, Minnesota Pollution Control Agency Jack Jones, University of M i ssouri Robert Kennedy, U.S. Army Corps of Engineers

# A **cknowledgments**

Th e authors w i sh to thank the following peer reviewers for their assistance in the preparation of this ma nuscript: R oger Bachman, U n iversity of Florida; N i na Caraco, I n stitute of Ecosystem Studies; Douglas K n aur, Wisconsin Department of Natural Resources; Matthew Liebman, USEPA Region I ; Jame s Peterson, University of Wisconsin; and Val Smith, University of Kansas. T heir detailed and insightful comme nts and criticisms are appreciated. Additional internal reviews, especially with respect to EPA me thods, policy, and regulations were provided by specialists from the Office of General Counsel, Office of Science and Technolog y - Standards and Applied Science D ivi sion; Office of Wetlands, Oceans and Watersheds; Office of Wastewater Management; and EPA Regional Nutrient Coordinators. State agencies and private interest gr oups also offered comme nts. All timely opinions were considered and addressed where possible in this edition. I n this respect, J o anna T ayl or, T h e CDM Group, I n c., patiently and g r aciously m ade repeated format changes to this m a nuscript as it w a s being completed. As with any prototype technical g u idance, differences about me thods and approaches are to be expected. T his and subsequent g u idance m a nuals for other water body types are not intended to be singular, one-time publications. A s experience accumulates, future editions will be prepared. Sug ge stions not presently incorporated m ay be revisited and appear in later v e rsions.

Nut r ient Criter ia—Lakes and Reser v oir s iii

# Disclaimer

Th is m a nual provides technical g u idance to States, Indian T r ibes, and other authorized j u risdictions to establish w a ter quality criteria and standards under the Clean Water A c t (CWA), to protect aquatic life from acute and chronic effects of nutrient overenrichment. Under the CWA, States and Indian T r ibes are to establish w a ter quality criteria to protect designated uses. State and Indian tribal decisionmakers retain the discretion to adopt approaches on a case-by

- case basis that differ from this g u idance when appropriate and scientifically defensible. While this m a nual constitutes EPA ’ s scientific recomme ndations regarding ambient concentrations of nutrients that protect resource quality and aquatic life, it does not substitute for the CWA or EPA’s regulations; nor is it a regulation itself. T hus, it cannot impose legally binding requirements on EPA, States, Indian T r ibes, or the regulated comm unity, and migh t not apply to a particular situation or circumstance. EPA m ay change this g u idance in the future.

iv Nut r ient Criteri a—Lakes and Reser v oir s

# Contents

Executive Summa ry
........................................................................ viii Chapter 1. In trod uc tion

.................................................................... 1-1
A. Purpose of This Docu ment

................................................................. 1-1 B. Relatio nship Be tweenW ater Quality Stan dards an d Criteria

....................................... 1-2 C. Us es of Nu trient Criteria

................................................................... 1-3 1. Identification of P roblem s .............................................................. 1-3 2. Management P l an ning

................................................................. 1-3 3. R eg ul atory Assessments

................................................................ 1-3 4. P roject Ev a luation s ................................................................... 1-4 5. Statu s and T r ends of Water R esour ces ..................................................... 1-4 D. Ov e rview of th e Nu trient Criteria Dev e lopment P r oces s .......................................... 1-4 1. Strateg y fo r R e ducin g Cultural Eutrophication

.............................................. 1-6 2. Nu trient Criteria Dev e lopment P r oces s .................................................... 1-7 Chapter 2. T he Basis for Lake and Reservoir Nutrient Criteria ................................... 2- 1
A. Historical Pers p ectiv e ..................................................................... 2-1 B. The Nu trient P aradig m .................................................................... 2-2 1. Pho sph o rus and Nitrogen as L im itin g Factors f o r A lga l B i omass ................................ 2-3 2. R ole of th e Waters h ed

................................................................. 2-4 3. T rophic Cau sa l Ch a in

.................................................................. 2-5 4. L ake A g in g .......................................................................... 2-6 C. Con n ectin g Waters he d L o adin g to th e L ake: AMas s Balance Model Approach

....................... 2-8 D. T rophic State Clas sifi cation Sy st em s ........................................................ 2-11 E. Us es of T rophic State In d ices

.............................................................. 2-16 Chapter 3. Preliminary Steps for Criteria Development

.......................................... 3-1
A. Definin g the R esour ce of Concern

........................................................... 3-1 B. Clas sifi cation

........................................................................... 3-2 1. Geog r aph i c Div isi on s .................................................................. 3-2 2. Non ge ographic Clas sifi cation s .......................................................... 3-3 3. Covariates

......................................................................... 3-10 Chapter 4. Establis hing an Ap pr opriate Databas e
............................................... 4-1
A. In troduction

............................................................................ 4-1 B. Ev a luatin g Existin g Data

.................................................................. 4-1 1. P otential Data Sources

................................................................. 4-2 2. Quality of Historical Data

.............................................................. 4-4 3. Data R e duction

....................................................................... 4-5 C. New Data Collectio n...................................................................... 4-6 1. Typ es of Monitorin g Asso ciated With Nu trient Criteria

....................................... 4-6 2. Samplin g Des ign

..................................................................... 4-8 D. Database Man agement

................................................................... 4-13 1. Modernized ST ORET

................................................................ 4-13 2. EDA S

............................................................................. 4-14

Nut r ient Criteri a—Lakes and Reser v oir s vChapter 5. Candidate Variables for Criteria Setting

............................................. 5-1
A. In troduction

............................................................................ 5-1 B. Nu trient Variables

....................................................................... 5-1 1. Phospho ru s .......................................................................... 5-1 2. Nitrogen

............................................................................ 5-3 C. Biolog i cal Variables

...................................................................... 5-4 1. Organic Carbon

...................................................................... 5-4 2. Ch l oroph y ll a

........................................................................ 5-5 3. Secchi Dis k Tr an sp arency .............................................................. 5-7 4. Dis so lved Ox ygen .................................................................... 5-8 5. Macroph yt es ......................................................................... 5-9 6. Biolog i cal Commun ity Stru c ture

........................................................ 5-10 D. L and Us e ............................................................................. 5-12 Chapter 6. I dentifying and Characterizing Reference Conditions

.................................. 6-1
A. Sig nifi cance o f Reference Co nd itio ns ........................................................ 6-1 B. Approaches to Establishin g Reference Condition s ............................................... 6-1 1. Direct Observ a tion of R eference L akes

.................................................... 6-2 2. P aleolimno log i cal Recon s tru c tion

........................................................ 6-4 3. Model P r ediction and Extrapolation

...................................................... 6-6 C. In itial Data R e trieval an d P roces sing to Support Ecoregional Nutrient C r iteria Development

.......................................................... 6-7 Chapter 7. Nutrient Criteria Development

..................................................... 7-1
A. Elements of Nu trient Criteria

............................................................... 7-1 1. In ves tigation of th e Historical Record

..................................................... 7-1 2. Establish me nt of the Reference Co nd itio n .................................................. 7-2 3. Us e of Models

....................................................................... 7-2 4. Ex p ert A ssessment of In f orm a tion

........................................................ 7-2 5. A ttention to Dow ns tream Ef f ects

......................................................... 7-2 B. Development of Ecoreg i onal Nu trient Criteria

.................................................. 7-3 1. R egion a l and L ake /Reserv o ir T yp e Clas sifi cation

............................................ 7-3 2. 	Con ve rsion of Ecoreg i onal Data to a Reference Condition an d Preliminary Nutrient C r iteria

........................................................... 7-3 3. Refine Ecoreg i onReference Co nd itio n Values

.............................................. 7-5 4. Ev a luation byR egion a l Team s ........................................................... 7-5 5. 	Ex am ples of the Deliberation Asso ciated with Development of a Nutrient C r iterion

.................................................................... 7-7 C. Development of State Nu trient Criteria

....................................................... 7-8 1. Desig na ted Us e ...................................................................... 7-8 2. Hy pothe tical Illustratio n of th e Relatio nship of State Criteria to Prot ect Desig na ted Uses Compared With an Ecoregion a l Criterion f or T P

......................................... 7-12 3. Frequency Distribution Approach

....................................................... 7-14 D. Developin g Nutrien t Criteria Implementation Pr ocedu r es ........................................ 7-14 1. Decis i on making

..................................................................... 7-16 2. Multivariable En r ich ment Index

......................................................... 7-16 E. Frequency an d Du r ation

.................................................................. 7-17

vi Nut r ient Criteri a—Lakes and Reser v oir sChapter 8. Using Nutrient Criteria T o Protect Water Q u ality

..................................... 8-1
A. State W a ter Quality Stan dard s .............................................................. 8-1 1. W ater Quality Standards and the Clean W ater Act

........................................... 8-1 2. P rotectin g Des igna ted Uses

............................................................. 8-2 3. Maintainin g Existin g Wa ter Quality

....................................................... 8-2 4. P rov i din g Flexibility in Implementation

................................................... 8-3 B. W ater Quality–Based Approach to P o llution Control

............................................ 8-4 Step 1: Identification of Impaired and Threatened Waters

........................................ 8-5 Step 2: Priority Ranking and Targeting

...................................................... 8-6 Step 3: Development of TMDLs

........................................................... 8-6 Step 4: Implementation of C o ntrols

......................................................... 8-7 Step 5: Assessment of C o ntrols

............................................................ 8-8 C. Nonpoin t Source P o llution Man agement

...................................................... 8-9 1. Gu i dance f o r Controllin g Nonpoin t Sources of Nutrien ts

..................................... 8-10 2. Nonpoin t Source Man agement P rog r am s .................................................. 8-11 3. Coas t al Nonpoin t P ollution Control Prog r am s .............................................. 8-12 4. Farm B ill Co n servatio n Prov isio ns ...................................................... 8-13 D. AComprehen sive P rocedu r e f o r Nutrien t Managemen t

.......................................... 8-15 1. Statu s Identification

.................................................................. 8-15 2. Back gr ou nd In ves tigation

............................................................. 8-15 3. Data Gatherin g and Diag nos tic Monitorin g ................................................ 8-17 4. Source Identification

................................................................. 8-19 5. Management P r actices f or Nu trient Control

................................................ 8-19 6. Detailed Man agement P lan

............................................................ 8-21 7. Im p lement ation and Communi cation

..................................................... 8-21 8. Ev a luation Monitorin g and P e riodic R evi ew ............................................... 8-22 9. Completion and Evalu a tion

............................................................ 8-22 10. Contin ue d Monitorin g of th e Sy s tem

.................................................... 8-22 E. R esources ............................................................................. 8-23 Chapter 9. M odel in g Tool s
................................................................. 9-1
A. In troduction

............................................................................ 9-1 B. R eview of L ake/R ese rvoir Eutrophication Modelin g Framework s .................................. 9-1 1. Em p irical Models

.................................................................... 9-1 2. Nu trient Budget/Mas s Balance Models

.................................................... 9-3 3. Nu trien t/F ood Ch ainModel s ............................................................ 9-5 C. Mo de l Use f o r A iding in th e Establish ment of Reference Co nd itio ns ................................ 9-7 1. Morphoedaphic In d ex ................................................................. 9-7 2. Mas s Balance Models w ithL oadin g Estimation

............................................. 9-7 D. Waters h ed Management Models

........................................................... 9-14 1. Mid- R an ge Waters h ed- S cale L o adin g Models

.............................................. 9-14 2. Detailed Waters he d L o adin g Models

..................................................... 9-17 References ............................................................................... R-1 Appendix A. Nutrient Region Descriptions .................................................... A-1 Appendix B. Case Studies .................................................................. B-1

Nut r ient Criteri a—Lakes and Reser v oir s v ii

# Executive Summary

Ov erenrichment of surface waters in the U n ited States has been a long -s tanding problem to the extent that approximately half of the waters reported by the States to be impaired are attributed to excess nutrients and related biological g r owth. T he EPA has established the National Nutrient Criteria Program to address this w a ter quality problem . T he surface w a ters of concern are lakes and reservoirs, stream s and rivers, estuaries and coastal m arine waters, and wetlands. Criteria representing enrichment conditions of surface w a ters that are mi nimally impacted by human developmental activities will be developed for each of the regions of the country . T hese will then become the basis for States and T r ibes of the United States to develop nutrient criteria to protect the designated uses of those waters. T his ma nual is designed to help accomplish this for lakes and reservoirs. Nitrogen and phosphorus are the primary causes of overenrichment and are obvious nutrient criteria variables, but biological response v ariables are also important in addressing the consequences of overenrichment. Limnologists and lake m a nagers have developed a g e neral consensus about freshwater lake responses to nutrient additions, that essentially an ambient total phosphorus (TP) concentration of g r eater than about 0.01 m g /L and or a total nitrogen (TN) of about 0.15 m g/L is likely to predict blue- g reen algal bloom problems during the g r owing season. Similarly, chronic overenrichment leads to lake quality degradation manifested in low dissolved oxy g en, fish kills, algal blooms, expanded macrophytes, likely increased sediment accumulation rates, and species shifts of both flora and fauna.
Ho weve r, because some parts of the country have naturally higher soil and parent m a terial enrichment and different precipitation regimes, the application of that g e neral consensus approach has to be adjusted by region. T herefore, an ecoregional and reference condition approach is necessary to develop nutrient criteria appropriate to each of the different g e ographical and climatological areas of the country . I nitially, the continental U n ited States has been divided into 14 separate ecoregions of similar ge ographical characteristics, and criteria will be developed for each. While additional v ariables m ay be used as nutrient criteria, the initial effort will concentrate on TP, TN , algal chlorophyll, and Secchi depth or similar measure of algal turbidity to reflect the primary production response to overenrichment. Thus, the criteria involv e four basic indicators of overenrichment. Other indicators, such as dissolved oxy ge n (DO) and macrophyte g r owth or speciation, and other flora and fauna changes are also deemed useful, but the first four are paramount, especially the two limiting nutrients. T hroughout the country, cultural eutrophication (or overenrichment) is largely caused by either too m u ch N or P or some combination of the two in their v arious forms. Nitrogen m ay not be critical to m a ny fresh w a ter lakes, but it does become significant in estuaries and coastal w a ters downstream

. An essential part of the process for developing nutrient criteria is to pay attention to downstream effects. T herefore, nitrogen as well as phosphorus reduction for lakes is needed to benefit the lower reaches of the overall system

. TNand T P are described as causal v ariables, and chlorophyll and algal turbidity are initial response variables. Measuring j ust the response v ariables clearly shows the existence of a problem, but waters w ith a short retention time could look clear and be aesthetically acceptable, and could still be sending an unacceptable load of N and P downstream to be someone else’s problem . T his is why EPA expects downstream effects to be considered as part of the nutrient criteria development process.

v iii Nut r ient Criteri a—Lakes and Reser v oir sNutrient criteria development consists of five elements: 1.	 Historical data and other information to provide an overall perspective on the status of the resource. 2. Present reference sites and their collective reference condition describing the current status. 3. Modeling to refine data implications and analysis above if necessary

. 4.	 Objective assessment of all of the above information by the States and by the EPA Regional T echnical Assistance Groups (RTAGs), a board of State and Federal specialists established in each EPA R egion to help develop and administer the N a tional N u trient Criteria Program, to establish the ecoregional criteria, and to review proposed State or T r ibal nutrient criteria. 5. Attention to downstream consequences before the criterion is finally established. Using this approach, EPA ecoregional benchmark criteria can be established that States and T r ibes can use to help set their own criteria to protect all their designated uses. A key responsibility of the RTAGs , with their best knowledge of regional w a ter quality and m a nagement potential, is the development of these ecoregional criteria and review of subsequent State and T r ibal criteria. A summ ary of the procedural approach for ecoregional criteria development is as follows:
The R TAGs collect as m u ch existing reference quality data for at least the four principal v ariables as possible from ST ORET, States and Tribes, universities, local g ove rnments, and other Federal agencies. Data collection is directed to the particular waterbody type of interest and to established physical classes of those waters, e.g., small, medium, and large v o lume lakes. B ecause the States are all represented on the R TAG , they are fully involved in the process.
•	 T he data are reviewed for quality and utility and then the distribution of data points throughout the ecoregion for each class is assessed and additional data g a thered if needed.

• When satisfied with the adequacy of the data distribution for the classes, the reference sites w ithin each ecoregion are compared. I f there are obvious shifts in reference v a lues (e.g. throug h cluster analysis) the ecoregion is subdivided accordingly or perhaps boundaries are shifted. T he same assessment should be m a de for temporal distribution to determine if seasonal criteria are needed. B oth of these divisions should help reduce v ariability in the reference condition as w e ll, albeit with the risk of reducing the population of applicable observations.
•	 I n the process, the RT AGs are expected to coordinate with their adjacent counterparts to promote consistent subregional boundaries and criteria. T he EPA Headquarters nutrient criteria g r oup w ill play a mediating and coordinating role in this process, but the initial determinations will be ma de by the RTAGs.

• The established reference conditions will then be incorporated with the other elements of criteria development—historical perspective, possible modeling of data, and concern to protect downstream waters—by the RTAG to set that particular ecoregional criterion for T P , T N, chlorophyll a , and Secchi depth or similar measure of organic based turbidity

.

Nut r ient Criteri a—Lakes and Reser v oir s ixTh ese ecoregional criteria would typically serve as the basis for proposing and promulgating a water quality standard w h en a State or T r ibe fails to adopt an acceptable standard. EPA expects the States and Tr ibes of the Continental U n ited States to develop nutrient criteria for each class of surface w a ter bodies within three years of the establishment of the ecoregional criteria for those waters. I t should be noted that States and T r ibes m ay elect to establish their criteria using methods other than those described in these EPA g uidance manuals. EPA promotes such flexibility so long as the proposed alternative is:

• Based on a scientifically defensible approach

• Contains sufficient parameters to address nutrient overenrichment causes and responses, i.e., consistent with the v ariables designated by EPA and with the five nutrient criteria elements listed abov e

• Protects and m a intains downstream w ater quality sufficient to preserve the beneficial uses of those waters. I n addition to criteria to protect the uses, States m u st adopt antidegradation policies and procedures to protect and m a intain existing w ater quality

. Hawa ii, A l aska, and U

. S. Trust Territories will develop separate ecoregions in conjunction with their RTAGs and the N a tional N u trient Criteria Program

. Th is manual concludes with chapters describing data models, and management options available to the States and Tribes to actively protect or restore their lake resources. Case histories illustrating nutrient criteria development and m a nagement efforts are also appended with the names of individual specialists to contact for m o re information. Ed itorial N o te Th roughout this text, reference is m a de to the roles and responsibilities of “States” or “States and Tribes.” This term or phrase is intended to mean those j u risdictions with the appropriate responsibility and authority and m ay also include the D i strict of Columbia, Territories, or other g ove rnmental entities.

x Nut r ient Criteri a—Lakes and Reser v oir s

# CHAPTER 1 A. Purpose of T his Document B. Relationship Between W a terQ ualit y Standards and Criteria C. Uses of Nutrient Criteria 

# Introduction D. Ov erview of the Nutrient Criteria

A. P urpose of This Document Nutrient overenrichment is a m ajo r source of water pollution in the United States. T he link between eutrophication—the overenrichment of surface w a ters with plant nutrients—and public health risks has long been presumed but not definitively documented (Bachman, personal com m

unication, 1999). Howeve r, corollaries with bacterial indicators such as (1) Escherichia coli and the spread of disease in sewage-enriched w a ters, (2) trihalomethanes in chlorine-treated eutrophic reservoirs, and (3) recent concerns over the incidence of Pfiesteria piscicida in eutrophic estuarine surface w a ters with suspected attendant human illnesses, all sug ge st that overenrichment pollution is not only an aesthetic, aquatic comm unity problem, but a public health problem as well. A major element of the U.S. Environmental Protection A g ency’s (EPA 

### � s) N a tional N u trient Strateg y for the D eve lopment of R egi onal N u trient Criteria (U.S. EPA, 1998), also referred to as the National Nutrient Strateg y , is the development of waterbody -typ e-specific technical g u idance documents that can be used to assess potential nutrient-related trophic state impairment and to develop region-specific nutrient criteria to help address this pollution problem . T his document provides this g u idance for lakes and reservoirs. A similar document is being prepared for rivers and streams, and future documents will be prepared for estuarine and coastal m arine areas and for wetlands. Because of diverse g e ographic and climate conditions, single national nutrient criteria for lakes and reservoirs are not appropriate. I nstead, nutrient criteria m u st be developed at the State, regional, or individual water body levels. T his document, therefore, does not attempt to set national criteria, but provides State and tribal w a ter quality m anagers with g u idance on how they can set criteria themselves. Th e document provides back gr ound information on classifying water bodies and selecting v ariables that can potentially be used as criteria, and it describes m e thods for developing appropriate v a lues for these criteria. T he document also provides information on sampling, data processing, and appropriate ma nagement techniques. Because nutrient overenrichment consistently ranks as one of the top causes of w a ter resource impairment, this initiative is designed to address that particular w a ter quality problem . I t is important to recogniz e w hat is meant by nutrient overenrichment. I n the context of this g u idance m a nual, overenrichment means the addition of nutrients causing adverse effects or impairment to designated use(s) of the water body or to the ecosystem

. Sy m ptoms of such impairment include but are not limited to frequent nuisance algal blooms, fish kills, overabundance or decline of macrophytes, and loss of top predators from the food chain.
Itis also important to recogniz e that the best way to m a nage for nutrient control is to reduce the human-caused fraction of the nitrogen, phosphorus, or related nutrients entering the waters. T his often is referred to as cultural eutrophication to distinguish this enrichment from the inherent nutrient load entering the water body from soils and parent m a terial indigenous to the area in the absence of disruptiv e
Nut r ient Criter ia—Lakes and Reser v oir s 1-1erosion. C ultural eutrophication results from such human endeavors as construction activities, sewag e discharges, agricultural practices, and residential development. T his g u idance m a nual is intended to help the user develop criteria useful for abating cultural eutrophication.
B. Relationship B e tween Water Quality Standards and Criteria States and authorized T r ibes are responsible for developing w ater quality standards to protect the physical, biological, and chemical integrity of their w a ters. A w ater quality standard defines the quality go als for a w a ter body by designating specific uses of a w a ter body, setting criteria to protect those uses, and establishing an antidegradation policy to protect existing w ater quality . T he uses of a w a ter body include “existing uses” that were attained on or after November 28, 1975 (the date of the promulgation by EPA of the first w a ter quality standards regulations) and “designated uses,” which are desired uses that m ay or m ay not already be attained. At a mi nimum, a water body 

### � s uses m u st include recreation in and on the water and propagation of fish and wildlife unless the State performs, and EPA approves, a use attainability analysis j u stifying a different designated use. O ther specific use categories such as boating , trout propagation, or potable water supply also m ay be adopted. 1 After designating the uses of a water body, the State m u st adopt numeric and/or narrative criteria to protect and support the specified uses (33 USC § 1313 (c) (2)). Such criteria m u st be based on a sound scientific rationale and m u st contain sufficient parameters to protect the designated use(s). Narrativ e criteria describe the desired w a ter quality conditions in a qualitative context. T hey are the basis for w a ter quality assessments. An example is shown below : All w a ters shall meet generally accepted aesthetic qualifications, shall be capable of supporting desirable aquatic life, and shall be free from substances, conditions, or combinations thereof attributable to human activities that produce objectionable color, odor, or taste or induce the growth of undesirable aquatic life.
Nu me ric criteria, on the other hand, are quantitative v a lues assigned to measurable components in the water body

. An example of a numeric criterion migh t be that a lake 

### � s average total phosphorus concentration should “not exceed 20 μ g /L during the summe r g r owing season.” Narrative and numeric criteria should work in combination to:
• F orm the basis for consistent measurement of environmental quality

• Provide distinct interpretations of acceptable and unacceptable conditions that can be debated by concerned parties

• Reduce ambiguity for m a nagement and enforcement decisions This document deals specifically w ith the establishment of nutrient criteria for lakes and reservoirs (under the authority of the Clean Water Act Section 304) as a means of addressing nutrient overenrichment problems. However, for these types of criteria to be effective, they should be accompanied by responsive nutrient management approaches.

1 The EP A water quality standards re gu lations are at40 CFR P art V31, and g u idanc e on their imple me ntation is in the EP A water qualitys tandards handbook (EP A -823-B-94-00Sa).

1- 2 Nut r ient Criteri a—Lakes and Reser v oir sA responsible nutrient m a nagement plan should meet three practical conditions. First, the plan and its component elements m u st be scientifically defensible, otherwise it migh t lead to well-intentioned ma nagement actions that are unnecessary or harmful. T his is like the admonition to physicians “abov e all do no harm.” Second, effective nutrient m a nagement m u st strive to be economically feasible. T he public and local affected interests are likely to support approaches that are economically feasible and that provide meaningful benefit compared with their cost. Finally, these approaches should be practical and acceptable to the comm unities involved. T he approaches should address appropriate social and political issues, such as conflicts that migh t exist between public agencies and landowners or between watershed residents and lake users. Any m anagement plan m ay fail if these three g e neral elements are not sufficiently addressed, and it is almost certain to fail if they are all ignored. C. Uses of Nutrient Criteria 1. Identification of Problem s EPA expects that the process of collecting current data and surveying m ore lakes and reservoirs than have been investigated previously w ill produce new information revealing conditions not heretofore recognized. By comparing the w a ter quality criteria for nutrients to actual w a ter quality, the resource ma nagement decisionmakers m ay well recogniz e overenriched lakes or reservoirs or portions of these water bodies for the first time. T hese new problems can be incorporated into the information system so that remediation can be initiated. 2. Management Planning
Th e nutrient criteria development process not only establishes these benchmarks identifying overenrichment, but it also m ake s it possible to rank the relative m agn itude of the problems with respect to each other. A scale of overenrichment with a frequency distribution can be created to readily identify the scope of the enrichment problems to be addressed and the numbers of lakes or impoundments in each state of degradation. Modeling plays a significant role here either to supplement existing data sets or to assess the projected effect of v arious options and combinations of m a nagement approaches.
T hus, a form of triage can be practiced to assign scarce m a npower and funds in an efficient way

. For example, a State m ay create a balance by (1) protecting m any high-quality lakes, (2) restoring several m oderately degraded lakes by implementing cost-effective land use changes early on, and (3) designating for restoration one or a few badly overenriched systems, realizing that only a long -t erm, protracted project and budget will suffice.
3. R egulatory Assessments Much of the m a nagement work done by EPA and the States is regulatory, and the nutrient criteria, once established, should be incorporated into State standards to become the basis of enforceable tools. These v a lues are used to develop limits in N a tional Pollutant Di scharge Elimination System (N PDE S) permits for point source discharges. T he permit limits for nitrogen, phosphorus, and other trace nutrients emitted from w aste w a ter treatment plants, factories, food processors, and other dischargers can be appropriately adjusted and enforced in accordance with the criteria. Similarly, total m a ximum daily load (TMDL) estimates used to allocate remediation responsibilities, especially regarding nonpoint sources on a watershed basis, can be established with respect to these nutrient criteria. Knowing the optimum nutrient load for a lake (and its downstream recipient waters)
Nut r ient Criteri a—Lakes and Reser v oir s 1-3make s it possible to divide and allocate that load among the tributary subwatersheds of the system

. Re source m a nagers then can begin land use improvements and other activities necessary to improve the system in a me thodical way and on a reasonable scale so that restoration can be achieved. The criteria portion of w a ter quality standards also m ay be used in antidegradation review s and can serve in the development of best m a nagement practices for State and local nonpoint source programs. 4. Project Evaluations
Nu trient criteria can be applied further to evaluate the relative success of m a nagement activities such as those described imme diately above. Although it m ay sometimes be expensive and frustrating , “before, during, and after” measurements of nutrient enrichment v ariables in the receiving wa ters, w h en compared with the criteria, provide an objective and direct assessment of the success of the m a nagement project. 5. Status and Trends of Water Resources
Th roughout the continuing process of problem identification, response and remediation, and evaluation to protect and enhance our water resources, the States and EPA are required by section 305(b) of the Clean Water Act to periodically report to Congress on the status of the Nation 

### � s waters. T he nutrient criteria would expand and refine that report by adding an additional set of both causal and response parameters to the measurement process. T he States and EPA w ill be able to compare the m easured enrichment conditions of their lakes and reservoirs and document the changes that hav e resulted and the relative progress m a de.
Th e rest of this g u idance m a nual presents detailed information that elaborates on this important ma terial. The intent is to present essentially a tw o- part g u idance document, the first half of w h ich is a presentation of the science and technolog y associated with the measurements required and processes associated with the development of the benchmark nutrient criteria needed to m ake enrichment identifications. T he second part addresses the equally important process of m aki ng m anagement decisions to protect and enhance the trophic state of our Nation 

### � s w a ters and to evaluate the relativ e success of that m a nagement so we can know what works and what does not, so that the next round of criteria development and m a nagement will be conducted from a truly expanded base of knowledge.
D. Overview of the Nutrient Criteria Development Process A distribution of lakes m ay exhibit a range of nutrient conditions. Using total phosphorus as an example, some lakes m ay have little or no enrichment and consequently a limited number of species and individuals or biomass. Lake Superior is a classic example of such conditions of oligotrophy

. At the other extreme of phosphorus enrichment is m a ssive overenrichment with so m u ch phosphorus in the w ater column that algal blooms or choking m acrophyte g r owth and frequent fish kills are comm on. Species diversity in these hypereutrophic lakes is also low even though biomass is usually v ery high. Th ese are the “pea soup” lakes most comm unities associate with badly degraded conditions. Phosphorus concentrations typical for both extremes can be measured, but an in-lake total phosphorus concentration of less than 10 μ g /L g e nerally is considered to be oligotrophic. Conversely , 100 μ g /L often is used as the threshold for hypereutrophication (Vollenweider, 1968; Wetzel, 1975; Carlson, R., personal comm unication, 1999). Although such levels are known to exist naturally, m o re often concentrations of this m agn itude are associated with extensive or intensive cultural development.

1- 4 Nut r ient Criteri a—Lakes and Reser v oir sNa tural enrichment ranges throughout these m agn itudes of concentration according to g e ographic and geological regions of the country

. Consequently, it would be necessary to determine the natural ambient back gr ound for each lake so that the eutrophication caused by human development and abuse can be addressed. Addressing this cultural eutrophication is the objective of this manual, but the development of nutrient criteria on a lake-by

- lake basis m ay be prohibitively time consuming and expensive for States and T r ibes. Alternatively, these lakes or reservoirs can be divided into regionally similar g r oups based on their physical characteristics within a proximal geographic area. T hose lakes of each established g r oup having the least land development or other human impact can be identified as the reference lakes for measuring relatively undisturbed nutrient conditions appropriate for that class and region. T his reference condition information, within an appropriate historical context and objectively interpreted, then can become a candidate criterion for use as a benchmark against which other similar lakes may be compared. Before the criterion is finally established, however, the scientists and resource m a nagers involved should assure themselves that it also will have a beneficial or at least neutral downstream effect on the lakes, reservoirs, streams, or estuaries within or j u st below the area of application. T his concept, as illustrated in Figure 1.1, is essentially the basis for the National Nutrient Criteria Program and is described v ariously throughout this text.

Figure 1.1.	 Conceptual basis for the Nation a l Nutrient Criteria Program using T P as an example variable.

Nut r ient Criteri a—Lakes and Reser v oir s 1-5Th e two extreme v a lues of hypereutrophy and pristine or presettlement conditions can be estimated from m onitoring, historical records, and paleolimnological determinations. T he reference condition, located within this measured range, and the derived criteria are scientifically based. But they also include a conscious decision to use areas of least human impact as indicators of low cultural eutrophication. A measure of best practical judg me nt is also necessary w here scientific me thods and data are not adequate for the decisions necessary for water resource protection.
Th e use of mi nimally impacted reference sites has been adapted from biological criteria development and is endorsed by EPA’s Science A dvi sory Board (1992). C onditions that represent mi nimal impacts provide a baseline that should protect the inherent beneficial uses of the Nation’s waters. T he use of scientific rationale together with practical resource m a nagement is called for in the selection of a percentile distribution of v a lues as a reference condition. T he term “mi nimally impacted” implies a highend percentile of conditions in reference lakes and a low

- end percentile of the conditions in all lakes (i.e., some enrichment is allowed, but not enough to cause adverse in-lake effects or adverse downstream effects). T he upper end of the range of data from purposely identified reference sites represents the bare mi nimum threshold of a reference condition, w h ereas lower percentiles of the reference site data represent high-quality conditions that m ay not need to be achieved or cannot be achieved in the entire population of lakes in an ecoregion. T he upper 25th percentile represents an appropriate margin of safety to add to the mi nimum threshold, excludes the effect of spurious outliers, and serves as a first-order recomme ndation of a sufficiently protective v a lue. D ata analyses performed to date indicate that the lower 25th percentile of data from a sample representative of the entire population of lakes in an ecoregion roughly approximates the upper 25th percentile of the reference data (see C h apter 6, section C , Minnesota case study). Where sufficient data are available, comparison and statistical analysis of causal and response v ariables can help determine effect thresholds and further refine reference conditions. Establishing the reference condition is but one element of the criteria development process. Reference condition v a lues are appropriately m odified based on examination of the historical record, modeling , expert judg me nt, and consideration of downstream effects. 1. Strategy for Reducing Cultural Eutrophication Six key elements are associated with the strateg y for reducing cultural eutrophication (U.S. EPA, 1998):

• EPA believes that nutrient criteria need to be established on a regional basis and need to be appropriate to each w a ter body type. T hey should not be established as a single set of national numbers or v a lues because there is simply too m u ch natural v ariation from one part of the country to another. Similarly, the expression of nutrient enrichment and its measurement by necessity v aries from one water body type to another. Streams do not respond to phosphorus and nitrogen the same w ay as lakes or coastal w a ters.

• Consequently, EPA has prepared g u idance for these criteria on a water -body -typ e- and region-specific basis. With detailed m a nuals available for data g a thering, criteria development, and m a nagement response, the g o al is for States and T r ibes to be able to conduct surveys and develop criteria to help them deal with the problem of nutrient overenrichment of their waters.

• To help achieve this g o al, the A g ency has initiated a system of EPA Regi onal technical and financial support operations each led by a Regional N u trient Coordinator—a specialist responsible for providing the help and g u idance necessary for States or T r ibes in his or her region to accomplish the necessary environmental investigations and remediations. T hese
1- 6 Nut r ient Criteri a—Lakes and Reser v oir sregional coordinators are g u ided and assisted in their duties by a team of inter-Agency and intra-Agency specialists from EPA Headquarters. T his team is responsible for providing both technical and financial support to the Regional Technical Assistance Groups (RTAGs) created by these coordinators so the job can be completed and comm unication established and m a intained between the policy making function in Headquarters and the actual environmental management in the Regions.

• EPA w ill develop basic ecoregional nutrient criteria v a lues for w a ter body types. T he regional teams and States/Tribes can use these v a lues as g u idance for developing criteria protective of designated uses; the A g ency also m ay use these v a lues if it elects to promulgate criteria for a State or Tribe. These criteria will have v a lue in two contexts: (1) as the basis of w a ter quality standards, NPDES permit limits, and as T M DL target v a lues and (2) as decisionmaking benchmarks for m a nagement planning and assessment.

• EPA plans to provide sufficient information for States and T r ibes to begin adopting nutrient standards by 2003.

• States/Tribes are expected to monitor and evaluate the effectiveness of nutrient m a nagement programs implemented on the basis of the nutrient criteria. EPA intends the criteria g u idance to reflect the “natural,” mi nimally impaired trophic condition of a g ive n regional class of w a ter body . O nce w a ter quality standards are established for nutrients based on these criteria, the relative success or failure of any m anagement effort, either protection or remediation, can be evaluated.
T hus, the six elements of the National Nutrient Criteria Program describe a process that encompasses taking measurements of the collective w a ter resources of an area; establishing nutrient criteria that can be used for evaluating the discrete waters within that region or area; assessing individual water bodies against these criteria and associated standards; designing and conducting the appropriate m a nagement; and, finally, evaluating its relative success.
2. Nu trient C riteria Development Process Provided below is a discussion of the activities that g e nerally comprise the nutrient criteria development process. T hey are listed in the order g e nerally followed and the subsequent chapters of this document follow this sequence. Figure 1.2 presents a schematic illustration of the criteria development process with parallel, appropriate chapter headings.



### � P reliminary Steps f o r Criteria Development (Chapter 3) Establishment of Regional Technical Assistance Groups
Th e R egi onal N u trient Coordinator in each EPA Regi on will contact and obtain the involv em ent of key specialist (e.g., limnologists, water resource managers, oceanographers, stream and wetland ecologists, water chemists, and land use specialist) in that Region with respect to the water bodies of concern, and these experts should be recruited from other Federal agencies, State agencies, universities

Nut r ient Criteri a—Lakes and Reser v oir s 1-7Figure 1.2. Flowchart of the nutrient criteria development proces s.

1- 8 Nut r ient Criteri a—Lakes and Reser v oir sand colleges. Particular Federal agencies of interest are the U.S. Geological Survey (USGS), Natural Resources Conserv a tion Serv i ce (NRCS), National Oceanic and Atm o spheric Administration (NOAA), U.S. Forest Serv i ce (USFS), and the U.S. Fish and Wildlife Serv i ce (USFWS). I n certain areas of the country, the U.S. Arm y Corps of Engineers (USACOE) or the Bureau of Land Management (BLM) or special g ove rnment agencies such as the T e nnessee Valley A uthority (T VA) m ay be pertinent. Similarly , for information and education activities, especially w ith respect to agriculture, the U SDA C ooperativ e Extension Service is a v a luable resource. State agencies with responsibilities relevant to this effort are variously named, but are comm only referred to as: Department of Natural Resources, Department of Water Resources, Department of the Environment, Department of Environmental Management, Fisheries and Wildlife Management, State Department of Agriculture, State Department of Forestry, and other land use m a nagement agencies. Most State land g r ant universities have faculty talent important to nutrient ma nagement, and almost all colleges and universities have applied science faculty w ith research interests and talents appropriate to this initiative. I n selecting participants for the g r oup, diverse expertise is an obvious prerequisite, but willingness to cooperate in the g r oup effort, integrity, and a lack of a strong alternative interest are also important factors to consider for selecting these essential people who m u st make collective and sometimes difficult determinations.
Th e experts chosen will constitute the R TAG , which will be responsible for m ajo r decisions in regional implementation of the program

. And the g r oup should be sufficiently large to have the necessary breadth of experience, but small enough to effectively debate and resolve serious scientific and ma nagement issues. A membership of about 30 approaches an unwieldy size, although that number m ay initially be necessary to m a intain an effective w o rking g roup of half that size.
Th e RTAG is intended to be a regional, Federal agency advisory body consisting of a v i able subset of scientists and resource m a nagers from each pertinent agency as described above together with their State counterparts. T he R TAG has a Federal responsibility and as such should not delegate or share this obligation with the private sector. T he perspectives of private citizens, academicians, and special interest gr oups are important, and these and other m emb ers of the public m ay attend RTAG meetings and offer opinions w h en invited, but the final deliberations and decisions are the responsibility of the Federal and State memb ers of the RTAG. T hey mu st also be able to meet and debate the issues without undue outside influence.
Ho weve r, as a m a tter of policy, EPA encourages the R TAGs to regularly provide access and reports to the public. T he meetings should g e nerally be open to the public and the schedule of those meeting s published in the local newspapers. At a mi nimum, RTAGs are encouraged to hold regular “stakeholders” m eetings so that environmental, industrial, and other interests m ay participate v i a a separate public forum associated with responding to the g r oup’s efforts. I t is important that citizens and public g r oups be involved, and any significant determinations of the Group should include a public session at which a current account of activities and determinations is presented and comme nts acknowledged and considered. I n addition, where specific land uses or practices are addressed, those property owners, farmers, fishermen, or other involved parties should be consulted in the deliberation and decisionmaking process. Itis reasonable to expect monthly or at least quarterly meetings of the RTAG, with working assignments and assessments conducted between these meetings. T o coordinate activities among the 10 RTAGS, and with the National Nutrients Team, regular conference calls have been established. At these sessions, new developments in the Program, technical innovations and experiences, budgets, and policy evolutions will be conveyed and discussed. I n the same context, an annual meeting of all R egi onal Nu trient Coordinators, State representatives, and involved Federal agencies is also held each spring in or
Nut r ient Criteri a—Lakes and Reser v oir s 1-9near Washington, DC. At this meeting, major technical reports are presented by specialists and issues significant to the Program are discussed.
Th e composition and coordination discussed above are intended to establish the shortest possible line of comm unication between the State, Region, and National Program staff memb ers so that a rapid but reasoned response is promoted to changing issues and techniques affecting nutrient m a nagement of our waters. I t is also designed to be responsive to the water resource user comm unity without becoming a part of user conflicts.
De lineation of N u trient Ecoregions Appropriate to the Development of C r iteria The initial step in this process has been taken through the creation of a national nutrient ecoregion map consisting of 14 North American subdivisions of the coterminous United States (Figure 1.3). T hese are aggregatio ns of Level III ecoregions revise d by Om e rnik (1998). Alaska, Hawaii, and the U.S. Te rritories will be subdivided into nutrient ecoregions later, with the advice and assistance of those States and g ov ernments. Th e initial responsibility of each R TAG w ill be to evaluate the present ecoregional m ap with respect to v ariability based on detailed observations and data available from the States and Tribes in that EPA Regi on. T his preliminary assessment of the nutrient ecoregional boundaries will further depend on the additional nutrient w a ter quality data obtained by those States. The databases, especially w ith respect to selected reference sites, will be used to refine the initial boundaries of the m ap in each EPA R egion.
Itis expected that the collective effect of these evaluations by all 10 EPA RTAGs w ill result in the further refinement and subdivision of m a ny of the 14 ecoregions, especially the large, m u lti-State ones. Th e boundaries will shift or be subdivided in accordance with the inherent trophic conditions and nutrient indicators of similar w a ter bodies in each locality

. Physical C l assification
Th e next step in evaluating the data is to devise a classification scheme for rationally subdividing the population of lakes in the State. Because identification of overenrichment is the objective of nutrient criteria development, trophic classification per se should be avoided, as should any classification based on levels of human development. Physical characteristics independent of m o st cultural enrichment sources are far m o re appropriate. Such classification m ay be done initially on a size basis (e.g., acres of surface area or square miles of watersheds). A volumetric variable that m ay be used for further subclassification based on median or ma ximum depth. Similarly, inherent w a ter quality characteristics such as m arl or bog lakes may also apply . I n fact, such lakes, especially if few in number, are usually separated out of the general population and identified as a separate and unique class. Hydroelectric reservoirs and effluent dominated system s are also examples. Once lakes have been classified, it is important to determine how m u ch information is available describing the enrichment status of these lakes. State agency records are the basis for an initial data

1-10 Nut r ient Criteri a—Lakes and Reser v oir sFigure 1.3. Draft aggregations of level III ecoregions for the National Nutrient Strategy.

Nut r ient Criteri a—Lakes and Reser v oir s 1-11search. I n many States, w a ter quality information resides in m o re than one agency

. For example, Maryland has a Department of Natural Resources and a Department of the Environment, both of which retain w a ter quality records. T o compound the search further, States m ay also have pertinent data sets in their D e partments of Fisheries and Public Health. I t is w i se to initiate the search for information with calls and questionnaires to colleagues in the State or T r ibal agencies likely to be involved so an appropriate list of contacts and data sets can be compiled. I n doing so, regional Federal agencies should not be overlooked either. T hese include the USFWS, Park Service, and U.S. and State Geological Sur veys .


### � Establishing an Appropriate Database (Chapter 4) Review of Historical Information Historical information is important to establish a perspective on the condition of a g ive n waterbody

. Ha s its condition changed radically in recent years? I s the system stable over time? H as there been a trend up or down in trophic condition? O nly an assessment of the historical record can provide these answers. Without this information, the m a nager risks setting reference conditions and subsequent criteria on the basis of present data alone, which m ay in fact be a degraded state. Valid historical information places the current information in its proper perspective.
Da ta Screening
Th e first step in the process of either assessing historical observations and data sets or m o re current data is to review this m a terial to determine the suitability of that information to support nutrient criteria development. Anecdotal information and observations are valuable, but the sources m u st be carefully considered. Fishermen’s accounts, local sport fishing news stories, and the observational logs of scientific field crews are all legitimate sources of information, but they are subject to different levels of scrutiny before a trend is determined. T he same applies to different databases. Nutrient information ga thered for the purpose of identifying failing w aste w a ter treatment plants cannot be assessed in the same light as similar data collected to determine overall lake quality or trophic state. T he analytical procedures used, type of sampling design and equipment, and sample preservation are other variables that mu st also be considered in any data review and compilation. Once this screening is done, the compiled data m ay be sorted according to named lakes or reservoirs. Nutrient Data Collection and Assessment EPA has initiated the data collection and assessment process by screening the existing ST ORET database for information on lakes, reservoirs, streams, and coastal w a ters with respect to four initial parameters of concern: total nitrogen (TN), total phosphorus (TP), chlorophyll a , and Secchi depth. Th ese four parameters were originally selected for robustness and conservativeness of estimation; however the preliminary screening of the ST OR ET data revealed that these measurements are also relatively abundant in the database. Although this is an entirely appropriate starting point for nutrient criteria development, States and T r ibes are not required to confine their investigations and data selection for enrichment assessment and criteria development to only these v ariables. States and T r ibes are encouraged to select measures above and beyond these initial characteristics that contribute to the m o st appropriate and reliable assessment of the enrichment of the waters of their region. I n particular, it is advisable to use both causal indicators (the nutrients introduced to the system especially species of nitrogen and phosphorus, and perhaps silica and carbon as indicated) and response
1-12 Nut r ient Criteri a—Lakes and Reser v oir sindicators (those measures of biotic productivity and activity reflecting the enrichment of the system ) including chlorophyll a ; Secchi depth; turbidity; algal taxa; plankton taxa; dissolved oxy ge n; macrophyte taxa, extent, and biomass; and fish taxa and numbers.
Th e combination of nutrient and biological system response information will y i eld the m o st definitive and comprehensive criteria. T o use only causal or only response v ariables in the criteria leaves the State or T r ibe in jeopardy of not protecting the waters from overenrichment. For example, an offensive w a ter body covered with an algal scum m ay be low in the causal v ariables of reactive nitrogen and phosphorus because they are tied up in biomass (in fact, T Nand T P w ere selected by EPA to avoid this problem). T herefore, the lake in question m ay m eet those criteria, but not its designated or existing use. T he converse m ay also occur, in which a highly enriched system with a rapid flushing rate appears to be acceptable w h en only the biota and dissolved oxy ge n are measured, but the load of nutrients being delivered downstream is degrading the receiving w aters. U sing a balanced combination of both causal and response v ariables in the criteria together with careful attention to seasonal v ariability should mitigate against these false positive and false negative results.



### � Candidate Variables for Criteria Setting (Chapter 5) EPA is beginning the National Nutrient Criteria Program with a survey of national computerized data sets such as STORET and NAWQA for T P , T N , chlorophyll a , and Secchi depth. T hese are believed to be the m o st comm on v ariables recorded with respect to enrichment investigations. T he information will be screened for suitability and then plotted o n regional m aps of the U n ited States for use by the R egi onal Nutrient Coordinators and RTAGs described above, and by the States. T his being the case, it is reasonable for individual States and T r ibes to begin with the same four indicators, although other causal and response v ariables are also discussed later in this m a nual (see Chapter 5).



### � Es tablishing R ef erence C o nditions (Chapter 6) Candidate reference lakes can be determined from compiled data and with the help of Regional experts familiar with the lake resources of the area. T here are two recomme nded w ays to go about this. On e is to select those lakes believed to be mi nimally impacted by human activity (e.g., with little or no riparian or watershed development). T hese lakes should be reviewed and v i sited to confirm their “natural” status. When satisfied with this list, a me dian v a lue (adjusted for seasonal and spatial variation) for T P , T N , chlorophyll a , Secchi depth, and other appropriate enrichment indicators can be prepared for each lake based on existing and/or new data collections. T he upper 25th percentile of the frequency distribution of these reference lakes can then be selected as the reference condition for each va lue (because these lakes represent the best obtainable and m o st “natural” condition, some allowance for v ariation should be m a de) (Figure 1.4(a)).
A nother option is to plot the frequency distribution of all of the lake data presently available by each variable and selecting percentiles for T P , T N , chlorophyll a , Secchi depth, and other similarly appropriate v ariables. The lower 25th percentile, reflecting high nutrient quality can be selected as the reference condition for each v a lue (because in this instance the pool of information likely includes lakes of considerably less than “natural” trophic condition) (see Figure 1.4(b)).

Nut r ient Criteri a—Lakes and Reser v oir s 1-13Figure 1.4. Tw o approaches for establishing a reference condition value using total phosphorus as the example variable.

Th e choice of the upper 25th and the lower 25th percentiles for the selected reference lakes and the random sample reference or census of all lakes in a class, respectively, is a rational but qualitativ e decision. I t represents the effort to avoid imposing an undue penalty on high-quality mesotrophic lakes in regions w h ere the lakes are predominantly oligotrophic. By selecting an upper percentile of the reference lakes, there is a g r eater likelihood that m o re of the broader population of lakes will comply

. C onversely, in regions of intense cultural enrichment, a lower percentile of the distribution of the remaining lakes used as reference m u st be selected to avoid establishing criteria based on degraded conditions. T he quarterly increments were chosen as a reasonable division of the data sets recognizable by the public, and the upper 25th percentile and lower 25th percentile as reasonable and traditional fractions of the range and frequency of distribution. T his approach promotes water quality enhancement and has broad application over the country

. A lthough these quantitative v a lues are believed appropriate to the objective of the program, w e recogniz e that some v ariation about such percentiles m ay be necessary . C ertainly, in severely degraded areas even a 25th percentile m ay be insufficient, and some lower fraction of the remaining reference v alues m ay be required. On the other hand, where all lakes or reservoirs are in remarkably g ood condition relative to cultural enrichment, the acceptable fraction of the reference condition m ay be ju stifiably increased. T he key point here is the presentation of a defensible scientific rationale for the determination. O therwise, EPA presumes the above g u idance will be appropriate.
Itis intended that these two frequency distributions, with different quartiles, will produce a similarly appropriate reference condition—all other factors being equal. I n either case, a number is g e nerated that can be used as an initial reference preliminary to criteria development, and as a source of comparison for individual lakes in the class.

1-14 Nut r ient Criteri a—Lakes and Reser v oir sTh is is the beginning of the process that eventually leads to adoption of nutrient criteria as part of the State or Tribal w a ter quality standards. O ther factors that m u st be addressed along the w ay are g aps in the database that m u st be filled by additional data collections, possible biases in the data or data interpretation (especially if the information w a s originally collected for another purpose such as fishery ma nagement or waste water investigations), sampling errors by field teams, and equipment changes or m easurement errors introduced by changes in analytical techniques.



### � Nutrient Criteria Development (Chapter 7) Nutrient Criteria Components
Th e m ove from data review and data g a thering to criteria development involves a sequence of fiv e interrelated elements:

• Examination of the historical record or paleolimnological evidence

• Compilation of reference condition data I n situations where a class of lakes in question are all significantly impaired and none can be perceived as approximately “natural,” then the best quality remaining constitutes the present day example of a reference condition. I n this instance the reverse of the earlier example of preselected mi nimally impaired reference lakes is true. Because m o st of the chosen lakes are assumed to be at least somewhat degraded, a lower percentile should be selected as a basis for the reference condition (e.g., the 25th percentile). To do otherwise is to ultimately lower the criteria to the level of present degradation and no restoration of the overenrichment condition w ill be achieved. Remember that the present day reference condition is only part of the criteria development process; historical conditions, data extrapolations, and the best objective judg me nt of the RTAG, including concern for downstream impacts are the other components that will collectively establish the criteria.
•	 I n some instances empirical modeling or surrogate data sets m ay be used where insufficient information exists. T his m ay be the case especially with reservoirs or significantly developed watersheds.
•	 T he objective and comprehensive interpretation of all of this information by a panel of specialists selected for this purpose (i.e., the RTAG). T hese experts should have established regional reputations and expertise in a v ariety of complimentary fields such as limnolog y , ecolog y, nutrient chemistry, and lake m a nagement.

• Finally, the criterion selected should first meet the optimal nutrient condition for that class of waterbody in the absence of cultural impacts and protect the designated use of that waterbody

. Second, it m u st be reviewed to ensure that the level proposed does not entail adverse nutrient loadings to downstream waterbodies. I n designating uses for a waterbody and developing criteria to protect those uses, the State or Tribe m u st take into consideration the w a ter quality standards of downstream waters. T his concern for downstream effect can be extended all the way to coastal w a ters, but in practice the imme diate downstream receiving wa ters will be the area of gr eatest attention for the resource m a nager. T his impact supersedes the level of optimal

Nut r ient Criteri a—Lakes and Reser v oir s 1-15enrichment for the target lake w a ters. I f a downstream impact is expected, the criteria for that lake or class of lakes should be revised downward accordingly

. On ce the initial criteria (either R egi onal or State/Tribal) have been selected, they can be v e rified and calibrated by testing the sampling and analytical m e thods and criteria v a lues against waterbodies of known conditions. T his ensures that the system operates as expected. T his can be accomplished either by field trials or by use of an existing database the quality of w h ich has been assured. This process m ay lead to refinements of either the techniques or the criteria.
Itshould be noted that criteria m ay be developed for m o re than one parameter. For example, all reference lakes of a g ive n class m ay be determined to m a nifest characteristics of a particular level for T P concentration, T Nconcentration, chlorophyll a , and Secchi depth. T hese four measures will comprise four criteria levels appropriate to optimal nutrient quality

. EPA expects a g ive n test lake to meet or surpass these levels for at least T Nand T P and one of the two response v ariables, and that a scientifically va lid explanation will be derived for the remaining exception before it can be determined to meet the criteria. The policy for such application will be developed by the State or Tribe in consultation with EPA

. The point here is that these four (or m o re) parameters used in this illustration are expected to be interrelated, and a consistent response for m o st if not all of them g ives a level of confidence to the resource m a nager that he has evaluated the lake properly

. When the lake in question reveals high T N and T P concentrations, but not the expected hig h chlorophyll a or low Secchi depth measurements, further investigation is indicated before deciding on whether criteria have been m e t. Flushing rates or inorganic turbidity or water color m ay be additional factors influencing the condition of the lake. Assessing Attainment with Criteria
A rule of compliance is then established for the criteria that have been selected for each indicator variable. T he four initial v ariables include two causal v ariables (T N and T P ) and two response v ariables (chlorophyll a and Secchi depth or a similar indicator of turbidity). Failure to meet either of the causal criteria should be sufficient to prompt action. However, if the causal criteria are m e t, but some combination of response criteria are not met, then there should be some form of decisionmaking protocol to resolve the question of whether the lake in question meets the nutrient criteria or not. T here are two approaches to this:
• E stablish a decisionmaking rule equating all of the criteria

• Establish an index that accomplishes the same result by inserting the data into an equation that relates the m u ltiple v ariables in a nondimensional comprehensive score With regard to m o re stringent State or T r ibal criteria or standards, Agency policy on antidegradation ge nerally requires that no lake or reservoir be allowed to degrade below its existing condition regardless of designated use or State or Regional criterion. (See Chapter 7, Section F, “Maintaining Existing Water Qu ality.”) This protects against the degradation of unique lakes of higher relative nutrient quality than migh t be stipulated in State or regional nutrient criteria.

1-16 Nut r ient Criteri a—Lakes and Reser v oir s

### � Management Response (Chapter 8)
Th ere are a v ariety of m a nagement responses possible to the overenrichment problem identified by the use of nutrient criteria. Chapter 8 describes a 10-step process that permits the resource m a nager to evaluate and select the best of these approaches to accomplish improvements in w a ter resource condition. Th e emphasis is on developing a scientifically responsible, practical, and cost-effective m a nagement plan. The chapter also describes three basic categories that encompass all m a nagement activities: education, funding, and regulation. I t closes with the admonition to always carefully evaluate the relativ e success of the management project, report results, and continue monitoring the status of the water resource. Finally, C h apter 9 and the appendices offer illustrations of the uses of models in the nutrient ma nagement process, a narrative description of the nutrient ecoregion m ap as presently developed, and examples of lake and reservoir nutrient m a nagement experiences. Future editions of this m a nual will incorporate actual Regional criteria v a lues and State/Tribal accounts of their use of the m a nual for nutrient criteria development.

Nut r ient Criteri a—Lakes and Reser v oir s 1-17

# CHAPTER 2 **The Basis for Lake and Reservoir Nutrient**  **Criteria**

A. Historical Perspective A. Histor ic al Per s pective B. T he Nutrient Paradi gm C. Connectin g W ater s hed Loadin g to the Lake: A Mas s Balance Model Approac h D. Tr ophic State Clas sifica tion S y st ems E. Us es of Tr ophic State Indices

Large-scale comparative studies of lakes have enabled scientists to identify key v ariables that influence lake structure and processes (Peters, 1986). T his empirical approach has its roots in regional studies (e.g., Naumann (1929) and T h ieneman (1921)) and in early among -l ake comparisons of lake function such as the role of m o rphometry on lake productivity (Rawson, 1955) and nutrient input regulation of lake fertility (Edmondson, 1961).
Th e eutrophication process was quantified by Vollenweider (1968, 1975, 1976), which brought the large-scale comparative approach to the forefront of limnolog y. Vollenweider developed a m a ss balance model using literature data from a diverse population of temperate lakes to demonstrate a surprisingly strong relationship between nutrient inputs to lakes and concentration of nutrients within the lake. T his relationship was sufficiently powerful to stand out against other sources of among -l ake v ariation and signaled that nutrient loading, as modified by hydrolog y, m orpholog y, and in-lake sedimentation, was the dominant factor explaining lake eutrophication.
Th e element phosphorus w a s the focus of study because overwhelming evidence sug ge sted that phosphorus limited algal growth in m a ny aquatic systems (Schindler, 1977). Phosphorus v a lues were highly correlated with algal biomass in lakes (Sakamoto, 1966); in turn, water clarity was shown to v ary with algal levels (Edmondson, 1972). With these linkages quantified, the science of lake m a nagement arose around the premise that reductions in nutrient loads would reverse eutrophication, as measured by reduced nutrient concentrations, algal levels, and g r eater w a ter clarity

. Empirical models provided limnologists with a quantitative basis for estimating the level of response to be expected from a given change in nutrient load from point and nonpoint sources. Models were the tools for forecasting the capacity of a lake to withstand change in its trophic state with v arious degrees of human development in its catchment (Dillon and Rigler, 1975). Recently, land use, as a surrogate for external nutrient loading, was used to effectively predict algal chlorophyll in lakes (Meeuwig and Peters, 1996); the strength of this approach stems from the strong correlation between nutrient losses and land use practices in catchments (Smart et al., 1985). T his linkage of land use to chlorophyll, a widely accepted measure of lake trophic state, is additional evidence for the importance of external control on lake processes.
Th e large-scale comparative approach placed individual lakes within a continuum, from least to m o st fertile. With this understanding, lakes lost some of their individuality because scientists now v iew ed them within the context of this continuum . T he functional relations between external nutrient loading , algal biomass, and water clarity were summarized in a small number of g e neral models. T hese models were typically based on regression analyses of data from individual lakes, averaged over a sampling

Nut r ient Criter ia—Lakes and Reser v oir s 2-1season. T he models quantified large-scale lake functions and provided the conceptual basis for lake ma nagement and restoration. Because these early data were drawn from a diverse g r oup of lakes, both in terms of lake type and ge ographic location, these models often are referred to as “global models.” An underlying assumption was that processes responsible for the large cross-sectional patterns in these g l obal relations also operate within single systems over time (Prairie and Marshall, 1995). About the time of Vollenweider 

### � s w o rk , Edmondson (1972) applied v i rtually the same concepts to data covering the enrichment and recovery of Lake Washington. Edmondson 

### � s work was tangible confirmation that a single lake responded to nutrient loading, as the pattern drawn from the data of m a ny lakes would sug ge st. T he remarkable feature during the 1970's was that a quantitative paradig m for lake function had been proposed based largely on data drawn from the literature. I t w a s a synthesis of ideas from earlier descriptive and empirical studies. A feature of predictions from empirical models w a s that there w a s a g r eat uncertainty in them; m a ny m odels exhibited an order of m agn itude v ariation. T his v ariation was a point of concern and the focus of subsequent study

. Du ring the two decades since the empirical period of the mi d-1970's, lake m a nagement has been influenced by several m ajo r thrusts that have modified, but not invalidated, the work of that period. With expanded data sets over the past 20 years, the original g l obal generalizations have been modified showing that in highly enriched lakes algal biomass does not increase in a uniformly linear relationship to phosphorus in all lakes (McCauley et al., 1989; Prairie et al., 1989; Watson et al., 1992) because other environmental factors also play a role. T he Organization for Economic Cooperation and Development (OECD, 1982) project was an early effort to systematically g ather data and quantify the relationship between nutrient load in w a ters and their trophic reaction. T his project, composed of four regional studies (Alpine, Nordic, Reservoir and Shallow Lakes, and North American), attempted to corroborate Vollenweider 

### � s generalizations. I ts approach shifted the focus of among -l ake comparisons from a global scale to studies within regions and studies of specific lake types. Since then, several regional studies have used the comparative approach to g e nerate empirical models specifically for local conditions. T hese regional studies have demonstrated the importance of other factors regulating algal biomass in lakes. Four other factors include nitrogen (Canfield, 1983; Pridmore, 1985), light limitation due to suspended solids (Hoyer and Jones, 1983; Jones and Knowlton, 1993), lake mo rphometry (Riley and Prepas, 1985), and g r azing by herbivores (Quiros, 1990).
B. The Nutrient P a radigm
Th e concept of nutrient criteria is based on the idea that nutrients produce changes in lakes and reservoirs that are considered to be detrimental to the function or use of the water body . T his idea of nutrient control of water body function is not new; it can be traced back to w h en Einar Naumann, the Swedish limnologist, elucidated the m ajo r part of the nutrient paradig m in 1929. His ideas of the relationship between nutrients and lakes can be summ arized in the following four statements:
•	 T he primary factors that determine algal biomass (the amount of plant organic m a terial) are the plant nutrients phosphorus and nitrogen.
•	 T he geolog y (and land use) within the lake 

### � s watershed determines the amount of nutrients that enter the lake and, therefore, plant biomass.

2- 2 Nut r ient Criteri a—Lakes and Reser v oir s• C hanges in the plant biomass affect the entire lake 

### � s biolog y. •	 T here is a natural ontogeny to lakes; the amount of plant biomass and, therefore, the entire biolog y of the lake increases as the lake ages.
A lthough there have been m a ny significant additions and improvements in our understanding of lakes since N a umann, his original concept of nutrients remains the basis of the nutrient paradig m. Below, each statement is examined as it refers to the need for and the development of nutrient criteria for lakes. 1. Phosphorus and Nitrogen as Limiting F a ctors for A l gal B i omass Th e primary factors that determine algal biomass (production) are the plant nutrients phosphorus and nitrogen. When Naumann (1929) sug ge sted this concept, he was probably drawing on a m u ch older concept, J u stus von Leibig 

### � s Law of the Minimum . T he law, as it is formulated today, states that the factor that is in shortest supply relative to the needs of the plants limits the g r owth of those plants. T he concept is central to the nutrient paradig m in lakes because it insists that v e ry few factors (usually only one factor, often a plant nutrient such as nitrogen or phosphorus) will actually limit plant g r owth.
If

only one factor, such as phosphorus, w a s always limiting, the task of developing nutrient criteria would be a simple m a tter of determining limits on that single factor. Unfortunately, the factor that limits plant biomass m ay (1) change seasonally or over longer periods of time, (2) vary depending on the land use, or (3) vary regionally . I t would m ake little sense to construct a single nutrient criterion w h en that nutrient m ay not necessarily limit a target lake or lakes. I t is for that reason that the emphasis of this document is the development of nutrient criteria based on both the nutrient inputs and the biological response. Th e causal v ariables such as phosphorus and nitrogen are essential criteria because they w ill be the limits necessary to establish m a nagement objectives and are usually directly related to discharge runoff abatement efforts. A lthough phosphorus is the limiting factor for m o st lakes and reservoirs, in som e regions the nutrient paradig m centers on nitrogen rather than phosphorus, especially where sewag e treatment plant effluent is involved (Canfield, 1983; Pridmore, 1985; Jones et al., 1989). T hese regions are often in the subtropics or at high latitude or altitude (Wurtsbaugh et al., 1985; Morris and Lewis, 1988) but are also found in parts of Britain. I n these lakes, nitrogen rather than phosphorus explains the among -l ake v ariance in algal chlorophyll, and chlorophyll-total nitrogen regressions m a tch the “fit and form” of chlorophyll-total phosphorus regressions developed for phosphorus-limited temperate lakes. Th e reason for nitrogen limitation is not y e t understood because of a long -h eld tenet in limnolog y that states that nitrogen fixation will compensate for shortfalls (Schindler, 1977) and that nitrogen limitation is not a persistent condition. T his belief does not seem as universal as once thought (Knowlton and J ones, 1996). I n some regions, nitrogen limitation m ay be a function of abundant phosphorus in the ge ological formation of the region (Canfield, 1983). Nitrogen limitation also m ay be tied to efficient nitrogen cycling in subtropical forests or m ay be a function of nitrogen uptake by rice and other crops in the subtropics. I n high-elevation lakes, phosphorus may be contributed by soil weathering, w h ereas nitrogen is rare in these low organic soils. Arecent literature review showed that nitrogen limitation w a s about as comm on as phosphorus limitation (Elser et al., 1990). Detailed water chemistry data from the mi dwestern lakes sug g est that nitrogen values in the epilimnion fall during summe r but that phosphorus v a lues remain m o re constant. T hese data sug ge st phosphorus m ay be cycled m o re efficiently than nitrogen and that without external inputs, late summer nitrogen limitation can be expected. T hese results do not imply that continued focus on phosphorus for
Nut r ient Criteri a—Lakes and Reser v oir s 2-3eutrophication control is unwarranted; however, a better understanding of the frequency and extent of nitrogen limitation is needed to discern lake function. Nitrogen criteria as well as phosphorus criteria are appropriate. Response v ariables such as chlorophyll a and algal or macrophyte species or biomass indicate the relative success of the nutrient m a nagement effort. By carefully incorporating both the causal and response elements, a State or T r ibe should be able to fine-tune its criteria to meet the necessary enrichment levels for a g ive n class of lakes. T h ese v ariables are described in m o re detail in Chapter 5. 2. Role of the Watershed
Th e g e olog y (and land use) within a lake 

### � s watershed determines the amount of nutrients that enter the lake and, therefore, plant biomass. T his statement is probably the primary reason for the development of nutrient criteria: human activity in the watershed affects a lake 

### � s function. I t is the reason behind the National Nutrient Assessment Workshop 

### � s conclusion that changes in land use can serve as an early warning system for changes in lakes (U.S. EPA, 1996).
I n simplest terms, a lake 

### � s nutrient concentration is affected primarily by the rate of weathering and erosion from the soils in the w a tershed. I f the underlying ge ological structure is g r anitic, then the rates of w eathering w ill be low and both the productivity of the terrestrial v ege tation and the concentration of nutrients in the runoff from the w a tershed will be low . O n the other hand, if the underlying bedrock is sedimentary, the weathering rates will be higher and the fertility of the soil and the nutrient content of the runoff water will be higher as well. C onsequently, Naumann (1929) observed that lakes in regions of sedimentary rock had higher algal densities (were g r eener) than lakes in g r anite-based w a tersheds. (For the purpose of this m a nual, atmospheric deposition of nitrogen and phosphorus, while possibly important, is accepted as a regional constant subject to further attention as our m a nagement technolog y improves.) Human activity has at least two effects on the natural load of nutrient input to lakes: (1) it disturbs the overlying v egetation, exposing the soil to increased weathering and erosion, and (2) it adds easily erodible nutrient-containing m aterial, such as fertilizers and animal w a ste, into the w a tershed. A s the biological surface of an undisturbed watershed is disrupted, and as people m o ve into the watershed, it can be expected that there will be increased soil and nutrient runoff. Of course the degree of disturbance relative to the size of the lake will affect the impact of the disturbance; building a summe r cottage would not have the same impact on a lake as would clear-cutting a forest or developing a condominium complex. Sometimes the term “assimilative capacity” is used to imply that the lake has a certain capacity to absorb the impact of disturbance. T his concept, althoug h comforting, probably has little basis in fact. Im pact, until demonstrated otherwise, is probably better thought of as a continuous response to nutrient increases. T he degree of change will depend on other factors, such as the size of the lake, and the change m ay not be immediately or even ever detectable to humans or their monitoring instruments. However, whether detected or not, changes do occur. I t is for this reason that w a tershed disturbance is a sensitive early w arning of lake change. C learly, biological impact within the lake will be directly related to the increased amount of nutrient loading, and that impact will occur, w h ether or not it is detected. Naumann (1929), nonetheless, used the relationship between nutrients and plants to establish a trophic state classification. He probably began his classification scheme with the perfectly reasonable go al of classifying lakes into those with low (oligotrophic) and high (eutrophic) plant biomass.
2- 4 Nut r ient Criteri a—Lakes and Reser v oir sO ligotrophic lakes were clear with little algae, w h ereas eutrophic lakes were g r een. H e then added to his classification system the causal factors that produced this degree of g r eenness, for example, the amounts of nitrogen or phosphorus. He called these the “factors of production.” Oligotrophic lakes were those that had low production (biomass) because they w ere low in nutrient concentrations. Eutrophic lakes we re g r een because there w e re abundant nutrients to support the g r owth of algae.
Th e combination of the factors that affected production (causal factors) with plant production itself (response v ariable) allowed for a suite of trophic classes that dissected lakes into g r oups of v arying production based on the factor or factors that were thought to limit that productivity . T he classic oligotrophy -e utrophy axis was based on limitation by nutrients. T he mesotrophic category was added to describe situations intermediate between oligotrophy and eutrophy . T he term “ hypereutrophic,” or hypertrophic, was added by Wetzel (1966) to describe situations of extreme eutrophy where light, not nutrients, is the dominant environmental factor controlling g rowth. T his continuum of trophic states is illustrated in Figure 2.1. 3. Trophic Causal Chain Naumann (1929) was very insightful in recognizing that the components of the lake are an interconnected system; as one component—the plants—responds to nutrient inputs, other biological, chemical, and even physical components would be affected as well. I ncreases in nutrient loading do not necessarily directly affect any component other than the plants, but by v arious pathways, other components of the lake ecosystem, such as zooplankton, fish, and hypolimnetic oxy ge n concentration, are affected as well. T his trophic state cascade is depicted in Figure 2.2. Because of these linkages between components, numerous v ariables m ay respond to v arying degrees to increases in nutrients. N ot only w ill algae or macrophytes increase, but zooplankton and fish biomass may increase as w e ll, plant and animal species m ay change (with some g o ing extinct), and hypolimnetic oxy ge n m ay be depleted. People react to the v arious changes or sy mp toms of lake condition reflected in the chemistry and biolog y that cascade from the change in loading, not directly to the change in loading or nutrient concentration itself.

Figure 2.1. A trophic continuum .

Nut r ient Criteri a—Lakes and Reser v oir s 2-5Figure 2.2. T he trophic causal chain.

Th is cascade of biological and chemical changes produces a variety of choices for the response variables needed to supplement the causal v ariables in the formulation of nutrient criteria. Choice of the response v ariable can be m a de based on sensitivity to change, cost of measurement and analysis, or importance to designated use. 4. Lake Aging
Th e idea that lakes undergo directional change in plant production as they ag e was probably related to the observation that shallower lakes appeared to have m o re plant biomass in them than deeper lakes. Th is observation later translated into the idea that increases in plant biomass w e re inevitable as a lake ages and fills in. This concept has lead to terms such as “natural eutrophication” to describe inevitable increases in plant biomass as a lake becomes older and shallower. I f natural eutrophication is thought to proceed at a rate related to inputs from the w a tershed, then w e might expect to see accelerated rates of eutrophication if cultural influences occur in the watershed (cultural eutrophication).
If

trophic state is a description of the biological condition of the lake, eutrophication describes a lake that is becoming mo re eutrophic (Figure 2.3). Specifically, it describes a change in the direction of eutrophy

. A lake does not have to become eutrophic to have undergone eutrophication; it only has to move in the direction of eutrophy. Oligotrophication describes the process of a lake m ovi ng in the alternative direction, towards oligotrophy

.

2- 6 Nut r ient Criteri a—Lakes and Reser v oir sFig u re 2 .3. Eutrophicatio n a nd olig ot rophicatio n in relatio n to the trophic continuum .

The term “nutrient enrichment” is in m a ny, if not m o st, instances an alternative term for eutrophication. However, the emphasis in that term is on the increase in nutrients rather than on the lake 

### � s response to that enrichment. I f causal factors such as nutrient enrichment are closely linked via our terminolog y with the lake response, problems can arise if, for example, a lake 

### � s biolog y changes without any change in nutrient loading or, conversely, if nutrient loading occurred without a coincident change in biolog y. T hese are not j u st hypothetical situations. T he addition or removal of a benthivorous fish, such as bullhead or carp, can change the internal regeneration of nutrients and change the biological condition of the lake without any enrichment, or at least external enrichment, of the lake. T he increase in gr azing on algae because of the addition of a piscivore or the removal of the zooplanktivores also can alter the amount of plant biomass without the need of an alteration of nutrient loading . T hese m anipulations, often called biomanipulations (Shapiro et al., 1975), are a type of lake manipulation that can alter the state of the lake without a change in nutrient load. Natural eutrophication should not be confused with naturally eutrophic. T he latter term describes lakes in watersheds where the natural load of nutrients is high despite the absence of human activity

. Natural eutrophication describes a belief that lakes, presumably all lakes, have m o re plant m a terial within them (become m o re eutrophic) as a natural part of becoming older.
Th e concept of natural eutrophication is probably correct to the extent that processes within the lake such as nutrient regeneration m ay enhance the effect of inputs from the watershed. T he importance of these internal processes are still not w e ll understood, especially along a gradient of lake aging . If becoming shallower were the only consideration, then the internal concentration of nutrient would increase only to a level as high as that in the incoming wa ter. Alake in a w a tershed in w h ich the concentrations of nutrients were v e ry low in the incoming water would not become that m u ch m o re eutrophic even if it did become shallower. However, a shallower lake also m ay have increased m acrophyte g r owth and increased regeneration of nutrients from the sediments. I n this case, the biological response would become increasingly independent of the external supply of nutrients.
A difficulty w ith dwelling on the possibility of natural eutrophication is that it emphasizes an inevitability of the eutrophication process; it also takes the focus off the imme diate effects of the
Nut r ient Criteri a—Lakes and Reser v oir s 2-7watershed on the lake. Natural eutrophication is a process that is measured in terms of thousands of y ears, whereas the problems we encounter m o st often with lakes are the effects of processes that take only a few years to develop. Watershed disturbance can rapidly m ove a lake to a new level of nutrient concentration and biological response. More important, in m o st or m a ny lakes, that response is, to some extent, reversible; we have not j u st m ove d rapidly down an irreversible path. Cultural eutrophication is, in fact, a reversible process, and nutrient criteria are an important element in this reversal. C. Connecting Watershed Loading to the Lake: A Mass B a lance Model Approach Like m a ny earlier nutrient loading m odels, Vollenweider used a m a ss balance model for the basis of the prediction (see Chapter 9 Section B). Below is a basic review of Vollenweider 

### � s model and how it is used to link loading to concentration in a lake or reservoir.
The term “m a ss balance model” comes from the assumption that a substance such as phosphorus cannot j u st appear or disappear from a reservoir; it m u st come from somewhere and it m u st g o somewhere. T he phosphorus g o ing into the reservoir m u st either go out again through some outflow, be sedimented to the bottom, incorporated into macrophyte biomass, or remain in the water in either dissolved or particulate forms. I t is this phosphorus that remains in the w a ter that is of interest because it is the amount that is available for algal growth. Mass balance modeling is done in a m a nner similar to keeping a checking account. T h e total amount of phosphorus entering the reservoir (loading) each year is measured. Loading describes the total amount of m a terial being m oved in a stream in a g ive n amount of time. T h e loading from any source ( i ) is calculated as: Loading ( J i ) = Water D i scharge ( Q i ) × Concentration ( Ci )

or J

i = Q i Ci The external loading, sy m bolized by Vollenweider by the letter J, can be calculated as the sum of the loading from all the external sources ( i ) to the lake:

n 

### J = 

## ∑ Q i 

### C i i = 1 Loading often is used to measure export of a nutrient or sediment from a watershed. For example, it is important to g a uge the effects of farming practices on erosion, so we migh t calculate the tons of sediment removed from a watershed over a year. On the other hand, if the stream enters a lake or reservoir, we migh t want to know how m u ch m a terial is entering that body of water. I n this case, nutrient loading might affect w a ter quality, and sediment loading might affect the fill-in rate. Predicting the internal concentration of a substance in a lake is also done using a mass balance equation. T he appropriate mass balance for this prediction is based on the idea that the rate of change of the total amount of a m a terial (M) in a lake (dM/dt) is dependent on the total amount of m a terial that enters a lake (J) and the total amount that leaves in the same time period:

2- 8 Nut r ient Criteri a—Lakes and Reser v oir sdM/dt = ( 

### � Q i C i )



### � Q o C o
or dM/dt = J



### � Q o C o If

the reservoir is not rapidly changing from one year to the next, the amount coming in one year should be equal to the amount g o ing out:
In flow = Outflow (i.e., dM/dt = 0)

or J = Q o C o If

we assume, as did Vollenweider, that the lake is completely mixed, then the lake concentration is equal to the outflow concentration:
C lake= C o Th erefore, the amount entering the lake will be equal to the amount leaving : J = Q o C lake Rearranging this equation, we obtain an equation predicting the concentration in the lake based on the external loading of the substance and the outflowing discharge of water:
C lake= J/Q o No tice that the term (J /Q o ) has the units of concentration. Consider that it is the incoming loading divided by the outgoing water discharge.
Th is model is designed to predict the concentration of any conservativ e ma terial. A conservativ e ma terial, such as chloride or sodium, does not sediment within the lake basin, and the amount leaving the basin over the outflow should be equal to the amount entering

. Conservative materials are not very interesting in themselves, but they are used as indicators of the accuracy of budgets of m a terials that do sediment within the lake. I f the input of a conservative element is not equal to the output, then som e other source of water and/or material has been neglected. A nonconservative m a terial, such as phosphorus, is one that is lost from the water column (e.g., sedimentation) within a lake basin. Because some m a terial is lost from the w a ter column, the input loading is not equal to the output loading . T o model a nonconservative m a terial, a sedimentation term mu st be added to the equation:
I nput = Output + Sedimentation Sedimentation was considered by Vollenweider to be proportional to the m a ss of the substance in the lake (M). T he total amount of m a terial in the lake (M) is calculated as:

Nut r ient Criteri a—Lakes and Reser v oir s 2-9M = C lake V wh ere V = v o lume of the lake (m 3 ) Vollenweider considered the amount of m a terial lost to the sediments. T his is designated by sM, wh ere s is a first order fractional loss of the m a ss settled per unit time (1/t) and M is the m a ss of substance in lake (C lake V). T he sedimentation coefficient, s, is really a net sedimentation term, because the m a terial m ay not only settle out of the w a ter column but also m ay be resuspended into the column from the sediments.
Th e m a ss balance equation, with the added sedimentation term, becomes dM/dt = J



### � Q o C o 

### � sM Vollenweider then assumed that over a calendar year the system w ould be near or at steady state, and the mass balance equation becomes: J = Q o C o + sM
No te that all the terms still have the dimensions of amount per time.
A n equation for predicting the lake concentration from loading can be produced by substituting C lake for C o (again assuming that the lake concentration is equal to the outflow concentration) and substituting C lake V for M: J = Q o C lake+ sC lake V Rearranging, we obtain the predictive equation:


### J C la ke = 

### Q o 

### + sV
Th e equation can be further rearranged into the form :


### J  1  C la ke 

### =   Q o 

###  1 + sV / Q o 

###  With this equation, several things became clearer about loading : •	 V ollenweider considers only the “total” form of the substance. He does not discriminate between dissolved and particulate forms.

2-10 Nut r ient Criteri a—Lakes and Reser v oir s• The term (J /Q o ) has the dimensions of concentration (m g/m -3 ) and represents the averag e incoming concentration of the substance (Vollenweider, 1976) assuming evaporation is mi nimal. Th is term is sometimes replaced by a sy m bol for incoming concentration, C I .

• The term (1/(1 + s(V/Q o )) is really a description of the fraction of the incoming concentration that is not retained within the basin. I n some models, retention is represented by the sy m bol R

o )), by (1- R ). and the term (1/(1 + s(V/Q

• The term (V/Q o ) has the units of time and is the hydrologic residence time, T or t, which represents the average time that w a ter remains within the lake. Using these simpler sy m bols, the equation can be reduced to a simple statement of the relationship between loading and lake concentration: 

###  1  C la ke 

### = C i   1 + sT  

wh ere Ci = average inflow concentration.
A lthough relatively simple, the equation illustrates the m ajo r aspects of prediction with m a ss balance m odels and trophic state:
•	 T he concentration of a substance such as phosphorus in the reservoir (C lake ) is directly determined by the concentration of that substance in the incoming streams (C i ). T he higher the concentration in the streams entering a reservoir, the higher the nutrient concentration will be in the reservoir itself.
•	 I nternal factors such as w a ter residence time (T) and the net sedimentation coefficient (s) determine the amount of m a terial that is sedimented, and therefore lost, from the water column. Th e longer the w a ter residence time, the g r eater the amount of m a terial that will be sedimented w ithin the reservoir, and the lower the reservoir concentration will be. Additional terms have been added to the equation to account for release of a nutrient from the sediments into the open w a ter or for the biological availability of the incoming phosphorus. T hese additional terms can m ake the predictions m o re specific to the particular reservoir being m odeled. See Chapter 9 for a discussion of these models. D. Trophic State Classification Systems
Th e concept of trophic state, with its relationship of the watershed to the chemistry and biolog y of the water body, has become one of the primary methods of classifying lakes. Despite controversies of definition, it has endured and probably w ill endure because of several important reasons:

• Hi story and tradition . T he language and implications of trophic state are deeply ingrained in limnolog y. I n a sense the concept of trophic state is the nutrient paradig m.

Nut r ient Criteri a—Lakes and Reser v oir s 2-11• Communication

. When a trophic state term, such as eutrophic or eutrophication, is used, there is a g e neral agreement as to what a lake is like in terms of nutrients and biolog y. T his implication of interrelationships tends to comm unicate far m o re information than can be implied with the statement of the v a lue of a single v ariable.

• Education . T he trophic state concept, even in qualitative terms, is a convenient v e hicle to educate the public on the simplicity, and indeed the complexity, of the relationship between land use and the biological consequences.
Tr ophic state classification m ay have begun as a continuum concept, but it rapidly evolved into a classification of “types.” Most, but not all, existing trophic classification systems, or indices, reflect this typological emphasis. T he representation of this type of classification scheme is simply of list of characteristics for a specific trophic type (Table 2.1). Lakes are assigned to a trophic class based on their agreement with the characteristics on the list. This type of classification runs into difficulty w hen specific v ariables m ay classify the lake in different categories. T his happens w h en the correlation between variables is not strong

. Th e essence of a typological trophic classification is the belief that there is a real type of lake called eutrophic in the sense that there is a real type of human called young, mi ddle aged, or elderly

. Lakes can, therefore, be classified and placed into one of these types. Eutrophication is the progressive directional change of a lake out of one type and into another. Once in a type, the lake takes on certain characteristics by which it can be recognized and, therefore, classified. Such classifications are easily recognized from lists of characteristics typical for each trophic state heading (Table 2.1).
Th e OECD index (Vollenweider and Kerekes, 1980) used a statistical approach to quantify the ranges of several v ariables within each trophic designation (Table 2.2). T his index w a s derived by asking a g r oup of scientists their opinion as to w h at w a s the average v a lue for each trophic class for each variable. T he summarized data w e re used to produce bell-shaped curves for each v ariable for each class (Figure 2.4). T he overlap that resulted emphasized that lakes of the same concentrations m ay be in m o re than one trophic class.
Th e second approach to trophic classification assumes that trophic types are not real but abstractions and, to some extent, arbitrary divisions of a continuum . T his approach is similar to Naumann 

### � s original classification. I n this case, the discussions have been g e nerally along the lines of what is the appropriate trophic state v ariable that should be divided into trophic state classes. T he discussion of appropriate variables for classification is continued in Chapter 5. Some continuum -b ased classification indices emphasize that trophic state reflects a number of variables, recalling the m u ltiple v ariable approach of typological schemes. For example, Huber et al. (1982) stated that “trophic state is the integrated expression of the nutritional status of a w a ter body . As such, it is w i dely accepted that no single trophic indicator or parameter is adequate to completely describe and/or quantify the concept.” Multiple v ariable indices differ from the typological indices largely in that they quantify the m u ltiple v ariables found in the trophic state list of characteristics. T hese approaches emphasize the collection of quantitative data and are a m ajo r advance over qualitativ e listings.

2-12 Nut r ient Criteri a—Lakes and Reser v oir s**Ta ble 2.1. Illustration of a Typological T**  **r ophic Classification System Based on Lake**  **Characteristics ( a**  **dapted from Rast and Lee, 1987)**

**Variable Gene**  **ral Characteristics Oligotrophic**  **E utrophic**  To tal a q uatic plant production Low Hi gh Number of al g al species Man y Fe w Characteristic al g al gr oups Gr eens, diatom s B lue- gr eens Rooted a q uatic plants Spar se Abundant Ox yg en in h y polimnion Present Absent Characteristic fish Deep-dwellin g , cold waterf is h such as trout, s a lmon, and cisco Sur face-dw ellin g , w arm w aterf is h such as pike, per c h, and bas s ; als o bottom -dw eller s such as ca tfish and carp Wa ter q ualit y f or domestic and industrial us e G ood Poor

**Ta ble 2.2.**  **O ECD Ranges Based on Scientists’ Opinions (af**  **t er Vollenweider and Carekes, 1980)** 
**Vari able**  **Oligotrophic M**  **esotrophic E**  **utrophic** To tal phosphorus m ean ra nge (n) 8 3-18 ( 21 ) 27 11-96 ( 19 ) 84 16-390 ( 71 ) To tal nitr og en m ean ra n ge (n) 660 310-1600 ( 11 ) 750 360-1400 (8) 1,900 390-6100 ( 37 ) Chloroph y ll a m ean ra nge (n) 1.7 0.3-4.5 ( 22 ) 4.7 3-11 ( 16 ) 14 2.7-78 ( 70 ) Peak c hloroph y ll a m ean ra nge (n) 4.2 1,3-11 (6) 16 5-50 ( 12 ) 43 10-280 ( 46 ) Sec ch i depth (m) m ean ra nge (n) 9.9 5.4-28 ( 13 ) 4.2 1.5-8.1 ( 20 ) 2.4 0.8-7.0 ( 70 )

No te: U n its a re � g/ l (or m g/ m 3 ), exc ept S ec chi depth; m eans are geometri c annual m eans (log 10), exc ept peak c hlorophyl l a
.

Nut r ient Criteri a—Lakes and Reser v oir s 2-13Figure 2 .4. Probability distribution curves for total phosphorus by trophic sta t us class.
Probably the m o st sophisticated of the m u ltivariate indices is that of B r ezonik and Shannon (1971), which uses principal components analysis to derive a trophic state index (TSI) based on seven variables: (1) TP, (2) primary production, (3) inverse of Secchi depth, (4) total organic nitrogen, (5) chlorophyll a , (6) specific conductance, and (7) the inverse Pearsall cation ratio ([Ca]+[Mg]/[Na]+[K]). Other less sophisticated indices g e nerally combine unweighted v ariables by one means or another. T he EPA Index (U.S. EPA, 1974) ranked lakes based on “the percentage of the 200+ lakes exceeding Lake X in that parameter”; the index w a s “simply the sum of the percentile ranks for each of the parameters used. ” T he variables used w e re T P , dissolved phosphorus, inorganic nitrogen, Secchi depth (500-Value [inches]), chlorophyll a , and mi nimum dissolved oxy ge n (15-DO mi n ).
Th ese m u ltivariate quantitative indices m ove trophic classification from a typological concept to one assuming a continuum of v a lues, but they suffer from several drawbacks. T h e indices require that all the variables be measured before an index v a lue is derived, thus g r eatly increasing the cost and analytical time required. A missing v alue eliminates a T SI determination. Changes in a single v ariable often will be overlooked in the index if other indices do not change. Conversely, if index v ariables are correlated, then a change in one m ay trig ge r a change in a number of v ariables causing an exag ge ration of the amount of change. Finally, a change in the index does not tell the reader what has changed; information
2-14 Nut r ient Criteri a—Lakes and Reser v oir sis lost. Carlson (1977) sug ge sted returning trophic state to its first principles: a quantifiable plant biomass-based concept that could fit easily into existing and future nutrient and lake models. He did not redefine trophic state but used Naumann 

### � s (1929) original idea of a classification according to plant biomass. I nstead of the distinct typological classes, Carlson assumed algal biomass to be from a continuous range of v a lues. He sug ge sted that the comm only used trophic classes were arbitrary divisions of the biomass continuum . T o emphasize the continuum nature of a biomass-based trophic state, he used a numeric rather than a nomenclatural scale, dividing the range of algal biomass based on a doubling of Secchi depth, a v ariable that is affected by algal density

. Th e original Secchi depth equation in Carlson (1977), reproduced below, illustrates how the index was constructed: 

###  ln SD  T S I ( S D ) = 10  6

− ln 2   
Th e basic Secchi disk index was constructed from a doubling and halving of Secchi disk transparency . T he base index v a lue is a Secchi depth of 1 m, the logarithm of w h ich is 0. ln 1 = 0 6



### � 0 = 6 10 × 6 = 60
Th erefore, the T SI of a 1 m Secchi depth is 60. I f the Secchi depth w e re 2 m , ln 2 / ln 2 = 1 6



### � 1 = 5 10 × 5 = 50
Th e index utilizes relationships between trophic v ariables to produce equations that allow the index to be calculated from v ariables other than Secchi depth. T he indices for the chlorophyll and T P are derived in a similar m a nner, but instead of a Secchi depth v a lue in the numerator, the empirical relationship between chlorophyll or T P and Secchi depth is g ive n instead. For example, the T SI equation for chlorophyll is:



### .  2 0 4

− 0.6 8 ln CH L  T S I ( C H L ) = 10  6

− ln 2   

Nut r ient Criteri a—Lakes and Reser v oir s 2-15The above forms of the equations illustrate how the indices w e re derived, but they can be simplified for everyday use:
TSI (SD) = 60



### � 14.41 ln SD
TSI (CHL) = 9.81 ln CHL + 30.6
TSI (TP) = 14.42 ln T P + 4.15
Th e v a lue of m u ltiple equations is that the same T SI va lue should be obtained no m a tter w h at variable is used to calculate it (i.e., a comm on scale). T his means that if data are mi ssing for chlorophyll, for example, a similar v a lue could be obtained from transparency

. A lthough these three v ariables should covary , they should not be averaged because neither transparency nor T P are independent estimators of trophic state. Using transparency or phosphorus as an estimator of chlorophyll is v e ry different from assuming equal and independent status of the v ariables. Secchi depth and T P should be used as a surrogate, not a covariate, of chlorophyll.
I n essence, this T SI scale is an indexed scale of algal biomass. B ecause it is directly related to lake phosphorus concentration, it fits easily into phosphorus loading m odels such as that of Vollenweider (1976). I f a loading m odel can predict phosphorus concentration in the water, then the trophic state can be predicted easily as well. Work by Kratzer and Brezonik (1981) allows the index to be predicted from nitrogen concentrations as well. TSI(TN ) = 54.45 + 14.43 ln(TN) [Nitrogen v a lues m u st be in units of m g/L]
Th eir index could be used especially if there is any indication that nitrogen, rather than phosphorus, is limiting

. E. Uses of Trophic State Indices
I ndices have several purposes. I n some instances, indices take uncorrelated variables and ag gr egate them into a single word or v a lue so that a g e neral condition m ay be easily comm unicated. For example, a pollution index migh t include concentrations of heav y me tals, pesticides, and phosphorus, which m ay or may not be correlated but could contribute to w h at the public considers to be pollution. T he multivariate trophic state indices are of this type. T hese indices assume that trophic state consists of a number of possible attributes of lakes, ranging from nutrient concentration to hypolimnetic oxy g en depletion. An index is necessary to somehow combine these v arious ingredients into the trophic stew and relate lakes to one another in a national continuum

. Alternatively, indices such as that of Carlson (1977) use the term “ index” to mean that the v ariable m easured is not trophic state, but an indicator of trophic state. For Carlson, trophic state is plant biomass. Chlorophyll, transparency, or even T P are v ariables that can estimate biomass but are really not living plant (autotroph) carbon. Even the measurement of organic carbon is not free from interferences from detritus or nonplant carbon. T rophic state is used as a surrogate for a real entity, plant biomass, that cannot be measured directly

.

2-16 Nut r ient Criteri a—Lakes and Reser v oir sA third use of the term “index” that combines aspects of the first and second definition is that of simplification of a concept of measurement. For example, few readers know that the R i chter scale, used to describe the m agn itude of an earthquake, is the m a ximum deviation of a needle on a seismograph 62 miles from the epicenter. Actually, m o st people do not need to know the mechanics of calculating the Richter scale to have a sense of the severity of an earthquake. I n the same sense, trophic state indices are shorthand me thods to convey information. T otal phosphorus or chlorophyll has little v a lue in comm unication unless there is some standard to w h ich the reader or listener can compare the v a lue. In this case, saying eutrophic or T SI of 60 rather than “chlorophyll concentration is 20 μ g/L” m ay convey information m o re easily because there are fewer terms to explain to an audience and fewer terms for the audience to put into the context of their own experiences.
I n each of these instances, the index helps the reader equate several parameters in one indicator of enrichment condition so that an interpretation of condition is conveyed and conclusions can be m a de. Whether the measures of w a ter quality compiled in a data set are used individually or collectively in an index, they are the essential, objective information the resource m a nager needs to determine the status of a lake or reservoir. With the representative information and a g u ide as benchmark criterion defining the relatively unimpaired and attainable w a ter quality condition for comparison, the m a nager can classify , select, and plan for the restoration and protection of the lakes and reservoirs in his or her region.

Nut r ient Criteri a—Lakes and Reser v oir s 2-17

# CHAPTER 3 A. Def i nin g the Resour ce of Concer n B. Cla ssi fi ca tion 

# Preliminary Steps for **Criteria Development**

A. Defining the Resource of Concern Defining the resource of concern begins the overall process of establishing nutrient criteria. Resources of concern here are lakes and reservoirs, and m a nagers m u st decide which water bodies are to be included in the population to w h ich criteria will be relevant and applicable. Many States define ju risdictional lakes (“waters of the State”) as those above a size threshold. For example, the inclusion of farm ponds and other similar small ponds can potentially result in an inordinately large population of lakes that would be required to be considered during the criteria establishing process. T hese practical considerations often m ake it desirable to eliminate small water bodies from the resource population.
States m ay have already established a regulatory size threshold that specifies what should be considered a lake from the State management perspective. For example, the Florida Department of Environmental Protection routinely samples only lakes larger than 10 acres, because there are m o re than 7,000 lakes of 10 acres or m o re in Florida (Huber et al., 1982) and lakes under 10 acres are thought to number 10,000 or m o re. Florida surface w a ter quality criteria apply to all lakes not wholly owned by a single person other than the State (Florida Amended Code, 62-340). States are encouraged to determine if the established threshold is appropriate for the nutrient criteria setting procedure described in this document and to adjust it as necessary . I f States have not set size limitations that define a lake, State water resource agencies should evaluate the lake resources in the State to determine appropriate siz e limitations. T he goal of such an exercise is to eliminate small w a ter bodies that, because of their siz e (and resulting hydrolog y) or uses (e.g., small agricultural impoundments), do not accurately represent typical lake conditions or do not exhibit expected responses to stressors. For the purpose of this document, lakes are defined as natural and artificial impoundments with a surface area g r eater than 10 acres and a mean water residence time of 14 or m o re days. Man- m ade lakes (i.e., artificial lakes) with the same characteristics m ay be v i ewed as part of the same system

. Reservoirs are m a n- ma de lakes for which the primary purpose of the impoundment is other than recreation (e.g., boating, swimmi ng) or fishing, and the water retention time and water body depth and v o lume v ary widely. Hydroelectric power g e neration, drinking water supply, and flood control are examples of typical uses of reservoirs.
Im poundments on rivers, especially ones on larger rivers, also require specific definition. Im poundments behind low-head dams for navigation, as on the Ohio and Mississippi Rivers, are hardly lakelike in their characteristics; in fact, they are called navigational pools. At what point does a pool on a river become a lake? Limnologists g e nerally consider lakelike characteristics to increase with w a ter mean residence time. Many studies sug ge st that phytoplankton do not accumulate at retention times less than 7 days (e.g., K imme l et al., 1990).



### Nutrient Criteria—Lakes and Reservo ir s 3- 1These definitions are provided for the purpose of illustration and consistency

. States with legal definitions of their lakes or reservoirs should obviously adhere to their own terms and interpret this gu idance accordingly

. B. Classification 1. Geographic Divisions
Th e establishment of a single, national nutrient criteria for lakes is not a realistic g o al because of the significant v ariability of w a ter bodies that exist across the country in a v ariety of climates, g e ographic locations, and ecosystems. On a national basis, individual lakes and reservoirs are affected by v arying degrees of development, and user perceptions of w a ter quality can differ even over small distances. A s a result, the nutrient criteria development process discussed in this document is based on an approach that acknowledges g e ographic differences in lakes across the country and within States and that uses a classification system to clarify those differences. The initial classification scheme used in this m a nual is the ecoregion approach (Omernick, 1987, 1988, 1995). However, m a ny v iable regionalization techniques exist for delineating g eographic regions.
Th e process of identifying ge ographic divisions (i.e., regionalization) is part of a hierarchical classification procedure with the purpose of g r ouping similar lakes together (i.e., to prevent comparison of unlike lakes). C lassifying lakes reduces the v ariability of lake-related measures (e.g., physical, biological, or w a ter quality v ariables) within classes and m a ximizes the v ariability among classes. Classification invariably involves professional judg me nt to arrive at a workable system that separates clearly different ecosystems, y e t does not consider each lake a special case. T he intent of classification is to identify g roups of lakes that under ideal conditions would have comparable characteristics (e.g., biological, ecological, physical). T o the extent possible, classification should be restricted to those characteristics of lakes that are intrinsic, or natural, and are not the result of human activities. These characteristics include size, maximum or mean depth, detention time, and shape.
Th e g e neral approach to the regionalization process is to establish divisions at the broadest level and then to continue to stratify to a reasonable point. I n this section, a regionalization system for the national scale is presented to provide a framework for developing nutrient criteria. EPA encourages States to identify State-specific subregions, if appropriate, and to use the national regionalization schem e discussed below as the basis for further subdivisions.



### � National Nutrient Ecoregions Ecoregions are a mapped classification system of ecological regions, that is, regions with assumed relative homogeneity of ecological characteristics (Omernik, 1987). EPA has developed m aps of ecoregions of the United States at v arious levels of resolution and ag gr egation (Omernik, 1987). T he mo st co mmo nly used is the Level III ecoregions, consisting of 79 ecoreg i ons in the contermi nous United States. Ecoregions were based on interpretations of the spatial coincidence in all g e ographic phenomena that cause or reflect differences in ecosystem patterns. T hese phenomena include g e olog y , physiography , vege tation, climate, soils, land use, wildlife, and hydrolog y. T he relative importance of each characteristic v aries from one ecoregion to another regardless of the hierarchical level. For the National Nutrient Criteria Program, a map of ag gr egations of the Level III ecoregions was developed to define broad areas, within w h ich there are g e neral similarities in the quality and types of ecosystems as well as in natural and anthropogenic characteristics that affect nutrients (see Figure 1.1).

3- 2 

### Nutrient Criteria—Lakes and Reserv o irsTh e regions are intended to provide a spatial framework for g e neral g u idance and reporting for the Na tional N u trient C r iteria Program

. Th ese nutrient regions and their component Level III ecoregions are described more fully in Appendix A. T he nutrient regions delineated in Figure 1.3 are not intended to be homogeneous. T hey are ag gr egations of ecoregions w h ere expectations within a nutrient region are m o re similar than expectations among nutrient regions. Some regions m ay be characterized by relative homogeneity; other regions m ay be characterized by extreme heterogeneity

. An example of a heterogeneous region is Region XI I , the Southern Coastal Plain, which has lakes ranging from ultra-oligotrophic lakes in sandy ridges and hills to highly eutrophic solution lakes in areas with phosphatic soils (Griffith et al., 1997). By comparison, Region V I , the Corn Belt and Northern Great Plains, is m o re homogeneous and is expected to be dominated by m esotrophic to eutrophic lakes, owing to the fertile plains soils and extensiv e agriculture. Region V III , the Nutrient Poor Larg e ly Glaciated Upper Midwest and Northeast, is dominated by oligotrophic lakes, but it also has small subregions with higher nutrient concentrations and me sotrophic lakes (Omernik et al., 1988; Rohm et al., 1995). The nutrient regions can form the basis for initial development of nutrient criteria. Expectations can be developed for nutrient concentrations and loadings in each of the regions and criteria derived from those expectations.



### � F urther Subregionalization The heterogeneity w ithin m a ny of the nutrient regions will require further subregionalization or subclassification to implement nutrient criteria. Using the ecoregion concept as a basis, EPA has developed lake regions based on phosphorus and other considerations for three areas: the Upper Midwest, comprising parts of nutrient reg i ons V I , V II , and V III in Minnesota, Wisconsi n, and Michig an (Omernik et al., 1988); the Northeast, comprising nutrient regions VI I , V III , and X IV rang i ng from northern Pennsylvania and New J e rsey through New York and the New England States (Rohm et al., 1995); and Florida, comprising a small part of nutrient region IX , m o st of Region XI I , and all of Region X III (Griffith et al., 1997). T he regionalizations for the Upper Midwest and Northeast are based on total phosphorus concentration because of the dominance of phosphorus as the principal limiting nutrient in cool temperate lakes of the world (e.g., Schindler, 1978). T he regionalization for Florida also takes into account total nitrogen concentration, algal chlorophyll, pH, color, Secchi depth, lake origin, and lake hydrolog y . In warm temperate and subtropical lakes, nitrogen concentration is often the principal limiting nutrient (e.g., Shannon and Brezonik, 1972; Carlson, 1992).
Th ese subregionalizations were developed from data on nutrient concentrations of sampled lakes in the regions, soils, and land use (Omernik et al., 1988; Rohm et al., 1995; Griffith et al., 1997). T he distributions of nutrient concentrations of each subregion w e re characterized (usually w ith a histogram ) if data were available. I n subregions where no data were available, the nutrient distributions were estimated based on similarity of soils and land use to regions where data were sufficient to characterize. Itis expected that as m o re data are developed through the National Nutrient Criteria Program, more nutrient ecoregions will be similarly subdivided. 2. Nongeographic Classifications Many lake classifications have been proposed in addition to trophic state and g e ography (Hutchinson, 1957). Lake classification can be further complicated by natural or human- induced conditions that can intrinsically affect the state of a lake and, therefore, how it can be classified. For 

### Nutrient Criteria—Lakes and Reserv o irs 3- 3example, acidic lakes (whether naturally acidic or from acid deposition) are comm only found in the Adirondacks of New York, Pennsylvania, and West V i rginia and in sand ridges of Florida. High mineral turbidity is found in reservoirs where streams have a high load of suspended fine sediment, typically in arid and semiarid regions. Although lake types can be explained to g r eater or lesser extent on geographic considerations, it m ay be m o re convenient to classify lakes by nongeographic v ariables, which m ay yi eld m o re explanatory power than geographic locations. Discussed below are certain factors that potentially can affect the classification process but that g e nerally fit the g e ographic-oriented focus of the above g e ographic approaches (e.g., ecoregional, w a ter quality characteristic).



### � L ake Origin Hutchinson (1957) lists 76 different types of lakes based solely on their origins. Although we often think of a lake simply as a hole in the g r ound with water in it, the number of different lake types should make us pause to consider how m a ny ways the origin shapes the area, the v o lume, and the shape of the lake basin. Lakes of v o lcanic origin are probably v ery deep, with v i rtually no littoral zone and small watersheds. Crater Lake (lake type 10), for example, is extremely deep and v e ry clear and has only the crater w a lls for a w a tershed. H owever, it is susceptible to nutrients introduced by septic leakage because of the v e ry small w a ter load. Lakes of tectonic origin such as those found in faults (lake type 9; e.g., Lake Baikal) m igh t behav e similarly . O ther lakes may be extremely shallow such as oxbow lakes (lake type 55) or m aritime coastal lakes (lake type 64). I n these instances, there m ay be extensive shallow areas and considerable interaction of the sediments with the overlying water. T he shape of the basin and watershed help determine the controlling v ariables of surface area, depth, v o lume, and retention time. R ather than use discrete classes (e.g., large lakes, small lakes), it m ay be m o re effective to treat the shape-related variables as a continuous characteristic. T his is discussed in m o re detail in Section 3.



### � Reservoirs Reservoirs and impoundments, created by the dammi ng of a stream, have characteristics of both rivers and lakes (Thornton, 1990). Reservoirs are divided into three zones—riverine, transitional, and lacustrine—which correspond to (1) flowing, riverlike conditions, (2) transition to lake conditions, and (3) nonflowing lakelike conditions near the dam, respectively

. With expected life spans ranging from several decades to a century or m o re, reservoirs are m o re ephemeral than m o st natural lakes and hav e several physical characteristics unique to reservoirs and natural reservoirs formed by natural dams (e.g., beaver dams, terminal m o raines, landslides). Reservoirs v ary widely in physical characteristics of shape, size, and hydrolog y. T hey can rang e from small, shallow impoundments (farm ponds) to deep storage reservoirs to “run of the river ” flowthrough navigational pools and hydroelectric reservoirs on large rivers. T hey are built and m a naged for widely different purposes, including flood control, navigation, municipal or agricultural water storage, hydroelectric g e neration, and g ame fish production. Many dams are constructed to allow discharge from the epilimnion, metalimnion, and/or hypolimnion, depending on management g o als of the water bodies. T his m u st be known before understanding the limnolog y of the reservoir. T h e m a nagement practices in turn affect physical, chemical, and biological characteristics of the reservoir.

3- 4 

### Nutrient Criteria—Lakes and Reserv o irsA lthough no natural reservoir reference conditions exist, the operational determination of nutrient reference conditions for reservoirs is the same as for natural lakes. R eservoirs can be classified according to hydrolog y , morphometry, management objectives, and other factors. Age of the reservoir may be important in determining expectations. Several considerations affect the classification of reservoirs as opposed to natural lakes:

• Di stribution

. Reservoirs and impoundments are m o st numerous in regions with few or no natural lakes. T he nonglaciated parts of North America have the largest number of reservoirs (except Florida, w h ich is a Karst landscape).

• Form . T he form or shape of a basin and watershed m ay be the m o st important distinction between natural and artificial lakes. Shape substantially influences hydrolog y and w a ter quality of impoundments. Large reservoirs are drowned river valleys and tend to be long and deep with numerous embay ments of tributary streams. T he watersheds of reservoirs are relatively m uch larger than those of natural lakes and contribute relatively g reater sediment loads.

• Longitudinal gradient

. Reservoirs have characteristics typical of both lakes and streams. T hey are streamlike at the head w h ere m ajo r tributaries enter and are m o re lakelike near the dam (Thornton, 1990).

• Turbidity and loading

. Many reservoirs are m o re turbid than natural lakes, and they receiv e mo re nutrients and organic m a tter from their tributary streams than do natural lakes. T his is partly related to the g r eater relative size of reservoir w a tersheds.

• Management . R eservoirs w e re built and are m a naged for specific purposes: hydropower, w a ter supply, and flood control. Fisheries and other uses are usually secondary

. Management migh t include extreme water level fluctuations and discharge depth controls, effects not present in m o st natural lakes. Most of the differences between reservoirs and natural lakes are resolved in the classification of the lake resource. T he needs for which they were designed dictate m a ny of the attributes of artificial water bodies. O perational strategies can influence reservoir characteristics and resultant w a ter quality (Kennedy and Walker, 1990; Kennedy et al., 1985). T he release of water from deep in the water column (hypolimnetic release) increases heat g a in and the dissipation of m a terials accumulated in bottom w aters (Martin and A r neson, 1978; Wright, 1967). Surface releases dissipate heat and retain materials. T h ese and other operational differences can provide a basis for g r ouping reservoirs within and among regions.
Re lationships between w h y a dam is built, how and w h ere it is built, how it is subsequently operated, and the characteristics of the resulting reservoir are reasonably w ell defined (Kennedy, 1999a). With regard to the establishment of nutrient criteria, can w e utilize these relationships to define appropriate gr oups within w h ich to identify reference conditions? T hree categories of reservoir characteristics seem ge rmane for this purpose: location within a drainage basin; structural and operational characteristics of the dam; and hydraulic residence time. Location in Drainage Basin
D ecisions about w h ere dams are located broadly define physical attributes of the resulting reservoir, which, in turn, strongly influence its limnological character (Kennedy, 1999a). For example, tributary storage reservoirs are located on lower order rivers in the upland areas of drainage basins and, thus, often 

### Nutrient Criteria—Lakes and Reserv o irs 3- 5reside in steeply sloping and dendritic basins with long, complex shorelines. Such reservoirs are frequently relatively deep and strongly stratified. I nflows are often lower for suspended sediment concentrations and m ay exhibit g r eat seasonal or short-term v ariability . C hanges in storage can result in m arked changes in pool elevation, and water residence times are often long

. By contrast, run-of-the-river and m a instem storage reservoirs, frequently operated to meet navigation and hydropower objectives, are located on higher order river reaches. Run-of-the-river reservoirs often are limited in lateral extent to the areas imme diately adjacent to the original river channel and seldom experience frequent or extensive changes in pool depth. Because they are comm only located at the downstream extent of large drainage basins, they receive high suspended sediment loads, are turbid, and flush rapidly

. Dams for m a instem storage reservoirs, on the other hand, g e nerally inundate broad river flood plains, offering extensive storage v o lumes. Despite relatively high inflow rates, water residence times can be long because of the large potential storage v o lume. Moderate changes in pool depth occur, and in-reservoir inorganic turbidity levels, w h ile initially relatively high due to riverine influences, often are reduced because of long w ater residence times. Dam Structure and Operation The purpose or purposes for w h ich dams are built determine, in g e neral, their structural design and their mode of operation. T he location of outlet structures relative to the depth of the water column, as we ll as the thermal structure of the w a ter column, determine the depth strata from w hich w a ter is released. As discussed previously, withdrawal depth can have significant implications for reservoir thermal cycles and the expression of trophic responses to changing nutrient levels. T hus, interactions between reservoir depth, depth from which water is released, the v o lume of water released, and thermal structure of the w a ter column must be considered w h en assessing relative similarities between reservoirs and lakes or among reservoirs.
As engineered systems designed to accomplish specific and often narrowly defined w a ter control objectives, dams and the reservoirs they impound exhibit prescribed characteristics dictated by functional requirements. T he scheduling of changes in reservoir v o lume (and, therefore, depth), for example, is determined by basin capacity, hydrolog y , and water uses. From an operational standpoint, this often involves the development and application of “rule curves,” or predetermined changes in reservoir surface elevation. For tributary storage reservoirs, particularly those operated for flood control, rule curves frequently require the lowering of surface elevations as a means to allow storage of subsequent flood waters, which m ay be retained for extended periods of time before their release downstream . T he result is m arked seasonal fluctuations in water column depth, reservoir v o lume, and water retention time. Op erational requirements for run-of-the-river reservoirs offer a contrasting example. Because the primary purpose of such reservoirs is navigation, reservoir surface elevations m u st be controlled within narrow limits. T hus, despite larger inflow v o lumes, rule curves for run-of-the-river reservoirs dictate mi nimal fluctuations in water column depth. I n the absence of changes in water storage v o lume, water residence times are determined by hydrologic conditions and are uncoupled from dam operation. From the above discussion and examples, it is obvious that dam structure and operation need to be considered when evaluating factors that influence the limnological attributes of reservoirs and the expression of trophic responses. I n addition to their importance to the development of nutrient criteria, these relationships also describe potential m a nagement opportunities unique to reservoirs.

3- 6 

### Nutrient Criteria—Lakes and Reserv o irsHydraulic Retention Time Hydraulic retention time, defined as lake or reservoir v o lume divided by outflow rate and expressed as days or years, strongly influences limnological processes in lakes and reservoirs (e.g., Straškraba et al., 1993). T hese influences include changes in m a terial retention rates (Straškraba et al., 1995; Kennedy , 1998), modifications to thermal structure, and impacts on the size and composition of planktonic comm unities (Straškraba and Straškrabova, 1975; Soballe and T h relkeld, 1985; Soballe and Bachmann, 1984). Residence times vary widely between natural lakes and reservoirs and among reservoirs. Thornton et al. (1980) evaluated data for selected U.S. Arm y Corps of Engineers reservoirs and lakes contained in the National Eutrophication Survey database, and the authors reported significantly higher g e ometric mean va lues for lakes (270 days) than for reservoirs (135 days). A similar assessment of data included in the National I n ve ntory of Dams (U.S. Arm y Corps of Engineers, 1998) indicates a broad range in water residence time for reservoirs impounded by U.S. dams (Kennedy, 1999b). Values for the nearly 65,000 reservoirs ranged from less than 1 day to m o re than 750 days; a similar range was observed for those operated by the Corps of Engineers. Many of those with short residence times are operated as run-of-the-river reservoirs for the purpose of navigation. Ry ding and R a st (1989) sug ge st that impoundment-related changes in w a ter quality w ill occur w h en doubling times for algae are less than water residence times. Since Reynolds (1997) sug ge sts that algal doubling rates are in the range of 1⁄2 to 11⁄2 per day, it is clear that nutrient-related influences on trophic state are possible at relatively short w a ter residence times. For reservoirs with longer residence times, anticipated differences in trophic responses between natural lakes and reservoirs will be mi nimized. In such cases, it m ay be possible to include both natural lakes and reservoirs with similar water residence times, assuming broad similarities in other attributes, in the same g r oup w h en establishing reference conditions or developing nutrient criteria. I n regions with a limited number of reservoirs, this will allow increased sample size for statistical treatments of the data. On the basis of the above considerations, a reasonable and defendable approach to the identification of appropriate g r oups of reservoirs would employ m ultiple descriptors based on operational and physical attributes. Sug ge sted measurement v ariables for each attribute are presented in T able 3.1. T aken together, this suite of physical and operational characteristics attempts to define factors influencing the expression of trophic responses to changing nutrient levels relative to reservoirs.
Th erefore, reservoirs having short detention times should be considered separately from natural and m an- m ade lakes because of their different origins, m o rphometry, and hydrodynamics. Reservoir studies have shown that the nutrient loading paradig m fits with some modifications (Canfield and Bachmann, 1981). T he rapid flushing rates and longitudinal g r adients that typify m ost m a instem reservoirs require m odifications of the models to account for down-reservoir changes in water from sedimentation and dilution with passage through the system

. Also, nutrient loading m odels that work well to explain in-lake concentrations in natural lakes overestimate v a lues measured in reservoirs (Jones and Bachmann, 1978); for a g iv en external load, reservoirs appeared to have lower in-lake phosphorus values than natural lakes. Differences between reservoirs and natural lakes were thought to be tied to the fact that reservoirs are constructed in erosional topography and receive m u ch larger inputs of suspended solids than m o st natural lakes. With g r eater sediment input, it follows that reservoirs would have g r eater sedimentation rates and that m o re phosphorus would be lost from the water column as compared with natural lakes.



### Nutrient Criteria—Lakes and Reserv o irs 3- 7**Ta ble 3.1.	 Categories and at**  **tr ibutes f**  **o r a Composite Classification Approach f**  **o r CE Reservoirs**  **an d**  **Su gg**  **ested M**  **easuremen t**  **Variables ( K**  **en nedy**  **, 1999b )** 

**Categ ory**  **Attr ib**  **ute M**  **easured Variable** Location and s ize Wa ter s hed dimension Reservoir dimension Draina g e area Location of dam in h y drolo g ic continuum Sur face ar ea Volum e Len g th Mean and m aximum depth Shoreline development r a tio Hy drolo gy Hy draulic loadin g Stor ag e d y namic s Inflow and outflowra tes Annual/seasonal h y draulic retention tim e Pool elevation/volum e Chan g e in pool elevation Structur e and operation Dam des ign Dam operation Dam hei g ht Ou tlet depth ( r elative to w a ter column depth) Q uantit y and seasonalit y of re lease volumes Depth of releas e Ot her respons e e ffe cts Li g ht r eg im e Mixin g r eg im e Nonal g al turbidit y Photic depth to m ix ed depth r a tio T her ma l s t abilit y Mixed la y er depth
Another factor contributing to apparent differences in water column nutrient v a lues is that reservoirs typically have large watersheds (Canfield and Bachmann, 1981). As a result, inflow enters from a parent river that, during stratified periods, forms a density flow below the w arm surface w a ter but above the colder bottom waters (tropholytic zone) that does not mi x or contribute nutrients to the photic zone (Ford, 1990). T iming of nutrient-laden inflows relative to seasonal stratification can be as important as their v o lume in controlling nutrient v a lues within the w a ter column. Water bodies with density currents do not always show a response to external inputs. I n these water bodies, loading m odels need to take into account the effects of inflow timing and flow stratification. T he relative timing of flow and stratification w ill v ary from y ear to year and could m ake nutrient content of the surface layer unpredictable except as a long -t erm average.



### � Water Chemistry (nonnutrient)
In trinsic water chemistry (not including nutrients) can be used to classify lakes. T he most likely variables include acid-base chemistry (any of alkalinity, pH, conductivity) and dissolved organic m a tter (water color). C olor and pH are cheaply and easily measured in the field and are therefore highly costeffective.
Lake w ater chemistry is largely determined by the hydrologic pathways of w a ter entering the lake and the material the water contacts along its path. Lakes with large inputs of water from shallow g r ound water, including wetlands, tend to be stained y e llow or brown with dissolved humic compounds. Water entering a lake as deeper g r ound w a ter tends to be clear but will contain the cations of the soils and

3- 8 

### Nutrient Criteria—Lakes and Reserv o irsaquifer. H ighly colored lakes have been termed dystrophic because they often are observed to have low productivity in spite of moderate to high nutrient concentrations (Wetzel, 1975). Colored water not only reduces light penetration, but the dissolved organic m a tter also can chelate nutrients, m aki ng them unavailable for algal uptake. T herefore, w a ter color is an important classification v ariable (or covariate; see below) for lake nutrient criteria.
Alka linity also influences lake productivity, in part because alkaline soils are richer in several nutrients (especially phosphorus and potassium) than are acid soils, and because the nutrients are m o re readily available to plants. T he world 

### � s m o st productive agricultural regions are in alkaline soils. Alkalinity, or its related v ariables pH and conductivity, are important classification v ariables for nutrient criteria. A s an example, Florida lakes were characterized as acidic or alkaline and as colored or clear, resulting in four lake types (Shannon and B r ezonik, 1972). A lthough pH and as color are continuous variables, it w a s m o re convenient to cluster the Florida lakes into four g r oups because response to nutrient enrichment and macroinvertebrate comm unities also clustered according to the four g r oups (Gerritsen et al., 1999).



### � Nonalgal Turbidity (suspended sediments) High concentrations of nonalgal suspended m a terials are prevalent in lakes in m a ny regions of the world and can inhibit g r owth of phytoplankton, causing light limitation. Nonalgal turbidity from suspended clay or organic m a tter is also strongly regional, depending on soil characteristics, v ege tation, and hydrolog y. I t is a prominent characteristic of many impoundments in Midwestern and arid Western States. Nonalgal turbidity can produce low algal chlorophyll-to-nutrient ratios and cause a lack of relationship between chlorophyll and phosphorus in some regions (Jones and Novak, 1981; Hoyer and J ones, 1983; Carlson, 1991; Jones and Knowlton, 1993). Light limitation of algal biomass in the mi xed z one of lakes occurs when irradiance absorbed by the phytoplankton comm unity is less than is required for net g r owth of biomass over time. Light limitation extended over periods of a week or longer is comm on in deep or turbid lakes during w inter because of low incident light, but it is less comm on in summe r when incoming irradiance is m a ximal and when mi xing depth is reduced by thermal stratification.
Th e Carlson trophic state index (TSI) (1977) can be used to identify certain conditions in the lake or reservoir in which algal biomass is not related to phosphorus or nitrogen. When m o re than one of the three v ariables are measured, it is probable that different index v a lues will be obtained. B ecause the relationships between the v ariables were originally derived from regression relationships and the correlations w e re not perfect, some v ariability between the index v a lues is to be expected. H owever, in some situations the v ariation is not random, and factors interfering with the empirical relationship can be identified. T hese deviations of the total phosphorus or the Secchi depth index from the chlorophyll index can be used to identify errors in collection or analysis of real deviations from the “standard” expected va lues (Carlson, 1980b). Some possible interpretations of deviations of the index v a lues are g ive n in Table 3.2 (Carlson, 1983, 1992).
I n turbid lakes, it is comm on to see a close relationship between the total phosphorus T SI and the Secchi depth T SI , while the chlorophyll index falls 10 or 20 units below the others. Clay particles contain phosphorus, and therefore, lakes with heav y clay turbidity w ill have the phosphorus correlated w ith the clay turbidity w hile the algae m ay neither utilize all the phosphorus nor contribute significantly to the light attenuation. T his relationship of the v ariables does not necessarily mean that the algae is limited by light, only that the measured phosphorus is not all being utilized by the algae.



### Nutrient Criteria—Lakes and Reserv o irs 3- 93. Covariatesr Several of the above factors have strong influences on lake trophic state and m ay be expected to vary widely within nutrient regions. Whether a g ive n factor needs to be considered separately in lake classification within regions depends on its v ariability in the region and its regional relevance in affecting trophic state. A dditional classification factors m ay be treated as additional classes (e.g., as classes of large and small lakes) or as continuous covariates (e.g., a regression model to predict natural trophic state of lakes according to lake size). State and regional experts can use their knowledge of lake characteristics to determine if any of the modifying factors should be considered as part of a State-level classification scheme.
Lake m o rphometry and lake hydrolog y affect trophic state through the influence of water m oveme nt, retention time, and stratification. I n-lake phosphorus dynamics in mi xed and stratified lakes can complicate the relationship between external loading and measurements of lake trophic state, m aki ng m odel-based predictions uncertain in some cases. I n mixed lakes, phosphorus has been shown to increase during the spring to summe r period (Riley and Prepas, 1985), presumably because of recycling due to mi xing of the water column and internal loading from the sediments (Osgood, 1988; Welch and Cooke, 1995). I n contrast, it is typical for phosphorus to decrease somewhat in stratified lakes because of sedimentation processes, with the me talimnion acting as a barrier to upward transport into the photic z one. Shallow lakes can efficiently cycle phosphorus and, under favorable light conditions, convert phosphorus into phytoplankton biomass. As a consequence of these internal loading m echanisms, shallow lakes do not always readily respond to reductions in external nutrient loading

. Among larg e stratified lakes, evidence exists that the efficiency of nutrient recycling increases with lake size; mixed layers in large lakes are m o re turbulent and thicker than in small lakes, and these processes increase the probability of nutrient regeneration within the mi xed layer rather than loss to the sediments. The response to g r eater nutrient regeneration is g r eater phytoplankton photosynthesis. T hese findings sug ge st that external nutrient loads should be converted into biological production m o re efficiently in stratified lakes than in small lakes. Water residence time can have a significant effect on the amount of algae in the water. T h e water mu st remain in the basin for a period longer than the doubling time of the algae or the algae will w a sh
**Ta ble 3.2. Conditions Associated w**  **i th V**  **ari ous T**  **r ophic State Index V**  **ari able Relationships**  **Relationship Between T SI V**  **ariables Conditions**  TS I (CHL) = TS I(CHL) = TS I(SD) Alg ae dominate li g ht attenuation TS I(CHL) > TS I(SD) Larg e particulates, such as Aphanizomenon f l akes , dominate TS I( TP) = T S I(SD) > TSI(CHL) Nonal g al particulates orco lor dominate li g ht attenuation TS I(SD) = TSI(CHL) > TSI( T P) Phosphorus limits al g al biomas s (T N/TP r a tio gr eater than 33:1) TS I( TP) > T S I(CHL) = TSI(SD) Z ooplankton g ra zing , nitr og en, or some f act or other than phosphorus limits al g al biomas s

3-10 

### Nutrient Criteria—Lakes and Reserv o irsout of the basin. T his means that for faster g r owing algae such as Ch lorella , the w a ter residence tim e would have to be at least 2 days. For slower g r owing species, the residence times would have to be m u ch longer. I n reservoirs with short residence times, the algae would not necessarily reach densities in w h ich nutrients w e re limiting to their g r owth. H owever, residence time m ay vary seasonally, and there m ay be times when the algae do become nutrient limited. Another consideration would be that in short residence time situations, attached plants (both macrophytes and attached algae) m ay proliferate, and criteria would have to be set in reference to attached rather than planktonic forms. Any continuous v ariable, such as pH, color, lake depth, or lake area, can be treated as a covariate in a classification. O ften, it m ay be m o re convenient to treat them as discrete classes (large and small; acid and alkaline). Whether to treat an important classification v ariable as discrete classes or as a continuous covariate m ay depend on the size of the database, the distribution of lakes across the g r adient, and whether the trophic response to the g r adient is linear. For example, a uniform or unimodal distribution across a g r adient would sug ge st treating the v ariable as a covariate (e.g., lake surface area), w h ile a bimodal distribution would sug ge st dividing into classes (e.g., pH classes of acidic and nonacidic lakes). If

a relationship is found between measures of lake size or hydrolog y and trophic state, then additional classes reflecting these factors, or treating them as a covariate, m u st be considered. B ecause relationships with m o rphometric v ariables are often linear, the covariate approach usually is preferred for those v ariables (area, depth, retention time). Conversely, water chemistry v ariables (pH, color, hardness) may cluster naturally due to g e olog y , soils, and v ege tation, so the class approach m ay be preferred for those v ariables.



### Nutrient Criteria—Lakes and Reserv o irs 3-11Case Study: Ecoregional Classif i cation of Min esota Lakesn Minnesota has over 12,000 lakes spread across diverse g e ographic areas. Previous studies had shown distinct regional patterns in lake productivity associated with regional differences in g e olog y, vege tation, hydrolog y and land use (Heiskary and Wilson, 1989). Minnesota contains seven ecoregions (Omernik, 1987), and four of the ecoregions contain 98 percent of the lakes. T h ese four ecoregions are the Northern Lakes and Forest (NLF), North Central Hardwood Forest (NCHF), Northern Glaciated Plains (NGP), and Western Corn Belt Plains (WCBP) (Figure, p. B-4). Minnesota uses these ecoregions as the framework for analy z ing data, developing m onitoring strategies, assessing use patterns, and developing phosphorus g o als and criteria for lakes (Heiskary, 1989).
Th e Minnesota Pollution Control Agency (MPCA) and several other g r oups collected data on chlorophyll a concentrations and several w a ter quality parameters (total phosphorus, total nitrogen, and Secchi transparency) in 90 reference lakes between 1985 and 1987. Secchi transparency data we re collected m o stly by vo lunteer participants in the Citizen Lake Monitoring Program. Reference lakes were chosen to represent mi nimally impacted sites within each ecoregion. Criteria used in selecting reference lakes included m a ximum depth, surface area, fishery classification, and recomme ndations from the Minnesota Department of Natural Resources (Heiskary and Wilson, 1989). Lake m o rphometry had previously been examined. In addition to the reference lake database, MPC A examined a statewide database containing data collected by these same g r oups on approximately 1,400 lakes form 1977 to 1987.
Differences in m o rpholog y , chlorophyll a concentrations, total phosphorus, total nitrogen, and Secchi transparency were found among lakes in the four ecoregions in both studies. Lakes in the two forested ecoregions (NLF and NCHF) are deeper (median m a ximum depth of 11 me ters) with slightly smaller surface areas (40 to 280 ha) than those in the plains ecoregions (N GP and WCBP). Lakes in the two plains ecoregions were typically shallow (median maximum depth of 3 meters) with larger surface areas (60 to 300 ha).
B ox-and- wh isker plots for chlorophyll a and w a ter quality measurements in the reference lake study paralleled the m o rphological differences seen among the ecoregions (Heiskary and Wilson, 1989). Th e two plains ecoregions had significantly higher chlorophyll a levels than either of the two forested ecoregions. Results of the statewide database analysis showed these same trends. T h e results of these two database analyses support the use of ecoregions in developing frameworks for data analysis, m onitoring strategies, assessing use patterns, and developing phosphorus g o als and criteria for lakes.

3-12 

### Nutrient Criteria—Lakes and Reserv o irs

# CHAPTER 4 A. Introduction B. Evaluatin g E xist ing Data C. New Data Collec t ion 

# Establishing an D. Database Mana g ement 

# A **ppropriate Database**

A. Introduction The development of nationwide regional nutrient criteria requires the availability of an extensiv e amount of data from across the country for evaluation. Data m ay come from existing sources or can be collected from new sampling programs. Nutrient-related data for lakes and reservoirs, collected by various agencies for m a ny different purposes, exist in v arious databases and have the potential to provide the basis for the development of nutrient criteria on a regional level. T his chapter presents an overview of existing nutrient criteria databases and presents a g e neral discussion on the evaluation of such data in terms of their use in the nutrient criteria development process. T he chapter also provides a description of the process undertaken by EPA to use existing data from STORET and perhaps other existing data sets (e.g., U.S. Geological Survey [USGS] NAWQA) to g e nerate preliminary nutrient criteria on an ecoregional level. I n addition to discussing the use of existing data, the chapter discusses new data collection, including sampling design and the types of monitoring to be considered as part of data collection activities. The chapter ends with a g e neral discussion of data m a nagement issues that are integral in the overall discussion of data storage and accessibility

. B. Evaluating Existing Data
I n many States, historical data on lakes are extensive and m ay be sufficient to identify lake classes and reference lakes and to establish interim criteria. With societal interest in cultural eutrophication during the 1970's—programs such as EPA 

### � s C l ean Lake s Program (C L P) and citizen 

### � s organizations such as LakeWatch— lakes have been extensively m onitored and studied. Many historical data are available and m ay suffice for developing lake nutrient criteria. Although existing data m ay be sufficient, program m anagers should recogniz e that g a thering, reducing, analy z ing, and interpreting existing data sets can be costly and time consuming

. Development of nutrient criteria using the reference site approach requires a database that can be used to characterize (1) reference lakes and (2) the biological response of lakes to nutrient enrichment. At a mi nimum, observations should include total nitrogen (TN) (or Kjeldahl nitrogen plus NO 2 -N O 3 -N ), total phosphorus (TP) (or total dissolved phosphorus plus particulate phosphorus), chlorophyll a , and Secchi depth. For each lake in the database, there should be information or inference on the status of anthropogenic nutrient loading to the lake. At a mi nimum, this information would be informed best professional judg me nt on whether anthropogenic nutrient loading was negligible or substantial for a give n lake. T he judg me nt could be based on personal observation, discharge information, land use information, or historical information. Such information m ay not reside together with the w a ter quality observation and m ay need to be found and obtained separately

. As mentioned above, the w a ter quality data should be sufficient to characterize a lake. A ll lakes in the database should have been sampled the same way and should be characterized the same. I deally , lakes will have been sampled once during an index period that characterizes nutrient or trophic state (e.g.,


### Nutrient Criteria—Lakes and Reservo ir s 4- 1during spring overturn) and with sampling methods that are assumed to characterize the lake (e.g., pumped or composite sample of the entire w a ter column). Some existing data sets m ay permit estimation of annual or g r owing season average nutrient concentrations.
A ppropriate data analysis will be determined by the data set. T he basic procedure is to consider each lake an independent sample unit and to estimate an annual characteristic v a lue (annual average, m e dian, mi nimum, maximum) of each w a ter quality observation for each lake. T hese annual characteristic v a lues are the information used to develop nutrient criteria and biological response of lakes to enrichment. T his procedure assumes that lakes are independent and that annual averages among y ears are independent. Th e investigators and the Regional Technical Assistance Groups should decide whether the independence assumptions are reasonable and whether any m odifications should be m a de. 1. Potential D a ta Sources
Da tabases could include w a ter quality m onitoring data from w ater quality agencies (often stored in STORET), national surveys such as the EPA Eastern Lakes Survey (Linthurst et al., 1986) or the Environmental Monitoring and Assessment Program (EMAP) (Paulsen et al., 1991), limnological studies, and v o lunteer monitoring information.



###  STORET
STORET is EPA 

### � s national data w arehouse for w a ter quality data. A ll State and Federal w a ter quality m onitoring agencies are required to submit their data to ST OR ET

. ST OR ET is huge, covering all 50 States since the 1970's; it includes lakes, streams, rivers, and estuaries and physicochemical and biological data. ST OR ET has no quality control for accepting or rejecting data, but it does require extensive m e tadata (data descriptors) that show how data were collected and what analytical me thods w ere used. A ll sampling sites are referenced by latitude and longitude, by the EPA R each File 3 (RF3), and by U SGS hydrologic unit codes. Extracting data from ST OR ET requires familiarity w ith the system as w e ll as selection criteria (date ranges, location ranges, specified measured v ariables, collecting agency w ith known quality control) to keep from being overwhelmed with irrelevant data.



###  National Eutrophication Survey (NES) EPA conducted NES in the early 1970's. Several hundred lakes were sampled and nutrient budgets we re estimated. T he lakes selected for the survey received discharges from m unicipal sewage treatment or the States requested they be included. NES contains a broad but incomplete sample of lakes, and therefore, the data from NES are not sufficient in themselves for developing reference conditions to support regional nutrient criteria. T h e NES data m ay be used for determining biological responses to enrichment and for developing site-specific criteria.



###  National Surface Water Survey (NSWS) EPA conducted NSWS in the mi d 1980's under the National Acid Precipitation Assessment Program

. Lakes were surveyed only in those regions w h ere they w ere initially thought to be at risk to acid precipitation: New England, the Adirondacks, the mi d-Atlantic highlands, the mi d-Atlantic coastal plain, the southeastern highlands (southern Appalachians and Ozark

- Ouachitas), Florida, the upper Midwest, and the montane West. NSWS sampled 2,300 lakes ranging in size from 4 to 2,000 hectares; thus, the smallest and largest lakes were not represented. NSWS was a stratified random sample of lakes in the

4- 2 

### Nutrient Criteria—Lakes and Reserv o irsselected region; therefore, inferences can be m a de to the populations defined by the regions. Sampling took place in the fall. N utrients w e re measured, so N S WS data could be used to help develop criteria.



###  E nvironmental Monitoring and Assessment P r ogram EPA 

### � s EMAP sampled lakes in N ew England and the A d irondacks in 1991, with a probability -b ased site selection procedure to obtain an unbiased sample (Paulsen et al., 1991). Further similar work is planned in the western States. T he EMAP lake sample should include potential reference lakes as well as stressed lakes and could be used to identify reference lakes and characterize reference conditions.



###  Clean Lakes P r ogram Th e EPA CLP for restoring public lakes included a monitoring and assessment component. Lakes in this program w ere selected because they w ere perceived to have w a ter quality impairment. Like data in the NES database, these data m u st be carefully scrutinized before being included in a database setting regional reference conditions to support nutrient criteria.



###  V olunteer Monitoring P r ograms •	 I ndividual State Lake Association Programs that m ay contain considerable information, m ay be contacted through the National Directory of Environmental Monitoring Program s (contact: Alice Mayo, U.S. EPA headquarters, Washington, DC).
•	 N ational data on Secchi disc transparency have been collected since 1994 by the “Secchi D i p- In” (Carlson et al., 1997). Elements of these databases could contribute to criteria development but, like the EMAP data, would need to be screened to identify reference and nonreference lakes.



###  State Monitoring P r ograms Most States monitor some subset of lakes and impoundments within their borders for eutrophication and nutrient v ariables. Several of the m o re extensive lake monitoring programs (e.g., Minnesota, Wisconsin, Maine, Florida) are profiled in this document as examples of using m onitoring data to help develop nutrient criteria. T he purpose of the survey should be assessed before using the data. See Representativeness, in Section 2 below.



###  U .S. A r my C o rps of Engineers
Th e U.S. Army Corps of Engineers is responsible for m o re than 750 reservoirs. Extensiv e m onitoring datahave been collected for m a ny of these reservoirs that could contribute to the development of nutrient criteria for reservoirs.



###  U.S. Department of the Interior, B u reau of Reclamation (BuRec)
Th e Bureau of Reclamation manages many irrigation and water supply reservoirs in the West. Data from their operations m ay be available for some of these.



### Nutrient Criteria—Lakes and Reserv o irs 4- 3

###  E lectric U t ilities Many electric utilities own reservoirs for hydroelectric power g e neration, and the utilities are required to monitor the reservoirs 

### � w ater quality

. The largest of these, the Tennessee Valley A uthority , has extensive chemical and biological monitoring data from m ost of its reservoirs from the early 1980' s to the present.
2. Q uality of Historical D a ta Th e quality of older historical data sets is a recurrent problem because the data quality is often unknown. T his is especially true of long -t erm repositories of data such as STORET and long -t erm State, academic, commi ssion, or municipal databases, w h ere objectives, methods, and investigators m ay hav e changed many times over the years. T he most reliable data tend to be those collected by a single agency using the same protocol for a limited number of years. Supporting documentation should be examined to determine the consistency of sampling and analysis protocols. When “mining” from large heterogeneous data repositories such as STORET , investigators m u st screen data for acceptance considering a number of variables, as discussed below

.


###  Location STORET data are g e oreferenced with latitude, longitude, and RF3 codes. T hese can be used to select specific locations or specific USGS hydrologic units. I n addition, STORET often contains a site description. I f selecting, for example, all lake sites within a g e ographic region, it is also important to know the rationale and m e thods of site selection by the original investigators. Such information m ay be included in STORET me tadata, if known.



###  Variables and Analytical Methods
T housands of v ariables are recorded in STORET records. Each separate analytical m e thod y i elds a unique v ariable (called parameter in STORET); thus, five ways of measuring T P results in five unique variables. Because me thods differ in accuracy, precision, and detection limits, it is g e nerally unwise to mi x m e thods in the same analysis. I f there is one me thod that the investigator judges to be best, then only observations using that particular me thod can be selected. Selection of a particular “best” m e thod may result in too few observations, in which case it m ay be m o re fruitful to select the m o st frequent me thod in the database. Some data m ay be mi ssed because some me thods m ay be synony m ous, and there is an unknown component of error from incorrect data entry

.


###  L aboratory Quality C o ntrol Laboratory quality control data (blanks, spikes, replicates, known standards, etc.) are g e nerally not reported in the larger data repositories. I t is m o re cost-effective to accept or reject all data of the collecting agency or laboratory based on overall confidence of their quality control. Ov erzealousness in eliminating lower quality data can be counterproductive, because the increase in v ariance caused by analytical laboratory error m ay be negligible compared with natural v ariability or sampling error, especially for nutrients and related indicators.

4- 4 

### Nutrient Criteria—Lakes and Reserv o irs

###  C ollecting A g encies
ST OR ET data are identified by the agency that collected the data. Selecting only data from particular agencies with known, consistent collection and analytical me thods and known quality w ill reduce v ariability due to unknown quality problems.



###  Time Period Long -t erm records are critically important for establishing trends. I n characterizing reference conditions for nutrient criteria, it is also important to determine if trends exist in the reference site database. For example, since passage of the Clean Water Act and elimination of m o st discharges to lakes, m a ny lakes have improved m arkedly

. Other lakes, subject to increased nonpoint-source runoff, may have declined in overall quality

.


###  IndexP eriod
If

nutrient and w a ter quality v ariables w e re measured m o re than once a year, an index period for estimating average concentrations m u st be set. T he index period m ay be the entire year, spring or fall mi xing (in regions where lakes stratify), or the summe r g r owing season. T he best index period is determined by investigators considering the characteristics of lakes of the region, the quality and quantity of data available, and estimates of temporal v ariability (if available).



###  R epresentativeness
Data m ay have been collected for specific purposes, such as developing nutrient budgets for eutrophic lakes. Such data are unlikely to be representative of the region or lake type of interest. T he investigator m u st ask whether the lakes in the database are representative of the population of lakes to be characterized. I f not, can a subset of representative lakes be selected from the database? I f a sufficient sample of representative lakes (i.e., one large enough to characterize reference conditions) cannot be found, a new survey w ill be necessary (see section C below). 3. Data Reduction To facilitate data m a nipulation and calculations, it is highly recomme nded that historical and present-day data be transferred to a relational database. Relational databases are powerful tools for data ma nipulation and initial data reduction (calculation of seasonal means, etc.). They allow selection of data by specific m u ltiple criteria (e.g., all observations June–September in reference lakes of low alkalinity), calculation of means and totals by criteria, and definition and redefinition of linkages among data components.
Da ta reduction requires a clear idea of the analysis that will be attempted and a clear definition of the sample unit for the analysis. For example, a sample unit migh t be defined as “a lake basin during J une–September.” For each v ariable measured, a mean v a lue would then be estimated for each lake basin in each June–September index period on record. Analyses are then done with the observations (estimated means, medians, or modes) for each sample unit, not with the raw data. Steps in reducing the data include:



### Nutrient Criteria—Lakes and Reserv o irs 4- 5• S electing the time period for analysis • Selecting equivalent depths of sampling • Selecting an index period to characterize lakes • Selecting relevant chemical measures: -Q uality of m e thods -C ombining data from different methods • Estimating v alues for analysis (mean, median, mode, mi nimum, maximum) based on the reduction selected C. New Data Col l ect io n When present-day and historical data do not exist or are inadequate for meeting desired objectives, collecting new m onitoring data m ay be the only remaining alternative. A w ell-designed monitoring program is essential for establishing nutrient criteria in lakes. Monitoring data are needed for a v ariety of purposes, from the initial classification of lakes to assessing the effectiveness of controls. This section presents a brief back g ound on statistical issues to consider when designing a monitoring program and provides recomme ndations for three types of monitoring associated with nutrient criteria. Several m a nuals and statistics books are available that provide information on sampling design. T he following m anuals deal specifically with the sampling of lakes and reservoirs:

• Carlson, R., and J. Simpson. 1996. A coordinator’s guide to volunteer lake monitoring methods

. North American Lake Management Society. February 1996. • Gaugush, R.F. 1986. Statistical m e thods for reservoir w a ter quality investigations . I nstruction Report E-86-2, U.S. Army Engineer Waterways Experiment Station, V i cksburg, Mississippi. • Gaugush, R.F. 1987. Sampling design for reservoir w a ter quality investigations . I nstruction Report E-87-1, U.S. Army Engineer Waterways Experiment Station, V i cksburg, Mississippi. • Reckhow, K

. H. 1979. Q uantitative techniques for the assessment of lake quality . U.S. EPA Office of Water Planning and Standards. EPA-440/5-79-015. • Reckhow, K

. H., and S.C. Chapra. 1983. Engineering approaches for lake management. Volumei 1: Data Analysis and Empirical Modeling . Ann Arbor: Butterworth Publishers (Ann Arbor Science). 1. Types of Monitoring Associated With Nutrient Criteria Monitoring is a critical component of nutrient criteria development and implementation. Monitoring is necessary after criteria are developed to determine trends and efficacy of w a ter quality m anagement in lakes and to improve the criteria with better information. I f historical or existing data are not suitable for developing nutrient criteria, then a field survey is necessary to acquire the relevant data. More intensiv e diagnostic surveys and monitoring would be necessary if a lake did not meet its nutrient criteria, followed by long -t erm m onitoring to determine if the m a nagement actions succeeded. N utrient criteria thus are supported by three types of monitoring surveys: classification survey m onitoring, diagnostic monitoring , and evaluation monitoring

.


###  Classif i cation Surveys to Support Nutrient Criteria Development
Th e purpose of a classification survey is to g a ther data that can be used to classify lakes or reservoirs into g r oups (classes) or along g radients with unique expected trophic status and trophic responses to enrichment. Classification depends on acquiring a database of lakes covering a gradient from least
4- 6 

### Nutrient Criteria—Lakes and Reserv o irsaltered (reference lakes) to m o st altered in the region. T h e g o al of the classification survey process is to identify classes of lakes independent of cultural eutrophication, that is, classes that would be recognizable if human cultural eutrophication w e re absent or mi nimal. Because the objective is to develop nutrient criteria, each lake class identified should have a unique suite of trophic conditions, as we ll as a unique response to cultural eutrophication, that sets each class apart from the other classes. Classes need not be discrete categories of lakes; classification also m ay identify natural environmental gr adients rather than categories. Existing regional lake databases potentially can be sufficient for classification in m a ny regions of the country, as has been done in Minnesota (Heiskary et al., 1989) and Florida (Griffiths et al., 1997). However, if adequate data do not exist, new data should be collected. Parameters to Surveyi
As m any as possible of the water quality response parameters discussed in C h apter 5 (e.g., T P , T N, chlorophyll, Secchi depth, and dissolved oxy ge n) should be sampled during classification monitoring . In addition, classification also requires collecting information that helps explain observed patterns, including region (e.g., ecoregion or lake region); watershed size; lake water characteristics such as pH, conductivity, alkalinity, total suspended solids, and color; watershed land use; and human population density

. Sampling Frequencyi Because the objective of classification monitoring is to characterize a large population of lakes, a single determination per lake m ay be the m o st cost-effective me thod (e.g., Linthurst et al., 1986). Multiple sample times (e.g., monthly) will y i eld a m o re precise estimate of annual averag e concentrations, but these m u st be weighed against the cost of sampling

. For a g ive n monitoring budget, it m ay be possible to sample 12 lakes 1 time for the same cost as sampling 1 lake 12 times. North temperate lakes or reservoirs are m o st effectively sampled during spring turnover for m a ss balance m odeling . H owever, in g e neral, ecoregional trophic state criteria will be indexed by EPA to the tim e period of optimal v ege tative g r owth. T his approach also is recomme nded for State and tribal sampling

. Sampling Locationi
Sev e ral alternatives are possible for sampling sites within lakes: single site (often the deepest point of the lake), m u ltiple sites, spatially composite samples from m ultiple locations in a lake, or spatially composite samples from m ultiple sections of large lakes. Sam p ling location and frequency w ill affect not only the cost of the program but also the inferences that can be made from the sample. I n general, composite samples are m o re cost-effective (information g a ined per dollar spent) than single sites or mu ltiple locations.
T o facilitate comparison, EPA recomme nds using the same spatial site location and discrete or compositing m ethods for both the classification survey and routine m a intenance monitoring . I f increased power is required for certain ki nds of m a intenance monitoring (see below), then the frequency of sampling should be increased, but the me thodolog y should not be changed. Diagnostic investigation has entirely different objectives, so consistency with the classification sampling and m a intenance monitoring is not necessary

.



### Nutrient Criteria—Lakes and Reserv o irs 4- 7A single site m ay be chosen as the mi dpoint of the central basin of the lake, and this site m ay be sufficient to classify lakes within a region. T he location of this single site should remain constant from one year to the next so that comparisons can be m a de during routine monitoring

. Co m posite samples are taken from several sites in a lake or lake zone and combined into a single sample for laboratory analysis. For example, water samples m ay be taken from four sites in a lake and poured into a single clean bucket. T he composite sample is subsampled for chlorophyll a and nutrients. Howeve r, Secchi depth, temperature, and dissolved oxy ge n are measured at each of the four sites. C are mu st be taken that the me thods and v o lume sampled are the same at each site. Composite samples characterize the lake better than a single sample, and they save laboratory costs. T he principal disadvantage of composite samples is that they do not allow estimation of spatial v ariability w ithin a lake. Because large riverine reservoirs have known g r adients of nutrients and productivity from the river inflow to the dam (Kennedy and Walker, 1990), a single site will not be appropriate. Large reservoirs w ould require a mi nimum of three sites, corresponding to the riverine, transitional, and lacustrine zones. Alternatively, and depending on reservoir design and size, sampling m ay be from the discharge or composited from the deepest portion of the reservoir. (See also Chapter 7, Section C, regarding a data reduction approach to ecoregional criterion.)



###  Diagnostic Monitoring Diagnostic monitoring provides m o re detailed information on a specific lake or reservoir and allows the manager to identify key problems and develop an appropriate management plan. Diagnostic m onitoring is carried out before and during lake restoration efforts, such as took place in the C l ean Lakes Program . T his process is m o re fully described in Chapter 8.



###  Evaluation Monitoring
Th e purpose of evaluation monitoring is to provide continuing information on the condition of a lake or reservoir. I t can be used to determine if a lake is continuing to meet its nutrient criteria or to assess the effectiveness of any m anagement controls that have been implemented. T he level of effort required for evaluation monitoring is considerably less than for diagnostic monitoring

. Examples of evaluation m onitoring include operational lake monitoring by ma ny State w a ter quality agencies and v o lunteer m onitoring efforts. Evaluation monitoring is discussed in m o re detail in Chapter 8. Each of these monitoring objectives requires a statistically appropriate design to meet its objectives. Th e three types of monitoring are not entirely distinct, because data g a thered for one purpose can be used for other purposes. Distinguishing between the different types of monitoring simply points out the need to identify ahead of time the purpose of the monitoring to m a ximize available resources. 2. Sampling Design



###  Speci fyin g the P o pulati o n and Sample Uni t Sampling is statistically expressed as a sample from a population of objects. I n some cases, the population is finite, countable, and easy to specify—for example, all lakes in state X, w h ere each lake is a single memb er of the population. I n other cases, the population is m o re difficult to specify and m ay be infinite—for example, lake w a ters of State X, w h ere any location in any lake defines a potential m emb er
4- 8 

### Nutrient Criteria—Lakes and Reserv o irsof the population (Thompson, 1992). Sampling units m ay be natural units (entire lakes, cobbles in a littoral zone), or they m ay be arbitrary (plot, quadrate, sampling g ear area, or v o lume) (Pielou, 1977). Finite populations m ay be sampled with corresponding natural sample units, but often the sample unit (e.g., a lake) is too large to measure in its entirety, and it m u st be characterized with one or m o re secondstage samples of the sampling g ear (bottles, benthic g r abs, quadrates, etc.) Each sample unit is assumed to be independent of other sample units. T he objective of sampling is to best characterize individual sample units to estimate some attributes (e.g., nutrient concentrations, dissolved oxy ge n) and their statistical parameters (e.g., mean, m e dian, v ariance, percentiles) of a population of sample units. T he objective of the analysis is to be able to say something about (estimate) the population. I t is critical to distinguish between m aki ng an inference about a population of many lakes (“Reservoirs in the Blue Ridge are deep and oligotrophic”) versus an inference about a single lake ( “ Lake has fewer fish species than unimpaired reference lakes”). T hese two ki nds of inferences require different sampling designs: T he first requires independent observations of m a ny lakes and does not require repeated observations within sample units (pseudoreplication) (Hurlbert, 1984); the second inference often requires repeated observations within a lake. Examples of sample units include:
•	 A point in a lake (may be characterized by single or m u ltiple sample device deploy me nts). The population then would be all points in the lake, an infinite population.
•	 A constant area (e.g., square m e ter, hectare). T he population could be all square m e ters of lake surface area in a State or region.
•	 A lake or a definable subbasin of a lake as a single unit. Because lakes are m o st often discrete environments, this is likely to be the m o st comm on sample unit. T h e population would be all lakes in a State or region, a finite population.



###  Specifying the R e porting U n it
Itis also necessary to specify the units for w h ich results will be reported. U sually, this is the population (e.g., all lakes), but often subpopulations (e.g., lakes within a g ive n nutrient ecoregion) and even individual locations (e.g., lakes of special interest) will be specified. To help develop the sampling plan, it is useful to create hypothetical statements of results in the w ay that they w ill be reported, for example:

• Status of a place: “Lake X is degraded.”

• Status of a region: “20% of the lake area in State X has elevated trophic state, above reference expectations”; “20% of lakes in State X have elevated trophic state. ”
• T rends at a place: “Nutrient concentrations in lake X have decreased by 20% since 1980. ”
•	 T rends of a region: “Average lake trophic state in State X has increased by 20% since 1980.”; “Average trophic state index v a lues in 20% of lakes of State X have increased by 15% or m o re since 1980.”



### Nutrient Criteria—Lakes and Reserv o irs 4- 9• Relationships among v ariables: “ 50% increase of phosphorus loading above natural back gr ound is associated with decline in taxa richness of benthic macroinvertebrates, below reference expectations”; “Lakes receiving runoff from large impervious parking lots have 50% g r eater probability of elevated trophic state above reference conditions than lakes not receiving such runoff.”



###  Sources of V ariability Variability of measurements has m a ny possible sources. The intent of m a ny sampling designs is to mi nimize the variability caused by uncontrolled or random effects and, conversely, to be able to characterize the v ariability caused by experimental or class effects. For example, lakes may be stratified by soil phosphorus content of the surrounding w atersheds (e.g., Kiilsgaard et al., 1993) so that lakes within a soil phosphorus class m ay be likely to have similar water column TP concentrations. T he population of lakes is stratified so that observations (sample units) from the same stratum w ill be m o re similar to each other than to sample units in other strata. Environmental measures v ary across different scales of space and time, and sampling design must consider the scales of variation. I n lakes, measurements of some variable such as T P or chlorophyll concentrations are taken at single points in space and time (center of the lake, 2 m depth, 10 a.m. on 2 Ju ly). I f the same measurement is taken at a different place (littoral zone, 1 m ) , lake, or time (30 Ja nuary), the measured v a lue m ay be different. Athird component of v ariability is the ability to accurately m easure the quantity in w h ich w e are interested, w h ich can be affected by sampling g ear, instrumentation, errors in proper adherence to field and laboratory protocols, and choice of methods used in m aki ng determinations.
Th e basic rule of efficient sampling and measurement is to sample so as to (1) mi nimiz e measurement errors; (2) m a ximize the components of v ariability that have influence on the central questions and reporting units; and (3) control other sources of v ariability that are not of interest, that is, mi nimize their effects on the observations. I n the example of chlorophyll concentrations, v ariability could be reduced by sampling each of several lakes in the deepest part, with a v e rtically integrated pum p sample taken in early spring before stratification appears. Many lakes are sampled to examine and characterize the v ariability due to different lakes (the sampling unit). Each lake is sampled in the sam e way , in the same place, and in the same timeframe to mi nimize variability caused by location, depth, and season, which are not of interest in this particular study

. I n the above example, chlorophyll concentrations v ary with location within a lake and among lakes and with time of sampling (day, season, year). I f the spatial and temporal components of v ariability within lakes are large (e.g., measurements of chlorophyll concentrations typically v ary mo re between spring and fall samples within a lake than they do among lakes), then it m ay be best either to use an index period sample or to estimate a composite from several determinations. For this reason, lake chlorophyll concentrations often are estimated as a g r owing season average, estimated from several determinations (e.g., monthly) during the g r owing season.
I n statistical terminolog y , there is a distinction between sampling error and measurement error that has little to do with actual errors in measurement. Sampling error is the error attributable to selecting a certain sample unit (e.g., a lake or a location within a lake) that m ay not be representative of the population of sample units. Statistical measurement error is the ability of the investigator to accurately characterize the sampling unit. T hus, measurement error includes components of natural spatial and temporal v ariability w ithin the sample unit as w e ll as actual errors of omission or commi ssion by the
4-10 

### Nutrient Criteria—Lakes and Reserv o irsinvestigator. Measurement error is mi nimized with me thodological standardization: selection of cost-effective low v ariability sampling m ethods, proper training of personnel, and quality assurance procedures to mi nimize m e thodological errors. I n analytical laboratory procedures, measurement error is estimated by replicate determinations on some subset of samples (but not necessarily all). Similarly, in field investigations, some subset of sample units should be measured m o re than once to estimate m easurement error. An alysis of v ariance can be used to estimate measurement error. A ll m u ltiple observations of a variable are used (from all lakes with m u ltiple observations), and lakes are the primary effect v ariable. Th e root means square error (RMSE) of the analysis of v ariance is the estimated v ariance of repeated observations within lakes. Note that a hypothesis test (F-test) is not of interest in this application, only the R M SE of the analysis.
Na tural v ariability that is not of interest for the questions being asked, but that m ay affect the ability to address them, should be estimated with the RMSE method above. I f the v ariance estimated from RM SE is unacceptably large (i.e., as large or larger than v ariance expected among sample units), then it is often necessary to alter the sampling protocol, usually by increasing sampling effort in some way, to further reduce the measurement error. Measurement error can be reduced by m ultiple observations at each sample unit, for example, m u ltiple ponar casts at each sampling event, m u ltiple observations in tim e during a growing season or index period, depth-integrated samples, or spatially integrated samples.
A less costly alternative to m u ltiple measures in space is spatially composite determinations. In nutrient or chlorophyll determinations, a water-column-pumped sample, where the pump hose is lowered through the water column, is an example of a spatially composite determination. Spatially integrating an observation and compositing the m a terial into a single sample is almost always m o re cost-effective than retaining separate m u ltiple observations. This is especially true for relatively costly laboratory analyses such as organic contaminants and benthic macroinvertebrates. Statistical power is the ability of a g ive n hypothesis test to detect an effect that actually exists, and it mu st be considered when designing a sampling program (e.g., Peterman, 1990; Fairweather, 1991). T he power of a test (1



### � b) is defined as the probability of correctly rejecting the null hypothesis (H0) w h en H 0 is false (i.e., the probability of correctly finding a difference [impairment] w h en one exists). For a fixed confidence level (e.g., 90%), power can be increased by increasing the sample size or the number of replicates. T o evaluate power and determine sampling effort, an ecologically meaningful amount of change in a v ariable m u st be set. Optimizing sampling design requires consideration of tradeoffs among the measures used, the effect size that is considered meaningful, desired power, desired confidence, and resources available for the sampling program

. Every study requires some level of repeated measurement of sampling units to estimate precision and measurement error. R e peated measurement at 10% or m o re of sites is common among m any m onitoring programs.



###  Alternative Sampling Designs Sampling design is the selection of a part of a population to observe the attributes of interest. To estimate the v a lues of those attributes for the whole population, classical sampling design makes assumptions about the v ariables of interest. I n particular, it assumes that the v a lues are fixed (but unknown) for each m emb er of the population until that memb er is observed (Thompson, 1992). T his assumption is perfectly reasonable for some v ariables —for example, length, weight, and sex of m emb ers 

### Nutrient Criteria—Lakes and Reserv o irs 4-11of an animal population—but it seems less reasonable for m o re dynamic variables such as nutrient concentrations, loadings, or chlorophyll concentrations of lakes. Designs that assume that the observed variables are themselves random v ariables are model-based designs, in which previous knowledge or assumptions are used to select sample units. Probability-Based D e signs ( r andom sampling)
Th e m o st basic probability -b ased design is simple random sampling, in w h ich all possible sample units in the population have the same probability of being selected, that is, all possible combinations of n sample units have equal probability of selection from among the N units in the population. I f the population N is finite and not excessively large, a list can be m a de of the N units, and a sample of n units is randomly selected from the list. T h is is termed list frame sampling . I f the population is v e ry large or infinite (such as locations in a lake), one can select a set of n random (x,y) coordinates for the sample. All sample combinations are equally likely in simple random sampling; thus, there is no assurance that the sample actually selected will be representative of the population. O ther unbiased sampling designs that attempt to acquire a m o re representative sample include stratified, systematic, and m u ltistag e designs. I n stratified sampling, the population is subdivided or partitioned into strata, and each stratum is sampled separately

. Partitioning is typically done so as to m ake each stratum m ore homogeneous than the overall population; for example, lakes could be stratified on ecoregion. Systematic sampling is the systematic selection of every k th unit of the population from one or m o re randomly selected starting units, and it ensures that samples are not clumped in one region of the sample space. Multistag e sampling requires selection of a sample of primary units, such as fields or hydrologic units, and then selection of secondary sample units, such as plots or lakes within each primary unit in the first-stag e sample. Estimation of statistical parameters requires w e ighting of the data with inclusion probabilities (the probability that a g ive n unit of the population will be in the sample) specified in the sampling design. In simple random sampling, inclusion probabilities are by definition equal, and no corrections are necessary . Stratified sampling requires w e ighting by the inclusion probabilities of each stratum

. Unbiased estimators have been developed for specific sampling designs and can be found in sampling textbooks, such as Thompson (1992). Model-Based Designs
Us e of probability -b ased sampling designs may miss relationships among v ariables (models), especially if there is a regression-type relationship between an explanatory and a response variable. As an example, elucidation of lake response to phosphorus loading with the Vollenweider model (Vollenweider, 1968) required a range of trophic states from ultraoligotrophic to hypereutrophic. A simple random sample of lakes is not likely to capture the entire range (i.e., there would be a large cluster of me sotrophic lakes with few at high or low ends of the trophic scale), and the random sample m ay therefore be biased with respect to the model.
I n model-based designs, sites are selected based on previous knowledge of auxiliary v ariables, such as estimated phosphorus loading, lake depth, and elevation. Often, these designs preclude an unbiased estimate of the population response v ariable (e.g., trophic state), unless the model can be demonstrated to be robust and predictive, in which case the population value is predicted from the model and from previous knowledge of the auxiliary (predictive) v ariables. Selection of unimpacted reference sites is an example of samples for a model (index development; response of index v ariables to measures of
4-12 

### Nutrient Criteria—Lakes and Reserv o irsanthropogenic influence) that cannot later be used for unbiased estimation of the biological status of lakes. I deally, it m ay be possible to specify a design that allows unbiased estimation of both population and model. Statisticians should be consulted in developing the sample design for a nutrient criteria and m onitoring program

. D. Database Management Critical to the success of any m onitoring and criteria development program is comprehensive data m anagement. Because agencies that engage in water quality m anagement are required to be accountable, because monitoring and assessment tools continue to be developed, and because desktop computers are now capable of m a ny of the same tasks as larger computers, data m a nagement m u st be addressed at the outset of a program or project. Storing data in filing cabinets or on spreadsheet files is no longer adequate.
The m o st powerful database architecture for storing large, complex data sets with m u ltiple relationships among the data elements are relational databases. T he hierarchical nature of a watershed and a survey and assessment program are reflected in a relational database: a watershed m ay contain ma ny sampling sites; each site m ay be sampled m u ltiple times during an investigation; and each sample may be tested for m u ltiple constituents. Nonrelational databases consist of one or m o re flat files. Examples include text files and spreadsheet files. Flat file databases have a number of disadvantages, including redundant data, m a intenance difficulties, and slow access to data. A number of relational database m a nagement systems (i.e., software) exist today, including Oracle, Sybase, DB2, I n formix, SQL server, and ACCESS.
I n the simplest form, a relational database begins as a collection of tables. Each table is related to at least one other table through one or m o re key fields that act as links (i.e., relationships) between tables. B ecause tables are related, information can be retrieved from m ore than one table at a time. T ables g enerally contain data about a particular subject. For instance, data about a station that is sampled would be in one table, whereas data about a sampling event would be in a separate but related table. Good database design includes reducing or eliminating duplicate information in tables and being able to m ake changes to the database tables as data needs change. Data should be easy to m a nage, ag gr egate, retrieve, and analy z e. EPA has sponsored the development of two relational databases that are available for data ma nagement for nutrient criteria, modernized STORET and Ecological Data Application System (ED AS ). 1. Modernized STORET
EPA 

### � s Office of Water has redesigned and modernized STORET . T he historical data contained in STORET , BIOS, and ODES are available in modernized STORET . T his database was designed to meet emerging data and information needs associated with watershed level environmental protection. T he features of the new system were carefully engineered to meet the information requirements of Federal, State, and local clients engaged in ambient w a ter quality and biological monitoring activities of all ki nds. Modernized STORET meets the following five requirements set by EPA:
• I t m u st be easy to enter and retrieve data, and the system m ust be web enabled.
• T he system m ust have menu access and browse capability

.


### Nutrient Criteria—Lakes and Reserv o irs 4-13•	 T he system m ust support the storage of quality assurance and quality control information on a project and result basis.
• T he system m ust be flexible and able to change with the changing needs of its users.
•	 T he system m ust provide a wide range of standard output forms, including Geographic In formation System environments.
ST OR ET centrally stores all data submitted by all agencies, and it allows each State or agency to enter, store, and use its own data. I t is a flexible and g e neralized data warehouse, both within-agency and nationwide, and as such does not have program

- specific analysis capabilities built in. 2. EDAS EDAS i s EPA 

### � s biological m e tric calculation software. I t is entirely compatible with ST OR ET , and final data should reside in ST OR ET

. ED AS contains built-in data reduction and recalculation queries that are used in biological assessment. I t is designed to enable the user to easily m anage, ag gr egate, integrate, and analy ze data to m ake informed decisions regarding the condition of a water resource. Biological assessment and monitoring programs require ag gr egation of raw biological data (lists and enumeration of taxa in a sample) into informative indicators. ED AS is designed to facilitate data analysis, particularly the calculation of biological m e trics and indexes. Predesigned queries that calculate a wide selection of biological me trics are included with EDAS.

4-14 

### Nutrient Criteria—Lakes and Reserv o irs

# CHAPTER 5 A. Introduction B. Nutrient Variables C. Biolo g ical Variables 

# Candidate Variables for **Criteria Setting**

A. Introduction
Th is chapter provides an overview of several trophic state v ariables that could be used to establish regional and water-body -s pecific nutrient criteria for lakes and reservoirs. T r ophic state v ariables are those v ariables that can be used to predict the trophic state of a water body . T rophic state v ariables include measures of nutrient concentration (e.g., T P , soluble reactive phosphorus, T N , total Kjeldahl nitrogen), plant (macrophyte or algal) biomass (e.g., organic carbon, chlorophyll a , Secchi depth), and watershed attributes (e.g., land use). All could be used for establishing criteria to address eutrophication concerns, but only a few are v i able candidates for early w arning v ariables. Based on the Proceedings of the National Nutrient Assessment Workshop (U.S. EPA, 1996), the m o st likely trophic state candidates are T P , T N , chlorophyll, Secchi transparency, and dissolved oxy ge n. I n addition, one w a tershed me tric—land use and the associated phosphorus loading—was recomme nded as an early warning variable. T hese v ariables (metrics or indicators) are briefly reviewed below

. EPA presently requires only T P, T N, chlorophyll a , and Secchi depth be used, but this set of criteria variables m ay be aug m ented by other measurements if the State or T r ibe prefers. Emphasis should be on the open water portion of the ecosystem, and as can be seen in T able 5.1, mo st of the comm only used biological v ariables are measures of the amount of organic m a terial in the open w a ter. A s discussed later, only a few attempts have been m a de to incorporate the littoral zone into the assessment of trophic state.
B. Nutrient Variables 1. Phosphorus Phosphorus and nitrogen are essential nutrients necessary for the g r owth of plants in lakes. O f these two nutrients, phosphorus is m o st often considered to be the nutrient that regulates the production of algae in lakes and is m o st amenable to control. As such, it is often the v ariable of concern in regards to lake and reservoir eutrophication. T ogether with algal chlorophyll a and Secchi disk transparency , phosphorus is routinely used to estimate trophic status of lakes and reservoirs (see Chapter 2). Vollenweider (1968) and Saw y er (1947) categorized trophic status according to phosphorus concentration. Lakes with phosphorus concentrations below 10 μ g/L were classified as oligotrophic; phosphorus concentrations between 10 and 20 μ g/L were indicative of me sotrophic lakes; and eutrophic lakes had phosphorus concentrations exceeding 20 μ g /L. Several forms of phosphorus can be measured. T otal phosphorus (TP) is a measure of all forms of phosphorus, dissolved or particulate, that are found in a sample. T P has been used throughout North America as a basis for setting trophic state criteria and in developing related models (N AL MS, 1992).



### Nutrient Criteria—Lakes and Reservo ir s 5- 1**Ta ble 5.1. Variables Used to Estimate T**  **r ophic State in Lakes** 
**Eu trophication-Related**  **Variables Appa**  **ren t M**  **easure In**  **te rference** 
Total phosphorus Total nitr o g en Total or g anic carbon Chloroph y ll pi gm ents

Suspended s o lids Transparenc y Turbidit y Direct al g al counts / Biovolum e Biochemical ox yg en demand ( BOD) Nutrient concentration, Biomas s Nutrient concentration, Biomas s Biomas s
Al g al biomas s , Photos y nthetic c apacit y Suspended biomas s Suspended al g al biomas s Suspended al g al biomas s Al g al biomas s
Al g al biomas s N onbiolo g ical, nonal g al f orms N onbiolo g ical, nonal g al f orms N onal g al s us pended particulates , dis so lved or g anic s Hi g hl y variable r e lationship between ch loroph y ll and al g al c ar bon or biovolum e N onal g al particulates N onal g al particulates, dis so lved c o lor N onal g al particulates N one, but dif ficu lt to do

N onal g al particulate and dis so lved car bon

TP concentrations in runoff or areal exports can be readily related to watershed land use as well (e.g., Reckhow and Simpson, 1980; Walker, 1985a), which m ake s it an excellent v ariable for addressing point and nonpoint source loads from the watershed. Soluble reactive phosphorus (SRP) is a measure of the filterable (filter passings, soluble, inorganic) fraction of phosphorus that is g e nerally thought to be the form directly taken up by plant cells. For this reason, SRP is usually in v e ry low concentrations in lake w a ter, unless phosphorus is not limiting to algal gr owth. T herefore, it serves m o re of an indicator of phosphorus limitation than of the trophic status of a lake. For a m o re complete discussion of the phosphorus forms and their biological significance, see Carlson and Simpson (1996).
TP concentrations v ary regionally, as demonstrated by the phosphorus m apping of Omernik (Omernik et al., 1988) and the nutrient ecoregion m ap in this m a nual (Chapter 1, Figure 1.3). For example, Minnesota T P concentrations vary substantially between the four ecoregions that contain 98 percent of the State 

### � s lakes (Heiskary and Wilson, 1989). Data from Minnesota 

### � s ecoregion reference lakes (representative, mi nimally impacted lakes) demonstrate the v ariability between and within ecoregions (Table 5.2). T he within-region variability can be accounted for in part by the depth of the lakes and mi xing status. T able 5.2 reveals the distinct within-region differences in T P as related to lake mi xing status. T h ese differences are m o st pronounced in the north central hardwoods forest lakes where me dian summe r- mean T P concentrations in class I dimictic lakes (mixed only in spring and fall) was 39 μg /L as compared with 89 μ g /L for lakes that are continuously mixed (class 3 dimictic or poly mictic) lakes. I t is likely that internal recycling of phosphorus becomes a significant portion of the phosphorus budget in the shallow eutrophic to hypereutrophic lakes in this ecoregion. Differences are quite

5- 2 

### Nutrient Criteria—Lakes and Reserv o irs� **Ta ble 5.2.**  **M edian T**  **o tal Phosphorus (**  **g/ L) Co**  **n cen**  **tr atio**  **ns as A**  **ff ected**  **by Mi xin**  **g Stat**  **us an**  **d Ec**  **oregion in M i**  **nnesota**

**Ecore gion**  **Mixi ng S**  **tat us**  **Class I Dimictic ( m**  **ixes only in spr**  **i ng and fall)**  **Inter m**  **ittently M**  **ixed Continuously** **M ixed**  Northern lakes and fo rests 20 26 29

North central hardwood f orest 39 62 89

West ern c orn belt plains 69 135 141

Number of lakes evaluated 257 87 199

S ource: Hei ska ry and Wils on, 1988. pronounced in the western corn belt plains ecoregion as well, but the population of class I dimictic lakes (based on available data) is quite small.



### � Analysis Phosphorus is relatively easy to measure using a colorimetric procedure (APHA, 1998). To use the procedure, all forms of phosphorus m u st be converted into orthophosphorus. SRP is a form that is defined as filterable and reactive with the m o lybdate reagent and g e nerally reflects the amount of orthophosphorus plus some polyphosphates in the sample. Acid- w ashed sample containers and analytical gl assware are essential to avoid incidental phosphorus conamination of the analysis.
Th e distinction between “particulate” and “dissolved” is primarily a function of the filter used. Tr aditionally, a 0.45μ pore size m emb rane or G F/F g l ass fiber filter is used (APH A , 1998). G lass fiber filters are used in some noncritical studies, and mi cropore filters are used in critical studies. T he particulate form of T P is converted to the ortho form with an acid hydrolysis step. T he strength and nature of the acid can affect the amount of phosphorus converted. Usually, acid potassium persulfate is used for the digestion (APHA, 1998; Ameel et al., 1993; Ebina et al., 1983; Smart et al., 1981; Menzel and Carwin, 1965). 2. Nitrogen Nitrogen is also an essential nutrient for algal growth. In contrast to phosphorus, control of nitrogen sources is m o re difficult because nitrogen can be assimilated directly from the atmosphere by several types of organisms, including some species of the Cyanophyta , the blue- g reen algae. I n addition, nitrogen is not as often limiting to plant g r owth,thus the focus on phosphorus in the m a jority of eutrophication-related efforts worldwide.



### Nutrient Criteria—Lakes and Reserv o irs 5- 3Th ere are several forms of nitrogen to consider, and its cycling is complex compared with phosphorus. T he most comm on forms of concern in eutrophication evaluation are nitrite, nitrate, amm onia, and organic nitrogen, as measured as total Kjeldahl nitrogen (TKN). T otal nitrogen (TN) is considered to be the sum of amm onia, nitrate, nitrite, and T K N. Ty pically nitrate, nitrite, and amm onia are at v e ry low levels in lakes or reservoirs unless there are some relatively recent loadings of m a nure or fertilizer present in runoff from the w a tershed or if nitrogen is not limiting to algal growth. T hese form s are rapidly used by algae and aquatic plants or converted to other forms of nitrogen. T he most useful m easurement from a modeling standpoint is either T Nor T K N. As with T P , T Nconcentrations v ary regionally

. Based on data from Minnesota, T Nconcentrations in the shallow agricultural lakes are about twofold higher than concentrations in the deeper lakes in the forested region. TN:TP ratios have been used as a basis for estimating w hich nutrient limits algal growth (e.g., Smith, 1982). Low T N :TP ratios (less than about 7:1) are indicative of nitrogen limitation, whereas ratios gr eater than 10:1 are increasingly indicative of phosphorus limitation. Based on data from Minnesota, low ratios occur in some shallow hypereutrophic lakes in the northern g l aciated plains. However, these low ratios are typically the result of v e ry high TP loads from point or nonpoint sources in the watershed rather than a shortage of nitrogen. Low TN:TP ratios also are found in lakes receiving significant amounts of sewage effluent.



### � Analysis Like phosphorus, nitrogen is divided into dissolved and particulate forms based on whether or not a particle passes through a filter. I t would be advisable to use the same size filter for both phosphorus and nitrogen. TN is similar in concept to TP, being the estimate of all nitrogen forms. Traditionally, TN is calculated as the sum of the analyses of all nitrogen forms (N O 3 � + NO 2 � + T KN � ). N ewer tests allow the conversion of all forms to NO 3 and are therefore direct equivalents to the T P test except alkaline persulfate digestion is used (APHA, 1998; Solorzane and Sharp, 1980; D'Elia et al., 1977). C. B iological Variables 1. Organic Carbon The term “biomass,” used so frequently in the ecological literature, refers to the w e ight of living ma terial in a unit of measure (in a bacterium, in a cubic m e ter of water, or in an ecosystem). T he bulk of that weight is in the form of organic carbon. Organic carbon production or productivity (the rate at which carbon is fixed in the aquatic ecosystem) has been the basis for numerous trophic state classification systems and for the definition of trophic state itself (Rodhe, 1969). T he rates of production and decomposition of carbon compounds and the resulting biomass are at the heart of the eutrophication problem

. Despite the central character of carbon in eutrophication and ecosystem structure and function, carbon has not been explicitly m easured or modeled in m o st standard eutrophication or nutrient/food chain frameworks. T his omission m ay have been, in large part, the result of the difficulty in measuring and interpreting organic carbon. Carbon analysis requires expensive, dedicated equipment, and each type of instrument produces slightly but significantly different estimates of carbon. A lthough the criticism of technique-specific results can probably be invoked for all of the v ariables discussed in this chapter, the expense of the equipment plus the v ariety of techniques available m ay have restricted the popularity of the routine analysis of carbon.

5- 4 

### Nutrient Criteria—Lakes and Reserv o irsA second reason for the limited use of carbon in eutrophication-related studies is that chlorophyll pig ments or direct measures of algae and macrophytes not only estimate plant biomass, but also directly indicate the photosynthetic capacity to produce carbon. Chlorophyll also remains the only economic means to directly m easure algal biomass free from significant interferences. H owever, the chlorophyll-to-carbon ratio in phytoplankton v aries by about a factor of 5 depending on ambient light and nutrient levels (Laws and Chalup, 1990). Consequently, measuring particulate organic carbon together with chlorophyll could better assess the amount of autochthonous carbon, particularly during bloom conditions.
Th ere are several reasons for measuring organic carbon. Organic carbon now can be measured m o re easily and precisely than in the past. T he use of carbon associated with algal metabolism and decomposition g r eatly facilitates the modeling of dissolved oxy ge n. Because m a ny shallower stratified systems experience hypolimnetic anoxia, models incorporating the carbon factor m u st be capable of accurately simulating this phenomenon. T he direct modeling of organic carbon becomes especially important for systems where both allochthonous and autochthonous carbon sources are important. T he use of eutrophication models as the basis for examining the transport and fate of toxic substances in lakes and impoundments requires that the amount and forms of organic carbon be specified. Such confounding problems include toxic organics, me tals, and disinfection byproducts. Finally, the state of the lake 

### � s bottom sediments is inextricably tied to the amount of carbon it receives from the overlying w aters. T his has ramifications for sediment oxy ge n and toxic substance sequestering

. 2. Chlorophyll a Chlorophyll is the m a jor photosynthetic pig m ent in plants, both algae and macrophytes. As such, it is the important v ariable when any estimate of the photosynthetic capacity of an ecosystem is desired. Chlorophyll is probably m ost often used as an estimator of algal biomass. T he relationship between chlorophyll and T P is well established for lakes and reservoirs across m u ch of the world. Despite the curious fact that the chlorophyll m o lecule itself contains no phosphorus while T P includes phosphorus dissolved in the water as well as in algal cells, relationships between T P and chlorophyll have dominated the empirical linkages between nutrients and the biological response of the algae in lakes. See Nurnberg (1996) for a recent review of these relationships. Chlorophyll is also a preferred v ariable because there are lakes where T P is not the sole or primary limiter of algal production or biomass, for example, lakes with high inorganic turbidity or high flushing rates. For instance, a chlorophyll a g oal of less than 30 μ g/L was used for Lake Pepin, a run-of-the-riv er reservoir on the Mississippi River between Minnesota and Wisconsin (Heiskary and Walker, 1995). In this reservoir, inorganic turbidity and high flushing rates w e re the primary factors controlling algal production during above-average flows (about 20,000 cfs or g r eater), and chlorophyll a routinely remained below 30 μ g /L at these flows. I n contrast, as flows declined below about 20,000 cfs and residence time increased above 10 to 14 days, chlorophyll a increased as the influence of residence time and inorganic turbidity declined, and the potential trophic status, as reflected by T P, was realized. Because of the relationship between chlorophyll and phosphorus and its linkage to algae biomass, chlorophyll is often a m a jor component of trophic state indices (Carlson, 1977) and w a ter quality criteria. Oregon has set an endpoint of 10 μ g /L for natural lakes that thermally stratify and 15 μ g/L for natural lakes that do not thermally stratify (NALMS, 1992). Similarly, North Carolina uses a standard of 40 μg/L for warm waters and 15 μ g /L for cold waters (NALMS, 1992). On the regional level, Raschke (1994) proposed a mean g r owing season limit of 15 μ g/L for water supply impoundments in the



### Nutrient Criteria—Lakes and Reserv o irs 5- 5southeastern United States and a value of 25 μ g/L for water bodies primarily used for other purposes (e.g., v i ewing pleasure, safe swimmi ng, fishing, boating).
I n addition to the use of chlorophyll in classification, the chlorophyll interval frequency (bloom frequency) can be predicted based on regression equations developed by Walker (1985b) relating bloom s to phosphorus. T hese chlorophyll a intervals can be related to v arying user perceptions of lake condition. Th e projected frequency of these extreme events, as a result of increased phosphorus loading can be readily understood by citizens and decisionmakers (Heiskary and Walker, 1988).


### � Analysis The term “chlorophyll” really represents a family of m o lecules, chlorophyll a , b , c , and d

. Chlorophyll a , because of its primary role in photosynthesis, is often the m o lecule of preference. Chlorophyll can be measured by several different methods. Most include steps of concentration of the algae, extraction of the chlorophyll with a solvent, and measurement of the chlorophyll m o lecule. Un fortunately, each of these techniques and choices of solvents, extraction times, and methods for m easuring the chlorophyll can produce widely different estimates of chlorophyll. Chlorophyll a is the primary photosynthetic pig ment and can be measured quite accurately w ith highperformance liquid chromatography (HPLC) analysis. T he use of colorimetric techniques to measure chlorophyll a free from all forms of interference from either decomposition products (phaeophytin, phaeophorbides, or chlorophyllides) or other chlorophylls (chlorophylls b and c ) is almost impossible. However, if the purpose of measuring chlorophyll is to estimate biomass rather than to know the absolute amount of photosynthetic pig m ent, the absolute accuracy obtained by H PLC is not necessary and the spectrophotometric techniques suffice. Most published relationships between T P and chlorophyll were ma de using these cruder spectrophotometric m e thods. Because chlorophyll a cannot be measured without interference, Carlson and Simpson (1996) recomme nd using total chlorophyll pig m ents (the estimated chlorophyll at a single wavelength) rather than subjecting the sample to further m a nipulations to obtain an estimate of chlorophyll a . However, the acidification step recomme nded in the Standard Methods (APHA, 1998) does remove some phaeophyton interferences, and the resultant chlorophyll concentration measured m ay be closer to the actual concentration than an unacidified measure. Fluorometry also can be used, especially if algal densities are ve ry low and a v e ry sensitive me thod of detection is needed. Ch lorophyll pig ments degrade easily

. Whole nonfiltered samples can apparently be ke pt for several days if left in the dark and in the refrigerator. Filtered samples should be ke pt dark and frozen. Filtered samples imme rsed in the solvent are apparently stable as long as they are ke pt dark

. More information on chlorophyll preservation can be obtained from Carlson and Simpson (1996) and the American Public Health Association (1998).
Th e important consideration for any of these techniques is that standardization of m e thodolog y is critical. A lteration of the extraction solvent, extraction time, type of filter used to concentrate the sample, or concentration of acid used to convert chlorophyll into phaeophytin all can alter the concentration estimates. T herefore, once a technique is chosen, for the sake of data consistency, the technique should be altered only with the knowledge that some of the previously collected data m ay not be compatible. T his is one reason for using total chlorophyll; it requires the least analytical m a nipulation and therefore is the m o st conservative estimator of chlorophyll. Caution also should be used when obtaining data from several sources that use different techniques that m ay produce discrepancies. T his is
5- 6 

### Nutrient Criteria—Lakes and Reserv o irsparticularly important w h en compiling several data sets to establish reference conditions for criteria development. 3. Secchi D isk Transparencyp Secchi disk transparency, or Secchi depth, can cheaply provide a g r eat deal of information on lake wa ter quality and, together with T P and chlorophyll a , has become routinely used as a measure of lake trophic status (e.g., C arlson, 1977). Secchi depth is routinely incorporated into citizen v o lunteer m onitoring programs, and in m a ny States, it often provides the best basis for identifying trends in trophic status over time (Heiskary et al., 1994). Smeltzer et al. (1989) found Secchi transparency to be the best variable for identifying statistically significant trends in trophic status because of the large number of observations that can be g a thered in a g ive n season and the ability to g a ther numerous years of data at little or no cost as compared with T P and chlorophyll a, w hich are typically m onitored at a m u ch reduced frequency and at a higher cost. A s with other v ariables, Secchi depth m ay vary considerably in a g iven lake between and within seasons; therefore, it is desirable to have an “indicator season.” I n many States, the m o st reliable timeframe for measuring Secchi transparency and estimating lake trophic status is summe r, typically mid- J une to mi d-September. Thus, this is the focus for m u ch of the citizen and professional data g a thering that takes place. Summe r- m ean measures of T P , chlorophyll a , and Secchi depth then are used to estimate lake trophic status. I t should be noted that Secchi depth measurements are inadequate for nutrient level estimations in lakes with colored w a ter or inorganic suspended solids. I n such instances, the TN and TP measurements are m o re telling indicators of enrichment.
Us er perception measurements m ay be taken in conjunction with Secchi readings. T hese user perceptions, especially w hen recorded by citizen v o lunteer monitors, can provide a good basis for associating designated uses and subjective perceptions of w a ter quality w ith actual measurements of wa ter quality . C itizen v o lunteer programs in Minnesota, Vermont, and N ew Yo rk routinely collect this information. Smeltzer and Heiskary (1990) found that user perceptions m ay vary between States and may v ary further between regions within a g iv en State. T his type of information can provide a perspective useful for criteria and g o al setting purposes (see Vermont and Minnesota case studies in Appendix B).


### � Analysis
Th e standard Secchi disk used in limnological investigations is a 20 cm diameter disk that either is all white or has alternating black and white quadrants. T echniques v ary as to how the depth should be m easured, and statistically significant differences between the techniques have been reported. Probably the best me thod is to lower the disk on the sunlight side of the boat to eliminate shading the disk or to have the disk disappear in a back gr ound darkened by the shadow of the boat. Glare on the water is eliminated by using a viewscope to v i ew the disk . T he disk is lowered until it cannot be seen, the depth is noted, and then the disk is raised until it can be seen again. The average between the depth of disappearance and the depth of appearance is called the Secchi depth. Considerable v ariations of this technique exist. Probably m ore programs lower the disk on the shady side of the boat and do not use a v i ewscope. The use of a v i ewscope or the side of lowering w ill g ive different results. The choice of an all- wh ite or a black -a nd- w hite disk also will g ive different readings, especially in clearer waters. T he point to be emphasized is that the particular method chosen m ay not be as important as consistency in the m e thod of Secchi depth determination. D ata consistency almost dictates that the technique cannot be changed without transforming part of the data record or losing



### Nutrient Criteria—Lakes and Reserv o irs 5- 7historical information. When consistently applied in conjunction with T P and T Ncalibrations, Secchi depth change is a helpful tool for blue- g reen algal bloom prediction in north temperate lakes. 4. Dissolved Oxygenp Dissolved oxy ge n (DO) and temperature profiles are routinely taken in eutrophication-related studies. T hese measurements are essential for characterizing the mi xing status and for determining the presence or absence of oxy ge n above the sediments, the rate of hypolimnetic oxy ge n depletion, the number of days of anoxia, and w h ether the lake has suitable habitat for sensitive fish species. A noxic conditions in lakes also m ay favor the g r owth of blue- g reen algae such as Microcystis (Reynolds and Walsby, 1975). T he lack of oxy ge n in the bottom waters causes sediments to release such dissolved constituents as inorganic phosphorus, amm onia, and hydrogen sulfide. T he initial disappearance of oxy g en in the hypolimnion can occur before any noticeable change in the productivity of algae in the epilimnion because of the amplification of organic epilimnetic inputs by the sediments (Gliwicz and Kowalczewski, 1981). T his m ake s the oxy ge n content of the hypolimnion and the rate of disappearance to be a potential early warning system of changes in trophic state. Oxy ge n concentrations and rates of depletion have been used to characterize lakes and can in some instances be related back to nutrient status. I n contrast to the previous v ariables w h ere epilimnetic or composite measurements w e re key, the focus for D O in lakes is primarily on hypolimnetic concentrations. DO concentrations in the hypolimnion can be related to epilimnetic T P and annual primary production and inversely to mean summe r Secchi depth (Cornett and Rigler, 1979). Checking for the presence or absence of hypolimnetic oxy ge n was an early method of discriminating between oligotrophic and eutrophic lakes (Thienemann, 1921) that is still used to some extent today

. Hypolimnetic oxy ge n depletion rates have been used as a v ariable of trophic state by several investigators (Mortimer, 1941; Rast et al., 1983). T his would not apply to allochthonous organic loading , which m ay deplete DO independent of nutrient concentrations. Because the presence or absence of hypolimnetic oxy ge n and oxy ge n depletion rates are confounded by the size of the hypolimnion, the rate usually is indexed to the area of the hypolimnetic surface and termed the areal hypolimnetic oxy ge n deficit (AHOD) (see Hutchinson, 1957; Wetz e l, 1975). Co mp ensating for the size of the hypolimnion will not necessarily g ive a v a lue correlated with the amount of productivity or nutrient status of the epilimnion because the rate of oxy ge n consumption is dependent on temperature as well. Latitudinal differences in AHOD will exist independent of the trophic status (biomass concentration) of the lake. T he hypolimnetic oxy ge n depletion rate is also affected by dissolved color; Hutchinson (1957) recomme nds that AHOD not be used on lake s with color greater than 10 Pt units. Walke r (1979) used trophic status, AHOD, mean hypolimnion depth, and oxy ge n concentration at spring turnover to predict the effective number of days of oxy ge n supply present in the hypolimnion after spring turnover. Nurnberg (1996) quantified hypolimnetic anoxia based on DO profiles and lake mo rphometry and related this anoxic factor to other trophic status variables. T hus, DO is an important variable to consider when assessing the impact of eutrophication, even though it does not define trophic state.


### � Analysis Measurements are typically taken at appropriate intervals from the surface to the bottom of the lake on each sample date. O xy ge n is typically taken using a remote sensing probe, although oxy ge n also can
5- 8 

### Nutrient Criteria—Lakes and Reserv o irsbe measured by analy z ing individual samples using the Azide Modification of the Winkler technique (APHA, 1995). T he minimum frequency for characterizing mixing and oxy ge n status of the lake is dependent on the rate at which oxy ge n can be depleted in the water body, which itself is dependent on the size and temperature of the hypolimnion and the potential amount of organic m a tter that m ay be settling into this region. I n some cases, the mi nimum frequency m ay be a month; in others, it m ay only be a few hours. Some shallow lakes experience daily oxy ge n depletion near the bottom

. 5. Macrophytesp The term “macrophyte” refers to any plant life larger than the mi croscopic algae in aquatic systems. It m ay be a plant rooted in the sediment, such as pond weeds or cattails, or that is free-floating, such as duckw eed or coontail. I t also includes large algae such as Chara

. Macrophytes are important in any consideration of trophic state because they are also plants and, therefore, are potential utilizers of incoming plant nutrients. A lthough a g r eat deal of research has been done on macrophytes, the ability to predict the extent of macrophytes based on nutrient load or even nutrient concentration still has not been attained.
A lthough macrophytes require nutrients for g r owth, the imme diate origin of those nutrients is still a ma tter of some controversy

. Originally it was thought that macrophytes m ay compete with algae for nutrients in the water; this m ay be the case for floating species, such as duckw eed or coontail. Evidence sug ge sts that rooted aquatic plants draw m o st, if not all, of their nutrients from the sediments, not from the water. I n this m a nner, they can obtain nutrients from the sedimented historical phosphorus. T his use of historical nutrients obscures or even eliminates correlations and predictions of macrophyte biomass based on contemporary nutrient loading . I t also discourages the m a nagement of macrophyte-based eutrophication by nutrient loading control because the macrophytes m ay persist and m o st likely ev en spread after nutrient reduction.
De spite the lack of correlation between macrophyte biomass and nutrient loading, they still m ay be related. N utrients attached to particles will settle out, bringing new substrate and nutrients to the m acrophytes. D ead algae will also settle, again increasing substrate and nutrients. T he presence of m acrophytes near water inputs m ay actually serve to intercept sediment particles, thus building up these regions faster than if the particles were allowed to sediment throughout the lake. I ncreased nutrient loading can be expected to enhance the sedimentation rate and thus increase the areal coverage of m acrophytes (Carpenter and Lodge, 1986). T he macrophytes m ay actually serve as a positive feedback m echanism that enhances the filling in of lakes, their own structures serving to fill in the littoral area and increasing the colonizable area even m o re. Considerable evidence sug ge sts that some sort of antagonism exists between macrophytes and floating algae in lakes and ponds. Macrophyte density m ay be suppressed w h en algal densities are high, presumably because the algae and/or epiphytes on plant surfaces shade out macrophytes. Conversely, if m acrophytes are dense, there are accounts of the algae not g r owing, even in the open areas outside the m acrophyte beds. I t has been hypothesized that a chemical is excreted by the macrophyte that suppresses algal g r owth. According to the m o st sweeping theory relating eutrophication to the relationship between algae and macrophytes, as a lake eutrophies it m ay become dominated by either algae or macrophytes, but not both (Scheffer, 1989; Scheffer et al., 1993). Catastrophic events, such as herbiciding or weed harvesting, can shift a macrophyte-based system entirely into an algal-based system

. Alternatively , killing the algae by algicides or by nutrient reduction will shift the system into a macrophyte-dominated system w ith little algae present. B oth of these systems are stable and will persist unless again shifted by external events. I f this model is correct, assessment and prediction of the response to nutrient loading 

### Nutrient Criteria—Lakes and Reserv o irs 5- 9increases or reductions will be difficult unless the mechanism underlying these alternate states is known. Howeve r, the ability to m a nipulate the system as Scheffer (1989) has sug g ested allows the selection of the m o st desirable type of condition, algae or macrophytes, for a g ive n use and enrichment level. Most trophic state v ariables and, indeed, all simple nutrient loading m odels ignore the g r owth and extent of macrophytes, probably reflecting the early limnological emphasis on open-water algae. T his neglect of the macrophytes hinders the determination of the impact of nutrients on the entire biological system . I f nutrient loading m odels or trophic state v ariables do not account for macrophyte biomass, they may underestimate the potential impact of nutrients in macrophyte-dominated lakes.



### � Analysis
Th e solution for macrophyte biomass determination could be very simple. Canfield et al. (1983) proposed the assessment of trophic state based on the T P concentration of the lake, including the amount of phosphorus in macrophytes in the lake. T he total macrophyte biomass in the lake (k g) is estimated by the equation:
TS MB = SA × C × B wh ere T S MB = total submersed macrophyte biomass, SA = lake surface area, C = percent cover of submersed aquatic macrophytes, and B = average biomass collected with a sampler. Canfield et al. (1983) estimated the T P in plant biomass based on the phosphorus in each species and the relative abundance of each species. T he TP content of the lake w a s obtained by adding the amount of phosphorus in the macrophytes to the amount estimated to be in the water column. T here seems to be no reason why the same approach could not be used to measure total plant biomass or chlorophyll. T rophic state could then properly include both macrophytes and algae and would have internally consistent units. Th is would be an instantaneous measure, as sediment phosphorus availability to the biota is assumed to be measured in the macrophytes and algae. 6. Biological Com m unity Structurep Some early trophic classifications were based on the biota of lakes. T hienemann (1921) simultaneously developed a classification scheme based on the species of benthic chironomids in lakes and on the hypolimnetic oxy g en concentration that affected their species composition. I t m u st hav e seemed reasonable at the time that the classifications of T h ienemann (1921) and Naumann (1929) could be joined, because N a umann 

### � s eutrophic lakes also lacked oxy ge n in the hypolimnion and had distinct benthic fauna (Thienemann, 1921).
Because of T h ienemann, the benthos of lakes has received a great deal of attention in trophic classification. T he array of Chironomids, clams, and oligochaete worms have been shown to change with trophic state. I n most cases, these changes are related to the loss of oxy g en in the hypolimnion. Algal species change as a lake becomes m o re eutrophic, with a dominance of diatoms shifting to cyanobacteria (blue- gr een algae). Certain species of diatoms are characterized as being found largely in oligotrophic lakes while others are found in eutrophic situations. Because the frustules of diatoms are preserved in the sediment, this change in species allows a paleolimnological investigation of past trophic states. Z ooplankton species change as well, but their change is confounded by alterations in the intensity of

5-10 

### Nutrient Criteria—Lakes and Reserv o irspredation upon them as the density of zooplanktivorous fish increases, perhaps the result of alterations in the density of the macrophytes that g ive the fish shelter from their predators.
I n general, fish y i eld increases as the productivity of the lake increases. However, there m ay be changes in the dominant fish species as a lake eutrophies (Oglesby et al., 1987) (Figure 5.1). I n northern lakes, salmonids m ay dominate in clear lakes having oxy ge nated hypolimnia. When primary productivity increases to the point that the hypolimnion becomes anoxic, salmonids m ay disappear to be replaced by percids; percids then are replaced by centrarchids; and finally, at the highest nutrient concentrations, rough fish such as carp or bullheads prevail.

Figure 5.1. Ch an ges in fis h sp ecies yield w ith trop hi c s t ate.



### Nutrient Criteria—Lakes and Reserv o irs 5-11

### � Analysis Unfortunately, changes in biological structure do not fit neatly into a nutrient-based classification because structural changes can occur along any environmental axis such as pH or temperature. T he bioassessment of aquatic habitats has its strength in the concept that the organisms can be sensitiv e variables of the condition of the aquatic environment. However, unless a g r eat deal is known about the requirements of the organisms themselves, the assessment does not necessarily indicate the nature of the disturbance. Such g e neral v ariables would be of little use as v ariables of nutrient change if they w ere susceptible to change by a large number of other factors as well.
Th e fact that the assessment of the species or species complexes in a lake m ay not be the sole indicator of nutrient-related changes does not mean that assessing and tracking the biological structure would not be useful. I t could be that subtle changes brought about by nutrient enrichment m ay affect one or m o re g r oups, and these changes may be m o re apparent in the structure than in the biomass.
D. Land Use Ch anges in land use in a lake 

### � s watershed is a v i able early warning indicator of potential lake eutrophication. Landscape data can be used to characterize the watersheds of a population of lakes and to estimate potential nutrient loadings under a v ariety of m a nagement scenarios. For example, the State of Maine seeks to protect lake w a ter quality by limiting the acceptable increase in phosphorus in their lakes that m ay result from changes in land use in the watershed. Very strict requirements for handling storm w ater are a primary aspect of their approach (see Maine case study in Appendix B ). T he changes in land use of m o st concern are typically the shift from forested or open uses to agricultural or urban land uses. Phosphorus exports and concentrations associated with v arious land uses are fairly well documented in the literature (e.g., Reckhow and Simpson, 1980) as w e ll as the effects of the increased loading on lakes. T hus, increases in phosphorus loading as related to changes in land use can be estimated, and the impact of the changes can be described by means of empirical models. Whenever possible, it is advisable to use phosphorus concentration and export data summarized based on w atersheds in a State or region because phosphorus export m ay v ary between regions as well as between land use types. Some g e neral notes and examples follow.
Th e g e neralized land use categories often considered for modeling or prediction purposes are forest, wa ter and m arsh, cultivated, pasture/open, and developed (urban and residential). While phosphorus exports and concentrations from a given land use m ay vary substantially in the literature, some g e neral patterns emerge. T he average phosphorus concentrations found by Omernik (Rohm et al., 1995) g ive some indication of the radical changes in concentration alone when land is disturbed. I f the changes in wa ter loading caused by increased impervious surfaces and decreased plant transpiration are included, the potential impact of human activity in the w a tershed can be easily seen. Phosphorus exports from forested lands are typically low, on the order of 0.1 to 0.15 k g phosphorus/ha/yr (Reckhow and Simpson, 1980; V e rry and T imm ons, 1982). Based on data from the predominantly forested Northern Lakes and Forest ecoregion of Minnesota (Table 5.2), stream TP concentrations typically range from 20 to 50 μ g/L (McCollor and Heiskary, 1993) (Table 5.3). T his range of exports and concentrations is often applicable for m arsh land use as well, although phosphorus export will v ary seasonally in m arshes. Pastured and open land use is a somewhat nebulous category that migh t include idle g r asslands (e.g., Conservation Reserve Program, [CRP]), park lands, or heavily pastured lands. Feedlots should not be
5-12 

### Nutrient Criteria—Lakes and Reserv o irs� included in this category but rather should be considered separately with estimates m a de on a per animal unit basis. Pastured and open park land exports often range from about 0.2 to 0.4 k g phosphorus/ha/yr. For example, two monitored subwatersheds in southwest Minnesota, with 60 percent or m o re of the watershed in CRP, had phosphorus exports of 0.25 to 0.40 k g phosphorus/ha/yr (Schueler, 1995). Phosphorus export from cultivated lands is frequently high and v ariable. R eckhow and Simpson (1980) note that phosphorus export migh t v ary between mi xed agriculture (0.4 to 2.3 k g phosphorus/ha/yr) and row crops (0.2 to 0.9 k g phosphorus/ha/yr). Phosphorus exports from two southwest Minnesota watersheds characterized by 81 percent and 49 percent cultivated land use were 0.4 and 0.6 k g phosphorus/ha/yr, respectively

. Phosphorus concentrations from streams in the highly agricultural western corn belt plains ecoregion of Minnesota typically range from 160 to 330 μ g/L (Table 5.3). Prairie and Kalff (1986) sug ge st however that phosphorus export from agricultural land v aries as a function of watershed size, and they present equations for calculation of phosphorus export by land use type and watershed size. I n general, as watershed size increases, phosphorus export tends to decrease in agricultural lands, with row crops and pasture exhibiting the g r eatest decrease. In practice, this often leads to phosphorus export coefficients on the order of 0.2 to 0.6 k g phosphorus/ha/yr for cultivated lands. This w a s not the case in forested w a tersheds, w h ere little change, as a function of w a tershed size, was noted.
Urban land uses tend to export phosphorus at rates often equivalent to or higher than some cultivated land uses. T he extent of impervious surfaces is a primary reason for higher export rates. T hese impervious surfaces are v e ry efficient conduits for exporting w ater and contaminants off the landscape.

**Ta ble 5.3.	 Interquar**  **t ile Range of Phosphorus Concentrations (**  � **g/L) for M i**  **nimally Impacted Streams in**  **M in**  **n eso**  **ta by Ecoreg**  **ion , 1970-1992** 

**Ecore gion**  **Percen t**  **ile 25%**  **50% 75%**  Northern lakes and fo rests 20 40 50

Northern Minnesota we tlands 40 60 90

North central hardwood fo rest 60 90 150

Northern g laciated plains 90 160 250

Red River valle y 110 190 300 West ern c orn belt plains 160 240 330

S ource: Mc Col lo r and Hei ska ry, 1993.



### Nutrient Criteria—Lakes and Reserv o irs 5-13T hus, high phosphorus exports from urban land uses migh t be m o re a function of efficiency of delivery rather than land use per se. Reckhow and Simpson (1980) sug ge st a range of 0.5 to 1.25 k g phosphorus/ha/yr for urban land uses. Walker (1985a) estimated urban phosphorus export of 0.5 k g phosphorus/ha/yr for low-density residential use in Minnesota and 1.2 kg phosphorus/ha/yr for mi xed urban and comme rcial use. T he higher range of phosphorus exports migh t be appropriate where storm sewers drain impervious areas without the benefit of intervening sedimentation basins. Bannerman et al. (1993) in a comprehensive study of storm water in Madison, Wisconsin, found T P concentrations, as m onitored at specific sites in the city, to range from a low of 150 μ g/L from roofs to 2,670 μ g/L from lawns. H owever, in terms of critical-source areas and contaminant-load percentages, streets and driveways, where runoff v o lumes were high, accounted for 78 percent of the overall T P loading from the residential land use area, while lawns, where runoff v o lumes were low, accounted for 14 percent in their study

.


### � Analysis The availability of land use data m ay vary between locales. H owever, with the increasing use of Geographic I n formation System (GIS) databases, this aspect of lake and watershed assessment should become easier in the future. I n general, the first step is to delineate the total w a tershed of the lake. It may be worthwhile to also delineate the imme diate watershed (that portion which drains directly to the lake without g o ing through another lake or m a jor wetland) because land use changes in that portion of the w a tershed m ay ultimately have the g r eatest impact on the lake of concern. O nce the w a tershed is delineated, land use information migh t be acquired from GI S data, aerial photos, and/or other records that migh t be available through soil and water conservation districts, local planning and zoning offices, or other sources. Land use categories should be m apped, and summaries in terms of the total area (e.g., hectares) and percent composition of the watershed by land use type should be noted. T his information combined with current monitoring data should provide a basis to begin evaluating the effect of future changes in land use on the w a ter quality of a lake. I t also m ay be instructive to have land use data from a representative subset of lake watersheds in a g ive n State or ecoregion for comparison purposes. For example, the land use composition of reference lake watersheds has been evaluated by ecoregion for Minnesota (Table 5.4). T his provides a basis for comparing the land use assemblage for the lake under study compared with the typical composition for lakes in the same region. T his comparison m ay, in part, explain deviations in w a ter quality from regional norms or typical v a lues. **Ta ble 5.4.**  **Ty pical W**  **ate rshed Land Use Composition f**  **o r M**  **i nnesot**  **a Ecoregion Reference Lakes**  **(b ased**  **on in**  **te rq**  **ua rtile ran**  **ge)**
**Lan d**  **Use ( %)**  **North ern Lakes**  **For ests**  **North Central Har**  **dw ood Forests**  **W estern Co**  **rn Belt Plains**  **Nort he**  **rn Gl**  **aciated Plain s**  Forest 54-81 6-25 0-15 0- 1 W ater and m arsh 14-31 14-30 3-26 8-26 Cultivated <1 22-50 42-75 60-82 Pastur ed 0-6 11-25 0- 7 5-15 Cultivated and pastured 0- 7 36-68 48-76 68-90
Developed 0- 7 2-9 0-16 0- 2

5-14 

### Nutrient Criteria—Lakes and Reserv o irs

# CHAPTER 6 **Identifying and Characterizing**  **Reference Conditions**

A. Significance of R eference C o nditions A. Si g nificance of Reference Conditions B.	 Approaches to Establishin g Referenc e Conditions C. Initial Data Retrieval and Proces sin g to Support Nutrient Criteria Development

Establishing lake reference conditions for each of the physical lake classes within each ecoregion or subdivision of that region is a critical part of the nutrient criteria development process. R eference conditions for each of these classes are the quantitative descriptions of lake conditions used as a standard for comparison purposes. I deally, reference conditions associated with nutrient-related v ariables such as phosphorus, nitrogen, and chlorophyll a are concentrations representative of lake conditions in the absence of anthropogenic disturbances and pollution. H owever, because it can be argued that m o st, if not all, lakes have been impacted by human activity to some degree, reference conditions realistically represent the least impacted conditions or what is considered to be the m o st attainable conditions. While the reference conditions themselves are not specifically established as criteria, they help to set the upper bounds of w h at can be considered the m o st natural and attainable lake conditions for a specific region. Knowing this “reference best case situation” together with the other four elements of a nutrient criterion allows resource m a nagers to set the criteria at appropriate levels; of course, other relevant factors such as attainment-of-use designation, regional perceptions of w a ter quality, and physical/geological influences need to be considered as well. B. A pproaches to Establishing R ef erence C o nditions
I n accordance with the five elements of nutrient criteria development, there are three g e neral approaches for establishing reference conditions:

• Di rect observation (data collection) of sites and estimation or inference of reference conditions

. Th is m ay take two forms: (1) observation of sites that meet reference site requirements and (2) observation (data) of an entire population of lakes. I t is assumed that some percentile of either distribution represents a reference condition.

• Paleolimnological reconstruction of past conditions . T his means inference of reference conditions from observations of nonreference sites. I t requires statistical models based on larg e data sets and a sample of dated sediment cores for the lake classes in question.

• Model-based prediction or extrapolation of reference conditions from related data sets or related knowledge . T he predictions m ay come from statistical models (usually regression m odels), m a ss balance models, or combinations of the two.
Th ese three approaches are not exclusive, and they require professional judg me nt and expertise to implement. Regional experts are often the m o st qualified to m ake determinations about which lakes in a region m o st likely represent “ideal” or m o st desirable conditions. Local expert knowledge of regional


### Nutrient Criteria—Lakes and Reservo ir s 6- 1characteristics, human-induced changes over time to regional lake and watershed conditions, patterns of development associated with a lake and its watershed, and current conditions as they relate to perceived impaired or unimpaired status can m a ny times be the m o st efficient and cost-effective way of identifying candidate reference lakes. T his me thod should be used only when it is clear that adequate professional expertise exists for a region. Experts who m ay be qualified to participate in the selection process could come from an array of disciplines such as limnolog y, biolog y, resource management, engineering, and other related fields. 1. Direct Observation of Reference Lakesc



###  R eference Lake Approach Reference lakes must be representative of a region and their conditions (including level of enrichment that m ay inherently range from oligotrophic to eutrophic or hypereutrophic) should represent the best range of mi nimally impacted conditions that can be expected of similar lakes within the region. Althoug h lakes that are undisturbed by human activities are ideal as reference sites, land use practices and atmospheric pollution have so altered the landscape and quality of w a ter resources nationally that truly undisturbed lakes are rarely available. A set of requirements m ay be established to help define a mi nimally impacted lake and, therefore, make the selection of reference sites a rule-based procedure. For example, reference lakes could be chosen only from park or preserve areas (i.e., areas that have not been subjected to any type of significant development within a reasonable period of time). I f relatively unimpacted conditions do not occur in the region, the selection process m ay be modified to be m o re realistic and to reflect the least altered lakes. Such selection can pertain to the condition of the watershed, as well as the lake itself. T he following are examples of conditions that can be defined to select reference lakes:

• Land use . N atural v ege tation has a positive effect on w a ter quality and hydrological response of streams. Reference lakes could be chosen from watersheds that have an established mi nimum percentage of existing natural v ege tation cover, such as 50 percent or m o re. Alternatively , reference criteria could be defined as less than a certain percentage of urban or residential land use in the watershed.

• Riparian zones . Z ones of natural v ege tation alongside the lakeshore and streams stabiliz e shorelines from erosion and contribute to the aquatic food source through allochthonous input. Th ey also reduce nonpoint pollution by absorbing and neutralizing nutrients and contaminants. Reference lakes could be chosen from watersheds that contain at least a set mi nimum area of existing natural riparian zone, regardless of land use outside the riparian buffers. For example, reference lakes could be required to have 65 percent or m o re of the lakeshore and its imme diate tributaries in natural bankside v ege tation to a distance of at least 10 m from the shoreline.

• Best management practices

. Urban, industrial, suburban, and agricultural nonpoint source pollution can be reduced with successful best m a nagement practices (BMPs). Watersheds from wh ich reference lakes are chosen could be required to have certain B M Ps in place, provided that the efficacy of the B M Ps has been demonstrated.

6- 2 

### Nutrient Criteria—Lakes and Reserv o irs• Discharges

. Point source discharges from industry and from m unicipal waste water treatment plants (e.g., National Pollutant Discharge Elimination System, storm water) and known areas of nonpoint source discharges (e.g., from agricultural areas) have the potential to negatively affect wa ter quality of streams, rivers, and lakes. R eference lakes could be chosen from w atersheds that have no discharges or that have a defined m a ximum level of discharges into surface w a ters.

• Management

. Management actions, such as controlling w ater level fluctuations for hydropower or flood control, can significantly influence lake conditions. R eference lakes could be limited to those lakes that are in no w ay affected or are affected only in a v e ry limited w ay by such ma nagement activities. Predefined reference conditions for lakes have been used in Minnesota to determine ambient phosphorus criteria (Heiskary, 1989) (see case study at the end of this chapter). Maine uses a similar approach in regulating the w a ter quality of streams (Davies et al., 1993). Characterizing Reference Conditions
Th e objective of reference condition characterization is to describe reference lake conditions in term s of the v ariables that have been chosen to express nutrient conditions. T o properly characterize reference conditions, adequate data associated with the reference lakes must be available. I f existing data are deemed to be insufficient for characterization purposes (see C h apter 4), then a sufficient number of reference lakes must be sampled to obtain the data necessary for characterization of reference conditions. There is no definitive rule for establishing a minimum number of reference sites appropriate to the development of a reference condition, and the g r eater number the better. T he amount of available data w ill dictate w h ere each lake is a sampling unit—perhaps a g e neral rule of thumb for reference sample siz e could be at least 10 percent of the lake class of concern and a mi nimum of 10 to 30 lakes per region (see Chapter 4 for a discussion of sampling approaches and me thodologies). Before sampling begins, candidate v ariables should be evaluated and target v ariables selected (see Chapter 5). All sampling and analytical activities should be conducted according to standard protocols to ensure v a lidity

. During sampling v isits, the candidate reference lakes should be examined to confirm whether they actually meet the reference site requirements. T his m ay include looking for discharges into the lake or its tributaries and a quick survey of the lake watershed to determine if new modifications m ay have changed the lake. I f a lake appears to have been significantly impacted, measurements should be made for in-lake and lake discharge nutrient concentrations and biological response v ariables such as chlorophyll concentration and fish, macroinvertebrate, macrophyte, and planktonic comm unity v ariables. Lakes that do not meet the physical reference requirements should be excluded from the reference data set. However, a high nutrient concentration present in an otherwise mi nimally developed lake watershed is not ju stification alone for exclusion. T his m ay be part of the natural back gr ound level to be identified by the reference condition process.
Significantly A l tered L a kes

If

a ll lake s in a re gi on are signif ican tlya ltered, it migh t not be possible to sele ct appropriate re ference sites. In such a case, an alternative would be to use lak e s f r om neighboring regions as ref e rence sites if those lak e s are deemed acceptab l e, b y prof e ssional judg me nt, with respe ctto impa ct a nd ov era ll comparability to the lake s of the affected re gi on. If lake s from ne arby re g ions ca nnot re as onably be c onsidered re fe renc e s ite s , then re fe renc e lakes mustbe identified and re fe renc e c onditions m ust be predic ted or inf e rred f r om other inform ation, including m odels a nd historic al data. In de sign ing s uch a n approa ch , the c ons ensus of a

pa nel of re gi onal e x perts helps e nsure an obje c tiv e a nd rational de sign. 

### Nutrient Criteria—Lakes and Reserv o irs 6- 3Once the desired lake reference data have been obtained, statistical approaches can be used to determine if individual lakes fit the preliminary reference lake classification. T he preliminary classification is refined through inspection of plotted data (e.g., using box and whisker plots, scatter plots, or other means of g r aphical analysis), professional judg me nt, and statistical tests of final classification hypotheses. Next, the v a lues and distribution of reference me trics are compared among ecoregion or lake type. Regions that appear to be similar to each other can be combined for the final classification. For tw o regions to be so combined, m o st of the me tric distributions m u st be similar. Chapter 7 further describes the derivation of criteria from these reference lake data sets. States that share an ecoregion are encouraged to also share data to determine reference conditions.



###  Lake P o pulati o n Distributi o n Approach
If

a fixed definition of reference condition is deemed to be overly restrictive or an impractical ideal, then an empirical w o rking definition is an alternative. For example, because natural conditions for reservoirs cannot be defined, the best existing conditions are used instead. T his approach is also useful in ecoregions with little contiguous natural v ege tation remaining, such as in the agricultural Midwest. T he approach does not involv e the identification of reference lakes, but sets reference conditions by using an entire population of lakes from within a region. I t is especially relevant for m a n- ma de impoundments and reservoirs, where no least-impaired systems exist, as well as for lakes subject to strong and relatively uniform human impacts, such as in large urbanized areas or in heavily agricultural regions. A representative sample of lakes is taken from the entire regional lake population. Lakes that are known to be severely impaired m ay be excluded from the sample, if desired. T he population distribution of each selected v ariable is determined, and the best quartile or lower 25th percentile of the distribution of each v ariable is taken as its reference v a lue. U sing the same logic described for Secchi depth, the opposite end of the distribution is used, and the quartile at the high-quality end of this distribution is selected so this reference v a lue is a “reasonable” upper limit (excluding outliers of the population distribution). See Chapter 7 for further discussion. A central assumption of the frequency distribution approach is that at least some sites in the population of lakes are high-quality lakes, w h ich will be reflected in the v a lues of the individual v ariables. B ecause they have no independent definition, reference conditions defined in this w ay mu st be taken as preliminary and subject to future reinterpretation, especially as lake m a nagement efforts produce improved conditions. Periodic examination of the reference v a lues for trends can detect deterioration or improvement. T his is necessary when reference criteria cannot be defined a priori or when all lakes under consideration are equally impaired. T he objective of the m e thod is to develop a measurement standard for assessing lakes. I ts validity is supported by external confirmation of the response of v ariables to stressors, usually from published or other independent studies. While direct observation of reference lakes is the preferred approach, paleolimnological reconstruction and model extrapolation are also possible approaches for reference condition determination. 2. Paleolimnological Reconstruction Many g roups of organisms in lakes leave remains in the bottom sediments. Some of the remains are resistant to decay and become a permanent biological record of life in the lake. By comparing past biota with present-day biota of m a ny lakes, past environmental conditions can be inferred. Several g r oups of organisms have been used for paleolimnolog y: diatoms and chrysophytes, sponges, bryozoans, cladocerans, and chironomid larvae. Of these, diatom frustules and chrysophyte scales have been used mo st often, and m o st successfully, to infer past chemical conditions (e.g., Charles and Smol, 1994). T he
6- 4 

### Nutrient Criteria—Lakes and Reserv o irspreserved diatoms provide an integrated record of the diatom assemblage in the lake. A sample of the top 1 to 2 cm of lake sediment contains a representative sample of diatoms from the m o st recent 1 to 3 years. If

the lake sediments remain undisturbed, then diatoms and chrysophytes preserved in lake sediments are integrators of lake history (Charles et al., 1994; Dixit et al., 1992).
In ference of past nutrient conditions from biological remains is based on strong relationships of biota w ith w a ter quality

. Many algal species are indicators of particular nutrient conditions, and the assemblag e found can therefore be used to infer nutrient conditions. Environmental v ariables such as alkalinity , aluminum, dissolved organic carbon, salinity, nickel, conductivity, calcium, T N , T P , Secchi transparency , and trophic state also have been inferred using diatom -b ased predictive models (Charles et al., 1994; Dixit et al., 1992; Fritz, 1990). Sediment cores can be calibrated with other information (e.g., v arves, known contamination events, radioisotopes, pollen) to obtain time series with resolution of up to 1 to 10 years. Th erefore, the diatom and chrysophyte fossil record can also aid in establishing reference conditions by enhancing the historical record of previous data collections and events. Paleolimnological analysis, part of the Environmental Monitoring and Assessment Program protocol (U.S. EPA, 1994b), requires development of a data set that associates current environmental conditions with current surficial diatom assemblages. Present-day associations are used to infer past conditions based on fossil diatom assemblages in deeper sediment layers. Q uantitative prediction is usually done in two steps: (1) development of predictive models (calibration or transfer functions) followed by (2) use of the models to infer environmental v ariables from fossil assemblages (Charles and Smol, 1994).



###  Inference of P ast C o nditions
In ference of past environmental conditions from fossil assemblages requires a sizable calibration data set that includes both assemblages and environmental (chemical) measurements. T he calibration data set typically consists of recent sediment samples (top 1 cm) with complete lake w a ter quality and chemical estimation from at least 50 lakes. T he calibration data set should include lakes that span the ranges of all important environmental v ariables that are being investigated. For example, development of predictiv e m odels for acidification requires a calibration data set that includes alkaline, neutral, and acidic lakes; development of predictive models for nutrient concentrations requires a calibration data set that includes lakes with high and low concentrations of nitrogen, phosphorus, and silica and combinations of the nutrients. T he sedimented diatom assemblage is identified and enumerated for each lake in the calibration sample.
Th e first step is to determine whether species-environment relationships are strong enough to permit development of predictive models for inference of environmental conditions. Currently, this is done using canonical correspondence analysis (CCA) (Dixit et al., 1992; Jong ma n et al., 1987; ter Braak, 1986). CCA is an ordination technique that orders sites on environmental g r adients. Unlike linear models such as canonical correlation, there is no assumption that species abundance is a linear response to environmental gr adients. I nstead, species are assumed to have a unimodal response to g r adients, such that abundance of a species is reduced above and below the optimum v alue of an environmental v ariable (ter Braak, 1986). Th e assumption of modal responses, w h ere each species has optimum v alues of nutrients, temperature, light, pH, etc., is m o re realistic for algae than are linear responses (e.g., Tilman, 1982). T he CCA identifies environmental v ariables that have strong associations with species composition and therefore are suitable for predictive model development. Models to predict v a lues of environmental v ariables (e.g., nutrients) are developed with weighted averaging regression (Charles and Smol, 1994). T he computer program WACALIB (Line et al., 1994) is 

### Nutrient Criteria—Lakes and Reserv o irs 6- 5an efficient way to perform these calculations. T he technique also uses the assumption of unimodal optima of environmental v ariables, as does CCA . T he optimum condition for each taxon is the average of m ean v a lues for the environmental v ariable at sites in which the taxon is found, weighted by the abundance of the taxon (Charles and Smol, 1994). T he inferred v a lue of the environmental v ariable is in turn the sum of optima (for that v ariable) for all taxa at a site, w e ighted by the relative abundance of each taxon. T echniques have also been developed to quantify error and uncertainty of the predictions (Birks et al., 1990). Further documentation of these me thods is in Charles and Smol (1994), Charles et al. (1994), Birks et al. (1990), and ter Braak and J uggi ns (1993).


###  Existing Diatom Databases Paleolimnological databases exist for several regions of the country . T he largest of these is the Paleoecological I n ve stigation of Recent Lake A c idification, w h ich is for the N o rtheast, but other databases exist for the Upper Midwest and Florida. Paleolimnolog y to establish reference conditions for impoundments and reservoirs is not recomme nded because impoundments undergo succession of several y ears or m o re following inundation. A reference as an attainable condition thus would be impossible to define for reservoirs from paleolimnological data. 3. Model Prediction and Extrapolation
If

few or no limnological data are available for a g ive n lake or region, reference conditions can be predicted by inference or extrapolation of v arious models. Although extrapolation of models beyond their original calibration data is risk y , it m ay be the only option to estimate reference conditions if no reference data exist or are likely to exist. T here are two approaches: (1) using the m o rphoedaphic index me thod (MEI) and (2) extrapolating natural back gr ound nutrient loading that would occur under undisturbed conditions followed by estimation of nutrient concentrations and trophic state with a m a ss balance model. Th ese methods are discussed in m o re detail in Chapter 8. The MEI is the ratio of total dissolved solids in lake w a ter to the mean depth of the lake. Several early studies sug ge sted that the MEI was correlated with fish and phytoplankton production of lakes (e.g., Rawson, 1951; Ryder, 1961; Oglesby, 1977). T he MEI approach was extended by V ighi and Chiaudani (1985) to predict phosphorus concentrations resulting from natural back gr ound loading in undisturbed watersheds—in short, to predict reference phosphorus concentrations. T he MEI approach is simple and appears to be highly successful for a limited set of cool-temperate lakes. I t has been largely ignored by No rth A merican limnologists, possibly because of its simplicity, and as a result, it has not been calibrated and tested for a wider v ariety of lakes. T he approach is promising, but it needs to be recalibrated and tested with regional reference lake data sets. Mass balance models are a means of estimating concentrations of substances (primarily nutrients) from knowledge of the loading into a lake and the hydrolog y of a lake (see Chapter 2, Section C). A mass balance model by itself will not establish reference conditions, but it will predict nutrient concentrations give n certain loading v alues. T herefore, use of a m a ss balance model to derive reference conditions requires an estimate of natural back gr ound nutrient loading to a lake.
If

a lake or lakes of a region are primarily stream -f ed, an estimate of back gr ound nutrient loading m ay be m a de from stream w ater quality data with some m e thod for selecting (or assuming ) a reference distribution or reference v a lue of stream nutrient concentrations.

6- 6 

### Nutrient Criteria—Lakes and Reserv o irsFulmer and Cooke (1990) used a frequency distribution approach combined with loading and m a ss balance models to estimate the reference conditions of a State 

### � s water bodies. T hey estimated the phosphorus concentration in 19 Ohio reservoirs based on the characteristics in the ecoregions in which the reservoirs w e re located. For the incoming phosphorus concentration, they used the 25th percentile of stream phosphorus concentration in four of Ohio 

### � s ecoregions (the best quartile). They termed the resulting phosphorus estimate the “attainable phosphorus concentration,” sug ge sting that this w a s a conservative estimate of the stream phosphorus concentration attainable through waste water treatment, improvements in agricultural practices, and treatment of urban runoff in the watershed.
Th e authors then compared this estimated phosphorus v a lue to that actually found in the reservoir after first transforming the v a lues to the trophic state index v a lues of Carlson (1977). T he difference between the trophic state indices was termed “the restoration potential” of the water body . T his would target those lakes that deviate the m o st from the attainable trophic state for that body . T his approach is important because it combines the use of the ecoregion to estimate reference conditions for the reservoir with the emphasis of differing restoration potentials based on the specific characteristics of the individual reservoir. T his simple but effective approach applies only to stream -f ed lakes (principally reservoirs). Ground-water-fed and head water lakes would require one of the other me thods for estimating loading that does not rely on stream concentrations. Many states have ongoing biological criteria programs and have identified least stressed streams as reference sites. T hese biological reference sites could likewise serve as reference sites for stream nutrient criteria and back gr ound nutrient concentrations and loading . T his me thod would be appropriate only for impoundments and flowage lakes, which are stream -f ed, and not for lakes with substantial g r ound water input. C. Initial Data Retrieval and P r ocessing to Support Ecoregional Nutrient Criteria Development
Nu trient data will be collected for site points (years 1990 to present) from ST ORET, the U

. S. Geological Survey 

### � s N A WQ A , and other acceptable databases and then will be g r ouped by nutrient ecoregion (O me rnik 

### � s Level III aggregations). T he headquarters nutrient team and Regional Technical A ssistance G r oups (R TAGs ) will assess the data and will determine regional reference condition v a lues for T P , T N , chlorophyll a , and Secchi depth. A regional reference condition can be selected using either of two approaches. I n both instances, the intention is to select an optimal reference condition v a lue from the distribution of an available set of lake data for a g ive n physical class of lakes or reservoirs.
On e approach is to select a percentile from the distribution of measured v ariables of known reference lakes (e.g., highest quality or least impacted lakes of that size class of all lakes in the region). The variables of initial concern are T P , T N , chlorophyll a , and Secchi depth. B ecause these reference lakes are already acknowledged to be in an approximately ideal state, it is reasonable to select an upper percentile (i.e., a representation of the lesser nutrient quality of the distribution of the reference lakes) as the reference condition. EPA g enerally recomme nds the upper 25th percentile (Figure 6.1(a)).
Th e other approach is to select a percentile from all lakes in the class or from a random sample distribution of all lakes in the class. I n this case, it should be a lower percentile (i.e., a representation of the better end of the range of all lakes) because the sample is expected to contain at least some degraded lakes if it is an entire population or a truly random selection. T his option is m o st useful in regions where the number of legitimate natural reference w a ter bodies is usually v ery small such as highly developed 

### Nutrient Criteria—Lakes and Reserv o irs 6- 7Figure 6.1. Tw o approaches for establishing a reference condition value. Note: P ercentiles are based on order s t at istics , s tatistics deri ve d f r om orderi ng data f r om l owt o h igh or h igh to low

. In the case of TP, T N, an d chloroph yll a , h ighe r co n centratio ns of the v ariable result in lo w er water q u ality

. Co n seq u ently, the scale p r esented ab ov e is o rde red from lo wto high. A s imilar analy sis of Secchi depth, however, w oul d require orderin g the data f r om high to lo w b ecause h ighe r Secchi d i sk readin gs are associated w ithh ig he r w a ter q u ality

. land use areas like the agricultural lands of the Midwest and the urbanized east or west coasts. EPA’s recommendation in this case is usually the lower 25th percentile, depending on the number of natural reference lakes available (Figure 6.1(b)). I f almost all reference lakes are impacted to some extent, then the lower 5th percentile migh t be used in an effort to approximate previous natural conditions.
Itshould be noted that the upper 25th percentile of a reference lake distribution and the lower 25th percentile from a representative sample distribution are g e neral recomme ndations. The actual distribution of the observations and knowledge of the inherent regional w a ter quality are also determinants of the threshold point chosen.
I n Figure 6.2, T P is the v ariable of concern and illustrates the presumption that, all else being equal, these two alternative me thods should approach a comm on reference condition along a continuum of data points. I n this figure, the upper 25th percentile of the collection of reference lakes produces a T P reference condition of 30 μ g /L. T he lower 25th percentile of the random sample of lakes produces a v a lue of 35 μ g /L. T he shaded portions of both distributions in Figure 6.2 indicate those lakes in each sample distribution that presumably w ould not meet reference expectations. I t should be noted that (1) v ariability about these selected points is a factor in any such estimation, (2) this is a reference condition v a lue subject to further evaluation before a nutrient criterion is developed, and (3) g ive n that overenrichment is a recognized w a ter quality problem, it m u st be expected that some fraction of the present measured w a ter bodies would be so identified.
B ecause there is little distinction in this case, the A g ency m ay choose to select either 30 μ g/L, 35 μg/L, or the intermediate 33 μ g /L as the T P reference condition v a lue. Each State or T r ibe should similarly calculate its reference condition using both approaches to first determine which m e thod is m o st protective. T hen they should use that m o st protective approach for their subsequent reference condition calculations.

6- 8 

### Nutrient Criteria—Lakes and Reserv o irsFi gure 6.2. Two approaches f o r establishing a reference condition value using total phosphorus as the example.

I n most instances, EPA w ill calculate regional nutrient criteria reference conditions by first subdividing the data set into size classes of lakes. T hese subdivided data then will be assessed to determine if further subdivision of the regional boundaries is necessary . I f data tend to cluster within a nutrient ecoregion, it m ay indicate the need for further refinement of those regional boundaries into subregions.
On ce the regional boundaries are determined, a frequency distribution selection for each lake class per region or subregion is established at the lower 25th percentile. T his is because the available data cannot usually be assured of being all reference condition quality

. The data are obtained from a wide v ariety of sources with an equally w ide array of documentation and quality assurance procedures. The A g ency policy is to choose consistently lower end percentiles to assure the appropriate protection of the uses. This conservative effort, together with consulting the R TAGs in determining these regional criteria, is designed to help protect against setting the regional criteria either too high or too low

. A nother element that m u st be considered in setting the reference conditions is w h ere and w h en the data were g a thered. I f the sample size is large enough, the time of year the individual samples were taken may not m a tter; either all seasons will be represented or m o st of the data will cluster about an appropriate index season. Similarly, surface g r ab or depth-selected samples or composite samples m ay not m a tter if the diverse data set is large enough. However, when these factors are significant, the m o st indicative time of the year should be used as the index period. A lternatively, criteria should be developed for each season of the year. Likewise, the depth and location of sampling in the lakes in question that best reveals the presence and amount of nutrients in that system should be used. T hese are usually within the upper me ter of surface w a ter from a central portion of the w a ter body or open w a ter area near the m a in discharg e location. T his g u ideline applies to measurement of both causal and response v ariables. Once again, it is preferable to err on the side of the environment. Once the reference condition is determined, the other four elements of criteria development should be incorporated in the process. First, the reference condition should be compared with the historical information for that area. A re things g e tting g enerally better or w o rse than before? Model predictions not only fill the v o id w h en there is a lack of sufficient reference condition data, but they m ay help answer this 

### Nutrient Criteria—Lakes and Reserv o irs 6- 9trend question. A ll of this accumulated diverse information requires careful and objective review by the RTAG specialists as part of the nutrient criteria development process.

Case Study

Dataf rom Minne so ta provide a n e xam ple of how this te c hnique might be applied to help determine appropriate re ference c onditions f or an e co re gi on. Though Minne so ta 's P c riteria , w hic h were even tually de ve loped, w e re not e s tablished using the specific te c hnique de sc ribed in this te x t, it is instructiv e to s ee how the pe rcen tile s compare betw een a re ference population a nd a random or pre ex isting da tabase (a s was the case in Minne so ta). The table below displa ys phosphorus c onc en tration a t the 75th perc en tile f or a distribution of re ference lake s and 25th perc en tile f or the distribution of total assessed lake s f or thre e ecoregi ons. In the NL F, the 75th perc en tile of the re ference lakes was s lightly higher than the 25th perc en tile f or the random population (note that the random population would include re fer ence lakes as we ll in this instanc e) . T he P cr iteria fo r that re gi on w as set just abov e the 75th perc en tile f or the re ference lake s. In the NCHF e co re gi on, the 75th perc en tile of the re ference lake s w as agai n higher than the 25th perc en tile f or the random population. T he P cr iteriaf or this re g ion f e ll betw een the se tw o va lue s. In the highly ag ricultural WCBP the 75th perc en tile of the re ference lakes was we ll abov e the random data se t; how ever , the random da ta se t is rather s ma ll and there is s ubstantial ov er lap betw een the tw o data se ts (i.e., 12 of 45 lakes in the random data set w ere reference lakes. In th e case th e P criteria was set b elo w both values but w as relatively clo se to the 25th pe rcen tile fo r the random da ta se t. T h is a naly sis suggests that this te c hnique may mer it attention in thos e re gi ons w here there are both re fe renc e a nd larg er random or pre ex isting data se ts f or the type of a naly sis. Finding Reference Con di tion V al u es for Ph osp ho ru s (μ g/ L) Concentration B ased on Reference an d Total Assessed Distri but io ns by Ec or egion in Mi nne sota Ecoreg ion 75t h P ercenti le of Reference Lakes 25t h P ercenti le of Total Assessed Lakes P Criteri a for Swi mma ble Use Northe rn lakes a nd f orests North c en tr al har dwood f orest We s te rn c orn belt plains 27 ( n= 30) 50 ( n= 38) 150 ( n= 12) 16 ( n= 543) 35 ( n= 368) 97 ( n= 45) 30 40 90

6-10 

### Nutrient Criteria—Lakes and Reserv o irs

# CHAPTER 7 **Nutrient Criteria Development** 

A. Elements of Nutrient Criteria A. Introduction: Elements of Nutrient Criteria B.	 Development of Ec ore g ional Nutrient Criteria C. Development of State Nutrient Criteria D.U sin g Cr i ter i a to As sess Wa ter Resour ce Attainment

As presented in Chapter 1, five principal elements should be used to develop nutrient criteria. T hese five elements are summarized below

. 1. Investigation of the Historical Record
In ve stigation of the historical record entails collecting and evaluating both anecdotal information and data sets relative to the lake and watershed of concern. T his information m ay be gathered from long

standing residents of the area, local fishermen, and county, State, and Federal natural resource ma nagement and land use planning agencies. A cademic institutions also are an excellent source of information; often, faculty w ill have extensive w a ter quality or fishery information collected over several y ears as research or teaching projects. O ccasionally, w a ter supply authorities will have collected long-term historical data records such as phytoplankton composition or Secchi depth. I n other instances, high-quality data sets m ay exist that are several decades old, such as the information collected by B irg e and Juday on Wisconsin lakes. But m o st historical data are likely to consist of isolated observations on a small subset of lakes. More recently , m onitoring data m ay be available from v olunteer monitoring organizations. B ecause these reports are not always comm on to routine literature review s of published m a terial, direct contact with the organizations m ay be necessary to obtain this information. T he same applies to the m a ny “gray literature” reports prepared by county, State, and Federal agencies.
Hi storical information, both quantitative and anecdotal, can be v a luable, but it is often the m o st difficult to interpret. N onetheless, it provides the investigator with a perspective on the relative quality of the resource over time. T he principal difficulty is compatibility of m e thods used to collect historical data with current data collection me thods and quality control. A lthough m e thodologies for w a ter quality and basic limnolog y have not changed greatly in the past 25 years, all data m u st be carefully evaluated to determine if m e thodological biases would be introduced by combining historical and recent data to determine trends and historical reference conditions. Ty pically, the m o st compatible data are those that require the least sophisticated equipment to collect: Secchi transparency, total suspended solids, and algal species composition (phytoplankton, periphyton). Nutrient concentrations and chlorophyll concentration are sensitive to m e thodological changes, and biases are m agn ified if the measured concentrations are near or below the me thod detection limit. EPA data sets on the STORET system are also available. I n addition, the National Nutrient Criteria Program has information selected from ST ORET and aug mented with additional State and academic information. I n many instances, these data are of recent origin (e.g., since 1990), and a true historical perspective is not possible without the additional, older information. A n illustration of the significance


### Nutrient Criteria—Lakes and Reservo ir s 7- 1of this historical information is the lake database available in Wisconsin. T he famous Birge and Juday studies extend back to the turn of the century, and in m a ny cases, these monitoring data have been m aintained by State or universities through the present. Such back gr ound information is invaluable in understanding the inherent nature of a particular system, and it lends the proper and accurate perspectiv e necessary to distinguish natural from cultural enrichment. A good historical database is important for setting proper nutrient criteria and standards because it provides knowledge of w h at has happened before, what the normal natural trends are, what disruption humans have or have not caused, and what remediation efforts are possible.
2. E stablishm e nt of the R e ference C o ndition Present optimal lake conditions for an area m u st be reliably established (see Chapter 1). T his is the other half of the lake assessment necessary for a responsible evaluation. T he historical record described above tells the historical conditions for the lake or lakes of concern. T he reference condition tells the best present status of those lakes. I n some instances, conditions were m u ch better in the past because of less development; the present reference condition reveals how m u ch the system has declined. On the other hand, depending on how far back the historical record extends, it m ay be that the present reference condition is better. For example, compare the degradation of the cut-out-and-get-out era of log gi ng in the early part of this century with the present-day forest reclamation and land m a nagement efforts. I n this instance, we can be apprised of improving or declining trends in nutrient status over past performance. 3. Use of Models Models that have been calibrated and v e rified can be used to extrapolate data to a projected nutrient condition w h ere existing data are either insufficient or unavailable. O ften this entails using data in a similar lake in the same region or m aki ng a reasoned projection, accompanied by a set of clearly stated assumptions, from data in one point in time to estimate conditions in the future. I n some instances, surrogate information such as Secchi depth and chlorophyll a concentration can be used to estimate phosphorus concentration. Chapters 2 and 9 contain m o re information in this regard. 4. Expert Assessment of Information Elements 1 through 3 are essentially data-gathering and data analysis processes. Elements 4 and 5 are interpretive processes because the information g a thered should be assessed for v e racity and application. T o do so, each EPA Region has a Regional Technical Assistance G r oup (RT AG) of specialists to help the A g ency and States establish the nutrient criteria for adoption into State w a ter quality standards. RTAG memb ers should be experts in limnolog y , water resource m a nagement, land resource m a nagement, and fisheries m a nagement as w e ll as other appropriate specialties necessary to make an objective and exhaustive evaluation of the information. RTAGs are described in m o re detail in Chapter 1. 5. Attention to Downstream Effects Before any criterion for any g iven class of lakes can be adopted, the potential impact on downstream waters m u st be considered. I f the criteria do not provide for the attainment and maintenance of proximal downstream w ater quality, the criteria in question should be adjusted accordingly

.

7- 2 

### Nutrient Criteria—Lakes and Reserv o irsB. Development of Ec oregional Nutrient C r iteria 1. Regional and Lake/Reservoir Type Classification
In itial efforts should deal with g e ographic classification. EPA has developed a national ecoregion-based classification system to initiate the process. T he country has been divided into nutrient ecoregions using the initial EPA nutrient ecoregion map (see Figure 1.3). States and regions are encouraged to develop subregions within the 14 m a in nutrient ecoregions, as supported by new data evaluation. T he subregions should be based on natural land forms and environmental characteristics such as soil type, parent m a terial, slope, natural v ege tative cover, climate, and hydrolog y , as opposed to cultural land uses.
Th e next step is to carry out physical classification procedures such as subdividing all lakes in the data set into similar classes, m o st comm only, lakes of similar size (e.g., 10 to 50 acres, 51 to 150 acres, 151 to 300 acres, and larger). Volume and retention time also should be used and are better related to likely biological responses in m o st nutrient loading m odels (see Chapters 6 and 9). Once the system of physical classification has been established, data for all lakes or reservoirs in that class should be compiled and subsorted. EPA also is developing a nutrient database using STORET and other data sources that will be available as an initial data collection effort. This database will include information for T N , T P , chlorophyll a , and turbidity as the four m a in parameters, as well as other potentially relevant measures. EPA w ill use this database to support development of the ecoregional nutrient criteria. T he database should be expanded by additional State, academic, and Federal information acquired from colleagues in the area. A ll data m u st be sorted for quality and applicability

. I ssues that should be addressed before incorporating a data set into the criteria development process (see also C h apter 4) include how carefully the samples w e re collected, from w hat season and locality the samples w e re taken (especially w hether samples w e re taken from degraded or reference quality w aters), how well analy z ed the samples are, how well the sample locations were pinpointed, and how often the samples w e re replicated.
Th is physical classification process m ay reveal unique lakes or sets of lakes that defy the routine classification approach. Examples m ay include remarkably oligotrophic lakes perceived as exceptional natural resources, dystrophic or stained acid bog lakes that m ay have a separate biological response to enrichment, and lakes or reservoirs that are already intentionally overenriched. Each State or T r ibe and EPA R egion will have to address such conditions as m o st appropriate to that region, w h ile still adhering to the objective of improving the trophic condition of those lakes by reducing cultural eutrophication.
2. Co nversion of Ec oregional Data to a R e ference C o ndition and Preliminary N u trient C riteria
From m etadata in the historical database, candidate reference sites (element 2) can be selected based on the location of the lakes and their relative lack of watershed development. T his effort should divide all lakes (or reservoirs) into potential reference and potential test systems. The least developed system s should be candidate references. T hese sites should be v i sited and sampled to confirm their quality . I t is important to recogniz e that seasonality m ust be accounted for, so the sampling and assessment process w ill take at least a year or two, and potential seasonal v ariability in the data should be assessed. (This is discussed in detail in Chapter 6.)
If

data are scarce, modeling (element 3) m ay be necessary to help establish the reference condition (i.e., that compilation of reference site characteristics that best represents the optimal trophic condition 

### Nutrient Criteria—Lakes and Reserv o irs 7- 3for lakes or reservoirs of that class). Modeling, like paleolimnolog y , can be used in a weight-of-evidence approach to develop nutrient criteria, m u ch like the frequency distribution approaches discussed in Section C (below), but the precision, accuracy, and suitability of the model(s) should be carefully assessed before deciding on this approach.
T he RTAG then should assess the classification system and attendant data (elements 1-3) to establish the reference lakes and derived reference condition (element 4). This will involv e selecting the appropriate cutoff point in the distribution of v a lues for each set of reference lakes for each physical classification. T hese adjusted v a lues becomes the candidate criteria.
Th e basic procedure described below is recomme nded to process available data to establish nutrient reference condition and subsequent nutrient criteria. T his approach m ay be taken on a regional or State scale, and the sharing of data and reference condition information requires that a consistent m e thodolog y be employed. States m ay elect to use approaches distinct from the me thods described in this m a nual, but such alternative approaches m u st be scientifically defensible and approved by EPA. T hey are not meant to be precluded from consideration simply because they are not described in this edition of the m a nual.



### � Da ta C o mpilation Data should be compiled from STORET and other pertinent Government files as well as State, university, and other sources. All information should be reviewed and converted to the comm on database already established by the National Nutrient Criteria Program (specific information m ay be obtained from the EPA Regional Nutrient Coordinator or EPA Program Headquarters in Washington, DC).
Id eally, the data collection and compilation procedures used for classification and criteria development will be the same as those used for assessment purposes. H owever, it is recognized that at least initially the procedures m ay differ.



### � Data Reduct i on Da ta reduction (from the data set that has been screened for impacted sites) should be conducted so that presumably m ost, if not all, data points remaining are candidate reference sites.
•	 I f m u ltiple data are recorded for a g ive n site on the same date and are adjustable to a normal distribution, select the me dian v a lue per station for each of the four primary v ariables of T P , T N, chlorophyll a , and Secchi depth (e.g., replicate samples or m u ltidepth sampling). T his equates mu ltiple data from some stations with single g r ab samples at others.

• Where analytical results are reported as below detection limits and the m e thod of analysis is an EPA-approved or “standard’ me thod, use the reported mi nimum detection limit to calculate the me dian v a lue. I f the m e dian exceeds these mi nimum detection v a lues, no further analysis is necessary . I f any of the mi nimum detection limit v a lues exceed the m e dian, statistical m e thods applicable to censored data should be used.
•	 I f indicated, separate data according to the season w h en the information was collected. In temperate regions, seasonal criteria m ay be needed.
•	 C ompile a single seasonal m e dian v a lue for each g ive n lake or reservoir from all m e dian station va lues for that water body

. 7- 4 

### Nutrient Criteria—Lakes and Reserv o irs

### � Ph ysical Classification Physical classification is based on the me tadata provided in the data set for each lake within a g iven ecoregion or subecoregion. Area and depth can be used to establish a v o lume-based classification scheme. Unique systems should be separated out as distinct categories. Further subdivision m ay be done on the basis of watershed size if necessary . T he process should be one of progressive subdivisions to smaller and smaller classes with less and less within-class v ariability

. These classes then can be tested for statistically significant differences using analysis of v ariance techniques. T his step m ay recombine some of the initial subdivisions so that an optimal set of lake classes results.



### � Ref erence C o ndition D e termination Reference condition determination can be based on a further review of the metadata to determine which lakes within a class have the least developed watersheds (e.g., perhaps 50 percent or m o re of the land area in natural v ege tative cover, usually forested and with a fairly expansive area of the shoreline [perhaps 65 or 70 percent] undeveloped). T hese lakes then can be designated as reference sites and their median values for T P , T N , chlorophyll a , and Secchi depth arrayed respectively in a frequency distribution from higher to lower water quality . T he upper 25th percentile then is selected as the ecoregional reference condition. When an adequate number of acceptable reference lakes is not available, the alternative is to use all of the data or take a random sample of what is available and use the lower 25th percentile as the ecoregional reference condition (see Figure 6.1 and accompanying text).
3. R efine Ec oregion Reference C o ndition Values Newly collected data can be combined with existing information to refine the reference v a lues for both the EPA regional reference conditions and the State or T r ibal references as well. Grants/contracts may be awarded to States and T r ibes v i a the regional coordinator to develop sufficient current databases, especially where information is lacking for particular water body types or g e ographic areas of the nutrient ecoregion. 4. Evaluation by Regional Team s to E s tablish Ecoregional Criteria
Th e RTAG obviously m ust incorporate all elements: history, reference condition, data models if employed, and downstream effects when establishing the ecoregional nutrient criteria. I n doing so there are several key factors which should be noted:



### � Ref erence C o ndition
RTAGs w ill be asked to review the preliminary m aterial described above and determine if the reference condition v a lues are appropriate for the States in that EPA Region. Because RT AGs w ill include State agency m embers, regional or local concerns should be able to be addressed in a timely ma nner. The EPA Na tional N u trient C r iteria Program data compilation and quality assurance procedures will help in the data sorting process. H eadquarters also will award g r ants/contracts as needed to States to help fill in data g aps through the establishment of data collection programs.



### Nutrient Criteria—Lakes and Reserv o irs 7- 5

### � Antidegradation
A critical requirement for the use of reference conditions associated with nutrient criteria is the EPA antidegradation policy, which protects against incremental deterioration of water bodies and reference conditions. An observed downward trend in the conditions of reference sites cannot be used to j u stify relaxing reference expectations, reference conditions, and the associated nutrient criteria. Once established, nutrient criteria should only be refined in a positive direction in response to improved conditions. Without antidegradation safeguards, even the establishment of reference conditions and nutrient criteria could still allow for continual deterioration of w a ter quality

. For example, construction and development in w a tersheds containing lakes considered to be of excellent quality and w h ich have been designated as reference lakes for a region could result in a degradation of nutrient levels and related v ariables and enhance eutrophication. I f a number of the reference lakes in a region have suffered such deterioration, the reference conditions established from the set of reference lakes will have been degraded relative to their earlier state, and the comparative standard will have been lowered.
T o combat this, the States should implement an effective antidegradation policy that promotes continually improving lake conditions. As an example, Maine has an antidegradation policy that requires that lakes remain stable or improve in trophic state (Courtemanch et al., 1989; NALMS, 1992). T he RTAG should assume a comparable sense of antidegradation responsibility

.


### � Es tablishing the Maximum Upper L i mit of Eutrophication
Th e review of reference condition data, an understanding of regional nutrient dynamics, and the description from Chapters 1 and 2 of clearly over-enriched conditions should all contribute to a sense of ju st how m uch v ariation about the reference condition the R TAG should accept in establishing criteria.
Th e light-limited condition of hypereutrophy (T SI 70, T P of 0.1 m g L -1 ) is characterized by dense algal and macrophyte comm unities and should be considered undesirable under all circumstances. I t is recomme nded that no criterion ever be set higher than this v a lue, regardless of designated use, unless it can be demonstrated that the natural reference condition is this high.



### � Designated Use
Th e States are expected to develop nutrient criteria to protect their designated uses. T he EPA ecoregional criteria should be protective of at least m o st of these uses.



### � Endangered Species
I n all instances, the EPA Na tional N u trient C r iteria Program w ill strive to ensure that nutrient criteria are protective of any identified threatened or endangered species in involved waters. RTAGs also should keep this responsibility in mi nd as they evaluate proposed State/Tribal nutrient criteria. T h e R TAG should coordinate with the regional USFWS office to determine if any endangered species are involved. Where threatened or endangered species m ay be affected, the nutrient conditions appropriate to their support should be included in the criteria.

7- 6 

### Nutrient Criteria—Lakes and Reserv o irs

### � Down stream E ff ects The final step in establishing the nutrient criteria is to assess the potential downstream effects (Section 131.10 (b) of the C l ean Water A c t) of setting a criterion for a g ive n class of lakes. Will this level of nitrogen and phosphorus and attendant algae or turbidity levels when present in the water body have detrimental effects on the downstream receiving wa ters? Will it provide for the attainment and ma intenance of w a ter quality standards in these w a ters? D ownstream receiving wa ters are considered to be those imme diately below the lake or reservoir and within a few miles of it. T he Nation’s estuaries and coastal m arine w a ters are ultimately the recipients of all discharges to surface w a ters and should benefit from such efforts, but the intent is to accomplish this indirectly by a sequential and cumulativ e improvement of our surface w a ters. For example, the Atlantic Ocean is eventually the beneficiary of lake enrichment improvements in the Cobbosee Lake Watershed in Maine, but the individual program ma nager need only w orry about the downstream effects on the Kennebec R ive r in setting nutrient criteria. Th e cumulative sequences of similar improvements progressing downstream are expected to help achiev e coastal nutrient abatement.
On ce the R TAG specialists agree and document their decision that no adverse effects will result and standards are m e t downstream, or that the downstream w aters will be enhanced, then the tentative criteria can be adopted. However, if downstream waters are not adequately protected at the level of discharg e associated with the proposed criteria, then that value should be adjusted accordingly

. Loading estimation m odels will be helpful in m aki ng this judg me nt as will enlisting the assistance of m a nagers associated with that downstream water body . I t m ay be possible to coordinate management efforts and criteria to the benefit of both water resources and at a cost saving s in m a nagement and monitoring by addressing conditions on both systems at the same time.
5. E xamples of the D e liberation Associated with Development of a N u trient C riterion
T o help illustrate the role and responsibility of the R TAGs , an abbreviated hypothetical illustration of the reasoning applied to nutrient criteria development follows: U sing the 33 μ g/L TP reference condition as an example, this v a lue can be evaluated against historical records for reference lakes. T he reference condition of 33 μ g /L sug ge sts a g r adual rise upward in ambient T P , from about 20 μg /L 100 years ago, with a projected further upward trend indicated by use of demographic, land use, and hydrological models. The R TAG therefore concludes that setting a criterion any higher than the present reference condition would eventually lead to an unacceptable trend in w a ter quality degradation due to expected development increases. T he group further determines that because m a ny of the reference lakes are located in the upper reaches of larger w a tersheds, these nutrient levels are inherently lower than those in lakes and reservoirs further downstream . I f the model projections are accurate, the downstream lakes also will be enriched, and any increased load implied by raising the criteria above reference levels will hasten their cultural eutrophication. T he R TAG therefore concludes that it will be prudent to set the criterion at 28 μ g /L T P.
A lternatively, the 33 μ g /L reference condition is determined to represent v e ry little change over time, sug ge sting a dynamic stability in the area. I n fact, the historical record shows, and a paleolimnological study by a local college confirms, that m a tters were m u ch worse j u st 50 years ago when postwar log gi ng and land development efforts peaked in the area. Many farms are now reverting to woodlots, and m u ch of the land is being purchased by the State for natural and recreational uses. T he reference lakes are all mu ch lower in nutrient loads because they w ere protected from development even 50 years ago. I t is concluded by the RTAG that the criterion can be safely set at 37 μ g/L, and when implemented, the lakes of the region will remain in their me sotrophic, recovered state. I n fact, further reductions for the other 

### Nutrient Criteria—Lakes and Reserv o irs 7- 7lakes may be unlikely because of sediment releases of the phosphorus they originally received, w h ile the demographic and loading projections strongly sug ge st that a m a nageable stability of between about 33 μg /L and 40 μ g /L is v e ry likely . D ownstream w aters will be unaffected by this action because ambient stream concentrations are presently in this range, and USFWS reports no endangered species in the area. Th erefore, the specialists conclude that 37 μ g/L is the appropriate criterion. We will use this hypothetical v a lue as an illustration for the remainder of this chapter. (Keep in mi nd, however, that the alternative of 28 μ g /L also is possible.)
T hus, the final derived ecoregional criteria for T P could be, depending on the circumstances, either the reference condition v a lue of 33 μ g /L, 28 μ g/L, or 37 μ g /L. T he bracketed reference condition v a lue in Figures 7.1, 7.2, and 7.3 shows this range of these hypothetical options. State and T r ibal nutrient criteria development can follow this same protocol described above except overall EPA ecoregional criteria should be used as a g u ide as States and T r ibes establish their own nutrient criteria levels to protect designated uses. C. Development of State Nutrient Criteria EPA encourages States and T r ibes to use the nutrient criteria technical g u idance m a nuals and ecoregional nutrient criteria when developing their own nutrient criteria. EPA intends to issue the regional nutrient g u idance under section 304(a) of the Clean Water Act (CWA). According to EPA 

### � s regulations, States/Tribes should establish their numeric w a ter quality criteria v a lues based on (1) EPA 

### � s section 304(a) g u idance (in this case, the appropriate regional nutrient criteria), (2) EPA 

### � s 304(a) gu idance modified to reflect site-specific conditions, or (3) other scientifically defensible me thods. (See 40 CFR §131.11(b)(1).) I f the State/Tribe has additional data that it believes justify adoption of a different v a lue or set of v a lues, the State/Tribe should be prepared to explain the site-specific conditions or scientifically defensible m e thods that m ake it reasonable to depart from the regional nutrient criteria gu idance. I f EPA approves the State 

### � s/Tribe 

### � s nutrient criteria, it becomes effective for the purposes of the CWA. I f no action is taken by the State or T r ibe involved, EPA m ay propose to promulgate criteria based on the regional v a lues and best available supporting science at the time. T hese v a lues then will be used as the nutrient criteria for that State or T r ibe. I t is important to note that although nutrient criteria may be new, the EPA–State criteria and standard process itself is already w ell established. 1. Designated Use Section 303(c) of the CWA as amended (Public Law 92-500 [1972], 33 U.S.C. 1251, et seq.) requires all States to establish designated uses for their w a ters. EPA 

### � s interpretation of the C WA requires that wherever attainable, standards should provide for protection and propagation of fish, shellfish, and wildlife and provide for recreation in and on the water (section 101(a)). Other uses identified in the act include industrial, agricultural, and public water supply

. However, no waters m ay be designated to be used as repositories for pollutants (see 40 CFR 131.10(a)). Each water body m ust have legally applicable criteria that protect and m a intain the designated use of that w a ter. Changes in lake condition that begin to occur at points or in regions along the trophic continuum could be informative as States establish criteria to protect designated uses. T able 7.1 illustrates some use-related problems that tend to occur along the trophic spectrum for temperate U.S. lakes.

7- 8 

### Nutrient Criteria—Lakes and Reserv o irsAlso discussed below are g e neral g u idelines for developing criteria to protect selected designated uses. T he values included here (and in T able 7.1) are not intended to represent proposed EPA or State ecoregional nutrient criteria. R ather, they illustrate ranges of parameters associated with the impairment of some traditional uses in some areas of the country

. Criteria to protect these uses should be developed on a regional basis and should be consistent with EPA ecoregion criteria.

**Ta ble 7.1.	 Changes in T**  **e mperate Lake A**  **t tributes According to T**  **r ophic State**  **(adapted from Carlson and Simpson, 1995)** 
**TSI Value**  **SD (m)**  **TP (μg/L)**  **A ttributes**  **Water Supply Recreation**  **Fisheries**

<30 >8 <6 Olig otroph y: Clear wa ter, oxyg en throu g hout the y ear in the h y polimnion Salmonid fisheries dominate

30-40 8-4 6-12 H y polimnia of shallower lakes ma ybecome anoxic Salmonid fisheries in deep lakes 40-50 4-2 12-24 Me sotroph y : W a ter moderatel yclear but increasin g probabilit yof hy polimnetic anoxia durin g summer Iron and man g anese evident durin g the summer. THM precursors exceed 0.1 m g /L and turbidit y >1 NT U Hy polimnetic anoxia results in loss of salmonids. Wa lle ye ma y predominate 50-60 2-1 24-48 Eutroph y : Anoxic hy polimnia, macroph y te problems possible Iron, man g anese, taste, and odor problems w o rsen Wa rm-water fisheries onl y . Bass ma ybe dominant 60-70 0.5-1 48-96 Blue- g reen al g ae dominate, al g al scums and macroph y te problems W eeds, al g al scums, and low transparenc y discoura ge swimmin g and boatin g 70-80 0.25- 0.5 96-192 Hy pereutroph y ( li g ht limited ) . Dense al g ae and macroph y tes >80 <0.25 192- 384 Al g al scums, few macroph y tes Ro ug h fish dominate, summer fish kills possible



### Nutrient Criteria—Lakes and Reserv o irs 7- 9

### � Outstanding N a tural R e source Waters Some waters of the State m ay require special criteria based on unique characteristics of that water body

. Such characteristics migh t include undisturbed or unique watersheds that are markedly different from other watersheds in the State. I n some States, naturally formed lakes are a rarity and m ay need to be protected by criteria different from those used for m a n-m a de lakes or reservoirs. Some lakes may include rare or endangered species of plants, invertebrates, or v e rtebrates that need to be protected. Such lakes are the v e ry best of the reference set and are m o st in need of protection by rigid State and T r ibal antidegradation policies and procedures.



### � A quatic L ife U ses A quatic life uses, including fisheries, are heavily dependent on the initial condition of the resource. Species will change as a function of trophic state, and it m ay be difficult to defend w h y one species is necessarily “better” than another. T he use of reference lakes and their accompanying biota is one m easure that can be used to predict the species that should be expected in a region. Few taxonomic g r oups have been observed over the entire trophic spectrum . T he best known are those that have been used as trophic state indicators because these are known to change with trophic state. Of these, perhaps the best, and oldest, indicators are the dipteran larvae of the family Chironomidae . T he Chironomids w e re known to change drastically as a lake became anoxic, and one of the first distinctions between oligotrophic (oxic hypolimnia) and eutrophic (anoxic hypolimnia) was the shift from a domination by Tanytarsus to one by Chironomus (Thienemann, 1921). Numerous algal groups also are known to change with trophic state. T he dominance of blue-greens in eutrophic waters is perhaps the m o st notorious, but changes in diatoms are well documented, perhaps if their frustules remain in the sediments. The paleolimnological record can help in setting the aquatic life criterion. Macrophytic plants also are known to change in density, location, m o rpholog y , and species richness (see above). Although our knowledge of the dynamics of change in the biota as a function of eutrophication requires further development, there is sufficient evidence to conclude that eutrophication will bring species changes. I f a lake has an existing aquatic life use, then that use m u st be maintained. Eutrophication will cause some species to change in relative abundance and cause others to disappear; therefore, nutrient enrichment m ay be incompatible with the m a intenance of a specific biota. T he ultimate extension of this concept is in the use classification of outstanding natural resource w a ters. Fisheries
Deve loping criteria to protect a specific fishery m ay be somewhat difficult because fish species in particular change as trophic state changes (Oglesby et al., 1987); therefore, different fishermen might be pleased or angry w ith each change in trophic state. For example, salmonids are dominant in w a ters with hypolimnetic oxy g en but diminish as hypolimnetic anoxia develops (see Figure 5.2). T his shift to a warm-water fishery m ay disappoint lake trout fishermen but delight walleye or perch fishermen. Carp and bullheads, which dominate the hypereutrophic waters, also have their advocates. I t m ay be that criteria to protect specific designated uses could be established at the points of transition between dominant fish g r oups. Based on the work of Oglesby et al. (1987), the following g eneral v a lues (based on the available hypolimnetic dissolved oxy ge n response) migh t be sug ge sted:

7-10 

### Nutrient Criteria—Lakes and Reserv o irsTSI Range TP Concentration Aquati c Li fe <TSI 40-50 TP = <24 μ g/L Salmonid fishery T SI 50-60 TP = 24-48 μ g/L Percid fishery TSI 60-80 TP = 48-192 μ g/L Centrarchid fishery >TSI 70-80 TP = >192 μ g/L Cyprinid fishery Such a fishery categorization m ay present problems because some w arm-water fisheries would thriv e in w a ters falling below the reference condition (i.e., 50 T SI). H owever, consultation with fisheries ma nagers and the public through the w a ter quality standards review process should help resolve the issue of robust fish in otherwise overenriched waters.
Dr inking W a ter On ly in the past decade have w e come to a full realization of the effect of eutrophication on drinking water (Cooke and Carlson, 1989). For years, the drinking water industry has recognized the effect of certain species of algae on taste and odor. However, trihalomethanes and other chlorinated byproducts also become connected with the effects of eutrophication (Palmstrom et al., 1988). I t is now recogniz ed that as a lake eutrophies, the species of algae will shift to those that affect taste and odor; these species w ill increase in density and increasingly affect the raw w ater quality

. Turbidity w ill increase as the algae become m o re dense. T he need to chlorinate then increases, and thus chlorination byproducts will increase as algae increase. Hy polimnetic anoxia will also increase the problems of iron and m a nganese control.
Th e reality is that drinking wa ter plants m u st deliver a safe and potable product. A s the effects of eutrophication are seen in the raw w ater, the cost of treatment increases. U nfiltered systems m u st g ive way to filtered w a ter, then powdered carbon, and finally activated carbon. T he run times of filters and of GAC filters decrease with increased algal densities. I n short, eutrophication dramatically changes the cost and even the treatment process itself. Several points along the trophic state continuum are relevant for drinking water supplies. T he first is at a trophic state index (TSI) of 40 to 50, when the hypolimnion becomes anoxic. T his is when iron and m anganese problems would first be evident. At a T SI of 50, the turbidity of the water migh t be expected to exceed 1 N TU , and filtration of the raw w ater would become necessary . I t is at a T SI of 50 that A rruda (1988) found that trihalomethane concentrations in the finished w a ter exceed 100 m g/L in some Kansas treatment plants. T herefore, it is at this trophic state that extra measures or changes in the treatment process are necessary to control taste and odor without increasing the chlorine dose.
Recreation Swimming/Primary Contact Recreation

. Criteria to protect a contact recreation use m ay be associated with the occurrence (or appearance) of certain phenomena that affect certain types of recreation. For example, in g e neral, swimme rs will not be affected by the trophic state of the lake, but resulting changes in transparency or change in species m ay be important. Some States and countries have prohibitions on swimmi ng based on the depth from which a body can be seen on the bottom . T his consideration is based on the possibility of seeing a drowning child. N ew Z ealand has a swimmi ng


### Nutrient Criteria—Lakes and Reserv o irs 7-11prohibition on transparencies of less than 1.5 m (Smith et al., 1991), and several States have prohibitions based on transparencies of 2 or 3 feet. T hese transparencies would be equivalent to a T SI va lue of approximately 60, which, if transparency is related to phosphorus, would be equivalent to a T P v alue of 45 to 50 μ g /L. T he density or frequency of algal scums also migh t discourage swimmi ng . B ecause scums are often the result of dense populations of blue-green algae, then their frequency and density migh t be expected to increase as a lake becomes enriched. Excess nutrients feed not only nuisance algae gr owth, but potentially health-endangering bacteria, especially when human and animal waste m ay be involved. Boating and Secondary Contact Recreation. . I t migh t be expected that the transparency of the water or the presence of algal scums would not deter boating, unless water skiing were involved. However, boating m ay be affected by the presence of dense beds of tall or floating m acrophytes. Little research has been done on the relationship of macrophyte type and trophic state, but a paper by Swindale and Curtis (1957) sug ge sts that the dominant taller plant forms increased as the conductivity of Wisconsin lakes increased. Because conductivity has been related to the back gr ound levels of nutrients in the water, a rough approximation would sug ge st that the trophic state where taller plants predominate would have a transparency of approximately 0.5 m, or a T SI of 70 (TP = 98 μ g/L). 2.	 Hypothetical Illustration of the Relationship of State Criteria to Protect Designated Uses Compared With an Ecoregional Criterion for TP
I n this hypothetical illustration (not applicable to any specific region), TP has been evaluated by EPA regional and Headquarters specialists for all reference lakes of a g ive n class in the EPA nutrient program data set for a particular nutrient ecoregion or subregion. T he distribution of the data has been assessed, and the upper 25th percentile of this distribution has been chosen as the ecoregional reference condition for T P (Figure 7.1). I n this illustration, the upper 25th percentile is 33 μ g/L, and the R TAG has developed the criterion of 37 μ g /L T P as described in Section B above.

Figure 7.1.3 Development of a hypothetical ecoregional reference condition for T P from an ecoregion data s e t of reference lakes .

7-12 

### Nutrient Criteria—Lakes and Reserv o irsCalculations of these ecoregional criteria are done by the EPA National Nutrient Criteria Program in conjunction with the appropriate EPA RTAGs. T he supporting data are obtained from Federal, State, and academic agencies and institutions in the region; all of these data become part of the national nutrient database. I n establishing these regional criteria, EPA relies on the same five elements of criteria development described earlier for State and T r ibal use (e.g., historical records, present reference site data, models if appropriate, regional expert interpretations, and consideration for downstream impacts).
Th e ecoregional criteria described in this m a nual are expected to be in part predicated on reference condition data g a thered from at least high and low flow conditions, if not from y ear-round data. T his is to m ake the process as straightforward and simple as possible while having consistent application of the me thodolog y to all parts of the country, even those with seasonal v ariation.
Ho weve r, it is evident that this approach m ay create a w i ndfall g ap between the criteria v a lues and seasonally selected measurements in some localities. T his would be analogous to conducting a perk test for a septic system in mi d-A ugu st, w h ich would have little bearing on the performance of the system during rainy A pril weather. States correct for this problem by setting their required test infiltration rates on a seasonal basis. Similarly, when large seasonal disparities exist in the reference data, the R TAG should develop two or m o re seasonal criteria instead of using an average criterion for each v ariable. O ne of these seasonal criteria should be for the g r owing season in that region. Sampling to evaluate water body attainment with the subsequent standards employing these criteria w ill have to be carefully defined to ensure that State or Tribal sampling is compatible with the procedures used to establish the criteria. I f State or T r ibal observations are averaged over the year, balanced sampling is essential and the average should not exceed the criterion. I n addition, to account for inherent v ariability, no m o re than 10 percent of the observations contributing to that average v a lue should exceed the criterion (see also section D below). Once an ecoregional criterion has been established and is subject to periodic review and calibration, any State or T r ibe in the region m ay elect to use it as the basis to develop its own criteria to protect designated uses for each class of lakes in the State. T his is entirely appropriate so long as the criterion is at least as protective as the basic EPA criterion for that region. T his ecoregional criterion represents EPA 

### � s “304(a)” recomme ndation for protection of aquatic life use and is the v a lue EPA would propose to promulgate in the absence of State or T r ibal criteria.
Us ing this initial benchmark, the State or T r ibe m ay proceed to classify its lakes first by size and other physical characteristics, and then further subclassify them by designated uses, e.g., criteria to protect large lakes and salmonids in a particular ecoregion or subecoregion. For each designated use class within the physical classifications, a set of reference lakes are again identified and the range of their TP concentrations plotted (from low to high), j u st done for the EPA regional criteria calculations. I n this instance, the State m ay, if the data are known to be from all high-quality lakes, select an upper percentile (upper 25th percentile is recomme nded) of the distribution as the candidate criterion. I f reference lakes are not available and the overall distribution of the lakes or a sample of the lakes is used instead, then the percentile should be selected from the lower end of the distribution (lower 25th percentile is recomme nded). T he reader should bear in mi nd that the reference condition alone does not constitute the State criterion. I t m u st be objectively assessed within an historical perspective and address downstream conditions before the criterion v a lue is finally established.



### Nutrient Criteria—Lakes and Reserv o irs 7-133. Frequency Distribution Approach
Th e comm on characteristic of the frequency distribution approach is that it is data dependent. Us ually, g o als or criteria will be based on the data of the lakes themselves. This allows the construction of criteria based on the actual situation for the individual State or region. T he establishment of nutrient criteria (much like establishing g rades to reflect performance in education) requires both basic v a lues or thresholds of expected accomplishment as w e ll as sufficient flexibility to accomm odate the uniqueness of each class. I n this w ay , optimum performance is attained and the desired g o al is reached.
Th e g r ading process, based on an accepted standard of performance (e.g., 75 percent is a passing gr ade), is analogous to the EPA ecoregional criteria derived from the best information available from existing reference lakes, paleolimnolog y , historical information and data sets, and appropriate models, as w ell as RT AG j udg m ent and downstream consideration. Conversely, establishing criteria for each designated aquatic life use in this m a nner compares to “grading on the curve,” w h ere the data characteristics of each use set the curve.
Th e EPA regional criterion means that a mi nimum expectation is established to prevent any decline in performance. B ut above the “passing g rade,” the individual State or T r ibe m ay develop its own criteria in accordance with the characteristics and designated use classification of its lakes. I n Figure 7.3, mo st of the designated use criteria meet or exceed the passing g rade. Figure 7.2 is a hypothetical illustration of T P criteria developed for select designated use categories for an overall distribution of specific-sized lakes. T he 37 μ g/L T P criterion is derived from the approach illustrated in C h apter 6 (see Figure 6.1) and the example of R TAG deliberations presented earlier in this chapter. Thus, for this example:
• B oating TP criterion = 40 μ g /L • Warm-w a ter fishing TP criterion = 30 μ g/L • C old-water fishing TP criterion = 24 μ g/L • Exceptional natural resource lake T P criterion = 10 μ g /L When this process is completed, Figure 7.2 can be simplified to show a series of criteria based first on the comm on physical similarity of the water bodies (they are in the same classification, e.g., sam e ecoregion, size range, and average depth) and next on their subclassification by designated uses (Figure 7.3). D. Developing Nutrient Criteria Implementation P r ocedures However done, a State’s or T r ibe’s nutrient criteria should include a procedural protocol to implement the newly adopted nutrient criteria. T he criteria and procedures should be reviewed by the RTAGs for concurrence and are subject to further EPA review and approval if submitted as part of State or T r ibal standards.
T he four initial criteria v ariables include two causal v ariables (T N and T P ) and two response variables (chlorophyll a and Secchi depth or a similar indicator of turbidity). Failure to meet either of the causal criteria should be sufficient to indicate a criteria “excursion,” and usually the biological response, as measured by chlorophyll a and Secchi depth, will follow this nutrient trend. H owever, if the causal criteria are me t but some combination of response criteria is not m e t, then there should be some

7-14 

### Nutrient Criteria—Lakes and Reserv o irsFigure 7.2.	 Development of T P criteria for s e lect designated uses relative to the reference condition and ecoregional criterion for lakes of a s p ecific s i ze clas s.

Figure 7.3. Simplified display of T P criteria for s e lect designated uses in a s p ecific s i ze clas s.



### Nutrient Criteria—Lakes and Reserv o irs 7-15means of determining if the lake in question meets the nutrient criteria. Two sug ge sted approaches are described below. 1. Decisionmaking Protocol One option is to establish a decisionmaking procedure equating all of the criteria. Such a rule migh t state: “Both T Nand T P causal nutrient criteria m u st be me t, and at least three out of five response criteria (e.g., chlorophyll a , turbidity, algal biomass, DO, macrophytes) m u st be met for three out of four sampling events during the June through August survey period over 2 consecutive calendar years of sampling . N o sampling events m ay be less than 3 weeks apart [to avoid clustering sampling activities near a particular flow condition or runoff event], and flow conditions m u st be recorded as well so that watershed base flow and runoff events are evident and can be factored into the data assessment process. ” 2. Multivariable En richm e nt Index
Th e second option is to establish an index that accomplishes the same result by inserting the data into an equation that relates the m u ltiple v ariables in a nondimensional comprehensive score m u ch the same way an index of biotic integrity (Karr, 1981) does. An example of an enrichment index approach is presented in T able 7.2.
**Table 7.2. Example of an Enrichment Index Using a Hypothetical Lake**

**Variable Criterion**  **Hypothetical Lake Mean Measured**  **Value Enrichment Index**  **(EI) Score*** **Ca usal variables**  To tal P (mg /L ) � 0.020 0.048 5 To tal N (mg /L) � 0.250 0.502 5 **Primary response variables** Secchi depth (M ) � 1.0 0.6 3 Ch loroph y ll a (m g /L) � 20 30 5 Ma croph y tes (% of phototrophic zone) � 25 52 5 Al g ae (% blue- g reens of spp. composition) � 25 75 5 **Secondary response variables** Dissolved oxyg en (m g /L in h y polimnion) � 6.0 3.5 3 Fish kills (no in last 5 y r) 0 2 5 **Enrichment Index Value**: = 36**
* Each of the eight variables receiv es an EI s co re. The s co ring procedure is : 0 = meets cr iterion; 2 = fails to meet c ri terio n by 10% ; 3 = fails to mee t cr i te rion by 25% ; 5 = fails to mee t cr i te rion by 50% or more. ** Enric hme nt Index Value is the s um of the EI s co res. The m aximum sco re achievable is 40.

7-16 

### Nutrient Criteria—Lakes and Reserv o irsIf necessary, the scoring process can be weighted by seasons. T hus, different emphasis can be g iven to the results of winter surveys as compared with summe r surveys, and year-round work can be conducted if necessary or desired. For example, g r eater w e ight perhaps by a factor of 2 could be g ive n to the primary response v ariables in w i nter for north temperate lakes because these v ariables would normally be expected to be improved at this time of year. Similarly, the criteria for T P and T N might both be changed to lower concentrations for w i nter because less runoff or fewer fertilizer applications are expected. I n the example, the lake fails any way because it failed the criterion for either T P or T N(in fact it failed both). With a score of 36 out of a possible 40, it is also a prime candidate for extensiv e remediation m a nagement. Such enrichment index scores are not intended at this time to be surrogate nutrient criteria. T hey may , however, serve as a “translator” to implement m u ltiparameter criteria. Howeve r, like biological criteria index scores such as the Index of Biotic I n tegrity, the enrichment index m ay be a useful assessment tool. T he merit of the index approach is that all lakes of a g ive n classification can be rank ordered by score. T his helps the resource manager plan the distribution of effort and funds over the entire resource base in one procedure.
E. F requency and Durati on Frequency and duration are important concerns when evaluating any lake with respect to meeting criteria. T his is a difficult process at this initial phase of the program because the data sources for criteria development are presently so diverse. I n general, however, the me thod of data g a thering for compliance should be as near as possible to that used to establish the criteria. Once this consistency is established, excursions from the criteria based on frequency and duration can be evaluated whether based on a decision rule or a m u ltivariable index. Frequency of “excursion” from a criterion is a decision that can be best established by the State or Tr ibe on the basis of their knowledge of the local water resources. An excursion that occurs less than 10 percent of the times w h en sampling is conducted (at regularly spaced or random intervals) m ay be considered acceptable. D uration of the excursion m ay be stipulated as a set period of time (e.g., 2 weeks, or as to not exist over m o re than two consecutive sampling intervals, whichever is the lesser period). T he State or Tribe in consultation with EPA w ill need to specifically define these terms as appropriate to the region and should also determine the combination of these factors that constitutes an “excursion.”



### Nutrient Criteria—Lakes and Reserv o irs 7-17Un ique A s pects of C riteria D e velopment f o r R e servoirs

Re se rvoirs are important and e ffec tiv e traps of nutrients a nd s e dime nts (e .g ., K e nnedy 1999, Straš kraba et a l., 1995). As such , the y are often s ign ific an t in the re g ulation of the mater ial budg ets of e ntire dra i na ge ba s ins . T he potential importanc e of total phosphorus re te ntion by re serv oirs a nd its m odif y ing influe nce on riv e rine nutrient budg ets are de m onstra ted by water quality data fo r a thre e -reservoir c ascade on the White Riv erin northw e stern Ark a nsa s a nd southern Missouri. T he three CE reservoirs, Beaver L ake, Table Rock L ake, an d Bull Sh oa ls Lake, exhibit d iffe rin g w ater resid en ce times an d phosphorus retention rates, and, despite their close prox imity on the same riv e r, receive in flow s with m arkedlyd if fe rent total phosphorus concentrations due to v ariations in load s f rom point and nonpoint sources (Fig u re 1). Beaver Lake receives inflow s w ith relativ ely high total phosphorus c onc en trations, owing to a g ric u ltura l land us es , but retains approxim ately 74% of the phosphorus load and releases water with m arkedly reduced total phosphorus concentrations. Upstream r eaches o f th e re se rvoir e x hibit high a lga l production and reduc ed water c larity, due to a m ple ava ilability of nutrients , w here as low a lg al production and incre ased water c larityare obse rve d in downstre am reaches coincide n t with declining nutrient availability

. Table R oc k Lake , the ne x t downstre am re serv oir in the cascade , be nef its f rom phosphorus re te ntion in B eaver Lake and receives in flow s with relatively lo w total phosphorus co n centrations. Wh ile release total phosphorus concentrations below Table Rock Lake are low, loading rates to the river are hi gh immedi atel y upstr eam f ro m Bu ll Shoals L ake an d total phosphorus c onc en trations are aga in ele va ted. H ow ever , the high rate of total phosphorus re te ntion in B u ll Shoals Lake (63%) a gai n reduc es total phosphorus c onc en trations in the White Riv er below the da m. T he ne t effectof the thre e -re se rvoir cascade is modulation of total phosphorus conc en trations along this 200 km r each of the W h ite River through phosphorus retention. In the abs ence of the thre e re se rvoirs , a nd g ive n the oc cu rrenc e of high rate s of total phosphorus loading to the riv e r, conc en trations higher than thos e obs erve d would be a nticipated.
Ke nnedy (1999) reports that phosphorus re te ntion by re ser v oirs is a f unction of water re s ide nce time a nd areal phosphorus loading ra te (Figure 2), and that s uch re te ntion ha s important implic ations f or the phosphorus budg ets of draina ge ba si ns . As demonstr ated above for the White Ri ver, reservo i rs can be viewed as nutrien t si nks within a d rai n age ba si n an d may serve to reduc e loading s to downstre am water re s ourc es , including other re se rvoirs

. In the c onte xtof nutrient criteria, the va lue of this f unction f o r re se rvoirs s hould be a topic of dis cussi on, s i nc e re se rvoirs identified a s nutrient sink s may exper ienc e wate r qualityc onditions (e .g ., high nutrient conc en trations) that dif fe r f r om thos e otherwis e an ticipated or de si red. N utrient c r it eria for such l akes co uld be modifi ed accord in gl y. Figure 1: Av er age inflow and outflow total phosphorus c onc en trations (ver tical bar s) and in-reservo ir total phosphorus c onc en tration ( s olid c irc le) for Be aver , Table Roc k , and Bull Shoals Lakes on the white Riv er , AR. R T and R P indicate wate r resi denc e tim e ( day s) and total phosphorus rete ntion ( percen t), respec tiv ely.

7-18 

### Nutrient Criteria—Lakes and Reserv o irsFigure 2: Relationship betwe en total phosphorus rete ntion and wate r resi denc e tim e va lue s for selected CE reserv oir s with diffe ri ng area l phosphorus loads

. Cur ves and as soci ated equations es timate re lationships betwe en total phosphorus re tention (RP) and w a te r resi denc e tim e (R T) for e ach of three area l phosphorus loading c a tegorie s (Ke nnedy 1999).



### Nutrient Criteria—Lakes and Reserv o irs 7-19

# CHAPTER 8 **Using Nutrient Criteria To Protect Water**  **Quality** A. State W a terQ ualit y Standards B. Wa terQ ualit y –Based Approach to Pollution Control C. Nonpoint Source Pollution Control D. Comprehensive Nutrient Mana g ement E. Resources

Th is chapter provides an introduction to the applications of nutrient criteria. Chapter 1 described the uses of nutrient criteria as (1) identification of problems, (2) m a nagement planning, (3) regulatory assessments, (4) project evaluations, and (5) status and trend determination of the water resource. I n this chapter, added discussion is provided for some of these uses of criteria. Sections A and B address regulatory assessments in the context of standards development and the w a ter quality–based approach to pollution control, including development of a total m a ximum daily load (TMDL) and National Pollution Discharge Elimination System (NPDES) permits. Section C focuses exclusively on nonpoint source ma nagement programs. T he chapter text ends with Section D, which addresses a comprehensiv e planning, application, and evaluation procedure for effective lake and reservoir nutrient quality ma nagement. Section E is a descriptive listing of some useful information resources associated with lake and watershed m a nagement. A. State Water Quality Standards 1. Water Q u ality Standards and the C l ean Water A ct The g o als of the C l ean Water A c t (CWA) are to achieve, wherever attainable, w a ter quality that provides for protection and propagation of fish, shellfish, and wildlife and recreation in and on the water. Th e CWA further specifies that States adopt, and EPA review, standards consisting of designated uses and criteria based on those uses that serve the purpose of the CWA. EPA’s implementing regulations require States to specify designated uses for their waters and consideration of the g o als of the CWA described above. Furthermore, States m u st adopt w a ter quality criteria that protect the designated uses. Criteria m u st be based on sound scientific rationale and m u st contain sufficient parameters or constituents to protect the designated uses. For waters with m u ltiple use designations, criteria m u st support the m o st sensitive use. Finally, in designating uses and establishing w ater quality criteria, States mu st ensure attainment of standards in downstream waters. With regard to nutrient criteria, Section 304(a) of the CWA directs EPA to develop and publish criteria that reflect the latest scientific knowledg e of the effects of pollutants on biological comm unity diversity, productivity, and stability, including information on the factors affecting rates of eutrophication for v arying types of receiving wa ters. I n its implementing regulation, EPA recomme nds that States adopt w a ter quality criteria to protect designated uses based on Section 304(a) criteria, Section 304(a) criteria modified to reflect site-specific conditions, or criteria based on other scientifically defensible m e thods.
As illustrated in Figure 8.1, w a ter quality standards for w a ters of the U n ited States comprise designated uses, criteria to protect those uses, an antidegradation policy to m a intain existing water quality, and implementation procedures for application to specific w a ters. O nce w a ter quality standards are adopted and approved, they become the basis for legally enforceable source control. Criteria as a component of standards are always established in the context of a designated use. T herefore, EPA, as we ll as States and T r ibes, m u st develop criteria that are directly applicable to designated uses.



### Nutrient Criteria—Lakes and Reservo ir s 8- 1Figure 8.1. Com ponents of w a ter q ua lity s t an da rd s.
2. Protecting Designated Uses
Ithas been amply demonstrated that nutrients are a m a jor contributor to use impairment in waters of the U n ited States. B ecause States are required to designate uses in consideration of the g o als of the CWA and adopt criteria that contain sufficient parameters or constituents to protect designated uses, and because it is EPA’s responsibility to provide recomme nded criteria, the A g ency m ust develop and publish Section 304(a) criteria for nutrients that provide for protection and propagation of fish, shellfish, and wildlife and recreation in and on the water. Furthermore, EPA’s Section 304(a) criteria should reflect the effects on biological comm unity diversity, productivity, and stability

. EPA’s Section 304(a) criteria will be issued on the basis of ecoregion and w a ter body type. T his approach to nutrient criteria development not only meets the above requirements but also provides a sound scientifically defensible approach that accounts for the characteristics of different types and locations of water bodies. EPA’s ecoregional nutrient criteria are intended to represent enrichment conditions of surface w a ters that are mi nimally impacted by human development activities, and will be developed and further refined based on the five elements described in this technical g u idance manual. Water quality criteria incorporating minimally impacted (i.e., reference) conditions should provide for protection and propagation of aquatic life and recreation, and reflect conditions that will not adversely affect the biological comm unity

. Both causal variables (e.g., T Nand T P ) and response variables (e.g., turbidity and chlorophyll a ) are necessary to provide sufficient protection of these uses before impairment occurs and to m a intain downstream uses. 3. Maintaining E x isting Water Q u ality
I n addition to adopting sufficient criteria to protect designated uses for their w a ters, States and authorized T r ibes m u st also adopt and implement an antidegradation policy to m a intain existing uses and to m a intain high water quality w here it exists—regardless of the specified designated uses and associated criteria. State and Tribal antidegradation policies m u st be consistent with the Federal antidegradation policy as described at 40 CFR 131.12 to g a in approval from EPA. Two key provisions of the Federal antidegradation policy are relevant to this discussion. T he first requires that the level of w a ter quality necessary to protect the existing uses m u st be m a intained and protected ( “ Tier 1”). For a variety of reasons, an existing use m ay differ from the designated use, and m ay require either less stringent or m o re stringent protection than afforded by the criteria intended to protect the designated use.

8- 2 

### Nutrient Criteria—Lakes and Reserv o irsTh e “Tier 2” provision is intended to provide protection for existing uses in cases where waters are not meeting their designated use, and also where the existing use happens to be better than the designated use. T his second provision requires that existing high-quality w aters (i.e., w a ter quality that exceeds criteria to protect “fishable and swimmable” uses) m u st be m a intained and protected unless it is demonstrated through a public process that a lowering of w a ter quality is necessary to accomm odate important economic or social development. I n lowering w ater quality, the existing uses (Tier 1) m u st still be fully protected. “Tier 3” of the antidegradation policy preserves outstanding national resource waters, which is the highest level of protection under this policy

. As nutrient criteria are developed and adopted, it is important that States also review their antidegradation policy and associated implementation procedures. Antidegradation requirements are typically trig ge red w h en an activity is proposed that m ay have some effect on existing w ater quality

. Th ese requirements apply at a mi nimum to activities regulated under State, T r ibal, or Federal law but can be m o re broadly applied. I n practice, States and T r ibes m ay encounter water where existing uses m ay not be protected by adopted criteria or existing high water quality exceeds adopted criteria. A ntidegradation policies and procedures m u st ensure public participation in decisions affecting, for example, the impact on unique lakes of higher relative nutrient quality than migh t be stipulated in State or regional nutrient criteria based on a m o re extensive data set. States and T r ibes should have effective antidegradation implementation procedures in place with criteria to ensure that existing w ater quality is m a intained and protected from degradation by existing future point and nonpoint sources. Any State or local nonpoint source control requirements should be included in an antidegradation review. 4. Providing Fl exibility in Implementation
A bundant flexibility is built into the criteria setting process and w a ter quality standard regulation to allow States to (1) develop their own criteria to protect specific uses or reflect m o re locally representative conditions, (2) use different techniques to develop criteria as long as they are protectiv e and scientifically defensible, and (3) conduct use attainability studies and refine their use designation, wh ere there is a conflict between designated uses and ecological criteria. States also have the flexibility to adopt numeric criteria to protect designated uses or to adopt me thods and procedures that translate narrative criteria to protect designated uses. Narrative criteria statements, often referred to as “general criteria” in States’ standards regulations, usually take the form of a description of desired w a ter quality condition or a preclusion of certain types of pollution or undesirable conditions (i.e., the “free from” provisions).
Narrative criteria are considered to be critical backstops for designated use protection and are a powerful means of achieving desired w a ter quality if they are interpreted in a clear and consistent ma nner. I n water quality standards, a “translator” identifies a process, methodolog y , or g u idance that States or Tribes will use to quantitatively interpret narrative criteria statements. Translators m ay consist of biological assessment m e thods (e.g., field measures of the biological comm unity), biological m onitoring m ethods (e.g., laboratory toxicity tests), models or formulate that uses input of site-specific information/data or other scientifically defensible me thods. T ranslators are particularly useful for addressing w ater quality conditions that require a g r eater degree of sophistication to assess than can be typically expressed by numerical criteria that apply broadly to all waters with a g ive n use designation. The translator m ay be either directly incorporated into State or Tribal w a ter quality standards or incorporated by reference. I n either case, specific limits or v a lues for a measurable pollutant derived using a translator that interpret a narrative criterion statement should be attached to the State or T r ibal regulations to ensure public review, as would be required of any site-specific numerical criterion. 

### Nutrient Criteria—Lakes and Reserv o irs 8- 3Th e existing w ater quality standards regulation, along w ith the associated policies and national gu idance, can provide the flexibility needed to accomm odate appropriate adoption of nutrient criteria and subsequent implementation of control measures. T he negative consequences of adopting inappropriate criteria include cases where the adopted criteria (and ensuing permit limits or other control measures) are not stringent enough and result in a loss of use, and cases where the adopted criteria are too stringent and lead to unnecessary source controls and increases to the list of impaired waters. I n specific situations where criteria are thought to be overly protective, regulatory alternatives such as refined use designation, site-specific criteria, or a v ariance could be employed to ensure that the appropriate uses and criteria to protect the uses are established. For example, if a regulated source faces expensive treatment to comply with a new or revised requirement, the State or T r ibe could seek a variance as described in 40 CFR 131.10(g) and determine if site-specific criteria are appropriate. Specific situations w h ere nutrient criteria are not sufficient to protect uses m ay be remedied throug h development of site-specific criteria, the need for which could be identified through an antidegradation review in situations involving high-quality w ater (i.e., nutrient concentrations below criteria levels). In situations w h ere uses are not attained, the TMDL process is intended to improve w a ter quality to meet the designated use. I n situations involving high-quality w ater, new or expanded nutrient loads from a regulated source will probably trig ge r an antidegradation review . I n addition to determining w hether lowering w ater quality is necessary to accomm odate important economic or social development, information g e nerated through this review could be used to derive appropriate site-specific criteria to protect uses. Water quality criteria published by EPA under Section 304(a) of the C WA such as criteria for nutrients serve as primary sources of information to States and T r ibes as they develop numeric criteria as part of their State or Tribal w a ter quality standards. U nder the C WA and EPA’s implementing regulations, States and T r ibes m ay also use other information, including local w a ter quality conditions, as they develop State or T r ibal standards. I n addition, EPA typically uses EPA’s water quality criteria as the principal basis for proposing and promulgation of a replacement w a ter quality standard w h ere a State or T r ibe fails to adopt an acceptable standard. Where a State or T r ibe does not adopt scientifically defensible nutrient criteria to protect designated and existing uses, EPA w ill, as necessary, propose to promulgate Federal w a ter quality standards for State or Tribal w a ters. I n doing so, EPA commits to a process that includes public review and comme nt. EPA w ill solicit data information from the public to determine if such proposed Federal nutrient criteria for State waters are sufficiently protective of uses. This public process will help ensure that promulgated Federal w a ter quality standards are neither too stringent nor overly permissive.
B. Water Quality–Based Approach to P o llution Control The w a ter quality–based approach to w a tershed m a nagement emphasizes the overall quality of w a ter within a watershed and provides a mechanism through which the amount of pollutant entering the water body is controlled based on the intrinsic conditions of the body of water and the standards set to protect it. Afundamental step in implementing the w a ter quality–based approach is establishing procedures to assess attainment of w a ter quality standards. With respect to nutrient criteria, States should identify and adopt, as appropriate, procedures for determining the attainment status that address factors such as:

• Monitoring strateg y • Spatial and temporal extent of sampling • Frequency and duration of exceeding nutrient criteria parameters (e.g., T N , T P , chlorophyll a , algal turbidity ) 8- 4 

### Nutrient Criteria—Lakes and Reserv o irs• Minimum number of samples required • Av eraging period for combining samples to compare to nutrient criteria parameters. Additional discussion of parameters to sample, sampling frequency, and sampling locations is provided in sections B.3 and B.10 of this chapter. T hese procedures should lend themselves to be reproducible, apply consistently to the w a ters w h ere the criteria are assigned to protect the designated use, and provide clear answers to the following questions:

• What parameters do I m onitor? • Where and w h en do I sample? • H ow do I evaluate the results? The information below summarizes how the different programs fit into an overall w a ter quality control scheme and is not intended as specific implementation g u idance. Im plementation of a program should be consistent with the specific programma tic regulations and g u idance documents provided by the program office. Step 1: Identification of Impaired and Threatened Waters Step 1 of the w a ter quality–based approach to watershed m a nagement encompasses two CWA requirements: 305(b) reporting and development of a 303(d) list. Both of these activities are separate CWA elements and EPA programs. T hey are cited here to illustrate their application to components of a comprehensive coordinated EPA effort to improve the Nation’s water quality

.


### � 305(b) Water Quality Inventory The C WA establishes a process for States to develop information on the quality of the N a tion’s water resources in Sections 106(e), 204(a), 303(d), 305(b), and 314(a). U nder Section 305(b), each State or Tr ibe m u st develop a program to monitor the quality of its surface and g r ound w a ters. T he primary purpose of the State monitoring program is to evaluate attainment with w a ter quality standards. Section 305(b) requires States to provide EPA w ith a report describing the status of w a ter quality every 2 years. Lake w a ter quality assessment is an integral part of a State 305(b) report. States should report summary statistics for use support and for causes and sources of impairment of lakes as described in the mo st recent Gu idelines for Preparation of the Comp rehensive State W a ter Quality Assessments (305(b) Reports) and Electronic Updates

. For all assessed lakes, States are required to include statistics on the degree of use support (fully supporting, threatened, or impaired), the degree of use support organized by use (e.g., aquatic life, swimmi ng), and the total size of waters impaired by v arious source categories (e.g., industrial point sources, silviculture).
Th e role of nutrient criteria in the 305(b) process is that nutrient criteria establish the benchmark used to judge the degree of use support and are, therefore, an integral part of the assessment and 305(b) reporting process. I n particular, for significant publicly owned lakes, each State should include in its 305(b) report a discussion of State w a ter quality standards as they apply to lakes. N utrient criteria that have been adopted into State water quality standards are an important component of this discussion. If nutrient criteria have been developed, but have not y e t been adopted into State w a ter quality standards, they could still be utilized to classify the trophic status of the lake and discussed in the context of a m easure used to determine lake status, rather than as a w a ter quality standard (see C WA Section 314(a)(1)(E)).



### Nutrient Criteria—Lakes and Reserv o irs 8- 5

### � Section 303(d) Lists Section 303(d)(1)(A) of the CWA established the requirement for the development of Section 303(d) lists of impaired w a ters. T he Section 303(d) list is a prioritized list of w a ter quality limited w a ters and identifies waters needing T MDLs. States prepare their 303(d) lists using the information contained in their 305(b) reports, as w e ll as other existing and readily available sources of w a ter quality information. States, Territories, and authorized T r ibes m u st submit their 303(d) lists to EPA for review and approval. If

EPA disapproves a Section 303(d) list, then EPA w ill establish a Section 303(d) list for them

. Step 2: Priority Ranking and Targeting Once water bodies needing T MDLs have been identified on the 303(d) list, a State, T e rritory, or authorized T r ibe should prioritize those w a ter bodies using established ranking procedures that consider all w a ter pollution control activities within the State, Territory, or lands of the authorized Tribe. The CWA states that the “State shall establish a priority ranking for such w a ters.” T he goal of priority ranking is to focus attention on the right water bodies at the right time, while enabling a State, T e rritory , or authorized T r ibe to m ake efficient use of its available resources and meet the objectives of the C WA.
I n addition to priority ranking the waters on the 303(d) list, States, T e rritories, and authorized T r ibes mu st develop a schedule for establishing T MDLs. T he schedule is not intended to rigidly constrain the process of establishing T MDLs and should be considered an opportunity to explain how T MDLs will be completed. When synchronized with the broader planning process of a State, Territory, or authorized Tr ibe, the schedule can be the basis for a practical plan for m a naging and completing the required TM DLs. Step 3: D evelopment of TMDLs
TMDL s are w r itten plans and analyses established to ensure that the w a ter bodies will attain and ma intain w a ter quality standards. The TMDL process is an essential element of the w a ter quality–based approach to watershed management. I t links development and implementation of control measures to attainment of w a ter quality standards. Through establishment and implementation of a TMDL, pollutant loadings from all sources are estimated, links are established between pollutants and sources, and appropriate control mechanisms can be established or modified so that w a ter quality standards can be achieved. Successful use of the TMDL process to develop an effective strateg y to improve w a ter quality requires accurately defining the problem, characterizing the impaired w a ter body and all pollutants contributing to the impairment, and understanding the political and economic constraints that affect implementation and acceptance of the T MDL. Establishment of T MDL s rests on the following premises:
• T he total pollutant load to a water body is derived from point, nonpoint, and back gr ound sources.

• Pollutant loads can be transported into a water body directly through effluent discharge, band and bar erosion (in streams, river, estuaries, and lakes), recirculation (e.g., nutrients in lakes, estuaries, and wetlands), solar heating, atmospheric deposition, and g r ound water flows or indirectly by overland flow caused by snowmelt or precipitation.

8- 6 

### Nutrient Criteria—Lakes and Reserv o irs•	 T he technical approach used to develop the T MDL w ill vary according to the nature of the problem, pollutant of concern, type of water body, types and number of pollutant sources, and political and economic constraints that affect a specific w a tershed. An essential step in developing a TMDL is determining the water body target for the pollutant of concern. From a broad m a nagement perspective, the purpose of target analysis is to define the relationship between designated uses, numeric measure(s) of success, and pollutant. T he primary g oals of target analysis are to (1) clarify w hether the ultimate objective of the TMDL is to comply w ith a numeric w a ter quality criterion, comply w ith an interpretation of a narrative w a ter quality criterion, or attain a desired condition that supports meeting a specified designated use; (2) identify the water body 's critical conditions; (3) identify appropriate ways to measure progress toward achieving stated g o als; and (4) tie the measures to pollutant loading

. Th e criteria development process described in this g u idance m a nual provides the necessary information to complete the target analysis component of a T M DL. Step 4: Implementation of Controls
TM DLs are required to consider the effects of processes that contribute pollutants to a water body

. Th ese processes m ay relate to thermal discharges, critical flow conditions, sedimentation, and riparian and channel processes. Control measures to implement T M DLs, therefore, are not limited to NPDES permits, but also m ay include State, Territorial, Tribal, and local authorities and actions to reduce nonpoint source pollution.



### � NPDES Perm its
Th e CWA requires waste water dischargers to have a permit establishing pollution limits, and specifying m onitoring and reporting requirements. More than 200,000 sources are regulated by NPDES permits nationwide. NPDES permits regulate household and industrial wastes that are collected in sewers and treated at municipal waste water treatment plants. Permits also regulate industrial point sources and concentrated animal feeding operations that discharge into other w a ste w a ter collection systems, or that have the potential to discharge directly into receiving wa ters. Permits regulate discharges with the g o als of (1) protecting public health and aquatic life and (2) ensuring that every facility treats w a ste w a ter. Typical pollutants regulated by N PDES are “conventional pollutants” such as fecal coliforms or oil and g r ease from the sanitary w astes of households, businesses, and industries, and “toxic pollutants” including pesticides, solvents, polychlorinated biphenyls, dioxins, and heav y metals that are particularly harmful to animal or plant life. “Nonconventional pollutants” are any additional substances that are not conventional or toxic that m ay require regulation, including nutrients such as nitrogen and phosphorus. Discharge monitoring data for pollutants limited and/or monitored pursuant to NPDES permits issued by States, T r ibes, or EPA are required to be stored in the central EPA Permit Compliance System (PCS). Assessment of point source loadings is not a simple process of assessing PCS data, even though PCS is an important data source. T he PCS database does not provide complete information for important nitrogen sources. Most PCS nitrogen data are g e nerated by w ater quality–based permit limitations on amm onia, often applied in discharges to smaller streams. Few data exist in PCS on other forms of nitrogen, or T N ; and data for T P are not frequently found in PCS. T his situation exists largely because mo st permits do not include limits and/or monitoring requirements for nitrogen or phosphorus. T he lack



### Nutrient Criteria—Lakes and Reserv o irs 8- 7of nutrient limits and/or monitoring requirements in permits is due to a g e neral lack of State w a ter quality standards for these parameters.



### � NPDES Storm Water Permitting P r ogram Storm water runoff is one of the remaining causes of contaminated lakes, streams, rivers, and estuaries throughout the country

. Pollution in storm w ater runoff is responsible for closing beaches and shellfish harvesting areas, contaminating fish, and reducing populations of water plants and other aquatic life. H igh flows of storm w ater runoff cause flooding, property damage, erosion, and heav y siltation. Th e CWA requires EPA and States/Tribes to implement a national storm water control program to correct these problems. NPDES permits are currently required for storm water discharges from m

unicipal separate storm sewer systems (MS4s) serving populations over 100,000, certain categories of industrial activities, and construction activity disturbing m ore than 5 acres. R evisions to the storm w ater regulations published December 8, 1999 (64 C FR 68722), will expand permit requirements to MS4s in urbanized areas serving populations under 100,000 and construction activity disturbing 1 to 5 acres.



### � N onpoint Source P o llution Under Section 319 of the CWA, States ( and Territories and approved Tribes ) address nonpoint source pollution by assessing nonpoint pollution problems and sources within the State, adopting ma nagement programs to control the nonpoint sources, and implementing the m a nagement programs. Th ese programs m ay contain a v ariety of v o luntary and regulatory approaches to controlling nonpoint source pollution. Section 319 also authorizes EPA to issue g r ants to the States to assist them in implementing EPA-approved nonpoint source m a nagement programs. Since 1990, EPA has issued $1 billion in nonpoint source m a nagement g r ants to States, T e rritories, and T r ibes. I n fiscal year 2000, C ongress appropriated $200 million for the implementation of State programs.
Th e Coastal Zone Act Reauthorization Amendments of 1990 (CZ A RA) required States with approved Coastal Zone Management Programs to develop and submit coastal nonpoint pollution control program s to EPA and the National Oceanic and Atm o spheric Administration (NOAA) for approval. Th ese State programs m u st include enforceable policies and mechanisms to ensure implementation of ma nagement measures for the control of nonpoint source pollution to restore and protect coastal waters. At their discretion, States m ay elect to include freshwater areas in their nonpoint pollution control programs. Section D of this chapter provides additional detail on nonpoint source pollution m a nagement programs. Step 5: Assessment of Controls Followup monitoring is an important step in the w a ter quality–based approach. T he following are among the key factors to consider when developing a followup monitoring plan:

• Need to evaluate TMDL components . T MDL problem identification, indicators, numeric targets, source estimates, and allocations migh t need reevaluation to determine w h ether they are accurate and effective.

• Need to evaluate implementation actions . I t is often important to determine whether actions needed to achieve loading allocation w e re actually carried out and w h ether these actions w e re effective in achieving the allocations.

8- 8 

### Nutrient Criteria—Lakes and Reserv o irs• Stakeholder goals for monitoring efforts

. Watershed stakeholders often participate in followup m onitoring, and their interests should be considered.

• Existing monitoring activities, resources, and capabilities

. Analysts should identify existing and planned monitoring activities to address followup monitoring needs in concert with these efforts, particularly where a long -t erm m onitoring program is envisioned, the study area is large, or water quality agency m onitoring resources are limited. Staff capabilities and training also should be considered to ensure that monitoring plans are feasible.

• Practical constraints to monitoring

. Monitoring options can be limited by practical constraints, such as problems with access to monitoring sites and concerns about indirect impacts of m onitoring on habitat. The role of nutrient criteria in followup monitoring is as follows:
• N utrient criteria will provide the measure of success for controls.

• Process m ay need to be revisited if followup monitoring and reference condition calibration indicate criteria should be revised.

• Process m ay need to be revisited if followup monitoring indicates designated uses should be revised. C. N onpoint Source P o llution Management Nonpoint source pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage, or hydrologic modification. Technically, the term "nonpoint source" is defined to mean any source of water pollution that does not meet the legal definition of "point source" in section 502(14) of the CWA. That definition states: The term “point source” means any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, fro9m which pollutants are or may be discharged. This term does not include agricultural storm water discharges and return flows from irrigated agriculture. Although diffuse runoff is generally treated as nonpoint source pollution, runoff that enters and is discharged from conveyances such as those described above is treated as a point source discharge and hence is subject to the permit requirements of the CWA. In contrast, nonpoint sources are not subject to Federal permit requirements. Nonpoint pollution is the pollution of our Nation’s waters caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural pollutants and pollutants resulting from human activity, finally depositing them into lakes, rivers, wetlands, coastal waters, and ground waters. In addition, hydrologic modification is a form of nonpoint source pollution that often adversely affects the biological and physical integrity of surface waters. A more detailed discussion of the range of nonpoint sources and their effects on water quality and riparian habitats is provided in subsequent chapters of this guidance.



### Nutrient Criteria—Lakes and Reserv o irs 8- 91. Guidance for Controlling Nonpoint Sources of Nutrients Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters (EPA, 1993) was developed by EPA for the planning and implementation of Coastal Nonpoint Pollution Programs. The guidance focuses on controlling five major categories of nonpoint sources that impair or threaten waters nationally, and provides useful guidance for nonpoint source pollution management in both coastal and noncoastal areas. Management measures are specified for (1) agricultural runoff, (2) urban runoff (including developing and developed areas), (3) silvicultural (forestry) runoff, (4) marinas and recreational boating, and (5) channelization and channel modification, dams, and streambank and shoreline erosion. EPA also includes management measures for wetlands, riparian areas, and vegetated treatment systems that apply generally to various categories of sources of nonpoint pollution. Management measures are defined in the CZARA as economically achievable measures to control the addition of pollutants to waters, which reflect the greatest degree of pollutant reduction achievable through the application of the best available nonpoint pollution control practices, technologies, processes, siting criteria, operating methods, or other alternatives. The following section outlines some of the management measures specified in the CZARA guidance for the various types of nonpoint sources. These measures should be considered when implementing programs targeting nutrient releases into waters of the U.S. Information on specific management practices is available in Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters (EPA, 1993).



### � Agricultural Runoff

• Erosion and sediment control • Control of facility waste water and runoff from confined animal facilities • Nutrient management planning on cropland • Grazing management systems • Irrigation water management



### � Urban Runoff

• Control of runoff and erosion from existing and developing areas • Construction site runoff and erosion control • Construction site chemical control (includes fertilizers) • Proper design, location, installation, operation, and maintenance of onsite disposal systems • Pollution prevention education (e.g., household chemicals, lawn and garden activities, golf courses, pet waste, onsite disposal systems) • Planning, siting, and developing roads, highways, and bridges (including runoff management)



### � Silvicultural Runoff

• Streamside management • Road construction and management • Forest chemical management (includes fertilizers) • Revegetation • Preharvest planning, harvesting management

8-10 

### Nutrient Criteria—Lakes and Reserv o irs

### � Marinas and Recreational Boating

• Sting and design • Operation and maintenance • Storm water runoff management • Sewage facility management • Fish waste management • Pollution prevention education (e.g., proper boat cleaning, fish waste disposal, and sewage pump out procedures) 

### � Hydromodification (i.e., channelization, channel modification, dams)

• Minimize changes in sediment supply and pollutant delivery rates through careful planning and design • Erosion and sediment control • Chemical and pollutant control (includes nutrients) • Stabilization and protection of eroding streambanks or shorelines



### � Wetlands, Rip arian Areas, V eg etated Treatment S y stems

• Protect the NPS abatement and other functions of wetlands and riparian areas through v ege tativ e composition and cover, hydrolog y of surface and g r ound w a ter, g e ochemistry of the substrate, and species composition • Promote restoration of preexisting function of damaged and destroyed wetlands and riparian system s • Promote the use of engineered v ege tated treatment systems w h ere they can serve a NPS pollution abatement function 2. Nonpoint Source Management Program s I n 1987, in v i ew of the progress achieved in controlling point sources and the g r owing national awareness of the increasingly dominant influence of nonpoint source pollution on w a ter quality , C ongress amended the C WA focus g r eater national efforts on nonpoint sources. In the Water Q u ality A ct of 1987, Congress amended Section 101, “Declaration of G o als and Policy,” to add the following fundamental principle:
Itis the national policy that programs for the control of nonpoint sources of pollution be developed and implemented in an expeditious m a nner so as to enable the g o als of this Act to be met through the control of both point and nonpoint sources of pollution. More importantly, Congress enacted Section 319 of the CWA, which established a national program to control nonpoint sources of water pollution. Under Section 319, States address nonpoint pollution by assessing nonpoint source pollution problems and causes within the State, adopting m anagement programs to control the nonpoint source pollution, and implementing the management programs. Although not required, m a ny States have incorporated the m a nagement measures specified in the 1993 CZARA g u idance into their State Nonpoint Source Management Programs.



### Nutrient Criteria—Lakes and Reserv o irs 8-11Section 319 also authorizes EPA to issue g r ants to States to assist them in implementing those ma nagement programs or portions of m a nagement programs that have been approved by EPA. Since 1990, $876.5 million dollars in g r ants have been g ive n to States, T e rritories, and T r ibes for implementation of nonpoint source pollution control programs. For additional information on the Nonpoint Source Management Program and distribution of Section 319 g r ants in your State, contact your State’s designated nonpoint source agency

. For m a ny states, the nonpoint source agency is the State Water Q u ality Ag ency . H owever, in several instances, other agencies or departments are g ive n nonpoint source responsibility (see T able 8.1). Table 8.1. States f o r Which the N o npoint Source A g ency Is N o t the Water Quality A g ency
State State N o npoint Source A g ency Arkansas State Department of Soil and Water Conservation Delaware State Department of Soil and Water Conservation Oklahom a S tate Department of Soil and Water Conservation Pennsylvania State Department of Soil and Water Conservation Te nnessee State Department of Agriculture
Te xas Department of Soil and Water Conservation (for agriculture) Te xas Water Q u ality B oard (all other nonpoint sources) Virginia State Department of Soil and Water Conservation
3. Coastal Nonpoint Pollution Control Program s I n November 1990, Congress enacted the CZARA. T hese amendments were intended to address several concerns, a m a jor one of which is the impact of nonpoint source pollution on coastal waters.
T o address m o re specifically the impacts of nonpoint source pollution on coastal w a ter quality , Congress enacted Section 6217, “Protecting C oastal Waters,” which was codified as 16 USC-1455b. T h is section provides that each State with an approved coastal zone m a nagement program m ust develop and submit to EPA and the NOAA for approval a Coastal Nonpoint Pollution Control Program. The purpose of the program “shall be to develop and implement m a nagement measures for nonpoint source pollution to restore and protect coastal w a ters, w o rking in close conjunction with other State and local authorities. ” States determine how far “upstream” their coastal zone m a nagement program applies; in some instances, the entire State is covered in a comprehensive attempt to m e rge coastal zone m a nagement and nonpoint source pollution m a nagement. States and Territories with Coast Nonpoint Pollution Control Programs m ay elect to implement alternative m a nagement measures as long as the alternative measures will achieve the sam e environmental results as those described in the 1993 CZARA g u idance , as discussed previously. A listing of States with Coastal Nonpoint Pollution Control Programs is presented in Table 8.2. For additional information on the programs in these States, contact the State water quality agency.

8-12 

### Nutrient Criteria—Lakes and Reserv o irsTable 8.2. States and Territories with Coastal Nonpoint Pollution Control Programs

Alabama Maine Oregon Alaska Maryland Pennsylvania American Samoa Massachusetts Puerto Rico California Michigan Rhode Island Connecticut Mississippi South Carolina Delaware New Hampshire Virgin Islands Florida New Jersey Virginia Guam New York Washington Hawaii North Carolina Wisconsin Louisiana Northern Mariana Islands

4. Farm Bill Conservation Provisions Technical and financial assistance for landowners seeking to preserve soil and other natural resources is authorized by the Federal Government under provisions of the Food Security Act (Farm Bill). Provisions of the 1996 Farm Bill relating directly to installation and maintenance of BMPs are summarized in the following sections. For State-specific information, contact your NRCS State Conservationist’s office.



### � En vironmental C o nservation Acrea g e R e serve P rogram (E CARP ) ECARP is an umbrella program established by the 1996 Farm Bill that contains the Conservation Reserve Program (CRP), Wetlands Reserve Program (WRP), and Environmental Quality Incentives Program (EQIP). It authorizes the Secretary of Agriculture to designate watersheds, multi-State areas, or regions of special environmental sensitivity as conservation priority areas that are eligible for enhanced Federal assistance. Assistance in priority areas is to be used to help agricultural producers comply with NPS pollution requirements of the CWA and other State or Federal environmental laws. The ECARP is authorized through 2002.



### � Co nservation R e serve P rog ram (C RP) First authorized by the Food Security A ct of 1985 (Farm B ill), this v o luntary program offers annual rental pay ments, incentive pay ments, and cost-share assistance for establishing long -t erm, resourceconserving cover crops on highly erodible land. CRP contracts are issued for a duration of 10 to 15 years for up to 36.4 million acres of cropland and m arginal pasture. Land can be accepted into the C RP through a competitive bidding process w h ere all offers are ranked using an environmental benefits index, or through continuous sign-up for eligible lands w h ere certain special conservation practices will be implemented.



### Nutrient Criteria—Lakes and Reserv o irs 8-13The Conservation R e serve Enhancement Program (C RE P) is a new initiative of C RP authorized under the 1996 Federal Agricultural I m provement and Reform Act. CREP is a joint, State–Federal program designed to meet specific conservation objectives. CREP targets State and Federal funds to achieve shared environmental g o als of national and State significance. T he program uses financial incentives to encourage farmers and ranchers to v o luntarily protect soil, water, and wildlife resources.



### � Wetlands Reserve P r ogram (WRP )
Th e WRP is a v o luntary program to restore and protect wetlands and associated lands. Participants may sell a permanent or 30- y ear conservation easement or enter into a 10- y ear cost-share agreement with USDA to restore and protect wetlands. T he landowner v o luntarily limits future use of the land, y et retains private ownership. T he Natural Resources Conservation Service (NRCS) provides technical assistance in developing a plan for restoration and maintenance of the land. T he landowner retains the right to control access to the land and m ay lease the land for hunting, fishing, and other undeveloped recreational activities.



### � Environmental Quality Incentives P r ogram (EQIP )
Th e EQ IP w as established by the 1996 Farm B ill to provide a v o luntary conservation program for farmers and ranchers who face serious threats to soil, w a ter, and related natural resources. EQ I P offers financial, technical, and educational help to install or implement structural, v ege tative, and m a nagement practices designed to conserve soil and other natural resource. C urrent priorities for these funds dictate that one half of the available monies be directed to livestock -r elated concerns. Cost-sharing m ay pay up to 75% of the costs for certain conservation practices. I ncentive pay m ents m ay be m a de to encourag e producers to perform land management practices such as nutrient management, manure management, integrated pest m a nagement, irrigation water m a nagement, and wildlife habitat m a nagement.



### � Wildlife Habitat Incentives Program (WHIP)
Th is program is designed for people who want to develop and improve wildlife habitat on private lands. Plans are developed in consultation with NRCS and local Conservation District. USDA will provide technical assistance and cost-share up to 75% of the cost of installing the wildlife practices. Participants g e nerally m ust sign a 5- to 10- y ear contract with the U.S. Department of Agriculture (USD A) , w h ich requires that they m aintain the practices.



### � Fo restry Incentives Program (FIP ) Originally authorized in 1978, the FIP allows cost sharing up to 65% (up to a m a ximum of $10,000 per person per year) for tree planting, timber stand improvement, and related practices on nonindustrial private forest land. T he FI P is administered by NRCS and the U.S. Forest Service. Cost share funds are restricted to individuals who own no m o re than 1,000 acres of eligible forest land.



### � Conservation of P rivate G r azing Land This program was authorized by the 1996 Farm Bill for the purpose of providing technical and educational assistance to owners of private grazing lands. It offers opportunities for better land management, erosion reduction, water conservation, wildlife habitat, and improving soil structure.

8-14 

### Nutrient Criteria—Lakes and Reserv o irsD. A C omprehensive P r ocedure f o r N u trient Management
I n addition to regulatory assessment and source control, criteria can serve as effective scientific tools for holistic resource m a nagement. Effective programs incorporate aspects of prevention and ma intenance as w e ll as restoration. I t is important that existing high-quality w aters be m a naged wisely as a public resource and that waters whose uses are not yet threatened or impaired, but nonetheless are at risk from ongoing pollution, are identified and managed such that beneficial uses are maintained in the future. Below is a g e neric 10-step m a nagement program that originated with the Wisconsin I n land Lakes Program (Gibson et al., 1983) and has been subsequently refined as a natural resources m a nagement approach. States and T r ibes can use this procedure in addition to their established regulatory protocols. Th is approach is intended to illuminate useful steps to take to ensure responsive m a nagement; it is not intended to establish or m a ndate any procedures as part of a regulatory requirement. Management of lakes and reservoirs m ay be approached in a rational progression of actions beginning with a statement of their m a jor stressors and sy mp toms and progressing logically to a course of action and final assessment to determine the relative success of the effort. T he following sequence of steps is one illustration of this management approach. States or comm unities are encouraged to adapt this technique to suit their particular needs and expectations. Where considerable information is already available, some of these steps m ay be unnecessary, but the me thodolog y is presented here for consideration. 1. Status Identification Data used during the preliminary nutrient criteria development process and the application of the criteria will present the resource m a nager with an image of the g e neral status of a lake/reservoir and the degree of need for responsive action. T he information associated with these efforts, however, usually indicates a broad status condition, for example, high nutrient concentrations, algal blooms, fish kills, or low dissolved oxy ge n. Available data should be evaluated carefully to tease out potential relationships w ith land use practices or recent changes in practices (e.g., fishing pressure, stocking or lack thereof). In particular, previous investigations should be reviewed to m ake a preliminary determination of anthropogenic cause(s) v e rsus natural cycling of the lake or reservoir. Essentially, one needs to conduct a preliminary evaluation of readily available or on-hand lake or reservoir data to ascertain that there is indeed a problem or potential problem of cultural overenrichment and that these sources probably can be addressed to the betterment of the water body and the public good. 2. Background Investigation Give n that the initial information reveals a v i able m a nagement concern, it then becomes necessary and justifiable to g a ther as m u ch back gr ound information as possible about the water body in question. Th ere are three primary sources of such information.



### � Literature Searches
Th e initial effort here should be the “gray literature” (often internal regional State and Federal agency reports that provide specific information about that lake). Sources of such information include natural resource and fisheries agencies, forestry services, w a ter quality administrations, hydrological and ge ological survey offices, planning offices, m u lti-State or county commi ssions, and comm unity or environmental g r oups. A second source would be peer-reviewed professional literature—journals and related publications such as proceedings of conferences and sy m posiums, which m ay include specific 

### Nutrient Criteria—Lakes and Reserv o irs 8-15studies of the lake or reservoir of concern. B ut their primary v alue probably w ill be discussions of methods and techniques of investigation and management. As the management investigation progresses, these sources of information become m o re pertinent.



### � Questionnaires
I n preparing a list of agencies from which reports m ay be solicited, the names of key personal contacts also should evolve. T hese contacts are the biologists, chemists, specialists, academics and resource m a nagers, and citizen activists m o st familiar with the lake(s) of concern. A s the literature and baseline data are reviewed, particular questions should develop, the answers to w h ich will provide a fuller understanding of the resource and lend direction to the investigation and eventual m a nagement plan. Particularly helpful will be an understanding of the historical antecedents of the present status of the lake or reservoir.
A standardized questionnaire can be prepared listing concerns such as the availability of any reports or data or understanding of the history of development in the watershed, perhaps including industries, agricultural practices, or development and structures associated with the lake. Particular episodes m ay be noted for comme nt in the questionnaire, such as fish kills, algal blooms, or spill events, as w e ll as historical problems, such as septic tank problems, agricultural runoff, erosion problems, or development concentrations. All discharge sites should be documented, such as waste water treatment plants, drains, concentrations of cottages with onsite waste water treatment, m arinas, m a jor road crossings, and tributaries potentially bearing loadings of sediments or nutrients. Problem land use areas along the shore also should be noted, for example, degraded wetlands, lobes of the lake or reservoir where blooms or fish kills regularly occur, or areas w h ere aquatic macrophytes have recently expanded or contracted. In addition, it is helpful to include a large, fairly detailed line drawing of the lake/reservoir and its watershed that the respondent m ay use to locate and identify particular observations.
If

at all possible, the questionnaire should be limited to no m o re than two pages of questions, including space for answers plus the line drawing . Q uestions should be direct and concise. D etermine exactly w hat you w i sh to learn and ask questions specifically related to this information. O pportunities for additional comments should be restricted to one open question at the end of the questionnaire.
T o get the best response to a questionnaire, the potential respondents should be called first to confirm the names on the m a iling list. T hey should be advised of the nature of the study and their cooperation then requested. Other potential respondents m ay be identified through these calls. I f a large survey is necessary, this preliminary step m ay not be possible. However, m o st such regional inquiries are usually to no m o re than 50 specialists, and the additional information g a ined is well worth the telephone calls.



### � Interview s By this point in the back gr ound investigation process, the key people to contact for detailed information should be evident. T heir names will have come up in conversations and on reports, and they w ill be the people providing the m o st helpful responses on the questionnaires. Other v a luable contacts are the USDA Cooperative Extension Service agents for the counties in which the lake/reservoir is situated, county planners, and long -t erm residents and fishermen of the area. Th eir anecdotal information can be invaluable and helps add perspective to other sources of data.
8-16 

### Nutrient Criteria—Lakes and Reserv o irsTh e basis for the interviews should be to assess the questionnaire data already g athered. T he interviews should clarify and elaborate on basic information g e nerated by the questionnaire. T he interview is also the means by which apparent contradictions in perceptions or observations m ay be at least partially resolved. I t should be noted that many people are uncomfortable with recorded interviews; note-taking is often a m o re complimentary and less intimidating way to record information. I n any case, imme diately after each interview, a record of answers and observations should be prepared w h ile the impressions of the interview are still fresh.
Th e compiled information from the back gr ound investigation will further clarify the initial problem statement. I t should help resolve any ambiguities about the dynamics of the lake/reservoir and the human comm unity . I n addition, it should clearly define areas w h ere m o re definitive, primary data collection is required to clearly understand the nutrient problems of that particular water body and provide direction for the subsequent m a nagement project. 3. Data Gathering and Diagnostic Monitoring Data obtained during the nutrient criteria development process is the m a instay of the database to be prepared for any subsequent investigation. T he intent of that survey was to develop a reasonable imag e of the status of the lake/reservoir. Diagnostic monitoring should expand on that structure and extend the understanding from status of the resource to a diagnosis of causes of the overenrichment. For example, wh ere three reaches of a lake/reservoir m ay have been sampled and two identified as being of concern, now the tributaries and other higher order streams m u st be sampled to further reduce the area to locations of probable loadings. While earlier sampling was to portray the trophic state of the lake or reservoir, these sample sites should be directed specifically toward near-shore areas of potential loadings, tributaries, and portions of the tributaries where loadings m ay originate.
Di agnostic monitoring supports the identification of w a ter quality problems and helps to develop an appropriate m a nagement plan. General g u idelines for conducting diagnostic monitoring are provided below.



### � P arameters To Sample Diagnostic monitoring is conducted after nutrient criteria have been established. I t migh t not be necessary, therefore, to sample some parameters that are not related to the criteria. Diagnostic sampling for nutrients requires an estimation of nutrient loading and sources. Major potential sources of nutrients (e.g., tributary streams, g r ound w a ter flow, runoff, illegal discharges, atmospheric deposition) should be identified and sampled in such a way as to obtain an estimate of annual loads from each source. For me thods and design considerations, see O l em and Flock (1990) and Wedepohl et al. (1990).
Th e variables and techniques employed in the preliminary survey should be reviewed for adequacy and either repeated or aug m ented. T he manager should not eliminate the basis of the original classification by dropping any v ariables or stations at this point. D ocumenting potential success or failure of the subsequent m a nagement program w ill require “before” and “after” databases, and the initial survey design should be modified only after careful consideration and due attention to reestablishing the baseline survey

.



### Nutrient Criteria—Lakes and Reserv o irs 8-17Flow measurements are also an essential part of this survey . I f nutrient concentrations are to be m eaningfully compared and loading estimates m a de, cross-sectional areas and flow rates for all tributary streams and discharges m u st be included in the survey design. T hese measurements m u st be m a de or extrapolated each time w a ter quality samples are collected. Without this information, it will be difficult or impossible to assign priorities to v arious loading sources identified in the investigation.



### � Sampling Frequency Sampling frequency w ill increase for diagnostic monitoring because the sample population is now an individual lake. Sampling should occur repeatedly during the g r owing season to be able to precisely characterize individual lakes as w e ll as discharges and loadings. Statistical power analysis can be used to determine the appropriate sample size based on the purpose of the sampling and the acceptable error (see Chapter 9).
I n addition to expanding the number of stations and parameters to accomm odate diagnostic determinations, the survey design should address the temporal v ariable by sampling these stations during each season of the year at times calibrated to that particular climate and locale. A ccomm odation m ay need to be m a de for periods of base flow, m a ximum runoff, turnovers, periods of m a ximum and mi nimum productivity, and, in some instances, migr atory patterns of fish or waterfowl. Seasonal changes in land use such as peak summ er or winter vacation periods, agricultural applications and harvests in the w a tershed, and seasonal comme rcial or industrial activities also should be addressed.
T o separate signals from seasonal noise, it m ay be necessary to g a ther survey data for 2 or m o re consecutive years to strengthen data assessments. Such assessments will require a robust statistical evaluation of the data; this element should be incorporated into the study design at the outset. As with the initial survey design, the preliminary statistical tools chosen m ay be carried into this subsequent design as well. Care should be taken to address the need for replicate sample collections to ensure representative sample design and confidence in the results to be obtained. Early inclusion of a skilled environmental statistician on the m a nagement team is advisable.



### � Sampling Location
If

turbidity, nutrients, and algae are known to be v ariable across the surface of a lake, then m u ltiple sample sites are required. I f g r adients are known to occur, as in m a ny large reservoirs, then sampling should be stratified by z ones. For example, in a reservoir one could define the three reservoir zones (riverine, transitional, lacustrine) as sampling strata and take two or m o re samples from each zone. The exact number of sampling sites in a lake or lake zone is determined by the spatial v ariability of nutrients, turbidity, and chlorophyll and the desired precision. I n general, within a basin or reservoir z one, v ariation in time is larger than v ariation in space (Knowlton and Jones, 1989). T hus, chlorophyll samples taken 2 weeks apart m ay differ by severalfold, but samples taken on the same day 500 me ters apart are likely to differ m u ch less. Depending on the questions being addressed in the investigation, spatially composite samples m ay be m o re cost-effective than separate samples from several sites in a lake (see Olem and Flock [1990] and Wedepohl et al. [1990]).
Th e design and placement of these sample stations will rely heavily on the land use information developed from the back gr ound investigation. T he overall premise should be to bracket suspected sources of nutrient loadings in the tributaries and near-bank areas so parcels can be either selected or eliminated as potential candidates for m a nagement attention.
8-18 

### Nutrient Criteria—Lakes and Reserv o irs4. Source Identification
Th e cumulative information g a thered should now provide a clear image of the state of the lake or reservoir, the m o st likely sources of nutrient loadings or related degradation, and their relativ e contributions to the problem . I t is important to note that this process reveals only local sources of the overenrichment. Atmospheric deposition of nitrogen compounds and other broad-scale impacts beyond the watershed scale are not specifically addressed and m u st be assumed as essentially an environmental constant. With all the risks this entails, it is probably not an undue assumption, because such remediation is probably beyond the scope of m o st nutrient m a nagement projects employing this g u idance.
Th e problems to be identified are likely to be as diverse as the geolog y , hydrolog y , and land use practices of the lake/reservoir and watershed. Ty pical elements include sediment resuspension and nutrient re-release; biotic imbalances affecting nutrient utilization by overfishing or stock mi smanagement; discharge of excess nutrients directly to the lake or reservoir by waste water treatment plants, storm w ater runoff, or failing septic systems; and runoff from subdivisions, farms, log g ing operations, g o lf courses, and shopping centers. Other problems have included concentrations of migr atory and resident w a terfowl contributing to an excess of nutrients, removal or filling of bank areas and w e tlands that once intercepted nutrient runoff, herbicide applications that killed macrophytes and promoted nuisance algal blooms, and chronic low dissolved oxy ge n problems attendant to overenrichment and v ege tative imbalances. Any combination of these in situ and land use problems are potential causes of the cumulativ e overenrichment problem

. Management planning requires identifying first the loading sources and, second, of those sources, the ones that are m o st significant. Proximity of a source to the lake or reservoir (or in some cases, the ubiquitous nature of a source throughout the watershed such as subdivision or farm runoff), the relative loading estimate of that source, and the likelihood of successful remediation are the key factors in deciding w hich problem sources are priorities for inclusion in a m a nagement plan. Loading estimation models such as those developed by Vollenweider and by Dillon and Rigler, the R eckhow -S impson model, and B A THTU B by Walker are v a luable for estimating the relativ e significance of v arious nutrient sources in the watershed with respect to the likely response of the lake. Ch apter 9 describes m a ny of these models and their relative utility

. Modeling permits the m a nager to try out v arious preliminary m anagement scenarios and combinations of m a nagement techniques to estimate their likely effectiveness. Some of these options for consideration in a lake nutrient m a nagement plan are discussed in the next step. 5. Management Practices for Nutrient Control Once the m a jor sources of concern are identified and agreed on by the m a nagement planners, remedial measures appropriate to these sources m u st be identified. Management practices are well defined and documented for a v ariety of land uses in EPA g u idance documents, USDA m a nuals, U.S. Forest Service m a nuals, and urban land use planning g uides. T he resource m a nager should study these references for likely approaches to consider and then consult regional experts in each of the subject land uses for qualification and other sug g ested management practice recomm endations. Bringing these specialists together as a small work gr oup is an effective, although sometimes contentious, way to develop the m o st technically sound approaches to these chosen problems.



### Nutrient Criteria—Lakes and Reserv o irs 8-19Fitting the v arious components together in a comprehensive m a nagement plan is challenging . I t calls for both imagination and a sense of cooperation. Usually no one approach stands out as the obvious best choice. I nstead, two or three permutations of several g e nerally agreed on B M Ps will evolve from the planning sessions. Selection of the optimal approach—or m o re likely, the best candidates—should first involv e a careful assessment by the planning work gr oup and then consultation with all elements of the watershed comm unity, both organized interest g r oups and private landowners. T he first phase of this selection process should include review by a threefold framework of evaluation. T his approach was developed by the Department of Resource Development at Michigan State University (Figure 8.2 ) T he premise behind this approach is essentially that the m o st effective and achievable m a nagement plan should be able to address three elements of practicality :

Fi gure 8.2. “Threefold f r amework” of evaluation.

• No resource or environmental m a nagement plan should even be considered unless it is scientifically v alid. T he technolog y proposed should be based in sound science and tested and v alidated. No attempt to manipulate the environment and peoples 

### � land use prerogatives should be m a de unless it can be demonstrated in advance that the technique is reliable or at least that the risks are quantifiable and understandable.
•	 T he approach proposed should be cost-effective and affordable by the comm unity

. EPA has a series of economic tests that can be applied to standards development that can be adapted to m anagement planning for a similar result. Among technically sound plans to achieve desired go als, the m o st cost-effective plans (typically those with elements that have the g r eatest benefit-cost ratios) are m o st likely the easiest to implement and the m o st likely to satisfy the public interest.
•	 T he management plan should have an adequate degree of social and political acceptability . T hat wh ich is eminently rational and cost-effective m ay conflict with the collective v a lues of m o st of the local public. T his is particularly important if taxing or regulatory actions are part of the ma nagement plan. Any form of regulation or permit action taken in addition to existing requirements should always be carefully researched through the responsible local, State, and 8-20 

### Nutrient Criteria—Lakes and Reserv o irsFederal agencies as to the justification, efficacy, lead time required, and likely effects on v arious seg ments of the comm unity

. Th e resource m a nager most likely to achieve success will consider and responsibly address each of these three elements. All candidate alternatives should be evaluated in this m a nner and revised as necessary . T his not only g enerates the optimal plan (or plans where competing but different strengths are evident), but it documents the rationale for that decision essential to public review before the final selection is m a de.

In vo lving the public in the process throughout is highly beneficial, and meetings or advisories to all potentially interested parties should be regularly provided, if not from the outset of the availability of definitive data, then certainly before the time w h en plan selection and approval are needed. Abalance in public information m u st be struck between m aki ng announcements too early, which m ay needlessly arouse people before sufficient information has been g e nerated, and m aki ng announcements too late, wh ich m ay lead to suspicions of keeping the public in the dark

. 6. Detailed Management Plan A detailed management plan should include all 10 steps of the process described here. T he first fiv e steps are necessary to g e t to the design of the plan, but they should also be included so that anyone reading it will understand w h at has gone into the effort. Natural resource m a nagement efforts can include these three elements: education, financing, and regulation. A ny resource m a nagement tool will fall into one of these broad categories, and it is good to try to initiate the v arious techniques in the same order as they are presented here. First, you should start with relatively low-cost information and education efforts to acquaint people with the problem and how y ou propose to address it—and not coincidentally, to g e t their sug ge stions and perceptions of the issue and approach. A good educational effort should be the incentive for v o lunteer agreements and cooperative action. A g rant-in-aid or other assistance is often the key element necessary to further encourage individuals to adopt appropriate local lake protection practices. Regulatory actions are necessary and appropriate when m a ndated by law, where cooperation and compliance are unlikely to occur otherwise, and when v o luntary efforts have clearly not been successful. 7. Implementation and Com m unication
I n addition to the discussion about comm unication above, the progress review periods during the ma nagement project are opportunities to provide reports to administrators, other involved agencies, politicians interested in the project, the general public and landowners, and other interest g r oups. Such reports should be brief and candid. T hey w ill be part of the public record so all parties are properly informed, help avoid the postproject cry of not being adequately advised of what was g o ing on, and document the techniques and m e thods used for future consideration. Regional public meetings and hearings are an excellent w ay to accomplish this comm unication. T he mo re controversial an issue, the m o re this is necessary and the m o re important it is to listen carefully to the responses and to objectively weigh appropriate adjustments to the plan. T o charge ahead in the face of significant opposition without evaluating the consequences is folly . T his is especially true if a chang e to a stepwise approach in the m a nagement plan with additional public consultation would still achiev e the same objective. 

### Nutrient Criteria—Lakes and Reserv o irs 8-218. Evaluation Monitoring and Periodic Review
Th e m a nagement plan should always include “before,” “during,” and “after” w a ter resource quality m onitoring to demonstrate the relative response of the system to m a nagement efforts. T his is why the initial survey stations should generally be maintained and expanded. Such monitoring data are important as a benchmark for evaluating progress and are an important component in the requisite progress reports described above. The change or lack thereof of the lake or reservoir is the ultimate determination of ma nagement success. Th ese built-in monitoring schedules should include seasonality and periodic data assessment intervals for m a nagement review to permit responses to changing circumstances, modifications of me thods, schedules, and changes of emphasis as needed. 9. Completion and Evaluation Management projects are frequently planned, initiated, and concluded, with new initiatives undertaken to meet pressing schedules, without sufficiently evaluating w hat w a s initially accomplished. Revi ew of the progress reports, of the original objectives, and of the monitoring data will reveal wh ether the lake or reservoir trophic state w a s successfully protected or improved. J ust as important, this evaluation provides the documentation necessary to determine if m e thods and techniques attempted in this instance can be applied elsewhere, perhaps with modification. A lternatively, it will also reveal if mi stakes were m a de that should be noted and avoided in future projects and perhaps that a sequel project is required to fully accomplish the original objectives. 10. Continued Monitoring of the System The database initiated and expanded in the course of the project can now be reduced to the periodic m easuring of key variables at critical times and locations. T he purpose now is to keep sufficiently informed of the status of the lake or reservoir to ensure that the protection or remediation achieved is ma intained. I f periodic evaluation monitoring indicates a return of trophic decline, intervention should be possible at an early point so that costs of preserving that which was achieved are reduced. T he evaluation and periodic monitoring steps of this process essentially close the loop. I f new issues arise, the m a nager returns to step one with a new problem statement. G eneral g u idelines associated with evaluation monitoring are provided below.



### � P arameters To Sample Each of the w a ter quality parameters discussed in the Indicators chapter (i.e., T P , T N , chlorophyll, Secchi depth, and dissolved oxy ge n) should be sampled during m aintenance monitoring

. Because the purpose of m a intenance monitoring is to determine if conditions change or if criteria are exceeded, other physical or chemical v ariables need not be measured.



### � Sampling Frequency
Sam p ling efforts for m a intenance monitoring can be adaptive and sequential, so that a certain mi nimum of information is collected at regular intervals, and if data indicate change or uncertainty, the sampling effort (in both time and space) can be increased to attempt to reduce the uncertainty

. For example, a lake in an undisturbed area could be sampled once every 5 years, from a single v i sit during an

8-22 

### Nutrient Criteria—Lakes and Reserv o irsindex period (say, spring turnover). I f results sug ge st a change in lake conditions beyond what is normally expected for a lake of its class, then additional sampling of the lake can be continued to determine if the departure from “normal” conditions is real and if it is ecologically significant. I f TP, TN , chlorophyll a , and Secchi depth relationships have been established, it m ay be cost-effective to use Secchi depth as a preliminary indicator; if a trig ge r v a lue is detected, m o re parameters would be m easured.

Th is also sug g ests different levels of maintenance monitoring, depending on existing k nowledge of a lake and expectations. Maintenance monitoring m ay be done for several purposes:
•	 R outine monitoring of a lake of known quality (i.e., has been sampled before) that is not expected to change g r eatly
• I nitial sampling of a lake of unknown quality

• Monitoring of a lake of known quality that is expected to change, as with w a tershed development or following restoration efforts
R outine monitoring of lakes of known quality is the least intensive and would typically require sampling once every several years, as in the example above. I nitial sampling of a lake of unknow n quality requires the same sampling effort, and parameters, as the classification survey

. Monitoring a known lake that is expected to change or suspected to have changed requires m o re intensive effort, typically an increase in sampling frequency to several times during the g r owing season to obtain seasonal averages of indicator v a lues.
Th e actual frequency of sampling should be determined by the number of samples required to detect an ecologically relevant change in the indicators of a single lake, resources available for the monitoring program, and amount of time for a change to be detected. T hese considerations require power analysis using existing or preliminary data (see Chapter 9), and tradeoffs of desired significance level, desired power, desired effect size that is detectable, ecological significance, and m o st important, resources (labor and money) available for the monitoring program

.


### � Sampling L o cation For routine monitoring, it is recomme nded that the sampling locations be the same as for the classification survey, whether a single mi dlake site, a spatially composite sample, or separate sampling sites within a lake.
E. Resources Listed below are selected publications concerning lake and watershed m a nagement and protection.

• Cooke, GD; W e lch, EB; Peterson, SA; Newroth, PR. 1993. Restoration and management of lakes and reservoirs, 2nd ed. Boca Raton: Lewis Publishers. Th is book is a current description of effective in-lake m anagement techniques and approaches. It is an extensive account of the state of the art and science of in-basin lake m a nagement techniques.



### Nutrient Criteria—Lakes and Reserv o irs 8-23• Sharpley, AN ( e d)

. 2000. Agriculture and phosphorus management: the Chesapeake Bay. Boca Raton: Lewis Publishers Th is text is a compilation of conference proceedings describing nutrient dynamics in the watershed of Chesapeake Bay with emphasis on agricultural loadings and practices. Althoug h directed at an estuarine environment, m u ch of the agriculturally based nutrient information has broad application.

• U.S. Environmental Protection Agency

. 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters. (EPA-840-B-92-002) The EPA Office of Water produced the 1993 guidance document to support the Coastal Zone Act Reauthorization Amendments of 1990. This document describes several management measures to control nonpoint sources of pollution, including nutrients.

• U.S. Environmental Protection Agency. 1990. Monitoring lake and reservoir restoration: technical supplement to lake and reservoir restoration guidance manual. (EPA-440/4-90-007) This document focuses on effective w a ter quality m onitoring techniques to assess status and trends of inland lakes and reservoirs. I twas prepared by a panel of highly experienced State lake ma nagement specialists and emphasizes practical and cost effective measurement techniques.

• U.S. Environmental Protection Agency

. 1995. Wa tershed Protection: A Project Focus (EPA 841-R-95-003) Th is document focuses on developing watershed-specific programs or projects. I t provides a blueprint for designing and implementing watershed projects, including references and case studies for specific elements of the process. The document illustrates how the broader principles of watershed m a nagement

— including all relevant Federal, State, T r ibal, local, and private activities—can be brought to bear on w a ter quality and ecological concerns.

• U.S. Environmental Protection Agency

. 1995. Wa tershed Protection: A Statewide Approach (EPA 841-R-95-004) This document is primarily designed for State w a ter quality m anagers. Acomm on framework for a statewide watershed approach focuses on organizing and m a naging a State 

### � s m a jor wa tersheds (called basins in this document). I n this statewide approach, activities such as w a ter quality m onitoring, planning, and permitting are coordinated for m u ltiple agencies on a set schedule within large watersheds or basins.

• U.S. Environmental Protection Agency

. 1997. Monitoring Consortiums: A Cost-Effective Means to Enhancing W a tershed Data Collection and Analysis (EPA 841-R-97-006) Th is document addresses coordination in watershed monitoring

. As demonstrated in the document's four case studies, consortiums can stretch the monitoring dollar, improve cooperation among partners, and increase sharing of expertise as well as expenses of data collection and ma nagement.

• U.S. Environmental Protection Agency

. 1997. Land Cover Digital Data Directory for the United States (EPA 841-B-97-005) Land cover, w h ich is the pattern of ecological resources and human activities dominating different areas of the earth's surface, is one of the m o st important data sources used in w a tershed analysis and the m a nagement of water resources throughout the country . T he 75 land cover data summaries in this directory include contact information to assist readers who m ay want to acquire copies of the digital data for their own use.
8-24 

### Nutrient Criteria—Lakes and Reserv o irs• U.S. Environmental Protection Agency

. 1997. Designing an Information Management System for W a tersheds (EPA 841-R-97-005) Th is document is an introduction to the information m a nagement responsibilities and challenges facing any watershed g r oup. T he document reviews the fundamentals of identifying information m anagement needs, integrating different databases, evaluating hardware and software options, and developing implementation plans.

• U.S. Environmental Protection Agency

. 1997. Information Management for the W a tershed Approach in the Pacific N o rthwest (EPA 841-R-97-004) This document centers on a series of interviews with leaders and key participants in the statewide wa tershed approach activities in the State of Washington. T he document review s Washington 

### � s statewide w a tershed activities in case study fashion.

• U.S. Environmental Protection Agency

. 1998. Inventory of W a tershed Training Courses (EPA 841-D-98-001) Th is inventory provides one-pag e summ aries of 180 watershed-related training courses offered by Federal and State agencies; it also lists resource professionals in the private sector.

• U.S. Environmental Protection Agency

. 1997. Statewide W a tershed Management Facilitation (EPA 841-R-97-011) This document addresses statewide w a tershed m a nagement and the process of facilitating the development or reorientation of statewide watershed programs. I t includes state case histories.

• U.S. Environmental Protection Agency

. 1996. Wa tershed Approach Framework (E PA 840-S-96-001) Th is publication revisits and updates EPA's v i sion for a watershed approach, first explained in a 1991 document entitled “Watershed Protection Approach Framework.” I t describes watershed approaches as coordinating frameworks for environmental management that focus public and private efforts to address the highest priority problems defined g e ographic areas, involving both gr ound and surface water flow

.

• U.S. Environmental Protection Agency

. 1997. Top 10 W a tershed Lessons Learned (EPA8 40-F-97-001) Watershed work has been g o ing on for m a ny y ears now, and this 60-page document summarizes the top lessons that have been learned by w atershed practitioners across the U n ited States regarding what works and what does not.

• U.S. Environmental Protection Agency

. 1999. Catalog of Federal Funding Sources for Wa tershed Protection ( s econd ed.) (EPA 841-B-99-003) Many sources of Federal funding are available to support different aspects of watershed protection and specific types of local-level watershed projects. T his document presents information on 52 Federal funding sources (grants and loans) that m ay be used to fund a v ariety of watershed projects.

• U.S. Environmental Protection Agency

. 1997. Wa tershed Training Opportunities (EPA 841-B-97-008) Th is is a 22-page booklet developed to highlight w a tershed training opportunities offered by EPA 's O ffice of Water and the Watershed Academ y. I t covers training courses and educational ma terials on watersheds produced throughout the EPA Office of Water. 

### Nutrient Criteria—Lakes and Reserv o irs 8-25• U.S. Environmental Protection Agency

. 1997. Stream Corridor Restoration: Principles, Processes and Practices (EPA 841-R-97-011) Th is document is a practical reference m a nual and logical framework to help environmental ma nagers recogniz e stream restoration needs and design and implement restoration projects.

• U.S. Environmental Protection Agency

. 1997. Protocol for Developing N u trient TMDLs (E PA 841-B-99-007) Th is protocol is an organizational framework for the T M DL development process for nutrients. It leads to an understandable and justifiable T M DL.

8-26 

### Nutrient Criteria—Lakes and Reserv o irs

# CHAPTER 9 A. Introduction B. Review of Lake/Reservoir Eutrophication Modelin g F ra mewo rk C. Model Use f or Aidin g in the Establishment of 

# Modeling Tools Reference Conditions D. Wa ter s hed Mana g ement Models

A. Introduction
A v ariety of models are available that are related to assessment of nutrients in lakes and reservoirs. Th e use of models can include a w i de range of applications, from evaluating in-lake trophic conditions to estimating loading from an entire w a tershed. A fter providing a brief review of lake and reservoir m odeling frameworks, this chapter focuses on two areas where modeling can be applied with regard to the development and m a nagement of nutrient criteria. T he first area is prediction or extrapolation of reference conditions, w h ich are used as a basis for setting nutrient criteria (see C h apter 6). The second area deals with the use of models as tools for m a nagement in the watershed once nutrient criteria hav e been established and implemented (see C h apter 8). R eaders are encouraged to consult the following references for m o re in-depth information on lake and reservoir modeling : • C hapra, S. 1997. Surface W a ter-Quality Modeling

. McGraw -H ill Publishers, I n c. •	 T homann, R.V., and J

. A. Mueller. 1987. Principles of Surface W a ter Quality Modeling and Control

. Harper & Row, New York.
•	 U .S. Environmental Protection Agency

. 1990. The Lake and Reservoir Restoration and Guidance Manual . EPA/440/4-90/006. Office of Water, Washington, DC.
•	 U .S. Environmental Protection Agency

. 1997. Compendium of Tools for W a tershed Assessment and TMDL Development

. EPA /841/b-97/006. Office of Water, Washington, DC.
B. Review of Lake/Reservoir Eutrophication Modeling F r ameworks Modeling framework s to simulate the impact of nutrients on the quality of standing w aters can be divided into three g e neral categories: • Emp irical models • N utrient budget/mass balance models • N utrient food chain models
Th ese models are listed in order of increasing complexity and higher mechanistic definition. It should be stressed that higher complexity does not necessarily connote inherent superiority

. 1. Empirical Models Empirical models are g r aphical approaches based on measurements from m any lakes and reservoirs. Th e pioneering w ork in this area was performed by Vollenweider (1968, 1976) and Dillon and R igl er



### Nutr i ent Criteria—Lakes and Reservo ir s 9- 1(1974). Other investigators, notably Rast and Lee (1987) and Reckhow (1977), extended and broadened the approach. Empirical models can be loosely divided into two categories: (1) phosphorus loading plots and (2) trophic parameter correlations. As depicted in Figure 9.1, phosphorus loading plots typically g raph lakes on a two-dimensional space with the log of the areal phosphorus loading on the ordinate and the log of hydrogeometric parameters on the abscissa. For example, Figure 9.1 has the log of ratio of the lake 

### � s m ean depth to its residence time as the abscissa. Lines are then superimposed to demarcate different trophic states. T he plots then can be used to predict the trophic state of a lake based on its loading and hydrogeometry

. Itshould be noted that a number of investigators (e.g., Thomann, 1977; Chapra and T arapchak, 1976; Vollenweider, 1976) have illustrated how such plots can be related to and derived from the simple phosphorus budget models to be described in the next section. T hus, aside from predicting trophic state, the plots can be structured to predict in-lake T P concentration as a function of loads.
Tr ophic parameter correlations are usually log

- log plots relating two trophic parameters. For example, Figure 9.2 shows a correlation between chlorophyll a and T P concentration. Empirical models have several strengths and weaknesses. T heir strengths are:
• T hey are extremely easy to use. • T hey provide a quick m eans to identify “ outlier” lakes. •	 I f they are based on regional or local databases of relatively homogeneous populations of lakes (e.g., lime lakes in northern Michigan), they are capable of producing adequate predictions.

Figure 9.1. Vol lenw ei d er’s l oad in g p l ot (1975).

9- 2 

### Nutrient Criteria—Lakes and Reserv o irsFig u re 9.2 . Relatio n ship between chlorophyll and phosphorus. T rophic parame ter correlation s are usua lly lo g-log p lots relatin g tw o tro ph ic p arame ters. Fo rex amp le, Fig ur e 9 .2 sh ow s a correlatio n be tween ch lorophy ll a an d TP concentration

.

Th eir primary weakness relates to the fact that, if based on g l obal data (e.g., north temperate lakes), they tend to have v e ry large standard errors of prediction. Unfortunately, the plots often are presented in a manner that does not m ake this uncertainty explicit. Hence, naive users can develop predictions and are unaware that their results m ay have substantial errors. A number of investigators, notably Reckhow and Walker, have worked to include uncertainty estimates with empirical model predictions.
I n summary, although they have some utility, empirical models (and particularly those based on gl obal data) do not usually have the required precision upon which high-cost decisions can be m a de. As such, empirical models should be relegated to broad screening applications and for identifying atypical lakes. However, they m ay have sufficient precision if developed and applied for regional populations of lakes and reservoirs. 2. Nutrient Budget/Mass Balance Models Early on (e.g., Vollenweider, 1969), it was recognized that simple m a ss balance models could provide similar predictions to phosphorus loading plots. T hese models do not attempt a detailed characterization of the division of phosphorus within the water column. Rather, they focus of characterizing m ajor inputs and outputs to predict the long -t erm trends of a lake 

### � s response to loading changes.



### Nutrient Criteria—Lakes and Reserv o irs 9- 3Th e simplest example of a T P budget model was developed by Vollenweider (1969) and modified by Chapra (1975):



### W V dp
= − Q p

− vA p dt
wh ere V = volume, p = TP concentration, t = time, W = loading , Q = outflow, v = an apparent settling ve locity, and A = surface area. A s depicted in Figure 9.3a, the key feature of this model is the simple way in which it characterizes the input-output terms for T P. I n particular, it attempts to characteriz e sedimentation losses as a simple one- way settling of TP.
As w ith loading plots, steady

- state solutions can be developed by setting the derivative to 0 and solving for p = W /(Q + vA ). I f levels of T P can be associated with trophic state, the model can be used to determine the loading required to m a intain a particular lake at a desired quality in a fashion similar to the loading plots. T he model also provides a framework to determine the temporal response of a lake to loading changes. T hus, it has the advantage over loading plots in that system dynamics can be characterized. Phosphorus budget models have been improved in several ways:

• For incompletely mixed systems, the lake can be divided into a system of interconnected well- mi xed systems. T his can be done horizontally or vertically

. For example, Chapra (1979)used two mass balances to characterize a lake with a m ajo r embay ment. I n a similar ma nner, O 

### � Melia (1972) and others have v e rtically divided the water column of thermally stratified lakes into surface and bottom layers

Fig u re 9.3 .	 Two phosphorus budget m o dels: (a ) characterizes sedimentatio n a s a simple o n e-w ay loss t o t he sediment s a nd ( b) includes sediment f eedback

9- 4 

### Nutrient Criteria—Lakes and Reserv o irs• Efforts have been m a de to better characterize sediment

– water interactions. Chapra and Canale represented a lake and its underlying sediments as a two-layer system (Figure 9-3b). Along with phosphorus settling, this model also allows sediment feedback . A simple oxy g en model is used to simulate hypolimnetic anoxia, which trig ge rs sediment release of T P into the overlying waters. Th is mechanism is significant, because sediment feedback can retard the recovery of lakes after TP load reductions. •	 Hy brid models have been developed that use mass balance and m u ltiple seg m ents to characteriz e transport, but to quantify kinetics, they use empirically derived relationships. Walker 

### � s BAT HTUB m odel for reservoirs is a good representative of this type.
I n summary, the phosphorus budget models use simple m a ss balance to characterize how phosphorus levels change in lakes in response to load modifications. T hus, the assumption is made that “as g o es phosphorus, so g o es eutrophication.” Such models can be useful for simulating the long -t erm trends in the quality of phosphorus-limited lakes and reservoirs. 3. Nutrient/Food Chain Models
I n contrast to the budget models described above, nutrient/food chain models attempt to m echanistically characterize the partitioning of m a tter within the lake on a seasonal timeframe. These m odels were first developed in the 1970 

### � s to expressly address the impact of nutrients on natural waters (e.g., Chen, 1970; Chen and Orlob, 1975; Di T o ro et al., 1971; Canale et al., 1974). T hey typically hav e a number of comm on characteristics, including transport characterization and ki netic characterization.



### � Transport Characterization An effort is m a de to characterize the internal physics of a lake or reservoir. T hus, rather than representing the lake as a single w e ll- mi xed entity, m u ltiple seg ments typically are used to model the internal physics. T he most comm on approach is to use two v e rtical layers to characterize thermal stratification. More refined v e rtical seg m entation is sometimes used to resolve hypolimnetic g r adients, particularly near the sediment–wa ter interface. I n addition, m u ltiple horizontal seg m ents are employed for incompletely mixed systems such as elongated reservoirs. T here are two ways in which the magn itude of mi xing and interflow between seg m ents is modeled:

• First, it can be treated as a model input. T his is done by specifying turbulent diffusion coefficients and interseg me nt flows. I n many such applications, the temperature distribution is also treated as a model input.

• Second, water m o tion can be calculated internally using energ y and m ome ntum balances. T hus, a separate hydrodynamic model is used to supply the physics. I n some cases, temperature is calculated as a part of the hydrodynamic simulation.



### � Kinetic Characterization Matter in the lake is divided into several forms of nutrients and a food chain. A typical example of how this is done is shown in Figure 9.4. Several nutrients are typically included. Hence, the model is capable of simulating m ultiple nutrient limitation. A s shown in the figure, phosphorus and nitrogen are the comm on choices. T hese usually are divided into available and unavailable components. T he latter can be broken down further, for example, into dissolved and particulate fractions. 

### Nutrient Criteria—Lakes and Reserv o irs 9- 5Th e food chain shown in the figure consists of a single algal compartment, along with two z ooplankton compartments. Algae g r owth is calculated as a function of temperature, light, and available nutrient concentrations. All other rates are temperature dependent. All three organisms experience respiration/excretion losses. A s shown in the figure, these can be released to either the available or unavailable nutrient pools. Grazing is inefficient, with a fraction of the g r azing egested to the unavailable pools.
Th is framework can be simplified by dropping a nutrient (usually nitrogen). I t is m o re likely to be ma de m o re complicated by adding nutrients (e.g., silicon) or m aki ng them m ore refined (e.g., breaking the unavailable components into dissolved and particulate fractions). T he food chain can be made m o re complex by breaking the single algal compartments into components (e.g., diatoms, g r eens and blue- g reens). Similar refinements can be m a de to the zooplankton. When this is done, feeding preferences usually m ust be specified. I t should be noted that other v ariables such as oxy ge n and pH can be integrated into these frameworks. I n these cases, it is usually necessary to simulate organic carbon.
Th is framework can be simplified by dropping a nutrient (usually nitrogen). I t is m o re likely to be ma de m o re complicated by adding nutrients (e.g., silicon) or m aki ng them m ore refined (e.g., breaking the unavailable components into dissolved and particulate fractions). T he food chain can be made m o re complex by breaking the single algal compartments into components (e.g., diatoms, g r eens and blue- g reens). Similar refinements can be m a de to the zooplankton. When this is done, feeding preferences usually m ust be specified. I t should be noted that other v ariables such as oxy ge n and pH can be integrated into these frameworks. I n these cases, it is usually necessary to simulate organic carbon.

Figure 9.4. Kinetic segm en tation .

9- 6 

### Nutrient Criteria—Lakes and Reserv o irsC. Model U s e f o r A i ding in the E s tablishment of R eference C o nditions 1. Morphoedaphic Index
Th e m o rphoedaphic index (MEI) is the ratio of total dissolved solids in lake water to the mean depth of the lake. Early studies sug ge sted that the MEI was correlated with fish and phytoplankton production of lakes (e.g., Rawson, 1952; Ryder, 1965; Oglesby, 1977). T he MEI approach was extended by V ighi and C h iaudani (1985) to predict phosphorus concentrations resulting from natural back gr ound loading in undisturbed watersheds. T his prediction can, therefore, be used to predict reference phosphorus concentrations. Using data from 53 cool-temperate lakes of North America and Europe, with negligible anthropogenic phosphorus input, Vig h i and Chiaudani (1985) developed a regression equation predicting m ean phosphorus concentration from the MEI, where MEI was calculated using either alkalinity or conductivity as a surrogate for total dissolved solids: Log [P] = 1.48 + 0.33 Log MEI alk ; r = 0.83 Log [P] = 0.75 + 0.27 Log MEI cond ; r = 0.71.
An alysis of covariance showed no significant differences between the European and N o rth A m erican lakes, and lakes with known anthropogenic phosphorus inputs all fell above the estimated regression line for undisturbed lakes (Vighi and Chiaudani 1985). T his MEIm odel is used by the Minnesota Pollution Control Agency (MPCA) to estimate back gr ound phosphorus concentrations and develop reference conditions for oligotrophic and me sotrophic lakes (see text box at end of this chapter). Many Minnesota lakes are similar to the lakes for w h ich the model w a s developed: relatively deep cool-temperate lakes of gl acial origin, which are oligotrophic to mesotrophic. T he approach has not been calibrated or confirmed for shallow lakes, naturally eutrophic lakes, warm -t emperate lakes, or impoundments. T he MEI approach is simple and appears to be highly successful for a limited set of cool-temperate lakes. Howeve r, because its use has not been w i despread (possibly because of its simplicity), it has not been calibrated and tested for a w i der v ariety of lakes. B ecause this approach has potential, it needs to be recalibrated and tested with regional reference lake data sets. 2. Mass Balance Models with Loading Estimation



### � Mass B a lance Models Mass balance models are a means of estimating concentrations of nutrients using knowledge of loading into a lake and hydrolog y of a lake. A m ass balance model by itself will not establish reference conditions—it will predict nutrient concentrations g ive n certain loading v alues. Therefore, to use a m a ss balance model to derive reference conditions for a lake, an estimate of the natural back gr ound nutrient loading to the lake is required. I n the m o st basic steady

- state mass balance phosphorus model, the equation for prediction of the concentration of phosphorus in a reservoir is produced by rearranging the ma ss balance equation (see C h apter 2) and solving for the concentration in the lake: Concentration (lake) = Concentration (incoming water) × Fraction NOT Sedimented or C L= C i × (1



### � R)



### Nutrient Criteria—Lakes and Reserv o irs 9- 7C Land C i are concentrations of the m a terial in the lake (L) and in the incoming wa ter (i), and R is the amount retained in the water column. C i is usually calculated as the nutrient loading, J (m g/year), divided by the amount of water flowing out of the reservoir (m 3 /year) to compensate for evaporation from the reservoir surface. T he letter R represents the fraction of the m a terial retained in the lake (i.e., sedimented). By subtracting the fraction sedimented from 1, the term “ (1



### � R) ” represents the fraction of the incoming concentration that can be found in the reservoir water (Dillon and R igl er, 1974). T here are a number of m e thods for estimating (1



### � R), but one of the simplest, and yet one of the m o st consistently accurate, has been found to be:
1 1 − = R 1 + sT where T is the water residence time (Vollenweider, 1976; Larsen and Mercier, 1976). T his equation implies that the retention of m a terials in the reservoir increases the longer the w a ter remains in the reservoir (as the w a ter residence time increases). T his m ake s intuitive sense because it means there is mo re time for the phosphorus to sediment out of the water column. T he effect is that the longer the water residence time, the lower the expected phosphorus concentrations in the reservoir. T his becomes especially significant because w a tershed development not only affects nutrient loading through increases in nutrient concentration but also increases water flow into the reservoir, thus decreasing the water residence time and further increasing the in-reservoir phosphorus concentration.
Th e final predictive equation becomes:
1 C L = C i s + 1 T
I n the context of estimating reference conditions, models of this type can be used to estimate the potential predisturbance condition of the water body . T he incoming concentration (C i ) does not necessarily have to represent the present or future concentration in the incoming stream . I f there are undisturbed streams in the region, then the concentrations in those streams can be used instead to estimate the theoretical undisturbed condition. Some error would be introduced because w a ter flow, and therefore the w a ter residence time (T), also m ay be affected by disturbance; the estimated v a lue would then underestimate the reference phosphorus condition.



### � R eceiving Water Models Receiving w ater models are used to examine the interactions between loadings and response, evaluate loading capacities, and test v arious loading scenarios. A s with w a tershed loading m odels, receiving wa ter models v ary w idely in complexity

. For traditional point source abatement, w h ere biodegradable pollutant discharges are the m ajo r concern, simple steady

- state models of the dissolved oxy g en balance are comm only used by planners and pollution control authorities. For assessment of eutrophication and toxics, m o re comprehensive models have evolved to incorporate a wider range of processes. O ther recent review s of receiving wa ter models include A m brose et al. (1995).
A fundamental concept for the analysis of receiving wa ter body response to point and nonpoint source inputs is the principle of m a ss balance (or continuity). Receiving wa ter models typically develop a m a ss balance for one or m o re interacting constituents, taking into account three factors: transport through the system, reactions within the system, and inputs into the system . T he first factor describes the

9- 8 

### Nutrient Criteria—Lakes and Reserv o irshydrologic and hydrodynamic regime of the water system; the second, the biological, chemical, and physical reactions that affect constituents; and the third, the inputs to or withdrawals from the system because of anthropogenic activities and natural phenomena (O 

### � Conner et al., 1975). T he complexity of a receiving wa ter model depends on the w ay in w h ich these three factors are incorporated. T he simplest m odels use a steady

- state one-dimensional framework with steady inputs. T he more complex models typically use hydrodynamic relationships, consider interactions between constituents, allow distributed nonpoint inputs, and are capable of providing dynamic, m u ltidimensional simulations.
Th e various physical, chemical, and biological processes considered by a receiving w ater model are represented m a thematically by m echanistic and/or empirical relationships between forcing functions and state v ariables (Jorgensen, 1995). Forcing functions are v ariables or functions of an external nature that are regarded in the model formulation as directly influencing the state of the receiving wa ter body

. Point and nonpoint source loadings to the water body are examples of forcing functions; other examples are temperature and solar radiation. State v ariables, such as dissolved oxy ge n and chlorophyll a concentrations, define the state of the receiving wa ter body

. When the predicted v a lues of state v ariables change because of changes to forcing functions, the state variables are regarded as model outputs. I n the context of T M DL development, the typical situation would involv e m anipulating forcing functions that are controllable (e.g., point source loadings and, to an extent, nonpoint source loadings) and observing the effect on state v ariables of interest.
R eceiving wa ter models are typically described in terms of their representation of space (spatial domain), time (temporal domain), flow simulation (hydrodynamics), transport processes, inputs (forcing functions), and state v ariables. O ther factors considered in the review of receiving wa ter models include user interface and inherent application complexity

. Receiving w ater models can be g r ouped generally into three classes—hydrodynamic models, steady

- state w a ter quality m odels, and dynamic water quality m odels. Water quality m odels can simulate the chemical and biological processes that occur within a w ater body system based on external and internal inputs and reactions. Because steady

- state water quality m odels are the m o st comm only used and the easiest to implement, a select few are described below

. For more information on hydrodynamic models and dynamic water quality m odels, the reader is referred to U.S. EPA, 1997.
Wa tershed and Lake Modeling Software ( E UTROMOD)
EUT R OMOD is a spreadsheet-based modeling procedure for eutrophication m a nagement developed at Duke University and distributed by the North American Lake Management Society (Reckhow, 1990). Th e steady

- state modeling system allows for internal calculations of both nonpoint source loading and lake response. T he system estimates nutrient loadings, various trophic state parameters, and trihalomethane concentrations in lake water. T he computation algorithms used in EUT R OMOD were developed based on statistical relationships and a continuously stirred tank reactor model. Model results include the m o st likely predicted phosphorus and nitrogen loading for the watershed and for each land use category . T he model also determines the lake response to v arious pollution loading rates. T he spreadsheet capabilities of the model allow g raphical representations of the results and data export to other spreadsheet systems for statistical analyses. T he model was used in conjunction with a Geographic In formation System (GIS) for establishing T MDLs to Wister Lake, Oklahoma (Hession et al., 1995). Seasonal and Long-Term Trends of Total Phosphorus and Oxygen in Stratified Lakes ( PHOS MO D) PHOSMOD is a budget model that can predict the long -t erm response of a lake to changes in phosphorus loading (Chapra and Canale, 1991). I n the model, the lake is treated as two layers: a water 

### Nutrient Criteria—Lakes and Reserv o irs 9- 9layer and a surface sediment layer. A T P budget for the w a ter layer is developed with inputs from external loading and recycling from the sediments and considering losses due to flushing and settling . In the sediment layer budget, T P is gained by settling and lost by recycling and burial. T he sediment-to-water recycling is dependent on the levels of sediment T P and hypolimnetic oxy ge n, with the concentration of the latter estimated with a semiempirical model. Chapra and Canale (1991) present an application of the model and an analysis to demonstrate how the model predictions replicate in-lake changes not possible with simpler phosphorus budget models.
BATHTUB FLUX, PROFILE, and BAT HTUB (Walker, 1986) are a collection of programs designed to assist in the data reduction and model implementation phases of eutrophication studies in lakes and reservoirs. FLUX is a tool for data reduction and preprocessing of tributary nutrient loadings from g rab sampling and flow records. T he program can assist in error detection and sampling program design. PROFILE provides displays of lake w a ter quality data and assists in analysis of sampling information. D ata analysis procedures include hypolimnetic oxy ge n depletion rates, spatial and temporal v ariability, and statistical summaries. BATHTUB allows the user to seg m ent the lake into a hydraulic network . N utrient balance and eutrophication models can be applied to the network to assess advection, dispersion, and nutrient sedimentation. Empirical relationships that have been calibrated and tested for reservoir applications are used to predict eutrophication-related w a ter quality conditions. T he seg m ented structure of BAT HTUB allows its application to single reservoirs, partial reservoirs, networks of reservoirs, or collections of reservoirs, permitting regional comparative assessments of reservoir conditions, controlling factors, and model performance. I nputs and outputs can be expressed in probabilistic terms to account for limitations in input data and intrinsic model errors. T he programs and models have been applied to U.S. Arm y Corps of Engineer reservoirs (Kennedy, 1995), as well as a number of other lakes and reservoirs. BATHTUB has been cited as an effective tool for lake and reservoir w a ter quality assessment and m a nagement, particularly where data are limited (Ernst et al., 1994). AQUATOX
A receiving wa ter and food chain model will soon be released by the EPA O ffice of Science and T echnolog y. AQUATOX is desig n ed to simulate the biological, physical, and chemical processes within a water body in response to stressors. Parameters include phosphorus, nitrogen, chlorophyll a , Secchi depth, dissolved oxy ge n, macrophytes, and several trophic g r oups of invertebrates and fish. I t is a time- variable model expected to predict seasonal changes, such as when different algal groups m ay bloom and lake ecosystem responses to changes in nutrient loading or other management measures. AQUATOX i s expected to prov i de the user wi t h a great deal of dat a i n the form of data l ib raries, which can be used “as is” or edited by the user to better characterize a water body . I t has been validated for nutrients on a stratified eutrophic lake in N ew Yo rk and a reservoir in I owa. I t will be undergoing peer review in 2000.



### � Simple Watershed-Scale Loading Models Watershed-scale loading m odels are good choices to use to estimate nutrient loads entering lakes and reservoirs. For discussion purposes, watershed-scale loading estimation methods can be divided into three g e neral categories based on complexity, operation, time step, and simulation technique—simple me thods, mi d-range models, and detailed models (U.S. EPA, 1997). Simple m e thods are the m o st

9-10 

### Nutrient Criteria—Lakes and Reserv o irssuitable for aiding in the prediction of reference conditions. Mid-range and detailed watershed-scale loading m odels are m o re advantageous for watershed m a nagement applications, as detailed below. Simple me thods are g e nerally empirical in nature. T he major advantage of empirical m e thods is that they can provide a means of developing regional reference conditions with less effort and data requirements than m o re complex simulation models. T hese methods are compilations of expert judg m ent and empirical relationships between physiographical characteristics of the watershed and pollutant export, or they are estimates based on existing data. T hey are the m o st suitable models for developing regional reference conditions and m aki ng regional predictions, but they are the least suitable models for aiding watershed m a nagement and lake m a nagement decisions. Ty pically, simple m e thods rely on large-scale ag gr egation and neglect important features of small patches of land. T hey rely on g e neralized sources of information and therefore have low to me dium requirements for site-specific data. Default v a lues provided for these me thods are derived from empirical relationships that are evaluated based on regional or site-specific data. T he estimations usually are expressed as mean annual v a lues. Simple m e thods provide ag gr egated (e.g., annual average) estimates of sediment and pollutant loadings, but they have limited predictive capability for short-term loading or events. T he empiricism contained in the models limits their transferability to other regions. B ecause they often neglect seasonal v ariability, simple m e thods migh t not be adequate to model short-term w ater quality problems for w h ich specific loadings of shorter duration are important. Pollutant loads are determined from export coefficients (e.g., the Watershed model) or as a function of the sediment y i eld (e.g., EPA screening procedures, SLOSS-PHOSPH). T he Simple Method, the U.S. Geological Survey (USGS) regression me thod, and the Federal Highway Administration model are statistically based approaches developed from past monitoring information. I n general, the application of empirical models is limited to the watershed types for which they were developed, with similar land uses or activities. A pplications to new areas requires recalibration with relevant data. Selected simple empirical watershed-scale loading m odels are described below (U.S. EPA, 1997). Reckhow-Simpson Model
Th is approach (Reckhow and Simpson, 1980) uses a simple m a ss balance model with empirical predictions of phosphorus loading rates from different land uses to predict mean lake phosphorus concentration. T he mass-balance equation uses phosphorus loading, water loading, and an empirically derived settling v elocity for phosphorus to estimate phosphorous concentration. U sers m u st derive high, me dian, and low estimates of phosphorus export coefficients from agricultural, forest, and urban land, as well as septic fields and precipitation. T he high and low estimates are used to bracket uncertainty of the best estimate. EPA Screening Procedures
Th e EPA screening procedures, developed by the EPA Environmental Research Laboratory in At hens, G e orgia (McElroy et al., 1976; Mills, 1985), include me thodologies to calculate pollutant loads from point and nonpoint sources, including atmospheric deposition, for preliminary assessment of w a ter quality . T he procedures consist of loading functions and simple empirical expressions relating nonpoint pollutant loads to other readily available parameters. Data required g e nerally include information on land use/land cover, m a nagement practices, soils, and topography

. Although these procedures are not coded into a computer program, several computer-based models have adapted the loading function 

### Nutrient Criteria—Lakes and Reserv o irs 9-11concept to predict pollutant loadings. A n advantage of this approach is the possibility of using readily available data as default v a lues w h en site-specific information is lacking . A pplication of these procedures requires mi nimum personnel training and practically no calibration. However, application to large, complex w a tersheds should be limited to planning activities. Many of the techniques included in the m a nual were incorporated into current models such as Generalized Watershed Loading Functions (GWLF). USGS SPARROW Regression Approach
Th e SPARROW regression is v e ry similar to the storm runoff model (described below), and is based on hydrologic unit-level discharge data from USGS g agi ng stations (Smith et al., 1997). T he model was developed from nationwide data (414 stations for up to 15 years). T he SPARROW approach considered four sources of total nitrogen and T P: point sources, fertilizer, livestock w aste, and runoff from nonagricultural land. A tmospheric nitrogen deposition also w a s included in the nitrogen model (Smith et al., 1997). T he model estimated land surface delivery (of nonpoint source runoff) and instream decay (denitrification or settlement) of the nutrients. Apossible drawback of the approach for estimating reference conditions is that nonagricultural land uses were lumped as a single category (Smith et al. 1997). T he model was developed from nationwide data; use of this me thod for extrapolation of regional reference conditions would require reestimation and calibration using relevant regional data. While tim e consuming and data intensive, regional recalibration should result in m o re precise estimates than the national model. Simple Method
Th e Simple Method is an empirical approach developed for estimating pollutant export from urban development sites in the Washington, DC, area (Schueler, 1987). I t is used at the site-planning level to predict pollutant loadings under a v ariety of development scenarios. I ts application is limited to small drainage areas of less than a square mile. Pollutant concentrations of phosphorus, nitrogen, chemical oxy ge n demand, biochemical oxy ge n demand, and me tals are calculated from flow- w eighted concentration v a lues for new suburban areas, older urban areas, central business districts, hardwood forests, and urban highways. T he method relies on the National Urban Runoff Program (NURP) data for default v a lues (U.S. EPA, 1983). A graphical relationship is used to determine the event mean sediment concentration based on readily available information. T his method is not coded into a computer program but can be easily implemented with a hand-held calculator. USGS Regression Approach
Th e regression approach developed by USGS researchers is based on a statistical description of historic records of storm runoff responses on a watershed level (Tasker and Driver, 1988). T his me thod may be used for rough preliminary calculations of annual pollutant loads when data and time are limited. Simple regression equations were developed using available monitoring data for pollutant discharges at 76 gaging stations in 20 States. Separate equations are g ive n for 10 pollutants, including dissolved and total nutrients, chemical oxy ge n demand, and me tals. I nput data include drainage area, percent imperviousness, mean annual rainfall, g e neral land use pattern, and mean mi nimum m onthly temperature. Application of this m e thod provides storm -mean pollutant loads and corresponding confidence intervals. Th e use of this me thod as a planning tool at a regional or watershed level might require preliminary calibration and v e rification with additional, m o re recent monitoring data.

9-12 

### Nutrient Criteria—Lakes and Reserv o irsSimplified Pollutant Yield Approach ( S LOSS-PHOS PH )
Th is m e thod uses two simplified loading algorithms to evaluate soil erosion, sedimentation, and phosphorus transport from distributed watershed areas. T he SLOSS algorithm provides estimates of sediment y i eld, whereas the PHOSPH algorithm uses a loading function to evaluate the amount of sediment-bound phosphorus. Application to watershed and subwatershed levels was developed by T im et al. (1991) based on an integrated approach coupling these algorithms with VirGIS (Virginia GIS). T he approach w a s applied to the N omi ni C r eek w atershed, Westmoreland County, Virginia, to target critical areas of nonpoint source pollution at the subwatershed level (U.S. EPA, 1992c). I n this application, analysis was limited to phosphorus loading; however, other pollutants for which input data or default va lues are available can be modeled in a similar fashion. T he approach requires full-scale G I S capability and trained personnel.
Wa tershed Watershed is a spreadsheet model developed at the University of Wisconsin to calculate phosphorus loading from point sources, combined sewer overflows, septic tanks, rural croplands, and other urban and rural sources. I t can be used to evaluate the tradeoffs between control of point and nonpoint sources (Walker et al., 1989). I t uses an annual time step to calculate total pollution loads and to evaluate the cost-effectiveness of pollution control practices in terms of cost per unit load reduction. T he program uses a series of w o rksheets to summarize w a tershed characteristics and to estimate pollutant loadings for uncontrolled and controlled conditions. B ecause of the simple formulation describing the various pollutant loading processes, the model can be applied using available default v a lues with mi nimum calibration effort. Watershed w a s applied to study the tradeoffs between controlling point and nonpoint sources in the Delavan Lake watershed in Wisconsin. Federal Highway Administration Model FHWA's Office of Engineering and Highway Operations has developed a simple statistical spreadsheet procedure to estimate pollutant loading and impacts to streams and lakes that receiv e highway storm water runoff (FHWA, 1990). T he procedure uses several worksheets to tabulate site characteristics and other input parameters, as well as to calculate runoff v o lumes, pollutant loads, and the magn itude and frequency of occurrence of instream pollutant concentrations. T he FHWA model uses a set of default v a lues for pollutant event- mean concentrations that depend on traffic v o lume and the rural or urban setting of the highway 's pathway

. FH WA uses this m e thod to identify and quantify the constituents of highway runoff and their potential effects on receiving wa ters and to identify areas that migh t require controls.
Wa tershed Management Model
Th e Watershed Management Model (WMM) was developed for the Florida Department of Environmental Regulation for watershed m a nagement planning and estimation of watershed pollutant loads (Camp et al., 1992). Pollutants simulated include nitrogen, phosphorus, lead, and z i nc from point and nonpoint sources. T he model is implemented in the Lotus 1-2-3 spreadsheet environment and will thus calculate standard statistics and produce plots and bar charts of results. Although it was developed to predict annual loadings, WMM can be adapted to predict seasonal loads provided that seasonal event m ean concentration data are available. I n the absence of site-specific information, the event concentrations derived from NURP surveys m ay be used as default v a lues. T he model includes computational components for stream and lake w a ter quality analysis using simple transport and 

### Nutrient Criteria—Lakes and Reserv o irs 9-13transformation formulations based on travel time. WMM has been applied to several watersheds, including the development of a m a ster plan for Jacksonville, Florida, and the Part I I estimation of wa tershed loadings for the N a tional Pollutant D i scharge Elimination System permitting process. I t also has been applied in Norfolk County, Virginia; to a watershed m a nagement plan for North Carolina; to a wa steload allocation study for Lake Tohopekaliga, near O r lando, Florida; and for w a ter quality planning in Austin, T e xas (Pantalion et al., 1995). D. Watershed Management Models As watershed-based assessment and integrated analysis of point and nonpoint source pollution hav e become the focus of g o ve rnmental water programs, modeling has been used to evaluate a wider range of pollutant g e neration, transport, control, and environmental response issues (U.S. EPA, 1997). Management g o als such as pollutant source identification and prioritization, prediction and estimation of lake and reservoir response to watershed nutrient control practices, and long -t erm evaluation of a watershed system 

### � s response to management efforts can be addressed using m odeling techniques. T his section discusses the use of watershed loading m odels and receiving w ater models for management purposes. 1. Mid-Range Watershed-Scale Loading Models
Th e advantage of mi d-range watershed-scale loading m odels is that they evaluate pollution sources and impacts over broad g e ographic scales and therefore can assist in defining target areas for pollution mitigation programs on a w a tershed basis. Several mi d-range models are designed to interface with GI Ss, w h ich g r eatly facilitate parameter estimation. G reater reliance on site-specific data g ives mi d-range models a relatively broad range of regional applicability . H owever, the use of simplifying assumptions can limit the accuracy of their predictions to within about an order of m agn itude (Dillaha, 1992) and can restrict their analysis to relative comparisons.
Th is class of model attempts a compromise between the empiricism of the simple m e thods and the complexity of detailed mechanistic models. Mid-range models use a m a nagement-level approach to assess pollutant sources and transport in watersheds by incorporating simplified relationships for the ge neration and transport of pollutants. Mid-range models, however, still retain responsiveness to ma nagement objectives and actions appropriate to watershed m a nagement planning (Clark et al., 1979). Th ey are relatively simple and are intended to be used to identify problem areas within large drainag e basins or to m ake preliminary, qualitative evaluations of best m a nagement practices (BMP) alternatives (Dillaha, 1992). Unlike the simple methods, which are restricted to predictions of annual or storm loads, mi d-rang e tools can be used to assess the seasonal or interannual v ariability of nonpoint source pollutant loading s and to assess long -t erm w ater quality trends. A lso, they can be used to address land use patterns and landscape configurations in actual watersheds. T hey are based primarily on empirical relationships and default v a lues. I n addition, they typically require some site-specific data and calibration. Mid-range models are designed to estimate the importance of pollutant contributions from m ultiple land uses and m a ny individual source areas in a watershed. T hus, they can be used to target important areas of pollution generation and identify areas best suited for controls on a watershed basis. Moreover, the continuous simulation furnished by some of these models provides an analysis of the relativ e importance of sources for a range of storm events or conditions. I n an effort to reduce complexity and data requirements, these models often are developed for specific applications. For instance, mi d-rang e
9-14 

### Nutrient Criteria—Lakes and Reserv o irsm odels can be designed for application to agricultural, urban, or mi xed watersheds. Some mi d-rang e m odels simplify the description of transport processes while emphasizing possible reductions available with controls; others simplify the description of control options and emphasize changes in concentrations as pollutants m ove through the watershed.
B ecause mi d-range models attempt to use smaller time steps to represent seasonal v ariability, they require additional me teorologic data (e.g., daily weather data for the GWLF, hourly rainfall for SITEMAP). They also attempt to relate pollutant loadings to hydrologic (e.g., runoff) and erosion (e.g., sedime nt yield) processes. T hese models usually include adequate input-output features (e.g., AGNPS, GWLF), m aki ng applications easier to process. Several of these models (SI T EMAP, Auto- QI ) were developed in existing computing environments (e.g., Lotus 1-2-3) to m ake use of their built-in g r aphical and statistical capabilities. N either the simple nor the mi d-range models consider degradation and transformation processes, and few incorporate adequate representation of pollutant transport within and from the watershed. Although their applications migh t be limited to relative comparisons, they can often provide w a ter quality m anagers with useful information for w a tershed-level planning decisions. Selected mi d-range models are described below:



### � Stormwater Intercept and Treatment Evaluation Model f o r A n alysis and P l anning (SIT EMAP)
SI TE MAP, previously distributed under the name NPSMAP, is a dynamic simulation program that computes, tabulates, and displays daily runoff, pollutant loadings, infiltration, soil m o isture, irrigation water demand, evapotranspiration, drainage to g r ound water, and daily outflows, water, and residual pollutant levels in retention basins or wetland systems (Omicron Associates, 1990). T he model can be used to evaluate user-specified alternative control strategies, and it simulates stream seg m ent load capacities in an attempt to develop point source w a steload allocations and nonpoint source load allocations. Probability distributions for runoff and nutrient loadings can be calculated by the model based on either single-event or continuous simulations. T he model can be applied in urban, agricultural, or complex watershed simulations. SI T EMAP operates within the Lotus 1-2-3 programmi ng environment and is capable of producing g raphical output. Although this model requires a mi nimum calibration effort, it requires moderate effort to prepare input data files. T he current v e rsion of the program considers only nutrient loading; sediment and other pollutants are not y e t incorporated into the program . T he model is easily interfaced with G I S (ARC/I N FO) to facilitate preparation of land use files. SI TE MAP has been applied as a component of a full watershed model to the T u alatin River basin for the Or egon D e partment of Environmental Q u ality, and to the Fairview Cr eek w atershed for the Metropolitan Service District in Portland, Oregon.



### � Ge neralized Watershed Loading Functions Model
Th e GWLF model was developed at Cornell University to assess the point and nonpoint loadings of nitrogen and phosphorus from urban and agricultural watersheds, including septic systems, and to evaluate the effectiveness of certain land use management practices (Haith et al., 1992). One advantag e of this model is that it w a s w r itten with the express purpose of requiring no calibration, m aki ng extensiv e use of default parameters. T he GWLF model includes rainfall/runoff and erosion and sediment ge neration components, as well as total and dissolved nitrogen and phosphorus loadings. T he current ve rsion of this model does not account for loadings of toxics and me tals. T he GWLF model uses daily time steps and allows analysis of annual and seasonal time series. T he model also uses simple transport routing based on the delivery ratio concept. I n addition, simulation results can be used to identify and rank pollution sources and evaluate basinwide m a nagement programs and land use changes. T he most 

### Nutrient Criteria—Lakes and Reserv o irs 9-15recent update of the model incorporates a septic (onsite w a ste w a ter disposal) system component. T he m odel also includes several reporting and g r aphical representations of simulation output to aid in interpretation of the results. T his model was successfully tested on a me dium -s ized watershed in New Yo rk (Haith and Shoemaker, 1987). A v ersion of the model with an enhanced user interface and linkages to national databases, the Watershed Screening Model has recently become available and is distributed w ith EPA 

### � s Office of Wetlands, Oceans and Watersheds Watershed Screening and T argeting T ool.



### � Urban Catchment Model (P 8 -UCM)
Th e P8- U CM program was developed for the Narragansett Bay Project to simulate the g e neration and transport of storm water runoff pollutants in small urban catchments and to assess impacts of development on w a ter quality w ith mi nimum site-specific data. I t includes several routines for evaluating the expected removal efficiency for particular site plans, selecting or siting B MPs necessary to achieve a specified level of pollutant removal, and comparing the relative changes in pollutant loads as a watershed develops (Palmstrom and Walker, 1990). Default input parameters can be derived from NURP data and are available as a function of land use, land cover, and soil properties. However, without calibration, the use of model results should be limited to relative comparisons. Spreadsheet-like m e nus and online help documentation m ake extensive user interface possible. O n-screen g r aphical representations of output are developed for a better interpretation of simulation results. T he model also includes components for performing m onthly or cumulative frequency distributions for flows and pollutant loadings.



### � Automated Q -I LLUDAS (AUTO -QI) AUTO-QI is a watershed model developed by the Illinois State Water Survey to perform continuous simulations of storm water runoff from pervious and impervious urban lands (Terstriep et al., 1990). It also allows the examination of storm events or storm sequence impacts on receiving wa ter. C ritical events also are identified by the model. However, hourly weather input data are required. Several pollutants, including nutrients, chemical oxy ge n demand, me tals, and bacteria, can be analy zed simultaneously . T his model also includes a component to evaluate the relative effectiveness of BMPs. A n updated v e rsion of A UTO-QI , with an improved user interface and linkage to a G I S (ARC/I NFO on PR IM E computer), has been completed by the Illinois State Water Survey . T his interface is provided to ge nerate the necessary input files related to land use, soils, and control measures. AUTO-QI was v e rified on the Boneyard C r eek in C h ampaign, Illinois, and applied to the C a lumet and Little R ive rs to determine annual pollutant loadings.



### � Ag ricultural N o npoint Source P o llution Model (A GNPS)
Dev el oped by t he U.S. Depar tme nt of Ag ri cul tu re ( USDA) Ag ric ul tural Research Ser vi ce, AGNPS addresses concerns related to the potential impacts of point and nonpoint source pollution on water quality (Young et al., 1989). I t w a s designed to quantitatively estimate pollution loads from agricultural watersheds and to assess the relative effects of alternative m a nagement programs. T he model simulates surface w a ter runoff along w ith nutrient and sediment constituents associated with agricultural nonpoint sources, as well as point sources such as feedlots, waste water treatment plants, and stream bank or g u lly erosion. T he av a ilable v e rsion of AGNPS is event based; however, a continuous v e rsion is under activ e development (Needham and Young, 1993). T he structure of the model consists of a square g r id cell system to represent the spatial distribution of watershed properties. T his g r id system allows the model to be connected to other software such as G I S and digital elevation models. This connectivity can facilitate

9-16 

### Nutrient Criteria—Lakes and Reserv o irsthe development of a number of the model's input parameters. Two new terrain-enhanced v e rsions of the m odel—AGNPS-C, a contour- b ased v e rsion, and AGNPS-G, a g r id- b ased v e rsion

—have been developed to automatically g enerate the g r id network and the required topographic parameters (Panuska et al., 1991). V ieux and Needham (1993) describe a GIS-based analysis of the sensitivity of AGNPS predictions to g r id-cell size. Engel et al. (1993) present GRASS-based tools to assist with the preparation of model inputs and v i sualization and analy s is of model results. T im and J o lly (1994) used AGNPS with ARC/IN FO to evaluate the effectiveness of several alternative m a nagement strategies in reducing sediment pollution in a 417-hectare watershed in southern I o wa. T he model also includes enhanced gr aphical representations of input and output information.



### � Source Loading and Management Model (SLAMM)
Th e SLAMM model (Pitt, 1993) can identify pollutant sources and evaluate the effects of a number of different storm water control practices on runoff. T he model performs continuous m a ss balances for particulate and dissolved pollutants and runoff v o lumes. Runoff is calculated by a method developed by Pitt (1987) for small storm hydrolog y. Runoff is based on rainfall mi nus initial abstraction and infiltration and is calculated for both pervious and impervious areas. Triangular hydrographs, parameterized by a statistical approach, are used to simulate flow. Exponential buildup and rain washoff and wind removal functions are used for pollutant loadings. Water and sediment from v arious source areas are tracked by source area as they are routed through various treatment devices. T he program considers how particulates filter or settle out in control devices. Particulate removal is calculated based on the design characteristics of the basin or other removal device. Storage and overflow of devices also are considered. A t the outfall locations, the characteristics of the source areas are used to determine pollutant loads in solid and dissolved phases. Loads from v arious source areas are summe d. SLAMM has been used in conjunction with a receiving wa ter quality m odel (H yd rological Simulation Program—FO RTRAN , HSPF) to examine the ultimate effects on urban runoff from T oronto for the On tario Ministry of the Env i ronment. SLAMM also w a s used to evaluate control options for controlling urban runoff in Madison, Wisconsin, using GI S information (Thum et al., 1990). T he State of Wisconsin uses SLAMM as part of its Priority Watershed Program . I t was used in Portland, Oregon, for a study evaluating combined sewer overflows. 2. Detailed Watershed Loading Models Detailed models best represent the current understanding of watershed processes affecting pollution ge neration. Detailed models are best able to identify causes of problems rather than simply describe overall conditions. I f properly applied and calibrated, detailed models can provide relatively accurate predictions of v ariable flows and w a ter quality at any point in a w a tershed. The additional precision they provide, however, comes at the expense of considerable time and resource expenditure. Detailed models use storm event or continuous simulation to predict flow and pollutant concentrations for a range of flow conditions. T he models are large and were not designed with emphasis on their potential use by the typical state or local planner. Many of these models were developed to research the fundamental land surface and instream processes that influence runoff and pollutant g e neration rather than to comm unicate information to decisionmakers faced with planning watershed m a nagement. Detailed models incorporate the m a nner in which watershed processes change over time in a continuous fashion rather than rely on simplified terms for rates of change (Addiscott and Wagenet, 1985). T hey tend to require rate parameters for flow v elocities and pollutant accumulation, settling, and 

### Nutrient Criteria—Lakes and Reserv o irs 9-17decay instead of capacity terms. T he length of time steps is v ariable and depends on the stability of numerical solutions as well as the response time for the system (Nix, 1991). Algorithms in detailed m odels m o re closely simulate the physical processes of infiltration, runoff, pollutant accumulation, instream effects, and g r ound w a ter/surface w a ter interaction. T he input and output of detailed models also have g r eater spatial and temporal resolution. Moreover, the manner in which physical characteristics and processes differ over space is incorporated within the g ove rning equations (Nix, 1991). Linkage to biological modeling is possible because of the comprehensive nature of continuous simulation models. I n addition, detailed hydrologic simulations can be used to design potential control actions.
Th ese models use small time steps to allow for continuous and storm event simulations. However, input data file preparation and calibration require professional training and adequate resources. Some of these models (e.g., STORM, SWMM, ANSWERS) were developed not only to support planning -l evel evaluations but also to provide design criteria for pollution control practices. I f appropriately applied, state-of-the-art models such as HSPF and SWMM can provide accurate estimations of pollutant loads and the expected impacts on w a ter quality . N ew interfaces developed for HSPF and SWMM, and link s w ith G I Ss, can facilitate the use of complex models for environmental decisionmaking . H owever, their added accuracy might not always j u stify the amount of effort and resources they require. A pplication of such detailed models is m o re cost-effective when used to address complex situations or objectives. Selected detailed models are described below.



### � Storage, Treatment, Overflow Runof f Model (STORM) STORM is a U.S. Army Corps of Engineers model developed for continuous simulation of runoff quantity and quality, including sediments and several conservative pollutants. I t also simulates combined sewer systems (Hydrologic Engineering Center, 1977). STORM has been widely used for planning and evaluation of the tradeoffs between treatment and storage control options for combined sewer overflows. Long -t erm simulations of runoff quantity and quality can be used for the construction of duration-frequency diagrams. T hese diagrams are useful in developing urban planning alternatives and designing structural control practices. STORM was primarily designed for modeling storm water runoff from urban areas. I t requires relatively m oderate to high calibration and input data. STORM was initially developed for m a inframe computer usage; however, several v e rsions have been adapted by various individual consultants for use on mi crocomputers. T he model has been applied recently to w a ter quality planning in the city of A u stin, T e xas (Pantalion et al., 1995).



### � A real N o npoint Source Watershed E n vironment R e sponse Simulation Model (A NS WE RS) ANSWERS is a comprehensive model developed at the University of Georgia to evaluate the effects of land use, m a nagement schemes, and conservation practices or structures on the quantity and quality of water from both agricultural and nonagricultural watersheds (Beasley, 1986). T he distributed structure of this model allows for a better analysis of the spatial as w e ll as temporal v ariability of pollution sources and loads. I t was initially developed on a storm event basis to enhance the physical description of erosion and sediment transport processes. Data file preparation for the ANSWERS program is rather complex and requires m a inframe capabilities, especially w hen dealing w ith large w a tersheds. The output routines are quite flexible; results m ay be obtained in several tabular and g r aphical forms. T he program has been used to evaluate m a nagement practices for agricultural watersheds and construction sites in I ndiana. I t has been combined with extensive monitoring programs to evaluate the relative importance of point and nonpoint source contributions to Saginaw Bay . T his application involved the computation of
9-18 

### Nutrient Criteria—Lakes and Reserv o irsunit area loadings under different land use scenarios for evaluation of the tradeoffs between load allocations and w a steload allocations. R ecent model revisions include improvements to the nutrient transport and transformation subroutines (Dillaha et al., 1988). B ouraoui et al. (1993) describe the development of a continuous v e rsion of the model.



### � Multi-Event Urban Runof f Quality Model (D R3 M-QU AL) DR3M is a watershed model for routing storm runoff through a branched system of pipes and/or natural channels using rainfall as input. T he model provides detailed simulation of storm runoff periods selected by the user and a daily soil m o isture accounting between storms. Kinematic wave theory is used for routing flows over contributing overland flow areas and through the channel network

. Storm hydrographs m ay be saved for input to DR3M-QUAL, which simulates the quality of surface runoff from urban watersheds. T he model simulates impervious areas, pervious areas, and precipitation contributions to runoff quality, as w e ll as the effects of street sweeping and/or detention storage. Variations of runoff quality are simulated for user-specified storm runoff periods. B etween these storms, a daily accounting of the accumulation and w a shoff of w a ter-quality constituents on effective impervious areas is ma intained. I nput to the model includes the storm hydrographs, usually from DR3M. T he program has been reviewed extensively within the USGS and applied to several urban modeling studies (Brabets, 1986; G u ay, 1990; Lindner-Lunsford and Ellis, 1987) .



### � Simulation f o r Water R e sources in R u ral B a sins—Water Quality (SWRRBWQ)
Th e SWRRBWQ model was adapt e d f rom th e f i eld-scale CREAMS model by USDA to si m ulat e hydrologic, sedimentation, nutrient, and pesticide m ovement in large, complex rural watersheds (Arnold et al., 1989). SWRRBWQ uses a daily time step to ev a luate the effect of m a nagement decisions on water, sediment y i elds, and pollutant loadings. T he processes simulated within this model include surface runoff, percolation, irrigation return flow, evapotranspiration, transmission losses, pond and reservoir storage, sedimentation, and crop g r owth. T he model is useful for estimating the order of magn itude of pollutant loadings from relatively small watersheds or watersheds with fairly uniform properties. I nput requirements are relatively high, and experienced personnel are required for successful sim u lations. SWRRBWQ was used by the National Oceanic and Atm o spheric Administration to evaluate pollutant loadings to coastal estuaries and embay m ents as part of its national C o astal Pollution Discharge I nv entory . T he model has been run for all m ajo r estuaries on the East Coast, West Coast, and Gulf Coast for a wide range of pollutants (Donig i an and Huber, 1991). Although SWRRBWQ is no longer under active development, the technolog y is being incorporated into the Soil and Water Assessment Tool as part of the Hydrologic Unit Model for the United States project at T emp le, T e xas (Arnold et al., 1993; Srinivasan and Arnold, 1994). EPA's Office of Science and Technolog y (OST ) recently developed a Microsoft Windows-based interface for SWRRBWQ to allow convenient access to temperature, precipitation, and soil data files.



### � Storm Water Management Model (SWMM) SWMM is a comprehensive watershed-scale model developed by EPA (Huber and Dickinson, 1988). It w as initially developed to address urban storm w ater and assist in storm event analysis and derivation of design criteria for structural control of urban storm water pollution, but it was later upgraded to allow continuous simulation and application to complex watersheds and land uses. SWMM can be used to m odel several types of pollutants provided that input data are available. Recent v e rsions of the model can be used for either continuous or storm event simulation with user-specified v ariable time steps. T he m odel is relatively data intensive and requires special effort for v a lidation and calibration. I ts application 

### Nutrient Criteria—Lakes and Reserv o irs 9-19in detailed studies of complex watersheds migh t require a team effort and highly trained personnel. SWMM has been applied to address various urban water quantity and quality problems in many locations in the U n ited States and other countries (Donigian and Huber, 1991; Huber, 1992). I n addition to developing comprehensive watershed-scale planning, typical uses of SWMM include predicting combined sewer overflows, assessing the effectiveness of BMPs, providing input to short-time-increment dynamic receiving wa ter quality m odels, and interpreting receiving wa ter quality m onitoring data (Donigian and Huber, 1991). Warwick and T a depalli (1991) describe calibration and v e rification of SWMM on a 10-square- mile urbanized watershed in Dallas, T e xas. T sihrintzis et al. (1995) describe SWMM applications to four watersheds in South Florida representing high- and low-density residential, comme rcial, and highway land uses. Ovbiebo and She (1995) describe another application of SWMM in a subbasin of the D uwami sh River, Washington. O ST distributes a Microsoft Windows interface for SWMM that m ake s the model m o re accessible. Apostprocessor allows tabular and g r aphical display of m odel results and has a special section to help with model calibration.



### � Hydrological Simulation P r ogram—F O RTRAN ( H SP F)
H SPF is a comprehensive package developed by EPA for simulating w ater quantity and quality for a wide range of organic and inorganic pollutants from agricultural watersheds (Bicknell et al., 1993). T he m odel uses continuous simulations of water balance and pollutant generation, transformation, and transport. T ime series of the runoff flow rate, sediment y i eld, and user-specified pollutant concentrations can be generated at any point in the watershed. T he model also includes instream quality components for nutrient fate and transport, biological oxy ge n demand, dissolved oxy ge n, pH, phytoplankton, z ooplankton, and benthic algae. Statistical features are incorporated into the model to allow for frequency

- duration analy s is of specific output parameters. Data requireme nts for HSPF are extensiv e , and calibration and verification are recommended. T he program is maintained on I B M mi crocomputers and DEC/VA X systems. Because of its comprehensive nature, the HSPF model requires highly trained personnel. I t is recomme nded that its application to real case studies be carried out as a team effort. T he m odel has been extensiv e ly used for both screening -l evel and detailed analy s es. HSPF is being used by the Chesapeake Bay Program to model total watershed contributions of flow, sediment, nutrients, and associated constituents to the tidal region of the B ay (Donigian et al., 1990; Donigian and Patwardhan, 1992). Moore et al. (1992) describe an application to model BMP effects on a T e nnessee watershed. Scheckenberger and K e nnedy (1994) discuss how HSPF can be used in subwatershed planning

. Ball et al. (1993) describe an application of HSPF in Australia. Lumb et al. (1990) describe an interactiv e program for data management and analysis that can be effectively used with HSPF. Lumb and Kittle (1993) present an expert sy s tem that can be used for calibration and application of HSPF.

9-20 

### Nutrient Criteria—Lakes and Reserv o irsUsing the Walker B A THTUB Model in Lake P e pin, Minnesota

BA THTU B w a s de ve loped f o r modeling re serv oir w ater qualitya nd is based on e m piric al data fr om U.S. ArmyCorps of Eng i ne er s’ re se rvoirs (W alke r, 1986). BATHTUB is routinely us e d in C lean Water Partne rs hip (C WP ) nonpoint sourc e studie s a nd f o r determining the ne ed f or e ffl uent-P limitations in Minnesota . T he CW P studie s are similar to Cle an Lakes Ph ase I studi es an d are typi cal ly d esi gned to obt ai n accurat e est im ates of w ater and P loading f ro m a lake’s m ajo r su bw atersheds. FL UX , a data red uc tio n to ol , is u s ed to red u ce f low an d co n centratio n data an d prov ide accurate estimates o faverage flow and concentration (typically flow-weighted means) for the period of concern (typically one water year). Flowwe ighted mean c onc en trations a nd f l ow data are us ed in BA THTU B. BA THTUB a llow s fo r s egmen tation of a

lake or reservoir and can be used to route flow s and load s between a series of lakes, thus accounting for upstream sedimentation. BATHTUB , Ve rs ion 5.3 (W alke r, 1996) a lso a llow s es tim ation of interna l phosphorus loading

. In the abs ence of m onitore d data (e.g., s ma ll subw ater sheds) phosphorus loading maybe es tim ated ba sed on land us e com position of the s ubw atershed , runof f coefficien ts, and literature-ba se d phosphorus c onc en trations f or as pe cific land us e (e.g. W a lk er , 1985b). T his is of ten the case when de termining effl uent-phosphorus limits w here de ta iled loading da ta are seld om availab l e. In manyin s tances with sm a ll d i schargers (typ ically less than 1 MGD) so me in

- lake d ata are availab l e, plant dis charge is known, and ba ckgr ound w a tershed phosphorus loading is es tim ated. BATHTUB is then us ed to determine the “effect” of the dis charge on the lake a nd the ne ed f or an e ffl uent-P limitation (typ ic a lly 1 m g P/L) on the dis charge to prote ctthe c ondition of the lake.
BA THTU B w as us ed to help e s tablish a ch lorophyll a goal f or L ake Pe pin, a run-of-the-riv e r re se rvoir on the Mis sissi ppi R ive r betw een Minne so taa nd W isc onsin (H eiskary a nd W a lk er , 1995). A ma jor intera ge nc y study of Lake Pe pin and the Mis sissi ppi Riv er was initiated in 1990 in re s pons e to m a jor nuis ance alga l bloom s , whic h oc cu rred during the low-flow summe r of 1988, and to a ssess the im pactof the 250 MG D Metropolitan Council’s Metro w a ste water tre atme nt f ac ility loc ated 80 kilometers upstre am of the lake. In L ake Pe pin inorg a nic turbiditya nd f l ow, in addition to phosphorus, s trongly influe nce ch lorophyll a concentrations. By choosing a model subroutine w hi ch accounted fo r these factors, reliable estimates of

c hlorophyll a , a s a f unction of f

low (re si denc e time) a nd inflow phosphorus c onc en tration w e re made. In turn, the in-lake phosphorus c onc en tration require d to a ch ie ve the c hlorophyll a g oal of 30 μ g /L (and thus minimiz e the f requenc y of severe nuis ance bloom s) ov e r a rang e in f l ow c onditions was es tim ated. T he f low s of c onc er n in this case rang ed f rom about 4,600 cfs (2% re oc curre nc e) up to about 20,000 c fs ( 50% reoccurre nc e). A f low of 20,000 c fs corres ponded to a resi denc e time of about 11 da ys in L ake Pe pin. Concurrent modeling of Lake Pe pin by the Metropolitan Council using WASP provide d comparab le re s ults (Lung a nd L arson, 1995). Both modeling effo rts rais ed que s tions about the role of interna l loading in this sys te m a nd to w hatde g re e interna l loading migh t inhibit re cove ry of the syste m (e ve n with substantial reductions in e xte rnal loading). Subsequent permit ne go tiations led to (1) interim phosphorus limits at the Me tro Plant; (2) provisions to purs ue bio-phosphorus re m ov al in a portion of the plant; and (3) f u rther modeling of Lake Pe pin and the Mis siss ippi R ive r to better understand the re lationship betw een ex terna l loading, interna l re cyc ling, and the production of a lg ae in the re serv oir. More r ecent permit negotiations (1998-99) led to perm anen t phosphorus limits f orthe Metro P lan t that will be acco mp lish ed thro ugh biolog ical phosphorus re mova l. De tailed mechan istic m odeling, conducted a s a require me nt of the pre v ious pe rmit, provided a n im p rov e d understanding of this c omple x run-of-the-riv e r re se rvoir. H ow ever , que s tions re ma ined on the mag nitude of interna l loading a nd how this migh t influe nce the ov e rall re cove ry of this syste m w ith reductions in e x ternal P loading

.



### Nutrient Criteria—Lakes and Reserv o irs 9-21CASE STUDY : The Minnesota Approach to Lake Eutrophicat i on Model ing
The Minne so taP ollution Control A ge nc y (MP CA) us es a su ite of m odels in the c ours e of lake e utrophic ation s tudie s. Applic ations include: g oal setting during Lake A ssessmen t P r ogra m (L AP ) studie s; de f ining water a nd nutrient m a ss-balanc es during nonpoint sourc e (Cle an Water Partne rs hip) studie s; a nd e s tablishing effl uent-phosphorus limits f or municipa l a nd industrial w astewater dis charges to lakes . The c hoic e of m odel is dictated by the ava ilability of dataa nd the de g re e of pre cis ion require d in the m odeling es tim ate . For e xam ple, the establishmen t of effl uent phosphorus limits f or large dis charge rs require s greater pre ci sion than is required f o r a simple goal -setting exe rcise . T he suite of m odels used by MP CA include (1) a simple regressi on model f or pr ed icting ba ckgr ound phosphorus c onc en tr ations, ( 2) an ecoregi on-ba se d model, ( 3) spreadsheet me thodologie s ba se d on the Reck how a nd Simpson (1980) te c hnique, (4) the BATHTUB m odel, and (5) mechan istic applic ations such a s WASP. A ll of the se m odels ha ve be en used a s a basis f o r g oal setting a nd c an a lso be used to de ve lop nutrient criteria, to pre d ict w hether lakes may ach ie ve certain c r iteria le ve ls, or to determine how point or nonpoint sourc es of phosphorus mayim pact a lake.
A re gr essi on model de ve loped by Vighi and C h iaudani (1985), w h ich is ba sed on the m orphoedaphic inde x (comm only us e d in fishery sc ienc e) , is f requently us e d in Minne so ta to e s tim ate ba ckgr ound T P f or lakes during LAP s tudie s. T he re g re ssi on e quation pre d icts TP ba se d on lake m orphometry (mean depth) and a lka linity or conductivitya nd provide s a quic k es tim ate of ba ckgr ound phosphorus c onc en trations f or a lake. When us ed in conjunction with re fe renc e- lake data se ts a nd other models it can be ve ry us ef ul f o r g oal se tting. It m ay also be particularly us ef ul f o r de ve loping phosphorus c riteria in re gi ons w here back gr ound conditions are assu me d to be naturally oligotrophic to me sotrophic because the m ode l-d e velo pment d ata set is b a sed on oligotrophic a nd meso trophic lakes . This m odel is be s t us ed in conjunction with other tools a nd datasets a nd m ay be of limited v a lue f or goal setting in v e ry shallow lake s, lake s with e xce ssiv e internal loading, or lake/reservoir c hai ns. The "M inne so taLake Eutrophic a tion A nalys is P roc e dure s" (MIN LEAP ), w as de ve loped by MP C A staff ba se d on a n a naly sis of data collected f ro m the reference lakes in each of Min ne sota’s ecoreg i ons. It is intended to be used as a screening tool f or estimating lake conditions with mi nimal input data (lak e mean depth and surface area, watershed area, ecoregio n , an d so me obs erve d dataf or comparison). MIN L EA P is de scr ibe d in g reater de ta il in Wilson and W a lk er (1989). Routine data fr om mi nim a lly-im p acted streams in each ecoregion are used as one ba s is for estimating inf l ow TP concentrations. Annua l pre ci pitation, e vaporation, and runof f are summariz ed ba sed on Minne so taDepar tme nt of Natura l Res ourc es a nd U SGS data and re gi onaliz ed f or us e in the m odel (Wilson, 1990). T he m odel pre d icts in-lake phosphorus c onc en trations ba sed on the Canfield a nd B achma nn (1981) natura l lake e quation. C h lorophyll a and S ecch i are est im ated b ased on regressi on eq uations d evel op ed fr om the eco re gi on-re fe renc e lake da ta se t. In addition, nuis ance fre quencie s of c hlorophyll a are predic ted ba sed on equations de ve loped byWalke r (1985a). The se nuis ance fre quenc y pre d ictions are particularly us ef ul f o r c omm unic ating the im pactof incre as ing in-lake phosphorus c onc en trations to lake us e rs a nd loc al g ov er nme nts

. The MINLEA P proc e dure ha s be en ex tre me ly use f ul f o r quic kly scre en ing lake c ondition and a s a basis f o r g oal setting. The Vigh i and Chiaudani re gr essi on is built into the m odel and allow s fo r c ompar isons be tween the tw o me thodologie s . The MINLEA P m odel tends to w o rk best f o r he adwater lake s or lake s with moderate-siz ed wate rsheds. T he m odel will tend to ov erpre d ict in-lake phosphorus c onc en trations f or lakes w ith larg e wa tersheds or f o r c hai ns of lakes , sinc e upstre am se dime ntation is not spe cifica lly incorporated into the m odel. T he progra m wa s originallyw ritten in BASIC but has be en c onv erted f o r use in Wi ndow s , thus incre as ing its utilitya nd m aki ng it potentiallya daptable f or additional e co re gi ons or f o r us e in other s tates. The ne xtle vel of m odeling routinelyem ploy ed by Minne so ta is the Re ck how a nd Simpson s p re adsheet m odel. T h is s pre adsheet is ba sed on R eck how a nd Simpson (1980) and underly i ng c onc ep ts are dis cussed in g r eater de ta il in Wilson (1990). T h is m ode l relie s on phosphorus ex port c oefficien ts a nd land us es as a ba sis fo r e s tim a ting phosphorus loading to a lake . Runof f coefficie nts a nd re gi onal pre ci pitation and e vaporation dataare us e d to e s tim ate the lake water budg et . T h is type of m odel c an be us ef ul f or es tim a ting the im pactof changes in land us e a nd m aki ng general es tim ates of the re lativ e c ontributions to the in-lake phosphor us c onc en tration f r om a var iety of s ourc es s uch a s the watershed (e .g ., s o ils), pre ci pitation, and shore la nd s e ptic sys te ms . The accuracyof the estimates is depen dent on good land use data, appropriate phosphorus export coef fi cients f or

the region, an d reliable in-lake data to initially test the m odel.
Appropriate phosphorus ex port c oefficien ts are of ten as hortcoming of the Reck how a nd Simpson te c hnique. T h is is es pe cia lly true f or lakes w ith larg e watersheds and/or lake s w h ich ha ve exte nsiv e lake or w e tland areas in their w ate rshed. In the se instanc es , routinely published e x port c oefficien ts w ill often ov eres tim ate actual phosphorus loading a nd produc e unreliable estimates. P rairie and Kalf f (1986) provide so me reg r ession equations that account f o r the size of the watershed, predominan t land us e , and the re te ntion of phosphorus that oc cu rs in larg e watersheds . T his often y iel ds m ore re as onable ex port e s tim ates.

The MP C A vers ion of the Reck how-Simpson s p re adsheet was m odified byW ilson to include a me thodolog y wh ich allow s fo r a n es tim ate of the potential loading f rom feed lots in the watershed (H e is karya nd Wilson, 1996). T his analys is is ba se d on e s tim a te s 9-22 

### Nutrient Criteria—Lakes and Reserv o irsof a nim a l units a nd literature es tim ates of phosphorus generated pe r a nim a l. This feature is us ef ul in w atersheds w ith e x tensiv e f eedlots or pasturing operations since routinely cited phosphorus exports f or “pa stu r ed u se” do not typically account f o r the h ig h phosphorus ex ports arising f rom feed lots (Shuler, 1995). A lthough a sp re adsheet m odel of this type may ha ve many shortcoming s, it often is the only re ad ilyava ilable m odel that c an be used to e s tim ate land use c hang es in the wate rshed w hen data are very limited (as is oft en the case for lo cal go vern ments n eed ing to assess the imp act of smal l scal e land use changes on the quality of a lake ).
Se ve ral other me thodologie s ar e somewhat s imilar to that de sc ribed here but m o re w ide ly ava ilable a nd m ay be us ef ul f or de ve loping or te s ting nutrient criteria or a ssessi ng the im pactof land us e changes in a lake ’s watershe d. P rominent a m ong the se w ould be EU TRO MO D (R eck how, 1990) and the W is c onsin L ake Model Spre adsheet(W IL MS; P a nus ka e t a l ., 1994). T he se two models a nd related models f or a ssessi ng the im pactof de ve lopmen t in a watershed (such a s P ondnet and Pondsiz) are re ad ily ava ilable f rom the N orth A me ric an Lake Mana geme nt Society (Phone: 608-233-2836).



### Nutrient Criteria—Lakes and Reserv o irs 9-23MI

. 

# REFERENCES

A ddiscott T M , Wagenet RJ. 1985. Concepts of solute leaching in soils: A review of modeling approaches. J Soil Sci 36:411-424.
Am brose R B , Barnwell T O , McCutcheon SC, et al. 1995. C o m puter models for water quality analysis. I n Ha ndbook of w a ter resources. N ew Yo rk: McGraw -H ill. Ameel J J , Axler RP, Owen CJ. 1993. Persulfate digestion for determination of total nitrogen and phosphorus in low-nutrient waters. Am Environ Lab 10:1-11. American Public Health Association. 1995. Standard me thods for the examination of water and wastewater. 19th ed. Washington, DC. American Public Health Association. 1998. Standard me thods for the examination of water and wastewater. 20th ed. Washington, DC. Arnold J G , Engel BA, R Srinivasan R. 1993. A continuous time, g r id cell watershed model. I n : Proceedings of Application of A d vanced I n formation Technologies for the Management of Natural Resources, sponsored by ASAE, June 17-19, 1993, Spokane, WA. Arnold J G , Williams J R , Nicks AD, et al. 1989. SWRRB, a basin scale simulation model for soil and water resources in rural basins. J Water Res Plan Manage 113(2):243-256. Ball J E , White MJ , Innes G de R, et al. 1993. Application of HSPF on the Upper Nepean Catchment. In: Proceedings of H y drolog y and Water R e sources Sy m posium, Newcastle, N ew South Wales, A u stralia, J une 30- Ju ly 2, 1993, pp. 343-348. Bannerman R, Owens D, Dodds R, et al. 1993. Sources of pollutants in Wisconsin stormw ater. Water Sci T echnol (28)3-5:241-259.
B easley D B. 1986. D i stributed parameter hydrologic and w a ter quality modeling. In: Giorgini, Z i ngales E, eds. Agricultural nonpoint source pollution: Model selection and application, pp. 345-362.
Bi cknell B R , I m hoff J C , Kittle J L , et al. 1993. H y drological Simulation Program - FO RTRAN (HSPF): User's m a nual for release 10.0. U.S. Environmental Protection Agency, Environmental Research Laboratory, Athens, GA. EPA 600/3-84-066.
B ouraoui E, Dillaha T A , Mostaghimi S. 1993. A NS WERS 2000: Watershed model for sediment and nutrient transport. ASAE Paper No. 93-2079. American Society of Agricultural Engineers, St. J o seph,

Br abets T P . 1986. Q u antity and quality of urban runoff from the C h ester C r eek Basin, A n chorage, Alaska. Water Resources I n vestigations Report 86-4312. U.S. Geological Survey, Denver, CO. Brezonik PL, Shannon EE. 1971. T r ophic state of lakes in north central Florida. Research Project T echnical Completion Report. OWRR Project No. B-004-FLA., Publ.. No. 13. Water Research Center, Un iversity of Florida.


### Nutrient Criteria—Lakes and Reservo ir s R-1Camp, Dresser, and Mckee (CDM). 1992. Watershed Management Model user’s m a nual, version 2.0. Prepared for the Florida Department of Environmental Regulation, T a llahassee, FL. Canale RP, Hinemann DF, Nachippan S. 1974. A biological production model for Grand T r averse Bay

. University of Michigan Sea Grant Program, Technical Report No. 37, Ann Arbor, MI

. Canfield D , Bachmann R. 1981. Prediction of total phosphorus concentrations, chlorophyll-a, and Secchi depths in natural and artificial lakes. Can. J Fish Aquat Sci 38:414-423. Canfield DE. 1983. Prediction of chlorophyll a concentrations in Florida lakes: T h e importance of phosphorus and nitrogen. Water Res Bull 19:255-262.
Ca nfield D E Jr. 1983. I m pact of integrated aquatic weed m a nagement on w a ter quality in a citrus g r ove. J Aquat Plant Manage 21:69-73. Canfield D E Jr, Langeland KA, Maceina MJ, et al. 1983. T r ophic state classification of lakes with aquatic macrophytes. Can J Fish Aquat Sci 40:1713-1718. Carlson RE. 1977. A trophic state index for lakes. Limnol Oceanogr 22:361-369. Carlson RE. 1980. More complications in the chlorophyll-Secchi disk relationship. Limnol Oceanog r 25(2):379-382. Carlson RE. 1983. Discussion: Using differences among Carlson' trophic state index values in regional w ater quality assessment, by Richard A. Osgood. Water Res B u ll 19(2):307-309. Carlson RE. 1991. Expanding the trophic state concept to identify non-nutrient limited lakes and reservoirs. In: Enhancing the State's lake management programs: Proceedings of a conference, C h icago, 1991, North American Lake Management Society, pp. 59-71. Carlson RE. 1992. Expanding the trophic state concept to identify non-nutrient limited lakes and reservoirs. In: Proceedings of a N a tional Conference on Enhancing the States' Lake Management Programs, Monitoring and Lake I m pact Assessment, Chicago. pp. 59-71. Carlson RE, Simpson J. 1996. A coordinator's g u ide to volunteer lake monitoring methods. North American Lake Management Society, Madison, WI

. Carpenter SR, Lodge DM. 1986. Effects of submersed macrophytes on ecosystem processes. Aquat Bot 341-370. Chapra S, Canale RR. 1991. Long -t erm phenomenological model of phosphorus and oxy ge n for stratified lakes. Water Res 25(6):707-715.
Chapra SC. 1975. Comme nt on An empirical m e thod of estimating the retention of phosphorus in lakes by Kirchner WB, Dillon PJ. Water Res 11(6):1033-1034. Chapra SC. 1979. Applying phosphorus loading models to embay ments. Limnol Oceanogr 24:163-168.

R-2 

### Nutrient Criteria—Lakes and Reserv o irsChen CW, Orlob GT. 1975. Ecological simulation for aquatic environments. I n : Patton BC, ed. System s analy s is and simulation in ecolog y . Vol. III . New York : Academic Press, p. 475. Chapra SC, T arapchak SJ

. 1976. A chlorophyll a model and its relationship to phosphorus loading plots for lakes. Water Res 12(6):1260-1264. Chen CW, Orlob GT. 1975. Ecological simulation for aquatic environments. I n : Patton BC, ed. System s analy s is and simulation in ecolog y . Vol. III . New York : Academic Press, p. 475. Cl ark WC , Jones D D , Holling CS. 1979. Lessons for ecological policy design: A case study of ecosystem ma nagement. Ecol Model 7:1-53. Cornett RJ, Rigler FH. 1979. Hypolimnetic oxy ge n deficits: Their prediction and interpretation. Science 205:580-581. D'Elia CF, Steudler PA, Corwin N. 1977. Determination of total nitrogen in aqueous samples using persulfate digestion. Limnol Oceanogr 22:760-764.
D illaha, T A . 1992. Nonpoint source modelling for evaluating the effectiveness of best m a nagement practices. NWQEP Notes 52(March):5-7. Dillon PJ, Rigler FH. 1975. A simple me thod for predicting the capacity of a lake for development based on lake trophic status. J Fish Res Board Can 31(9):1519-1531. Donigian AS J r , Bicknell BR, Linker LC, et al. 1990. Chesapeake Bay Program Watershed Model application to calculate bay nutrient loadings: Preliminary Phase I findings and recomme ndations. Prepared for the U.S. Chesapeake Bay Prog ram , Annapol is , MD, by AQUA T E RRA Consul ta nts.
D onigian A S , Huber WC. 1991. Modeling of nonpoint source w a ter quality in urban and non-urban areas. U.S. Environmental Protection Agency, Washington, DC. EPA/600/3-91/039. Donigian AS J r , Patwardhan AS. 1992. Modeling nutrient loadings from croplands in the Chesapeake Bay Watershed. I n : Proceedings of w a ter resources sessions at Water Forum '92, B a ltimore, MD, A ugu st 2-6, 1992, pp. 817-822. Ebina J, et al. 1983. Simultaneous determination of total nitrogen and total phosphorus in water using peroxydisulfate oxidation. Water Res 17:1721-1726. Edmondson WT. 1961. Changes in Lake Washington following an increase in the nutrient income. Ve rhandl I n t V e rein T h eoret Angew Limnol 14:167-175. Edmondson WT. 1972. Nutrients and phytoplankton in Lake Washington. I n : Likens GE, ed., Nutrients and eutrophication. Lawrence, K S : A merican Society of Limnolog y and Oceanography, pp. 172-193. Elser J J , Marzolf ER, Goldman CR. 1990. Phosphorus and nitrogen limitation of phytoplankton g r owth in the freshwaters of North America: A review and critique of experimental enrichments. Can J Fish Aquat Sci 47:1468-1477.



### Nutrient Criteria—Lakes and Reserv o irs R-3Engel B A , Srinivasan R, Rewerts C. 1993. Modeling erosion and surface water quality. Geographic In formation Systems: Proceedings of the Seventh Annual G RA SS U s ers Conference, Lakewood, CO , March 16-19, 1992. National Park Service Technical Report NPS/NRGISD/NRTR-93/13. Ernst MR, Frossard W, Mancini J L . 1994. T w o eutrophication models m ake the g r ade. Water Environ T echnol November:15-16. Fairweather PG. 1991. Statistical power and design requirements for environmental monitoring. Aus J Mar Freshwater Res 42:555-67. Federal Highway Administration. 1990. Pollutant loadings and impacts from highway stormw ater runoff. U.S. Department of T r ansportation, Research, Development, and Technolog y , McLean, V A. Ford DE. 1990. Reservoir transport processes. In: Thornton KW , K imme l BL, Payne FE, eds. Reservoir limnolog y: Ecological perspectives. New York: Wiley -In terscience, pp. 15-41. Gerritsen J, Jessup B, Leppo E, et al. 1999. Development and testing of a biological index for Florida lakes. Prepared for Florida Department of Environmental Protection, T a llahassee, FL. Gibson G, Wedepohl R, K n auer D. 1983. Lake protection by watershed m a nagement for Wisconsin lake districts. Proceedings of the N o rth A merican Lake Management Society, Vancouver, B r itish C o lumbia, Canada. EPA 440/5-83-001.
G liwicz ZM, Kowalczewski A. 1981. Epilimnetic and hypolimnetic sy mp toms of eutrophication in G r eat Mazurian Lakes, Poland. Freshwater Biol 11:425-433. Griffith GE, Canfield DE J r , Horsburgh CA, et al. 1997. Lake regions of Florida. Map published by Florida Department of Environmental Protection and U.S. Environmental Protection Agency , Ta llahassee, FL.
Gu ay J R. 1990. Simulation of urban runoff and river water quality in the San J o aquin R i ver near Fresno, Ca lifornia. I n : Sy m posium Proceedings on U rban H y drolog y , A merican Water R e sources Association, Denver, CO, November 4-8, 1990, pp. 177-182. Haith DA, Mandel R, Wu RS. 1992. GV VL F-Generalized Watershed Loading Functions, V e rsion 2.0 Us er's m a nual. C o rnell U n iversity, D e partment of A g ricultural Engineering, Ithaca, N Y. Haith DA, Shoemaker LL. 1987. Generalized watershed loading functions for stream flow nutrients. Water Res Bull 107(EEI):121-137.
He iskary S, Lindbloom J, Wilson C B . 1994. D e tecting water quality trends with citizen volunteer data. Lake Reservoir Manage 9(1):4-9. Heiskary SA. 1989. Lake assessment program: A cooperative lake study program. Lake Reservoir Manage 5:85-94. Heiskary SA, Anhorn R, Noonan T, et al. 1994. Minnesota lake and watershed data collection m a nual. Environmental Q u ality Board-Lake s Task Force, D a ta and I n formation C ommittee. Minnesota Lakes A ssociation.

R-4 

### Nutrient Criteria—Lakes and Reserv o irs115. Heiskary SA, Walker WW J r . 1988. Developing phosphorus criteria for Minnesota lakes. Lake Reservoir Manage 4(1):1-10. Heiskary SA, Walker WW J r . 1995. Establishing a chlorophyll-a g o al for a run-of-the-river reservoir. Lake Reservoir Manage 11(1):67-76.
H eiskary SA , Wilson C B . 1988. Minnesota Lake Water Q u ality Assessment Report. Minnesota Pollution Control Agency, St. Paul.
He iskary SA, Wilson C B . 1989. T h e regional nature of lake w a ter quality across Minnesota: An analysis for improving resource m a nagement. J Minn Acad Sci 55:71-77. Hession WC, Storm DE, Burks SL, et al. 1995. Using EUTROMOD with a GIS for establishing total ma ximum daily loads to Wister Lake, O klahoma. I n : I m pact of animal w a ste on the land- wa ter interface. Lewis Publishers, pp. 53-60. Hoyer MV, Jones J R . 1983. Factors affecting the relation between phosphorous and chlorophyll a in mi dwestern reservoirs. Can J Fish Aquat Sci 40:192-199. Huber WC. 1992. Experience with the USEPA SWMM Model for analysis and solution of urban drainage problems. I n : D o lz J, Gomez M, Martin J P , eds. Proceedings, Inundaciones Y Redes D e Drenaj e Urbano, pp. 199-220. C o legio de ingenieros de C ami nos, C a nales Y Puertos, U n iversitat Politecnica de Catalunya, Barcelona, Spain. Huber WC, Brezonik PL, Heaney JP. 1982. A classification of Florida lakes. Report to the Florida Department of Environmental Regulation. Report ENV

- 05-82-1. Huber WC, Dickinson RE. 1988. Storm water m a nagement model version 4. User's m a nual. U.S. Environmental Protection Agency, Athens, GA. EPA/600/3-88/001a (NT IS PB88-236641/AS). Hurlbert SH. 1984. Pseudoreplication and the design of ecological field experiments. Ecol Monog 54(2):187-211.
J ones J R , Bachmann RW. 1978. Trophic status of I o wa lakes in relation to origin and g l acial g e olog y. Hydrobiologia 57:267-273.
J ones J R , Knowlton MF. 1993. Limnolog y of Missouri reservoirs: An analysis of regional patterns. Lake Reservoir Manage 8:17-30.
J ones J R , Knowlton MF, Swar DB. 1989. Limnological reconnaissance of waterbodies in central and southern Nepal. Hydrobiologia 184:171-189.
J ones J R , Novak J T. 1981. Limnological characteristics of Lake of the Ozarks, Missouri. Verhandl I n t Ve reinig Theoret Angew Limnol 21:919-925.
Jo rgensen SE. 1995. State of the art of ecological modelling in limnolog y . Ecol Model 78(1995):101-

Karr J R . 1981. Assessment of biotic integrity using fish comm unities. Fisheries 6(6):21-27. 

### Nutrient Criteria—Lakes and Reserv o irs R-5Kennedy R H. 1998. Basinwide considerations for water quality management: importance of phosphorus retention by reservoirs. Water Q u ality Technical N o te MS-03, U

. S. A rmy Engineer Waterway s Experiment Station, Vicksburg, MS. Kennedy RH. 1999a. Reservoir design and operation: Limnological implications and m a nagement opportunities. In: Tundisi J G , Straskraba M, eds. Theoretical reservoir ecolog y and its applications. Br azil and the N e therlands: I n ternational I n stitute of Ecolog y , Brazilian Academy of Sciences, and Backhuys Publishers, pp. 1-28. Kennedy R H. 1999b. N u trient criteria: Considerations for C o rps of Engineers reservoirs. Water Q u ality T echnical Note, U.S. Army Engineer Waterways Experiment Station, V i cksburg, MS.
Ke nnedy RH, Walker WW. 1990. Reservoir nutrient dynamics. In: Thornton KW , K imme l DL, Payne FE, eds. Reservoir limnolog y: Ecological perspective. New York: John Wiley, pp. 109-131.
Ke nnedy RH, Thornton KW , Ford D. 1985. Characterization of the reservoir ecosystem. I n : Gunnison D, ed. Microbial processes in reservoirs. Boston: Dr. W. Junk Publishers. Kiilsgaard C W , Rohm CM, Pierson SM, et al. 1993. T o tal phosphorus regions for lakes in the No rtheastern U n ited States. Prepared for ManTech Environmental Technolog y , Inc., C o rvallis, O R , and the U

. S. Environmental Protection A g ency, C o rvallis, O R. Kimme l BL, Lind OT, Paulson LJ. 1990. Reservoir primary production. In: Thornton K W , K immel BL, Payne FE, eds. Reservoir limnolog y: Ecological perspectives. New York: Wiley -In terscience, pp. 133-193. Knowlton MF, Jones J R . 1989. Comparison of surfaces and depth integrated composite samples for estimating algal biomass and phosphorus values, and notes on the vertical distribution of autotrophs in Midwestern lakes. Arch Hydrobiol 83 (Suppl):175-196. Knowlton MF, Jones J R . 1996. N u trient addition experiments in a nitrogen-limited high plains reservoir where nitrogen-fixing algae seldom bloom. J Freshwater Ecol 11:123-130. Kratzer CR, Brezonik PL. 1981. A Carlson-type trophic state index for nitrogen in Florida lakes. Water Res Bull 17:713-715. Laws EA, Chalup MS. 1990. A microalgal g r owth model. Limnol Oceanogr 35(3):597-608. Lindner-Lunsford J B , Ellis SR. 1987. C o mp arison of conceptually based and regression rainfall-runoff m odels, Denver Metropolitan A r ea, C o lorado, and potential applications in urban areas. Water Resources In vestigation Report 87-4104. U.S. Geological Survey, Denver, CO. Lindner-Lunsford J B , Hutchinson GE. 1957. A treatise on limnolog y . Vol. 1. Geography, physics, and chemistry. New York: John Wiley

. Linthurst RA, Landers DH, Eilers J M , et al. 1986. Characteristics of lakes in the eastern United States. Vol. 1: Population descriptions and physico-chemical relationships. Office of Research and Development, U.S. Environmental Protection Agency

.

R-6 

### Nutrient Criteria—Lakes and Reserv o irsLumb AM, Kittle J L , Flynn KM. 1990. U s ers m a nual for A NI VIE, A computer programfor interactive hydrologic analyses and data m a nagement. Water Resources I n vestigation Report 89-4080. U.S. Geological Survey, Reston, V A. Lumb AM, Kittle J L . 1993. Expert system for calibration and application of watershed models. I n : Proceedings of the Federal I n teragency Workshop on H y drologic Modeling Demands for the 90's. U

. S. Ge ological Survey Water R e sources I n vestigation R e port 93-4018. Fort C o llins, C O , June 6-9, 1993. Martin RG, Arneson RD. 1978. Comparative limnolog y of a deep-discharge reservoir and a surface-discharge lake on the Madison R i ver, Montana. Freshwater B i ol 8:33-42. McCauley E, Downing J A, Watson S. 1989. Sig m oid relationships between nutrients and chlorophyll among lakes. Can J Fish Aquat Sci 46:1171-1175. McCollor S, H e iskary S. 1993. Selected w a ter quality characteristics of mi nimally impacted streams from Minnesota's seven ecoregions. Minnesota Pollution Control Agency, St. Paul, MN. McElroy AD, Chiu SW, Nabgen J W , et al. 1976. Loading functions for assessment of water pollution for non-point sources. U.S. Environmental Protection Agency. EPA 600/2-76/151 (NT IS PB-253325). Meeuwig J J , Peters RH. 1996. Circumventing phosphorus in lake m a nagement: A comparison of chlorophyll a predictions from land-use and phosphorus loading models. Can J Fish Aquat Sci 53:1795- 1806. Menzel DW, Corwin N. 1965. T h e measurement of total phosphorus in sea water based on the liberation of organically bound fraction by persulfate oxidation. Limnol Oceanogr 10:280-282. Mills WB, B o rcella B B , Ungs MJ, et al. 1985. Water quality assessment. A screening procedure for toxic and conventional pollutants in surface and g r ound w a ter. Part 1. U

. S. Environmental Protection A g ency , Environmental Research Laboratory, Athens, GA. EPA/600/6-85/002a. Moore LW, Chew CY, Smith RH, et al. 1992. Modeling of Best Management Practices on North Reelfoot Creek, T e nnessee. Water Environ Res 64(3):241-247. Morris DP, Lewis WM J r . 1988. Phytoplankton nutrient limitation in Colorado mountain lakes. Freshwater Biol 20:315-327. Mortimor CH. 1941. T h e exchange of dissolved substances between mud and water in lakes. J Ecol 30:147-201. Moss B, Madgewick J, Phillips G. 1996. A gu ide to the restoration of nutrient-enriched shallow lakes. Broads Authority, Norwich, UK. 180 pp. Naumann E. 1929. T h e scope and chief problems of regional limnolog y . Int Revue Ges Hydrobiol 21:423. Needham SE, Young, RA. 1993. ANN-AGNPS: A cont i nuous si mu lati on watershed model. I n Proceedings of the Federal I n teragency Workshop on H y drologic Modeling Demands for the 90's, Fort Co llins, C O , June 6-9, 1993. U

. S. G e ological Survey Water R e sources I n vestigation R e port 93-4018. 

### Nutrient Criteria—Lakes and Reserv o irs R-7Nix J S . 1991. Applying urban runoff models. Water Environ Technol June 1991. North American Lake Management Society. 1992. Developing eutrophication standards for lakes and reservoirs. Report prepared by the Lake Standards Subcommittee. Alachua, FL. 51 pp. Nurnberg GK. 1996. T r ophic state of clear and colored, soft- and hardwater lakes with special consideration of nutrients, anoxia, phytoplankton and fish. J Lake Reservoir Manage12:432-447.
O'C onner D J , Thomann R X , D i Toro D M . 1975. Water quality analyses of estuarine systems. I n : Estuaries, g e ophysics, and the environment. National Academ y of Sciences, Washington, DC. Oglesby RT

. 1977. Relationships of fish y i eld to lake phytoplankton standing crop, production, and mo rphoedaphic factors. J Fish Res Board Can 34:(12)2271-2279. Og lesby RT , Leach J H , Forney J. 1987. Potential Stizostedion y i eld as a function of chlorophyll concentration with special reference to Lake Erie. Can J Fish Aquat Sci 44(Suppl. 2):166-170. Olen H, Flock G, eds. 1990. Lake and reservoir restoration g u idance m a nual, 2nd ed. U.S. Environmental Protection Agency. EPA-440/4-90-006. O'Melia CR. 1972. An approach to modeling of lakes. Schweiz Zeitschr Hydrol 34:1-34. Omernik JM. 1976. T h e influence of land use on stream nutrient levels. U.S. Environmental Protection Agency. EPA-600/3-76-014. Omernik JM. 1987. Ecoregions of the conterminous United States. Ann Assoc Am Geogr 77(1):118-125. Omernik JM. 1995. Ecoregions: A framework for m a naging ecosystems. George Wright Forum 12(1):35-50. Omernik JM. 1998. EPA ecoregion map. NHEERL-WED, U.S. Environmental Protection Agency , Co rvallis, O R Omernik JM, Larsen DP, Rohm CM, et al. 1988. Summe r total phosphorus in lakes: A m ap of Minnesota, Wisconsin, and Michigan. Environ Manage 12:815-825. Omernik JM, Rohm CM, Clark SE, et al. Summe r total phosphorus in lakes: A m ap of Minnesota, Wisconsin, and Michigan, USA. Environ Manage 12(6):815-825. Omicron Associates. 1990. Nonpoint pollution source model for analysis and planning (NPSMAP)—Users m a nual. Omicron Associates, Portland, OR. Organization for Economic Co-operation and Development (OECD). 1982. Eutrophication of waters-

- m onitoring assessment and control. OECD, Paris. 154 p. Osgood RA. 1988. Lake mi xis and internal phosporous dynamics. Arch Hydrobiol 113:629-638.

R-8 

### Nutrient Criteria—Lakes and Reserv o irsO vbiebo T, She N. 1995. U rban runoff quality and quantity modeling in a subbasin of the D uwami sh river using XP-SWMM. I n : Proceedings of a Sy m posium, Water Management Planning for the 21st Century, American Society of Civil Engineers, San Antonio, T X , August 14-16, 1995, pp. 320-329. Palmstrom N, Walker WW J r . 1990. P8 urban catchment model user's g u ide, program documentation, and evaluation of existing models, design concepts, and Hunt-Potowomut data inventory. T he Narragansett Bay Project Report No. NBP-90-50. Pantalion J, Scharlach A, Oswald G. 1995. Water quality master planning in an urban w a tershed. I n : Watershed Management: Planning for the 21st C e ntury, proceedings of the A SCE's First I n ternational Conference of Water Resources Engineering, San Antonio, T X , August 14-16, 199S, pp. 330-339. Panuska J C , Moore J D , Kramer LA. 1991. T e rrain analysis: I n tegration into the agricultural nonpoint source (AGNPS) pollution model. J Soil Water Conserv 46(l):59-64. Paulsen SG, Larsen D P , K a ufmann PR, et al. 1991. EMAP - surface w a ters monitoring and research strateg y , fiscal year 1991. U.S. Environmental Protection Agency, Office of Research and Development, Washington, D C , and Environmental Research Laboratory, Corvallis, O R . EPA

- 600-3-91-002. Peterman RM. 1990. T h e importance of reporting statistical power: T h e forest decline and acidic deposition example. Ecolog y 71:2024-2027. Peters RH. 1986. T h e role of prediction in limnolog y . Limnol Oceanogr 31:1143-1159. Pielou EC. 1977. Mathematical ecolog y . New York: John Wiley. Pitt R. 1987. Small storm urban flow and particulate w a shoff contributions to outfall discharges. Ph.D

. dissertation, Civil and Environmental Engineering Department, University of Wisconsin, Madison, WI

. Pitt R. 1993. Source loading and m a nagement model (SLAMM). Presented at the N a tional Conference on Urban Runoff Management, March 30-April 2, 1993, Chicago, I L. Prairie YT, Duarte CM, Kalff J. 1989. Unifying nutrient-chlorophyll relationships in lakes. Can J Fish Aquat Sci 46:1176-1182. Prairie YT, Marshall CT. 1995. On the use of structured time-series to detect and test hypotheses about within-lake relationships. Can J Fish Aquat Sci 52:799-803. Prairie YT, K a lff J. 1986. Effect of catchment size on phosphorus export. Water Res Bull 22(3):465-470. Pridmore RD, V a nt WN, Rutherford J C . 1985. Chlorophyll-nutrient relationships in North I s land Lakes (New Zealand). Hydrobiologia 121:181-189. Quiros R. 1990. Factors related to variance or residuals in chlorophyll-total phosphorus regression in lakes and reservoirs of Argentina. Hydrobiologia 200/201:343-355. Raschke RL. 1994. Phytoplankton bloom frequencies in a population of small Southeastern impoundments. Lake Reservoir Manage 8(2):205-210. 

### Nutrient Criteria—Lakes and Reserv o irs R-9Rast W, Lee GF. 1983. Nutrient loading estimates for lakes. J Env Eng 109:502-517. Rast W, Lee GF. 1987. Summary analysis of the North American OECD eutrophication project: Nutrient loading

- lake response relationships and trophic state indices. U.S. Environmental Protection Agency. EPA 600/3-78-008. Rawson DS. 1952. Mean depths and the fish production of large lakes. Ecolog y 33:513-521. Rawson DS. 1955. Morphometry as a dominant factor in the productivity of large lakes. Verhandl I n t Ve rein T h eoret Angew Limnol 12:164-175. Reckhow K H , Simpson J T . 1980. A procedure using modeling and error analysis for the prediction of the lake phosphorus concentration from land use information. Can J Fish Aquat Sci 37:1439-1448. Reynolds CS. 1997. Vegetative processes in the Pelagic: A model for ecosystem theory. Ecolog y In stitute, O l dendorf/Luhe, G e rmany. 371 p. Reynolds CS, Walsby AE. 1975. Water blooms. Biol Rev 50:437-481. Riley ET , Prepas EE. 1985. Comparison of the phosphorus-chlorophyll relationships in mi xed and stratified lakes. Can J Fish Aquat Sci 42 (4):831-835.
R odhe W. 1969. C rys tallization of eutrophication concepts in northern Europe. In: Eutrophication: Causes, consequences, correctives. National Academ y of Sciences, pp. 50-64. Rohm CM, Omernik JM, Kilsgaard CW. 1995. Regional patterns of total phosphorous in lakes of the northeastern United States. Lake Reservoir Manage 11:1-14. Ryder RA. 1965. A method for estimating the potential fish production of north-temperate lakes. T r ans Am Fish Soc 94:214-218. Ryding SO, Rast W. 1989. The control of eutrophication of lakes and reservoirs. Man and the Bioshere Series, United Nations Educational Scientific and Cultural Organization, Paris, France. 314 pp. Sakamoto M. 1966. Primary production of phytoplankton comm unity in some J apanese lakes and its dependence on lake depth. Arch Hydrobiol 62:1-28.
Saw y er C N . 1947. Fertilization of lakes by agricultural and urban drainage. N Engl Water Works Assoc 61:109-127. Scheckenberger RB, K e nnedy AS. 1994. T h e use of HSPF in subwatershed planning. I n : J ame s W, ed. Cu rrent practices in modelling the m a nagement of stormw ater impacts. B o ca R a ton, FL: Lewis Publishers, pp. 175-187. Scheffer M. 1989. Alternative stable states in eutrophic shallow freshwater systems: A minimal model. Hydrobiol Bull 23:73-85. Scheffer M, H o sper SH, Meijer M-L, et al. 1993. Alternative equilibria in shallow lakes. Trend Ecol Evolut 8:275-279.

R-10 

### Nutrient Criteria—Lakes and Reserv o irsSchindler DW. 1977. Evolution of phosphorus limitations in lakes. Science 195:260-262. Schindler DW. 1978. Factors regulating phytoplankton production and standing crop in the world' s freshwaters. Limnol Oceanogr 23:478-486. Schueler T. 1987. Controlling urban runoff. A practical m a nual for planning and designing urban B M Ps. Metropolitan Washington Council of G o vernments, Washington, D C. Schuler D. 1995. Lake Shaokatan restoration project. Land Water May/June:12-15. Shannon EE, Brezonik PL. 1972. Limnological characteristics of north and central Florida lakes. Limnol Oceanogr 17:97-110. Shapiro J, Lamarra V, Lynch M. 1975. Biomanipulation—An ecosystem approach to lake restoration. Proceedings of a Sy m posium on Water Q u ality Management T h rough Control, U n iversity of Florida. Smart MM, Reid FA, Jones J R . 1981. A comparison of a persulfate digestion and the K j eldahl procedure for determination of total nitrogen in freshwater samples. Water Res 15:919-921. Smart MM, Jones J R , Sebaugh J L . 1985. Stream -w aterhsed relations in the Missouri Ozark Plateau province. J Environ Qual 14:79-82. Smeltzer E, Heiskary SA. 1990. Analysis and applications of lake user survey data. Lake Reservoir Manage 6:109-118. Smeltzer E, Walker WW, Garrison V. 1989. Eleven years of lake eutrophicatioon monitoring in Vermont: A critical evaluation. In: Enhancing State's Lake Management Programs. U.S. Environmental Protection Agency and North American Lake Management Society, pp. 52-62. Smith R A , Schwartz GE, Alexander R B . 1997. R egi onal interpretation of w a ter quality monitoring data. Water Res 33:2781-2798. Søballe DM, Bachmann RW. 1984. Removal of Des Moines River phytoplankton by reservoir transit. Can J Fish Aquat Sci 41:1803-1813. Søballe DM, T h relkeld ST. 1985. Advection, phytoplankton biomass, and nutrient transformation in a rapidly flushed impoundment. Arch Hydrobiol 105:187-203. Solorzano L, Sharp J. 1980. Determination of total dissolved nitrogen in natural waters. Limnol Oceanogr 25:751-754. Srinivasan R, Arnold J G . 1994. I n tegration of a basin-scale w a ter quality model with G I S. Water R es Bull 30(3):453-462. Straškraba M, Straškrabova V. 1975. Management problems od Slapy Reservoir, Bohemia, Cz echoslovakia. I n : Proceedings of a Sy m posium on the Effects of Storage on Water Q u ality, Reading University, Reading, England, pp. 449-484.



### Nutrient Criteria—Lakes and Reserv o irs R-11DC. Straškraba M, Tundisi J G , Duncan A. 1993. State-of-of-the-art of reservoir limnolog y and w a ter quality ma nagement. In: Straškraba M, Tundisi J G , Duncan A, eds. Comparative reservoir limnolog y and water quality management. The Netherlands: Kluwer Academic Publishers, pp. 213-288. Straškraba M, D o stálk o vá I, Hej z lar J, et al. 1995. T h e effect of reservoirs on phosphorus concentration. In t Rev Gesamt Hydrobiol 80:403-413.
Ta sker G D , Driver N E . 1988. N a tionwide regression models for predicting urban runoff w a ter quality at unmonitored sites. Water Res Bull 24(5):1091-1101.
Te rstriep ML, Lee MI, Mills EP, et al. 1990. Simulation of urban runoff and pollutant loading from the gr eater Lake C a lumet area. Prepared for the U

. S. Environmental Protection A g ency, R egi on 5, Water Di vision, Watershed Management U n it, C h icago, I L , by the Illinois State Water Survey

. T etra Tech, I n c. 1995. H y drodynamic and water quality mathematical modeling study of N o rfolk Harbor, Connecticut - F inal report. T e tra Tech, I n c., Fairfax, VA

. Th ienemann A. 1921. Seetypen. Naturwissenschaften 18:1-3.
T homann RV. 1977. Comparison of lake phytoplankton models and loading plots. Limnol Oceanog r 22:370-373.
T hompson SK. 1992. Sampling. New York: John Wiley

. T hornton KW . 1990. Sedimentary process. In: Thornton K W , K imme l BL, Payne FE, eds, Reservoir limnolog y: Ecological perspectives. New York: John Wiley, pp. 43-69.
T hornton KW, Kennedy R H, Carroll J H , et al. 1980. R e servoir sedimentation and w a ter quality—A n heuristic model. I n : Proceedings of the Sy m posium on Surface Water I m poundments, A S CE, 2-5 June 1980, Minneapolis, MN, pp. 654-664.
T hum RG, Pickett SR, Niemann J rBJ , et al. 1990. LIS/GIS: I n tegrating nonpoint pollutant assessment with land development planning. Wisc Land I n f Newsl 5(2):1-12.
Tim US, J o lly R. 1994. Evaluating agricultural nonpoint-source pollution using integrated g e ographic information systems and hydrologic/water quality model. J Environ Q u al 23:25-35.
Tim US , Mostaghimi S, Shanholtz VO , et al. 1991. I d entification of critical nonpoint pollution source area using geographic information systems and simulation modeling. In: Proceedings of the A m erican Society of Agricultural Engineers (ASAE) I n ternational Winter Meeting, Albuquerque, NM, June 23-26, 1991.
Ts hihrintzis VA, H ami d R, Fuentes H R . 1995. C a libration and verification of w a tershed quality model SWMM in sub-tropical urban areas. I n : Proceedings of the First I n ternational Conference-Water Resources Engineering, American Society of Civil Engineers, San Antonio, T X , August 14-18, 1995, pp. 373-377.
U.S. Arm y Corps of Engineers. 1998. National I n ventory of Dams. Office of the Chief, Washington,

R-12 

### Nutrient Criteria—Lakes and Reserv o irsU.S. Environmental Protection Agency. 1974. An approach to a relative trophic index system for classifying lakes and reservoirs. Working Paper No. 24. National Eutrophication Survey, C o rvallis, O R. U.S. Environmental Protection Agency. 1983. Results of the nationwide urban runoff project. V o l. 1. Office of Water, Washington DC. U.S. Environmental Protection Agency. 1992a. Science Advisory Board report to Administrator Br owner reviewing "Biological C r iteria: Technical G u idance for Streams and Small R i vers." Office of Research and Development, Washington, DC. U.S. Environmental Protection Agency. 1992b. T M DL Case Study #4: Nomimi Creek Watershed. T M DL Case Study Series. Office of Water, Washington, DC. EPA 841-F-93-004.
U. S. Environmental Protection A g ency. 1996. Proceedings of the N a tional N u trient Assessment Workshop, December 4-6, 1995. EPA-822-R-96-004. U.S. Environmental Protection Agency. 1997. Compendium of tools for watershed assessment and TM DL development. Office of Water, Washington, DC. EPA 841-b-97-006. U.S. Environmental Protection Agency. 1998. National strateg y for the development of regional nutrient criteria. EPA-822-R-98-002.
Ve rry ES, T imm ons DR. 1982. Waterbourne nutrient flow through an upland-peatland watershed in Minnesota. Ecolog y 63(5):1456-1467.
Vieux B E , Needham S. 1993. Nonpoint-pollution model sensitivity to g r id-cen size. J Water Res Plan Manage 119(2):141-157. Vollenweider RA. 1968. T h e scientific basis of lake and stream eutrophication with particular reference to phosphorus and nitrogen as eutrophication factors. Technical Report DAS/DSl/68.27, Organization for Economic Cooperation and Development, Paris, France. Vollenweider RA. 1975. Input-output models with special reference to the phosphorus loading concept in limnolog y . Schweiz Zeitschr Hydrol 37:53-84. Vollenweider R A . 1976. A d vances in defining critical loading levels for phosphorus in lake eutrophication. Mem Ist Ital I d robiol 33:53-83.
Vo llenweider RA, K e rekes J J . 1980. Back gr ound and summary results of the OECD cooperative program on eutrophication. I n : Proceedings of an I n ternational Sy m posium on I n land Waters and Lake Restoration, pp. 26-36. U.S. Environmental Protection Agency. EPA 440/5-81-010. Walker WW J r . 1979. Use of hypolimnetic depletion rate as a trophic status index for lakes. Water Res 15:1463-1470. Walker, W.W. 1985a. Statistical bases for mean chlorophyll a criteria. pp. 57-62 In Lake and Reservoir Management: Practical Applications. Proceedings of the Fourth Annual Conference and I n ternational Sy m posium. October 16-19, 1984. McAfee, NJ, North American Lake Management Society

.


### Nutrient Criteria—Lakes and Reserv o irs R-13366. Walker WW J r . 1985b. Urban nonpoint source impacts on surface w a ter supply. Perspectives on nonpoint source pollution. Proceedings of a national conference, Kansas City, MO, May 19-22, 1985, pp. 129-137. U.S. Environmental Protection Agency. EPA 440/5-85-01. Walker WW. 1986. Empirical methods for predicting eutrophication in impoundments; Report 4, Phase 11. Applications Manual. Technical Report E-81-9, U.S. Army Engineer Waterways Experiment Station, Vi cksburg, MS. Walker WW J r . 1987. Empirical m e thods for predicting eutrophication in impoundments. Report 4. Phase III: Applicati on manual, Technical Report e-81-9. USACE WES, Vick s burg, MS. Walker WW J r . 1996. Simplified procedures for eutrophication assessment and prediction: User m a nual. prepared for USACE, USWES, V i cksburg MS. W-96- 2 Walker JF, Pickard SA, Sonzogni WC. 1989. Spreadsheet watershed modeling for nonpoint-source pollution m a nagement in a Wisconsin basin. Water Res Bull 25(1):139-147. Warwick JJ , Tadepalli P. 1991. Efficacy of SWMM application. J Water R e s Plan Manage 117(3):352-
Watson SE, McCauley E, Downing J A. 1992. Sig m oid relationships between phosphorus, algal biomass and algal comm unity structure. Can J Fish Aquat Sci 49:2605-2610. Wedepohl RE, K n auer DR, Wolbert GB, et al. 1990. Monitoring lake and reservoir restoration. U.S. Environmental Protection Agency. EPA 440/4-90-007. Welch EB, Cooke GD. 1995. Internal phosphorus loading in shallow lakes: I m portance and control. Lake Reservoir Manage 11:273-281. Wetzel RG. 1966. Variations in productivity of Goose and hypereutrophic Sylvan lakes, Indiana I n vest I ndiana Lakes Streams 7:147-184. Wetzel RG, ed. 1975. Limnolog y . New York: W.B. Saunders. Wilson C B . 1990. Lake w a ter quality modeling: An overview of the basics. I n : Enhancing States' Lake/Wetland Programs. NIPC, NALMS, U.S. Environmental Protection Agency, pp. 133-141. Wright HE J r . 1967. A square-rod piston sampler for lake sediments. J Sediment Petrol 37:975-976. Wurtsbaugh WA, Vincent WF, Alfaro T apia R, et al. 1985. Nutrient limitation of algal growth and nitrogen fixation in a tropical alpine lake, Lake Titicaca (Peru/Bolivia). Freshwater Biol 15:185-195. Young RA, Onstad CA, Bosch DD, et al

. 1989. AGNPS: A nonpoint source pol lu ti on model for evaluating agriculture watersheds. J Soil Water Conserv 44:168-173.

R-14 

### Nutrient Criteria—Lakes and Reserv o irs

# A **PPENDIX A Nutrient Region Descriptions** 
**I. Willamette and Central Valleys**

• Broad, arable, western valleys that are drier and flatter than the neighboring Western Forested Mountains (II)
• Soils are typically nutrient rich and more naturally fertile than those of the adjacent Western Forested Mountains (II)
• Cropland agriculture is the dominant landuse and contrasts with that of surrounding nutrient regions; associated fertilizer use and irrigation return has affected surficial water quality
• Areas of high human population density occur, unlike in most of the Western Forested Mountains (II) 

### II. Western Forested Mountains

• High relief, mostly forested mountains; they contrast with the agriculturally dominated Willamette and Central Valleys (I) as well as the unwooded Xeric West (III) and the Great Plains Grass and Shrublands (IV)
• Elevational vegetation banding occurs. Highest elevations are wet, low-nutrient, glacially modified alpine areas with locally numerous tarns. High areas are dominated by coniferous forests and contain steep-gradient perennial streams. Deciduous trees become more common at lower elevations and grow with conifers in mixed stands that have a grass understory. Lowest areas are more xeric and can be dominated by shrubland and grassland; however, mountain-fed, perennial streams that are lined by riparian vegetation can be common
• Logging is a common landuse and can strongly affect water quality
• Grazing occurs in the Western Forested Mountains (II) especially on shrublands and grasslands; associated nutrient problems occur
• Relatively small areas of agriculture are found in the Puget Lowland (2), near the Pacific Ocean, and within some mountain valleys 

### III. Xeric West

• Dry, unforested basins and plateaus with scattered mountains and buttes; the Xeric West (III) is climatically, physiographically, and vegetationally distinct from the Western Forested Mountains (II)
• Xeric West (III) is drier than surrounding nutrient regions
• Perennial streams are rare; those that occur typically originate outside the Region III in the Western Forested Mountains (II)
• Natural vegetation is often desertic and is typically dominated by sagebrush, creosote bush, and grassland; areas of woodland also occur
• Low density grazing is the common landuse of the Xeric West (III); it has affected vegetal cover, surficial water quality, and stream flow characteristics. The landuse mosaic is distinct from that of the Willamette and Central Valleys (I), Western Forested Mountains (II), and South Central Cultivated Great Plains (V)



### Nutr ient Criteria—Lakes and Reservo ir s A- 1• Agriculture is found only locally. It is often irrigated, such as in the Imperial, Snake, and Gila valleys, and is characterized by large anthropogenic inputs of nitrogen from artificial fertilizers. Nonirrigated agriculture also occurs, including grain farming in the Palouse
• Locally, areas of high human population density occur along with associated nutrient inputs 

### IV. Great Plains Grass and Shrublands

• Semiarid high plains with intermittent or ephemeral streams; perennial streams also occur but usually originate in the Western Forested Mountains (II)
• Great Plains Grass and Shrublands (IV) is drier than the Corn Belt and Northern Great Plains (VI) but moister than the Xeric West (III)
• Natural vegetation is short grass prairie and is distinct from that of the Western Forested Mountains (II), the Xeric West (III), and much of the Corn Belt and Northern Great Plains (VI)
• The Great Plains Grass and Shrublands (IV) is composed mostly of grassland and is largely nonarable; cropland is much less common than in the Corn Belt and Northern Great Plains (VI) and the South Central Cultivated Great Plains (V)
• Grazing is the common landuse and has reduced vegetal cover and affected stream quality
• Cropland occurs locally such as in the Northwestern Glaciated Plains (42) ecoregion 

### V. South Central Cultivated Great Plains

• Part of the Great Plains
• The natural vegetation is mostly grassland and is distinct from that of the Western Forested Mountains (II)
• The South Central Cultivated Great Plains (V) is now mostly cropland that is dominated by sorghum and winter wheat farming; the landuse mosaic is distinct from that of the surrounding nutrient regions
• Dense concentrations of animal feed lots are found in the South Central Cultivated Great Plains (V); associated nutrient problems also occur 

### VI. Corn Belt and Northern Great Plains

• Rolling glaciated terrain is common; nearly-level, poorly-drained proglacial lakebeds occur locally
• The Corn Belt and Northern Great Plains (VI) is typically covered by nutrient-rich soils that are typically more fertile than those of the Great Plains Grass and Shrublands (IV), Nutrient Poor Largely Glaciated Upper Midwest and Northeast (VIII), and Southeastern Temperate Forested Plains and Hills (IX)
• Soils were derived from glacial drift; alfisols are found in the east while mollisols occur in the west
• The natural vegetation was mostly tall grass prairie and is distinct from that of the Great Plains Grass and Shrublands (IV) and the South Central Cultivated Great Plains (V)
• Today, the Corn Belt and Northern Great Plains (VI) is dominated by cropland agriculture, and extensive corn, soybean, and wheat farming occurs. The landuse mosaic is different from that of surrounding nutrient regions
• Poorly drained areas occur locally and are typically nearly level and clayey; they must be tiled to be arable, and streams are resultantly impacted by severe turbidity problems
• Fertilizers have been extensively applied and nitrates can be found in the ground water
• Locally, feedlots and areas of high human population density occur together with associated nutrient problems.
• Lakes occur locally and are usually eutrophic

A- 2 

### Nutrient Criteria—Lakes and Reserv o irs

### VII. Mostly Glaciated Dairy Region

• The Mostly Glaciated Dairy Region (VII) is transitional between the Nutrient Poor Largely Glaciated Upper Midwest and Northeast (VIII) and the Corn Belt and Northern Great Plains (VI)
• Region VII has a mix of nutrient-rich and nutrient-poor soils whereas Region VIII is dominated by relatively thin, nutrient-poor soils and Region VI has nutrient-rich soils
• Region VII contains fewer lakes than Region VIII and more than Region VI
• The lakes of Region VII have varying trophic states while those of Region VIII are typically of better quality
• The length of its growing season is in between that of the cooler Region VIII and the milder Region VI
• The landuse mosaic is dominated by dairying and is generally distinct from that of the Corn Belt and Northern Great Plains (VI); corn farming also occurs like in Region VI but is mostly used for silage
• Dairy cattle are often in close proximity to the region’s perennial streams; associated impact on streams and lakes is widespread
• Locally, areas of high human population density and associated nutrient inputs occur 

### VIII. Nutrient-Poor Largely Glaciated Upper Midwest and Northeast

• The forested Nutrient-Poor Largely Glaciated Upper Midwest and Northeast (VIII) has a high concentration of oligotrophic lakes; lake density and quality is a contrast with those of the Corn Belt and Northern Great Plains (VI) and the Mostly Glaciated Dairy Region (VII)
• Soils are thinner and more nutrient poor than surrounding nutrient regions
• Human population density is low 

### IX. Southeastern Temperate Forested Plains and Hills

• Irregular plains and hills
• Originally, the Southeastern Temperate Forested Plains and Hills (IX) was mostly forested in contrast to the South Central Cultivated Great Plains (V); areas of savannah and grassland also occurred
• Today, Region IX is a mosaic of forest, cropland, and pasture
• The Southeastern Temperate Forested Plains and Hills (IX) is not as arable as the South Central Cultivated Great Plains (V) or the Corn Belt and Northern Great Plains (VI). However, there is much more cropland than in the Central and Eastern Forest Uplands (XI)
• Lateritic soils are common and are a contrast to the soils of the surrounding nutrient regions
• Areas of depleted soils are found in Region IX and are the result of cotton or tobacco farming
• Major poultry and aquaculture operations are found locally in the Southeastern Temperate Forested Plains and Hills (IX) and associated anthropogenic inputs of nutrients have occurred 

### X. Texas – Louisiana Coastal and Mississippi Alluvial Plains

• Alluvial and coastal plains
• Alluvial soils are naturally rich in contrast to those of the Southeastern Temperate Forested Plains and Hills (IX); they once supported southern floodplain forest
• Coastal plain soils once supported grassland
• The landuse mosaic of Region X is different from the Great Plains Grass and Shrublands (IV) and the Southeastern Temperate Forested Plains and Hills (IX)
• The dominant landuse of the Texas – Louisiana Coastal and Mississippi Alluvial Plains (X) is cropland agriculture. Cotton, soybeans, rice, sorghum, corn, and wheat are commonly grown 

### Nutrient Criteria—Lakes and Reserv o irs A- 3• Fertilizers have been extensively applied and have affected surficial water quality
• Locally, areas of high human population density occur along with associated nutrient inputs 

### XI. Central and Eastern Forest Uplands

• Mostly forested low mountains and high hills; streams are generally fast moving and are typically clearer than the low gradient streams of the Southeastern Temperate Forested Plains and Hills (IX)
• Scattered areas of intensive agriculture occur, such as in the limestone valleys of the Ridge and Valley (67)
• Major poultry and aquaculture operations are found locally in the Central and Eastern Forest Uplands (XI) along with associated anthropogenic inputs of nutrients 

### XII. Southern Coastal Plain

• Flat, hot coastal plain that is physiographically distinct from the Southeastern Temperate Forested Plains and Hills (IX)
• Many solution and coastal plain lakes of varying trophic states occur; phosphate deposits locally affect lake quality
• The Southern Coastal Plain (XII) is dominated by extensive areas of citrus orchards and vegetable farming; its landuse mosaic is different from that of the Southeastern Temperate Forested Plains and Hills (IX), the Southern Florida Coastal Plain (XIII), and the Eastern Coastal Plain (XIV)
• Areas of high human population density occur along with associated nutrient inputs 

### XIII. Southern Florida Coastal Plain

• The Southern Florida Coastal Plain (XIII) is a tropical, nearly level coastal plain with broad wetlands; lakes are much less common than in the Southern Coastal Plain (XII)
• Today, Region XIII is extensively drained for agriculture and sugar cane farming is widespread; its landuse mosaic is distinct from that of the Southern Coastal Plain (XII)
• Locally, areas of high human population density occur along with associated nutrient inputs 

### XIV. Eastern Coastal Plain

• Coastal plain
• Swampy or marshy areas are found in the southern and central sections and forests grow in the northern portion
• Poorly-drained soils are common in the central and southern portion and nutrient poor soils are found in the northern section
• Cropland is generally limited in extent
• Areas of high human population density occur along with associated nutrient inputs
• Major poultry and aquaculture operations are found locally in the Eastern Coastal Plain (XIV); associated anthropogenic inputs of nutrients have occurred

A- 4 

### Nutrient Criteria—Lakes and Reserv o irs

# A **PPENDIX B**

**STATEWIDE OR REGIONAL APPROACHES** 1. GEORGI A The G e orgia Lake Standards Legislation (M. Walker) 2. 	 MINNESOTA Ecoregional Classification of Minnesota Lakes (S. Heiskary) 3. NO RTH CAROLINA Nutrient Control in Nort h Carol in a’s Lakes and Reservoirs (D. Reid) 4. S OU TH DA KOT A A Watershed Approach - South Dakota (W. Stewart) 5.	 VIRGINI A The Virginia Nutrient Enriched Waters Designation (J. Gregory) 6.	 WISCONSIN Wisconsin Lake P h osphorus Criteria (G. Searle) 7.	 TENNESSEE VALLEY The Tennessee Valley Authority Reservoir Vital Signs Monitoring P r ogram: Chlorophyll and Nutrients Rating Scheme (N. Carriker and D. Meinert) 8.	 BRITISH C OLU MBIA Th e British Columbia Water U s e Based Approach (R. N o rdin) 9. ON TARI O Ra tionale F o r a R e vised P h osphorus C r iterion f o r Precambrian Shield Lakes in Ontario (N. Hutchinson)



## LAKE OR RESERVOIR SPECIFIC APPROACHES 10.	 DILLON RESERVO IR , COLORADO D illon Reservoir Phosphorus Standard, Load Allocation, and Crediting System (R. Ray) 11.	 EVERGLADES, F L ORIDA Interim P h osphorus Standards f o r the Everglades (W. W. Walker) 12.	 LAKE CHAMP L AIN, VERMO N T, NEW Y O RK, AND Q U EBEC To tal P h osphorus C r iteria f o r L a ke C h amplain (E. Smeltzer)



### Nutrient Criteria—Lakes and Reservo ir s B- 1

# 1. Geor **g ia Lake Standards Le**  **g islation**  by Max Walker, Georgia Department of Natural Resourcesl

I n 1990, the G e orgia General Assembly adopted a lake standards bill (O.C.G.A. 12-5-23.1). Acopy of the bill is reproduced below . T he legislation requires that the G e orgia Environmental Protection Divi sion (EPD) conduct comprehensive studies and develop w a ter quality standards for lakes with a surface area of 1,000 acres or m o re. T he General Assembly provided no funds to support implementation of the legislation. Phase I Di agnostic-Feasibility Studies have been completed by EPD using USEPA Clean Lakes funds on Lakes West Point, Walter F. George, and Jackson. Based on the information collected as a part of the Phase I studies, w a ter quality standards w e re developed and adopted for each lake. Phase I studies are ongoing on Lakes Lanier, Allatoona, Blackshear, and Carters. Atsuch time as the studies are completed, the EPD w ill use the information and develop and adopt water quality standards for these lakes. 

### 12-5-23.1 **W ater quality standards for lakes; monitoring; studies and reports;**  **development, approval, and publication of water quality standards.** (a) As used in the Code section, the word “lake” means any publicly owned lakes or reservoir located wholly or partially within this state which has a normal pool level surface average of 1,000 or more acres. (b) T he director shall establish w a ter quality standards for each lake w h ich require the lake to be safe and suitable for fishing and swimmi ng and for use as a public w a ter supply, unless a use attainability analysis conducted within requirements of this article demonstrates such standards unattainable. (c) For purposes of this subsection, a m u ltiple parameter approach for lake w a ter quality standards shall be adopted. Numerical criteria including, but not limited to, those listed below shall be adopted for each lake: (A) pH (maximum and mi nimum): (B ) Fecal coliform bacteria; (C) Chlorophyll a for designated areas determined as necessary to protect a specific use; (D ) Total nitrogen; (E) T otal phosphorus loading for the lake in pounds per acre feet per year; and (F) D issolved oxy ge n in the epilimnion during periods of thermal stratification. (d) T he standards for w a ter quality of each lake shall take into account the g e ographic location of the lake within the state and the location of the lake within its w a tershed as w e ll as horizontal and ve rtical v ariations of hydrological conditions within each lake. The director shall also establish nutrient limits for each of the lakes’ m ajo r tributary streams including streams with permitted discharges. Such limits shall be consistent with the requirements of subsection (b) of this Code section and shall be established on the basis of accepted limnological techniques and as necessary in accordance with the legal and technical principles for total m a ximum daily loads. T h e nutrient limits for tributary streams shall be established at the same time that the lake w a ter quality standards are established. (e) A fter w a ter quality standards are established for each lake and its tributary streams, the division shall monitor each lake on a regular basis to ensure that the lake reaches and m a intains such standards.
B- 2 

### Nutrient Criteria—Lakes and Reserv o irs(f) T he data from such monitoring shall be public information. T h e director shall have the authority to close a swimmi ng area if data from samplings indicates, in the opinion of the director, that such action is necessary for public safety

. (g ) Provided funds are available from any source, there shall be a comprehensive study of each lake prior to adopting lake w a ter quality standards for the lake. Study components and procedures will be established after consultation with local officials and affected organizations. T he comprehensiv e study for Lake Sidney Lanier, Lake Water F. George, and West Point Lake shall be initiated during 1990. A tleast three comprehensive studies for participating lakes shall be initiated in each subsequent y ear. T h e duration of each study shall not exceed two years. A scientific report on each comprehensive study shall be published within 180 days after the completion of the study. Draft recomme ndations for numerical criteria for each of the w a ter quality parameters will be simultaneously published, taking into account the scientific findings. A public notice of the draft recommendations, including a copy of the recommendations, will be made available to the public. Public notice in accordance with C h apter 13 of Title 50, the “Georgia Administrative Procedure Act, ” shall be provided for such recomme ndations. T h e notice shall be m a de available at least 30 days prior to board action in a regional public library or county courthouse. T h e recomme ndations will be provided to persons submitting a written request. A comme nt period of not less than 45 days nor m o re than 60 days will be provided. (h) T he director or the director’s designate shall conduct a public hearing within the above-referenced comme nt period in the v i cinity of the lake before the final adoption of lake w a ter quality standards for the lake. T h e director shall announce the date, time, place, and purpose of the public hearing at least 30 days prior to the hearing. A ten-day period subsequent to the hearing w ill be allowed for additional public comme nt. (i) T he Department of N a tural R e sources will evaluate the comme nts received during the comme nt period and during the public hearing and will then develop recomme nded final standards and criteria for submission to the Board of Natural Resources for consideration and approval. (j ) The final recomme ndations of the director for lake w a ter quality standards shall be m a de to the Board of Natural Resources within 60 days after the close of the comme nt period subsequent to the public hearing provided for in subsection (h) of this Code section. T h e standards, with such m odifications as the board m ay determine, shall be considered for adoption by the Board of Natural Re sources within 60 days after receiving the recomme ndations from the director. Such standards shall be published by the department and m a de available to all interested local g ove rnment officials and citizens of the area served by the lake. (k ) At the discretion of the direction, comm ent periods and deadlines set forth above m ay be extended, but in no circumstance shall m o re than one year elapse between the completion of the lake study and the adoption of the final recomme ndations. (Code 1981, § 12-5-23.1, enacted by Ga. L. 1990, p. 1207, § 1.)



### Nutrient Criteria—Lakes and Reserv o irs B- 3

# 2.	 Ecore **g ional Classification of**  **Minnesota Lakes** by Steven Heiskary, Minnesota Pollution Control A g ency

Minnesota has over 12,000 lakes spread across diverse g e ographic areas. Previous studies had shown distinct regional patterns in lake productivity associated with regional differences in g e olog y , vegetation, hydrolog y , and land use (Heiskary and Wilson, 1989). Minnesota contains seven ecoregions (Omernik , 1987), and four of the ecoregions contain 98 percent of the lakes. T h ese four ecoregions are the Northern Lakes and Forest (NLF), North Central Hardwood Forest (NCHF), Northern Glaciated Plains (NGP), and Western Corn Belt Plains (WCBP) (Figure 1). Minnesota uses these ecoregions as the framework for analy z ing data, developing m onitoring strategies, assessing use patterns, and developing phosphorus go als and criteria for lakes (Heiskary, 1989). **Figure 1: Minnesota Ecor e**  **gions**

B- 4 

### Nutrient Criteria—Lakes and Reserv o irsTh e Minnesota Pollution Control Agency (MPCA) and several other g r oups collected data on chlorophyll a concentrations and several w a ter quality parameters (total phosphorus, total nitrogen, and Secchi transparency) in 90 reference lakes between 1985 and 1987. Secchi transparency data w e re collected m o stly by vo lunteer participants in the Citizen Lake Monitoring Program. Reference lakes were chosen to represent mi nimally impacted sites within each ecoregion. Criteria used in selecting reference lakes included m a ximum depth, surface area, fishery classification, and recomme ndations from the Minnesota Department of Natural Resources (Heiskary and Wilson, 1989). Lake m o rphometry had previously been examined. In addition to the reference lake data base, MPCA examined a statewide data base containing data collected by these same g r oups on approximately 1,400 lakes form 1977 to 1987. Differences in m o rpholog y , chlorophyll a concentrations, total phosphorus, total nitrogen, and Secchi transparency were found among lakes in the four ecoregions in both studies. Lakes in the two forested ecoregions (NLF and NCHF) are deeper (median m a ximum depth of 11 me ters), with slightly smaller surface areas (40 to 280 ha), than those in the plains ecoregions (N GP and WCBP). Lakes in the tw o plains ecoregions w e re typically shallow (median m a ximum depth of 3 m e ters) with larger surface areas (60 to 300 hectares). Box-and-whisker plots for chlorophyll a and w a ter quality measurements in the reference lake study paralleled the m o rphological differences seen among the ecoregions (Heiskary and Wilson, 1989). T he two plains ecoregions had significantly higher chlorophyll a levels than either of the two forested ecoregions. Results of the statewide data base analysis showed these same trends. T h e results of these two data base analyses support the use of ecoregions in developing frameworks for data analysis, m onitoring strategies, assessing use patterns, and developing phosphorus g o als and criteria for lakes.



### Nutrient Criteria—Lakes and Reserv o irs B- 5

# 3.	 Nutrient Control in North Carolina’s **Lakes and Reservoirs** by Dianne Reed, North Carolina Department of Environmental Management

No rth C arolina’s approach to the control of eutrophication could serve as a model for how to use specific criteria and special programs along w ith special use classifications to achieve restoration and protection of lakes and reservoirs under the C l ean Water A c t. T h is approach provides the flexibility necessary to develop m a nagement strategies for the wide v ariety of responses to nutrient loading seen in No rth C arolina lakes and reservoirs. I n the late 1970s, in response to extensive algal blooms in a coastal river (Chowan River), which has ma ny characteristics similar to a lake, North Carolina adopted a chlorophyll a standard of 40 

### � g/L for warm waters and 15 

### � g/L for cold w a ters as part of its w a ter quality standards. Another important aspect of this standard w a s the inclusion of a narrative that g ive s the D i rector of the D ivi sion of Water Q u ality authority to prohibit or limit any discharge into surface w a ters if the D i rector determines that this discharge would contribute to exceedances of the chlorophyll a standard. T h is narrative has allowed the inclusion of m o re stringent nutrient limits in several permits throughout the state without reclassification or development of basinwide plans. As a result of the work done on the Chowan River, the Division established an algal bloom program

. Th is program analy z es phytoplankton, chlorophyll a, and nutrients, as well as other parameters from lakes, reservoirs, and slow- mov ing rivers throughout North Carolina. Data collected through this program resulted in a legislative ban on phosphate detergents for the entire state. Another action that contributed significantly to nutrient control in North Carolina was the development of the N u trient Sensitive Waters (NSW) supplemental classification. T h e N SW supplemental classification allows the state to seek abatement of the point and nonpoint source releases of nutrients upstream from a priority water body through the rule- making process. T h ere are a total of six areas that have been declared N S W in N o rth Carolina. Tw o of the areas were m ajo r reservoir watersheds, Falls of the Neuse Lake and J o rdan Lake. Sufficient data were available to adapt nitrogen, phosphorus, and chlorophyll a loading/response models and to assess the impact of predicted population g r owth and changes in wastewater inputs and land use. As a result of the modeling, new wastewater treatment plants, as well as m ajo r existing ones, are required to meet a total phosphorus effluent limitation of 2.0 m g/L. Nonpoint pollution sources also are addressed. T h e state legislature created a targeted agricultural wa ter quality cost sharing program to provide an incentive for producers and g r owers to use nutrient abatement practices. T h e program provides a 75 percent cost share and has been enthusiastically received. To control urban nonpoint sources, the state issued developmental (land use) g u idelines to counties and municipalities in the lake w a tersheds for controlling urban pollutants through local ordinances. With the NPDES stormw ater permit program and water supply watershed use designation, North Carolina is well positioned to control eutrophication in its lakes and reservoirs. Another way that North Carolina is addressing eutrophication of its waters is within the basinwide w ater quality m anagement process and plans. O n e example of how these management plans are being successfully used is in Lake Wylie (Catawba River Basin). In 1992, North Carolina documented eutrophic conditions in Lake Wylie and several of its m ajo r tributaries. B o th point and nonpoint pollution sources w e re identified as contributing to high nutrient loadings resulting in v i olations of the State chlorophyll a standard. To address eutrophication in Lake Wylie, the State adopted a point and nonpoint
B- 6 

### Nutrient Criteria—Lakes and Reserv o irsnutrient control strateg y for the Lake Wylie watershed. T h e basis for these actions was the chlorophyll a standard and its caveat allowing the Director to require nutrient controls at his or her discretion. For point sources, the strateg y required state-of-the-art nutrient removal for all new or expanding wastewater discharges in the v i cinity of the lake. For nonpoint sources, this strateg y included targeting of funds from the state’s Agricultural Cost Share Program for the Reduction of Nonpoint Source Pollution for implementation of best m a nagement practices on agricultural lands in highly impacted watersheds of Lake Wylie. I n conjunction with the 1995 Catawba River basinwide planning effort, the Lake Wylie m a nagement strateg y wa s reexamined and updated. A s a result of the update, no new discharges will be allowed to the lake m a instem or its tributaries, unless an evaluation of engineering alternatives shows that such a discharge is the m o st environmentally sound alternative. Any new discharges that meet this requirement w ill be required to apply advanced removal technolog y. New facilities (including expansions) with a permitted design flow of g r eater than or equal to 1 million g a llon per day (MG D) are required to meet monthly average limits of 1 m g/l total phosphorus and 6 m g /l total nitrogen (nitrogen limits to apply for the months A p ril through O c tober only). New facilities and expansions with a permitted design flow of less than 1 MG D but g r eater than 0.05 MG D are required to meet a total phosphorus limit of 2 m g /l. T h e industries in the m a nagement area are to control T P and TNto best available technolog y levels as agreed upon with state regulators. I tis entirely possible that discharges could receive m o re stringent nitrogen and phosphorus limits on a case-by

- case basis if supported by sampling data and approved by the Director. T o reduce nutrient enrichment in the two m o st eutrophic arms of Lake Wylie, additional recomme ndations were m a de for point source discharges to the Catawba Creek and Crowders Creek watersheds. In both watersheds, incentives are to be established to encourage the privately owned facilities to tie on to larger municipal WWTPs.



### Nutrient Criteria—Lakes and Reserv o irs B- 7

# 4. Watershed Approach in South Dakota by William Stewart, South Dakota D e partment of En vironment and N a tural R e sources

Th e State of South D ako ta has had ambient w a ter quality standards in place for lakes since the late 1960’s. T h ese standards exist in both numeric and narrative forms. Phosphorus is not listed as a parameter in the numeric standards but is covered by the narrative section. At this time, there are no numeric limits on phosphorus on any surface w a ters of the state. Th e Watershed Protection Program is part of the South Dakota Department of Environment and Natural Resources. T h is program is responsible for nonpoint source pollution control and lake m anagement. T h e Watershed Protection Program is based on requests for assistance from local g r oups such as lake associations or conservation districts. Virtually all of the watershed and lake restoration projects in the state are done on a v o luntary basis and enforcement is seldom used, except in extreme cases. B y far and away, the largest problem for South D ako ta lake w a ter quality is sediment and nutrients from agricultural nonpoint source pollution. Th e first step in conducting a lake restoration project in South Dakota is the assessment of the lake and its w a tershed. A typical assessment project is a two- y ear effort, including intensive w a ter quality m onitoring of the lake and tributaries, stream g auging, biological sampling, land-use modeling, and public outreach. A m a thematical relationship developed by Vollenweider and Kerekes (1980) is used to model the relationship between phosphorus inflows and ambient total phosphorus concentrations in the lake. By changing the phosphorus inflows in the equation, corresponding changes in in-lake phosphorus are estimated. In this way, we are able to model changes in chlorophyll a concentrations and the response of in-lake phosphorus concentration to the reduction of tributary phosphorus levels. Once we have determined the target reduction in in-lake phosphorus, we use the Agricultural Nonpoint Source (AGNPS) model to estimate load reductions from the watershed. In order to use the AGN PS program, the watershed is divided into 40-acre cells and 21 parameters are collected for each cell. T h e model estimates loads of nitrogen, phosphorus, and sediment to the lake. By adding v arious Be st Management Practices to the model, it is possible to determine w h ich practices are needed to reach the estimated watershed phosphorus reduction to produce the desired ambient in-lake phosphorus concentration. Th e information from the lake/watershed assessment is used to develop an implementation plan for restoration. T h e South D ako ta Watershed Protection Program has had considerable success with this procedure. T h e lake and w a tershed stakeholders g e nerally accept the assessment reports and find them to be useful planning tools in the development of restoration plans. 

### References Vo llenwieder, R.A. and J. K erekes, 1980. The loading c oncept as a basis for controlling eutrophication

. Philosophy and preliminary results of the OECD Pr ogramme on Eutrophication. Prog

. Water T echnol. 12:3-38.

B- 8 

### Nutrient Criteria—Lakes and Reserv o irs

# 5.	 The Vir **g inia Nutrient Enriched**  **Waters Desig nation**  by Jean Gregory, V irginia D e partment of En vironm e ntal Q u ality

The quality of Virginia’s surface w a ters, particularly those in the C h esapeake B ay drainage area, is affected by the presence of nutrient enrichment. I n recognition of this, the State Water Control B o ard (SWC B) , now the D e partment of Env i ronmental Q u ality, has developed a strateg y to protect the surface waters of the Comm onwealth of Virginia from the effects of nutrient enrichment. I n the mi d-1980’s, the State’s General Assembly formed a j o int legislative subcommittee to study these problems in the C h esapeake B ay . One of the recomme ndations in their final report w a s to direct the SWC B to develop w a ter quality standards by J uly 1, 1988, to protect C h esapeake B ay and its tributaries from nutrient enrichment. The SWC B decided to expand this standards-setting activity statewide to include other river basins and lakes where there were known nutrient enrichment problems. A second legislative m a ndate to develop implementation strategies for carrying out these w a ter quality standards was m a de j o intly to the SWCB, which has j u risdiction for point sources, and the Division of Soil and Water, which is responsible for nonpoint source controls. As a result, SWCB developed two regulations that became effective on May 25, 1988. T h e first established a w a ter quality standard that designated as “nutrient enriched w a ters” those waters of the Comm onwealth that show evidence of degradation due to the presence of excessive nutrients. A companion policy regulation w a s created to control certain point source nutrient discharges affecting State w a ters designated as “nutrient enriched w a ters.” To assist them in developing the w a ter quality standard, the SWC B formed a Technical A d vi sory Committee (TA C) composed of 19 scientists from east coast universities and the Federal g ove rnment. Th ere w e re specific issues the B o ard w a s seeking advice on prior to developing these standards, including such issues as whether narrative or numerical standards were needed, appropriate parameters and numerical levels, and the appropriate monitoring, sampling, and evaluation m e thods. Th e SWCB used a v ariety of policy analysis techniques to obtain recomme ndations from the committee for the best indicators of nutrient enrichment. First, SWCB m a iled a series of three delphi questionnaires to the 19 T A C scientists asking them to identify m ajor issues and thereby reach som e consensus on topics to focus on. Responses w e re anony m ous so that the scientists would not bias each other. SWCB followed this process with a two-day spring (May 14-15, 1987) workshop held in Williamsburg by the U n iversity of Virginia’s Institute of Environmental N ego tiation. A summary report wa s compiled. Th e Technical Advisory Committee recomme nded four parameters that could be used as in-stream indicators of nutrient enrichment. Listed in descending order of importance they are chlorophyll a , dissolved oxy g en (D.O.) fluctuations, total phosphorus, and total nitrogen. Note that the first two parameters are sy mp toms of nutrient enrichment rather than direct measurements of nutrients. Each of these four parameters was considered to develop a recomme ndation for fresh water lakes. 

### Chlorophyll a • Most T A C m emb ers favored use of a chlorophyll a criterion for lakes. A numerical level of 25 

### � g /l as a monthly average with a m a ximum one-time exceedence level of 50 

### � g/l was proposed. T h ese v a lues received general support from the g r oup. T h ere w a s a discussion about w h ether the chlorophyll criterion should be based on planktonic chlorophyll only or whether some consideration should be g ive n to



### Nutrient Criteria—Lakes and Reserv o irs B- 9m acrophytic chlorophyll as well. I twas determined that a planktonic measure would be easier to sample and would accurately reflect the eutrophic condition of the lake. It w as sug g ested that monitoring samples be taken at one-half the Secchi depth as long as that depth was g r eater than 1 foot. An alternative proposal was to use an integrated mi xed layer sample which, according to some memb ers, would y i eld m o re reliable results. T h e use of Secchi depth is, however, a well-recognized and reliable m e thod and it was favored for its simplicity

. TA C m emb ers thought the numerical chlorophyll criterion for lakes should be combined with a narrative element that would deal with the problems caused by high chlorophyll levels

— taste, odor, and clog ge d filters at w a ter treatment plants. 

### Dissolved Oxygen • Itwas the consensus of the T A C g r oup that due to wide v ariation in D.O. at different depths and the difficulty this creates in setting standards and sampling techniques, and the fact that D .O . problems are sy mp toms that would be reflected in other standards, no lake criterion for D.O. should be recomme nded. Th e g r oup did agree that a narrative component addressing the conditions associated with D .O . problem s should be drafted. 

### Total Phosphorus • Th e T A C g r oup sug ge sted two possible lake criteria for total phosphorus in lake waters: a level of 50 

### � g /l as a weighted mean based on the water m a ss, or a level of 25 

### � g/l as a mi xed layer mean. T h ese levels were judged to be of equal v a lidity as a measure of total P. (It was noted that if chlorophyll were sampled on a mi xed layer basis this migh t be the preferred approach because the two samples could be taken at the same time.) 

### Total Nitroge n • Th e T AC gr oup discussed the possibility of linking the criterion for total nitrogen to the criterion for phosphorus. I twas sug ge sted that some N to P ratio could be used or that the nitrogen criterion could be set at ten times the phosphorus criterion. After discussion, the g r oup agreed that no nitrogen criterion should be set. Phosphorus is almost always the limiting factor in the eutrophication of Virginia’s warm wa ter lakes, and the g r oup thought a nitrogen criterion would be unnecessary

. 

### Recommendations of the TAC I n freshwater lakes the state should consider setting a chlorophyll a criterion of 25 

### � g/l as a monthly average, with a one-time exceedence level of 50 

### � g/l with both measured at one-half the Secchi depth (if > 1 foot). T h is should be combined with a total phosphorus criterion of 50 

### � g/l as a weighted mean or 25 

### � g /l as a mi xed layer mean. A narrative component should be developed as well to address m o re g e neral chlorophyll a and D.O. problems in lakes. Taki ng into consideration the recomme ndation of the committee, the SWCB decided to base its designations for lakes and all other surface w a ters on the first three parameters. A reference to these parameters w a s included in the introduction to the w a ter quality standard regulation for designating nutrient enriched w a ters. SWC B wa s intentionally silent on the numerical limits because unacceptable amounts of these parameters could v ary depending on the type of water body, whether it were a lake, free-flowing river, or tidal estuary. Because every designation would require an amendment to Virginia’s wa ter quality standards, and full public participation is required by the agency and State rules for adopting regulations, SWCB felt that the public would be properly notified in every case of the appropriate scientific and numeric basis for these designations.

B-10 

### Nutrient Criteria—Lakes and Reserv o irsAverage seasonal concentrations of chlorophyll a exceeding 25 m g/l, dissolved oxy ge n fluctuations, and high water column concentrations of total phosphorus have been the indicators used to date to evaluate the historical data and to identify those waters affected by excessive nutrients. Chlorophyll a , a pig m ent found in all plants, w a s used as the primary indicator because it indicates the quantity of plant growth. Ba sed on a review of historical w a ter quality records, the SWC B designated as “nutrient enriched wa ters” three lakes, one tributary to a lake, nine embay ments or tributaries to the Potomac River, the Virginia portion of the Chesapeake Bay, and a large portion of the Bay’s tributaries. Since this initial round of designations, SWCB has amended the standard to designate the tidal freshwater portion of the Chowan River Basin in V i rginia. SWCB intends to continue to review these designations and, during each triennial review of w a ter quality standards, will consider additions and deletions to the list. For example, Lake Chesdin is proposed for designation during the current triennial review of the water quality standards regulation. As SWC B has authority to issue N a tional Pollution D i scharge Elimination System (N PDE S) permits, and thereby control point source discharges of nutrients, a policy for controlling certain point sources of nutrients to those waters designated as “nutrient enriched” was established. (Another agency, the Division of Soil and Water, developed strategies for m a naging nonpoint sources of nutrients to “nutrient enriched w a ters.”) The policy requires certain municipal and industrial organizations that discharg e effluents containing phosphorus to maintain a monthly average total phosphorus concentration of 2 m g /L or less. The 2 m g /L limit w a s based on the following criteria:
• Limits that are readily achievable by chemical addition processes, as demonstrated by experiences in other parts of the country
• Sug ge sted achievable limits for biological phosphorus removal contained in several reports as w e ll as in State pilot plant studies. SWCB has found that this level of phosphorus removal would result in meeting the 40 percent reduction go al of total phosphorus for point source discharges from Virginia entering into the Chesapeake Bay

. Municipal and industrial dischargers that release phosphorus in concentrations above 2 m g/l to these “nutrient-enriched w a ters” are subject to this policy if they have a design flow of 1.0 MGD or g r eater and a permit issued on or before J u ly 1, 1988. T h ese dischargers were required to meet the 2 m g/l effluent limitation as quickly as possible and, in any event, within three years following m odification of the NPDE S permit. I f the discharger v o luntarily accepted a permit that required nitrogen removal to meet a m onthly average total nitrogen effluent limitation of 10 m g/l for April thorough October, the discharger was allowed an additional year to meet the phosphorus effluent limitation. All new source dischargers with a permit issued after J u ly 1, 1988, and a design flow g r eater than or equal to 0.05 MGD that propose to discharge to “nutrient-enriched w a ters” are also required to meet a m onthly average total phosphorus effluent limitation of 2 m g/l. All dischargers to “nutrient-enriched wa ters” that, at the time of that designation, were subject to effluent limitations m o re stringent than the 2 mg/l monthly average total phosphorus are required to continue to meet the m o re stringent phosphorus limitation. Th e policy regulation also contains language that allows SWCB to require monitoring of discharges when the permittee has the potential for discharging m onthly average total phosphorus g r eater than 2 mg/l and also allows adjoining States to petition the B o ard to consider rulemaking s to control nutrients entering tributaries to their nutrient-enriched w a ters. Th e policy regulation states that after the point source controls are implemented and the effects of this policy and the nonpoint source control programs are evaluated, the SWCB recognizes that it m ay be necessary to impose further limitations on dischargers for additional nutrient control to prevent undesirable g r owths of aquatic plants. T h is policy can thus be v i ewed as the first phase of a strateg y to protect Virginia’s waters from the effects of excessive nutrients. 

### Nutrient Criteria—Lakes and Reserv o irs B-11

# 6. Wisconsin Lake Phosphorus Criteria by Greg Searle, Wisconsin Department of Natural Resources

I n 1991 the Wisconsin Department of Natural Resources (WDNR) began development of water quality criteria for phosphorus for lakes and impoundments. T h e Phosphorus Technical Work gr oup (PTW) was charged with developing scientifically defensible phosphorus w a ter quality criteria and passing the criteria on to a Technical Advisory Committee for implementation consideration. T h e PT W has completed the development of phosphorus “numbers” (the use of the term “numbers” will be explained after the development section) and has passed those numbers on to a Watershed Advisory Committee. 

### Development of Phosphorus “Numbers” Historical total phosphorus data were obtained from the STORET database for lakes and impoundments across the state. T h e dataset was censored in the following ways:
• Minimum surface area w a s equal to or exceeded 25 acres.
• Sample dates were restricted to those collected between June 1 and September 15, inclusive.
• Surface data w e re utilized and defined as samples that w e re collected from a depth of four feet or less. Th e reduced dataset was further categorized by drainage type and known summer thermal stratification patterns (mixed or stratified). With respect to drainage type, the waterbodies were designated as drainage or seepage w a terbodies. T h e definition of drainage type w a s associated with the presence or absence of an outlet and not the source of water entering the waterbody

. To account for regional patterns of summe r total phosphorus, the ST OR ET data w e re overlaid on each of 21 sub-ecoregions of Wisconsin proposed by Omernik et al. (1988). Evaluation of these data led to the conclusion that mi nimal data in m a ny of the sub-ecoregions restricted the ability to accurately deriv e wa ter quality criteria. Recent efforts of Lillie et. al. (1993) to develop a T r ophic State Index (TSI) for Wisconsin lakes showed clear associations between water clarity, chlorophyll a , and T P on a regional basis. T h e PTW agreed that the ST OR ET data should be evaluated using Lillie’s proposed regions. WDNR staff concluded that a three-way separation (north, central, and south) of phosphorus regions for lakes was supported by the comparison of mean total phosphorus data. When comparing similarly impacted lakes in the proposed North v s . South regions, there was a trend of significance. Mean total phosphorus concentrations in lakes categorized as being m oderately or slightly impacted were different, whereas they were not for those lakes categorized as being highly impacted or those that were unranked altogether. T h is analysis did not support g r ouping the two regions together. In comparing both the proposed North or the South to the Central region, a consistent difference was not found in mean total phosphorus concentrations. T h ese data clearly indicate that, while the Central region m ay be g r ouped with either the North or South Region, it does not bridge the two regions, and therefore supports a different set of w a ter quality standards. Like the regional inconsistencies observed in the comparative total phosphorus v a lues for lakes, there were also inconsistencies observed in mean total phosphorus v a lues for impoundments. Mean total phosphorus concentrations in the proposed South region were not significantly higher than those for the North. T h e mean total phosphorus v a lues for the Central region were statistically different when compared with the North and South regions. Since the mean total phosphorus v a lues m ay be similar in the North and South, but not the North and Central or the South and Central, it was decided to separate the three regions altogether.
B-12 

### Nutrient Criteria—Lakes and Reserv o irsHavi ng decided to further evaluate total phosphorus data using the three regions identified by Lillie et al. (1993), the ST OR ET data w e re combined for each region by drainage type and potential for thermal stratification. B a sed on PTW consensus, lower quartiles (25 percent quantile) w e re g e nerated using SA S univariate procedures on all individual total phosphorus v a lues in the censored STORET dataset. Once the lower quartile values were generated, they w ere further modified by rounding them down to the nearest m u ltiple of five. Several discussions occurred in previous PTW meetings regarding the significance of using the lower quartile numbers. PTW memb ers exercised their “best professional judg ment” and seemed to believe that the lower quartile would provide a conservative estimate of back gr ound total phosphorus concentrations in Wisconsin's lakes and impoundments. T h e m emb ers believed that there were m o re technical means of determining back gr ound v a lues (i.e., paleolimnological studies, lake-specific or impoundment-specific m odeling, etc.). T h ey acknowledged, however, that there were resource limitations and agreed that the lower quartiles w e re the best available m e thod for estimating ambient w a ter quality standards that would lead to satisfactory w ater quality if m e t. In accepting the concept of lower quartile-based w a ter quality standards, there was unanimous agreement among PT W m embers that the g r oup would recomme nd to the Watershed A dvi sory C ommittee that w h atever administrative rule revisions w e re eventually m ade, there mu st be language that allows for the development of site-specific criteria w h ere sufficient data are available. Following the g e neration of the lower quartile v a lues using each of the individual data points, a “trip” analysis was performed on mean total phosphorus values for lakes and impoundments to determine the relative proportion of w a terbodies in a region that would likely exceed the lower quartile estimate. T h is analysis had been sug g ested by the PTW m emb ership as a means of stating the degree of impact related to lower quartile-based w a ter quality standards. A similar analysis had been performed in 1991 on a Bureau of Research dataset collected in 1979 in support of a statewide limnological survey of Wisconsin lakes. T h e key to this dataset was that the data were representative of a random collection of lakes and impoundments. T h is was in direct contrast to the STORET dataset, which is v e ry reflective of “problem ” waterbodies that, in m a ny cases, were studied intensively by the WDNR in an effort to better m a nag e those resources. Due to the random nature of the random lakes data and the fact that they did not necessarily represent “problem” w a terbodies, lower quartile and trip analyses w e re performed on those data in an effort to compare them to the result of the ST OR ET data analyses. Af ter reviewing the quartile and trip analysis data for both datasets (ST OR ET and random lakes) the PTW agreed that the random lakes data should be used for any subsequent development of draft water quality criteria. T h e PTW did not w a nt to totally abandon the ST OR ET data, especially w hen the random lakes data were collected nearly 15 years earlier in 1979. I n stead, the PTW memb ership agreed that a comparison of recently collected ST OR ET data would be compared to the random lakes data to determine if w a ter quality conditions had remained similar. More specifically, it w a s agreed that ST OR ET data collected in a recent period of consecutive sample years would be analy z ed to develop comparative quartiles. The “recent” dataset was to include all data collected in 1989-1993. No data collected in 1988 w a s to be included because it w a s a significant drought year. T h e resulting quartiles would be compared to those already g enerated for the random lakes dataset, and the PTW would review the comparison at a subsequent meeting. This exercise was begun, but it was found that there was a lack of data from lakes and impoundments that were the same between both datasets. T h e PTW m a de a decision not to compare the random dataset and recent ST OR ET data because of this lack of data and also because of the conservativeness of the standards. Th e PTW also agreed that impoundments should not be differentiated by drainage type because it is the nature of impoundments to have an outlet. All future standards development for impoundments should only consider the potential for thermal stratification in addition to the regional separation described earlier. T h e draft lake and impoundment criteria are as listed in T ables 1 and 2.



### Nutrient Criteria—Lakes and Reserv o irs B-13�

� **Ta ble 1: Ambient Water**  **Quality Criter i**  **a for PhosphorusE in Natural Lakes (**  � **g/L)E**
**Drainage/MixedE Drainage/StratifiedE**  **Seepage/MixedE Seepage/StratifiedE**  Nor th 15 10 10 10 Central 5 5 5 5 South 25 15 15 10

**Ta ble 2: Ambient Water**  **Quality Criter i**  **a for Phosphorus in Impoundments (** � **g/L)E**

**MixedE StratifiedE**  North 15 10 Central 5 5 South 25 15


### Recommendations to the Watershed Advisory CommitteeE After thorough review and discussion of the available scientific information on phosphorus andphosphorus-related impacts in lakes and impoundments, the PTW has concluded that meaningful standalone categorical statewide phosphorus water quality standards cannot be developed on a state or regional basis. T h e determination of whether lakes and impoundments have undesirable phosphorusrelated impacts should ultimately be m a de on a site-specific basis, utilizing technical information and partner input. For this reason it is recomme nded that the numbers developed for use as w a ter quality criteria be used as “trig ge rs” or “flags” to require further action, if exceeded. T h e numbers w e re sent forward unlabeled (not criteria) for the Watershed A dvi sory C ommittee to determine the proper implementation m e thods. Th e PTW endorses the use of a watershed-based regulatory approach that looks holistically at water quality w ithin the w a tershed and utilizes partner involv em ent to prioritize and implement w a ter quality initiatives within the watershed. With respect to phosphorus management, the PTW recomm ends use of an integrated approach that:

• Uses a screening step to identify those lakes and impoundments that m ay require a m o re thorough evaluation for phosphorus-related impacts.
• Establishes a formal evaluation process for these lakes and impoundments that m ay lead to the development of a site-specific or resource-specific standard, expressed as an in-stream phosphorus concentration, a total maximum daily load (TMDL), or some other appropriate m easurement (e.g., chlorophyll a density).

B-14 

### Nutrie nt Criteria—Lakes and Reserv o irs**ReferencesE** Omernik . J. M. and A.L. Gallant. 1988. See Map In sert in: Ecoregions of the Upper Midwest States . Un ited States Env i ronmental Protection Ag ency : Env i ronmental Re search La bor atory - C orvallis, Or egon. EPA/600/3-88/037. Lillie, R.A., S. G r aham, and P. Rasmussen. 1993. Trophic State Index Equations and Regional Predictive Equations for W i sconsin Lakes . Research Management Finding s Number 35. Wisconsin Department of Natural Resources. Madison, Wisconsin. 53707.



### Nutrient Criteria—Lakes and Reserv o irs B-15

# 7.vThe Tennessee Valley Authority**E Reservoir Vital Si**  **g ns Monitorin**  **g E Pro**  **g ram: Chlorophyll and Nutrients E**  **Ratin g SchemeE**  by N e il Carriker and D e nnis Meinert, Tennessee V a lley A u thority



### Philosophical Approach and BackgroundE Algae are the base of the aquatic food chain; consequently, measuring algal biomass or primary productivity is important in evaluating ecological health. Without algae converting sunlight energ y, carbon dioxide, and nutrients into oxy ge n and new plant m a terial, a lake or reservoir could not support other aquatic life. Chlorophyll a is a simple, long -s tanding, and w e ll-accepted measurement for estimating algal biomass, algal productivity, and trophic condition of a lake or reservoir (Carlson, 1977). Developing appropriate expectations is critical to evaluating the implications of chlorophyll concentrations on reservoir ecological health. Generally, lower chlorophyll concentrations in the oligotrophic range are thought of as indicating g ood w a ter quality conditions. C onversely, hig h chlorophyll concentrations are usually considered indicative of cultural eutrophication. However, these ge neralizations m u st be tempered by g eologic and cultural considerations. T h e range of chlorophyll concentrations considered indicative of good, fair, and poor ecological conditions m u st be tailored to reflect knowledge of back gr ound or natural conditions within each watershed. Itis unrealistic to expect m o st T e nnessee Valley reservoirs to have low chlorophyll concentrations because m a ny are located in w a tersheds that have nutrient-rich, easily erodible soils. Most lakes and reservoirs in the T e nnessee Valley naturally contain sufficient nutrients to support algal populations with chlorophyll concentrations in the me sotrophic range, even in the absence of anthropogenic sources and cultural eutrophication. H owever, two w a tersheds in the T e nnessee Valley, the Little T e nnessee R iver and the Hiwassee River watersheds, have soils (and consequently waters) with naturally low nutrient levels. T he streams in these watersheds drain the Blue Ridge Ecoregion, which is largely characterized by thin soils and is underlain m o stly w ith hard crystalline and m e tasedimentary rocks. Th e classification scheme for evaluating chlorophyll concentrations in T e nnessee Valley reservoirs is based on expected “natural” nutrient levels for each w a tershed. Professional judg me nt w a s used to identify concentration ranges indicative of good, fair, and poor conditions. T his approach separates Te nnessee Valley reservoirs into into two classes for chlorophyll expectations—those expected to be naturally oligotrophic because they are in w a tersheds with naturally low nutrient concentrations and those expected to be naturally m esotrophic. T he reservoirs expected to be oligotrophic are in the Blue Ri dge Ecoregion. T his g r oup includes H iwa ssee, C h atuge, N o ttely, B l ue R i dge, and Parksville reservoirs in the H iwa ssee R ive r drainage; and Tellico and Fontana reservoirs in the Little Tennessee R iver drainage. T he remainder, both m a instream T ennessee River reservoirs and reservoirs on tributaries to the Te nnessee River, are expected to be m e sotrophic. Th e concentration ranges identified to represent good, fair, and poor conditions are m u ch lower for reservoirs in the nutrient-poor watersheds. T h e primary concern for those reservoirs is early identification of cultural eutrophication. With early identification, appropriate actions can be taken to m a nage nutrient loadings and prevent shifts to higher trophic states. For the reservoirs expected to be m e sotrophic, the principal concern is that algal productivity (and chlorophyll levels) not become too g r eat because of the B-16 

### Nutrient Criteria—Lakes and Reserv o irsundesirable characteristics associated with eutrophic lakes (dense algal blooms, poor water clarity, low DOs, and predominance of noxious blue- g reen algae). For mesotrophic reservoirs where sufficient nutrients are available but chlorophyll concentrations remain low, some other factor such as excessiv e turbidity or toxicity usually is present that inhibits algal growth. Consequently, the rating for chlorophyll a is lowered when those conditions are observed. 

### Data Collection MethodsE Depth-integrated composite chlorophyll a samples are collected monthly (April-October) from the photic zone (defined as twice the Secchi depth or 4 m e ters, w h ichever is g r eater). C oncurrent algae and z ooplankton samples are collected for screening and semi-qualitative examination of the plankton comm unity assemblage. I n addition, in-situ water column profiles of temperature, dissolved oxy g en, pH, conductivity; and Secchi depth measurements are obtained each time samples are collected. Finally, on three of the monthly surveys (April, June, and August), the photic zone composite samples are analy zed for nutrient levels (total phosphorus, amm onia-nitrogen, nitrate+nitrite-nitrogen, and organic nitrogen) to help in evaluating the chlorophyll data and to help support trophic state assessments. In 1996, physical/chemical water quality v ariables were measured at 33 locations on 19 Tennessee Valley reservoirs. Additional details on collection m e thods are available in an informal T V A report. 

### Chlorophyll Rating SchemeE Chlorophyll ratings at each sampling location are based on the average summe r concentration of m onthly, composite photic zone samples collected from April through October (or September). I f nutrients are present (e.g., total phosphorus g r eater than 0.01 m g/L and nitrate+nitrite-nitrogen g r eater than 0.05 m g /L) but chlorophyll a concentrations are g e nerally low (e.g., < 3 

### � g/L), other limiting or inhibiting factors (e.g., high stream flows, turbidity, toxicity, etc.) are considered to be present, and the chlorophyll a rating is decreased one unit.

**References,** Carlson, R.E. 1977. A trophic state index for lakes. Limnol. Oceanogr . 22:361-369.



### Nutrient Criteria—Lakes and Reserv o irs B-17

# 8.vThe British Columbia Water UseE **Based ApproachE** by R i chard N o rdin, B ritish Columbia Ministry of the En vironm e ntl

Br itish C o lumbia has elected to establish criteria according to different uses (Nordin, 1986). In three of the water uses they have defined—drinking water, protection of aquatic life, and recreation and aesthetics—nutrients are important. T h e sequence for determining criteria is shown in Figure 1. Literature review, input from other agencies (e.g., existing criteria), and evaluation of problems that exist or have existed in B r itish C o lumbia lakes were used to derive the criteria. The literature review focused on interrelationships between nutrients, primary productivity, and hypolimnetic oxy gen **Figure 1: Sequence for Determining Water Quality Criter**  **iaE**

B-18 

### Nutrient Criteria—Lakes and Reserv o irsdepletion; cold w a ter fishery requirements; and public perception of w a ter quality. B r itish C o lumbia' s criteria are presented in Table 1. Phosphorus concentration was used because there is ample evidence in the literature that quantitative interrelationships exist between it and chlorophyll and transparency, its acceptance as an index of eutrophication, and the advantage of quantifying the controlling parameter. No rdin (1986) notes that these criteria are proposed specifically for B r itish C o lumbia, w h ere the lakes fall largely into the oligotrophic category and m ay not be directly applicable to other areas. Criteria for lakes supporting warm -w ater fish were not included (Nordin, 1985). Nordin (1986) notes the difficulty in trying to establish criteria for lakes where a w arm -w ater fishery is the m o st important use, stating that a phosphorus concentration below 10 

### � g/L is probably too low (leading to low fish productivity) and that concentrations up to 40 

### � g/L m ay be tolerable for lakes where recreational fisheries are important and conditions are suitable. T h e lack of either empirical or experimental data was cited as a m ajo r impediment to sug ge sting criteria for nutrient concentrations for fish or aquatic life other than the salmonid fishes (salmon and trout) that are of primary concern in B r itish C o lumbia. In applying these criteria and checking them against existing w ater quality, the w a ter exchange time of the lake m u st be taken into account. T h e phosphorus concentration is measured at spring overturn (when the epilimnetic w a ter residence time is g r eater than six months) or the mean epilimnetic g r owing season concentration is measured (if the epilimnetic residence time is less than six months). Th e second step in the process is to apply the criteria to individual lakes. T h e criteria v a lue m ay be m odified up or down into an “objective” depending on the water uses or other circumstances that m ay apply for that specific lake. The various factors considered (i.e., data g a thered) in establishing the objectives include hydrolog y , water uses, w a ste discharges, w a ter quality data (including dissolved oxy ge n and temperature profiles, g e neral chemistry nutrients, chlorophyll, and transparency),

**Ta ble 1: British Columbia’s Lake W**  **a ter Q**  **u alit**  **y Criteria for NutrientsE**  **Most Sensitive UseE Phosphorus CriteriaE**  Drink in g w ater <10 μg /L R ecreation and aesthetics <10 μg /L Aq uatic life ( cold-water fish ) 5-15 μg /L*

*A ran ge is suggested as the criterio n that can b e u s ed as the b a sis f o r site-specif ic waterquality obje c tiv es. Sourc e: N ordin, 1985.



### Nutrient Criteria—Lakes and Reserv o irs B-19phosphorus loading, algal species composition, and sediment chemistry. Details on the use of these factors m ay be found in N o rdin (1985). T h e resulting w ater quality objectives by themselves have no legal standing and would not be directly enforced (McKean et al., 1987) but are used as a me thod for planning or for initiating other m a nagement techniques or administrative orders. Th e objectives are considered policy g uidelines for resource m a nagers to protect water uses in the specified w a ter bodies. T h ey g uide the evaluation of w a ter quality; the issuing of permits, licenses, and orders; and the m a nagement of the fisheries and the province's land base. They w ill also provide a reference against w h ich the w a ter quality in a particular w a ter body can be checked, and aid decisions on wh ether to initiate basin- wi de w a ter quality studies. In cases w h ere objectives are set, the policy is to put into place a monitoring program for a period of at least three years to evaluate the lake to w h ich the w a ter quality objectives have been applied. I n some cases interim or intermediate g o als for lake phosphorus concentrations have been used where ambient concentrations g r eatly exceeded the proposed criteria. 

### Uses of Lake Standards in British ColumbiaE Br itish C o lumbia's phosphorus criteria serve as a tool for protecting the m o st sensitive lake uses. Th ese uses typically include drinking , cold- w ater fish or other aquatic life, recreation, and aesthetics. T he two primary applications of the criteria are:
• To evaluate data on w a ter, sediment, and biota for w a ter quality assessments.
• To establish site-specific w a ter quality objectives. Water quality objectives serve as policy g uidelines for resource m a nagers in their mi ssion to protect wa ter uses in specified w a ter bodies. Water quality objectives g u ide the resource m a nager in the evaluation of w a ter quality; issuance of permits, licenses, and orders; and m a nagement of fisheries and the w a tershed (McKean et al., 1987). T h ey also provide a reference against w h ich the w a ter quality status in a particular water body can be monitored, and as a basis for m aki ng decisions on the initiation of basin- wi de w a ter quality studies. In many instances, the w a ter quality objectives serve as the primary m eans of planning for the protection and evaluation of water quality (Ministry of Environment, 1985 and 1997). Th e Ministry of Environment (1985) promotes the criteria as a means of avoiding the need for costly and high-precision loading studies. In contrast to accuracy needed to establish "critical" loadings in w a ste allocations, loading estimates in the context of w a ter quality objectives are used only to determine relative contributions from v arious sources. The loading contribution estimates are then used to prioritiz e the importance of v arious inputs. In O k anagan Lake, where the w a ter quality objective for the lake w as the same as the 1985 phosphorus concentration (10 

### � g/L), the m a nagement strateg y focused on ma intaining concentrations (Ministry of Environment, 1985). In this case, if increased “trading” from development and municipal effluent were to occur, then reductions from the sources (e.g., agricultural sources or septic tanks) would need to be sought. T h is sug ge sts that point/nonpoint source “trading” is among B ritish C o lumbia's m a nagement tools to ensure that w a ter quality objectives are m e t. Specific w a ter quality objectives have been set in about 15 lakes where the entire objective setting (rigorous evaluation) has been done. T h e criteria have been applied to evaluating hundreds of other lakes. I n some of the lakes in the province where long -t erm eutrophication problems exist and where phosphorus concentrations g r eatly exceeded the criteria (several lakes with phosphorus concentrations gr eater than 50 

### � g/L), the objectives w e re either set to the criteria (5 to 15 

### � g/L) or an interim g oal (30 

### � g/L) (Wood Lake in Ministry of Environment, 1985 or Charlie Lake in Nordin and Pomme n, 1985). Th e m o st recent approach has been to combine the phosphorus objectives with biological objectives that specify phytoplankton comm unity composition where, for instance, reduction in the frequency or numbers of cyanobacteria is a g o al for w a ter quality protection (Cavanagh et al., 1994).

B-20 

### Nutrient Criteria—Lakes and Reserv o irsOv erall the approach to using a water-use-based approach has been w e ll accepted within B r itish Columbia and is also used by the Canadian federal g ove rnment in specifying its criteria for a v ariety of wa ter quality parameters.


### References

Br itish C o lumbia Ministry of Environment. 1985. The phosphorus in the Okanagan Valley Lakes: sources, w a ter quality objectives and control possibilities . Water Management Branch, Waste Management B r anch. Province of B r itish C o lumbia. 

### B ritish Columbia Ministry of Environment. 1997. Water Quality in British Columbia - Objectives attainment 1995 . Victoria, B C . 120p. Cavanagh, N., R.N. Nordin, and J

. E. Bryan. 1994. Ch ristina Lake W a ter Quality Assessment and Ob jectives . B r itish C o lumbia Ministry of Environment, Victoria, B C . Summary report 18p. Technical Report 106p. McKean, C.J., N.K. Nagpal, and N.A. Z i rnhelt. 1987. W illiams Lake w a ter quality assessment and objectives . Ministry of Env i ronment and Parks, Province of B r itish C o lumbia. Nordin, R.N. 1985. Wa ter quality criteria for nutrients and algae . B r itish C o lumbia Ministry of Environment, Victoria. No rdin, R .N . 1986. N u trient w a ter quality criteria for lakes in B r itish C o lumbia. Lake Reserv. Manage

. 2:110-113. Nordin, R.N. and L.W. Pomme n. 1985. Peace River area, Charlie lake sub-basin, w a ter quality assessment and objectives ( t echnical appendix) . BC Ministry of Environment, V i ctoria, BC. 34p.



### Nutrient Criteria—Lakes and Reserv o irs B-21

# 9.) Rationale for a Revised **PhosphorusI Criterion for Precambrian ShieldI**  **Lakes in OntarioI** by N e il Hutchinson , Ontario Ministry of Environment and Energy

The O n tario Ministry of Env i ronment and Energ y (OMEE) manages environmental quality primarily through two pieces of provincial legislation, the Environmental Protection A c t and the O n tario Water Re sources A c t. Policies and procedures for m a nagement of surface w a ter quality that arise from this legislation are elaborated in implementation documents such as Wa ter Management: Policies, Gu idelines, Provincial W a ter Quality O b jectives of the Ministry of Environment and Energy (1994) (OMEE, 1994). Th e g o al of surface w a ter m a nagement in O n tario is: “to ensure that the surface w a ters of the province are of a quality w h ich is satisfactory for aquatic life and recreation. ” On tario established Provincial Water Q u ality O bjectives (PWQ Os ) in the 1970s in order to meet this go al. T h e first objectives were m o stly adopted from other agencies, such as the I n ternational J o int Commi ssion, but were later developed in Ontario (OMEE, 1992). “PWQ Os are numerical and narrative ambient surface w a ter quality criteria. T h ey are applicable to all waters of the province (e.g., lakes, rivers, and streams) except in those areas influenced by OMEE approved point source discharges. In specific instances where gr oundwater is discharged to surface w a ters, PWQ Os m ay also be applied to the gr oundwater. PWQ Os represent a desirable level of w a ter quality that the O M EE strives to ma intain in the surface w a ters of the province. In accordance with the g o als and policies in Water Management (OMEE, 1994), PWQ Os are set at a level of w a ter quality w hich is protective of all forms of aquatic life and all aspects of the aquatic life cycle during indefinite exposure to the water. T he objectives for protection of recreational water uses are based on public health and aesthetic considerations” (MOEE, 1994). Tw o policies are used to interpret the water management g o al and application of the PWQOs to specific water bodies (MOEE, 1994).
• Policy 1 “In areas w h ich have w a ter quality better than the Provincial Water Q u ality O bjectives, wa ter quality shall be m a intained at or above the O bj ectives. A lthough some lowering of wa ter quality is permissible in these areas, degradation below the Provincial Water Q u ality Obj ectives will not be allowed, ensuring continuing protection of aquatic comm unities and recreational uses.”
• Policy 2 “Water quality w hich presently does not meet the Provincial Water Q u ality O bjectives shall not be further degraded and all practical measures shall be taken to upgrade the water quality to the O bj ectives.” Ontario’s PWQO development process was developed specifically to deal with toxic substances. I t uses published studies on the effects of pollutants to estimate a safe concentration for indefinite exposure. T he only data that are m a ndatory for PWQO development are data on toxicity , B-22 

### Nutrient Criteria—Lakes and Reserv o irsbioaccumulation, and m u tagenicity (MOEE, 1992), but the process does permit the development of a PWQO based upon aesthetic impairment, such as taste or odor. I f insufficient data are not available a “guideline” or “interim objective” status is assigned to the resultant w a ter quality criterion. 

### Existing PWQO for Total Phosphorus Th e existing PWQO for total phosphorus was developed in the late 1970s (OMEE, 1979). I tdrew on the trophic status classification scheme of Dillon and R igl er (1975) to protect against aesthetic deterioration and nuisance concentrations of algae in lakes and excessive plant g r owth in rivers and streams. T h e rationale (OMEE, 1979) acknowledges that elemental phosphorus can be toxic, but that it is rare in nature and so toxicity is rarely of concern. (In fact, there is only one documented case of elemental phosphorus poisoning an aquatic [marine] system in Canada). I nstead, the purpose of the objective was to protect the aquatic ecosystem non-toxic forms of phosphorus : “phosphorus m u st be controlled, however, to prevent any undesirable changes in the aquatic ecosystem due to increased algal growth.... ” (OMEE, 1979). Th e 1979 PWQO was g ive n the status of a “guideline” both to reflect the uncertainty regarding the effects of phosphorus and to acknowledge the difference between m a naging toxic and non-toxic pollutants. “Current scientific evidence is insufficient to develop a firm objective at this time. Accordingly, the following phosphorus concentrations should be considered as general guidelines w h ich should be supplemented by site-specific studies:
• To avoid nuisance concentrations of algae in lakes, average total phosphorus concentrations for the ice-free period should not exceed 20 

### � g/L. •	 A high level of protection against aesthetic deterioration will be provided by a total phosphorus concentration for the ice-free period of 10 

### � g/L or less. This should apply to all lakes naturally below this value.
• Excessive plant growth in rivers and streams should be eliminated at a total phosphorus concentration below 30 

### � g/L.” 

### The Need For RevisionI A lthough the 20 intervening y ears have shown that the phosphorus g u ideline is sound, m o re recent science has revealed new concerns that were not addressed in the original. I n 1996, therefore, Ontario decided to review its PWQO for total phosphorus. T he bulk of Ontario’s 226,000 lakes (Cox, 1978) lie on the Precambrian Shield, and the scientific basis for a new PWQ O had previously been developed for these lakes (Hutchinson et al., 1991). Accordingly, the three- y ear review process targetted Precambrian Shield lakes first, with off-shield lakes, the G r eat Lake s, and streams and rivers reviewed later in the process. Th e rationale for revisiting the PWQ O for phosphorus does not lie exclusively in better information on the effects of phosphorous as a pollutant. I nstead, better understanding of watershed processes, biodiversity, and cumulative impact assessment over the past 20 years led to the corporate adoption of these considerations in the water m a nagement process (OMEE, 1994). T h is knowledge revealed several shortcomings with the existing, tw o- tiered g u ideline of 10 

### � g/L for “a high level of protection against aesthetic deterioration” and 20 

### � g/L “to avoid nuisance concentrations of algae.” Although these numeric objectives are designed to m a intain water clarity and aesthetic v a lues and have performed well for over 20 years, they fall short in the area of protecting the diversity of the provincial resource of water quality and any associated biodiversity

.



### Nutrient Criteria—Lakes and Reserv o irs B-23

### Trophic Status ConsiderationsI Th e existing numeric objectives for total phosphorus ignore fundamental differences between lake types and their nutrient status in the absence of human impact. Ontario’s Precambrian Shield lakes presently span a range of phosphorus concentrations ranging from oligo to mesotrophic, and all are represented in roughly equivalent proportions in the provincial lake resource (Figure 1). Within this range, however, there is still a large diversity of w a ter clarity, controlled by both total phosphorus concentrations and dissolved organic carbon (Dillon et al., 1986). Th e logical outcome of a two-tiered objective is that, over time, all recreational waters would converge on one or the other of the w a ter quality objectives. T h is would produce a cluster of lakes slightly below 10 

### � g/L and another slightly below 20 

### � g/L, decreasing the provincial diversity in water quality in lakes and, with it, lower diversity of their associated aquatic comm unities. Th e second shortcoming is that, over time, some lakes would sustain unacceptable changes in water quality w hile others would be unimpacted, producing both ecological and economic asy mme tries as the resource was developed. A lake with a natural phosphorus concentration of 4 ug/L is a fundamentally different lake from one that exists at 9 

### � g/L. Both lakes, however, would be allowed to increase to 10 

### � g/L under the existing PWQO. One lake would experience no perceptible change (9 - 10 

### � g/L) and be overprotected, but the other (4 - 10 

### � g/L) would be underprotected and change dramatically. In both cases, human perceptions of aesthetics are ignored in the objective. Allocation of phosphorus loading s between these two lakes would be unfair as well. T he higher-phosphorus lake could sustain a g r eater change than the low-phosphorus lake but would be restrained to a m u ch lower load. A final concern is that the existing PWQ O does not explicitly consider the impact of phosphorus on hypolimnetic oxy ge n or aquatic biota. I t does, however, m ake reference to site-specific studies in the assessment process. I n summ ary, the existing numeric objectives overprotect some lakes and do not protect others adequately . A llocation of phosphorus loadings is unnecessarily restricted in some lakes and overly ge nerous in others. Neither biotic nor aesthetic attributes are adequately protected. Over time the diversity of trophic status that is presently represented in O n tario will decrease. **Env i**  **ronment a**  **l Baselines and M**  **easured Water Q u**  **alit y I**  A n emerging concern in environmental assessment is the need for a standard baseline for comparison against environmental change. Inland lakes respond quickly to point-source phosphorus inputs. Detection of change is m u ch m o re difficult, however, for non-point sources such as leachate from domestic septic systems. Existing approvals and interpretation of the existing PWQO are based on measurements of water quality

. Measurements of phosphorous m a de in the period between development of a shoreline and expression of change in trophic status, however, will significantly underestimate its impact and m ay wrongfully conclude that the lake has not responded to phosphorus loading

.

B-24 

### Nutrient Criteria—Lakes and Reserv o irs**Figure 1: E x**  **isting Distribution of 921 Ontario lakes by Phosphorus ConcentrationI**

Th e incremental nature of shoreline development (no lake is ever developed all at once) results in a slow and g r adual increase in trophic status. T he high degree of seasonal and annual variance in phosphorus levels in lakes (Hutchinson and Clark, 1992) means that changes may not be detectable without an intensive monitoring program, based on m a ny samples and a precise and replicable analytical me thod. Finally, a slow increase in trophic status over a g e neration m ay not be noticed by human observers. Environmental change that occurs over one g e neration becomes the status quo for the next. Over a long period, therefore, any assessment baseline that is based on measurements of total phosphorus will increase. An y phosphorus objective that relies exclusively on measured w a ter quality w ill therefore suffer from : • Detection problems due to natural v ariance and analytical problem s • T he lag time between addition of phosphorus to a watershed and its expression in a lake • F ailure to detect incremental changes in w a ter quality • H uman perceptual conditioning that reduces the apparent change in w a ter quality over time As a result, an increasing assessment baseline and incremental increases in w a ter quality w ill slowly degrade w a ter quality past any objective. I m pacts will accumulate by v irtue of delay in their expression, repetition over time and space, extension of the impact boundary by downstream transport, or by trig ge ring indirect changes in the system, such as anoxic sediment release. Non-point source phosphorus pollution, particularly from septic systems serving shoreline development, is thus an excellent example of a pollutant that produces cumulative impacts to the aquatic environment. T he emergence and v a lidation of m a ss balance phosphorus models for lakes, however, offers an opportunity to correct some of the disadvantages of w a ter quality m easurements and conventional assessment techniques. 

## Total **Phosphorus and the PWQO Development ProcessI** Development of a PWQO for total phosphorus is distinctly different from that for toxic substances. I t is therefore inappropriate to adhere strictly to the established procedures (MOEE, 1992). Because phosphorus is not toxic, insufficient scientific evidence on its toxicity should not be the rationale for its



### Nutrient Criteria—Lakes and Reserv o irs B-25gu ideline status. I n stead, g u ideline status should reflect the subjectivity inherent in m a naging a non-toxic pollutant. Most pollutants are directly toxic to some target tissue, such as the fish gill, even if some of them are required nutrients at trace amounts, i.e., copper or z i nc. A s a result, the health of aquatic organisms, and hence the ecosystem, declines rapidly at concentrations slightly above ambient levels (Figure 2). Phosphorus, on the other hand, is a m ajo r nutrient. Concentrations can increase substantially with no direct toxic effects. I n fact, the first response of the aquatic system is increased productivity and biomass. Beyond a certain point, however, indirect detrimental effects become apparent, which ultimately decrease system health. Because phosphorus is not toxic, it is used as a surrogate for attributes such as w a ter clarity or dissolved oxy ge n that we wish to protect. T he first responses of a lake to enrichment (i.e., water clarity , algal blooms) are aesthetic and of concern only to humans. Assessment of aesthetic impacts is highly subjective; perceived changes in w a ter clarity are based largely on w h at one is used to (Smeltzer and Heiskary , 1990). T h e development of a phosphorus objective m u st therefore acknowledge an element of subjectivity in dealing with human concerns. T h e objective-development process may also consider that aesthetic impacts begin where a change in w a ter clarity is first noticeable to the human eye, or w h ere the mean w a ter clarity first exceeds natural v ariation. Biotic impacts of phosphorus enrichment, such as the loss of oxy ge nated hypolimnetic habitat for cold water species (i.e., lake trout [ Salvelinus namaycush ]) are known and can be addressed objectively (Maclean et al., 1990) . D issolved oxy g en concentrations are explicitly protected by the O n tario PWQ O for Dissolved Oxy ge n (MOEE, 1994) and are not intended as a direct consideration in phosphorus objective development. N evertheless, recent advances in oxy ge n-phosphorus models (i.e., Molot et al., 1992) allow direct estimation of the impact of phosphorus concentrations on dissolved oxy ge n in lakes. Any protection of dissolved oxy ge n that is achieved, even indirectly, by the phosphorus objective is beneficial, and its consideration prevents the possibility of one PWQ O inadvertently contradicting another. Finally, trophic status indicators such as water clarity, chlorophyll a , or dissolved oxy ge n cannot be ma naged directly, but only through m a nagement of phosphorus. I n addition, there m ay be delays of up to decades between the addition of phosphorus sources to a w a tershed (i.e., septic systems), its m oveme nt from the source to surface water (Robertson, 1995) and its expression as a change in trophic status. Shoreline residential development represents a significant contribution to eutrophication of Ontario’s Precambrian Shield lakes (Dillon et al., 1986). A s a result, phosphorus management in O n tario requires the extensive use of models relating shoreline development to the trophic status of the receiving wa ter. Phosphorus m a nagement m ay therefore be considered as a process of “ predicting the predictor.”

B-26 

### Nutrient Criteria—Lakes and Reserv o irs**Figure 2: Generalized responses of an ecosystem to toxic and non-toxic pollutants**



## Proposal for a Revised PWQO Recent advances in phosphorus modeling, understanding of w a tershed dynamics, and cumulativ e impact assessment have been used to propose a new PWQO for Ontario’s Precambrian Shield lakes. T he proposal encompasses two innovations: the use of models to establish a baseline for changes in trophic status and a proportional increase from that baseline due to anthropogernic phosphorus loadings. The challenge now lies in expanding this understanding beyond shoreline development in Precambrian Shield lakes, for w h ich it w a s originally developed, to apply it to all the w a ters of the province, including offshield lakes and the Great Lakes, rivers, and streams. 

### M

**odeled assessment baseline**

The basis of the revised PWQ O is increased reliance on w a ter quality m odeling in the objectivesetting process. R ecent advances in trophic status models allow us to calculate the “pre-development” phosphorus concentrations of inland lakes (Hutchinson et al., 1991). T his is done by m odeling the total phosphorus budget for the lake, comparing the predicted concentration to a reliable w a ter quality measurement, and subtracting that portion of the budget attributable to human activities. Further w o rk is necessary for w a ter bodies lying off of the Precambrian Shield, but the basic premise is applicable to any water body where a phosphorus budget can be calculated. Th e m a in advantage of the modeling approach is establishment of a constant assessment baseline. A m odeled “predevelopment” baseline is based on an undeveloped w a tershed and so will not change over time. This serves as the starting point for all future assessments. Every g eneration of w a ter quality ma nagers will therefore have the same starting point for their decisions, instead of a steadily increasing baseline of phosphorus measurements.



### Nutrient Criteria—Lakes and Reserv o irs B-27We therefore propose a PWQO for total phosphorus that is based on a modeled “predevelopment” phosphorus concentration. T his will provide w a ter quality m anagers with: • A constant assessment baseline, • A buffer against incremental loss of w a ter quality, and • A buffer against v ariable w a ter quality measurements. Th e predevelopment phosphorus concentration should not be interpreted as a PWQO. Pristine phosphorus levels have not existed in Ontario for over a century and their attainment is not cost-effectiv e in a heavily developed society . T he modeled predevelopment concentration only serves as the starting point for the PWQ O and a reference point for future changes. A model-based objective would have two additional advantages. First, the modeled response of the watershed to future changes is instantaneous. I t applies new development directly against capacity , w ithout the intervening decades it takes for phosphorus to m o ve to a lake and be expressed as a measured change in water quality

. Second, O n tario’s trophic status model is based on entire watersheds and so allows explicit consideration of downstream phosphorus transport in the assessment. 

### Proportional Increase Th e second component of the objective is a proportional increase from the modeled predevelopment condition. T h e proportional increase accomodates regional v ariation in natural or “back gr ound” water quality through the use of one numeric objective for all Precambrian Shield lakes. I tis, in fact, a broader, ye t simpler, application of the regionally specific, m u lti-tiered objectives proposed in other j u risdictions as a m eans of accomm odating regional v ariation in back gr ound w a ter quality (i.e., Minnesota—see Heiskary, this v o lume, and Wisconsin—see Searle, this v o lume). Ontario is proposing an allowable increase of 50% above the predevelopment level from anthropogenic phosphorus sources. Under this proposal, a lake that was modeled to a predevelopment phosphorus concentration of 4 

### � g/L would be allowed to increase to 6 

### � g/L. Predevelopment concentrations of 6, 10, or 12 

### � g/L would increase to 9, 15, or 18 

### � g/L, respectively

. A cap at 20 ug/L w ould still be m a intained to protect against nuisance algal blooms. Th ere are numerous advantages to this approach:
• Each w a ter body w ould have its own w a ter quality objective, but this could be described with one number (i.e., predevelopment plus 50%).
• Development capacity would be proportional to a lake’s original trophic status. •	 A s a result, each lake would m a intain its original trophic status classification. A 4 

### � g/L lake would be developed to 6 ug/L and therefore m a intain its distinction as oligotrophic. A 9 

### � g/L lake would be developed to 13.5 

### � g/L, would m a intain its trophic status, and development would not be unnecessarily constrained to 10 

### � g/L. •	 T he existing diversity of trophic status in Ontario would be m a intained, instead of a set of lakes at 10 

### � g/L and another at 20 

### � g/L. 

### Rat **i onale f**  **o**

**r 50% Increase** Water Clarity Water clarity in O n tario’s Precambrian Shield lakes is controlled by both dissolved organic carbon (D OC ) and phosphorus (Dillon et al., 1986). A ny phosphorus objective should therefore consider D OC as w e ll as phosphorus in its derivation. Molot and Dillon (pers. comm. ) used 14 years (1976-1990) of data from lakes in south-central Ontario to produce the following relationship, summ arized in Figure 3. SD = 6.723 - (0.964 x DOC) + (9.267/TPep)
B-28 

### Nutrient Criteria—Lakes and Reserv o irsFigure 4 shows the response of water clarity to v arious proportional increases in total phosphorus concentration, predicted for v arious DOC levels using the same equation. Responses are g r ouped to include all lakes with initial phosphorus concentrations between 2 and 14 ug/L, and so a 50% increase represents final values of 3 to 21 ug/L. T here is no clear threshold of changed water clarity, a point where further increases in phosphorus would induce a markedly m ore severe change in water clarity

. In stead, Figure 3 shows a g r adual loss of water clarity as phosphorus concentrations are increased from 10% to 100%. T he allowable percentage increase cannot, therefore, be determined on the basis of water clarity alone. 

### Detection of Change in Phosphorus and Water Clarity Th e average coefficient of v ariation in Secchi depth for a series of Southern O n tario Precambrian Shield lakes was 17%-21% over a 14- y ear period of record (Clark and Hutchinson, 1992). A change of 25% in water clarity would therefore represent a significant departure from natural v ariation and be detectable against it. A 50% increase in phosphorus concentration produces an average 25% loss of Secchi depth across the range of initial phosphorus (2-14 

### � g/L) and DOC (2-7) shown in Figure 3 and Table 1. In addition, a 50% increase protects the clearest and m o st desirable water clarity and allows a gr eater proportional change only in those lakes with high DOC where water clarity is limited by DOC instead of by the phosphorus/chlorophyll relationship (Table 1).

**Figure 3: Relationship of P r**  **edicted Water Quality to T o**  **tal Phosphorus and DOC Concent**  **r ations in Precambrian Shield**  **L akes in So**  **uth- Central Ont**  **a rio** 



### Nutrient Criteria—Lakes and Reserv o irs B-29� **Figure 4: Predicted Response of Secchi Depth in 10-100% Increases in Phosphorus Concentration From Initial Values of 2-14**  **g/L**

**Ta ble 1:**  **Av erage loss of Secchi depth w**  **i th a 50% increase in total phosphorus concentration**  **as a function of dissolved or g**  **anic carbon concentration**
**DOC=2 DOC=4**  **DOC=6 DOC=7**  **Av erage**  % loss of clarit y 14 18 27 41 25.3
Note: The 50% incre ase in TP is taken f rom a star ting ra nge of 2-14 μ g /L to produc e fi nal v a lue s of 3-21 μ g /L

. Hutchinson et al. (1991) reported a natural coeffcient of v ariation in total phosphorus concentrations in South-Central Ontario lakes of about 20%. Detection of a 20% change in total phosphorus requires only 2 years of spring overturn measurements or 1 year of 4-5 measurements in the ice-free season (Clark and Hu tchinson, 1992). A phosphorus objective 50% g r eater than the predevelopment conditions would therefore be detectable with even the m o st rudimentary sampling program and would limit changes in wa ter clarity to an average of 25%, a level just beyond the range in natural v ariation of Secchi depth. 

### Pr otection of Dissolved Oxygen Di ssolved oxy ge n concentrations are explicitly protected by the O n tario PWQ O for D i ssolved Oxy ge n. T he existing PWQO for D.O. is 6 m g/L at 10 o C for cold- w ater (stratified) lakes (OMEE, 1994). Th is m arks the upper limit of typical hypolimnetic water temperature, and represents the optimum for the production of lake trout, an esteemed cold- w ater species in Ontario (Maclean et al., 1990). Althoug h dissolved oxy ge n concentrations are not intended as a direct consideration in phosphorus objectiv e development, any protection achieved, even indirectly, by the phosphorus objective is beneficial, and its consideration prevents the possibility of one PWQ O inadvertently contradicting another. O xyg enphosphorus models can be used for direct estimation of the impact of phosphorus on dissolved oxy ge n in lakes. Th e Molot et al. (1992) model predicts the hypolimnetic oxy ge n profile at the critical end-of-summer period, when lakes are warmest and oxy ge n depletion is near m a ximum . I t was used to model the impact of a 50% increase in phosphorus on dissolved oxy ge n (Hutchinson, 1997, unpubl.). Four stratified lake

B-30 

### Nutrient Criteria—Lakes and Reserv o irstypes w e re modeled, spanning a range from highly sensitive (shallow and small) to least sensitive (deep and large). Responses were expressed as v o lume- w eighted average hypolimnetic oxy ge n concentration and as the v o lume of hypolimnion exceeding the PWQ O of 6 m g/L. On average, a 50% increase in phosphorus protects dissolved oxy ge n in any lake that is larger than 67 ha and 28m or deeper and has less than 12 

### � g/L of predevelopment phosphorus. Some portion of the hypolimnion remained at 6 m g /L of D.O. or better in all such lakes modeled. Lakes with predevelopment concentrations of 7 

### � g/L or less were particularly well protected but the 50% increase did not protect lakes that w e re naturally at 12 

### � g/L T P or g r eater, because of their higher initial phosphorus concentrations. 

## References Clark, B. and N.J. Hutchinson. 1992. Measuring the trophic status of lakes: sampling protocols. Ontario Ministry of the Environment. September, 1992. PIBS 2202. I S BN 0-7778-0387-9. 36pp. Cox, E.T. 1978. Counts and measurements of Ontario lakes 1978. Fisheries Branch, Ontario Ministry of Natural Resources. 114pp. Dillon, P.J. and F.H. Rigler. 1975. A simple me thod for predicting the capacity of a lake for development based on lake trophic status. J. Fish. Res. Bd. Can. 32: 1519 - 1531. D illon, P.J., K.H. Nicholls, W.A. Scheider, N

. D . Yan, and D

. S. J e ffries. 1986. Lakeshore C apacity Study: T r ophic Status. Final Report. Ontario Ministry of Municipal Affairs. May 1986. I S BN 07743- 8077-2. 89pp. Heiskary , S.A. and W.W. Walker. 1988. Developing phosphorus criteria for Minnesota lakes. Lake Reserv. Manage. 4: 1-10. Hu tchinson, N .J ., Neary, B.P., and P.J. Dillon. 1991. Validation and use of O n tario’s trophic status m odel for establishing lake development g u idelines. Lake Reserv. Manage. 7: 13-23. MacLean, N.G., J

. M. Gunn, F.J. Hicks, P.E. Ih ssen, M. Malhiot, T

. E. Mosindy, and W. Wilson. 1990. Environmental and g e netic factors affecting the physiolog y and ecolog y of lake trout. Lake T r out Synthesis - Physiolog y and Ecolog y Working Group. Ontario Ministry of Natural Resources. T o ronto. 84pp. Molot, L.A., P.J. Dillon, B.J. Clark, and B.P. Neary. 1992. Predicting end-of-summe r oxy ge n profiles in stratified lakes. Can. J. Fish. Aquat. Sci. 49: 2363-2372. OMEE. 1979. Rationale for the establishment of Ontario’s Provincial Water Q u ality O bjectives. O n tario Ministry of the Environment. 236pp. OMEE. 1992. Ontario’s Water Q u ality O bjective D eve lopment Process. O n tario Ministry of the Environment. 42pp + app. OM EE. 1994. Water Management: Policies, G u idelines, Provincial Water Q u ality O bjectives of the Ministry of Environment and Energ y . Ontario Ministry of Environment and Energ y. J uly 1994. 32pp. PIBS 3303E. I S BN 0-7778-3494-4. Robertson, W.D. 1995. Development of steady

- state phosphate concentrations in septic system plumes. J

. Contam. Hydrolog y . 19: 289-305. Smeltzer, E. and S.A. Heiskary

. 1990. Analysis and applications of lake user survey data. Lake and Reserv. Manage. 6: 109-118.



### Nutrie nt Criteria—Lakes and Reserv o irs B-31

# 10.	 Dillon Reservoir Phosphorus **Standard, Load Allocation, and Creditin**  **g System** by Robert Ray, Northwest Colorado Council of Governments

Dillon Reservoir is located in Summit County, Colorado, at an elevation of 9,000 feet. Constructed in 1963 as Denver's primary water supply, the reservoir holds 254,000 acre feet of water and has a surface area of 3,300 acres. Dillon R e servoir has also become a recreational center for fishing, camping, and boating. One of the reservoir's m a in attractions is its reputation for clear, deep blue water. During the late 1970's and early 1980’s, Summit County was one of the fastest g r owing areas of the country. About this time, w a ter quality degradation in the reservoir became apparent with the onset of algal blooms. A “Clean Lakes” study identified phosphorus as the limiting factor for algal growth in the reservoir. Studies of phosphorus loading to the reservoir revealed that approximately one-half of the phosphorus load came form natural sources, w h ile the other half w a s from human activities including m

unicipal wastewater effluent, parking lot runoff, construction site runoff, seepage from septic systems, and other nonpoint sources (Elmore et al., 1985). A stakeholder committee (the Summit County Phosphorus Policy C ommittee) w a s established to develop a strateg y for protection of w a ter quality in the reservoir. The C o mmittee included representatives from the towns, the county, the sanitation districts, the Denver Water Department, a sk i area, and a mi ning company. The newly formed Committee established a g o al of m a intaining the 1982 w ater quality in Dillon Reservoir. T h is corresponded to an in-lake phosphorus concentration of 7.4 

### � g/ l during the algal growing season of J u ly through O c tober, adjusted to 1982 hydrologic conditions. B a sed on this g o al, a control regulation w a s established by the State's Water Q u ality C ontrol C ommi ssion in 1984, which included an in-lake phosphorus standard, a wasteload allocation, and languag e acknowledging local land use regulations for the control of nonpoint source phosphorus loads. Th e four municipal wastewater dischargers to the reservoir installed advanced treatment equipment to control phosphorus, and the wasteload allocation was developed based on build-out projection flows and a phosphorus effluent concentration of 0.2 m g/l (the plants are currently discharging less than 0.05 m g/l phosphorus). Th e phosphorus standard served as the numerical basis for back

- calculating the necessary load reductions to achieve the desired conditions at zoned “build-out” of the basin. T h e overall strateg y requires a “2 for 1” credit between nonpoint source phosphorus reductions and point source wasteload allocation increases, effective erosion and sediment control practices, mitigation for increases in nonpoint source phosphorus loading from new development, and the use of CDPS (Colorado Discharg e Permit System) permits for enforcement if necessary

. Th ere have been three approved applications for phosphorus credits to wasteload allocations to date. Itis likely that the m a in reason that m o re projects for phosphorus credits have not occurred is the fairly large buffer between the wastewater treatment plants' existing annual loads and their wasteload allocations. T h e buffer w a s created by the extremely efficient operations of the w a stewater treatment plants. The reservoir continues to be monitored by the Summit Water Q u ality C ommittee (SWQ C) , w h ich is funded by its participants - the towns, county, and sanitation districts. T h e SWQC has developed a Phosphorus Accounting System, which was developed to address the concern that the model developed as part of the Clean Lakes study continues to project that at “build out” of the basin, phosphorus loads

B-32 

### Nutrient Criteria—Lakes and Reserv o irsw ill exceed the in-lake standard. T h e County is using its land use authority to require pound-for-pound mitigation of increased phosphorus loads from increases in zoning density during the Planned U n it Development process. Th e reservoir continues to meet its phosphorus standard and chlorophyll a g oal.



### Nutrient Criteria—Lakes and Reserv o irs B-33

# 11.	 Interim Phosphorus Standards for **the Ever g**  **lades** by William W. Walker, Jr.
Eutrophication induced by anthropogenic phosphorus loads poses a long -t erm threat to Everglades ecosystems. Substantial shifts in macrophyte and mi crobial comm unities have been observed in regions located downstream of agricultural discharges (Belanger et al., 1989; Nearhoof, 1992; Davis, 1994). T h is problem developed over a period of three decades following construction of the C e ntral and Southern Florida Flood Control Project and drainage of w e tland areas south of Lake O keechobee to support intensive agriculture (Figure 1). I n 1988, a lawsuit was filed by the federal g o ve rnment against the local regulatory agencies (Florida Department of Environmental Regulation and South Florida Water Management District (SFWMD)) for not enforcing w ater quality standards in Loxahatchee N a tional Wildlife R e fuge (LN WR) and Everglades Na tional Park (ENP). The lawsuit ended in an out-of-court Settlement A g reement (SA ) (U SA et al., 1991) and federal consent decree in 1992.

**Figure 1: Pr**  **ojects in South Florida**

B-34 

### Nutrient Criteria—Lakes and Reserv o irsTh e SA establishes interim and long -t erm requirements for w a ter quality, control technolog y , and research. Generally, interim standards and controls are designed based upon existing data and known technologies T h e interim control program includes implementation of agricultural Best Management Practices (BMP’s) and construction of wetland Stormw ater T r eatment Areas (ST A’ s) to reduce phosphorus loads from the Everglades Agricultural Area (EAA) by approximately 80 percent, relative to a 1979-1988 baseline. Subsequently, SFWMD adopted the EAA Regulatory Rule (SFWMD, 1992; Whalen and Whalen, 1994), which requires implementation of BMP’s in the EAA to achieve an annual-average phosphorus load reduction of at least 25 percent. T h e State of Florida (1994) passed the Everglades Forever Act, which defines a construction project and funding mechanism for STA’s. I n terim phosphorus standards w ill apply after interim control technologies are in place (1999-2006 for LNWR and 2003-2006 for EN P Shark Slough I n flows). Long -t erm standards (>2006) and control technologies will be developed over a period of several years and require a substantial research effort to develop supporting data. Specific statistical procedures for tracking progress of the restoration effort and for determining compliance with interim and long -t erm objectives are built into the Settlement A g reement, EA A Regu latory R ule, and Everglades Forever Act. T h ese procedures provide measures of performance that are important from technical, political, and legal perspectives. This report describes the g e neral model upon which these procedures are based. Specific applications include: • P standards for inflows to ENP (2 basins) • P standards for m arsh stations in LNWR
• Load-reduction requirements for the EAA Each tracking procedure w a s developed within the constraints of historical data to accomplish a specific objective. T h ey share a model structure w h ich is g e nerally applicable in situations w h ere historical monitoring data are to be used as a frame of reference for interpreting current and/or future m onitoring data. T h is would be the case when the management g o al is to restore the system to its historical condition, to prevent degradation beyond its current condition, or to require improvement relative to its historical or current condition. T h is paper describes the model and its application to ENP Shark River Slough inflows. Other applications are briefly summ arized. 

## General **M odel**  Explicit consideration of v ariability is the key to formulating a valid tracking procedure. Procedures are developed by calibrating the following g eneral model to historical data: Response = Average + T em poral Effect + Hydrologic Effect + Random Effect (1) Th e Response is the measurement to be tracked (e.g., concentration or load, averaged over appropriate spatial and temporal scales, linear or log

- transformed). T h e A v erage represents the mean va lue of the Response during the calibration period. T h e T em poral Effect represents a long -t erm trend in the historical data (if present); this m ay reflect anthropogenic influences (e.g., land development, new point-source discharges, etc.). T h e Hydrologic Effect represents correlations of the Response with other measured v ariables, such as flow, water level, and/or rainfall (if present). T h e Random Effect is essentially an error term which represents all other sources of v ariance, including sampling error, analytical error, and v ariance sources not reflected in the T em poral or Hydrologic terms. As demonstrated below, inclusion of T em poral and Hydrologic terms increases the statistical power of the tracking procedure (reduces risk of T y pe I and T y pe I I errors). T h ese terms can be excluded in situations where long -t erm trends are not present or where significant correlations between the response variable and hydrologic v ariables cannot be identified. In such a situation, the response would be treated as a purely random v ariable and the model would be identical to that described by Smeltzer et al. (1989)


### Nutrient Criteria—Lakes and Reserv o irs B-35for tracking long -t erm v ariations in lake w a ter quality. The model can be expanded to include m u ltiple Hydrologic Effects, interactions between T em poral and Hydrologic Effects, as well as other deterministic terms. Seasonal Effects (if present) can be considered by adding another term or eliminated by defining the Response as an annual statistic (average, median, etc.). Th e model is not constrained to any particular mathematical form. For example, Hydrologic Effects can be predicted by a simulation model, provided that uncertainty associated with such predictions (Random Effects) can be quantified. T h e applications described below invoke relatively simple, m u ltiple regression models which provide direct estimates of parameter uncertainty. T h e Hydrologic term provides a basis for adjusting historical and future monitoring data back to an average hydrologic condition, so that changes in the long -t erm mean (typically reflecting anthropogenic influences) can be tracked and not confused with random climatologic v ariability (e.g., w e t- y ear v s dry -y ear differences). Table 1 outlines three applications of the model to the Everglades. D a ta from a consistent, long -t erm m onitoring program are desirable for calibrating and applying the model. I deal data sets are rarely encountered, however, particularly if historical monitoring programs w e re not designed explicitly to collect data for this purpose. Everglades applications are based upon data sets ranging from 7 to 11 years in duration with monitoring frequencies ranging from biweekly to monthly. One strength of the data is that sampling and analyses have been consistently performed by a single agency (SFWMD). T h e following sections describe calibration and application of the model to ENP Shark River Slough inflows. 

### Model Calibration to Historical Monitoring Data In terim standards for ENP Shark River Slough were designed to provide annual, flow- w eighted- m ean concentrations equivalent to those measured between March 1, 1978, and March 1, 1979, the legally established base period consistent with ENP’s designation as an Outstanding Florida Water (OFW). An alysis of monitoring data collected between December 1977 and September 1989 collected at fiv e inflow structures (S12A,B,C,D & S333) revealed significant increasing trends in phosphorus concentrations and negative correlations between concentration and flow (Walker, 1991). To reduce possible influences of season and shifts in the flow distribution across the five inflow structures, the annual-average, flow- w eighted- mean concentration across all five structures was selected as a response v ariable and basis for the interim standard. Annual values for Water Years 1978-1990 (OctoberSeptember) were used to calibrate a regression model of the following form : Y = Ym + b 1 ( T - Tm ) + b2 ( Q - Qm) + E ( 2) wher e Y = observed annual, flow- w eighted- m ean concentration (ppb) T = w ater year (1978-1990) Q = b asin total flow (1000 acre-ft/yr) E = r andom error term m = s ubscript denoting average v a lue of Y, T , or Q in calibration period Prior to calibration, biweekly concentration data used to calculate annual flow- w eighted means were screened for outliers from a log

- normal distribution w h ile accounting for correlations between concentration and flow (Snedocor & Cochran, 1989); a single sample was rejected on this basis. Data from Water Years 1985 and 1986 w e re excluded from the calibration because of unusual operating conditions which promoted discharge of high-phosphorus canal flows (vs. m arsh sheet flows) through the inflow structures. T h e flow- w eighted- mean concentrations were 33 and 21 ppb, respectively, as compared with a range of 7 to 18 in other Water Years. T h ese unusual operating conditions are not expected to be repeated in the future.

B-36 

### Nu trient Criteria—Lakes and Reserv o irs

### Table 1: M ode l applications to the Eve rg lade s Lo cat ion E verg la des Agricul t ural Area ENP Sh ark Sl oug h Inf lows Lox ahatchee Nat i onal W ildlife Re fuge Re fe renc e EAA Re gu latory Rule (1992) Whalen & Whalen (1994) Interim Standards Settle me nt Ag re emen t (1991) Interim Standards Settle me nt Ag re emen t (1991)
Ob je c tiv e 2 5% Load R e duction v s . O c t 1979- Sept 1988 1978-79 conditions; ba se line pe r i od f or outstanding Floridawaters 1978-79 conditions; ba se line pe r i od f or outstanding Floridawaters Re s pons e variab le To tal P loa d T ota l P c onc en tration T otal P c onc en tration Tem por al averagi ng May- Ap ril water y ear Flow -weighted mean S eptOct w a ter year Monthly
Sp atial averagin g To tal EAA thru 18 structu r es, adjus ted fo r inputs f rom other ba si ns & re leases fr om Lake Okeec hobe e Combined inflow s f rom 5 structu r es in Sh ark River slo ugh Geometric mean across 14 marsh s tations

Ca libration period Ma y 1979-Ap ril 1988 9 wa ter years 2058 s amp le s Oc t 1977-Sept 1990 11 w a ter y ear s 222 s amp ling dates 1115 s am ple s Ju ly 1978-J u ly 1983 14 s amp ling r ounds 191 s amp le s

Sa mp le s excl ude d 3 s tatistic al outliers Oc t 1984-Sept 1986 (2 w ate r year s , unusual operation) 1 statistic al outlie r 2 dates with m ean st age < 15.42 f t(missi ng va lue s; marsh sa mp ling dif ficu lt) Tempor al eff ect No ne Lin ear tr en d Step change af ter ba se pe ri od Hy drologic ef

f ect(s) Basin rainf a ll, 9 stations Thie ssen average Rainf a ll s tatistic s: annual total, CV of m onthly totals, s kew ne ss of m onthly totals Basin total f l ow To tal thru 5 structure s St age (water surface elev) Av erage of 3 stations

Tr an sform a tion Natural log arithm None Natural log arithm Variance exp laine d 90% 80% 67%

Resi dual s ta ndar d erro r 0.18 ( � 18% ) 1 .87 ppb ( � 16% ) 0 .31 ( � 31% )

Base pe r iod Water year s 1980-88 Wate r year s 1978-79 J une 1978-Ma y 1979 First f u ll y ear of data Tar get 75% of ba se pe r i od ( 2 5% loa d re duction) 100% of ba se pe r iod 100% of ba se pe r iod

Limit 90th perc en tile 90th perc en tile 90th perc en tile Ex ceedence c ondition > limit in a ny year , or > targ etin � 3 cons ecu tive y ears > limit in a ny year > limit in > 1 month in a ny co ns ecu tive 12- month pe ri od



### Nutrient Criteria—Lakes and Reserv o irs B-37Table 2 lists calibration data and results. T h e model explains 80% of the v ariance in the historical data set with a residual standard error of 1.87 ppb. T h e fit is illustrated in Figure 2. Figure 2A plots observed and predicted concentrations against time. T h e 80 percent prediction interval (10th, 50th, and 90th percentiles) are shown in relation to the observed data. B o th regression slopes are significant at p < .05. T h e partial regression concept (Snedocor & Co chran, 1989) is applied below to illustrate the importance of each term in the model.

**Ta ble 2: Derivation of inter**  **i m standar**  **d s for**  **E NP**  **S har**  **k River**  **S lough inflow**  **s** Flow-W eigh ted-Me an T ota l P Conc en tration Water y ear Ba si n Flow Observed Pr ed icte d Flow - De trende d 50% target 90% limit kac-f t/yr ppb ppb Ad justed ppb ppb ppb ppb 78 522.8 6.7 8.4 6.7 7.0 8.4 11.7 79 407.0 9.8 9.6 9.2 9.59.0 12.3 80 649.2 10.6 9.0 11.2 9.7 9.6 11.1 81 291.7 12.4 11.3 11.4 11.0 10.2 12.9 82 861.3 8.4 9.2 10.0 6.3 10.8 10.1 83 1061.3 7.0 8.9 9.54.4 11.4 9.4 84 842.8 12.0 10.513.4 8.7 12.0 10.2 87 276.6 15.9 14.9 14.8 10.9 13.8 13.0 88 585.5 15.6 14.1 15.9 10.0 14.4 11.4 89 116.9 13.516.9 11.6 7.3 15 14.0 .0 90 148.2 18.1 17.3 16.3 11.2 15.6 13.8 Me an 523.9 11.8 11.8 11.8 8.7 8.7 11.8 Variab le s: Y = obs er ve d T P (ppb), T = wa ter y ear , b 1 ,b 2 = re g re ssi on s l ope s , m = s ubs cr ipt denoting mean va lue, Q = obs erved fl ow (k ac-f t/yr), E = random e rror (ppb), SE = re gressi on s ta ndard error of es tim ate (ppb), m = s ubs cr ipt denoting mean va lue..
Regr essi on model: Y	 = Y m = b 1 (T - T m ) + b 2 (Q - Q m ) + E

= 11.8 + 0.5932 ( T - 83.7) - 0.00465 ( Q - 523.9) + E
Regressio n results: R 2 = 0.80, SE = 1.873 ppb, Y m = 11.8 ppb, T m = 83.7, Q m = 523.9 k ac-f t/yr, b 1 = 0.5932, Var(b 1 ) = 0.02366, b 2 = - 0.00465, Var(b 2 ) = -0.0046, C ov(b 1 ,b 2 ) = 0.00013, t

, dof = 1.397, n = 11.

Y Q = Flow- ad ju sted TP = Y + b 2 (Q m - Q) = Y - 0.00465 (523.9 - Q) Y T = Detre nded T P = Y + b 1 (T o - T) = Y + 0.5932 (78.5 - T) Target = Y m + b 1 ( 78.5 - T m ) + b 2 (Q - Q m ) = 11.16 - 0.00465 Q Limit = Targe t + S t

, dof = 11.16 - 0.00465 Q + 1.397 S S = [SE 2 ( 1 + 1/n) + Var(b 1 ) (T o - T m ) 2 + V ar(b 2 ) (Q c- Q m ) 2 + 2 Cov (b 1 ,b 2 ) ( 78.5 - T m )(Q c- Q m )] 0.5 = [ 6.377 - 0.00591 Q + 0.00000436 Q 2 ] 0. 5

B-38 

### Nutrien t Criteria—Lakes and Reserv o irs**Figure 2: M**  **odel calibration to E NP Sh**  **ark River S**  **lough inflow s** 



### Nutrient Criteria—Lakes and Reserv o irs B-39Th e concentration measured in any y ear (Y) can be adjusted back to an average flow condition (Q m) using the following equation for flow-adjusted concentration (YQ): YQ =Y + b 2 (Qm - Q) (3) Figure 2B plots observed and predicted flow-adjusted concentrations against time. T h e long -t erm trend is m o re readily apparent in this display because effects of flow v ariations have been filtered out. Similarly, the concentration in any y ear can be adjusted back to any base period (To) using the following equation for a time-adjusted or de-trended concentration (YT): YT = Y + b 1 ( To - T) (4) I n this case, a base period v a lue of To = 78.5 is used to represent the 1978-1979 OFW time frame. Using this equation, Figure 2C plots observed and predicted time-adjusted concentrations against flow. Th e inverse correlation between concentration and flow is apparent. T h e figure shows the predicted relationship between concentration and flow if long -t erm mean were equivalent to that experienced in 1978-1979. Th e model can be used to evaluate the likelihood that current monitoring results (Yc, Qc) are equivalent to the 1978-1979 base period, w h ile accounting for hydrologic and random v ariability . T his is accomplished using the following terms w h ich characterize the prediction interval for a 1978-1979 tim e frame under a g ive n flow condition: Target =Y m + b 1 (To - Tm) + b 2 (Qc - Qm) Limit =Target + S t ,dof S =[ SE2 (1 + 1/n) + V ar(b 1 ) (To - Tm)2 + Var(b 2 ) (Qc - Qm )2

+ 2 Cov(b 1 ,b 2 ) (78.5 - Tm )(Qc - Qm) ].5 (7) wher e Target = 50th Percentile of Prediction I n terval = Predicted Mean (ppb) Limit = 90th Percentile of Prediction I n terval (ppb) S = Standard Error of Predicted Value (ppb) SE = Regression Standard Error of Estimate (ppb) t = O n e-tailed Student’s t statistic Significance Level = 0.10 dof = Degrees of Freedom = n - 3 n=Number of Years in Calibration Data Set = 11 Var = Variance O p erator Cov = C ovariance O p erator (5) (6)

I n Figure 2C, the Target and Limit lines correspond to the 50th and 90th percentile predictions, respectively. The required parameter estimates and v ariance/covariance terms are derived from a standard m u ltiple regression analysis. I f the current long -t erm flow -w eighted- mean is less than the 1978- 1979 long -t erm m ean (adjusted for hydrologic effects), there would be less than a 50 percent chance that the yearly m ean (Yc) would exceed the Target and less than a 10 percent chance that Y c w ould exceed the Limit. T h e difference between the T arget and Limit reflects the m agn itude of the Random Effects term and uncertainty in model parameter estimates (b 1 , b 2 , Ym).

B-40 

### Nutrient Criteria—Lakes and Reserv o irs**Ty pe I and T**  **y pe II Errors**  

### Under the terms of the Settlement Agreement, an exceedence of the Limit in any y ear would trig ge r further scientific investigations which, in turn, may lead to implementation of additional phosphorus control measures. The significance level for the compliance test (.10) represents the maximum Type-I error rate (probability of exceeding the Limit if the future and 1978-1979 long

term means are exactly equal). Unless a model can be constructed to explain all of the variance in the data, there is no way to design a compliance test without explicitly adopting a maximum Type-I error. In this case, the .10 value was arrived at by negotiation and with the understanding that results of the test would be interpreted by a scientific panel in light of the inherent risk of Type I error. Ty pe I I error (failure to detect an exceedence or excursion from the standard) is another unavoidable feature of compliance tests. In this case, a T y pe I I error would occur w h en the actual long -t erm m ean exceeds the 1978-1979 flow -a djusted mean but the measured annual mean is still below the Limit. R i sk of T y pe I I error depends upon the specified maximum Ty pe I error (10%), model error variance (Random Effects Term), and the m agn itude of the excursion from the long -t erm mean. Figure 3 illustrates T y pe I and T y pe I I error concepts. T h e probability that the annual mean exceeds the Limit is plotted against the difference between the actual long -t erm mean and the target. Probabilities are calculated using standard statistical procedures (Snedecor and Cochran, 1989; Walker, 1989). T y pe I errors (false exceedence) m ay occur w h en the actual long -t erm mean is below the target. T h e risk of Type I error equals the probability shown on the left-hand side in Fig u re 4 and has m a ximum v alue of 10 percent (by design). T y pe I I errors (failure to detect exceedence) m ay occur w h en the actual mean exceeds the target. T h e risk of T y pe I I error equals 100 percent mi nus the probability shown on the righthand side of Figure 4 and has a m a ximum v alue of 90 percent. As deviation from the target increases, risks of T y pe I and T y pe I I errors decrease. **Figure 3: Typ**  **e I and T y**  **pe II errors**



### N utrient Criteria—Lakes and Reserv o irs B-41Probability curves are shown for two v a lues of residual standard error in Figure 3. Without applying the regression model, the Random Effects term in the model would have a standard deviation of 3.73 ppb ( = standard deviation of annual flow- w eighted- means in the calibration period). With the regression m odel, the standard deviation is reduced to 1.87 ppb. Removing variance associated with trend and flow increases the probability of exceeding the Limit w h en the long -t erm mean exceeds the target. For example, if the true long -t erm m ean w e re 5 ppb above the target, the probability of detecting an excursion (measured annual v a lue above Limit) would be ~90 percent with the regression model, but only ~50 percent without the regression model. Risk of T y pe I error when the actual mean is below the target is also lower with the regression model. T h e regression approach thus enables a m o re powerful compliance test than would result from treating the calibration data set as a random time series. 

### Model Application to Recent Monitoring Data Figure 4 shows monitoring results for the Water Years 1991-1996 (6 years following the 1978-1990 calibration period). Although interim standards will not be enforced until 2003, the procedure is useful for tracking responses to control measures implemented over the 1991-2002 period. Such measures include adoption of the EAA Regulatory Rule (requiring a 25% reduction in EAA phosphorus load) in 1992 and operation of the Everglades Nutrient Removal Project (ENR, pilot scale STA removing an additional ~9% percdent of the EAA phosphorus load) (Guardo et al., 1995; SFMWD, 1997) starting in August 1994. Figure 4A shows observed values before and after the calibration period in relation to the 80% prediction interval derived from the above regression model. Values in Figure 4A reflect both long -t erm trend and flow v ariations. Observed v a lues in 1992-1996 fall near the lower boundary of the 80% prediction interval (10th percentile). Figure 4B shows flow-adjusted concentrations (equation 3) in relation to the 80% prediction interval. Th e prediction interval extrapolates the increasing trend in the 1978-1990 data to the later years. Theoretically, flow -r elated v ariations are filtered from this time series, so that observed and predicted va lues reflect v ariations in the long -t erm mean. T h e plot sug ge sts that the increasing trend present during the calibration period has been arrested in recent years. Figure 4C plots concentrations against flow in relation to the 80 percent prediction interval for 1978- 1979 conditions. O b served v a lues during the 1978-1991 calibration period have been adjusted to the 1978-1979 time frame (equation 4). T h e mi ddle and upper values in the prediction interval correspond to the T arget and Limit v a lues at any flow. C omp liance with the interim standards (when they are in effect) w ill require that the observed (unadjusted) flow -w eighted mean fall below the Limit line in every y ear.


### Discussion Extremely w et conditions experienced in recent years relative to the calibration period impose significant limitations on tracking results. Figure 5 plots annual basin flow against time. Flow exceeded the maximum v alue experienced in the base period (1061 kac-ft/yr) in 3 out of 6 Water Years after 1990. I n these cases, the model is being extrapolated beyond the range of the calibration data set. T he extrapolation is particularly large in Water Year 1995, w h en the average flow exceeded the calibration ma ximum by approximately 2.5-fold. Because of the extrapolation into high flow regimes, the model does not provide reliable assessments in recent w e t years. Nonetheless, the model does provide the best currently available scientific assessment of long -t erm trends in phosphorus at these structures. Figure 4B sug g ests that the increasing trend in the long -t erm mean present prior to 1991 has been arrested in years following adoption of the EAA Regulatory Rule in 1992 and operation of the ENR in 1994. For the 6- y ear period between May 1992 and April 1997, the tracking procedure for EAA phosphorus load (Table 1) indicates an average load reduction of 46% relative to the May 1979-April

B-42 

### Nutrient Criteria—Lakes and Reserv o irs**Figure 4: M**  **odel Application to E NP Sh**  **ark River S**  **lough Inflow s** 



### Nutrient Criteria—Lakes and Reserv o irs B-43

### Figure 5. Flow **v ariations.** 

Le g end: D iamonds = calibration period ( 1978-1990 ) ; trian g les = after calibration period ( 1991-1996 ) ; horizontal line = maximum flow in calibration period O c t-Sept w a ter y ears. 1988 base period for the Rule and adjusted for variations in rainfall. Figure 6 shows annual variations in phosphorus concentration and adjusted load from the EAA. Compared with the model discussed above, the model for tracking EAA phosphorus loads is calibrated to a slightly different base period and employs a different Water Year definition (May -A pril). A regression against rainfall statistics (Table 1) is used to adjust measured loads to average hydrologic conditions during the base period. T h e accuracy of EA A adjusted load estimates is also limited by w et conditions experienced in recent years, however. EA A runoff concentrations are not adjusted because they are weakly correlated with rainfall. Prediction intervals for concentration are derived by assuming that the Random -E ffects term of the model follows a log

- normal distribution calibrated to base-period results. Ot her possible factors contributing to w a ter quality improvements at ENP inflows during recent w et y ears include (1) increased phosphorus retention under high-stage conditions in the Water Conservation Areas and (2) shifts in the distribution of flow across the T ami ami T r ail. A higher percentage of flow is released through the S12's (western) as opposed to S333 (eastern) in wet years because of flow

- control constraints in the Eastern Everglades. Historically, P concentrations at S333 have been higher than those at measured at the S12's, because flows passing through S333 contain a higher percentage of canal flow (vs. m arsh sheet flow). Because of limitations in the tracking methodolog y during recent w e t years, several years of monitoring under average and dry conditions will provide a m o re reliable assessment of ENP inflow w ater quality conditions in relation to the 1978-1979 O F W period. De spite signs of improvement, it is unlikely that the interim control objective for ENP Shark Sloug h inflows has been achieved, since the flow -a djusted means in recent years are consistently above the 1978-1979 flow-adjusted mean (~ 8 ppb, Figures 2B, 4B). Observed concentrations in 1992-1996 cluster

B-44 

### Nutrient Criteria—Lakes and Reserv o irs

### Figure 6. Variations in EA**A runoff P concentratin and adjusted load** 

Le g end: D iamonds = calibration period ( 1980-88 ) ; trian g les = after calibration period ( 1989-97 ) ; lines = 80% prediction intervals; A = flow-wei g hted-mean total P concentration; B = total P load, ad j usted for v a riations in rainfall; C = avera g e rainfall and runoff.. Ma y -April water y ears.



### Nutrient Criteria—Lakes and Reserv o irs B-45around the Limit line in Figure 4C. I f the interim objectives were achieved, the observed values would be expected to cluster around the T arget line (center of distribution). U nder the provisions of the Settlement A g reement, the m a ximum flow during the calibration period (1061 kac-ft/yr) will be used to calculate the Limit in years w h en the observed flow exceeds that v a lue. Th is essentially prevents extrapolation of the regression beyond the calibration range. T h e dashed line in Figure 3C shows the Limit calculated according to this procedure. O n e could argue whether this procedure provides a better estimate of the 90th percentile at high flows than the extrapolated (solid) line. Th e distribution of observed values after 1991 is such that the determination of “compliance” (if the standard were in effect) would be influenced only in the case of the extreme high-flow year (1995). In the remaining y ears, the system would have been in compliance in 2 out of 5 years (1994 and 1996), regardless of w h ich limit line is used. 

## References Belanger, T.V., D.J. Scheidt, J.R. Platko II, “Effects of Nutrient Enrichment on the Florida Everglades”, Lake and Reservoir Management, Volume 5, No. 1, pp. 101-111, 1989. Davis, S.M., “Phosphorus Inputs and Vegetation Sensitivity in the Everglades”, in Everglades - The Ecosystem and Its Restoration, S.M. Davis and J.C. Ogden (Editors), St. Lucie Press, Florida, pp. 357-378, 1994. Guardo, M., L. Fink, T.D. Fontaine, S. Newman, M. Chimney, R. Bearzotti, G. Goforth, “Large-Scale Constructed Wetlands for Nutrient Removal from Stormwater Runoff: An Everglades Restoration Project”, Environmental Management, Volume 19, No. 6, pp. 879-889, 1995. Nearhoof, F.L., “Nutrient-Induced Impacts and Water Quality Violations in the Florida Everglades”, Florida Department of Environmental Protection, Water Quality Technical Series, Volume 3, Number 4. 1992. Smeltzer, E., W.W. Walker, and V. Garrison, “Eleven Years of Lake Eutrophication Monitoring in Vermont: A Critical Evaluation”, in “Enhancing States’ Lake Management Programs”, U.S. Environmental Protection Agency and North American Lake Management Society, pp. 52-62, 1989. Snedocor, G.W., and W.G. Cochran. “Statistical Methods”, Iowa State University Press, Ames, Iowa, Eighth Edition, 1989. South Florida Water Management District, “Surface Water Improvement and Management Plan for The Everglades, Appendix E, Derivation of Phosphorus Limits for Everglades National Park and Phosphorus Levels for Loxahatchee National Wildlife Refuge,” West Palm Beach, Florida, March 13, 1992. South Florida Water Management District, “Works of the District, Chapter 40-E63, Everglades Agricultural Area Regulatory Program,” West Palm Beach, Florida, 1992. South Florida Water Management District, “Everglades Nutrient Removal Project, 1996 Monitoring Report”, submitted to Florida Department of Environmental Protection, March 1997. State of Florida, “Everglades Forever Act”, 1994. United States of America, South Florida Water Management District, Florida Department of Environmental Regulation, “Settlement Agreement”, Case No. 88-1886-CIV-HOEVELER, July 1991. Walker, W.W., “LRSD.WK1 - Lake/Reservoir Sampling Design Worksheet,” Software Package Number 3, North American Lake Management Society, 1989. Walker, W.W., “Derivation of Phosphorus Limits for Inflows to Everglades National Park”, prepared for U.S. Department of Justice, Environment and Natural Resources Division, May 1991. Walker, W.W., “Derivation of Phosphorus Limits for Loxahatchee National Wildlife Refuge”, prepared for U.S. Department of Justice, Environment and Natural Resources Division, May 1991. Walker, W.W., “Water Quality Trends at Inflows to Everglades National Park”, Water Resources Bulletin, Volume 27, No. 1, pp. 59-72, 1991. Whalen, B.M., and P.J. Whalen, “Nonpoint Source Regulatory Program for the Everglades Agricultural Area”, American Society of Agricultural Engineers, Paper Number FL94-101, 1994.
B-46 

### N utrient Criteria—Lakes and Reserv o irs

# 12.	 Total Phosphorus Criteria for Lake **Champlain** by E ric Smeltzer, V e rmont D e partment of En vironm e ntal Conservation
Lake Champlain is a 170 km long natural lake shared by the States of V e rmont and New York and the Province of Quebec, with a basin population of over 600,000. T he major use of the lake is for recreation, although the lake also serves as a water supply for 180,000 people. T here are 88 point source phosphorus discharges in the Lake Champlain Basin, although nonpoint sources represent over 70% of the total phosphorus loading to the lake (Smeltzer and Quinn, 1996). T otal phosphorus concentrations vary spatially within Lake Champlain over a range of 9-58 μ g/L. To tal phosphorus concentration criteria have been established for 13 seg ments of Lake Champlain in the Vermont Water Q u ality Standards and in a N ew Yo rk, Q u ebec, and Vermont Water Q u ality Agreement for Lake Champlain. T he phosphorus criteria were derived in part from an analysis of lake user survey data. The user survey analysis established quantitative relationships between total phosphorus concentrations and the frequency of aesthetic problems and recreational use impairments caused by algae. T he criteria were used to g u ide a process involving phosphorus load measurements and m ass balance modeling that resulted in a phosphorus reduction agreement and basin plan completed in accordance with the federal Lake Champlain Special D e signation A c t of 1990. A llowable phosphorus loads w e re established for each sub- wa tershed in Vermont, N ew Yo rk, and Q u ebec in order to attain the in-lake phosphorus criteria.


### Us er Survey Analy sis and D eriva tion of the C rit er ia Lake user surveys have been used in Vermont, Minnesota, and elsewhere to identify specific total phosphorus, chlorophyll a, or Secchi disk v alues at w h ich algal nuisances and impairment of recreation are perceived by the public (Heiskary and Walker, 1988; Smeltzer and Heiskary , 1990; North American Lake Management Society, 1992). T he user survey form used in Lake Champlain from 1987-1991 as part of a citizen v o lunteer w a ter quality m onitoring program is shown in Table 1. The first survey question (A) asked the observers to describe the physical condition of the lake water at the time samples we re taken. T h e second question (B) sought an opinion on the recreational suitability of the lake at the time of sampling . T he survey responses w e re accompanied by simultaneous w a ter quality m easurements using standard sampling and analytical procedures employed by the Vermont Lay Monitoring Program (Picotte, 1997).

Th e results from the five years of user survey data in Lake Champlain included over 900 individual observations distributed among 28 lake stations in w h ich citizen monitors completed the survey form at the same time measurements w e re m a de of total phosphorus, chlorophyll-a, and Secchi disk depth. T he results are illustrated in Fig u re 1. Figure 1 shows the transitions that occur in lake user perceptions and enjoy m ent as the degree of eutrophication increases in Lake Champlain. Where total phosphorus and chlorophyll-a concentrations are low, and transparency high, few observers indicate that they see high algae levels or find their enjoy ment of the lake substantially reduced by algae in the water. However, as phosphorus and



### Nutrient Criteria—Lakes and Reserv o irs B-47**Table 1. User Sur vey**  **Form Used in Lake Champlain from 1987 to 1991 A.**  **Please circle the one number that best describes the physical conditions of the lake w a**  **ter today**
**.** 1. Cr y stal clear w a ter. 2. Not q uite cr y stal clear, a little al g ae. 3. Definite al g al g reenness, y ellowness, or brownness apparent. 4. Hi g h al g al levels w i th limited clarit yand/or mild odor apparent. 5. Severel yhi g h al g ae levels w i th one or more of the followin g : massive floatin g scums on lake or w a shed up on shore, stron g foul odor, or fish kill. **B.	 Please circle the one number that best describes your opinion on how suitable the lake w a**  **ter is for recreation and aesthetic enjoyment today** 
**.** 1. Beautiful, could not be an ynicer. 2. Ver yminor aesthetic problems; excellent for swimmin g , boatin g , en joy ment. 3. Swimmin g and aesthetic en joy ment sli g htl yimpaired because of al g ae levels. 4. D esire to swim and level of en joy ment of the lake substantiall yreduced because of al g ae levels. 5. Swimmin g and aesthetic en joy ment of the lake nearl yimpossible because of al g ae levels.

chlorophyll levels increase and transparency declines, indications of obvious algal greenness in the water, and impairment of lake use, become m o re frequent responses.

Th e results shown in Figure 1 were used to quantify the instantaneous phosphorus levels at which critical transitions in user perceptions occur in Lake C hamplain. U ser descriptions such as "a little algae" and "very minor problems" predominate when total phosphorus concentrations are below about 25 μ g /L. Above the 25 to 30 μ g/L phosphorus interval, responses such as "definite algal greenness" and "use slightly impaired" are m o st comm only noted. More severe nuisance perceptions involving "hig h algae levels" and "enjoy me nt substantially reduced" also begin to become frequent as phosphorus levels increase above 25 μ g /L. T hese results sug ge sted that an instantaneous total phosphorus concentration of 25 μ g /L could be used to derive eutrophication criteria v a lues for Lake Champlain. Lake eutrophication criteria are best expressed as season or annual mean values, rather than as instantaneous "not to exceed" v a lues. Means are estimated with g r eater statistical stability by m onitoring programs and are m o re readily predicted by lake models (Walker, 1985; North American Lake Management Society, 1992). An analysis of within-season temporal frequency distributions for total phosphorus in Lake Champlain was used to define a summe r mean v a lue corresponding to an appropriately low frequency of occurrence of the 25 μ g/L instantaneous nuisance criterion, using Walker’s (1985) statistical algorithm

. Simple nonparametric tabulation approaches have also been used for this purpose (Heiskary and Walker, 1988).

Th e relationship between the summ er station- mean total phosphorus concentration and the frequency of v a lues g r eater than 25 μ g /L recorded at Lake Champlain monitoring stations is shown in Figure 2. Figure 2 was used to derive a mean phosphorus criterion of 14 μ g/L, representing a value at which the 25 μg /L nuisance v a lue would be exceeded only 1% of the time during the summe r.

B-48 

### Nutrient Criteria—Lakes and Reserv o irs**Figure 1. Lake Champlain user survey results, 1987-1991**



### Nutrient Criteria—Lakes and Reserv o irs B-49**Figure 2. Relat io**  **nshi p**  **bet w**  **een t**  **he summer mean t**  **otal phosphorus concent r**  **at ion a**  **nd the fr**  **equency of**  **occurrence of i**  **nstant a**  **neous nuisance valu**  **es (g**  **reater th**  **an 25**  **μg/L) at Lake Champlai**  **n w ater qual**  **ity moni**  **t oring stat**  **io ns.**  A mean total phosphorus criterion of 14 μ g/L was established for seven seg m ents of Lake Champlain, as shown in T able 2. I n other lake seg ments, higher or lower criteria v a lues were established based on limitations of practical attainability, or to provide antidegradation protection w h ere existing phosphorus levels are below 14 μ g /L. T he Lake Champlain phosphorus criteria listed in T able 2 were adopted by rule as part of the Vermont Water Q u ality Standards in 1991, and were later endorsed as j o int ma nagement g o als for Lake C hamplain in a w a ter quality agreement signed by N ew Y ork , Q uebec, and Ve rmont (Lake Champlain Phosphorus Management T a sk Force, 1992).

Th e user survey analysis provided a reasonably objective and empirically based m e thod for deriving phosphorus criteria to protect recreational use and enjoy ment of Lake Champlain. However, several limitations of the approach should be noted. T he user survey was not based on a randomly chosen sample of public opinion, and should not be used to assess the g e neral impressions of Lake Champlain wa ter quality by the entire user public. O ther potential eutrophicaion impacts such as shoreline periphyton and aquatic plant g r owth, hypolimnetic dissolved oxy g en depletion, fisheries impacts, and water supply impairment were not considered in deriving the phosphorus criteria for Lake Champlain. Th e approach assumed that the instantaneous phosphorus v a lue was an appropriate surrogate v ariable for the m o re direct causes of eutrophication nuisances such as high algal densities. Finally, a comparison of user survey results in Vermont and Minnesota revealed striking regional differences in user perceptions of lake w a ter quality (Smeltzer and H e iskary , 1990). I f a user survey approach is to serve as a basis for developing lake w a ter quality criteria, then the data should be as specific to the lake region of concern as possible.

B-50 

### Nutrient Criteria—Lakes and Reserv o irsTa ble 2. To tal phosphorus criteria f o r L a ke C h amplain segments, compared w i th currently existing mean values. The criteria are applied as summer or annual mean values in central, open-water regions of each lake segment (Vermont Water R e sources Board, 1996; Lake C h amplain P h osphorus Management Task F o rce, 1993). C urrent levels are fr om Smeltzer and Quinn (1996).

Lake Seg m ent C riterion Value (μ g/L) Cu rrent Lev e l (μ g/L) Main Lake 10 12 Malletts B ay 1 0 9 Shelburne Bay 14 15 Bur lingt on Bay 14 13 Cumber l and Bay 14 14 Nor th eas t Ar m 14 14 Is le La Motte 14 12 Otter Creek 14 15 Port Henry 14 15 St. Albans Bay 17 24 Missisquoi Bay 2535 South Lake A 2 534 South Lake B 2 55 8 

### Appli c ation of the C rit er ia A phosphorus budget and m a ss balance modeling analysis for Lake Champlain (Vermont DEC and New York State DEC, 1997; Smeltzer and Quinn, 1996) was used to determine the allowable phosphorus loadings from point and nonpoint sources in each state and each lake seg ment watershed. O ptimization techniques were applied to the phosphorus m a ss balance model to find the mi nimum

- cost set of wa tershed target loads that would attain the in-lake criteria listed in Table 2. Specific w a tershed phosphorus loading targets were then negotiated between the States of Vermont and New York and the U. S. Environmental Protection A g ency . T he loading targets and a 20- y ear implementation timetable we re incorporated into a comprehensive plan for the Lake C h amplain B a sin prepared by the Lake Champlain Management Conference (1996).

Th e phosphorus criteria developed for Lake Champlain were essential to the phosphorus ma nagement process for the lake. The criteria provided the basis for a negotiated political agreement on phosphorus reduction in Lake C h amplain. T he agreement was based on a quantitative modeling analysis and optimized implementation strategies. T his analysis and agreement would not have been possible without the prior establishment of numeric, in-lake phosphorus concentration g o als consistently between the three g ove rnment j u risdictions.


### Nutrient Criteria—Lakes and Reserv o irs B-51

### Refer ences Heiskary , S.A. and W.W. Walker. 1988. Developing phosphorus criteria for Minnesota lakes. Lake and Reserv. Manage. 4:1-10.

Lake C h amplain Management Conference. 1996. Opportunities for action. An evolving plan for the future of the Lake Champlain Basin. Pollution prevention, control, and restoration plan. Lake Champlain Basin Program. Grand I s le, V T . 92 pp. Lake Champlain Phosphorus Management T a sk Force. May 14, 1993 report prepared for the Lake Champlain Steering Committee. New York State Department of Environmental Conservation, Adirondack Park Agency, Quebec Ministry of the Environment, and V e rmont Agency of Natural Resources. 17 pp. North American Lake Management Society. 1992. Developing eutrophication standards for lakes and reservoirs. Report prepared by the Lake Standards Subcommittee. Alachua, FL. 51 pp. Picotte, A. 1997. 1996 Lake Champlain Lay Monitoring Report. V e rmont Department of Environmental Conservation. Waterbury, V T . 85 pp Smeltzer, E. and S.A. Heiskary

. 1990. Analysis and applications of lake user survey data. Lake and Reserv. Manage. 6:109-118. Smeltzer, E. and S. Quinn. 1996. A phosphorus budget, model, and load reduction strateg y for Lake Champlain. Lake and Reserv. Manage.12:381-393.

Ve rmont Department of Environmental Conservation and New York State Department of Environmental Conservation. 1997. A phosphorus budget, model, and load reduction strateg y for Lake Champlain. Lake Ch amplain diagnostic-feasibility study final report. Waterbury, VT and A l bany, N Y . 129 pp.

Vermont Water R e sources B o ard. 1996. Vermont Water Q u ality Standards. Montpelier, VT. 45 pp. Walker, W.W. 1985. Statistical bases for mean chlorophyll a criteria. pp. 57-62 In Lake and Reservoir Management: Practical Applications. Proceedings of the Fourth Annual Conference and I n ternational Sy m posium. October 16-19, 1984. McAfee, NJ. North American Lake Management Society

.

B-52 

### Nutrient Criteria—Lakes and Reserv o irs