United States

Environmental Protection

Agency

Office of Water

4304

EPA 822-B-00-011

December 2000

Ambient Water Quality

Criteria Recommendations

Information Supporting the Development

of State and Tribal Nutrient Criteria

Lakes and Reservoirs in 

Nutrient Ecoregion IX
EPA-822-B-00-011

AMBIENT WATER QUALITY CRITERIA RECOMMENDATIONS

INFORMATION SUPPORTING THE DEVELOPMENT OF STATE AND TRIBAL

NUTRIENT CRITERIA

FOR

LAKES AND RESERVOIRS IN NUTRIENT ECOREGION IX

Southeastern Temperate Forested Plains and Hills

including all or parts of the States of:

Maryland, Pennsylvania, Virginia, North Carolina, South Carolina, Georgia, Florida, Alabama,

Mississippi, Tennessee, Kentucky, Indiana, Illinois, Iowa, Missouri, Kansas, Oklahoma,

Arkansas, Louisiana, Texas, New Jersey 

and the authorized Tribes within the Ecoregion

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF WATER

OFFICE OF SCIENCE AND TECHNOLOGY

HEALTH AND ECOLOGICAL CRITERIA DIVISION

WASHINGTON, D.C.

DECEMBER 2000
ii

FOREWORD

This document presents EPA’s nutrient criteria for Lakes and Reservoirs in Nutrient

Ecoregion IX. These criteria provide EPA’s recommendations to States and authorized Tribes

for use in establishing their water quality standards consistent with section 303(c) of CWA. 

Under section 303(c) of the CWA, States and authorized Tribes have the primary responsibility

for adopting water quality standards as State or Tribal law or regulation. The standards must

contain scientifically defensible water quality criteria that are protective of designated uses. 

EPA’s recommended section 304(a) criteria are not laws or regulations – they are guidance that

States and Tribes may use as a starting point for the criteria for their water quality standards. 

The term “water quality criteria” is used in two sections of the Clean Water Act, Section

304(a)(1) and Section 303(c)(2). The term has a different impact in each section. In Section 304,

the term represents a scientific assessment of ecological and human health effects that EPA

recommends to States and authorized Tribes for establishing water quality standards that

ultimately provide a basis for controlling discharges or releases of pollutants or related

parameters. Ambient water quality criteria associated with specific waterbody uses when

adopted as State or Tribal water quality standards under Section 303 define the level of a

pollutant (or, in the case of nutrients, a condition) necessary to protect designated uses in ambient

waters. Quantified water quality criteria contained within State or Tribal water quality standards

are essential to a water quality-based approach to pollution control. Whether expressed as

numeric criteria or quantified translations of narrative criteria within State or Tribal water quality

standards, quantified criteria serve as a critical basis for assessing attainment of designated uses

and measuring progress toward meeting the water quality goals of the Clean Water Act.

EPA is developing section 304(a) water quality criteria for nutrients because States and

Tribes consistently identify excessive levels of nutrients as a major reason why as much as half of

the surface waters surveyed in this country do not meet water quality objectives, such as full

support of aquatic life. EPA expects to develop nutrient criteria that cover four major types of

waterbodies – lakes and reservoirs, rivers and streams, estuarine and coastal areas, and wetlands –

across fourteen major ecoregions of the United States. EPA’s section 304(a) criteria are

intended to provide for the protection and propagation of aquatic life and recreation. To support

the development of nutrient criteria, EPA is publishing Technical Guidance Manuals that describe

a process for assessing nutrient conditions in the four waterbody types. 

EPA’s section 304(a) water quality criteria for nutrients provide numeric water quality

criteria, as well as procedures by which to translate narrative criteria within State or Tribal water

quality standards. In the case of nutrients, EPA section 304(a) criteria establish values for causal

variables (e.g., total nitrogen and total phosphorus) and response variables (e.g., turbidity and

chlorophyll a). EPA believes that State and Tribal water quality standards need to include

quantified endpoints for causal and response variables to provide sufficient protection of uses and

to maintain downstream uses. These quantified endpoints will most often be expressed as

numeric water quality criteria or as procedures to translate a State or Tribal narrative criterion

into a quantified endpoint. EPA will work with States and authorized Tribes as they adopt water

quality criteria for nutrients into their water quality standards. EPA recognizes that States and
iii

authorized Tribes require flexibility in adopting numeric nutrient criteria into State and Tribal

water quality standards. States and authorized Tribes have several options available to them. 

EPA recommends the following approaches, in order of preference:

(1) Wherever possible, develop nutrient criteria that fully reflect localized conditions and

protect specific designated uses using the process described in EPA’s Technical Guidance

Manuals for nutrient criteria development. Such criteria may be expressed either as

numeric criteria or as procedures to translate a State or Tribal narrative criterion into a

quantified endpoint in State or Tribal water quality standards.

(2) Adopt EPA’s section 304(a) water quality criteria for nutrients, either as numeric

criteria or as procedures to translate a State or Tribal narrative nutrient criterion into a

quantified endpoint.

(3) Develop nutrient criteria protective of designated uses using other scientifically

defensible methods and appropriate water quality data.

 

Geoffrey H. Grubbs, Director

Office of Science and Technology
iv

DISCLAIMER

This document provides technical guidance and recommendations to States, authorized

Tribes, and other authorized jurisdictions to develop water quality criteria and water quality

standards under the Clean Water Act (CWA) to protect against the adverse effects of nutrient

overenrichment. Under the CWA, States and authorized Tribes are to establish water quality

criteria to protect designated uses. State and Tribal decision-makers retain the discretion to adopt

approaches on a case-by-case basis that differ from this guidance when appropriate and

scientifically defensible. While this document contains EPA’s scientific recommendations

regarding ambient concentrations of nutrients that protect aquatic resource quality, it does not

substitute for the CWA or EPA regulations; nor is it a regulation itself. Thus it cannot impose

legally binding requirements on EPA, States, authorized Tribes, or the regulated community, and

it might not apply to a particular situation or circumstance. EPA may change this guidance in the

future.
v

EXECUTIVE SUMMARY

 

Nutrient Program Goals

EPA developed the National Strategy for the Development of Regional Nutrient Criteria

(National Strategy) in June 1998. The strategy presents EPA=s intentions to develop technical

guidance manuals for four types of waters (lakes and reservoirs, rivers and streams, estuaries and

coastal waters, and wetlands) and produce section 304(a) criteria for specific nutrient ecoregions

by the end of 2000. In addition, the Agency formed Regional Technical Assistance Groups

(RTAGs) which include State and Tribal representatives working to develop more refined and

more localized nutrient criteria based on approaches described in the waterbody guidance

manuals. This document presents EPA=s current recommended criteria for total phosphorus, total

nitrogen, chlorophyll a, and turbidity for lakes and reservoirs in Nutrient Ecoregion IX

(Southeastern Temperate Forested Plains and Hills) which were derived using the procedures

described in the Lakes and Reservoirs Nutrient Criteria Technical Guidance Manual (U.S. EPA,

2000a). 

EPA’s ecoregional nutrient criteria are intended to address cultural eutrophication-- the

adverse effects of excess nutrient inputs. The criteria are empirically derived to represent

conditions of surface waters that are minimally impacted by human activities and protective of

aquatic life and recreational uses. The information contained in this document represent starting

points for States and Tribes to develop (with assistance from EPA) more refined nutrient criteria.

In developing these criteria recommendations, EPA followed a process which

included, to the extent they were readily available, the following elements critical to criterion

derivation: 

! Historical and recent nutrient data in Nutrient Ecoregion IX. 

Data sets from Legacy Storet, NASQAN, NAWQA Auburn University, and EPA Region

4 were used to assess nutrient conditions from 1990 to 1998.

! Reference sites/reference conditions in Nutrient Ecoregion IX.

Reference conditions presented are based on 25th percentiles of all nutrient data including a

comparison of reference condition for the aggregate ecoregion versus the subecoregions. 

States and Tribes are urged to determine their own reference sites for rivers and streams

within the ecoregion at different geographic scales and to compare them to EPA’s

reference conditions.

! Models employed for prediction or validation.

EPA did not identify any specific models used in the ecoregion to develop nutrient 

criteria. States and Tribes are encouraged to identify and apply appropriate models to

support nutrient criteria development. 
vi

! RTAG expert review and consensus.

EPA recommends that when States and Tribes prepare their nutrient criteria, they obtain 

the expert review and consent of the RTAG.

! Potential Downstream effects.

EPA encourages the RTAG to assess the potential effects of the proposed criteria on

downstream water quality and uses.

In addition, EPA followed specific QA/QC procedures during data collection and

analysis: All data were reviewed for duplications. All data are from ambient waters that were not

located directly outside a permitted discharger. The following States, Florida, Georgia, Illinois,

Iowa, Indiana, Maryland, Missouri, North Carolina, South Carolina, and Tennessee. indicated that

their data were from samples collected and analyzed using either Standard methods or EPA

approved methods. 

The following tables contain a summary of Aggregate and level III ecoregion values for

TN, TP, water column chl a, and Secchi depth:

BASED ON 25th PERCENTILE ONLY

Nutrient Parameters Aggregate Nutrient Ecoregion

IX Reference Conditions

Total phosphorus (μg/L) 20

Total nitrogen (mg/L) 0.36 

Chlorophyll a (μg/L) (Fluorometric

method)

4.93

Secchi depth (meters) 1.53

For sub ecoregions 29, 33, 35, 37, 40, 45, 64, 65, 71, 72, and 74, the ranges of nutrient

parameter reference conditions are:
vii

BASED ON 25th PERCENTILE ONLY

Nutrient Parameters Range of Level III Subecoregions

Reference Conditions

Total phosphorus (μg/L) 10 - 62.5

Total nitrogen (mg/L) 0.30 - 0.96

Chlorophyll a (μg/L) (Fluorometric

method)

1.87 - 12.95

Secchi depth (meters) 0.46 - 2.04
viii

NOTICE OF DOCUMENT AVAILABILITY

 This document is available electronically to the public through the INTERNET at:

(http://www.epa.gov/OST/standards/nutrient.html). Requests for hard copies of the document

should be made to EPA’s National Service Center for Environmental Publications (NSCEP),

11029 Kenwood Road, Cincinnati, OH 45242 or (513) 489-8190, or toll free (800) 490-9198. 

Please refer to EPA document number EPA-822-B-00-011.
ix

ACKNOWLEDGMENTS

 The authors thankfully acknowledge the contributions of the following State and Federal 

reviewers: EPA Regions 2, 3, 4, 5, 6, and 7; the States of New Jersey, Maryland, Pennsylvania,

Virginia, North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Tennessee,

Kentucky, Indiana, Illinois, Iowa, Missouri, Kansas, Oklahoma, Arkansas, Louisiana, and Texas

and; the Tribes within the Ecoregion; EPA Headquarters personnel from the Office of Wetlands,

Oceans and Watersheds, Office of Wastewater Management, Office of General Counsel, Office of

Research and Development, and the Office of Science and Technology. EPA also acknowledges

the external peer review efforts of Eugene Welch (University of Washington), Robert Carlson

(Kent State University), Steve Heiskary (Minnesota Pollution Control Agency), Greg Denton and

Sherry Wang (Tennessee Department of Environment and Conservation), and Gerhard Kuhn

(U.S. Geological Survey). 
x

LISTS OF TABLES AND FIGURES

Figures

Figure 1 Aggregate Ecoregion IX ............................... 8

Figure 2 Aggregate Ecoregion IX with level III ecoregions shown ...... 8

Figure 3 Sampling locations within each level III ecoregion .......... 12

Figure 4a Illustration of data reduction process for lake data ........... 24

Figure 4b Illustration of reference condition calculation ............... 26

Tables

Table 1 Lakes and Reservoirs records for Aggregate Ecoregion IX

Southeastern Temperate Forested Plains and Hills .......... 13

Table 2 Reference conditions for Aggregate Ecoregion IX lakes ...... 16

Table 3a-k Reference conditions for level III ecoregion lakes ........... 17
xi

TABLE OF CONTENTS

 

Foreword ................................................................. ii

Disclaimer ............................................................... iv

Executive Summary .......................................................... v

Notice of Document Availability .............................................. viii

Acknowledgments ......................................................... ix

List of Tables and Figures ..................................................... x

Table of Contents .......................................................... xi

1.0 Introduction (program background and nutrient criteria process) ................... 1

2.0 Best use of this information .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.0 Area Covered by this Document (waterbody type and ecoregion) ................... 6

3.1 Description of Aggregate Ecoregion IX --Southeastern Temperate Forested Plains

and Hills ............................................................ 6

3.2 Geographical Boundaries of Aggregate Ecoregion IX ...................... 7

3.3 Level III Ecoregions within Aggregate Ecoregion IX ...................... 8

4.0 Data Review for Lakes and Reservoirs in Aggregate Ecoregion IX ................ 10

4.1 Data Sources ................................................... 11

4.2 Historical Data from Aggregate Ecoregion IX (TP, TN, Chl a, Secchi) ........ 11

4.3 QA/QC of Data Sources ........................................... 11

4.4 Data for All Lakes/Reservoirs within Aggregate Ecoregion IX .............. 11

4.5 Statistical Analysis of Data ......................................... 11

4.6 Classification of Lake/Reservoir Type ................................. 15

4.7 Summary of Data Reduction Methods ................................. 15

5.0 Reference Sites and Conditions in Aggregate Ecoregion IX ...................... 26

6.0 Models Used to Predict or Verify Response Parameters ......................... 26

7.0 Framework for Refining Recommended Nutrient Criteria for Lakes and Reservoirs in

Ecoregion IX ............................................................. 27

7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion Nutrient 

 Criteria ........................................................ 27
xii

7.2 Tables of Refined Nutrient Water Quality Criteria for Aggregate Ecoregion IX and

Level III Subecoregions ............................................... 28

7.3 Setting Seasonal Criteria ........................................... 30

7.4 When Data/Reference Conditions Are Lacking .......................... 30

7.5 Site-Specific Criteria Development ................................... 30

8.0 Literature Cited ....................................................... 31

9.0 Appendices ........................................................... 31
1

1.0 INTRODUCTION

Background

Nutrients are essential to the health and diversity of our surface waters. However, in

excessive amounts, nutrients cause hypereutrophication, which results in overgrowth of plant life

and decline of the biological community. Excessive nutrients can also result in potential human

health risks, such as the growth of harmful algal blooms - most recently manifested in the

Pfiesteria outbreaks of the Gulf and East Coasts. Chronic nutrient overenrichment of a

waterbody can lead to the following consequences: low dissolved oxygen, fish kills, algal blooms,

overabundance of macrophytes, likely increased sediment accumulation rates, and species shifts of

both flora and fauna. 

Historically, National Water Quality Inventories have repeatedly shown that nutrients are a

major cause of ambient water quality use impairments. EPA’s 1996 National Water Quality

Inventory report identifies excessive nutrients as the leading cause of impairment in lakes and the

second leading cause of impairment in rivers (behind siltation). In addition, nutrients were the

second leading cause of impairments reported by the States in their 1998 lists of impaired waters. 

Where use impairment is documented, nutrients contribute roughly 25-50% of the impairment

nationally. The Clean Water Act establishes a national goal to achieve, wherever attainable, water

quality which provides for the protection and propagation of fish, shellfish, and wildlife and

recreation in and on the water. In adopting water quality standards, States and Tribes designate

uses for their waters in consideration of the Clean Water Act goals, and establish water quality

criteria that contain sufficient parameters to protect those uses. To date, EPA has not published

information and recommendations under section 304(a) for nutrients to assist States and Tribes in

establishing numeric nutrient criteria to protect uses when adopting water quality standards.

In 1995, EPA gathered a set of national experts and asked the experts how to best deal

with the national nutrient problem. The experts recommended that the Agency not develop single

criteria values for phosphorus or nitrogen applicable to all water bodies and regions of the

country. Rather, the experts recommended that EPA put a premium on regionalization, develop

guidance (assessment tools and control measures) for specific waterbodies and ecological regions

across the country, and use reference conditions (conditions that reflect pristine or minimally

impacted waters) as a basis for developing nutrient criteria.

With these suggestions as starting points, EPA developed the National Strategy for the

Development of Regional Nutrient Criteria (National Strategy), published in June 1998. This

strategy presented EPA’s intentions to develop technical guidance manuals for four types of

waters (lakes and reservoirs, rivers and streams, estuaries and coastal waters, and wetlands) and,

thereafter, to publish section 304(a) criteria recommendations for specific nutrient ecoregions. 

Technical guidance manuals for lakes/reservoirs and rivers/streams were published in April 2000

and July 2000, respectively. The technical guidance manual for estuaries/coastal waters will be

published in spring 2000 and the draft wetlands technical guidance manual will be published by

December 2001. Each manual presents EPA’s recommended approach for developing nutrient

criteria values for a specific waterbody type. In addition, EPA is committed to working with
2

States and Tribes to develop more refined and more localized nutrient criteria based on

approaches described in the waterbody guidance manuals and this document. 

Overview of the Nutrient Criteria Development Process

For each Nutrient Ecoregion, EPA developed a set of recommendations for two causal

variables (total nitrogen and total phosphorus) and two early indicator response variables

(chlorophyll a and some measure of turbidity). Other indicators such as dissolved oxygen and

macrophyte growth or speciation, and other fauna and flora changes are also deemed useful. 

However, the first four are considered to be the best suited for protecting designated uses.

The technical guidance manuals describe a process for developing nutrient criteria that

involves consideration of five factors. The first of these is the Regional Technical Assistance

Group (RTAG), which is a body of qualified regional specialists able to objectively evaluate all of

the available evidence and select the value(s) appropriate to nutrient control in the water bodies of

concern. These specialists may come from such disciplines as limnology, biology, natural

resources management-- especially water resource management, chemistry, and ecology. The

RTAG evaluates and recommends appropriate classification techniques for criteria determination,

usually physical within an ecoregional construct.

The second factor is the historical information available to establish a perspective of the

resource base. This is usually data and anecdotal information available within the past ten-twenty

five years. This information gives evidence about the background and enrichment trend of the

resource.

The third factor is the present reference condition. A selection of reference sites chosen to

represent the least culturally impacted waters of the class existing at the present time. The data

from these sites is combined and a value from the distribution of these observations is selected to

represent the reference condition, or best attainable, most natural condition of the resource base at

this time.

A fourth factor often employed is theoretical or empirical models of the historical and

reference condition data to better understand the condition of the resource.

The RTAG comprehensively evaluates the other three elements to propose a candidate

criterion (initially one each for TP, TN, chl a, and some measure of turbidity).

The last and final element of the criteria development process is the assessment by the

RTAG of the likely downstream effects of the criterion. Will there be a negative, positive, or

neutral effect on the downstream waterbody? If the RTAG judges that a negative effect is likely,

then the proposed State/Tribal water quality criteria should be revised to ameliorate the potential

for any adverse downstream effects.
3

While States and authorized Tribes would not necessarily need to incorporate all five

elements into their water quality criteria setting process (e.g., modeling may be significant in only

some instances), the best assurance of a representative and effective criterion for nutrient

management decision making is the balanced incorporation of all five elements, or at least all

elements except modeling.

Because some parts of the country have naturally higher soil and parent material

enrichment, and different precipitation regimes, the application of the criterion development

process has to be adjusted by region. Therefore, an ecoregional approach was chosen to develop

nutrient criteria appropriate to each of the different geographical and climatological areas of the

country. Initially, the continental U.S. was divided into 14 separate ecoregions of similar

geographical characteristics. Ecoregions are defined as regions of relative homogeneity in

ecological systems; they depict areas within which the mosaic of ecosystem components (biotic

and abiotic as well as terrestrial and aquatic) is different than adjacent areas in a holistic sense. 

Geographic phenomena such as soils, vegetation, climate, geology, land cover, and physiology

that are associated with spatial differences in the quantity and quality of ecosystem components

are relatively similar within each ecoregion. 

The Nutrient ecoregions are aggregates of U.S. EPA=s hierarchal level III ecoregions. As

such, they are more generalized and less defined than level III ecoregions. EPA determined that

setting ecoregional criteria for the large scale aggregates is not without its drawbacks - variability

is high due to the lumping of many waterbody classes, seasons, and years worth of multipurpose

data over a large geographic area. For these reasons, the Agency recommends that States and

Tribes develop nutrient criteria at the level III ecoregional scale and at the waterbody class scale

where those data are readily available. Data analyses and recommendations on both the large

aggregate ecoregion scale as well as more refined scales (level III ecoregions and waterbody

classes), where data were available to make such assessments, are presented for comparison

purposes and completeness of analysis. 

Relationship of Nutrient Criteria to Biological Criteria

Biological criteria are quantitative expressions of the desired condition of the aquatic

community. Such criteria can be based on an aggregation of data from sites that represent the

least-impacted and attainable condition for a particular waterbody type in an ecoregion,

subecoregion, or watershed. EPA’s nutrient criteria recommendations and biological criteria

recommendations have many similarities in the basic approach to their development and data

requirements. Both are empirically derived from statistical analysis of field collected data and

expert evaluation of current reference conditions and historical information. Both utilize direct

measurements from the environment to integrate the effects of complex processes that vary

according to type and location of waterbody. The resulting criteria recommendations, in both

cases, are efficient and holistic indicators of water quality necessary to protect uses.

States and authorized Tribes can develop and apply nutrient criteria and biological criteria

in tandem, with each providing important and useful information to interpret both the nutrient

enrichment levels and the biological condition of sampled waterbodies. For example, using the
4

same reference sites for both types of criteria can lead to efficiencies in both sample design and

data analysis. In one effort, environmental managers can obtain information to support

assessment of biological and nutrient condition, either through evaluating existing data sets or

through designing and conducting a common sampling program. The traditional biological

criteria variables of benthic invertebrate and fish sampling can be readily incorporated to

supplement a nutrient assessment. To demonstrate the effectiveness of this tandem approach,

EPA has initiated pilot projects in both freshwater and marine environments to investigate the

relationship between nutrient overenrichment and apparent declines in diversity indices of benthic

invertebrates and fish.

2.0 BEST USE OF THIS INFORMATION

EPA recommendations published under section 304(a) of the CWA serve several

purposes, including providing guidance to States and Tribes in adopting water quality standards

for nutrients that ultimately provide a basis for controlling discharges or releases of pollutants. 

The recommendations also provide guidance to EPA when promulgating Federal water quality

standards under section 303(c) when such action is necessary. Other uses include identification of

overenrichment problems, management planning, project evaluation, and determination of status

and trends of water resources. 

State water quality inventories and listings of impaired waters consistently rank nutrient

overenrichment as a top contributor to use impairments. EPA’s water quality standards

regulations at 40 CFR §131.11(a) require States and Tribes to adopt criteria that contain

sufficient parameters and constituents to protect the designated uses of their waters. In addition,

States and Tribes need quantifiable targets for nutrients in their standards to assess attainment of

uses, develop water quality-based permit limits and source control plans, and establish targets for

total maximum daily loads (TMDLs).

EPA expects States and Tribes to address nutrient overenrichment in their water quality

standards, and to build on existing State and Tribal initiated efforts where possible. States and

Tribes can address nutrient overenrichment through establishment of numerical criteria or through

use of new or existing narrative criteria statements (e.g., free from excess nutrients that cause or

contribute to undesirable or nuisance aquatic life or produce adverse physiological response in

humans, animals, or plants). In the case of narrative criteria, EPA expects that States and Tribes

establish procedures to quantitatively translate these statements for both assessment and source

control purposes. 

The intent of developing ecoregional nutrient criteria is to represent conditions of surface

waters that are minimally impacted by human activities and thus protect against the adverse

effects of nutrient overenrichment from cultural eutrophication. EPA’s recommended process for

developing such criteria includes physical classification of waterbodies, determination of current

reference conditions, evaluation of historical data and other information (such as published

literature), use of models to simulate physical and ecological processes or determine empirical

relationships among causal and response variables (if necessary), expert judgement, and

evaluation of downstream effects. To the extent allowed by the information available, EPA has
5

used elements of this process to produce the information contained in this document. The values

for both causal (total nitrogen, total phosphorus) and biological and physical response

(chlorophyll a, turbidity) variables represent a set of starting points for States and Tribes to use in

establishing their own criteria in standards to protect uses.

In its water quality standards regulations, EPA recommends that States and Tribes

establish numerical criteria based on section 304(a) guidance, section 304(a) guidance modified to

reflect site-specific conditions, or other scientifically defensible methods. For many pollutants,

such as toxic chemicals, EPA expects that section 304(a) guidance will provide an appropriate

level of protection without further modification in most cases. EPA has also published methods

for modifying 304(a) criteria on a site-specific basis, such as the water effect ratio, where sitespecific conditions warrant modification to achieve the intended level of protection. For nutrients,

however, EPA expects that, in most cases, it will be necessary for States and authorized Tribes to

identify with greater precision the nutrient levels that protect aquatic life and recreational uses. 

This can be achieved through development of criteria modified to reflect conditions at a smaller

geographic scale than an ecoregion such as a subecoregion, the State or Tribe level, or specific

class of waterbodies. Criteria refinement can occur by grouping data or performing data analyses

at these smaller geographic scales. Refinement can also occur through further consideration of

other elements of criteria development, such as published literature or models.

The values presented in this document generally represent nutrient levels that protect

against the adverse effects of nutrient overenrichment and are based on information available to

the Agency at the time of this publication. However, States and Tribes should critically evaluate

this information in light of the specific designated uses that need to be protected. For example,

more sensitive uses may require more stringent values as criteria to ensure adequate protection. 

On the other hand, overly stringent levels of protection against the adverse effects of cultural

eutrophication may actually fall below levels that represent the natural load of nutrients for certain

waterbodies. In cases such as these, the level of nutrients specified may not be sufficient to

support a productive fishery. In the criteria derivation process, it is important to distinguish

between the natural load associated with a specific waterbody and current reference conditions,

using historical data and expert judgement. These elements of the nutrient criteria derivation

process are best addressed by States and Tribes with access to information and local expertise. 

Therefore, EPA strongly encourages States and Tribes to use the information contained in this

document and to develop more refined criteria according to the methods described in EPA’s

technical guidance manuals for specific waterbody types.

To assist in the process of further refinement of nutrient criteria, EPA has established ten

Regional Technical Advisory Groups (experts from EPA Regional Offices and States/Tribes). In

the process of refining criteria, States and authorized Tribes need to provide documentation of

data and analyses, along with a defensible rationale, for any new or revised nutrient criteria they

submit to EPA for review and approval. As part of EPA’s review of State and Tribal standards,

EPA intends to seek assurance from the RTAG that proposed criteria are sufficient to protect

uses.
6

In the process of using the information and recommendations contained in this document,

as well as additional information, to develop numerical criteria or procedures to translate narrative

criteria, EPA encourages States and Tribes to:

C Address both chemical causal variables and early indicator response variables. Causal

variables are necessary to provide sufficient protection of uses before impairment occurs

and to maintain downstream uses. Early response variables are necessary to provide

warning signs of possible impairment and to integrate the effects of variable and

potentially unmeasured nutrient loads.

C Include variables that can be measured to determine if standards are met, and variables

that can be related to the ultimate sources of excess nutrients.

C Identify appropriate periods of duration (i.e., how long) and frequency (i.e., how often) of

occurrence in addition to magnitude (i.e., how much). EPA does not recommend

identifying nutrient concentrations that must be met at all times, rather a seasonal or

annual averaging period (e.g., based on weekly measurements) is considered appropriate. 

However, these seasonal or annual central tendency measures should apply each season or

each year, except under the most extraordinary of conditions (e.g., a 100 year flood).

3.0 AREA COVERED BY THIS DOCUMENT

The following sections provide a general description of the aggregate ecoregion and its

geographical boundaries. Descriptions of the level III ecoregions contained within the aggregate

ecoregion are also provided.

3.1 Description of Aggregate Ecoregion IX - Southeastern Temperate Forested Plains

and Hills

Region IX is composed of 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 more rugged

Central and Eastern Forested Uplands (XI). Lateritic soils are common and are a contrast to the

soils of the surrounding regions. Areas of depleted soils are found in Region IX. Major poultry

and aquaculture operations occur locally in the Southeastern Temperate Forested Plains and Hills

(IX).

Stream quality in the Southeastern Temperate Forested Plains and Hills (IX) has been

significantly affected by urban, suburban, and industrial development as well as by poultry,

livestock, silviculture, and aquaculture operations. Downstream of sewage treatment plants,

poultry farms, and hog operations, nutrient levels and fecal coliform bacteria concentrations can

be very high. There are a large number of intensive chicken, turkey, and hog operations in Region

IX; effluent from intensive livestock production poses a substantial eutrophication threat to

surface waters. In contrast, streams draining relatively undisturbed and forested watersheds have

low median concentrations of fecal coliform bacteria, sulfate, dissolved solids, and phosphorus. 
7

Silviculture, agriculture, and urban development have impacted suspended sediment levels in

streams especially where soils are highly erodible. Coal mining has degraded water quality and

affected aquatic biota in several areas including southern Iowa, northern Missouri, and eastern

Pennsylvania. Excessive PCB and DDT concentrations have been detected in the Schuylkill River

of Pennsylvania and have led to advisories against local fish consumption.

3.2 Geographical Boundaries of Aggregate Ecoregion IX

Ecoregion IX is an expansive region encompassing parts of twenty States (Figure 1). The

region’s northeastern border is the southeastern corner of Pennsylvania. The region runs

southward through the States of New Jersey, Maryland, Virginia, North Carolina, South Carolina,

Georgia and Florida. Only the northwestern corner of Florida is included in the region. West of

Georgia, the region includes parts of Alabama, Mississippi, Louisiana and Texas. The region runs

north up through the middle of the country to include parts of Oklahoma, Arkansas, Kansas,

Missouri, Tennessee, Kentucky, Iowa, Illinois and Indiana. The northwestern boundary of the

region is approximately described by the southeastern corner of Iowa, the southern half of Illinois

and the southwestern third of Indiana.

Figure 1. Aggregate Ecoregion IX.
8

3.3 Level III Ecoregions Within Aggregate Ecoregion IX

There are eleven Level III ecoregions contained within Aggregate Ecoregion IX (Figure

2). The following provides brief descriptions of the climate, vegetative cover, topography, and

other ecological information pertaining to these subecoregions.

29. Central Oklahoma/Texas Plains

The Central Oklahoma/Texas Plains ecoregion is a transition area between the once prairie, now

winter wheat growing regions to the west, and the forested low mountains of eastern Oklahoma. 

The region does not possess the arability and suitability for crops such as corn and soybeans that

are common in the Central Irregular Plains to the northeast. Transitional “cross-timbers” (little

bluestem grassland with scattered blackjack oak and post oak trees) is the native vegetation, and

presently rangeland and pastureland comprise the predominant land cover. Oil extraction has

been a major activity in this region for over eighty years.

33. East Central Texas Plains

Also called the Claypan Area, this region of irregular plains was originally covered by a post oak

savanna vegetation, in contrast to the more open prairie-type regions to the north, south and west

and the piney woods to the east. The bulk of this region is now used for pasture and range.

Figure 2. Aggregate Ecoregion IX with level III ecoregions shown
9

35. South Central Plains

Locally termed the “piney woods”, this region of mostly irregular plains was once blanketed by

oak-hickory-pine forests, but is now predominantly in loblolly and shortleaf pine. Only about one

sixth of the region is in cropland, whereas about two thirds is in forests and woodland. Lumber

and pulpwood production are major economic activities

37. Arkansas Valley

A region of mostly forested valleys and ridges, the physiography of the Arkansas Valley is much

less irregular than that of the Boston Mountains to the north and the Ouachita Mountains to the

south, but is more irregular than the ecological regions to the west and east. About one fourth of

the region is grazed and roughly one tenth is cropland. In the Arkansas Valley, even streams that

have been relatively unimpacted by human activities have considerably lower dissolved oxygen

levels, and hence support different biological communities, than those of most of the adjacent

regions.

40. Central Irregular Plains

The Central Irregular Plains has a mix of land use types and tends to be topographically more

irregular than the Western Corn Belt Plains to the north, where most of the land is in crops;

however, the region is less irregular and less forest covered than the ecoregions to the south and

east. The potential natural vegetation of this ecological region is a grassland/forest mosaic with

wider forested strips along the streams compared to the region to the north. The mix of land use

activities in the Central Irregular Plains also includes mining operations of high-sulfur bituminous

coal. The disturbance of these coal strata in southern Iowa and northern Missouri has degraded

water quality and affected aquatic biota.

45. Piedmont

Considered the nonmountainous portion of the old Appalachians Highland by physiographers, the

northeast-southwest trending Piedmont ecoregion comprises a transitional area between the

mostly mountainous ecoregions of the Appalachians to the northwest and the flat coastal plain to

the southeast. Once largely cultivated, much of this region has reverted to pine and hardwood

woodlands.

64. Northern Piedmont

The Northern Piedmont is transitional region of low rounded hills, irregular plains, and open

valleys in contrast to the low mountains of ecoregions to the north and west and the flat coastal

plains of the ecoregion to the east. Potential natural vegetation here was predominantly

Appalachian oak forest as compared to the mostly oak-hickory-pine forests of the Piedmont

ecoregion to the southwest. 

65. Southeastern Plains

These irregular plains have a mosaic of cropland, pasture, woodland, and forest. Natural

vegetation is mostly oak-hickory-pine and Southern mixed forest. The Cretaceous or Tertiaryage sands, silts, and clays of the region contrast geologically to the older igneous and

metamorphic rocks of the Piedmont, and the older limestone, chert, and shale found in the Interior

Plateau. Streams in this area are relatively low-gradient and sandy-bottomed.
10

71. Interior Plateau

The Interior Plateau is a diverse ecoregion extending from southern Indiana and Ohio to northern

Alabama. Rock types are distinctly different from the coastal plain sands and alluvial deposits to

the west, and elevations are lower than the Appalachian ecoregions to the east. Mississippian to

Ordovician-age limestone, chert, sandstone, siltstone and shale compose the landforms of open

hills, irregular plains, and tablelands. The natural vegetation is primarily oak-hickory forest, with

some areas of bluestem prairie and cedar glades. The region has a diverse fish fauna.

72. Interior River Lowland

The Interior River Lowland is made up of many wide, flat-bottomed terraced valleys, forested

valley walls, and dissected glacial till plains. In contrast to the generally rolling to slightly

irregular plains in adjacent ecological regions to the north, east and west, where most of the land

is cultivated for corn and soybeans, a little less than half of this area is in cropland, about 30

percent is in pasture, and the remainder is in pasture. 

74. Mississippi Valley Loess Plains

This ecoregion stretches from near the Ohio River in western Kentucky to Louisiana. It consists

primarily of irregular plains, with oak-hickory and oak-hickory-pine natural vegetation. Thick

loess tends to be the distinguishing characteristic. With flatter topography than the Southeastern

Plains ecoregion to the east, streams tend to have less gradient and more silty substrates. 

Agriculture is the dominant land use in the Kentucky and Tennessee portion of the region, while

in Mississippi there is a mosaic of forest and cropland.

Suggested ecoregional subdivisions or adjustments.

EPA recommends that the RTAG evaluate the adequacy of EPA nutrient ecoregional and

subecoregional boundaries and refine them as needed to reflect local conditions. 

4.0 DATA REVIEW FOR LAKES AND RESERVOIRS IN AGGREGATE

ECOREGION IX

The following section describes the nutrient data EPA has collected and analyzed for this

Ecoregion. This includes an assessment of data quantity and quality. The data tables present the

data for each causal parameter, total phosphorus, total nitrogen (both reported and calculated

from TKN and nitrite/nitrate), and the primary response variables (some measure of turbidity -

either secchi depth for lakes or turbidity units for streams - and chlorophyll a. These are the

parameters which EPA considers essential to nutrient assessment because the first two are the

main causative agents of enrichment, and the two response variables are the early indicators of

system enrichment for most of the surface waters. (See Chapter 5 of the Lakes and Reservoirs

Nutrient Criteria Guidance Manual [U.S. EPA, 2000a] for a complete discussion on choosing

causal and response variables.)
11

4.1 Data Sources 

Data sets from Legacy STORET, NASQAN, NAWQA, Auburn University, and EPA

Region 4 were used to assess nutrient conditions from1990 to1999. EPA recommends that the

RTAGs identify additional data sources that can be used to supplement the data sets listed above. 

In addition, the RTAGs may utilize published literature values to support quantitative and

qualitative analyses.

4.2 Historical Data from Aggregate Ecoregion IX (TP, TN, Chl a and Secchi Depth)

EPA recommends that States/Tribes assess long-term trends observed over the past 50

years. This information may be obtained from scientific literature or documentation of historical

trends. To gain additional perspective on more recent trends, it is recommended that States and

Tribes assess nutrient trends over the last 10 years (e.g., what do seasonal trends indicate?)

4.3 QA/QC of data sources

An initial quality screen of data was conducted using the rules presented in Appendix C. 

Data remaining New Jersey, after screening for duplications and other QA measures (.e.g., poor

or unreported analytical records, sampling errors or omissions, stations associated with outfalls,

storm water sewers, hazardous waste sites) is the data used in statistical analyses

The following States indicated that their data were sampled and analyzed using either

Standard methods or EPA approved methods: Florida, Georgia, Illinois, Iowa, Indiana,

Maryland, Missouri, North Carolina, South Carolina, and Tennessee. In all cases, States indicated

a Standard method or an approved EPA method was used. Other States in Ecoregion IX did not

provide information prior to the publication of this document.

4.4 Data for All Lakes and Reservoirs Within Aggregate Ecoregion IX 

Figure 3 shows the location of the sampling stations within each sub ecoregion. Table 1

presents all data records for all parameters for Aggregate Ecoregion IX and subecoregions within

the Aggregate Ecoregion. 

4.5 Statistical Analysis of Data

EPA’s Technical Guidance Manual for Developing Nutrient Criteria for Lakes Reservoirs

describes two ways of establishing a reference condition. One method is to choose the upper 25th

percentile (75th percentile) of a reference population of streams. This is the preferred method to

establish a reference condition. The 75th percentile was chosen by EPA since it is likely associated

with minimally impacted conditions, will be protective of designated uses, and provides

management flexibility. When reference streams are not identified, the second method is to

determine the lower 25th percentile of the population of all streams within a region. The 25th
12

Figure 3. Sampling locations within level III ecoregions
13

 Table 1. Lake records for Aggregate Ecoregion IX - Southeastern Temperate Forested Plains and Hills

Aggregate

Ecoregion

IX

Sub

ecoR 29

Sub

ecoR 33

Sub

ecoR 35

Sub

ecoR 37

Sub

ecoR 40

Sub

ecoR 45

Sub

ecoR 64

# of Lakes / Reservoirs 987 94 17 68 26 116 268 13

# of Lake Stations 2,965 154 32 122 36 200 741 406

Key Nutrient Parameters

(listed below)

 - # of records for Secchi

depth

24,869 786 186 1,144 150 1,041 4,380 21

- # of records for Chlorophyll

a (all methods)

3,558 360 118 451 25 1,114 3,409 21

- # of records for Total

Kjeldahl Nitrogen (TKN)

18,132 1,111 140 934 59 1,780 7,252 160

- # of records for Nitrate +

Nitrite (NO2 + NO3)

18,019 992 95 624 129 1,067 6,154 51

- # of records for Total

Nitrogen (TN)

1,492 0 0 0 0 0 0 19

- # of records for Total

Phosphorus (TP)

23,261 1,242 211 1,188 149 2,071 7,472 158

Total # of records for key

nutrient parameters

89,331 4,491 750 4,341 512 7,073 28,667 430
14

 Table 1 (continued). Lake records for Aggregate Ecoregion IX -

Southeastern Temperate Forested Plains and Hills

Sub 

ecoR 65

Sub

ecoR 71

Sub

ecoR 72

Sub

ecoR 74

# of Lakes / Reservoirs 175 91 126 12

# of Lake Stations 584 168 501 21

Key Nutrient Parameters (listed

below)

 - # of records for Secchi

depth

3,568 1,586 11,933 73

- # of records for Chlorophyll

a (all methods)

3,510 1,571 3,171 35

- # of records for Total

Kjeldahl Nitrogen (TKN)

6,230 1,282 2,654 62

- # of records for Nitrate +

Nitrite (NO2 + NO3)

2,775 2,552 3,472 105

- # of records for Total

Nitrogen (TN)

1,473 0 0 0

- # of records for Total

Phosphorus (TP)

4,608 2,520 4,485 105

Total # of records for key

nutrient parameters

22,164 9,511 25,715 380
15

Definitions used in filling Table 1

1. # of records refers to the total count of observations for that

parameter over the entire decade (1990-1999) for that particular

aggregate or subecoregion. These are counts for all seasons over

that decade.

2. # lake stations refers to the total number of lake and reservoir

stations within the aggregate or subecoregion from which nutrient

data was collected. Since lakes and reservoirs can cross ecoregional

boundaries, it is important to note that only those portions of a lake

or reservoir (and data associated with those stations) that exist

within the ecoregion are included within this table.

percentile of the entire population was chosen by EPA to represent a surrogate for an actual

reference population. Data analyses to date indicate that the lower 25th percentile from an entire

population roughly approximates the 75th percentile for a reference population (see case studies

for Minnesota lakes in the Lakes and Reservoirs Nutrient Criteria Technical Guidance Document

[U.S. EPA, 2000a], the case study for Tennessee streams in the Rivers and Streams Nutrient

Criteria Technical Guidance Document [U.S. EPA, 2000a], and the letter from Tennessee

Department of Environment and Conservation to Geoffrey Grubbs [TNDEC, 2000]). New York

State has also presented evidence that the 25th percentile and the 75th percentile compare well

based on user perceptions of water resources (NYSDEC, 2000).

Tables 2 and 3a-k present potential reference conditions for both the aggregate ecoregion

and the subecoregions using both methods. However, the reference lake column is left blank

because EPA does not have reference data and anticipates that States/Tribes will provide

information on reference lakes. Appendix A provides a complete presentation of all descriptive

statistics for both the aggregate ecoregion and the level III subecoregion.

4.6. Classification of Lake/Reservoir Type

It is anticipated that assessing the data by lake type will further reduce the variability in the

data analysis. There were no readily available classification data in the National datasets used to

develop these criteria. States and Tribes are strongly encouraged to classify their lakes before 

developing a final criterion.

4.7. Summary of Data Reduction Methods

All descriptive statistics were calculated using the medians for each lake within ecoregion

IX, for which data existed. For example, if one lake had 300 observations for phosphorus over

the decade or one year’s time, one median resulted. Each median from each lake was then used in

calculating the percentiles for phosphorus for the aggregate nutrient ecoregion/subecoregion

(level III ecoregion) by season and year (Figure 4a & b).
16

 Table 2. Reference conditions for aggregate ecoregion IX lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 605 0.023 4.85 0.38

NO2 + NO3 (mg/L) 591 0 5.799 0.017

TN (mg/L) - calculated NA 0.023 10.649 0.397

TN (mg/L) - reported 26 0.238 2.025 0.358

TP (ug/L) 727 0 1,145 20

Secchi (meters) 651 0.101 230 1.53

Chlorophyll a (ug/L) - F 253 0.575 75.9 4.925

Chlorophyll a (ug/L) - S 331 0 108.805 5.18

Chlorophyll a (ug/L) - T 149 0.66 108.15 6.52

 P25: 25th percentile of all data

P75: 75th percentile of all data

* 75th percentile for Secchi

** as determined by the Regional Technical Assistance Groups (RTAGs)

+ Median for all seasons’ 25th percentiles. E.g. this value was calculated from

four seasons’ 25th percentiles. If the seasonal 25th percentile (P25) TP values

are - spring 10μg/L, summer 15μg/L, fall 12μg/L, and winter 5μg/L, the

median value of all seasons P25 will be 11μg/L. 

++ N = largest value reported for a decadal season.

 TN calculated is based on the sum of TKN + NO2+NO3. 

 TN reported is actual TN value reported in the database for one sample.

F Chlorophyll a measured by Fluorometric method with acid correction.

S Chlorophyll a measured by Spectrophotometric method with acid correction.

T Chlorophyll a b c measured by Trichromatic method

NA Not Applicable

Tables 3a-k present potential reference conditions for lakes and reservoirs in the Level III

subecoregions within the Aggregate Ecoregion. Note that the footnotes for Table 2 apply to

Tables 3a-k.
17

Table 3a. Reference conditions for level III ecoregion 29 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 59 0.05 2.665 0.41

NO2 + NO3 (mg/L) 51 0.007 2.85 0.01

TN (mg/L) - calculated NA 0.057 5.515 0.42

TN (mg/L) - reported 0 -- -- --

TP (ug/L) 61 2.5 260 19.063

Secchi (meters) 38 0.203 1.708 1.26

Chlorophyll a (ug/L) - F 0 -- -- --

Chlorophyll a (ug/L) - S 53 0.775 34.063 2.875

Chlorophyll a (ug/L) - T -- -- --

Table 3b. Reference conditions for level III ecoregion 33 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 8 0.538 1.14 0.778

NO2 + NO3 (mg/L) 4 0.01 0.42 0.029

TN (mg/L) - calculated NA 0.548 1.56 0.807

TN (mg/L) - reported 0 – – --

TP (ug/L) 10 10 795 55

Secchi (meters) 10 0.46 1.614 1

Chlorophyll a (ug/L) - F 0 -- -- --

Chlorophyll a (ug/L) - S 9 2.665 21.3 5.05

Chlorophyll a (ug/L) - T – – –
18

Table 3c. Reference conditions for level III ecoregion 35 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 29 0.26 1.223 0.459

NO2 + NO3 (mg/L) 24 W 0.008 0.41 0.033

TN (mg/L) - calculated NA 0.268 1.633 0.492

TN (mg/L) - reported 0 – – --

TP (ug/L) 37 8 237.5 32.5

Secchi (meters) 29 0.335 3.325 1.1

Chlorophyll a (ug/L) - F 0 -- -- --

Chlorophyll a (ug/L) - S 24 0.488 19.95 2.834

Chlorophyll a (ug/L) - T – – –

Table 3d. Reference conditions for level III ecoregion 37 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 11 W 0.275 0.85 0.385

NO2 + NO3 (mg/L) 11 0.01 0.225 0.01

TN (mg/L) - calculated NA 0.285 1.075 0.395

TN (mg/L) - reported 0 – – --

TP (ug/L) 14 3.75 206.25 20

Secchi (meters) 4 0.126 0.49 0.46

Chlorophyll a (ug/L) - F 0 – – --

Chlorophyll a (ug/L) - S 9 F 4.425 14.55 4.95

Chlorophyll a (ug/L) - T – – –
19

Table 3e. Reference conditions for level III ecoregion 40 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes

**

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 73 0.148 2.91 0.568

NO2 + NO3 (mg/L) 80 0.007 1.865 0.093

TN (mg/L) - calculated NA 0.155 4.775 0.661

TN (mg/L) - reported 0 – – –

TP (ug/L) 95 8.125 477.5 40

Secchi (meters) 86 0.126 2.05 0.988

Chlorophyll a (ug/L) - F 0 – – –

Chlorophyll a (ug/L) - S 82 2.3 68.675 5.588

Chlorophyll a (ug/L) - T – – --

Table 3f. Reference conditions for level III ecoregion 45 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes

**

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 200 0.025 1.908 0.245

NO2 + NO3 (mg/L) 153 0.002 3.799 0.059

TN (mg/L) - calculated NA 0.027 5.707 0.304

TN (mg/L) - reported 0 – – --

TP (ug/L) 198 5 265 22.5

Secchi (meters) 175 0.263 6.225 1.655

Chlorophyll a (ug/L) - F 132 0.963 31.938 4.513

Chlorophyll a (ug/L) - S 40 2.2 45.8 5.95

Chlorophyll a (ug/L) - T – – --
20

Table 3g. Reference conditions for level III ecoregion 64 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes

**

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 8 0.313 0.945 0.35

NO2 + NO3 (mg/L) 2 F 0.605 1.13 0.605

TN (mg/L) - calculated NA 0.918 2.075 0.955

TN (mg/L) - reported 4 0.615 1.943 0.818

TP (ug/L) 10 33.75 187.5 45

Secchi (meters) 7 0.5 4.013 1.544

Chlorophyll a (ug/L) - F 0 – – –

Chlorophyll a (ug/L) - S 1 7.68 7.68 7.68

Chlorophyll a (ug/L) - T – – –

Table 3h. Reference conditions for level III ecoregion 65 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 92 0.075 4.85 0.32

NO2 + NO3 (mg/L) 95 0 1.324 0.009

TN (mg/L) - calculated NA 0.075 6.174 0.329

TN (mg/L) - reported 20 0.238 1.585 0.348

TP (ug/L) 128 0 527.5 10

Secchi (meters) 116 0.21 230 2.041

Chlorophyll a (ug/L) - F 55 0.875 53.25 5.125

Chlorophyll a (ug/L) - S 40 0 67.25 1.873

Chlorophyll a (ug/L) - T – – –
21

Table 3i. Reference conditions for level III ecoregion 71 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 47 0.213 1.644 0.365

NO2 + NO3 (mg/L) 67 0.001 1.663 0.101

TN (mg/L) - calculated NA 0.214 3.307 0.466

TN (mg/L) - reported 0 – – --

TP (ug/L) 67 2 380 16.563

Secchi (meters) 64 0.235 3.855 1.841

Chlorophyll a (ug/L) - F 52 1.8 49.063 6.2

Chlorophyll a (ug/L) - S 8 5.125 14 6.25

Chlorophyll a (ug/L) - T – – –

Table 3j. Reference conditions for level III ecoregion 72 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 81 0.272 2.08 0.609

NO2 + NO3 (mg/L) 97 0.001 3.475 0.005

TN (mg/L) - calculated NA 0.273 5.555 0.614

TN (mg/L) - reported 0 – – --

TP (ug/L) 97 9.5 845 30

Secchi (meters) 115 0.132 3.15 1.093

Chlorophyll a (ug/L) - F 10 2.1 60.2 9.1

Chlorophyll a (ug/L) - S 74 4.253 108.805 12.945

Chlorophyll a (ug/L) - T – – –
22

Table 3k. Reference conditions for level III ecoregion 74 lakes and reservoirs.

 Parameter

No. of

Lakes

 N ++

Reported values 25th Percentiles based on all

seasons data for the Decade

Reference Lakes **

Min Max P25* all seasons + P75 all seasons

TKN (mg/L) 6 0.273 0.527 0.305

NO2 + NO3 (mg/L) 10 0.033 0.37 0.048

TN (mg/L) - calculated NA 0.306 0.897 0.353

TN (mg/L) - reported 0 – – –

TP (ug/L) 10 23.125 233.75 62.5

Secchi (meters) 7 0.277 0.975 0.71

Chlorophyll a (ug/L) - F 5 F 5.625 61.675 9.8

Chlorophyll a (ug/L) - S 0 – – –

Chlorophyll a (ug/L) - T – – --
23

Definitions used in filling Tables 2 and 3 - Reference Condition tables

1. Number of Lakes in Table 2 refers to the largest number of lakes and reservoirs for

which data existed for a given season within an aggregate nutrient ecoregion.

2. Number of Lakes in Table 3 refers to the number of lakes and reservoirs for which

data existed for the summer months since summer is generally when the greatest amount of

nutrient sampling is conducted. If another season greatly predominates, notification is

made (s=spring, f=fall, w=winter).

3. Medians. All values (min, max, and 25th percentiles) included in the table are based on

waterbody medians. All data for a particular parameter within a lake for the decade were reduced to

one median for that lake. This prevents over-representation of individual waterbodies with a great

deal of data versus those with fewer data points within the statistical analysis.

4. 25th percentile for all seasons is calculated by taking the median of the 4 seasonal 25th

percentiles. If a season is missing, the median was calculated with 3 seasons of data. If less than 3

seasons were used to derive the median, the entry is flagged (z).

5. A 25th percentile for a season is best derived with data from a minimum of a 4

lakes/season. However, this table provides 25th percentiles that were derived with less than

4 lakes/season in order to retain all information for all seasons. In calculating the 25th

percentile for a season with less than 4 lake median, the statistical program automatically

used the minimum value within the less-than-4 population. If less than 4 lakes were used in

developing a seasonal quartile and or all-seasons median, the entry is flagged. by zz.

Preferred Data Choices and Recommendations When Data Are Missing

1. Where data are missing or very low in total records for a given parameter, use 25th

percentiles for parameters within an adjacent, similar subecoregion within the same aggregate

nutrient ecoregion or when a similar subecoregion can not be determined, use the the 25th

percentile for the Aggregate ecoregion or consider the lowest 25th percentile from a subecoregion

(level III) within the aggregate nutrient ecoregion. The rationale being that without data, one may

assume that the subecoregion in question may be as sensitive as the most sensitive subecoregion

within the aggregate.

2. TN calculated: When reported Total Nitrogen (TN) median values are lacking or very low in

comparison to TKN and Nitrate/Nitrite-N values, the medians for TKN and nitrite/nitrate-N were

added, resulting in a calculated TN value. The “N” value for calculated TN is not filled in since

there are two N populations from TKN and nitrite/nitrate-N. N/A is placed in this box. 

3. TN reported: This is the median based on reported values for TN from the database.
24

Rainy Lake Median

Fish Reservoir Median

Swan Lake Median

Moon Lake ...

Timber ...

Rainy Lake Median

Fish Reservoir Median

Swan Lake Median

Moon Lake ...

Timber ...

Rainy Lake Median

Fish Reservoir Median

Swan Lake Median

Moon Lake ...

Timber ...

Rainy Lake Median

Fish Reservoir Median

Swan Lake Median

Moon Lake ...

Timber ...

Figure 4a. Illustration of data reduction process for lake data.

Pine

Lake

Data

Ashley

Lake

Data

Clear

Lake

Data

Swan

Lake

Data

Moon

Lake

Data

Fish

Reservoir

Data

Green

Reservoir

Data

Marsh

Lake

Data

Bear

Reservoir

Data

Sandy

Reservoir

Data

Timber

Lake

Data

Ecoregion

Observations for All Lakes/Reservoirs

Winter Spring Summer Fall

Data Reduced

to

Median Value

for each

Lake/Reservoir

by

Season
25

Select 25th Percentile

from Distribution

of Median

Values

25th 25% 25% 25%

Winter Spring Summer Fall

Calculate Median

Value of the

25th Percentiles

for the Four Seasons

Half values

Below Median

Half values

Above Median

25%

Season D

25%

Season A

25%

Season B

25%

Season C

Median = Reference Condition for the Ecoregion

TP

TN

TKN

NO2+NO3

DO

SECCHI

} 25%

} 75%

Figure 4b.Illustration of reference condition calculation.
26

4. Chlorophyll a: medians based on all methods are reported, however, the acid corrected

medians are preferred to the uncorrected medians. In developing a reference condition from a

particular method, it is recommended that the method with the most observations be used. 

Fluorometric and Spectrophotometric are preferred over all other methods. However, when no

data exists for Fluorometric and Spectrophotometric methods, Trichromatic values may be used.

Data from the variance techniques are not interchangeable.

5. Periphyton: Where periphyton data exists, record separately.

6. Secchi depth: The 75th percentile is reported for secchi depth since this is the only variable for

which the value of the parameter increases with greater clarity.

7. Turbidity units: all turbidity units from all methods are reported. FTUs and NTUs are

preferred over JCUs. If FTUs and NTUs do not exist, use JCUs. These units are not

interchangeable. (For streams only)

8. Lack of data: A dash (-) represents missing, inadequate or inconclusive data. A zero (0) is

reported if the reported median for a parameter is 0 or if the component value is below detection. 

5.0 REFERENCE SITES AND CONDITIONS IN AGGREGATE ECOREGION IX

Reference conditions represent the natural, least impacted conditions or what is

considered to be the most attainable conditions. This section compares the different reference

conditions determined from the two methods and establishes which reference condition is most

appropriate.

Apriori determination of reference sites The preferred method for establishing reference

condition is to choose the upper percentile of an a priori population of reference lakes. States

and Tribes are encouraged to identify reference conditions based on this method.

Statistical determination of reference conditions (25 percentile of entire database.) See Tables 2

and 3a-k in section 4.0. 

RTAG discussion and rationale for selection of reference sites and conditions in Ecoregion IX

The RTAG should compare the results derived from the two methods described above and

present a rationale for the final selection of reference sites. 

6.0 MODELS USED TO PREDICT OR VERIFY RESPONSE PARAMETERS

The RTAG is encouraged to identify and apply relevant models to support nutrient criteria

development. The following are three scenarios under which models may be used to derive

criteria or support criteria development

C Models for predicting correlations between causal and response variables
27

C Models used to verify reference conditions based on percentiles

C Regression models used to predict reference conditions in impacted areas

7.0 FRAMEWORK FOR REFINING RECOMMENDED NUTRIENT CRITERIA

FOR LAKES AND RESERVOIRS IN AGGREGATE ECOREGION IX

Information on each of the following six weight of evidence factors is important to refine

the criteria presented in this document. All elements should be addressed in developing criteria,

as is expressed in our nutrient criteria technical guidance manuals. It is our expectation that EPA

Regions, States, and Tribes (as RTAGs) will consider these elements as States/Tribes develop

their criteria. This section should be viewed as a work sheet (sections are left blank for this

purpose) to assist in the refinement of nutrient criteria. If many of these elements are ultimately

unaddressed, EPA may rely on the proposed reference conditions presented in Tables 3a-k and

other literature and information readily available to the HQ nutrient team to develop nutrient

water quality recommendations for this ecoregion..

7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion

Nutrient Criteria

C Literature sources

C Historical data and trends

C Reference conditions

C Models
28

C RTAG expert review and consensus

C Downstream effects

7.2 Tables of Refined Nutrient Water Quality Criteria for Aggregate Ecoregion IX and

Level III Subecoregions for TP, TN, Chl a, Secchi Depth (where sufficient data exist)

Aggregate Ecoregion IX- Southeastern

Temperate Forested Plains and Hills

Proposed Criterion

Total Phosphorus (μg/L)

Total Nitrogen (mg/L)

Chlorophyll a (μg/L or mg/m2)

Secchi Depth (meters)

Other (Index; other parameter such as DO)

C Literature sources

C Historical data and trends
29

C Reference conditions

C Models

C RTAG expert review and consensus

C Downstream effects

Ecoregion #29 Central Oklahoma/Texas

Plains 

Proposed Criterion

Total Phosphorus (μg/L)

Total Nitrogen (mg/L)

Chlorophyll a (μg/L or mg/m2)

Secchi Depth (meters)

Other (Index; other parameter such as DO)
30

7.3 Setting Seasonal Criteria

The recommendations presented in this document are based, in part, on medians of all the

25th percentile seasonal data (decadal), and as such are reflective of all seasons and not one

particular season or year. It is recommended that States and Tribes monitor in all seasons to best

assess compliance with the resulting criterion. States/Tribes may choose to develop criteria which

reflect each particular season or a given year or season when there is significant variability

between seasons/years or designated uses that are specifically tied to one or more seasons of the

year (e.g., recreation, fishing). Using the tables in Appendix A and B, one can set reference

conditions based on a particular season or year and then develop a criterion based on each

individual season. Obviously, this option is season-specific and would also require increased

monitoring within each season to assess compliance. 

7.4 When Data/Reference Conditions are Lacking

When data are unavailable to develop a reference condition for a particular parameter(s)

within a subecoregion, EPA recommends one of three options: (1) Use data from a similar

neighboring subecoregion. E.g., If data are few or nonexistent for the northern cascades, consider

using the data and reference condition developed for the cascades; or (2) Use the 25th perecentiles

for the Aggregate ecoregion or (3) Consider using the lowest of the yearly medians for that

parameter calculated for all the subecoregions within the Aggregate Ecoregion.

7.5 Site-specific Criteria Development 

Criteria may be refined in a number of ways. The best way to refine criteria is to follow

the critical elements of criteria development as well as to refer to the Lakes and Reservoirs

Nutrient Criteria Technical Guidance Manual (U.S. EPA, 2000a). The Technical Guidance

Manual presents sections on each of the following factors to consider in setting criteria:

- refinements to ecoregions and classification of waterbodies (Chapter 3)

- setting seasonal criteria to reflect major seasonal climate differences and accounting for 

significant or cyclical rainfall events - high flow/low flow conditions (Chapter 4). 

NOTE: In setting criteria for reservoirs only (The technical guidance manual recommends that

data be separated for lakes and reservoirs and treated independently if possible because of

differing physical conditions that occur in lakes and reservoirs. In this document all data from

both reservoirs and lakes were considered together since STORET does not allow for the

differentiation of data except by waterbody name.) 
31

8.0 LITERATURE CITED

NYSDEC (New York State Department of Environment and Conservation). 2000. 

Memorandum from Scott Kishbaugh to Jay Bloomfield, September 26, 2000, regarding

reference lakes for nutrient criteria.

TNDEC (Tennessee Department of Environment and Conservation). 2000. Letter to

Geoff Grubbs, October 5, 2000, containing comments on draft nutrient criteria

recommendations.

U.S. EPA. 2000a. Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs,

U.S. Environmental Protection Agency, Washington, DC. EPA-822-B00-001.

U.S. EPA. 2000b. Nutrient Criteria Technical Guidance Manual: Rivers and Streams,

U.S. Environmental Protection Agency, Washington, DC. EPA-822-B00-002.

9.0 APPENDICES

A. Descriptive Statistics Data Tables for Aggregate Ecoregion

B. Descriptive Statistics Data Tables for Level III Subecoregions within Aggregate Ecoregion 

C. Quality Control/Quality Assurance Rules
APPENDIX A

Descriptive Statistics Data Tables for Aggregate Ecoregion
 

 Aggregate Nutrient Ecoregion: IX 

1

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Fluo_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 139 16.9 1.00 91.00 15.4 1.31 91 2.20 6.20 12.0 24.0 52.1

 SPRING 135 10.3 .750 55.70 8.30 0.71 81 1.50 4.35 7.80 14.3 26.5

 SUMMER 253 14.3 .250 112.10 15.0 0.94 105 1.90 5.50 9.45 17.7 41.7

 WINTER 58 6.94 .400 60.80 9.86 1.29 142 0.75 1.80 4.00 7.15 29.1

 Aggregate Nutrient Ecoregion: IX 

2

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Pheo_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1 4.27 4.27 4.27 . . . 4.27 4.27 4.27 4.27 4.27

 SPRING 1 2.80 2.80 2.80 . . . 2.80 2.80 2.80 2.80 2.80

 SUMMER 1 7.21 7.21 7.21 . . . 7.21 7.21 7.21 7.21 7.21

 WINTER 1 1.34 1.34 1.34 . . . 1.34 1.34 1.34 1.34 1.34

 Aggregate Nutrient Ecoregion: IX 

3

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_A_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 183 17.6 .000 138.84 21.8 1.61 124 0.98 4.41 9.82 20.2 62.6

 SPRING 157 15.0 .000 78.77 15.0 1.20 100 2.14 5.95 9.44 17.5 52.5

 SUMMER 331 22.6 .000 155.00 26.4 1.45 117 2.14 7.11 12.2 28.2 86.2

 WINTER 56 6.85 .250 68.73 12.2 1.62 178 0.25 1.70 3.20 6.54 37.0

 Aggregate Nutrient Ecoregion: IX 

4

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_U_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1 6.70 6.70 6.70 . . . 6.70 6.70 6.70 6.70 6.70

 SPRING 1 4.56 4.56 4.56 . . . 4.56 4.56 4.56 4.56 4.56

 SUMMER 1 10.7 10.7 10.65 . . . 10.7 10.7 10.7 10.7 10.7

 WINTER 1 2.55 2.55 2.55 . . . 2.55 2.55 2.55 2.55 2.55

 
 

 Aggregate Nutrient Ecoregion: IX 

5

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Tric_U_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 94 26.9 .000 134.98 24.8 2.56 92 2.53 9.03 19.3 38.3 68.8

 SPRING 94 17.3 .000 81.31 18.0 1.86 104 1.25 4.00 12.0 24.3 59.3

 SUMMER 149 34.5 1.25 151.00 31.7 2.59 92 3.00 10.0 23.5 51.3 97.0

 WINTER 25 11.4 1.25 65.37 13.9 2.78 122 1.48 4.00 5.50 12.8 31.0

 Aggregate Nutrient Ecoregion: IX 

6

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter DIP_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 SPRING 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 SUMMER 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 WINTER 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 Aggregate Nutrient Ecoregion: IX 

7

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter DO_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 207 7.52 1.20 12.80 1.62 0.11 22 4.25 6.75 7.60 8.50 9.70

 SPRING 217 8.82 4.40 13.70 1.37 0.09 16 6.10 8.30 9.00 9.60 10.8

 SUMMER 430 7.28 1.05 13.10 1.81 0.09 25 3.70 6.40 7.60 8.25 10.0

 WINTER 130 10.0 5.90 13.70 1.30 0.11 13 7.60 9.30 10.1 10.7 12.2

 Aggregate Nutrient Ecoregion: IX 

8

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter NO2_NO3_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 355 0.14 .000 6.60 0.46 0.02 325 0.00 0.01 0.03 0.12 0.54

 SPRING 386 0.28 .000 5.00 0.52 0.03 189 0.00 0.03 0.13 0.31 1.00

 SUMMER 591 0.12 .000 6.83 0.44 0.02 379 0.00 0.01 0.01 0.07 0.51

 WINTER 196 0.27 .000 2.23 0.32 0.02 119 0.02 0.07 0.16 0.36 0.87

 
 

 Aggregate Nutrient Ecoregion: IX 

9

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter SECCHI_m_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 352 1.90 .100 243.00 12.9 0.69 680 0.25 0.61 0.94 1.54 3.10

 SPRING 369 1.79 .102 217.00 11.3 0.59 631 0.23 0.55 0.94 1.60 3.00

 SUMMER 651 1.48 .100 187.00 7.33 0.29 496 0.27 0.61 0.99 1.50 2.88

 WINTER 139 3.45 .150 307.00 26.0 2.20 751 0.30 0.58 0.94 1.51 3.96

 Aggregate Nutrient Ecoregion: IX 1

0

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TKN_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 309 0.69 .020 4.90 0.55 0.03 81 0.20 0.40 0.55 0.82 1.50

 SPRING 369 0.62 .025 4.80 0.44 0.02 72 0.20 0.36 0.51 0.72 1.38

 SUMMER 605 0.67 .020 4.60 0.49 0.02 73 0.20 0.40 0.56 0.80 1.55

 WINTER 196 0.59 .025 5.20 0.53 0.04 91 0.16 0.31 0.45 0.71 1.18

 Aggregate Nutrient Ecoregion: IX 1

1

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TN_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 26 0.75 .235 2.55 0.51 0.10 68 0.34 0.40 0.59 0.94 1.67

 SPRING 21 0.50 .290 1.14 0.22 0.05 44 0.30 0.34 0.43 0.59 0.93

 SUMMER 24 0.64 .240 1.50 0.37 0.08 58 0.28 0.37 0.54 0.74 1.34

 WINTER 22 0.73 .195 4.32 0.86 0.18 118 0.23 0.35 0.46 0.68 1.33

 Aggregate Nutrient Ecoregion: IX 1

2

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TP_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 420 79.1 .000 1050.00 120 5.85 152 5.00 20.0 40.0 80.0 270

 SPRING 444 66.6 .000 1240.00 100 4.75 150 6.25 20.0 40.0 75.0 185

 SUMMER 727 75.4 .000 1695.00 117 4.33 155 5.00 20.0 41.3 80.0 260

 WINTER 227 62.5 2.50 715.00 87.8 5.82 140 2.50 20.0 40.0 70.0 195

 
APPENDIX B

Descriptive Statistics Data Tables for Level III Subecoregions within Aggregate Ecoregion
 Aggregate Nutrient Ecoregion: IX 1

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Fluo_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 56 11.7 1.30 32.28 8.65 1.16 74 2.00 4.83 9.18 17.1 29.0

 45 SPRING 62 9.79 1.40 27.05 6.57 0.83 67 2.25 4.20 8.24 14.3 21.0

 45 SUMMER 132 12.0 .625 85.25 10.5 0.91 88 2.00 5.50 9.13 16.3 30.3

 45 WINTER 43 6.41 .400 31.60 6.93 1.06 108 0.90 1.80 4.60 8.70 20.9

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 19 16.4 1.00 45.70 11.3 2.60 69 1.00 8.35 14.6 20.5 45.7

 65 SPRING 17 11.1 1.10 33.83 9.05 2.20 82 1.10 6.25 7.45 15.4 33.8

 65 SUMMER 55 11.0 .250 81.15 12.8 1.73 117 0.25 4.00 7.00 15.3 34.6
 Aggregate Nutrient Ecoregion: IX 2

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Fluo_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 12 9.34 .750 60.80 17.7 5.10 189 0.75 1.50 2.23 5.38 60.8

 71 FALL 49 18.5 2.30 91.00 17.0 2.44 92 3.30 7.80 13.6 24.6 54.8

 71 SPRING 45 10.2 .750 31.83 7.93 1.18 78 1.20 4.60 8.30 13.5 26.5

 71 SUMMER 52 18.5 1.30 66.30 15.8 2.19 85 3.70 6.70 11.7 28.4 52.1

 71 WINTER 2 5.83 5.70 5.95 0.18 0.13 3 5.70 5.70 5.83 5.95 5.95

 72 FALL 10 29.6 2.90 60.20 21.6 6.84 73 2.90 9.70 32.8 52.1 60.2

 72 SPRING 8 5.58 1.60 8.50 2.79 0.99 50 1.60 3.05 6.30 7.90 8.50

 72 SUMMER 10 29.6 2.10 112.10 33.7 10.6 114 2.10 9.10 16.7 45.7 112

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 5 35.9 5.35 74.60 28.2 12.6 79 5.35 13.7 33.7 52.0 74.6

 74 SPRING 3 28.5 5.90 55.70 25.2 14.6 89 5.90 5.90 23.8 55.7 55.7

 74 SUMMER 4 43.3 10.5 67.65 27.0 13.5 62 10.5 21.3 47.6 65.4 67.7

 74 WINTER 1 3.20 3.20 3.20 . . . 3.20 3.20 3.20 3.20 3.20

 Aggregate Nutrient Ecoregion: IX 3

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Pheo_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .
 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 1 4.27 4.27 4.27 . . . 4.27 4.27 4.27 4.27 4.27

 65 SPRING 1 2.80 2.80 2.80 . . . 2.80 2.80 2.80 2.80 2.80

 65 SUMMER 1 7.21 7.21 7.21 . . . 7.21 7.21 7.21 7.21 7.21

 Aggregate Nutrient Ecoregion: IX 4

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Pheo_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 1 1.34 1.34 1.34 . . . 1.34 1.34 1.34 1.34 1.34

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 0 . . . . . . . . . . .

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 0 . . . . . . . . . . .

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 5

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_A_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 18 6.13 1.30 16.73 4.08 0.96 66 1.30 3.20 4.35 8.50 16.7

 29 SPRING 16 7.53 .250 51.40 12.0 3.00 160 0.25 2.55 3.98 6.85 51.4

 29 SUMMER 53 10.5 1.80 77.40 13.4 1.84 128 2.40 3.50 5.90 11.8 40.6

 29 WINTER 17 3.47 .250 14.70 3.79 0.92 109 0.25 0.25 2.53 5.10 14.7

 33 FALL 4 6.85 .250 17.80 8.41 4.20 123 0.25 0.25 4.68 13.5 17.8

 33 SPRING 8 10.8 5.08 29.20 7.80 2.76 72 5.08 6.90 8.20 11.1 29.2

 33 SUMMER 9 16.5 9.30 24.80 6.04 2.01 37 9.30 10.9 16.7 22.2 24.8

 33 WINTER 5 5.43 .250 13.45 4.92 2.20 91 0.25 3.20 4.60 5.64 13.5

 35 FALL 12 5.94 .250 12.00 4.58 1.32 77 0.25 1.43 5.60 10.4 12.0

 35 SPRING 12 10.2 .725 27.90 7.97 2.30 78 0.73 5.58 7.42 11.9 27.9

 35 SUMMER 24 12.9 .250 57.90 14.1 2.89 110 0.25 3.45 10.1 14.6 46.0

 35 WINTER 8 5.01 1.30 9.61 3.20 1.13 64 1.30 2.22 4.78 7.58 9.61

 37 FALL 9 6.71 1.85 18.50 5.58 1.86 83 1.85 2.90 4.20 10.1 18.5

 37 SPRING 3 8.97 7.00 10.60 1.82 1.05 20 7.00 7.00 9.30 10.6 10.6

 37 SUMMER 0 . . . . . . . . . . .
 37 WINTER 0 . . . . . . . . . . .

 40 FALL 39 15.3 .975 100.15 18.6 2.98 122 1.50 4.70 8.90 18.2 49.8

 40 SPRING 18 12.4 3.20 37.20 9.01 2.12 72 3.20 6.15 9.90 11.9 37.2

 40 SUMMER 82 20.4 2.00 120.80 24.9 2.75 122 4.45 8.35 12.1 18.2 62.4

 40 WINTER 6 12.4 2.60 37.00 12.6 5.12 102 2.60 5.03 8.39 12.7 37.0

 45 FALL 6 6.77 2.20 14.53 4.62 1.89 68 2.20 3.29 5.51 9.60 14.5

 45 SPRING 9 10.7 3.20 45.80 13.3 4.42 125 3.20 5.95 6.15 7.70 45.8

 45 SUMMER 40 30.0 2.00 155.00 36.0 5.68 120 2.34 7.27 14.9 37.2 118

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 1 7.68 7.68 7.68 . . . 7.68 7.68 7.68 7.68 7.68

 64 SPRING 1 7.88 7.88 7.88 . . . 7.88 7.88 7.88 7.88 7.88

 64 SUMMER 1 5.21 5.21 5.21 . . . 5.21 5.21 5.21 5.21 5.21

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 29 8.69 .000 73.50 14.4 2.68 166 0.00 1.32 3.53 11.0 33.8

 65 SPRING 25 10.2 .000 61.00 12.6 2.53 124 0.00 4.50 8.00 9.50 27.2

 65 SUMMER 40 13.8 .000 87.80 19.9 3.14 144 0.00 2.43 8.46 13.3 65.9

 Aggregate Nutrient Ecoregion: IX 6

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_A_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 15 6.74 .250 55.23 13.7 3.54 203 0.25 1.00 2.63 4.70 55.2

 71 FALL 8 8.66 5.25 14.00 3.33 1.18 38 5.25 5.75 7.75 11.5 14.0

 71 SPRING 8 12.3 7.75 20.50 4.56 1.61 37 7.75 9.00 10.6 15.6 20.5

 71 SUMMER 8 9.69 5.00 14.00 3.23 1.14 33 5.00 6.75 10.3 12.3 14.0

 71 WINTER 3 2.83 1.00 6.00 2.75 1.59 97 1.00 1.00 1.50 6.00 6.00

 72 FALL 57 34.8 4.62 138.84 26.8 3.55 77 6.89 15.1 27.8 46.3 89.3

 72 SPRING 57 23.2 2.14 78.77 18.3 2.43 79 4.01 10.8 16.0 31.7 61.4

 72 SUMMER 74 39.9 3.89 152.57 28.7 3.33 72 8.01 20.1 30.2 51.8 91.8

 72 WINTER 2 36.7 4.67 68.73 45.3 32.0 123 4.67 4.67 36.7 68.7 68.7

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 7

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .
 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 1 6.70 6.70 6.70 . . . 6.70 6.70 6.70 6.70 6.70

 65 SPRING 1 4.56 4.56 4.56 . . . 4.56 4.56 4.56 4.56 4.56

 65 SUMMER 1 10.7 10.7 10.65 . . . 10.7 10.7 10.7 10.7 10.7

 Aggregate Nutrient Ecoregion: IX 8

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 1 2.55 2.55 2.55 . . . 2.55 2.55 2.55 2.55 2.55

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 0 . . . . . . . . . . .

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 0 . . . . . . . . . . .

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .
 Aggregate Nutrient Ecoregion: IX 9

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Tric_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 1 16.0 16.0 16.00 . . . 16.0 16.0 16.0 16.0 16.0

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 1 8.00 8.00 8.00 . . . 8.00 8.00 8.00 8.00 8.00

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 1 1.70 1.70 1.70 . . . 1.70 1.70 1.70 1.70 1.70

 35 SPRING 1 2.20 2.20 2.20 . . . 2.20 2.20 2.20 2.20 2.20

 35 SUMMER 1 1.60 1.60 1.60 . . . 1.60 1.60 1.60 1.60 1.60

 35 WINTER 1 1.48 1.48 1.48 . . . 1.48 1.48 1.48 1.48 1.48

 37 FALL 2 14.5 9.70 19.20 6.72 4.75 46 9.70 9.70 14.5 19.2 19.2

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 2 17.9 14.4 21.45 4.99 3.53 28 14.4 14.4 17.9 21.5 21.5

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 7 8.55 1.25 16.00 5.30 2.00 62 1.25 3.13 9.65 12.0 16.0

 40 SPRING 6 6.08 1.25 17.45 6.38 2.60 105 1.25 1.25 3.41 9.68 17.5

 40 SUMMER 9 6.15 1.25 10.10 3.05 1.02 50 1.25 3.48 6.00 8.05 10.1

 40 WINTER 1 1.25 1.25 1.25 . . . 1.25 1.25 1.25 1.25 1.25

 45 FALL 3 4.65 2.53 6.68 2.08 1.20 45 2.53 2.53 4.74 6.68 6.68

 45 SPRING 3 3.90 2.40 6.60 2.34 1.35 60 2.40 2.40 2.70 6.60 6.60

 45 SUMMER 32 45.0 2.33 131.20 36.9 6.53 82 2.50 12.9 43.9 66.7 112

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 1 5.58 5.58 5.58 . . . 5.58 5.58 5.58 5.58 5.58

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 23 16.0 .000 50.00 13.3 2.77 83 1.25 6.50 15.0 23.0 42.8

 65 SPRING 23 9.05 .000 32.75 9.79 2.04 108 0.00 2.75 5.50 11.0 30.0

 65 SUMMER 24 24.9 2.00 134.00 33.4 6.82 134 2.50 6.00 12.5 27.8 107

 Aggregate Nutrient Ecoregion: IX 10

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter Chla_Tric_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 21 10.1 2.50 31.00 8.46 1.85 84 2.75 4.00 6.00 12.8 25.0

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 4 4.38 2.00 7.50 2.29 1.14 52 2.00 3.00 4.00 5.75 7.50

 71 SUMMER 4 10.4 2.00 18.00 6.92 3.46 67 2.00 5.00 10.8 15.8 18.0

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 57 35.8 5.18 134.98 27.1 3.59 76 7.59 14.7 28.6 49.8 93.2
 72 SPRING 57 23.7 1.94 81.31 19.7 2.61 83 2.54 11.3 15.8 30.2 64.4

 72 SUMMER 75 39.4 3.50 151.00 28.4 3.28 72 7.53 18.8 30.7 54.6 90.4

 72 WINTER 2 34.8 4.25 65.37 43.2 30.6 124 4.25 4.25 34.8 65.4 65.4

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 11

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter DIP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 65 SPRING 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 65 SUMMER 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00
 Aggregate Nutrient Ecoregion: IX 12

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter DIP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 1 1.00 1.00 1.00 . . . 1.00 1.00 1.00 1.00 1.00

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 0 . . . . . . . . . . .

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 0 . . . . . . . . . . .

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 13

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter DO_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 6 6.88 3.95 8.98 1.71 0.70 25 3.95 6.48 7.00 7.85 8.98

 29 SPRING 16 8.19 6.10 9.70 1.02 0.25 12 6.10 7.44 8.34 9.09 9.70

 29 SUMMER 38 7.11 4.06 9.40 1.27 0.21 18 4.95 6.20 6.93 7.95 9.35

 29 WINTER 13 10.5 8.55 12.70 1.24 0.34 12 8.55 9.80 10.5 11.1 12.7

 33 FALL 3 6.88 6.00 7.70 0.85 0.49 12 6.00 6.00 6.95 7.70 7.70

 33 SPRING 8 7.98 6.20 9.50 1.18 0.42 15 6.20 7.09 8.05 8.95 9.50

 33 SUMMER 10 6.07 1.80 8.90 2.22 0.70 37 1.80 5.90 6.21 7.43 8.90

 33 WINTER 5 9.38 8.40 9.93 0.60 0.27 6 8.40 9.30 9.45 9.80 9.93

 35 FALL 13 7.18 4.98 9.40 1.07 0.30 15 4.98 6.70 7.20 8.00 9.40

 35 SPRING 17 7.24 4.40 9.50 1.45 0.35 20 4.40 6.50 7.40 8.65 9.50

 35 SUMMER 38 6.39 2.60 9.30 1.58 0.26 25 2.70 6.10 6.63 7.40 8.60

 35 WINTER 25 9.15 5.90 11.05 1.32 0.26 14 6.40 8.80 9.50 10.0 10.6

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 2 8.30 7.00 9.60 1.84 1.30 22 7.00 7.00 8.30 9.60 9.60

 37 SUMMER 11 5.10 2.95 7.00 1.66 0.50 33 2.95 3.70 4.55 7.00 7.00

 37 WINTER 1 11.2 11.2 11.23 . . . 11.2 11.2 11.2 11.2 11.2

 40 FALL 12 7.41 2.10 12.10 2.77 0.80 37 2.10 5.58 7.53 9.43 12.1

 40 SPRING 7 7.87 4.80 10.50 2.04 0.77 26 4.80 5.50 8.60 9.00 10.5

 40 SUMMER 25 6.87 3.10 13.10 2.29 0.46 33 3.75 5.25 7.15 7.80 10.8

 40 WINTER 3 8.56 6.08 12.20 3.22 1.86 38 6.08 6.08 7.40 12.2 12.2

 45 FALL 68 8.00 4.25 10.20 1.04 0.13 13 6.40 7.45 8.06 8.66 9.45

 45 SPRING 73 9.20 6.60 11.30 0.87 0.10 9 7.55 8.70 9.20 9.75 10.3

 45 SUMMER 155 8.02 3.40 12.50 1.32 0.11 16 5.75 7.55 8.00 8.60 10.2
 45 WINTER 52 10.5 8.80 13.70 0.89 0.12 9 9.55 9.95 10.2 11.0 12.2

 64 FALL 1 9.70 9.70 9.70 . . . 9.70 9.70 9.70 9.70 9.70

 64 SPRING 1 11.0 11.0 10.95 . . . 11.0 11.0 11.0 11.0 11.0

 64 SUMMER 3 9.77 8.70 10.50 0.95 0.55 10 8.70 8.70 10.1 10.5 10.5

 64 WINTER 1 12.7 12.7 12.70 . . . 12.7 12.7 12.7 12.7 12.7

 65 FALL 34 6.99 3.20 9.15 1.55 0.27 22 3.93 6.80 7.23 7.80 8.90

 65 SPRING 31 8.43 6.60 10.80 1.08 0.19 13 6.68 7.35 8.53 9.23 10.3

 65 SUMMER 76 6.50 1.05 11.43 1.87 0.21 29 2.80 5.35 6.90 7.73 8.80

 Aggregate Nutrient Ecoregion: IX 14

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter DO_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 23 9.53 6.93 11.70 1.08 0.23 11 8.00 8.95 9.28 10.2 10.9

 71 FALL 53 7.33 1.20 12.80 1.93 0.26 26 4.10 6.35 7.45 8.28 10.6

 71 SPRING 51 9.55 5.90 13.70 1.33 0.19 14 6.65 9.00 9.35 10.3 11.2

 71 SUMMER 57 7.76 1.20 11.15 2.00 0.27 26 4.15 7.05 8.08 8.90 11.0

 71 WINTER 6 10.4 7.60 11.60 1.45 0.59 14 7.60 10.4 10.8 11.3 11.6

 72 FALL 12 7.85 6.00 9.40 1.09 0.31 14 6.00 6.85 8.00 8.60 9.40

 72 SPRING 8 9.21 8.60 9.60 0.33 0.12 4 8.60 9.00 9.35 9.40 9.60

 72 SUMMER 12 7.60 6.20 9.90 1.21 0.35 16 6.20 6.55 7.53 8.35 9.90

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 5 7.55 3.60 11.35 2.74 1.23 36 3.60 7.40 7.60 7.80 11.4

 74 SPRING 3 6.73 4.80 10.05 2.89 1.67 43 4.80 4.80 5.35 10.1 10.1

 74 SUMMER 5 6.07 3.90 8.80 1.92 0.86 32 3.90 4.95 5.60 7.10 8.80

 74 WINTER 1 10.8 10.8 10.75 . . . 10.8 10.8 10.8 10.8 10.8

 Aggregate Nutrient Ecoregion: IX 15

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter NO2_NO3_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 23 0.06 .010 0.30 0.07 0.02 118 0.01 0.01 0.04 0.09 0.18

 29 SPRING 51 0.16 .010 5.00 0.70 0.10 423 0.01 0.01 0.01 0.10 0.29

 29 SUMMER 51 0.12 .003 5.40 0.75 0.11 617 0.00 0.01 0.01 0.01 0.11

 29 WINTER 47 0.13 .003 0.70 0.14 0.02 109 0.03 0.04 0.10 0.16 0.53

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 2 0.33 .238 0.42 0.13 0.09 39 0.24 0.24 0.33 0.42 0.42

 33 SUMMER 4 0.02 .010 0.03 0.01 0.00 46 0.01 0.01 0.02 0.02 0.03

 33 WINTER 4 0.15 .010 0.43 0.19 0.10 126 0.01 0.03 0.08 0.28 0.43

 35 FALL 13 0.14 .010 0.51 0.13 0.04 98 0.01 0.04 0.14 0.17 0.51

 35 SPRING 14 0.10 .010 0.31 0.11 0.03 109 0.01 0.03 0.04 0.18 0.31

 35 SUMMER 22 0.02 .003 0.14 0.03 0.01 150 0.01 0.01 0.01 0.02 0.04

 35 WINTER 24 0.17 .005 0.98 0.23 0.05 136 0.01 0.04 0.07 0.19 0.65

 37 FALL 10 0.04 .010 0.20 0.06 0.02 139 0.01 0.01 0.01 0.06 0.20

 37 SPRING 11 0.06 .010 0.25 0.07 0.02 124 0.01 0.01 0.03 0.08 0.25

 37 SUMMER 11 0.02 .005 0.04 0.01 0.00 71 0.01 0.01 0.03 0.03 0.04
 37 WINTER 11 0.12 .025 0.30 0.11 0.03 90 0.03 0.03 0.10 0.20 0.30

 40 FALL 38 0.27 .003 1.40 0.33 0.05 123 0.00 0.06 0.18 0.34 1.29

 40 SPRING 29 0.61 .010 3.99 0.80 0.15 132 0.01 0.15 0.40 0.84 1.85

 40 SUMMER 80 0.18 .003 1.50 0.28 0.03 154 0.00 0.01 0.06 0.25 0.70

 40 WINTER 10 0.48 .025 2.23 0.64 0.20 135 0.03 0.13 0.30 0.45 2.23

 45 FALL 72 0.21 .003 6.60 0.78 0.09 371 0.00 0.01 0.06 0.16 0.57

 45 SPRING 81 0.22 .000 1.00 0.19 0.02 85 0.01 0.11 0.20 0.29 0.64

 45 SUMMER 153 0.11 .000 6.83 0.56 0.05 494 0.00 0.01 0.02 0.09 0.32

 45 WINTER 57 0.29 .030 0.95 0.21 0.03 71 0.03 0.13 0.26 0.39 0.63

 64 FALL 2 1.50 .635 2.37 1.23 0.87 82 0.64 0.64 1.50 2.37 2.37

 64 SPRING 2 0.99 .575 1.40 0.58 0.41 59 0.58 0.58 0.99 1.40 1.40

 64 SUMMER 1 0.51 .510 0.51 . . . 0.51 0.51 0.51 0.51 0.51

 64 WINTER 1 0.86 .860 0.86 . . . 0.86 0.86 0.86 0.86 0.86

 65 FALL 48 0.12 .000 1.23 0.26 0.04 225 0.00 0.00 0.01 0.08 0.79

 65 SPRING 44 0.20 .000 1.09 0.25 0.04 126 0.00 0.01 0.12 0.31 0.82

 65 SUMMER 95 0.09 .000 1.42 0.20 0.02 218 0.00 0.01 0.02 0.09 0.37

 Aggregate Nutrient Ecoregion: IX 16

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter NO2_NO3_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 26 0.44 .000 1.80 0.53 0.10 122 0.00 0.04 0.19 0.67 1.77

 71 FALL 62 0.07 .000 1.04 0.14 0.02 204 0.00 0.02 0.03 0.07 0.20

 71 SPRING 60 0.41 .001 2.33 0.40 0.05 97 0.03 0.19 0.31 0.53 1.02

 71 SUMMER 67 0.14 .001 2.29 0.36 0.04 256 0.00 0.01 0.03 0.07 0.80

 71 WINTER 5 0.55 .410 0.62 0.08 0.04 15 0.41 0.54 0.56 0.60 0.62

 72 FALL 82 0.10 .001 3.80 0.43 0.05 452 0.00 0.00 0.01 0.04 0.27

 72 SPRING 84 0.25 .001 4.80 0.67 0.07 268 0.00 0.01 0.06 0.22 1.14

 72 SUMMER 97 0.11 .001 3.15 0.44 0.05 399 0.00 0.00 0.00 0.01 1.40

 72 WINTER 10 0.38 .070 1.13 0.34 0.11 88 0.07 0.11 0.29 0.53 1.13

 74 FALL 5 0.09 .035 0.19 0.07 0.03 76 0.04 0.04 0.06 0.15 0.19

 74 SPRING 8 0.35 .030 1.52 0.50 0.18 142 0.03 0.06 0.14 0.43 1.52

 74 SUMMER 10 0.07 .020 0.29 0.09 0.03 136 0.02 0.02 0.02 0.06 0.29

 74 WINTER 1 0.45 .450 0.45 . . . 0.45 0.45 0.45 0.45 0.45

 Aggregate Nutrient Ecoregion: IX 17

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter SECCHI_m_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 6 0.93 .280 1.78 0.64 0.26 69 0.28 0.38 0.79 1.58 1.78

 29 SPRING 14 0.71 .102 1.57 0.40 0.11 55 0.10 0.49 0.63 0.91 1.57

 29 SUMMER 38 0.93 .126 2.40 0.58 0.09 62 0.15 0.48 0.82 1.22 2.03

 29 WINTER 11 0.87 .380 1.64 0.40 0.12 47 0.38 0.55 0.80 1.30 1.64

 33 FALL 4 0.89 .555 1.37 0.35 0.17 39 0.56 0.66 0.81 1.12 1.37

 33 SPRING 8 0.77 .350 1.73 0.46 0.16 59 0.35 0.48 0.58 1.00 1.73

 33 SUMMER 10 0.81 .390 1.50 0.32 0.10 40 0.39 0.55 0.76 1.00 1.50
 33 WINTER 5 0.93 .530 1.83 0.54 0.24 58 0.53 0.60 0.68 1.00 1.83

 35 FALL 11 1.02 .380 3.80 0.96 0.29 93 0.38 0.50 0.85 0.94 3.80

 35 SPRING 15 0.93 .320 2.85 0.64 0.17 69 0.32 0.52 0.68 1.20 2.85

 35 SUMMER 29 1.27 .350 4.00 0.88 0.16 69 0.38 0.70 1.17 1.48 3.80

 35 WINTER 14 0.86 .310 1.73 0.41 0.11 48 0.31 0.52 0.81 1.00 1.73

 37 FALL 2 0.20 .100 0.30 0.14 0.10 71 0.10 0.10 0.20 0.30 0.30

 37 SPRING 2 0.41 .127 0.69 0.39 0.28 97 0.13 0.13 0.41 0.69 0.69

 37 SUMMER 4 0.34 .125 0.60 0.24 0.12 72 0.13 0.13 0.31 0.54 0.60

 37 WINTER 1 0.38 .380 0.38 . . . 0.38 0.38 0.38 0.38 0.38

 40 FALL 45 0.64 .100 1.80 0.40 0.06 63 0.13 0.34 0.56 0.88 1.30

 40 SPRING 29 0.70 .152 1.90 0.53 0.10 76 0.20 0.30 0.55 0.83 1.85

 40 SUMMER 86 0.77 .100 2.20 0.46 0.05 59 0.18 0.38 0.76 1.10 1.50

 40 WINTER 8 1.25 .300 4.69 1.45 0.51 116 0.30 0.48 0.64 1.39 4.69

 45 FALL 52 1.63 .400 6.20 1.11 0.15 68 0.50 0.96 1.35 1.70 4.25

 45 SPRING 61 1.47 .300 4.10 0.90 0.12 61 0.50 0.75 1.20 2.00 3.20

 45 SUMMER 175 1.41 .225 6.25 0.91 0.07 64 0.50 0.80 1.20 1.61 3.25

 45 WINTER 42 1.42 .150 7.20 1.56 0.24 110 0.25 0.58 0.92 1.40 4.19

 64 FALL 4 0.97 .600 1.88 0.61 0.30 63 0.60 0.65 0.70 1.29 1.88

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 7 1.87 .400 6.15 1.95 0.74 105 0.40 0.60 1.30 1.80 6.15

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 62 5.79 .200 243.00 30.6 3.89 529 0.61 1.00 1.61 2.30 4.60

 65 SPRING 75 4.48 .220 217.00 24.9 2.87 556 0.36 0.80 1.33 2.10 4.27

 65 SUMMER 116 3.02 .200 187.00 17.3 1.60 571 0.40 0.75 1.18 1.66 4.40

 Aggregate Nutrient Ecoregion: IX 18

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter SECCHI_m_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 46 8.13 .250 307.00 45.1 6.64 554 0.46 0.91 1.26 1.98 3.96

 71 FALL 58 1.36 .200 3.66 0.77 0.10 56 0.50 0.76 1.10 1.83 2.83

 71 SPRING 57 1.58 .102 5.20 1.00 0.13 63 0.27 0.91 1.30 2.10 3.58

 71 SUMMER 64 1.45 .270 4.05 0.80 0.10 55 0.54 0.89 1.35 1.85 3.09

 71 WINTER 6 0.89 .300 1.12 0.33 0.13 37 0.30 0.70 1.05 1.10 1.12

 72 FALL 103 0.88 .100 3.10 0.61 0.06 70 0.25 0.46 0.70 1.12 2.13

 72 SPRING 101 0.88 .114 3.20 0.67 0.07 76 0.18 0.43 0.74 1.07 2.29

 72 SUMMER 115 0.92 .150 4.12 0.67 0.06 72 0.27 0.51 0.71 1.12 2.35

 72 WINTER 5 0.86 .457 2.21 0.76 0.34 89 0.46 0.48 0.52 0.61 2.21

 74 FALL 5 0.61 .165 1.15 0.42 0.19 68 0.17 0.25 0.61 0.89 1.15

 74 SPRING 7 0.43 .300 0.85 0.19 0.07 45 0.30 0.30 0.40 0.41 0.85

 74 SUMMER 7 0.50 .254 1.10 0.29 0.11 58 0.25 0.31 0.41 0.62 1.10

 74 WINTER 1 0.80 .800 0.80 . . . 0.80 0.80 0.80 0.80 0.80
 Aggregate Nutrient Ecoregion: IX 19

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TKN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 23 0.55 .050 2.03 0.37 0.08 67 0.30 0.40 0.50 0.55 0.96

 29 SPRING 59 0.61 .050 3.30 0.42 0.05 69 0.30 0.42 0.50 0.66 1.10

 29 SUMMER 59 0.66 .380 3.40 0.45 0.06 68 0.40 0.50 0.58 0.70 1.11

 29 WINTER 47 0.53 .050 1.80 0.25 0.04 48 0.30 0.40 0.50 0.60 0.80

 33 FALL 1 0.96 .960 0.96 . . . 0.96 0.96 0.96 0.96 0.96

 33 SPRING 4 0.77 .400 1.10 0.29 0.15 38 0.40 0.56 0.79 0.98 1.10

 33 SUMMER 8 1.15 .675 2.15 0.50 0.18 43 0.68 0.84 0.98 1.37 2.15

 33 WINTER 5 0.83 .400 1.18 0.29 0.13 35 0.40 0.72 0.87 0.98 1.18

 35 FALL 15 0.65 .300 1.03 0.24 0.06 38 0.30 0.40 0.62 0.91 1.03

 35 SPRING 15 0.64 .200 1.27 0.26 0.07 41 0.20 0.50 0.59 0.80 1.27

 35 SUMMER 29 0.69 .270 1.49 0.27 0.05 40 0.30 0.47 0.69 0.80 1.22

 35 WINTER 26 0.63 .250 1.18 0.23 0.05 37 0.30 0.45 0.65 0.78 0.89

 37 FALL 10 0.48 .200 0.70 0.16 0.05 34 0.20 0.40 0.48 0.60 0.70

 37 SPRING 10 0.78 .350 1.90 0.46 0.15 59 0.35 0.40 0.65 0.95 1.90

 37 SUMMER 2 0.45 .370 0.53 0.11 0.08 24 0.37 0.37 0.45 0.53 0.53

 37 WINTER 11 0.49 .050 1.00 0.30 0.09 60 0.05 0.30 0.40 0.77 1.00

 40 FALL 27 0.96 .355 4.00 0.68 0.13 71 0.40 0.60 0.82 1.10 1.62

 40 SPRING 30 0.85 .270 1.60 0.34 0.06 40 0.30 0.63 0.75 1.00 1.51

 40 SUMMER 73 0.84 .025 3.52 0.55 0.06 66 0.03 0.54 0.75 1.05 1.86

 40 WINTER 7 1.06 .025 2.30 0.88 0.33 83 0.03 0.05 1.06 2.06 2.30

 45 FALL 79 0.41 .025 1.20 0.23 0.03 56 0.10 0.24 0.39 0.55 0.86

 45 SPRING 86 0.39 .025 2.57 0.33 0.04 85 0.03 0.24 0.32 0.47 0.73

 45 SUMMER 200 0.53 .108 4.60 0.43 0.03 81 0.20 0.30 0.43 0.60 1.10

 45 WINTER 58 0.40 .025 1.25 0.25 0.03 61 0.10 0.25 0.34 0.46 0.97

 64 FALL 7 0.62 .400 1.44 0.37 0.14 59 0.40 0.40 0.53 0.60 1.44

 64 SPRING 2 0.37 .290 0.45 0.11 0.08 31 0.29 0.29 0.37 0.45 0.45

 64 SUMMER 8 0.83 .325 1.86 0.48 0.17 58 0.33 0.55 0.72 0.98 1.86

 64 WINTER 1 0.30 .300 0.30 . . . 0.30 0.30 0.30 0.30 0.30

 65 FALL 37 0.65 .020 4.90 0.81 0.13 125 0.15 0.32 0.41 0.64 2.14

 65 SPRING 42 0.60 .130 4.80 0.72 0.11 119 0.17 0.32 0.40 0.70 1.10

 65 SUMMER 92 0.57 .020 3.95 0.60 0.06 105 0.10 0.30 0.47 0.62 1.25

 Aggregate Nutrient Ecoregion: IX 20

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TKN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 28 0.80 .190 5.20 1.11 0.21 139 0.22 0.33 0.44 0.70 3.95

 71 FALL 44 0.68 .210 2.05 0.40 0.06 59 0.26 0.45 0.59 0.73 1.63

 71 SPRING 47 0.50 .215 1.54 0.23 0.03 46 0.26 0.36 0.45 0.60 0.93

 71 SUMMER 47 0.58 .200 1.75 0.32 0.05 55 0.24 0.37 0.49 0.75 1.12
 71 WINTER 1 0.33 .325 0.33 . . . 0.33 0.33 0.33 0.33 0.33

 72 FALL 65 1.03 .260 3.35 0.63 0.08 61 0.32 0.61 0.95 1.20 2.20

 72 SPRING 68 0.87 .210 2.11 0.39 0.05 44 0.32 0.61 0.80 1.13 1.52

 72 SUMMER 81 0.97 .283 2.05 0.42 0.05 44 0.35 0.71 0.88 1.25 1.80

 72 WINTER 11 0.92 .300 1.55 0.40 0.12 44 0.30 0.60 0.84 1.40 1.55

 74 FALL 1 0.27 .265 0.27 . . . 0.27 0.27 0.27 0.27 0.27

 74 SPRING 6 0.45 .280 0.66 0.16 0.07 35 0.28 0.29 0.45 0.61 0.66

 74 SUMMER 6 0.42 .190 0.63 0.16 0.07 38 0.19 0.33 0.42 0.57 0.63

 74 WINTER 1 0.42 .423 0.42 . . . 0.42 0.42 0.42 0.42 0.42

 Aggregate Nutrient Ecoregion: IX 21

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 4 1.34 .850 2.55 0.81 0.41 61 0.85 0.90 0.98 1.78 2.55

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 4 1.02 .380 1.34 0.44 0.22 43 0.38 0.74 1.18 1.30 1.34

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 22 0.65 .235 1.67 0.38 0.08 59 0.34 0.38 0.52 0.71 1.34

 65 SPRING 21 0.50 .290 1.14 0.22 0.05 44 0.30 0.34 0.43 0.59 0.93

 65 SUMMER 20 0.56 .240 1.50 0.31 0.07 56 0.26 0.35 0.49 0.63 1.35
 Aggregate Nutrient Ecoregion: IX 22

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 22 0.73 .195 4.32 0.86 0.18 118 0.23 0.35 0.46 0.68 1.33

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 0 . . . . . . . . . . .

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 0 . . . . . . . . . . .

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 23

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 24 36.1 10.0 105.00 26.6 5.44 74 10.0 18.1 27.5 50.0 90.0

 29 SPRING 59 40.6 2.50 350.00 53.0 6.91 131 2.50 20.0 30.0 50.0 140

 29 SUMMER 61 49.9 2.50 545.00 75.5 9.67 151 2.50 20.0 30.0 50.0 140

 29 WINTER 47 36.2 2.50 170.00 35.9 5.24 99 2.50 10.0 25.0 50.0 110

 33 FALL 4 400 10.0 820.00 334 167 84 10.0 170 385 630 820

 33 SPRING 8 313 10.0 1240.00 445 157 142 10.0 60.0 108 460 1240

 33 SUMMER 10 266 40.0 770.00 311 98.2 117 40.0 50.0 82.5 625 770

 33 WINTER 6 259 10.0 715.00 341 139 132 10.0 21.3 62.5 680 715

 35 FALL 15 92.5 7.50 295.00 98.1 25.3 106 7.50 30.0 40.0 160 295

 35 SPRING 18 76.0 8.00 245.00 68.4 16.1 90 8.00 35.0 45.0 90.0 245

 35 SUMMER 37 79.6 8.00 230.00 60.6 9.96 76 11.3 40.0 60.0 110 230

 35 WINTER 27 60.1 8.75 180.00 47.1 9.07 78 12.5 30.0 42.5 77.5 163

 37 FALL 12 66.0 2.50 295.00 80.4 23.2 122 2.50 20.0 40.0 77.5 295

 37 SPRING 11 39.1 10.0 80.00 23.1 6.97 59 10.0 20.0 35.0 60.0 80.0

 37 SUMMER 14 87.1 5.00 460.00 114 30.4 131 5.00 35.0 67.5 80.0 460

 37 WINTER 11 38.4 2.50 117.50 35.8 10.8 93 2.50 10.0 30.0 60.0 118

 40 FALL 50 117 2.50 875.00 139 19.7 120 10.0 45.0 80.0 160 255

 40 SPRING 35 84.9 10.0 310.00 62.2 10.5 73 10.0 40.0 70.0 113 190

 40 SUMMER 95 106 6.25 645.00 102 10.4 96 10.0 35.0 80.0 145 265

 40 WINTER 8 58.8 20.0 120.00 30.9 10.9 53 20.0 40.0 50.0 75.0 120

 45 FALL 86 50.1 5.00 270.00 49.3 5.31 98 5.00 20.0 36.3 60.0 170

 45 SPRING 85 50.2 5.00 145.00 33.2 3.60 66 10.0 30.0 40.0 60.0 125
 45 SUMMER 198 47.6 .000 300.00 48.5 3.45 102 5.00 20.0 35.0 60.0 120

 45 WINTER 58 56.0 5.00 260.00 51.6 6.78 92 5.00 25.0 40.0 60.0 165

 64 FALL 9 74.2 .000 235.00 69.8 23.3 94 0.00 40.0 50.0 95.0 235

 64 SPRING 2 97.5 55.0 140.00 60.1 42.5 62 55.0 55.0 97.5 140 140

 64 SUMMER 10 77.8 17.5 305.00 86.5 27.4 111 17.5 25.0 45.0 100 305

 64 WINTER 1 50.0 50.0 50.00 . . . 50.0 50.0 50.0 50.0 50.0

 65 FALL 73 57.3 .000 565.00 104 12.2 182 0.00 10.0 30.0 60.0 250

 65 SPRING 74 52.9 .000 930.00 110 12.8 208 3.75 10.0 30.0 57.5 140

 65 SUMMER 128 49.0 .000 490.00 58.7 5.19 120 1.50 13.1 33.8 65.0 143

 Aggregate Nutrient Ecoregion: IX 24

 Lakes and Reservoirs

 Descriptive Statistics by Decade and Season

 Parameter TP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 52 64.2 5.00 455.00 96.6 13.4 150 5.00 10.0 30.0 55.0 305

 71 FALL 61 54.6 2.50 702.50 91.1 11.7 167 2.50 20.0 40.0 62.5 130

 71 SPRING 60 42.6 1.50 300.00 49.8 6.43 117 4.25 13.1 30.0 50.0 141

 71 SUMMER 67 47.8 1.50 460.00 82.5 10.1 173 1.50 10.0 25.0 50.0 160

 71 WINTER 5 51.5 2.50 105.00 36.8 16.5 71 2.50 45.0 45.0 60.0 105

 72 FALL 81 119 9.00 1050.00 161 17.9 136 10.0 30.0 65.0 138 430

 72 SPRING 84 95.2 10.0 640.00 98.1 10.7 103 15.0 30.0 65.0 125 260

 72 SUMMER 97 149 8.00 1695.00 220 22.4 148 9.50 30.0 85.0 195 460

 72 WINTER 11 120 25.0 290.00 77.0 23.2 64 25.0 60.0 115 150 290

 74 FALL 5 131 30.0 405.00 156 69.6 119 30.0 55.0 60.0 105 405

 74 SPRING 8 118 16.3 260.00 73.4 26.0 62 16.3 70.0 113 153 260

 74 SUMMER 10 73.8 11.3 160.00 46.2 14.6 63 11.3 36.3 72.5 100 160

 74 WINTER 1 208 208 207.50 . . . 208 208 208 208 208
APPENDIX C

Quality Control/Quality Assurance Rules
Support for the Compilation and Analysis of National Nutrient Data

15 Nutrient Ecoregion/Waterbody Type Summary Chapters 

Prepared for:

Robert Cantilli

Environmental Protection Agency

OW/OST/HECD

Prepared by:

INDUS Corporation

1953 Gallows Road

Vienna, Virginia 22182

Contract Number: 68-C-99-226

Task Number: 04

Subtask Number: 4

August 8, 2000
ii

CONTENTS

1.0 BACKGROUND ........................................................ 1

1.1 Purpose .......................................................... 1

1.2 References ....................................................... 1

2.0 QA/QC PROCEDURES ................................................ 2

2.1 National Data Sets ............................................... 3

2.2 State Data ..................................................... 3

2.3 Laboratory Methods .............................................. 4

2.4 Waterbody Name ................................................ 4

2.5 Ecoregion Data ................................................. 5

3.0 STATISTICAL ANALYSIS REPORTS .................................... 5

3.1 Data Source Reports ............................................. 6

3.2 Remark Code Reports ............................................ 7

3.3 Median of Each Waterbody ........................................ 7

3.4 Descriptive Statistic Reports ........................................ 7

3.5 Regression Models ............................................... 8

4.0 TIME PERIOD ....................................................... 8

5.0 DATA SOURCES AND PARAMETERS FOR THE AGGREGATE NUTRIENT

ECOREGIONS ....................................................... 9

5.1 Lakes and Reservoirs ............................................ 9

5.1.1 Aggregate Nutrient Ecoregion 2 ............................... 9

5.1.2 Aggregate Nutrient Ecoregion 6 .............................. 10

5.1.3 Aggregate Nutrient Ecoregion 7 .............................. 10

5.1.4 Aggregate Nutrient Ecoregion 8 .............................. 11

5.1.5 Aggregate Nutrient Ecoregion 9 .............................. 12

5.1.6 Aggregate Nutrient Ecoregion 11 ............................. 12

5.1.7 Aggregate Nutrient Ecoregion 12 ............................. 13

5.1.8 Aggregate Nutrient Ecoregion 13 ............................. 13

5.2 Rivers and Streams .............................................. 14

5.2.1 Aggregate Nutrient Ecoregion 2 .............................. 14

5.2.2 Aggregate Nutrient Ecoregion 3 .............................. 15

5.2.3 Aggregate Nutrient Ecoregion 6 .............................. 16

5.2.4 Aggregate Nutrient Ecoregion 7 .............................. 16

5.2.5 Aggregate Nutrient Ecoregion 9 .............................. 17

5.2.6 Aggregate Nutrient Ecoregion 11 ............................. 18

5.2.7 Aggregate Nutrient Ecoregion 12 ............................. 19

5.2.8 Aggregate Nutrient Ecoregion 14 ............................. 20
iii

APPENDIX A Process Used to QA/QA the Legacy STORET Nutrient Data Set

APPENDIX B Process for Adding Aggregate Nutrient Ecoregions and Level III

Ecoregions

APPENDIX C Glossary
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

1

1.0 BACKGROUND 

The Nutrient Criteria Program has initiated development of a national Nutrient Criteria Database

application that will be used to store and analyze nutrient data. The ultimate use of these data will

be to derive ecoregion- and waterbody-specific nutrient criteria ranges. EPA converted STOrage

and RETrieval (STORET) legacy data, National Stream Quality Accounting Network

(NASQAN) data, National Water-Quality Assessment (NAWQA) data, and other relevant

nutrient data from universities and States/Tribes into the database. The data imported into the

Nutrient Criteria Database will be used to develop national nutrient criteria ranges. 

1.1 Purpose

The purpose of this deliverable is to provide EPA with information regarding the data used to

create the statistical reports which will be used to derive ecoregion- and waterbody-specific

nutrient criteria ranges for Level III ecoregions. There are fourteen aggregate nutrient

ecoregions. Each aggregate nutrient ecoregion is divided into smaller ecoregions referred to as

Level III ecoregions. EPA will determine criteria ranges for the waterbody types and Level III

ecoregions within the following aggregate nutrient ecoregions:

• Lakes and Reservoirs

- Aggregate Nutrient ecoregions: 2, 6, 7, 8, 9, 11, 12, 13

• Rivers and Streams 

- Aggregate Nutrient ecoregions: 2, 3, 6, 7, 9, 11, 12, 14

1.2 References

This section lists documents that contain baselines, standards, guidelines, policies, and references

that apply to the data analysis. Listed editions were valid at the time of publication. All

documents are subject to revision, but these specific editions govern the concepts described in this

document. 

Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs (Draft). EPA, Office of

Water, EPA 822-D-99-001, April 1999.

Nutrient Criteria Technical Guidance Manual: Rivers and Streams (Draft). EPA, Office of

Water, EPA 822-D-99-003, September 1999.

Guidance for Data Quality Assessment: Practical Methods for Data Analysis. EPA, Office of

Research and Development, EPA QA/G-9, January 1998.
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

2

2.0 QA/QC PROCEDURES

In order to develop nutrient criteria, EPA needed to obtain nutrient data from the states. EPA

requested nutrient data from the states and forwarded the data sets to INDUS via e-mail and/or

US mail. In addition, EPA tasked INDUS to convert data from three national data sets. EPA

provided INDUS with a Legacy STORET extraction to convert into the database. The United

States Geologic Survey (USGS) sent INDUS a CD-ROM with NASQAN data to convert. 

INDUS downloaded NAWQA files from the USGS Web site to convert the data. In total,

INDUS converted and imported the following national and state data sets into the Nutrient

Criteria Database:

• Legacy STORET

• NAWQA

• NASQAN

• Region 1

• Region 2 - Lake Champlain Monitoring Project

• Region 2 - NYSDEC Finger Lakes Monitoring Program

• Region 2 - NY Citizens Lake Assessment Program

• Region 2 - Lake Classification and Inventory Survey

• Region 2 - NYCDEP (1990-1998)

• Region 2 - NYCDEP (Storm Event data)

• Region 2 - New Jersey Nutrient Data ( Tidal Waters)

• Region 5

• Region 3 

• Region 3 - Nitrite Data

• Region 3 - Choptank River files

• Region 4 - Tennessee Valley Authority

• Region 7 - Central Plains Center for BioAssessment (CPCB)

• Region 7 - REMAP

• Region 2 - Delaware River Basin Commission (1990-1998)

• Region 3 - PA Lake Data

• Region 3 - University of Delaware

• Region 10 

• University of Auburn

As part of the conversion process, INDUS performed a number of Quality Assurance/Quality

Control (QA/QC) steps to ensure that the data was properly converted into the Nutrient Criteria

Database. Section 2 explains the steps performed by INDUS to convert the data.
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

3

2.1 National Data Sets

INDUS converted three national data sets into the Nutrient Criteria Database: Legacy STORET

data, NASQAN data, and NAWQA data. A previous EPA contractor performed the extraction of

Legacy STORET data and documented the QA/QC procedures used on the data. This

documentation is included in Appendix A. INDUS performed minimal QA/QC on the Legacy

STORET data set because the previous contractor completed the steps outlined in Appendix A. 

INDUS and EPA also agreed to convert the NAWQA and NASQAN data sets with minimal

QA/QC on the assumption that the source agency, the USGS, QA/QC'd the data. 

For each of the three national data sets, INDUS ran queries to determine if 1) samples existed

without results and 2) if stations existed without samples. Per Task Order Project Officer

(TOPO) direction, these records were deleted from the system. For analysis purposes, EPA

determined that there was no need to keep station records with no samples and sample records

with no results. INDUS also confirmed that each data set contained no duplicate records. 

In addition, INDUS deleted all composite results from the Legacy STORET data. Per TOPO

direction, it was decided that composite sample results would not be used in the statistical

analysis.

2.2 State Data

Each state data set was delivered in a unique format. Many of the data sets were delivered to

INDUS without corresponding documentation. INDUS analyzed each state data set in order to

determine which parameters should be converted for analysis. INDUS obtained a master

parameter table from EPA and converted the parameters in the state data sets according to those

that were present in the EPA parameter table. INDUS converted all of the data elements in the

state data sets that mapped directly to the Nutrient Criteria Database; data elements that did not

map to the Nutrient Criteria Database were not converted. In some cases, state data elements

that did not directly map into the Oracle database were inserted into a comment field within the

database. Also, INDUS maintained an internal record of which state data elements were inserted

into the comment field. 

As part of the data clean-up efforts, INDUS determined whether or not there were any duplicate

records in the state data sets and deleted the duplicate records. INDUS checked the waterbody,

station, and sample entities for duplicate records. In addition, INDUS deleted station records

with no samples and sample records with no results. INDUS also deleted waterbody records that

were not associated with a station. In each case, INDUS maintained an internal record of how

many records were deleted. 

If INDUS encountered referential integrity errors, such as samples that referred to stations that

did not exist, or if INDUS was unsure of whether a record was a duplicate, INDUS contacted the

agency directly via e-mail or phone to resolve any issues that arose. INDUS saved an electronic
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

4

copy of each e-mail correspondence with the states to ensure that a record of the decision was

maintained. INDUS also contacted each agency to determine which laboratory methods were

used for each parameter.

Finally, INDUS examined the remark codes of each result record in the state data sets. INDUS

mapped the remark codes to the STORET remark codes listed in Table 2 of Appendix A. If any

of the state result records were associated with remark codes marked as "Delete" in Table 2 of

Appendix A, the result records were not converted into the database.

2.3 Laboratory Methods 

Many of the state data sets did not contain laboratory method information. In addition, laboratory

method information was not available for the three national data sets. In order to determine

missing laboratory method information, EPA tasked another contractor to contact the data

owners to obtain the laboratory method. In some cases, the data owners responded and the

laboratory methods were added to the database. 

2.4 Waterbody Name and Class Information

A large percentage of the data did not have waterbody-specific information. The only waterbody

information contained in the three national data sets was the waterbody name, which was

embedded in the station 'location description' field. Most of the state data sets contained

waterbody name information; however, much of the data was duplicated throughout the data sets. 

Therefore, the waterbody information was cleaned manually. For the three national data sets, the

'location description' field was extracted from the station table and moved to a temporary table. 

The 'location description' field was sorted alphabetically. Unique waterbodies were grouped

together based on name similarity and whether or not the waterbodies fell within the same county,

state, and waterbody type. Finally, the 'location description' field was edited to include only

waterbody name information, not descriptive information. For example, 110 MILE CREEK AT

POMONA DAM OUTFLOW, KS PO-2 was edited to 110 MILE CREEK. Also, if 100 MILE

CREEK was listed ten times in New York, but in four different counties, four 100 MILE CREEK

waterbody records were created.

Similar steps were taken to eliminate duplicate waterbody records in the state data sets. If a

number of records had similar waterbody names and fell within the same state, county, and

waterbody type, the records were grouped to create a unique waterbody record.

Most of the waterbody data did not contain depth, surface area, and volume measurements. EPA

needed this information to classify waterbody types. EPA attempted to obtain waterbody class 
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

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information from the states. EPA sent waterbody files to the regional coordinators and requested

that certain class information be completed by each state. The state response was poor; therefore,

EPA was not able to perform statistical analysis for the waterbody types by class.

2.5 Ecoregion Data

Aggregate nutrient ecoregions and Level III ecoregions were added to the database using the

station latitude and longitude coordinates. If a station was lacking latitude and longitude

coordinates or county information, the data were not included in the statistical analysis. Appendix

B lists the steps taken to add the two ecoregion types (aggregate and Level III) to the Nutrient

Criteria Database. The ecoregion names were pulled from aggregate nutrient ecoregion and Level

III ecoregion Geographical Information System (GIS) coverages. In summary, the station latitude

and longitude coordinates were used to determine the ecoregion under the following

circumstances:

• The latitude and longitude coordinates fell within the county/state listed in the station

table.

• The county data was missing.

The county centroid was used to determine the ecoregions under the following circumstances:

• The latitude and longitude coordinates were missing, but the state/county information was

available.

• The latitude and longitude coordinates fell outside the county/state listed in the station

table. The county information was assumed to be correct; therefore, the county centroid

was used.

If the latitude and longitude coordinates fell outside the continental US county coverage file 

(i.e., the point fell in the ocean or Mexico/Canada), the nearest ecoregion was assigned to the

station.

3.0 STATISTICAL ANALYSIS REPORTS

Aggregate nutrient ecoregion tables were created by extracting all observations for a specific

aggregate nutrient ecoregion from the nutrient criteria database. Then, the data were reduced to

create tables containing only the yearly median values. To create these tables, the median value

for each waterbody was calculated using all observations for each waterbody by Level III

ecoregion, year, and season. Tables of decade median values were created from the yearly

median tables by calculating the median for each waterbody by Level III ecoregion by decade and

season.
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The Data Source and the Remark Code reports were created using all observations (all reported

values). All the other reports were created from either the yearly median tables or the decade

median tables. In other words, the descriptive statistics and regressions were run using the

median values for each waterbody and not the individual reported values.

Statistical analyses were performed under the assumption that this data set is a random sample. If

this assumption cannot be verified, the observations may or may not be valid. Values below the

1st and 99th percentile were removed from the Legacy STORET database prior to the creation of

the national database. Also, data were treated according the Legacy STORET remark codes in

Appendix A. 

The following contains a list of each report and the purpose for creating each report: 

• Data Source Created to provide a count of the amount of data and to identify the

source(s).

• Remark Codes Created to provide a description of the data. 

• Median of Each Waterbody by Year This was an intermediate step performed to obtain a

median value for each lake to be used in the yearly descriptive statistics reports and the

regression models. 

• Median of Each Waterbody by Decade This was an intermediate step performed to obtain

a median value for each lake to be used in the decade descriptive statistics.

• Descriptive Statistics Created to provide EPA with the desired statistics for setting criteria

levels.

• Regression Models Created to examine the relationships between biological and nutrient

variables. 

Note: Separate reports were created for each season.

3.1 Data Source Reports

Data source reports were presented in the following formats:

• The number and percentage of data from each data source were summarized in tables for

each aggregate nutrient ecoregion by season and waterbody type.

• The number and percentage of data from each data source were summarized in tables for

each Level III ecoregion by season and waterbody type.

The 'Frequency' represents the number of data values from a specific data source for each

parameter by data source. The 'Row Pct' represents the percentage of data from a specific data

source for each parameter. 
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3.2 Remark Code Reports

Remark code reports were presented in the following formats:

• The number and percentage of data associated with a particular remark code for each

parameter were summarized in tables by Level III ecoregion by decade and season.

• The number and percentage of data associated with a particular remark code for each

parameter were summarized in tables by Level III ecoregion by year and season.

The 'Frequency' represents the number of data values corresponding to the remark code in the

column. The 'Row Pct' represents the percentage of data that was associated with the remark

code in that row.

In the database, remark codes that were entered by the states were mapped to Legacy STORET

remark codes. Prior to the analysis, the data were treated according to these remark codes. For

example, if the remark code was 'K,' then the reported value was divided by two. Appendix A

contains a complete list of Legacy STORET remark codes.

Note: For the reports, a remark code of 'Z' indicates that no remark codes were recorded. It does

not correspond to Legacy STORET code 'Z.'

3.3 Median of Each Waterbody

To reduce the data and to ensure heavily sampled waterbodies or years were not over represented

in the analysis, median value tables (described above) were created. The yearly median tables and

decade median tables were delivered to the EPA in electronic format as csv (comma separated

value or comma delimited) files.

3.4 Descriptive Statistic Reports

The number of waterbodies, median, mean, minimum, maximum, 5th, 25th , 75th , 95th

percentiles, standard deviation, standard error, and coefficient of variation were calculated. The

tables (described above) containing the decade median values for each waterbody for each

parameter were used to create descriptive statistics reports for:

• Level III ecoregions by decade and season

• Aggregate nutrient ecoregions by decade and season

In addition, the tables containing the yearly median values for each waterbody for each parameter

were used to create descriptive statistics reports for:

• Level III ecoregions by year and season
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3.5 Regression Models

Simple linear regressions using the least squares method were performed to examine the

relationships between biological and nutrient variables in lakes and reservoirs, and rivers and

streams. Regressions were performed using the yearly median tables. Chlorophyll(s) in

micrograms per liter (ug/L), secchi in meters (m), dissolved oxygen in milligrams per liter (mg/L),

turbidity, and pH were the biological variables in these models. When there was little or no data

for chlorophyll, then pH or dissolved oxygen was substituted for chlorophyll. Secchi data were

used in the lake and reservoir models, and turbidity data were used in the river and stream models. 

The nutrient variables in these models include: total phosphorus in ug/L, total nitrogen in mg/L,

total kjeldahl nitrogen in mg/L, and nitrate and nitrite in mg/L. Regressions were also run for

total nitrogen and total phosphorus for ecoregions where both these variables were measured. 

Note: At the time of creation of this document only regressions for aggregate nutrient ecoregion 7

for lakes and reservoirs were delivered to the EPA. Regressions for the remaining aggregate

nutrient ecoregions will be delivered in August 2000.

4.0 TIME PERIOD

Data collected from January 1990 to December 1999 were used in the statistical analysis reports. 

To capture seasonal differences, the data were classified as follows:

• Aggregate nutrient ecoregions: 6, 7, and 8

 - Spring: April to May 

 - Summer: June to August 

 - Fall: September to October

 - Winter: November to March

• Aggregate nutrient ecoregions: 1, 2, 9, 10, 11, 12, and 13

 - Spring: March to May

 - Summer: June to August 

 - Fall: September to November

 - Winter: December to February 
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5.0 DATA SOURCES AND PARAMETERS FOR THE AGGREGATE NUTRIENT

ECOREGIONS

This section provides information for the nutrient aggregate ecoregions that were analyzed by

waterbody type. Each section lists the data sources for the aggregate nutrient ecoregion

including: 1) the data sources, 2) the parameters included in the analysis, and 3) the Level III

ecoregions within the aggregate nutrient ecoregions.

Note: For analysis purposes, the following parameters were combined to form Phosphorous,

Dissolved Inorganic (DIP):

Phosphorus, Dissolved Inorganic (DIP) 

Phosphorus, Dissolved (DP) 

Phosphorus, Dissolved Reactive (DRP)

Orthophosphate, dissolved, mg/L as P 

Orthophosphate (OPO4_PO4)

5.1 Lakes and Reservoirs

5.1.1 Aggregate Nutrient Ecoregion 2

Data Sources:

Legacy STORET

EPA Region 10

Parameter:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, Total Reactive (ug/L)

SECCHI (m)

pH
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Level III ecoregions:

1, 2, 4, 5, 9, 11, 15, 16, 17, 19, 21, 23, 41, 77, 78

5.1.2 Aggregate Nutrient Ecoregion 6

Data Sources:

Legacy STORET

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

46, 47, 48, 54, 55, 57

5.1.3 Aggregate Nutrient Ecoregion 7

Data Sources:

LCMPD

Legacy STORET

NYCDEP

EPA Region 1

Parameters:

Chlorophyll A, Fluorometric Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)
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Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

51, 52, 53, 56, 60, 61, 83

5.1.4 Aggregate Nutrient Ecoregion 8

Data Sources:

LCMPD

Legacy STORET

NYCDEP

NYCDEC

EPA Region 1

EPA Region 3

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B (ug/L)

Chlorophyll C (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

49, 50, 58, 62, 82
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5.1.5 Aggregate Nutrient Ecoregion 9

Data Sources:

Auburn University

Legacy STORET

EPA Region 4

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Pheophytin (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

29, 33, 35, 37, 40, 45, 64, 65, 71, 72, 74

5.1.6 Aggregate Nutrient Ecoregion 11

Data Sources:

Auburn University

Legacy STORET

NYSDEC

EPA Region 3

EPA Region 4

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Pheophytin (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)
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Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

36, 38, 39, 66, 67, 68, 69, 70

5.1.7 Aggregate Nutrient Ecoregion 12

Data Sources:

Legacy STORET

Parameters:

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

75

5.1.8 Aggregate Nutrient Ecoregion 13

Data Sources:

Legacy STORET
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Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

76

5.2 Rivers and Streams

5.2.1 Aggregate Nutrient Ecoregion 2

Data Sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 10

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) Reactive (ug/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)
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Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

1, 2, 4, 5, 8, 9, 11, 15, 16, 17, 19, 21, 23, 41, 77, 78

5.2.2 Aggregate Nutrient Ecoregion 3

Data Sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 10

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

6, 10, 12, 13, 14, 18, 20, 22, 24, 79, 80, 81
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5.2.3 Aggregate Nutrient Ecoregion 6

Data Sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 5

EPA Region 7

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Organic, Phosphorus (ug/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

46, 47, 48, 54, 55, 57

5.2.4 Aggregate Nutrient Ecoregion 7 

Data Sources:

LCMPD

Legacy STORET

NASQAN

NAWQA

NYCDEP
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Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Organic, Phosphorus (ug/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

51, 52, 53, 56, 60, 61, 83

5.2.5 Aggregate Nutrient Ecoregion 9

Data Sources:

Auburn University

Legacy STORET

NASQAN

NAWQA

EPA Region 3

EPA Region 5

EPA Region 7

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)
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Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll B, Phytoplankton, Spectrophotometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Organic, Phosphorus (ug/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

29, 33, 35, 37, 40, 45, 64, 65, 71, 72, 74

5.2.6 Aggregate Nutrient Ecoregion 11

Data Sources:

Auburn University

Legacy STORET

NASQAN

NAWQA

EPA Region 3

EPA Region 5

EPA Region 7

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Organic, Phosphorus (ug/L)
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Phosphorus, Orthophosphate, Total as P (ug/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

36, 38, 39, 66, 67, 68, 69, 70

5.2.7 Aggregate Nutrient Ecoregion 12

Data Sources:

Legacy STORET

NASQAN

NAWQA

Parameters:

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, Spectrophotometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (NTU)

Level III ecoregions:

75
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5.2.8 Aggregate Nutrient Ecoregion 14

Data Sources:

Legacy STORET

NASQAN

NAWQA

NYCDEP

EPA Region 1

EPA Region 3

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Nitrogen, Total (TN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

59, 63, 84
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A-1

APPENDIX A

Process Used to QA/QA the Legacy STORET Nutrient Data Set
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A-2

1. STORET water quality parameters and Station and Sample data items were retrieved from

USEPA's mainframe computer. Table 1 lists all retrieved parameters and data items.

TABLE 1: PARAMETERS AND DATA ITEMS RETRIEVED FROM STORET

Parameters Retrieved

(STORET Parameter Code)

Station Data Items

Included

(STORET Item Name)

Sample Data Items Included

(STORET Item Name)

TN - mg/l (600)

TKN - mg/l (625)

Total Ammonia (NH3+NH4) - mg/l (610)

Total NO2+NO3 - mg/l (630)

Total Nitrite - mg/l (615)

Total Nitrate - mg/l (620)

Organic N - mg/L (605)

TP - mg/l (665)

Chlor a - ug/L (spectrophotometric method,

32211) 

Chlor a - ug/L (fluorometric method

corrected, 32209)

Chlor a - ug/L (trichromatic method

corrected, 32210)

Secchi Transp. - inches (77)

Secchi Transp. - meters (78)

+Turbidity JCUs (70)

+Turbidity FTUs (76)

+Turbidity NTUs field (82078)

+Turbidity NTUs lab (82079)

+DO - mg/L (300)

+Water Temperature (degrees C, 10/degrees

F, 11)

Station Type (TYPE)

Agency Code (AGENCY)

Station No. (STATION)

Latitude - std. decimal degrees

(LATSTD)

Longitude - std. decimal degrees 

(LONGSTD)

Station Location (LOCNAME)

County Name (CONAME)

State Name (STNAME)

Ecoregion Name - Level III

(ECONAME)

Ecoregion Code -Level III

(ECOREG)

Station Elevation (ELEV)

Hydrologic Unit Code

(CATUNIT)

RF1 Segment and Mile

(RCHMIL)

RF1ON/OFF tag (ONOFF)

Sample Date (DATE)

Sample Time (TIME)

Sample Depth (DEPTH)

Composite Sample Code 

(SAMPMETH)

+ If data record available at a station included data only for this or other such marked parameters, data record was deleted

from data set.

The following set of retrieval rules were applied to the retrieval process:

• Data were retrieved for waterbodies specified only as 'lake', 'stream', 'reservoir', or 'estuary'

under "Station Type" parameter. Any stations specified as 'well,' 'spring,' or 'outfall' were

eliminated from the retrieved data set.

• Data were retrieved for station types described as 'ambient' (e.g., no pipe or facility

discharge data) under the "Station Type" parameter.

• Data were retrieved that were designated as 'water' samples only. This includes 'bottom'

and 'vertically integrated' water samples.
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• Data were retrieved that were designated as either 'grab' samples and 'composite' samples

(mean result only).

• No limits were specified for sample depths.

• Data were retrieved for all fifty states, Puerto Rico, and the District of Columbia.

• The time period specified for data retrieval was January 1990 to September 1998.

• No data marked as "Retired Data" (i.e., data from a generally unknown source) were

retrieved.

• Data marked as "National Urban Runoff data" (i.e., data associated with sampling

conducted after storm events to assess nonpoint source pollutants) were included in the

retrieval. Such data are part of STORET's 'Archived' data. 

• Intensive survey data (i.e., data collected as part of specific studies) were retrieved.

2. Any values falling below the 1st percentile and any values falling above the 99th percentile

were transformed into 'missing' values (i.e., values were effectively removed from the data

set, but were not permanently eliminated).

3. Based on the STORET 'Remark Code' associated with each retrieved data point, the

following rules were applied (Table 2): 

TABLE 2: STORET REMARK CODE RULES

STORET Remark Code Keep or Delete Data Point

blank - Data not remarked. Keep

A - Value reported is the mean of two or more

determinations.

Keep

B - Results based upon colony counts outside the acceptable

ranges.

Delete

C - Calculated. Value stored was not measured directly, but

was calculated from other data available.

Keep

D - Field measurement. Keep
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E - Extra sample taken in compositing process. Delete

F - In the case of species, F indicates female sex. Delete

G - Value reported is the maximum of two or more

determinations.

Delete

H - Value based on field kit determination; results may not

be accurate.

Delete

I - The value reported is less than the practical

quantification limit and greater than or equal to the method

detection limit.

Keep, but used one-half the reported value as the new value.

J - Estimated. Value shown is not a result of analytical

measurement.

Delete

K - Off-scale low. Actual value not known, but known to be

less than value shown.

Keep, but used one-half the reported value as the new value.

L - Off-scale high. Actual value not known, but known to

be greater than value shown.

Keep

M - Presence of material verified, but not quantified. 

Indicates a positive detection, at a level too low to permit

accurate quantification.

Keep, but used one half the reported value as the new value.

N - Presumptive evidence of presence of material. Delete

O - Sample for, but analysis lost. Accompanying value is

not meaningful for analysis.

Delete

P - Too numerous to count. Delete

Q - Sample held beyond normal holding time. Delete

R - Significant rain in the past 48 hours. Delete

S - Laboratory test. Keep

T - Value reported is less than the criteria of detection. Keep, but replaced reported value with 0.
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U - Material was analyzed for, but not detected. Value

stored is the limit of detection for the process in use. 

Keep, but replaced reported value with 0.

V - Indicates the analyte was detected in both the sample

and associated method blank.

Delete

W - Value observed is less than the lowest value reportable

under remark "T."

Keep, but replaced reported value with 0.

X - Value is quasi vertically-integrated sample. No data point with this remark code in data set.

Y - Laboratory analysis from unpreserved sample. Data

may not be accurate.

Delete

Z - Too many colonies were present to count. Delete

If a parameter (excluding water temperature) value was less than or equal to zero and no remark code was present, the value

was transformed into a missing value.

Rationale - Parameter concentrations should never be zero without a proper explanation. A method detection limit should

at least be listed.

4. Station records were eliminated from the data set if any of the following descriptors were

present within the "Station Type" parameter:

< MONITR - Source monitoring site, which monitors a known problem or

to detect a specific problem.

< HAZARD - Site of hazardous or toxic wastes or substances.

< ANPOOL - Anchialine pool, underground pools with subsurface

connections to watertable and ocean.

< DOWN - Downstream (i.e., within a potentially polluted area) from a

facility which has a potential to pollute.

< IMPDMT - Impoundment. Includes waste pits, treatment lagoons, and

settling and evaporation ponds.

< STMSWR - Storm water sewer.

< LNDFL - Landfill.

< CMBMI - Combined municipal and industrial facilities.

< CMBSRC - Combined source (intake and outfall).

Rationale - these descriptors potentially indicate a station location that at which an

ambient water sample would not be obtained (i.e., such sampling locations are potentially 
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

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biased) or the sample location is not located within one of the designated water body types (i.e,

ANPOOL). 

5. Station records were eliminated from data set if the station location did not fall within any

established cataloging unit boundaries based on their latitude and longitude.

6. Using nutrient ecoregion GIS coverage provided by USEPA, all station locations with

latitude and longitude coordinates were tagged with a nutrient ecoregion identifier

(nutrient region identifiers are values 1 - 14) and the associated nutrient ecoregion name. 

Because no nutrient ecoregions exist for Alaska, Hawaii, and Puerto Rico, stations located

in these states were tagged with "dummy" nutrient ecoregion numbers (20 = Alaska, 21 =

Hawaii, 22 = Puerto Rico).

7. Using information provided by TVA, 59 station locations that were marked as 'stream'

locations under the "Station Type" parameter were changed to 'reservoir' locations. 

8. The nutrient data retrieved from STORET were assessed for the presence of duplicate

data records. The duplicate data identification process consisted of three steps: 1)

identification of records that matched exactly in terms of each variable retrieved; 2)

identification of records that matched exactly in terms of each variable retrieved except for

their station identification numbers; and 3) identification of records that matched exactly in

terms of each variable retrieved except for their collecting agency codes. The data

duplication assessment procedures were conducted using SAS programs. 

Prior to initiating the data duplication assessment process, the STORET nutrient data set

contained:

41,210 station records

924,420 sample records

• Identification of exactly matching records

All data records were sorted to identify those records that matched exactly. For

two records to match exactly, all variables retrieved had to be the same. For

example, they had to have the same water quality parameters, parameter results

and associated remark codes, and have the same station data item and sample data

item information. Exactly matching records were considered to be exact

duplicates, and one duplicate record of each identified matching set were

eliminated from the nutrient data set. A total of 924 sample records identified as

duplicates by this process were eliminated from the data set. 

• Identification of matching records with the exception of station identification

number

All data records were sorted to identify those records that matched exactly except

for their station identification number (i.e., they had the same water quality
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

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parameters, parameter results and associated remark codes, and the same station

and sample data item information with the exception of station identification

number). Although the station identification numbers were different, the latitude

and longitude for the stations were the same indicating a duplication of station data

due to the existence of two station identification numbers for the same station. For

each set of matching records, one of the station identification numbers was

randomly selected and its associated data were eliminated from the data set. A

total of 686 sample records were eliminated from the data set through this process. 

• Identification of matching records with the exception of collecting agency codes

All data records were sorted to identify those records that matched exactly except

for their collecting agency codes (i.e., they had the same water quality parameters,

parameter results and associated remark codes, and the same station and sample

data item information with the exception of agency code). The presence of two

matching data records each with a different agency code attached to it suggested

that one agency had utilized data collected by the other agency and had entered the

data into STORET without realizing that it already had been placed in STORET

by the other agency. No matching records with greater than two different agency

codes were identified. For determining which record to delete from the data set,

the following rules were developed: 

< If one of the matching records had a USGS agency code, the USGS

record was retained and the other record was deleted. 

< Higher level agency monitoring program data were retained. For

example, federal program data (indicated by a "1" at the beginning

of the STORET agency code) were retained against state (indicated

by a "2") and local (indicated by values higher than 2) program

data. 

< If two matching records had the same level agency code, the record

from the agency with the greater number of overall observations

(potentially indicating the data set as the source data set) was

retained.

A total of 2,915 sample records were eliminated through this process. 

As a result of the duplicate data identification process, a total of 4,525 sample records and

36 individual station records were removed from the STORET nutrient data set. The

resulting nutrient data set contains the following:

41,174 station records

919,895 sample records
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APPENDIX B

Process for Adding Aggregate Nutrient Ecoregions and Level III Ecoregions
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Steps for assigning Level III ecoregions and aggregate nutrient ecoregion codes and names to the

Nutrient Criteria Database (performed using ESRI's ARCView v 3.2 and its GeoProcessing

Wizard). This process is performed twice; once for the Level III ecoregions and once for the

aggregate nutrient ecoregions:

- Add the station .dbf data table, with latitude and longitude data, to project by 'Add

Event Theme'

- Convert to the shapefile format

- Create 'stcojoin' field, populate the 'stcojoin' field with the following formula:

'County.LCase+State.LCase'

- Add field 'stco_flag' to the station shapefile

- Spatially join the station data with the county shapefile (cntys_jned.shp)

- Select 'stcojoin' (station shapefile) field = 'stco_join2' (county shapefile) field 

- Calculate stco_flag = 0 for selected features

- Step through all blank stco_flag records, assign the appropriate stco_flags, see list

on the following page

- Select all stco_flags = 4 or 7, switch selection

- Calculate ctyfips (station) to cntyfips (county)

- Stop editing and save edits, remove all joins

- Add in 2 new fields 'x-coord1' and 'y-coord1' into station table

- Select all stco_flags = 1, 2, and 6

- Link county coverage with station coverage

- Populate 'x-coord1' and 'y-coord1' with 'x-coord' and 'y-coord' from county

coverage

- Select all stco_flags = 1, 2, and 6, export to new .dbf file

- Add new .dbf file as event theme

- Convert to shapefile format

- Add the following fields to both tables (original station and station126 shapefiles):

'eco_omer', 'name_omer', 'dis_aggr', 'code_aggr', 'name_aggr'

- Spatially join station126 and eco-omer coverage

- Populate the 'eco_omer' field with the 'eco' value

- Repeat the previous step using the nearest method (line coverage) to determine

ecoregion assignment for the line coverage, if some records are blank

- Spatially join the ecoregion line coverage to station coverage, link the LPoly#

(from the spatially joined table) to Poly# (of the ecoregion polygon coverage)

- Populate the Eco fields with the appropriate information.

- Follow the same steps to the Rpoly#

- Remove all table joins

- Link the useco-om table with station126 table and populate 'name-omer' field

- Spatially join station aggr coverage and populate the rest of the fields. Follow the

same procedures as outlined above

- Remove all joins

- Make sure the new Eco field added into the station126 shapefile are different than
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the ones in the original station shapefile

- Join station126 and station coverage by station-id

- Populate all the Eco fields in the original station coverage

- Remove all joins

- Save table

- Make sure that all ctyfips records are populated; the county shapefile may have to

be joined to populate the records, if the stco_flag = 4

- Create 2 new fields, 'NewCounty' and 'NewState'

- Populate these new fields with a spatial join to the county coverage

- Select by feature (ecoregion shapefile) all of the records in the station shapefile

- Switch selection (to get records outside of the ecoregion shapefile)

- If any of the selected records have stco_flag = 0 (they are outside the ecoregion

shapefile boundary), calculate them to stco_flag = 3

stco_flags (state/county flags in order of importance)

0 The state and county values from the data set matched the state and county values 

from the spatial join.

(Ecoregions were assigned based on the latitude/longitude coordinates.)

1 The state and county values from the data set did not match the state and county

values from the spatial join, but the point was inside the county coverage 

boundary.

(Ecoregions were assigned based on the county centroid.)

2 The state and county values from the data set did not match the state and county 

values from the spatial join because the point was outside the county coverage 

boundary; therefore, there was nothing to compare to the point (i.e., the point 

falls in the ocean/Canada/Mexico). This occurred for some coastal samples.

(Ecoregions were assigned based on the county centroid.)

3 The state and county values from the data set matched the state and county from

the spatial join, but the point was outside the ecoregion boundary.

(Ecoregions were assigned to the closest ecoregion to the point.)

(No ecoregions were assigned to AK, HI, PR, BC, and GU.)

4 Latitude/longitude coordinates were provided, but there was no county 

 information.

(Ecoregions were assigned based on the latitude/longitude coordinates.)

5 The state and county values from the data set did not match the state and county 

 values from the spatial join due to spelling or naming convention errors.

The matches were performed manually. 

(Ecoregions were assigned based on the latitude/longitude coordinates.)

6 No latitude/longitude coordinates were provided, only state and county

information was available.

(Ecoregions were assigned based on the county centroid.)

7 No latitude/longitude coordinates were provided, only state information was 

available; therefore, no matches were possible.

(Ecoregions were not assigned. Data is not included in the analysis.)
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APPENDIX C

Glossary

Coefficient of Variation- Equal to the standard deviation divided by the mean multiplied by 100.

Maximum- The highest value.

Mean- The arithmetic average.

Median- The 50th percentile or middle value. Half of the values are above the median, and half of

the values are below the median.

Minimum- The lowest value.

Standard Deviation- Equal to the square root of the variance with the variance defined as the sum

of the squared deviations divided by the sample size minus one.

Standard Error- Standard error of the mean is equal to the standard deviation divided by the

square root of the sample size.