State of Florida

Numeric Nutrient Criteria

Development Plan

March 2009

Prepared by:

Bureau of Assessment and Restoration Support

Division of Environmental Assessment and Restoration

Florida Department of Environmental Protection

Tallahassee, FL
State of Florida Numeric Nutrient Criteria Development Plan March 2009

ii

Florida Department of Environmental Protection
State of Florida Numeric Nutrient Criteria Development Plan March 2009

iii

Contents

LIST OF ACRONYMS AND ABBREVIATIONS......................................................................VIII

1. BACKGROUND AND CRITERIA DEVELOPMENT PROCESS........................................... 1

1.1 Use of a Technical Advisory Committee................................................................. 9

1.2 Post-TAC Rule Development ..................................................................................10

2. NUTRIENT CRITERIA DEVELOPMENT AND IMPLEMENTATION ...................................11

2.1 EPA Guidance..........................................................................................................11

2.2 FDEP’s Approach ....................................................................................................12

2.3 Implementation........................................................................................................15

3. TECHNICAL APPROACHES .............................................................................................15

3.1 Initial Investigations ................................................................................................15

3.2 Biological Criteria Development.............................................................................17

3.3 Nutrient Gradient Stream Study .............................................................................17

3.3.1 Study Objectives..........................................................................................18

3.3.2 Study Methodology......................................................................................18

3.3.3 Anticipated Study Outcomes and Statistical Approach............................19

3.4. Development and Initial Application of the Nutrient Benchmark 

Distributional Approach..........................................................................................20

3.4.1 Identification of Candidate Benchmark Sites (LDI)....................................21

3.4.2 Additional Benchmark Site Evaluation.......................................................23

3.4.3 Field Evaluation of Peninsula Bioregion Benchmark Stream Sites..........24

3.4.4 Statistical Outlier Analyses .........................................................................31

3.4.5 Calculation of Annual WBID Geometric Mean ...........................................31

3.4.6 Defining Nutrient Limits...............................................................................31

3.4.7 Ongoing and Future Efforts ........................................................................32

3.5 Stressor Identification Study..................................................................................32

3.6 Development of the Stream Periphyton Index.......................................................34

3.7 Downstream Effects of Nutrients in Selected Florida Rivers/Estuaries 

(Nutrient Longitudinal Study).................................................................................35

3.7.1 Project Objectives........................................................................................36

3.7.2 Project Description ......................................................................................36

3.7.3 Project Outcomes ........................................................................................37

3.8 Nitrate-Nitrite Analysis in Streams/Spring Runs ...................................................37

3.9 Lake Algal and Macrophyte Response...................................................................38

3.10 Recreation-Based Criteria.......................................................................................39

3.11 Application of Benchmark Distributional Approach to Lakes..............................40

3.12 Approach for Estuaries ...........................................................................................41

3.13 Microcystin Round Robin .......................................................................................44

4. RELATION TO STATE USE CLASSIFICATIONS..............................................................45
State of Florida Numeric Nutrient Criteria Development Plan March 2009

iv

5. RELATION TO BIOGEOGRAPHIC CLASSIFICATION......................................................45

6. DATA SOURCES ...............................................................................................................46

6.1 Inventory of Existing Data.......................................................................................46

6.2 FDEP’s Ambient Monitoring Program....................................................................46

6.3 Requirements for New Data Collection..................................................................47

7. COORDINATION WITH BORDERING STATES.................................................................47

8. PRIORITIZATION OF WATERS AND SCHEDULE FOR DEVELOPMENT AND 

ADOPTION .........................................................................................................................47

8.1 Lakes and Streams (1st Priority) .............................................................................48

8.2 Estuaries (2nd Priority).............................................................................................49

8.3 Wetlands (3rd Priority)..............................................................................................49

9. FLORIDA’S ONGOING INVESTMENT IN NUTRIENT CRITERIA DEVELOPMENT ..........50

10. PAST, CURRENT, AND FUTURE SCHEDULE FOR NUTRIENT CRITERIA 

DEVELOPMENT FOR FLORIDA’S WATERS ....................................................................50

REFERENCES CONSULTED OR CITED.................................................................................56

APPENDICES...........................................................................................................................61

Appendix A: FDEP’s Review of EPA’s Recommended Nutrient Criteria for 

Streams and Lakes..................................................................................................61

Appendix B: Selection of Benchmark Sites (Characterized by Low Levels of 

Human Disturbance) Using the LDI Index .............................................................73

Appendix C: Peninsular Benchmark Site Summaries ...................................................83
State of Florida Numeric Nutrient Criteria Development Plan March 2009

v

List of Tables

Table 1. EPA-generated nutrient criteria recommendations for nutrient 

ecoregions, including all or part of Florida ....................................................4

Table 2. FDEP Nutrient Criteria TAC members.............................................................10

Table 3. Summary of regulatory structure and progress towards adopting 

nutrient criteria in Florida................................................................................16

Table 4. Parameters monitored during the peninsula bioregion benchmark 

survey ...............................................................................................................25

Table 5. Recent and planned funding for nutrient criteria development in 

Florida...............................................................................................................51

Table A-1. EPA recommendations for streams using the lower 25th percentile 

approach of a dataset of unknown site quality ..............................................63

Table A-2. EPA recommendations for lakes/impoundments using the lower 

25th percentile approach of a dataset of unknown site quality .....................64

Table A-3. Summary of seasonal values chlorophyll a concentrations used by 

EPA to derive the recommended Ecoregion IX rivers and streams 

chlorophyll a criteria........................................................................................65

Table A-4. Summary of seasonal values chlorophyll a concentrations used by 

EPA to derive the recommended Ecoregion XII rivers and streams 

chlorophyll a criteria........................................................................................65

Table B-1. Comparison of FWCI scores using Fisher’s one-way multiple 

comparison test for three separate species assemblages (diatoms, 

macrophytes, and macroinvertebrates) for depressional palustrine 

wetlands............................................................................................................75
State of Florida Numeric Nutrient Criteria Development Plan March 2009

vi

List of Figures

Figure 1. Draft aggregations of Level III ecoregions for the national nutrient 

strategy in Florida ............................................................................................3

Figure 2. Level IV subecoregions for Florida: Small/wadeable streams.....................6

Figure 3. Level IV subecoregions for Florida lakes .......................................................7

Figure 4. Stream bioregions of Florida...........................................................................8

Figure 5. Plots of SCI versus TP concentrations at sites visited during the 

peninsula benchmark stream survey..............................................................27

Figure 6. Plots of SCI versus TN concentrations at sites visited during the 

peninsula benchmark stream survey..............................................................28

Figure 7. Plots of percent (A) Bacillariophyta, (B) Cryptophycophyta, and (C) 

Cyanophycota collected on natural substrates versus site period of 

record geometric mean TP concentrations....................................................29

Figure 8. Plots of percent (A) Bacillariophyta, (B) Cryptophycophyta, and (C) 

Cyanophycota collected on natural substrates versus site period of 

record geometric mean TN concentrations....................................................30

Figure 9. Probability of observing LVI value less than 37 in Florida lakes if 

specified TP concentration is exceeded.........................................................39

Figure 10. Probability of observing LVI value less than 37 in Florida lakes if 

specified TN concentration is exceeded ........................................................40

Figure A-1. Aggregations of Level III ecoregions for national nutrient strategy............. 62

Figure A-2. Location of sampling stations used by EPA to derive Ecoregion IX 

recommended nutrient criteria for rivers and streams and lakes................. 63

Figure A-3. Stream bioregions of Florida...........................................................................67

Figure A-4. Cumulative frequency distributions of (A) total phosphorus, (B) 

total nitrogen, (C) chlorophyll a, and (D) turbidity in confirmed 

peninsula bioregion reference streams..........................................................68

Figure A-5. Adverse biomass changes in Suwannee River periphyton related to 

anthropogenic nitrate-nitrate levels................................................................69

Figure A-6. Increases in Vaucheria sp. (nuisance algae) in Florida spring runs 

related to anthropogenic nitrate-nitrate levels (graph lists TN as 

axis, but this was predominantly nitrate-nitrate) ...........................................69

Figure A-7. Cumulative frequency distributions of (A) total phosphorus, (B) 

total nitrogen, and (C) chlorophyll a in Florida lakes with healthy 

aquatic plant communities (LVI ≥ 37)..............................................................70

Figure B-1. Area-weighted LDI Index versus phosphorus pollutant load in 64 

hydrologic units (subwatersheds) of the St. Marks River watershed........... 76

Figure B-2. Box plot comparison of macroinvertebrate FWCI scores among LDI 

groups, including Group 1 (LDI = 1.0), Group 2 (1.0 < LDI ≤ 2.0), 

Group 3 (2.0 < LDI ≤ 3.0), and Group 4 (LDI > 3.0)..........................................77
State of Florida Numeric Nutrient Criteria Development Plan March 2009

vii

Figure B-3. Box plot comparison of SCI scores and LDI values calculated 

based on a 100 m buffer area extending 10 km upstream of the 

sample point.....................................................................................................77

Figure B-4. Comparison of average number of sensitive stream 

macroinvertebrate taxa for sites within different LDI groups .......................78

Figure B-5. Log of lake median chlorophyll a concentrations versus LDI.......................79
State of Florida Numeric Nutrient Criteria Development Plan March 2009

viii

List of Acronyms and Abbreviations

AGP Algal Growth Potential

BCG Biological Condition Gradient

BMP Best Management Practice 

BMAP Basin Management Action Plan 

BioRecon BioReconnaissance 

BOD Biochemical Oxygen Demand

CADDIS Causal Analysis/Diagnosis Decision Information System

CWA Clean Water Act

DO Dissolved Oxygen

EPA U.S. Environmental Protection Agency

ERC Environmental Regulation Commission 

ETAC Everglades Technical Advisory Committee

F.A.C. Florida Administrative Code

FDEP Florida Department of Environmental Protection

FWCI Florida Wetland Condition Index

GED Gulf Ecology Division 

GOMA Gulf of Mexico Alliance 

IWRM Integrated Water Resource Monitoring 

HA Habitat Assessment

HAB Harmful Algal Bloom 

HA Habitat Assessment

HDG Human Disturbance Gradient

HUC Hydrologic Unit Code

IRL Indian River Lagoon

IWR Impaired Surface Waters Rule

Km Kilometer

LDI Land Development Intensity

LOPP Lake Okeechobee Protection Plan

LSD Least Significant Difference

LVI Lake Vegetation Index

kg N/ha/yr Kilograms of Nitrogen per Hectare per Year

m Meter

mg/L Milligrams per Liter

mg/m3 Milligrams per Cubic Meter

NASQAN National Stream Quality Accounting Network

NAWQA National Water Quality Assessment

NEP National Estuary Program

NPDES National Pollutant Discharge Elimination System

NTU Nephelometric Turbidity Unit

PLRG Pollutant Load Reduction Goal

QA/QC Quality Assurance/Quality Control

RPS Rapid Periphyton Survey

RTAG Regional Technical Assistance Group

SAV Submerged Aquatic Vegetation

SBIO Statewide Biological Database

SCI Stream Condition Index

sej Solar Emergy Joule

SFWMD South Florida Water Management District
State of Florida Numeric Nutrient Criteria Development Plan March 2009

ix

SJRWMD St. Johns River Water Management District

SOP Standard Operating Procedure

SPI Stream Periphyton Index

STORET Storage and Retrieval (Database)

SWIM Surface Water Improvement and Management

TAC Technical Advisory Committee

TKN Total Kjeldahl Nitrogen

TMDL Total Maximum Daily Load

TN Total Nitrogen

TOC Total Organic Carbon

TP Total Phosphorus

TSI Trophic State Index

TSS Total Suspended Solids

USGS U.S. Geological Survey

WBID Waterbody Identification Number

WRAP Wetland Rapid Assessment Procedure

μg/L Micrograms per Liter

μmho/cm Micromohs per Centimeter
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

1

STATE OF FLORIDA NUMERIC NUTRIENT CRITERIA 

DEVELOPMENT PLAN

1. Background and Criteria Development Process

The state of Florida intends to adopt quantitative nutrient water quality standards to facilitate the 

assessment of designated use attainment for its waters and to provide a better means to protect 

state waters from the adverse effects of nutrient over enrichment. To that end, the Florida 

Department of Environmental Protection (FDEP) plans to develop numeric criteria for causal 

variables (phosphorus and nitrogen) and/or response variables (potentially chlorophyll a and 

transparency), recognizing the hydrologic variability (waterbody type) and spatial variability 

(location within Florida) of the nutrient levels of the state’s waters, and the variability in 

ecosystem response to nutrient concentrations. 

It is FDEP’s intent to establish numeric nutrient criteria that are protective of designated uses 

and consistent with Florida’s existing narrative nutrient criterion, which states that “in no case 

shall nutrient concentrations of body of water be altered so as to cause an imbalance in natural 

populations of flora or fauna.” Therefore, FDEP’s preferred approach is to develop cause/effect 

relationships between nutrients and valued ecological attributes, and to establish nutrient criteria 

that ensure that the designated uses of Florida’s waters are maintained. 

Nutrients are unlike any other “pollutant” regulated by the federal Clean Water Act (CWA). Most 

water quality criteria are based on a toxicity threshold, evidenced by a dose-response 

relationship, where higher concentrations can be demonstrated to be harmful, and acceptable 

concentrations can be established at a level below which adverse responses are elicited

(usually in laboratory toxicity tests). In contrast, nutrients are not only present naturally in 

aquatic systems, they are absolutely necessary for the proper functioning of biological 

communities, and are sometimes moderated in their expression by many natural factors.

Therefore, the development of protective nutrient criteria is immensely more complicated than 

that for toxic substances. It must be recognized that nutrients should not be regulated at levels 

that are artificially lower than those concentrations required for normal ecosystem functioning. If 

humans were to reduce nutrients below the levels that natural aquatic systems are accustomed 

to, adverse biological effects (disruption of trophic dynamics, loss of representative taxa) would 

occur. This would be counter to the CWA charge in Section 101 to “protect the physical, 

chemical, and biological integrity” of the state’s waters and, coincidentally, against Florida law,

which prohibits FDEP from conducting remediation for natural conditions. Ideally, nutrients 

should be managed in a range of concentrations with some consideration of a margin of safety 

on both the upper and lower bounds of the range.

A memorandum from the Director of the U.S. Environmental Protection Agency’s (EPA) Office 

of Science and Technology, Geoff Grubbs (2001), indicated that states are allowed the 

flexibility to develop and adopt nutrient criteria other than those currently proposed by EPA for 

waterbody types in specific Nutrient Ecoregions which were aggregated from Level III (EPA,

1998) (Figure 1 and Table 1). As proposed, the EPA criteria recommendations that would 

include Florida (EPA, 2000a, 2000b, 2000c, 2000d, and 2000e) do not fully reflect localized 

conditions or specific waterbody designated uses within the State of Florida, FDEP proposes to 

undertake activities to develop criteria for lakes, streams, estuaries, coastal waters, and 

wetlands within the state, based on state-specific, subregional data. Upon issuance of §304(a) 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

2

Ecoregional Nutrient Criteria Recommendations, and since that time, EPA has encouraged 

states to refine their approach where possible in order to reflect more state-specific data and 

conditions. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

3

Figure 1. Draft aggregations of Level III ecoregions for the national nutrient 

strategy in Florida
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

4

Table 1. EPA-generated nutrient criteria recommendations for nutrient 

ecoregions, including all or part of Florida

Lakes and Reservoirs

Parameter Region

IX 1 Region XII 2 Region XIII 3

TP (μg/L) 20 10 17.5

TN (mg/L) 0.36 0.52 1.27

Chlorophyll a (μg/L) 4.93 2.6 12.35

Secchi Depth (m) 1.53 2.1 0.79

m – Meters.

μg/L – Micrograms per liter.

mg/L – Milligrams per liter.

Rivers and Streams

Parameter Region

IX 4 Region XII 5 Region XIII 6

TP (μg/L) 36.56 40.0 N/A

TN (mg/L) 0.69 0.9 N/A

Chlorophyll a (μg/L) 0.93 0.40 N/A

Periphyton Chlorophyll a (mg/m3) 7 20.35 N/A N/A

Turbidity (NTU) 5.7 1.9 N/A

mg/m3 – Milligrams per cubic meter.

N/A – Not available.

NTU – Nephelometric turbidity unit.

TP – Total phosphorus.

TN – Total nitrogen.

1 EPA, 2000a. 2 EPA, 2000b. 3 EPA, 2000c. 4 EPA, 2000d. 5 EPA, 2000e. 6 EPA has not issued ambient water quality criteria recommendations in support of the development 

of nutrient criteria for rivers and streams in Nutrient Ecoregion XIII.

7 Only the guidance for rivers and streams in Nutrient Ecoregion IX included recommendations for 

periphyton chlorophyll a.

The development of criteria for these subregions has been and will continue to be prioritized 

based on Florida’s watershed program needs and the availability and order of EPA guidance 

documents. FDEP will evaluate both ecoregions and bioregions as potential subregionalization 

bases for numeric nutrient criteria. Florida ecoregions were delineated in the early 1990s as 

part of Florida’s biocriteria development efforts for streams and lakes. Those efforts yielded 13 

Level IV subecoregions (Griffith et al., 1994) for wadeable streams (Figure 2) and 47 Level IV 

subecoregions (Griffith et al., 1997) for lakes (Figure 3). Additionally, FDEP has analyzed 

stream reference site macroinvertebrate community patterns in all 9 ecological subregions north 

of Lake Okeechobee (Barbour et al., 1996). From that analysis, FDEP concluded that the data 

indicated the presence of 4 distinct bioregions, within which there were similar biological 

community composition and structure (Figure 4).

While FDEP plans to develop nutrient criteria that are applicable to specific regions which will

serve to prevent impairment, the conceptual approach outlined in this document also 

incorporates the state’s responsibilities to address existing nutrient impairment through the 

development of Total Maximum Daily Loads (TMDLs) or Pollutant Load Reduction Goals 

(PLRGs), as described in state laws and rules, both of which may serve to develop more site-
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

5

specific nutrient targets that could supersede regional criteria, if subsequently adopted and 

approved as site specific alternative criteria. For example, FDEP has developed and received 

approval from EPA Region 4 for the Lake Okeechobee phosphorus TMDL, which established 

the phosphorus concentration that would address undesirable algal blooms in that system. 

Similarly, the Tampa Bay Estuary Program has adopted chlorophyll a targets for portions of 

Tampa Bay that were specifically designed to protect and restore seagrass communities within 

the bay. The program has established a protocol that considers the magnitude, frequency, and 

duration of changes to algal biomass in the bay and implemented through agreements, a 

program to control excess nitrogen in the watershed.

It should be noted that FDEP intends to develop numeric nutrient criteria for adoption in Chapter 

62-302, Florida Administrative Code (F.A.C.), as water quality criteria, and in addition, is 

exploring the incorporation of numeric nutrient thresholds into the Impaired Surface Waters Rule 

(IWR) (Chapter 62-303, F.A.C.), which establishes the state’s methodology to identify and verify 

impaired waters (waters not meeting applicable water quality standards). While the IWR 

already includes thresholds for response variables that serve as translators for Florida’s 

narrative nutrient standard (a quantification of imbalance of flora and fauna) which are used in 

addition to consideration of other factors to assess waters for nutrient impairment the IWR 

does not currently include numeric causal thresholds for either streams or estuaries. Such 

additional numeric nutrient thresholds adopted in the IWR would serve as nutrient impairment 

thresholds for those waterbody types. Once developed, numeric nutrient criteria are intended to 

both protect healthy, well-balanced natural populations of flora and fauna from the effects of 

excess nutrient enrichment, as well as provide a basis to identify waters already impaired by 

nutrients.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

6

Figure 2. Level IV subecoregions for Florida: Small/wadeable streams

Alabama

Georgia

Gulf of Mexico

Atlantic

Ocean

Southern Pine Plainsand Hills (656)

Dougherty/Marianna Plains (657)

Tifton Upland/Tallahassee Hills (658)

Gulf Coast Flatwoods (751)

Southwestern Florida Flatwoods (752)

Central Florida Ridgesand Uplands (753)

Eastern Florida Flatwoods (754)

Okefenokee Swamps and Plains (755)

Sea Island Flatwoods (756)

Everglades (761)

Big Cypress (762)

Miami Ridge/Atomic Coastal Strip (763)

Southern Coast and Islands (764)

Level IV Subecoregions for Florida

Small / Wadeable Streams

N

0 50 100 150 200 Miles

Map prepared April 18, 2002 by: the GISsubsection

Bureau of Watershed Management

Division of Water ResourceManagement

This map is arepresentation of ground condition and is

Not intended for delineations or analysis of the features shown. For more information, contact devan.branscum@dep.state.fl.us

Griffith 1994
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

7

Figure 3. Level IV subecoregions for Florida lakes

Alabama

Georgia

Gulf of Mexico

Atlantic

Ocean

65-01 WesternHighlands

65-02 Dougherty/Marianna Plains

65-03 New Hope Ridge/Greenhead Slope

65-04 Tifton/Tallahassee Uplands

65-05 Norfleet/Spring Hill Ridge

65-06 Northern Peninsula Karst Plains

75-01 Gulf Coast Lowlands

75-02 Okefenokee Plains

75-03 Upper Santa Fe Flatwoods

75-04 Trail Ridge

75-05 Northern Brooksville Ridge

75-06 Big Bend Karst

75-07 Marion Hills

75-08 CentralValley

75-09 Ocala Scrub

75-10 Eastern Flatlands

75-11 Crescent City/DeLand Ridges

75-12 Tsala Apopka

75-13 Southern Brooksville Ridge

75-14 Lake Weir/Leesburg Upland

75-15 Mount Dora Ridge

75-16 Apopka Upland

75-17 Weeki Wachee Hills

75-18 Webster DryPlain

75-19 Clermont Uplands

75-20 Doctor PhillipsRidge

75-21 Orlando Ridge

75-22 Tampa Plain

75-23 Keystone Lakes

75-24 Land-o-Lakes

75-25 Hillsborough Valley

75-26 Green Swamp

75-27 Osceola Slope

75-28 PinellasPeninsula

75-29 Wimauma Lakes

75-30 Lakeland/Bone ValleyUpland

75-31 Winter Haven/Lake HenryRidges

75-32 Northern Lake Wales Ridge

75-33 Southern Lake Wales Ridge

75-34 Lake WalesRidge Transition

75-35 Kissimmee/Okeechobee Lowland

75-36 Southwestern Flatlands

75-37 Immokalee Rise

76-01 Everglades

76-02 Big Cypress

76-03 Miami Ridge/AtlanticCoastalStrip

76-04 Southern Coast and Islands

Level IV Subecoregions for Florida Lakes

N

0 50 100 150 200 Miles

Map prepared April 18, 2002 by: the GISsubsection

Bureau of Watershed Management

Division of Water ResourceManagement

This map is arepresentation of ground condition and is

Not intended for delineations or analysis of the features shown.

For more information, contact devan.branscum@dep.state.fl.us

Griffith 1997
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

8

Figure 4. Stream bioregions of Florida
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

9

1.1 Use of a Technical Advisory Committee

To assist in the development of numeric nutrient criteria, FDEP convened a Nutrient Criteria 

Technical Advisory Committee (TAC) in 2003, comprising individuals with expertise in areas 

related specifically to water quality and biological community response to nutrients in Florida

(Table 2). The TAC membership is diverse, consisting of representatives with significant 

experience in the ecology of specific aquatic systems (lacustrine, riverine, estuarine, and/or 

palustrine) and the interpretation of water quality data through the use of statistical modeling 

tools. These individuals were chosen for their ability to provide advice and guidance in the 

dynamics of these aquatic systems, as well as to represent the diverse parties in Florida 

interested in the development of nutrient criteria. They include representatives of academic and 

public institutions, along with individuals possessing significant technical experience who were 

drawn from industry, agricultural, and environmental groups. 

The TAC is charged with reviewing the existing knowledge base related to these aquatic 

systems and developing recommendations to FDEP on numeric nutrient criteria. The TAC is 

supported by FDEP staff assigned to provide data assembly and analysis. The TAC process to 

date, along with further in-depth evaluations of available data and the existing knowledge base

by FDEP staff have clearly indicated that there are numerous remaining technical complexities 

and limitations associated with the verification, analysis, and synthesis of the currently available 

data for the derivation of numeric nutrient criteria. Given these complexities, FDEP has decided 

to extend the TAC process through 2009 at a minimum. FDEP anticipates that smaller 

subgroups may need to be formed to consult with other experts in addressing specific 

waterbody types (e.g., south Florida canals, or estuaries) for which criteria are under 

development. 

FDEP has assigned a dedicated staff member to coordinate the development of numeric 

nutrient criteria. This nutrient coordinator is responsible for communicating with EPA, the TAC, 

and other interested parties on the development of nutrient criteria, and also ensuring that the 

process is properly integrated with other FDEP program areas.

In accordance with Florida’s Sunshine Law, all meetings of the TAC have been and will continue 

to be open to the public. To further promote public awareness and involvement in the process, 

each TAC meeting incorporates designated periods for informal public participation and 

comment. In recognition of the large geographic span of the state, TAC meetings are held at 

different locations within Florida on a rotating basis. Also, a link on the FDEP website 

(http://www.dep.state.fl.us/water/wqssp/nutrients/index.htm) has been established to report all 

TAC activities.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

10

Table 2. FDEP Nutrient Criteria TAC members

Name Affiliation Experience Relevant to TAC 

Appointment

Kevin Carter

South Florida Water Management 

District

Nominated by Florida League of Cities

Estuarine systems

Canals

Douglas Durbin, Ph.D.

Biological Research Associates, Inc.

Nominated by Florida Phosphate 

Council

Riverine systems

Lacustrine systems

Wetland systems

Canals

Mark W. Clark, Ph.D. University of Florida, Department of Soil 

and Water Sciences

Wetland systems

Nutrient dynamics and eutrophication

Ed Decker EPA Region 4, Atlanta

EPA Regional Nutrient Coordinator

Aquatic biology and chemistry

Wastewater treatment

Nonpoint source control

Surface water monitoring & assessment

Anthony Federico

MacVicar, Federico and Lamb, Inc.

Nominated by Florida Department of 

Agriculture and Consumer Services

Lacustrine systems

Estuarine systems

Riverine systems

Water quality modeling

FDEP Lake Okeechobee TAC 

Robert Fisher, Ph.D.

National Council for Air and Stream 

Improvement, Inc.

Nominated by Florida Pulp and Paper 

Association

Riverine systems

EPA Gulf of Mexico Program Nutrient 

Enrichment Focus Team

John Hendrickson St. Johns River Water Management 

District

Lacustrine systems

Riverine systems

FDEP Impaired Waters TAC (Alternate)

Mark Kraus, Ph.D. Everglades Foundation Wetland systems

Estuarine systems

Frank Marshall, Ph.D., P.E.

Environmental Consulting & 

Technology, Inc.

Nominated by Florida Stormwater 

Association

Estuarine systems

Canals

Water quality modeling

Scott McClelland Camp Dresser & McKee, Inc. Water quality modeling 

FDEP Impaired Waters TAC 

1.2 Post-TAC Rule Development

After the completion of TAC activities and before the submittal of potential criteria to the state’s 

Environmental Regulation Commission (ERC), FDEP will hold rule development workshops, 

share draft rule text with the public, and allow for public review and comment, as required by

both state and federal regulations. The ERC is an unpaid citizenry board appointed by the 

Governor of Florida. In exercising its authority, it considers scientific and technical validity, 

economic impacts, and relative risks and benefits to the public and the environment of all 

proposed rules and standards related to environmental resources. It is anticipated that ERC 

activities can be completed in 6 to 12 months, barring major dissent or administrative challenge. 

However, the level of control that FDEP has over the schedule of the ERC’s approval process 

for such rules is limited, making the establishment of a firm completion date for nutrient criteria 

adoption difficult. If there is an administrative challenge to the proposed criteria, the 

administrative hearing process would likely take at least another year. FDEP however, remains 

committed to a timely completion of this effort.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

11

2. Nutrient Criteria Development and Implementation

2.1 EPA Guidance

EPA’s Nutrient Criteria Technical Guidance Manual: Rivers and Streams (Buck et al., 2000) 

described three general approaches, with certain options, for the development of numeric 

nutrient criteria for streams. The most comprehensive and scientifically defensible approach

(the state’s preferred approach) is to establish criteria to protect against dependably measured 

adverse biological responses. EPA suggests that an observed dose-response relationship 

could be described by a model (e.g., trophic state classification, regional predictive model, 

biocriteria, etc.), which in turn would link nutrient concentrations to the relative risk of 

environmental harm. 

FDEP supports this approach, since it establishes a cause/effect relationship between nutrients 

and valued ecological attributes, and is linked to maintaining designated uses. FDEP is 

currently pursuing response-based thresholds for use as water quality criteria for inclusion in the 

state’s water quality standards rule, Chapter 62-302, F.A.C. In a series of studies (described in 

detail in Section 3), FDEP is investigating the relationship between nutrients and biological 

measures such as the Stream Condition Index (SCI), Lake Vegetation Index (LVI), Stream 

Periphyton Index (SPI) (currently under development), and phytoplankton chlorophyll a.

In the absence of data quantitatively describing biological dose-response relationships, EPA

recommends as the next best alternative, setting criteria based on an inclusive distribution of 

values obtained from minimally disturbed reference sites in a designated ecoregion (based on 

climate and geology) and recommends projection an upper percentile value to represent a level 

of nutrient concentration that will inherently protect aquatic life. It should be noted that EPA’s 

guidance for both rivers & streams, and lakes & reservoirs suggests using the 75th percentile

(but only as a suggestion), and that a higher percentile might be chosen when associated with 

higher confidence in the reference set that can reduce uncertainty with regard to protection. 

EPA’s more recent guidance for wetlands suggests that using the 75th to 95th percentile may be 

appropriate. According to published EPA guidance, reference reaches may be identified for 

each class of stream within a state based on best professional judgment. FDEP also supports 

this methodology, since it would ensure that nutrient concentrations associated with biologically 

healthy, well-balanced communities would be considered acceptable as protective of those 

communities. 

However, this approach as described above is an inference model, and does not definitively 

demonstrate that exceeding the threshold established by the distribution of reference sites 

results in harm (impairment) to the aquatic life in a particular waterbody. Multiple factors can 

strongly influence the expression of biological responses to nutrients across waterbodies, such 

as water velocity, residence time, availability of the other nutrient, presence of grazers, 

availability of light (due to tree cover and/or water transparency), and availability of suitable 

habitat. In fact, FDEP has found in Florida waters that additional stressors (e.g., degraded 

habitat, unfavorable hydrology) often influence biological impairments more than the actual 

concentration of nutrients at a given point. The “minimally affected reference water approach”

identifies concentrations that are presumed to be inherently protective of the waterbody 

(including downstream waters) because these concentrations are associated with demonstrated 

minimally disturbed systems with healthy biological communities. Actual biological thresholds 

can be site-specific and arguably more precise. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

12

The third and least preferred approach of those suggested by EPA is offered for use in 

situations where sufficient known reference sites are unavailable, either absent or not 

identifiable. This approach is often referred to as the “all streams” approach, and involves 

establishing criteria using a lower distribution (e.g., 5th to 25th percentile) of a pool of sites of 

undetermined ecological quality, as long as the pool is sufficiently large enough to represent all 

waters and can be presumed to reasonably reflect the full range of ambient conditions with a 

disturbance gradient from least to most impacted. Due to the intended scale of application and 

the availability of data, EPA used this method to develop and publish under CWA §304(a) 

recommended nutrient criteria for streams and lakes in Nutrient Ecoregions IX, XII, and XIII. 

However, after careful review of these recommended criteria, FDEP has concluded that they are 

not sufficiently defensible (see Appendix B). In FDEP’s opinion, this “all sites data distribution 

approach” does not directly link nutrient concentrations to valued ecological attributes (healthy,

well-balanced populations of flora or fauna), and consequently, FDEP believes that other 

options are preferable and more scientifically justified. For this reason, FDEP considers the “all 

sites data distribution approach” to have limited defensibility in Florida, and therefore does not 

intend to pursue it any further.

2.2 FDEP’s Approach

The CWA provides states with three alternative paths for development of protective numeric

criteria (40 CFR 131.11). Numeric criteria may be established based upon (1) published 

Section 304(a) guidance, or (2) 304(a) guidance modified to reflect site-specific conditions, or 

(3) by use of other scientifically defensible methods (referred to later in this document as 

“Option 3”). Based on extensive experience with the development of biocriteria, FDEP has 

gained significant knowledge and expertise in the objective quantification of human disturbance 

and characterization of biological response. Therefore, FDEP intends to pursue the CWA

option that allows criteria to be based on a state-defined, scientifically defensible method 

(Option 3) for the purposes of developing numeric nutrient criteria to provide protection and 

maintenance of aquatic life use in Florida.

FDEP plans to develop numeric nutrient criteria using response-based relationships that are 

consistent with the existing narrative criterion for nutrients, which states “In no case shall 

nutrient concentrations of body of water be altered so as to cause an imbalance in natural 

populations of flora or fauna.” The determination that an “imbalance” has occurred requires an 

evaluation of the relationship between nutrients and biological health (while attempting to control 

for confounding variables) and includes the following:

• Defining the expected biological integrity (aquatic community structure and 

function) by examining minimally disturbed sites in the ecosystem. This is 

accomplished by developing and calibrating biological indices. FDEP has, or is 

developing, indices for stream invertebrates, lake plant communities, and stream 

algae.

• Sampling key water quality parameters and biological communities (e.g., algae, 

macrophytes, and invertebrates) across a nutrient gradient. 

• Determining where along the nutrient gradient, and at what concentrations, 

significant departures in the expected community structure and function occur 

compared with acceptable conditions, using EPA’s Biological Condition Gradient 

(BCG) approach (Davies and Jackson, 2006; Stoddard et al., 2006). 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

13

The BCG concept definitively describes how the following ten ecological attributes change in 

response to increasing levels of stressors:

• Historically documented, sensitive, long-lived, or regionally endemic taxa;

• Sensitive and rare taxa;

• Sensitive but ubiquitous taxa;

• Taxa of intermediate tolerance;

• Tolerant taxa;

• Non-native taxa;

• Organism condition;

• Ecosystem functions;

• Spatial and temporal extent of detrimental effects; and

• Ecosystem connectedness.

Based on the above attributes, the BCG model segregates biological condition into six tiers, as 

follows, which FDEP believes are especially useful for nutrient criteria development efforts:

(1) Native structural, functional, and taxonomic integrity is preserved; ecosystem 

function is preserved within the range of natural variability.

(2) Virtually all native taxa are maintained, with some changes in biomass and/or 

abundance; ecosystem functions are fully maintained within the range of natural 

variability.

(3) Some changes in structure occur due to the loss of some rare native taxa; there 

are shifts in the relative abundance of taxa, but sensitive–ubiquitous taxa are 

common and abundant; ecosystem functions are fully maintained through

redundant attributes of the system.

(4) Moderate changes in structure occur due to the replacement of some sensitive–

ubiquitous taxa by more tolerant taxa, but reproducing populations of some 

sensitive taxa are maintained; there is overall balanced distribution of all expected 

major groups; ecosystem functions are largely maintained through redundant 

attributes.

(5) Sensitive taxa are markedly diminished; there is a conspicuously unbalanced 

distribution of major groups from that expected; organisms show signs of 

physiological stress; system function shows reduced complexity and redundancy; 

increased buildup or export of unused materials occurs.

(6) Extreme changes in structure take place; there are wholesale changes in 

taxonomic composition; extreme alterations from normal densities and 

distributions occur; organism conditioning is often poor; ecosystem functions are 

severely altered.

The BCG model is consistent with ecological theory and enables ecologically relevant 

interpretations of the response of aquatic biota to stressors. EPA has extensively tested the 

BCG model in various parts of the country with regionally diverse panels of biologists, (often

including an FDEP representative), who typically converge on agreement in assigning specific 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

14

taxa in samples of macroinvertebrates or fish to the six tiers as described above. This process 

has proved to be a very reliable and consistent to interpret stress on aquatic life and inform 

agency decision making processes. Based on two independent calibrations of Florida’s 

biological indices, as well as input from several National BCG Workshops, FDEP has 

determined that sites associated with BCG scores of 5 and 6 do not meet the criteria for the 

state’s designated use of “healthy, well-balanced communities of aquatic flora and fauna.”

For numeric nutrient criteria development purposes, the use of the BCG has several 

implications. Its use may result in the determination that acceptable levels of nutrients may (or 

may not) be higher than historical background conditions, since well-defined biological response 

endpoints are used for the assessment. Also, because biological communities respond to all 

sources of stress (natural and anthropogenic), the model offers a mechanism to evaluate 

potential stressors and to control for confounding variables during the assessment process. 

Finally, since the BCG model is based on sound, nationally accepted ecological concepts, the 

ranges of nutrients deemed acceptable through its use will result in scientifically defensible 

criteria.

While FDEP has and will continue to pursue all scientifically defensible approaches to derive 

numeric nutrient criteria, it prefers to base criteria on dose-response relationships. In 

acknowledgement of the challenges associated with identifying statistically significant 

relationships between nutrient concentrations and biological responses, FDEP is also 

developing nutrient criteria using a “benchmark distributional approach” that will serve as 

potential “backup” criteria if that statistically sound dose response–based criteria cannot be

initially determined. However, in addition FDEP may adopt criteria developed from the 

benchmark distributional approach in Chapter 62-303, rather than Chapter 62-302, F.A.C., and 

may require biological confirmation before listing waters as impaired. 

The nutrient benchmark distributional approach builds on methodologies originally developed to 

quantify human disturbance for biocriteria development purposes. By FDEP’s definition,

nutrient benchmark sites are only influenced by low levels of human disturbance, enabling full

support of the most sensitive designated use—i.e., support of a healthy, well-balanced 

population of fish and wildlife. FDEP intends to use the upper end of nitrogen and phosphorus 

frequency distributions from benchmark sites to define nutrient thresholds that FDEP expects to 

be both defensible and reliable for protection of aquatic life in Florida waters. 

If the benchmark-based nutrient thresholds are adopted in Section 62-303.300, F.A.C., these 

thresholds would be used to identify waters that are potentially impaired for nutrients. Waters 

with nutrient concentrations above these thresholds would be placed on the state’s Planning List

of potentially impaired waters and prioritized for additional monitoring. A subsequent biological 

confirmation linking biological impairment instream at that point, or possibly downstream, to 

excess nitrogen or phosphorus would be required for a waterbody to be included on the Verified 

List of impaired waters (Section 62-303.400, F.A.C.). If no biological impairment can be 

demonstrated for waters (or downstream of waters) placed on the Planning List for nutrients, or 

if the biological impairment is shown to be due to factors other than nutrients, then these waters

would not be considered impaired due to nutrient enrichment.

FDEP believes that a site-specific biological confirmation is required to demonstrate a link 

between nutrients and adverse biological responses for nutrient benchmark approach–derived 

criteria. Multiple factors can strongly influence the expression of biological responses to 

nutrients across natural waterbodies, and multiple additional stressors (e.g., habitat, hydrology) 

are often more influential on biological impairments than nutrients. The benchmark 

distributional approach identifies nutrient concentrations that are presumed protective because 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

15

these concentrations are associated with relatively low human disturbance and healthy

biological communities instream at that point, and shown to be protective downstream. Actual 

biological thresholds will be site-specific and could occur at concentrations above or below the 

benchmark thresholds, depending on circumstances.

2.3 Implementation

The specific rules in which nutrient criteria are adopted affect the breadth of the CWA programs 

under which they are implemented. While nutrient thresholds adopted in the IWR may result in 

identifying waters to be addressed by the development of TMDLs which will establish effluent 

limitations via wasteload allocations, these thresholds would only apply for the purposes of 

assessment and listing under CWA Sections 303(d) and 305(b). In contrast, criteria established 

in Chapter 62-302, F.A.C., would be implemented in the IWR and would also be used to directly 

establish effluent limits and water quality targets for TMDLs.

Table 3 provides a basic overview of the regulatory structure in which criteria will be adopted in 

Florida and summarizes the progress made or planned for such adoption.

3. Technical Approaches

FDEP is committed to using technically defensible methods and the most robust dataset 

feasible to develop protective nutrient criteria for Florida’s waters. Since there is a lack of data 

describing biological dose-response relationships for nutrients, FDEP initially pursued a nutrient 

benchmark distributional approach. However, the state’s preference is to develop criteria linked 

to biological response. Given this preference, FDEP has continued efforts, including initiating 

studies in 2008, to develop response-based criteria for adoption in Chapter 62-302, F.A.C. 

FDEP’s ongoing and planned studies are described below.

3.1 Initial Investigations

In 1999, FDEP’s Division of Water Resource Management initiated the implementation of a 

watershed approach patterned after EPA guidance (EPA, 1991, 1995), including the 

prioritization of waterbodies for TMDL development. FDEP has drawn on the lessons learned 

and knowledge gained through these processes to prioritize the development of numeric 

nutrient standards. FDEP also managed five external projects, completed between 2001 and 

2003, that focused on specific approaches outlined in EPA nutrient guidance documents 

(USEPA, 2000; USEPA, 2000). The idea was to see if these approaches would be feasible on 

a regional scale. The projects were as follows:

(1) Paleolimnological characterization of predisturbance water quality in two Florida 

lake regions;

(2) Sedimented algal pigment profiles in the Florida paleolimnological study lakes;

(3) Development of stream diatom population indices for Florida streams;

(4) Comparison of nutrient criteria approaches for Florida lakes with 

recommendations for TN, TP, chlorophyll a, and Secchi depth criteria; and

(5) Another paleolimnological study with further resolution on the lakes in Studies 1 

and 2 above.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

16

It was determined that some of these approaches, while excellent for a specific waterbody, were 

too time- and cost-intensive for a subregional approach. However, these efforts provided 

information and insight into both the causal and response aspects of waterbody nutrient status 

at both site-specific and ecoregional levels. FDEP also anticipates the possibility of applying for 

funding on additional projects. 

Table 3. Summary of regulatory structure and progress towards adopting 

nutrient criteria in Florida

Rule and Applicable 

Waterbody Type

Causal Variables

(Nitrogen and Phosphorus) Response Variables

Section

62-303.300s, 

F.A.C.;

Planning List

Rivers & 

Streams

Under Development (planned for 2010)

Will either revise rule to implement criteria 

adopted in Chapter 62-302, F.A.C., or will 

adopt benchmark-based thresholds in rule

Chlorophyll a (adopted*)

SCI (adopted)

Turbidity (adopted)

Lakes

Under Development (planned for 2010)

Will either revise rule to implement criteria 

adopted in Chapter 62-302, F.A.C., or will 

adopt benchmark-based thresholds in rule

Trophic State Index (TSI) (adopted*)

LVI (planned for 2009)

Estuaries Kickoff in 2008 (planned for 2010) Chlorophyll a (adopted*)

Wetlands Lower Priority

Wetland Condition Index, which includes 

vegetation, algae, and invertebrates. This 

index still needs development, calibration 

and validation.

Section 

62-303.400s, 

F.A.C.;

Verified List

Rivers & 

Streams

Under Development (planned for 2010)

Will either revise rule to implement criteria 

adopted in Chapter 62-302, F.A.C., or will 

adopt benchmark-based thresholds in rule

Chlorophyll a (adopted*)

SCI (adopted)

Turbidity (adopted)

Lakes

Under Development (planned for 2010)

Will either revise rule to implement criteria 

adopted in Chapter 62-302, , F.A.C., or will 

adopt benchmark-based thresholds in rule

TSI (adopted*)

LVI (planned for 2009)

Estuaries Kickoff in 2008 (planned for 2010) Chlorophyll a (adopted*)

Wetlands

Everglades phosphorus criteria via 

application of criterion in Chapter 62-302, 

F.A.C.

Lower Priority

Wetland Condition Index, which includes 

vegetation, algae, and invertebrates. This 

index still needs development, calibration 

and validation.

Section 

62-302.500s, 

F.A.C.;

TMDLs &

Permit Limits

Rivers & 

Streams

Under Development (planned for 2010)

Proposed nitrate criteria for springs as part 

of ongoing Triennial Review (2009)

Transparency Criterion (adopted, with plans 

to specifically address submerged aquatic 

vegetation [SAV] in 2009)

SCI (planned for 2009)

Periphyton Index (planned for 2011)

Lakes Under Development (planned for 2010)

Transparency Criterion (adopted, with plans 

to specifically address SAV in 2009)

LVI (planned for 2009)

Estuaries Kickoff in 2008,

Under Development (planned for 2010)

Transparency Criterion (adopted, with plans 

to specifically address SAV in 2009)

Under Development (planned for 2011)

Wetlands

Everglades phosphorus criteria (adopted)

Under Investigation

(science incomplete, lower priority)

Wetland Condition Index, which includes 

vegetation, algae, and invertebrates. This 

index still needs calibration and validation.

* approved by EPA as “one-sided” thresholds which serve as translators for the state’s existing narratives in 

assessment activities by providing a threshold above which waters are impaired, but not by design, a threshold below 

which uses are known to be protected.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

17

3.2 Biological Criteria Development

FDEP has made very significant progress in the development of biological indices specifically 

designed to assess the health of aquatic biological communities. Fore et al. (2007a) developed 

an SCI to assess the biological condition of macroinvertebrates in Florida streams. Additionally, 

Fore et al. (2007b) developed an LVI to assess the biological condition of aquatic plant 

communities in Florida lakes. FDEP plans to adopt both the SCI and LVI into the state 

standards as water quality criteria during its ongoing triennial review, which started in 2008.

In order to further strengthen its bioassessment capabilities, FDEP is adding another tool that 

can be expected to augment or compliment the SCI and LVI described above, and provide a 

potential indicator with increased sensitivity to nutrients. Work to develop a Stream Periphyton 

Index (SPI) for Florida began during the last quarter of 2007, and significant progress is 

expected by early 2009. FDEP also began using a Rapid Periphyton Survey (RPS) 

methodology for streams in early 2007 (FDEP Standard Operating Procedure [SOP] FS 7230) 

(FDEP, 2008). The RPS provides an assessment of the extent and thickness of periphyton in

streams and the type of periphyton present (i.e., diatom or filamentous). Both the SCI and LVI 

were successfully calibrated for Florida waters, and FDEP has actively worked with EPA to hold 

a BCG workshop for the SPI in late February, 2009, but it is too early to tell whether FDEP will 

have the same success with periphyton.

The biological criteria and indices developed for Florida provide measures of biological heath 

that can be used to support the derivation of protective numeric nutrient criteria. Nutrient 

concentrations associated with “healthy or exceptional” bioassessment index values would be 

compared to nutrient concentrations associated with “impaired” biological index scores to 

establish protective nutrient criteria (including adoption of an appropriate margin of safety). 

Biological health measures can be used to both demonstrate healthy, well-balanced populations 

of flora or fauna within benchmark waters and as thresholds of biological impairment for stressor

response–based approaches. Additionally, the adoption of the SCI and LVI into state water 

quality standards will provide FDEP with additional measures of biological impairment that can 

be linked to violations of the existing narrative nutrient criteria1

3.3 Nutrient Gradient Stream Study

and thus provide an added level 

of protection against the anthropogenic nutrient enrichment of Florida’s waters. FDEP’s 

significant investment in the development of biological indices and criteria has put the state in a

strong position to complete the development of highly defensible numeric nutrient criteria within 

the time frames described in Section 9 of this plan.

As noted previously, the most comprehensive and protective approach to develop numeric 

nutrient criteria is to establish criteria to protect against scientifically determined adverse 

biological responses. EPA suggests that an observed dose-response relationship should be

described by a model (e.g., trophic state classification, regional predictive model, biocriteria), 

which in turn would link nutrient concentrations to the relative risk of environmental harm.

Although Florida will continue to work on the development of numeric nutrient thresholds using 

the benchmark distributional approach as a backup, FDEP is actively investigating approaches 

that more directly link nutrient levels to biological responses. A study designed to establish 

 1 Nutrients must be identified as the causative or contributing pollutant prior to a determination that there is a violation of the 

narrative criterion. The impairment of biological criteria can also be linked to other stressors such as toxicants, habitat, or hydrologic 

modifications.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

18

nutrient concentrations associated with adverse biological responses, called the Nutrient 

Gradient Study, was initiated in the spring of 2008.

3.3.1 Study Objectives

The study is specifically designed to provide information necessary to develop nitrogen and 

phosphorus criteria for streams, although chlorophyll and transparency measures will also be 

evaluated and considered. Its objectives are as follows:

• Collect physical, chemical, and biological data on Florida streams to establish the 

relationship between nutrient levels and adverse biological responses; and

• Analyze the resulting dataset as one line of evidence in FDEP’s effort to establish 

numeric nutrient criteria.

3.3.2 Study Methodology

Unlike other pollutants, nutrients are not only naturally present, they are necessary at some 

level for the proper functioning of ecosystems. Biological communities evolve in response to the 

existing physical and chemical characteristics to which they are exposed. In the case of 

nutrients, the biological communities that develop are the ones best able to compete for and 

utilize the available nutrients in an ecosystem, given the other characteristics of the system. 

Changes in the natural nutrient regime—either increased or decreased nutrient levels—can 

cause shifts in the structure of the biological communities present and ultimately the function of 

the system. To derive appropriately protective nutrient criteria, this approach related nutrients to 

ecological health and biological response. Other factors that also affect biological health (e.g., 

hydrologic modification, habitat, canopy cover) were measured to help determine their relative 

influence on the biological responses under the observed nutrient regimes.

Each of FDEP’s six District offices sampled 12 to 15 sites from a list of 20 potential nutrient 

gradient sites. Two sampling events were conducted, one during spring/summer 2008 and the 

other during fall/winter 2008–09. All samples were collected according to FDEP-SOP-001/01. 

Sampling will be completed by January 2009. The Bureau of Laboratories in Tallahassee will 

analyze all samples. 

The following were performed at each site:

• Hydrologic Modification Scoring;

• SCI;

• Habitat Assessment (HA);

• Percent Canopy Cover;

• Rapid Periphyton Survey;

• Qualitative Periphyton Collection;

• Linear Vegetation Survey;

• Meter Readings (dissolved oxygen [DO], specific conductivity, pH, and 

temperature); and

• Water Chemistry (total Kjeldahl nitrogen [TKN], TP, ammonia, nitrate-nitrite, 

turbidity, chlorophyll a, color, total organic carbon [TOC], total suspended solids

[TSS]). 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

19

A majority of the sites were selected from a previous statewide intensive Dissolved Oxygen 

Study conducted in 2005 and 2006, and included sites with a variety of Land Development 

Intensity (LDI) Index scores and nutrient regimes. Additional sites were located near National 

Pollutant Discharge Elimination System (NPDES) point sources with known nutrient-enrichment 

issues. Sites were geographically diverse in an attempt to represent as much of the state as 

possible. The following two types of sites were sampled:

• Sites located upstream and downstream from high-nutrient point source 

discharges; and

• Sites located along a nutrient gradient, with low, medium, and high nutrient 

regimes.

Since the objective of the study was to emphasize the effects of nutrients on biota, attempts 

were made to minimize or account for confounding factors, such as poor habitat and highly 

modified hydrologic regime. This especially applied to the sites not affected by point sources. 

In an effort to reduce the effects of confounding variables, only sites with minimal to moderate 

levels of habitat or hydrologic modification, as determined by Florida’s HA and Hydrologic 

Modification Scoring, were selected. For the sites upstream and downstream from point 

sources, the most important factor was to ensure similar habitat and hydrology at the paired 

sites to emphasize the nutrient influences from the discharge. 

A primary purpose of this study was to determine the effects of nutrient concentrations on 

biological health. Habitat suitability (substrate diversity and abundance), flow, and length of 

inundation were taken into account when deciding appropriate sites to sample. An HA, 

Hydrologic Modification Score, and Percent Canopy Cover were obtained at all sites to 

adequately characterize these important variables. Additionally, staff carefully assessed the 

existing and antecedent flow conditions of each site to determine that conditions were 

appropriate for the purpose of the study. A site reconnaissance was also performed to make 

sure the sites chosen were appropriate for the study objectives.

Throughout the course of the study, each District collected one water chemistry blank and 

performed duplicate sampling at a site with adequate habitat in order to assess the variability in 

SCI, RPS, and Qualitative Periphyton Collection results.

3.3.3 Anticipated Study Outcomes and Statistical Approach

It is anticipated that this work, together with FDEP’s existing extensive statewide biological 

database (SBIO), will provide information to establish causal links between water column 

nutrient levels and adverse biological responses in plant, algal, and macroinvertebrate 

communities. Nutrient concentrations associated with “exceptional” or “healthy” biological index 

scores (SCI, LVI, or SPI) will be statistically evaluated against the nutrient concentrations of 

sites with “impaired” index scores to determine potential dose-response relationships, including 

the exploration of responses in individual metrics or attributes. If such cause-effect relationships 

are discerned, the resulting criteria would include an appropriate margin of safety to ensure the 

protection of healthy, well balanced aquatic communities.

Furthermore, it is anticipated that the study will help to elucidate the effects of other variables 

(e.g., habitat, flow, canopy cover) on the expression of nutrients. A concurrently planned study 

on stressor identification and the development of a statewide stressor identification model will 

complement this proposed work.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

20

FDEP anticipates that the statistical analysis of the resulting data will be sufficiently rigorous to 

detect biological responses to nutrient enrichment. The ability to statistically determine patterns 

in the data depends on sample size, the degree of variability in the data, the level of significance

used, and the desired power to detect differences among groups. FDEP will use the most 

robust statistics appropriate to the data characteristics generated from the study. It intends to 

investigate relationships between nutrient concentrations and biological response with several 

statistical tools, including the following:

• Ordinary least squares regression; 

• Quantile regression;

• Conditional probability analysis; and

• Change point analysis.

FDEP will initially investigate biological responses to nutrient enrichment as univariate functions

of either phosphorus or nitrogen, using the statistical tools listed above. However, because 

biological response to nutrients is complex and influenced by numerous other ecological, 

hydrological, and biogeochemical factors, simple univariate models may not be sufficiently 

rigorous to support numeric nutrient criteria. If this is the case, FDEP will investigate more 

complex multivariate techniques that will take into account the influence of factors other than 

nutrients on biological response. Under this scenario, FDEP will investigate statistical 

techniques such as the following: 

• Multiple regression;

• Classification and ordination; 

• Cluster analysis; 

• Principle components analysis; and,

• Canonical correspondence analysis.

This study will fill significant informational gaps in the understanding of stream flora and fauna 

responses to excess nutrient enrichment. Thus, it will help the state continue to make progress 

towards the timely adoption of numeric nutrient criteria in the time frames presented in Section 

9. Specifically, the state anticipates completing sample collection by January 2009 and data 

analysis and synthesis within an additional four to five months thereafter. FDEP anticipates

deriving numeric phosphorus and nitrogen criteria for Florida streams by December 2009, 

assuming the successful completion of this project. 

Note, however, that if the results from the study are of insufficient statistical rigor to promulgate 

scientifically defensible criteria, additional sampling and analysis may be needed, resulting in a 

time extension. The results derived from the study will be presented before FDEP’s Nutrient 

Criteria TAC.

3.4. Development and Initial Application of the Nutrient Benchmark 

Distributional Approach

The TAC and FDEP staff discussed the benchmark distributional approach over the course of 

numerous meetings. The TAC indicated its support for FDEP’s proposed application of the 

overall approach (which includes the option of requiring confirmation of biological impairment
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

21

and use of the resultant thresholds in the IWR rather than in Chapter 62-302, F.A.C.) and 

recommended that FDEP needed to provide sufficient documentation substantiating low human 

disturbance levels and biological health (i.e., supporting the designated use) of the selected 

benchmark sites. 

Based on the direction provided during TAC discussions in 2006, FDEP staff conducted a pilot 

study to develop nutrient criteria for streams in the peninsula bioregion (Figure 4) using the 

benchmark distributional approach. FDEP developed and utilized an extensive multi-step 

evaluation of potential benchmark sites to ensure that the sites used in the derivation of nutrient 

thresholds for the peninsula bioregion truly represented low levels of human disturbance. This 

multi-step evaluation included the following: 

(1) Screening for sites with an LDI score less than or equal to 2.0;

(2) Screening to exclude waters on the state’s 303(d) list of impaired waters;

(3) Verifying surrounding land use using high-resolution aerial photographs;

(4) Obtaining input from district biologists knowledgeable about the area;

(5) Conducting a statistical outlier analysis; and 

(6) Carrying out an extensive field evaluation of approximately 10% of the remaining 

waterbodies (identified by Waterbody Identification number, or WBID2

) containing 

benchmark sites.

3.4.1 Identification of Candidate Benchmark Sites (LDI)

Candidate benchmark sites were initially selected based on an application of the LDI. Brown 

and Vivas (2005) developed the LDI as an estimate of the intensity of human land uses based 

on nonrenewable energy flow. The application of the LDI is based on the ecological principle 

that the intensity of human-dominated land uses in a landscape affects the ecological processes 

of natural communities. More intense activities will result in greater effects on ecological 

processes. Natural landscapes with little or no agricultural or urban development will likely have 

intact ecological systems and processes. The intended use of the LDI was as an index of the 

Human Disturbance Gradient (HDG).

The LDI is calculated as the area-weighted value of the land uses within an area of influence. 

Using the land use coefficients and the percent area occupied by each land use as determined 

by geographic information system (GIS) land use coverages developed from high-resolution 

aerial photographs, the LDI is calculated as follows:

LDITotal = Σ (LDCi * %LUi)

where,

LDITotal = LDI for the area of influence;

%LUi

 = percent of total area of influence in land use i; and

LDCi = LDI coefficient for land use i.

 2 WBIDs were originally developed for 303(d) assessment purposes and were based on drainage basins defined by the U.S. 

Geological Survey (USGS) eight-digit Hydrologic Unit Codes (HUCs).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

22

For the purposes of candidate benchmark site selection, LDI values were calculated from land 

uses within a buffer area of 100 m on each side of the stream and 10 kilometers (km) upstream 

of the sampling point. Fore (2004) previously demonstrated that LDIs calculated using a 100 m 

buffer were slightly better predictors of biological health (i.e., SCI) than LDIs calculated on the 

entire upstream catchment area (watershed). 

The fact that an LDI calculated using the 100 m corridor was a better predictor of ecological 

health was most likely due to the demonstrated effectiveness of riparian buffer zones in 

removing pollutants, especially nutrients, from stormwater inputs (both surface and subsurface 

flow). Studies have shown that buffer zone widths of up to 60 m are sufficient to reduce the 

nutrient load by up to 95% before reaching the stream (Peterjohn and Corell, 1985). 

Additionally, buffer zones in the Coastal Plain areas are the most effective in retaining nutrients 

because of gradual slopes, permeable soils, and the abundance of roots that enter the shallow 

ground water zones (Lowrance, 1997). Since phosphorus is typically found bound to 

sediments, riparian zones retain most of the incoming phosphorus by capturing sediments. 

Similarly, nitrate in shallow ground water beneath riparian zones was removed by 85 to 90% 

due to plant uptake and denitrification in riparian zones 50 to 70 m wide (Lowrance, 1992;

Jordan et al., 1993; Jacobs and Gilliam, 1985; Lowrance, 1997).

While numerous studies have concluded that buffer widths of 50 to 70 m are sufficient to reduce 

stormwater nutrient loads to streams by as much as 95%, additional buffer width will provide 

additional protection to a waterbody. Based on these literature findings and the better 

correlations with biological health described above, FDEP concluded that an LDI calculated 

using a 100 m corridor is an appropriately rigorous method of selecting candidate benchmark 

sites with minimal human disturbance and healthy biological communities.

As discussed in Appendix A, the LDI was specifically designed as a measure of human 

disturbance. LDI values less than or equal to 2.0 within the 100 m buffer area indicate very 

minimal levels of human disturbance. Numerous studies and evaluation have demonstrated, 

across multiple waterbody types and taxonomic groups, that the LDI is an accurate predictor of 

biological health—i.e., healthy, well-balanced biological systems are much more likely to occur 

at sites with low LDIs (≤ 2.0) than at higher disturbance levels (Fore , 2004; Niu, 2004; Brown 

and Reiss, 2006; Fore et al., 2007a). Furthermore, it has been demonstrated that a LDI of 2.0 is

a consistent and conservative biologically significant breakpoint that can be used to distinguish 

benchmark conditions from potentially disturbed areas. 

Although it would be ideal to incorporate direct measures of biological health into the selection 

of benchmark sites, paired nutrient and biological data were not available for all sites in the 

peninsula bioregion. Appendix A provides a more detailed discussion of the LDI and its use at

select benchmark sites. Since it has been demonstrated that the LDI is highly correlated with 

multiple measures of biological health, selecting benchmark sites based on an LDI threshold 

less than or equal to 2.0 is a conservative and ecologically reliable method. 

The initial set of candidate benchmark sites in the peninsula bioregion, with available nutrient 

data of known quality and LDI values less than or equal to 2.0, identified by FDEP consisted of 

379 sites distributed among 155 WBIDs. These sites were considered candidate benchmark 

sites pending further review to demonstrate that they do in fact reflect low levels of human 

disturbance and are representative of the region.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

23

3.4.2 Additional Benchmark Site Evaluation 

The candidate benchmark site list developed from the LDI was then further assessed to ensure 

that the final set consisted of only minimally disturbed sites capable of supporting healthy, wellbalanced biological communities. And due to the nature of nutrients, it is also necessary to 

confirm that downstream biological communities are free from any impact of transported 

nutrients at these upstream levels. The following assessments were designed to capture recent 

land use changes and exclude sites that might not support the designated use—i.e., sites within 

impaired waterbodies: 

• Sites located within waterbodies (WBIDs) placed on the Verified 303(d) Lists as 

impaired for nutrients or DO, where nutrients were identified as the causative 

parameters, were excluded as benchmark sites. Additionally, sites within WBIDs 

placed on the Verified or Planning 303(d) Lists for biological impairments, 

regardless of cause, were excluded from the benchmark population.

• It should be noted that, since the benchmark sites exhibit low LDIs and human 

disturbance, WBIDs identified as impaired for DO with factors other than nutrients 

as the cause likely represent natural conditions for those sites. Further, moderate 

DO excursions below Florida’s current criterion of 5.0 mg/L have not been 

associated with any adverse biological impacts. Therefore, such sites were not 

initially excluded from the benchmark dataset for nutrient threshold development. 

However, FDEP further evaluated these sites using the Stream Condition Index 

(designed to measure healthy, well balanced communities) to ensure DO was not 

an adverse issue. For example, despite the naturally low dissolved oxygen at the 

Middle Prong of the St. Marys River at SR 125 (measured at 2.7 mg/L during the 

benchmark study) the SCI score was in the “Exceptional” category, exhibiting an 

unusually diverse assemblage of sensitive invertebrates and indicating the site is 

clearly meeting its Class III designated use.

• The low level of human disturbance of every candidate site was confirmed via a 

review of recent (2004) high-resolution (1 m ground resolution) aerial photographs. 

This review consisted of searching the photos for recent land clearing or 

development, with particular emphasis on identifying any disturbance that

encroached into the 100 m buffer area used to calculate the LDI. Sites not 

representative of freshwater streams (e.g., tidally influenced or channelized) in the 

peninsula bioregion were also excluded. 

• Twenty-seven sites were excluded based on the review of aerial photographs. Ten 

of the excluded sites appeared to be within canals or channelized streams and 

therefore were not considered representative of a minimally disturbed stream 

condition. An additional 7 sites were excluded because they were potentially 

estuarine or tidally influenced based on proximity to the coast and a subsequent 

review of specific conductance data. All potentially estuarine sites routinely had 

specific conductance levels above 1,275 micromohs per centimeter (μmho/cm)

and episodic values above 4,500 μmho/cm. A conductivity of 4,500 μmho/cm is 

approximately equivalent to a chloride concentration of 1,500 mg/L, which is used 

in Florida as the threshold between predominantly fresh and marine waters. 

• FDEP District staff familiar with streams within their area of the state were asked to 

provide feedback on the list of candidate benchmark sites. Specifically, they were 

presented with the following information and question:

“For ongoing nutrient criteria development, we are identifying sites with benign 

land uses in their upstream watershed (LDI < 2) to define the reference condition. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

24

Ken Weaver has produced the attached table of low LDI peninsular reference 

sites. Can you please look over the list to determine if there are any human 

activities at particular sites, which may not have been captured by the LDI, that 

would disqualify the site from being used to define "reference" for nutrient criteria?”

Twenty-two peninsula pilot study sites were excluded from the benchmark set 

based on feedback and best professional judgment comments provided by District 

staff. Staff identified additional channelized streams, estuarine sites, and 

potentially disturbed sites. It should be noted that all the excluded sites were 

previously identified and confirmed as having a low LDI. In some cases, staff 

identified potential point source discharges or localized disturbances (e.g., cattle in 

a stream) that may not have been captured in the LDI calculation. In other cases,

sites were excluded because the reviewer was aware of moderate to high levels of 

development in the watershed that were outside the 100 m buffer but potentially 

had an indirect (e.g., ground water) or minor effect on stream conditions; however, 

the sites may still be representative of low human disturbance levels. The 

exclusion of these potentially disturbed sites represents a conservative component

of the FDEP approach designed to ensure that the benchmark set consists solely of 

sites with low human disturbance levels that are supporting the designated use.

3.4.3 Field Evaluation of Peninsula Bioregion Benchmark Stream Sites

In February 2007, FDEP initiated an intensive field study of the candidate peninsula bioregion 

benchmark sites to provide additional assurance that the sites truly supported healthy, wellbalanced aquatic communities and had low human disturbance levels. A subset of the 

population of candidate benchmark sites was selected for additional review, with the objective of 

building additional confidence in FDEP’s extensive multi-step validation process for identifying 

benchmark sites. Biological data were collected with the objective of confirming that the sites 

did in fact support healthy, well-balanced biological communities and to demonstrate that an 

upper percentile (i.e., 75th to 95th percentile) was protective of this biological community. 

Experienced FDEP staff visited a total of 30 candidate benchmark sites, representing 26 

WBIDs, between February 5, 2007, and March 7, 2007, and assessed then for inclusion in the 

final set of benchmark sites. The candidate benchmark sites evaluated in this study were 

initially selected using an LDI less than or equal to 2.0 and other assessments described above. 

Study sites were selected to cover the range of phosphorus concentrations exhibited by the 

population of candidate benchmark sites. Sites were grouped by their geometric mean TP 

concentrations for the period of record (sites with means ≥ 90, < 90-60, and < 60 μg/L). At least

10 sites within each concentration range were visited and evaluated during this study. Overall, 

long-term geometric mean TP concentrations at study sites ranged from 30 to 140 μg/L,

and long-term geometric mean TN concentrations ranged from 0.6 to 2.1 mg/L. Sites were also 

selected to be representative of most of the WBIDs in the candidate benchmark dataset. The 

site with the most extensive and longest period of record was selected to represent the WBID. 

Site evaluations included a survey of anthropogenic inputs and surrounding land uses. The 

survey included both an on-site inspection of the stream channel at least 200 m upstream of the 

sample point and a driving tour of accessible areas in the watershed upstream of the sampling 

site. Field investigations of the watersheds were guided by high-resolution aerial photographs 

taken in 2004 and maps of the entire drainage basin. Investigators made observations 

concerning potential human disturbances in the watershed that might affect conditions within a 

given stream. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

25

Additionally, experienced staff characterized the sites using both FDEP’s standard HA and 

Hydrologic Modification Scoring systems as objective measures of human disturbance. FDEP 

biologists routinely calculate the HA index whenever stream macroinvertebrate samples are 

collected (FDEP, 2008). The index evaluates substrate condition and availability, water velocity, 

habitat smothering (e.g., by sand and silt), channelization, bank stability, and the width and 

condition of riparian vegetation. The Hydrologic Modification Scoring system was originally 

developed to support the development of Florida’s SCI and is scored based on knowledge of 

water removal, ditching and draining, control structures, impervious surfaces, and hydrographs 

for the sites under evaluation (Fore, 2004; Fore et al., 2007a).

At each site, trained and experienced FDEP staff also collected and analyzed the biological, 

chemical, and physical parameters listed below following standard FDEP SOPs: 

(http://www.dep.state.fl.us/labs/sop). Water levels were evaluated both by reviewing

hydrographs from the given stream or other streams in the general vicinity and by visual 

inspection of the stream habitats. Biological samples (e.g., SCI) were not collected if, based on 

the judgment of the experienced investigator, a majority of the aquatic habitat was exposed to 

the air rather than being inundated. 

Bioassessments could not initially be conducted at 17 out of the 31 sites visited due to 

protracted drought conditions prior to and following the study. However, significant rainfall 

occurred in August, 2008 (Tropical Storm Fay), and FDEP staff conducted follow-up biological 

assessments during December 2008 at the previously dry or low flow sites. Sampled 

parameters were selected both to verify the benchmark status of candidate sites and to support 

anticipated future efforts such as statewide numeric nutrient criteria and biological index (e.g., 

RPS, periphyton index) development. 

It should be noted that no calibrated interpretative tool existed for the periphyton parameters

when these data were analyzed; therefore, the interpretation of results was primarily qualitative. 

Methods for the RPS are still under development and no interpretation framework for the 

method currently exists; thus, RPS results have not yet been evaluated. The RPS may be used 

as a response variable in the future to help refine nutrient thresholds, after more data have been 

collected and benchmark expectations have been established.

3.4.3.1 Parameters Monitored During the Survey

Information acquired during the site and watershed evaluations was used to provide final 

confirmation that the remaining candidate sites were in fact representative of the benchmark 

stream condition for the bioregion. Taken together with the LDI and other screening criteria, the 

results of the peninsula benchmark stream survey provide an extremely high level of confidence 

that FDEP’s benchmark set represents a low level of human disturbance that is supportive of 

the designated use, and these facts are documented in the benchmark site summaries 

(Appendex C) attached as separate documents. Table 4 lists the parameters monitored during 

the peninsula bioregion benchmark stream survey. 

Table 4. Parameters monitored during the peninsula bioregion benchmark 

survey

Biological Parameters Chemical and Physical Parameters

• SCI • TP

• RPS • Nitrite + Nitrate

• Natural Substrate Periphyton 

(i.e., periphyton taxonomy)

• TKN

• Ammonia
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

26

• HA • Color

• Chlorophyll a • Turbidity 

• Phaeophytin • Specific Conductance (in situ)

• Algal Growth Potential (AGP) • DO (in situ)

• pH (in situ)

• Water Temperature (in situ)

Although FDEP staff were unable to collect biological samples at some sites due to low water 

conditions, the available data indicate that the benchmark sites support healthy, well-balanced 

populations of flora and fauna even at nutrient concentrations above the 90th percentile of the 

benchmark distribution (Figures 5 and 6). Exceptional biological communities (SCI ≥ 68) were 

found at sites with TP concentrations as high as 350 μg/L and long-term mean concentrations 

up to 128 μg/L. Similarly, exceptional biological communities (SCI ≥ 68) were found at sites with 

TN concentrations exceeding 1.7 mg/L. After this preliminary analysis was completed, 

additional biological and water quality data were collected at the sites that could not initially be 

sampled due to low water (see Appendix C).

Therefore, it can be confidently concluded that TP concentrations at least as high as the 90th

percentile, which is derived and discussed below, are protective of the natural populations of 

flora and fauna in streams with low human disturbance. Furthermore, the percent composition 

of major algal taxonomic groups (phyla) were very similar across the range of nutrient 

concentrations investigated (Figures 7 and 8). The periphyton communities at all the sites were 

highly dominated by diatoms (Bacillariophyta), with low percentages of green (Chlorophycota) or 

blue-green (Cyanophytcota) algae. Additionally, taxa richness was high (40–66) at all 

benchmark sites, except for Robert’s Branch (SEM426LV).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

27

Figure 5. Plots of SCI versus TP concentrations at sites visited during the 

peninsula benchmark stream survey

The dashed vertical line in each graph is the 90th percentile TP concentration of the benchmark distribution. 

Phosphorus values are given as both the sample concentration on the SCI collection date (A) and the period of 

record geometric mean (B) for the site. SCI values of 68 or above are considered to be indicative of an exceptional 

biological community, while values to 35 are considered healthy and well-balanced (Fore et al., 2007a). Values 

below 35 are considered impaired. The slopes on the regression lines are not significantly different from 0, indicating 

that there is no relationship between TP and SCI within this concentration range.

Geometric Mean Total Phosphorus (mg/L)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

SCI

0

20

40

60

80

100

Total Phosphorus (mg/L)

0.0 0.1 0.2 0.3 0.4

SCI

0

20

40

60

80

100

Exceptional

Healthy

Impaired

y = 2.5x + 67.5

R2 = 0.0004

p=0.956

Exceptional

Healthy

Impaired

y = -16.018x + 69.142

R2 = 0.015

p=0.908

A.

B.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

28

Figure 6. Plots of SCI versus TN concentrations at sites visited during the 

peninsula benchmark stream survey

The dashed vertical line in each graph is the 90th percentile TN concentration of the benchmark distribution. Nitrogen 

values are given as both the sample concentration on the SCI collection date (A) and the period of record geometric 

mean (B) for the site. SCI values of 68 or above are considered to be indicative of an exceptional biological 

community, while values to 35 are considered healthy and well-balanced (Fore et al., 2007a). Values below 35 are 

considered impaired. The slopes on the regression lines are not significantly different from 0, indicating that there is 

no relationship between TN and SCI within this concentration range.

Geometric Mean Total Nitrogen (mg/L)

0.0 0.5 1.0 1.5 2.0

SCI

0

20

40

60

80

100

Total Nitrogen (mg/L)

0.0 0.5 1.0 1.5 2.0

SCI

0

20

40

60

80

100

Exceptional

Healthy

Impaired

y = -5.7x + 72

R2 = 0.031

p=0.602

Exceptional

Healthy

Impaired

y = -2.5x + 70.3

R2 = 0.0033

p=0.866

A.

B.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

29

Figure 7. Plots of percent (A) Bacillariophyta, (B) Cryptophycophyta, and (C) 

Cyanophycota collected on natural substrates versus site period of 

record geometric mean TP concentrations

The dashed vertical line in each graph is the 90th percentile TP concentration of the benchmark site distribution. Percent Bacillariophyta

50

60

70

80

90

100

Percent Chlorophcota

0

2

4

6

8

10

Geometric Mean TP (mg/L)

0.04 0.06 0.08 0.10 0.12 0.14

Percent Cyanophytcota

0

5

10

15

20

25

C.

A.

B.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

30

Figure 8. Plots of percent (A) Bacillariophyta, (B) Cryptophycophyta, and (C) 

Cyanophycota collected on natural substrates versus site period of 

record geometric mean TN concentrations

The dashed vertical line in each graph is the 90th percentile TN concentration of the benchmark site distribution. Percent Bacillariophyta

50

60

70

80

90

100

Percent Chlorophytcota

0

2

4

6

8

10

Geometric Mean TN (mg/L)

0.50 0.75 1.00 1.25 1.50 1.75

Percent Cyanophcota

0

5

10

15

20

25

C.

A.

B.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

31

3.4.4 Statistical Outlier Analyses

An analysis of statistical outliers was performed to identify data and sites that were

uncharacteristic of the general peninsula dataset used to derive nutrient criteria for the 

bioregion. This was done to help evaluate the dataset and prevent the nutrient criteria for the 

bioregion from being unjustifiably biased by a small number of sites that are not representative

of the peninsula bioregion (including data from areas affected by significant natural phosphate 

deposits). 

The outlier analysis was performed using standard statistical methods by defining the outlier 

limit as:

75th percentile + 1.5 * Interquartile Range

Data points identified as outliers were excluded from the dataset. In addition, if more than 50% 

of the data for an individual site were identified as outliers, then all the data for that site were 

excluded, since the remaining data for the site cannot be considered representative of the site.

3.4.5 Calculation of Annual WBID Geometric Mean

A number of the benchmark waterbodies were sampled numerous times and by different 

agencies. The sampling sites used by the different samplers were often located within several 

hundred meters of each other. Therefore, to avoid biasing the analyses toward the larger 

waterbodies with multiple sampling sites near to each other, the station level data were

aggregated by WBID. 

The data were also aggregated over time through the calculation of the annual WBID geometric 

mean. An annual period was selected because elevated nutrient levels are not acutely toxic in 

the aquatic environment; instead, their effects are chronic and cumulative over time. Nutrient 

concentrations typically vary over time and exhibit a log-normal distribution in the aquatic 

environment. Therefore, instantaneous criteria are not generally considered practical or 

appropriate for nutrients, and are better expressed as an average over a longer period. 

Additionally, the geometric mean is often used to provide a more accurate representation, rather 

than an arithmetic mean, of the central tendency of positively skewed data (e.g., log-normal), 

such as nutrients. The use of the annual geometric mean mutes short-term variability and

provides a more reliable, long-term value for assessing the nutrient status in aquatic 

environments.

3.4.6 Defining Nutrient Limits

A key issue of the pilot study was the selection of the appropriate percentile to use for the 

numeric criterion. Since benchmark sites are optimally functioning systems supportive of the 

designated use, selecting a percentile at the upper end of the distribution (i.e., 90th to 95th

percentile) as a criterion is an appropriate decision. This method establishes the range of 

nutrients characteristic of these biologically healthy sites, with a necessary allowance for 

confidence in protection, balanced against the possibility of only 5 to 10% of these biologically 

healthy sites being potentially misidentified as impaired. The range of nutrient concentrations 

associated with benchmark sites is considered to represent nutrient levels expected in areas 

with low levels of human disturbance. An upper percentile distribution of the benchmark site 

population will yield an ecologically justifiable, inherently protective criterion. 

Due to the high degree of confidence in the benchmark sites derived through FDEP’s multi-step 

selection process, FDEP used the 90th percentile annual WBID geometric mean TN and TP 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

32

concentrations for benchmark sites (grouped by WBID) in the peninsula bioregion as the basis 

for protective numeric nutrient criteria for streams in the bioregion. The extensive verification of 

the benchmark sites provided a high level of confidence that the resulting benchmark 

distribution truly represented low levels of human disturbance that fully achieved the designated 

use of the streams (supporting healthy populations of aquatic flora and fauna). Local use 

support can be confirmed via coincident nutrient and bioassessment sampling, with the 

hypothesis that nutrients associated with these minimally disturbed upstream reaches will be 

inherently protective of downstream waters. The “proof of concept” that downstream conditions 

still support healthy, well balanced communities will be demonstrated by the Longitudinal Study.

The use of the 90th percentile is further supported by the fact that numerous waterbodies with 

phosphorous concentrations up to and including this level of phosphorus were shown to support 

healthy populations of aquatic flora and fauna and fully achieved their designated use. Further, 

to ensure that the data used were of the highest quality, only data from sources in which the 

quality of the data could be verified were utilized in the analysis. The application of this method 

gives calculated criteria of 1.7 mg/L for TN and 113 μg/L for TP.

3.4.7 Ongoing and Future Efforts

During the fall and winter of 2008, FDEP conducted an intensive benchmark site validation 

process, developed and tested during the peninsular pilot study, to candidate benchmark sites 

in the panhandle and northeast bioregions. In addition, peninsular benchmark sites that could 

not be previously sampled due to low water levels were revisited in December 2008. Field 

reconnaissance and data collection trips for all benchmark sites were completed in December 

2008. These statewide site evaluations were conducted for the following reasons:

(1) To confirm and build confidence that the benchmark sites are affected by only low 

levels of human disturbance;

(2) To support the use of an upper percentile nutrient concentration inclusive of the 

benchmark distribution as a numeric nutrient criterion; and 

(3) To confirm that healthy, well-balanced biological communities (flora and fauna) 

are protected and maintained at or below a criterion established at the selected 

upper percentile (e.g., 90th percentile). 

3.5 Stressor Identification Study

Historically, FDEP has focused on water quality as the predominant means for assessing water 

body integrity (i.e., impairment status). Through the use of EPA Section 319 funding, FDEP has 

developed biological assessment tools (e.g., Florida’s SCI, BioReconnaissance [BioRecon], and 

LVI) and habitat assessment procedures as additional means of identifying impairment, 

especially related to nonpoint source issues. Although bioassessments are useful in 

determining biological impairment, they do not identify the cause of the impairment, which is 

required under the Florida Watershed Restoration Act before listing a waterbody as impaired. 

Currently, a Best Professional Judgment methodology is used to identify the pollutant of 

concern. The development of a statistically based model(s) for the identification of impairment 

causes would improve the effectiveness and defensibility of FDEP decisions.

Additionally, identifying the primary causative factors most influential in contributing to biological 

failures would allow FDEP to focus its limited resources on properly mitigating the responsible 

stressor(s). Therefore, a legally defensible procedure to determine the causative factor(s) is 

needed. EPA has developed procedures for stressor identification (e.g., Causal 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

33

Analysis/Diagnosis Decision Information System [CADDIS]) that are useful only for selected 

sites after fairly substantial data collection efforts. Florida plans to build on these stressor 

identification concepts to develop a statistical model or multiple models (Statewide Stressor 

Identification Model[s]) that incorporates the major nonpoint source stressors widespread in 

Florida:

• Hydrologic modification; 

• Habitat alteration; and,

• Water quality issues (e.g., nutrients, sediments, and biochemical oxygen demand

[BOD]).

The development of a calibrated statewide model would prevent Florida from having to perform 

EPA-style, site-specific stressor identification studies at all biologically impaired sites (a 

cumbersome and expensive task). It is anticipated that the Statewide Stressor Identification 

Model(s) will allow FDEP to streamline restoration efforts by identifying the most pervasive 

human nonpoint stressors in Florida. 

The overall approach for this project will involve the assessment and collection of a complex 

suite of data in order to develop the Statewide Stressor Identification Model(s). Initial emphasis 

will be on current FDEP tools used to measure the algal (periphyton and phytoplankton), 

invertebrate, and macrophyte community health of streams, and EPA’s list of common 

candidate causes, which include the following:

• Nutrient inputs,

• Flow alterations,

• Sediments,

• Metals,

• DO,

• Temperature, 

• Ionic strength, and

• Habitat assessment.

FDEP plans to use multivariate statistics to investigate the relationships between all available 

physical, chemical, and biological data, evaluating significant variables and their relative 

influence on a system. An iterative process will be employed, consisting of data analysis and 

the exploration of conceptual models, with discovered relationships used as inputs for 

developing even more effective models. FDEP will pose a series of hypotheses (conceptual 

models) and then statistically examine the relationship between stressor(s) and responses. 

Examples of hypotheses include the following:

• Turbid runoff, leading to sediment smothering, will cause low SCI scores;

• High nutrients, coupled with sunlight and sluggish flow, will lead to excessive 

periphyton in habitats and reductions in periphyton community and invertebrate 

health; and
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

34

• Extreme hydrologic fluctuations, regardless of ambient water quality, will lead to low 

SCI scores, etc.

Additionally, biological Stressor Indices (i.e., response signature metrics) may be developed that 

provide better resolving power in identifying specific types of stress. The Stressor Identification 

Model(s) will be constructed once significant stressor relationships are known. The model(s) 

will identify the relative influence of major stressors in contributing to biological impairments. 

From this more complex model, FDEP will investigate the possibility of a simplified model with 

reduced inputs. Finally, EPA-style stressor identification will be performed at a number of sites 

to verify the model(s).

The tasks associated with this project are anticipated to include but are not necessarily limited 

to the following:

• Analyze current data: Review water quality and biological data and identification 

of data gaps for future data collection;

• Evaluate and modify Stressor Indices as necessary: Investigate response 

signature metrics for the construction of Stressor Indices;

• Identify possible conceptual model(s): Determine conceptual model(s) 

designed to predict the relationship between the stream Stressor Index and 

causative variables;

• Collect additional data: Collect data to fill data gaps identified in previous tasks; 

• Develop Stressor Identification Model: Develop appropriate model(s) based on 

water quality and biological data; and

• Validate Model(s): Validate model(s) with an independent dataset and verify by 

comparing the model(s) output with the output of deterministic stressor 

identification (e.g., CADDIS).

Once this model is developed, it can be used to better quantify the relationship between nutrient 

levels and stream health, given all the different factors influencing aquatic life.

3.6 Development of the Stream Periphyton Index

FDEP recently developed and validated a multimetric index based on periphyton samples from 

Florida streams (the SPI), but the index has yet to be calibrated. The following briefly describes

this ongoing process.

(1) Evaluate algal distributional patterns: FDEP identified patterns of taxonomic 

distribution for algal species. If needed, metrics will be calibrated separately 

within each region to ensure that the final index value represents the same level 

of biological condition independent of natural features.

(2) Develop gradients of human disturbance: The HDG combined measures of 

water quality, habitat condition, hydrologic condition, and LDI. In addition, a 

multimetric nutrient index based on probabilistic data was developed to combine 

measures of in-stream nutrient concentrations. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

35

(3) Identify and calculate candidate metrics for stream algae: Appropriate 

biological metrics were identified and calculated from published taxa lists for both 

diatom and nondiatom (soft) algae taxa. 

(4) Test taxa against the HDG: Using the HDG, this analysis tested the response of 

individual diatom and nondiatom taxa to an independently derived measure of site 

condition. The Florida sensitive taxa and the very tolerant taxa metrics were

identified using this process. 

(5) Test metric response to human disturbance: FDEP tested the association 

between the metrics and the HDG and the nutrient index. Metrics were evaluated 

for the influence of natural features such as stream size, latitude, and bioregion. 

After selecting the metrics with a reliable response to disturbance, the redundancy 

of individual metrics was evaluated. Effective metrics that will be incorporated into 

the SPI include the number of algal cells requiring high oxygen, the number of 

oligosaprobic cells, Van Dam’s TSI, the percent Florida sensitive cells, and the 

percent Florida tolerant cells. Additional “soft algae” metrics are still be 

investigated.

(6) Develop multimetric index: Metrics were converted into a final index which 

scores from 0-100. Stream classification was evaluated to determine whether 

metric scoring rules should compensate for any underlying regional difference, 

such as pH. The index was tested against the HDG and outliers identified and 

evaluated for additional sources of disturbance.

(7) Validate results: FDEP used an independent dataset to validate results from the 

initial periphyton index analysis. The index and its component metrics were

calculated for at least 50 new sites as an independent test of the observed algal 

response to disturbance.

(8) Conduct power analysis: Using repeat visits, the percentage of change that the 

multimetric index can detect was determined. FDEP also evaluated the influence 

of repeat sampling for increasing the precision of stream algal assessments.

(9) Calibrate the BCG: In conjunction with EPA, in February, 2009 Florida is 

convening a panel of national periphyton and ecological experts to calibrate the 

SPI via the BCG approach. It is anticipated that this may potentially provide a 

numeric target for the determination of an impairment threshold, which then would 

be used to establish protective nutrient criteria.

It is anticipated that the resulting SPI will be an extremely useful response variable for 

determining impairment associated with nutrient enrichment in streams, and it may also be 

adopted as Biocriteria in Chapter 62-302, F.A.C. (water quality standards).

3.7 Downstream Effects of Nutrients in Selected Florida 

Rivers/Estuaries (Nutrient Longitudinal Study)

FDEP initiated a Nutrient Longitudinal Study during the summer of 2008 designed to evaluate 

downstream biological responses to naturally high nutrient levels. Biological responses to 

excess nutrients can be separated in space and time from actual enrichment sources—i.e., an 

adverse response to nutrients may occur well downstream from the actual enrichment. FDEP’s 

hypothesis is that within systems with low levels of human disturbance and intact ecological 

processes, naturally high levels of nutrients can be assimilated into biota and sediments without 

causing adverse biological responses, including downstream estuaries. The goal of this study is 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

36

to demonstrate that nutrient concentrations representative of the upper portion of the 

benchmark site distribution actually support the designated use of downstream reaches. 

3.7.1 Project Objectives 

The objectives of the study were as follows:

(1) Collect physical, chemical, and biological data throughout the length of selected 

Florida river/estuary systems to establish the relationship between nutrient levels 

and adverse biological responses, including the most sensitive (generally 

downstream) reaches; and

(2) Analyze the resulting dataset as one line of evidence in FDEP’s effort to establish 

numeric nutrient criteria, particularly relating to the protection of downstream 

waters.

3.7.2 Project Description

The study focused on relating the effects of nutrients on various biological systems, from 

upstream to downstream, including the most sensitive areas, which typically are slowly flowing 

lower reaches or estuaries. Two systems were studied: Waccasassa River and Estuary and

Steinhatchee River and /Estuary. 

Semiannual sampling was carried out for the biological components and water quality 

parameters. The first sampling occurred in summer 2008, and the second was done in January 

2009. All samples were collected according to FDEP-SOP-001/01. The FDEP Bureau of 

Laboratories in Tallahassee will analyze water, biological, and sediment samples.

The following was performed at sites where appropriate (dependant on salinity, etc.); the 

location of sites in each system was established after a reconnaissance trip:

• Water Chemistry (TKN, TP, ammonia, nitrate-nitrite, turbidity, chlorophyll a, color, 

TOC, TSS) (monthly);

• Meter Readings (DO, specific conductivity, pH, and temperature) (monthly);

• Phytoplankton Community Composition (monthly);

• Microcystin Analyses (if warranted from results of algal ID) (to be determined);

• SCI (quarterly);

• HA (quarterly);

• Percent Canopy Cover (quarterly);

• RPS (quarterly);

• Qualitative Periphyton Collection (quarterly);

• Linear Vegetation Survey (quarterly);

• Sediment Nutrients (semiannually);

• Sediment Nutrient Flux Experiments (semiannually); and

• Hydrologic Modification Scoring (once).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

37

Both systems were selected to represent conditions of relatively low human disturbance, 

especially with respect to nutrient enrichment. The nutrient regime at the Waccasassa ranges 

toward values that are less than the peninsular benchmark site distribution average, while the 

Steinhatchee ranges from near the average to the upper end (90th percentile) of the benchmark

site nutrient distribution average.

Since the objective of the study is to emphasize the effects of nutrients on biota, attempts were

made to minimize or account for confounding factors during site selection. Habitat suitability 

(substrate diversity and abundance), flow, and length of inundation were examined when 

deciding appropriate sites to sample. An HA, Hydrologic Modification Score, and Percent 

Canopy Cover determination was performed at all sites to adequately characterize these 

important variables. Additionally, staff carefully assessed the existing and antecedent flow 

conditions of each site to determine that they were appropriate for the purpose of the study.

There were some issues associated with extremely low flow during the first field sampling effort. 

It is anticipated that winter rains have increased water velocities, and those conditions will be 

reflected during the January 2009 sampling event.

3.7.3 Project Outcomes

FDEP hopes that this work will provide evidence that criteria developed using the benchmark 

distributional approach are protective of downstream waters. The knowledge that biota in 

downstream waters are sufficiently protected would help in establishing numeric nutrient 

thresholds or criteria using the benchmark distributional approach. Furthermore, it is anticipated 

that the study will help to elucidate the effects of other variables (e.g., habitat, flow, canopy 

cover) on the expression of nutrients. FDEP will complete sample collection in January 2009

and will analyze/synthesize the results in an additional six to eight months. 

3.8 Nitrate-Nitrite Analysis in Streams/Spring Runs

Florida springs are highly valued for their aesthetic and recreational attributes. The state has 

approximately 600 springs, which are visited by millions of people each year for swimming and 

boating because of their beautiful, clear waters. Human activities during the past 40 years have 

resulted in increased nitrate-nitrite concentrations in many springs, and anecdotal evidence 

suggests that this has contributed to the currently observed nuisance plant and macroalgal 

accumulations in many springs. FDEP recently evaluated nitrate trends at 22 Florida springs 

and determined that the mean nitrate-nitrite concentration in the 1960s was about 0.2 mg/L,

while the average is currently around 1.0 mg/L.

Multiple lines of evidence indicate that reducing nitrate-nitrite concentrations in springs should 

substantially reduce macroalgal growth rates (Stevenson et al., 2007; Niu and Gao, 2007). In 

turn, the reduced growth rate is expected to result in the reduced frequency, intensity, and 

duration of nuisance macroalgal growths in spring systems. Both nitrogen and phosphorus 

reductions in Florida springs should limit the growth of macroalgae species and subsequently 

reduce macroalgal accumulations. Such reductions should be effective as long as target 

concentrations (e.g., nutrient criteria) are below nutrient concentration thresholds that promote 

excessive algal growth. 

In almost all springs, however, nitrogen (i.e., nitrate-nitrite) reductions may be the only practical 

restoration strategy because natural phosphorus concentrations (those not influenced by 

humans) are generally higher than the levels necessary to constrain algal growth. Results from 

experimental and in situ studies were used to establish the nitrate-nitrite concentration 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

38

necessary to prevent biological imbalances (i.e., to restrict the growth and accumulations of 

nuisance macroalgae and to preserve the native periphyton community structure).

The most accurate and conservative experimental results, those from micro-centrifuge tube 

experiments, suggest that nitrate concentrations less than 0.230 mg/L are needed to slow the 

growth of Lyngbya wollei. Similarly, to reduce the growth of Vaucheria under laboratory 

conditions, nitrate concentrations below approximately 0.261 mg/L would be required

(Stevenson et al., 2007). 

The results of periphyton field surveys conducted at a large number of spring systems indicated 

that nitrate concentrations would need to be reduced below the observed 0.454 mg/L nitratenitrite threshold to reduce the nuisance abundance and cover of Vaucheria sp. in Florida springs 

(Pinowska et al., 2007). Since the 0.454 mg/L threshold represents the lower range of nitrate 

concentrations for sites with excessive algal growth and cover, an appropriate safety margin 

would need to be applied to turn the threshold into a protective criterion.

In addition, nearly a decade of scientific results from periphytometers deployed in the springdominated Suwannee, Santa Fe, and Withlacoochee (north) Rivers clearly indicated an 

imbalance threshold (significant biomass increases and alterations in taxonomic community 

structure) at 0.441 mg/L of nitrate-nitrite. A margin of safety, derived from an analysis of the 

variability in the nitrate-nitrite concentrations in this system, resulted in the final 0.35 mg/L 

nitrate-nitrite criterion. 

Based on the best, most comprehensive scientific data currently available, this criterion provides 

FDEP with reasonable assurance that imbalances of aquatic flora are unlikely to occur below 

this level. The data also indicate that imbalances do occur at nitrate-nitrite concentrations near 

0.45 mg/L and above. Therefore, a nitrate-nitrite criterion of 0.35 mg/L for springs was 

proposed during the ongoing triennial review, which was initiated in July 2008. 

3.9 Lake Algal and Macrophyte Response

FDEP intends to evaluate both algal and macrophyte response thresholds in Florida lakes. 

Staff presented preliminary conditional probability analyses between the LVI and TP and TN

concentrations at the February 25, 2008, meeting of the Nutrient Criteria TAC (Figures 9 and 

10). The analysis with phosphorus showed that the probability of occurrence of an LVI score 

less than 37 (the impairment threshold) increased up to a lake TP concentration of 

approximately 50 μg/L, at which point the probability of impairment leveled off. However, there 

was significant uncertainty at concentrations above 45 μg/L, given the small sample size for 

lakes with concentrations above this level. Similarly, the probability of occurrence of an LVI less 

than 37 increased with increasing TN concentrations. 

These preliminary analyses demonstrate a likely relationship between in-lake nutrients and 

macrophyte community health. Because the paired LVI and nutrient dataset is currently limited, 

particularly in lakes with TP concentrations above 45 μg/L, FDEP conducted additional LVIs with 

paired nutrient samples during the summer and fall of 2008. A subset of lakes previously 

sampled as part of the state’s randomized status and trends monitoring was targeted for LVI 

and water quality sample collection. Although samples were apportioned across the entire 

range of nutrient concentrations, priority was given to lakes with TP concentrations between 45 

and 200 μg/L in an attempt to reduce the uncertainty (i.e., confidence interval width) by 

increasing sample size in this range of nutrient concentrations.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

39

FDEP also intends to evaluate algal responses to nutrients. Initially, the evaluation will be 

based on relationships between nutrients and chlorophyll a concentrations. Secondarily, the 

evaluation will look for relationships between nutrients and metrics contained in the LVI. These 

analyses will include the evaluation of regression models as well as conditional probability using 

ecologically significant thresholds. Conditional probability analysis may include a joint analysis 

of the probability of exceeding either chlorophyll a or LVI impairment targets, since any given 

lake may be either algal or macrophyte dominated. Community-based analyses may follow if 

necessary and pending the development of a calibrated lake phytoplankton index.

3.10 Recreation-Based Criteria

The University of Florida LakeWatch Program conducted a study that correlated Florida lake 

residents’ aesthetic perceptions with simultaneously measured nutrient and chlorophyll a data. 

In the study, residents perceived that lake water was less conducive to swimming and aesthetic 

enjoyment when chlorophyll a concentrations ranged from approximately 17 to 22 μg/L. FDEP 

may potentially use such information as a line of evidence when establishing appropriate lake 

chlorophyll a thresholds; however, it is not pursuing additional studies of this nature at this time.

Figure 9. Probability of observing LVI value less than 37 in Florida lakes if 

specified TP concentration is exceeded

Dashed lines are 90% confidence intervals from bootstrap estimation.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Xc Total Phosphorus Concentration (mg/L)

Probability LVI < 37 | X c

Raw Data Probability

90% C.I.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

40

3.11 Application of Benchmark Distributional Approach to Lakes

The majority of FDEP’s nutrient criteria efforts to date have focused on streams; however, much 

of the data and information necessary to apply the benchmark distributional approach to lakes 

currently exists within the state’s extensive database. If needed, FDEP will have the option of 

applying an approach to lakes using a process similar to that developed for streams. The 

approach will include the same multi-step validation process incorporating land use evaluations 

(e.g., LDI, recent aerial photographs, and field reconnaissance) coupled with confirmations of 

healthy biological communities using the LVI.

Because of the successful calibration of the LVI, FDEP is close to developing response-based 

nutrient criteria for lakes. Therefore, the benchmark distributional approach will only be pursued 

as a secondary line of evidence and will be used only to derive criteria if the recreational-based 

and algal and macrophyte response evaluations fail to identify significant relationships with 

nutrient enrichment.

Figure 10. Probability of observing LVI value less than 37 in Florida lakes if 

specified TN concentration is exceeded

Dashed lines are 90% confidence intervals from bootstrap estimation. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3 3.5 4

Xc TN Concentration (mg/L)

Probability LVI < 37 | X c

Raw Data Probability

90% C.I.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

41

3.12 Approach for Estuaries

Florida estuaries tend to be dynamic, many with widely varying water residence times and 

highly fluctuating salinities, and some with transparency regimes dominated by riverine color 

inputs. Since a direct comparison between any two specific estuaries is difficult, the “EPA 

reference waters” approach appears to be less practical than the “dose-response” approach in 

estuaries. In the approach to estuarine nutrient criteria development, FDEP is seeking to 

establish empirical and other scientific relationships between nitrogen and phosphorus loads 

and response variables that represent a quality of water that supports a particular use. In doing 

so, those estuaries that are currently minimally disturbed will be protected from future adverse 

impacts associated with nitrogen and phosphorus enrichment. Furthermore, criteria for both 

causal and response variables will provide a basis for improving water quality in those estuaries 

currently impacted by excessive nitrogen and/or phosphorus loads. 

FDEP currently intends to utilize its existing TAC—coordinated with the Florida Oceans and 

Coastal Council and the Gulf of Mexico Alliance (GOMA)—and EPA to help develop nutrient 

criteria for estuaries and coastal waters. FDEP is still evaluating whether to augment the TAC 

with additional members or to convene a smaller working group with expertise in estuarine and 

coastal systems. FDEP initiated the development of estuarine nutrient criteria at the beginning 

of 2008 and began a public process on June 5 and 6, 2008, with an estuarine nutrient criteria 

development workshop (http://www.dep.state.fl.us/water/wqssp/nutrients/tac_archive.htm). The 

objective of this meeting was to discuss the state of nutrient science, research, and monitoring 

for Florida’s coastal waters, as well as potential numeric criteria derivation methods. FDEP 

invited scientists who had performed research on selected Florida estuaries and asked that they

do the following:

• Describe the system, including the hydrodynamics and sources and fates of 

nutrients;

• Describe the type, quality, community structure, areal extent, etc., of valued 

ecological attributes (biological communities), emphasizing those shown to 

respond to anthropogenic nutrient enrichment;

• Provide scientific evidence quantifying the relationship between anthropogenic 

nutrient inputs and adverse effects on biological communities; and

• Propose numeric targets needed for system protection or restoration, as well as 

demonstrate the bases for the nutrient targets.

Of the ten estuary studies presented, half focused on the relationship between nutrient loading 

(mostly nitrogen) causing excess algal growth (as measured by chlorophyll a production), which 

resulted in decreased transparency and, consequently, light limitation/stress to SAV. In some 

estuaries, this complex relationship was established; in others, there was a relationship between 

nutrient loading directly on SAV (no chlorophyll issues); while in others, no relationship between 

nutrients and biological attributes could be quantified. In one instance, inorganic nutrients were 

elevated enough to foster harmful algal blooms (HABs) and concomitant declines in animal food 

webs, even though chlorophyll was low. 

From the workshop, it appears that Florida estuaries generally fall into one of three groups, as 

follows:

(1) Systems where nutrient dose-response relationships are sufficiently understood to 

warrant proposing criteria (e.g., Tampa Bay, Perdido Bay, North Indian River 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

42

Lagoon (IRL), Lower St. Johns River, and potentially Sarasota Bay). These 

systems have historically demonstrated nutrient issues, and many are recovering 

due to restoration efforts. Note that in many of these systems, the strongest 

relationship between nutrients and SAV response was based on loadings, not 

concentrations. Time series data from these estuaries would be valuable in 

helping model dose-response relationships.

(2) Systems where factors other than nutrients appear to be more influential in 

defining biological community structure, making it currently difficult to propose 

scientifically defensible nutrient criteria (Caloosahatchee, South IRL, Pensacola 

Bay, parts of Florida Bay, and Charlotte Harbor). For these estuaries, some sort 

of reasonable assurance (e.g., from a model) that a particular nutrient regime 

protects the designated use would be needed.

(3) Systems that currently appear to be healthy and well-functioning and a “maintain 

the status quo” approach for nutrients may be appropriate (e.g., Apalachicola, 

Apalachee, St. Andrews, Nassau/Amelia/St. Marys, Tolomato, Guana, Matanzas, 

Ten Thousand Islands).

FDEP is particularly interested in an approach used by the St. Johns River Water Management 

District (SJRWMD) for the North IRL in which:

• SAV was related to a watershed loading regression model;

• Transparency depth targets to protect SAV photosynthesis in the IRL ranged from 

1.2 to 1.8 m; and

• Turbidity, chlorophyll a, and color targets were based on preventing a transparency 

reduction of greater than 10%.

Using a model by Valiela and Cole (2002), total allowable nitrogen load limits for each segment 

could be calculated, and it was estimated that the loading needed to be below 20 kilograms of 

nitrogen per hectare per year (kg N/ha/yr) (based on water area) to protect SAV. A critical 

component is water residence time.

The EPA National Nutrient Criteria Technical Guidance Manual for estuarine and coastal marine 

waters recommended that appropriate response variables include chlorophyll, water clarity and 

other variables recognized in the scientific literature as responsive to nutrient inputs, including 

dissolved oxygen, seagrass or other biological components of the estuarine ecosystem. FDEP 

expressed the desire to target nutrient criteria development to protect seagrass habitats, a 

valued estuarine resource throughout the State that supports particular uses. The scientific 

literature recognizes that the effects of nutrients on seagrass are well-known, but also that these 

effects are largely indirect. To a first approximation, elevated nutrient loads enhance both 

phytoplankton production and growth of epiphytic algae on seagrass leaves. Together with 

colored dissolved organic matter and suspended particulates, these factors reduce water clarity 

and light availability for seagrass growth. 

FDEP is currently working with EPA to gather the information necessary to develop a Floridaspecific estuarine nutrient cause/effect relationship, potentially similar to the Valiela and Cole 

(2002) model, but tested against, and potentially adapted to, Florida estuaries. The following 

elements describe, in general, several critical information and data needs, computations and 

evaluations that will be undertaken by EPA’s Gulf Ecology Division (GED) and/or EPA 

contractors include the following:
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

43

• Estuary Delineation. EPA and FDEP will establish a common approach to delineating 

the boundaries of estuaries and their watersheds in the State, and to identifying the 

resulting estuaries for which nutrient criteria will be developed.

• Nutrient Load Estimation. EPA and FDEP, with assistance from USGS, will develop a 

common approach to estimating monthly and annual nitrogen and phosphorus loads to

each Florida estuary for a suitable period of record, including loads from atmospheric 

deposition, point and non-point sources, and, if possible, from ground water and oceanic 

sources. In addition to loads, estimates of freshwater discharge and source water 

nutrient concentrations will be needed. 

• Water Quality Database. EPA and FDEP will evaluate the suitability and 

representativeness of water quality variables within existing FDEP databases. Priority 

variables include: salinity, temperature, nutrients (TN, TP, NOx, etc), dissolved organic 

matter, total suspended solids, Secchi depth, color, and chlorophyll a. Available data on 

historical seagrass coverage across Florida will also be compiled. 

• Empirical Analysis. EPA and FDEP will analyze and evaluate empirical relationships 

between causal and response variables for each estuary using appropriate 

computational/statistical methods. The evaluation will include analysis of cause-effect 

relationships for all Florida estuaries combined, or some subset of estuaries based upon 

a defined criteria or categorization approach. For example, some Florida estuaries are 

naturally turbid due to a natural background of colored dissolved organic matter, 

whereas others lack significant natural turbidity. Moreover, some Florida estuaries 

naturally lack appreciable seagrass coverage. Efforts to identify and evaluate 

appropriate response variables that represent desired water quality and support 

designated uses will ensure that the proposed criteria are protective of all estuarine 

waters.

FDEP also plans to adopt regional response variable nutrient criteria based on site-specific 

thresholds developed for many of the larger coastal systems in the state (e.g., Tampa Bay, IRL,

Caloosahatchee, St. Lucie) and subsequently deriving causal variable criteria based on 

statistical relationships between these response variables and the causal variables. However, it 

should be noted that in many cases such relationships may not exist, as was the case in 

Sarasota Bay. Under this scenario, FDEP may only propose response variable–based criteria 

until the relationships are determined on a site-specific basis.

As a result of the state’s 1987 Surface Water Improvement and Management (SWIM) Act and 

the National Estuary Program (NEP), efforts to develop nutrient-related thresholds for many of 

the state’s largest estuaries and coastal waters are well under way and are briefly described 

below.

Tampa Bay

Tampa Bay NEP has established chlorophyll a targets for the different segments of the bay

based on a goal of restoring seagrass beds to 38,000 acres within the bay. The bay now 

supports 28,299 acres of seagrass. The Tampa Bay chlorophyll a targets were established 

based on the effects of chlorophyll on light attenuation and ultimately on the depth of seagrass 

occurrence. TN loadings were in turn related to chlorophyll a concentrations, using a threemonth lag time during the analysis. Ambient nitrogen concentration was not shown to directly 

affect light attenuation or seagrass condition. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

44

IRL and Banana River

The IRL/Banana River Lagoon PLRG study set maximum loading targets for TN, TP, and TSS

as a function of seagrass depth limits in the lagoon. The PLRG study found strong, negative 

correlations between watershed loadings of nutrients and TSS and the depth limit of seagrass. 

EPA proposed a TMDL in April 2007 based on the IRL/Banana River Lagoon PLRG, and FDEP 

proposed a state TMDL for the main stem of the Indian River and Banana River in fall 2008.

Caloosahatchee and St. Lucie Estuaries

The Northern Everglades and Estuaries Protection Program expanded the Lake Okeechobee 

Protection Plan (LOPP) requirements to the Caloosahatchee and St. Lucie River watersheds. 

This legislation created the Caloosahatchee and St. Lucie River Watershed Protection Program, 

which includes the development of Watershed Protection Plans for both rivers. Each 

Watershed Protection Plan must include a watershed construction project, a watershed pollutant 

control program, and a watershed research and water quality monitoring program. Under this 

legislation, the South Florida Water Management District (SFWMD), in collaboration with 

coordinating agencies, was directed to develop River Watershed Protection Plans for the 

Caloosahatchee and St. Lucie watersheds by January 1, 2009. 

A primary objective of the program to address the Caloosahatchee and St. Lucie Estuaries is to 

develop “pollutant load reductions based upon adopted total maximum daily loads established in 

accordance with s. 403.067” (Senate Bill 392, 2007). After the TMDLs are completed, Basin 

Management Action Plans (BMAPs) will be developed. The TMDL for the St. Lucie estuary was

proposed for final agency action on December 31, 2008. A notice of change to correct a minor 

typographical error in the rule will be published in the Friday, January 23, 2009 issue of the 

Florida Administrative Weekly. As of January 14, 2009, a draft TMDL for tidal portions of the 

Caloosahatchee River and Estuary is near completion, and it is anticipated that it will be 

completed, reviewed, and made publicly available by early February 2009.

In addition to the site-specific efforts previously mentioned, FDEP is actively involved in GOMA. 

It is working with the other Gulf states to develop broader-based strategies for developing 

nutrient criteria and control programs within the shared waters of the Gulf of Mexico. FDEP has 

assigned two staff members to directly participate in GOMA. Nutrient criteria–related activities 

are being coordinated between these staff and FDEP’s Water Quality Standards Program. An 

example of these ongoing activities includes a comprehensive session on water quality 

sampling and quality assurance (QA) that was provided to GOMA staff by the Standards and 

Assessment Section during the summer of 2008.

FDEP recognizes that inland water criteria must protect downstream uses, and since estuarine 

condition is affected by the nutrient loads delivered from upstream, there will be effort made to 

synchronize these two criteria development efforts.

3.13 Microcystin Round Robin 

In an effort to initiate the development of a useful response threshold to HABs, FDEP has begun 

a series of QA “round robin” studies to evaluate the precision and accuracy of laboratory 

analytical results for microcystins. Because of the moderately large interlaboratory variability 

associated with these analytical results, further work to achieve consistency between labs is 

needed to further develop reliable indicators of HABs.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

45

4. Relation to State Use Classifications

The CWA requires that the surface waters of each state be classified according to designated 

uses. Florida has five classes with associated designated uses, which are arranged in order of 

the degree of protection required: Class I (potable water supplies); Class II (shellfish 

propagation or harvesting); Class III (recreation, propagation of fish and wildlife); Class IV

(agricultural water supplies); and Class V (navigation, utility, and industrial use). Under the 

current classification system, the majority of the state’s waterbodies (i.e., lakes, streams, 

estuaries, and wetlands) are Class III and are held to the same water quality criteria, with some 

differences between predominately fresh and marine waters

5. Relation to Biogeographic Classification

FDEP initially used Level IV ecological subregions, separately defined for streams (Griffith et al.,

1994) and lakes (Griffith et al., 1997) in Florida’s biocriteria development program, as a starting 

point for regionalization efforts necessary to establish nutrient criteria. FDEP has analyzed 

stream reference site macroinvertebrate community patterns in all nine ecological subregions 

north of Lake Okeechobee (Barbour et al., 1996). The data indicated the presence of the 

following four distinct bioregions, within which there were similar biological community 

composition and structure (Figure 4): the panhandle (Regions 65f, 65g, and 65h, and the 

majority of 75a), the northeast (Regions 75e and 75f), the peninsula (Regions 75b, 75c, and 

75d, and a small part of 75a), and the Everglades (Regions 76a, 76b, 76c, and 76d). 

Similar patterns of relatively homogeneous groupings in the peninsula versus the panhandle 

have been observed in wetlands macrophyte, algae, and invertebrate data (Lane et al., 2003). 

Lake macrophyte (for percent invasive species) and invertebrate (based on ecoregion, pH, and 

color) indices also utilize a similar bioregion scheme, with the three peninsular ecoregions being 

collapsed into a single peninsular bioregion (Fore, 2005; Gerrittsen et al., 2000). FDEP is 

currently evaluating the potential of using ecological subregions collapsed into biological regions 

as the basis for future nutrient criteria groupings, although the issue is still a matter of continued 

discussion with the TAC (Weaver, 2006b, 2006c; Weaver and Frydenborg, 2006).

Based on the observed biological community resemblance within a bioregion, it is logical that 

these biologically similar regions will have analogously comparable responses to nutrient 

concentrations. If additional data indicate an alternate spatial classification scheme is more 

appropriate, the current system may be revised; however, current biological data suggest that 

bioregions are the most defensible approach to establish the appropriate protection of biota. 

The current bioregions were derived based on macroinvertebrate assemblage patterns, which 

may not be entirely indicative of homogeneous response to nutrients. FDEP and its consultants

are currently evaluating bioregions based on stream periphyton assemblages. If these 

evaluations reveal significantly different biological regions, the nutrient spatial classifications will 

be adjusted accordingly.

FDEP and the TAC are also evaluating scientifically defensible bases for the subregionalization

of known naturally high-phosphate areas in the central peninsula and north-central Florida

(Weaver, 2006c). Currently, in the peninsula bioregion pilot study, FDEP used an outlier 

analysis to exclude these naturally high-phosphate areas. It intends to evaluate other methods 

to explicitly subregionalize these areas. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

46

6. Data Sources

6.1 Inventory of Existing Data

Florida has invested significantly in the acquisition and storage of scientifically defensible water 

quality and biological data. The state water quality database currently houses over 19 million 

data records, including over 890,000 phosphorus, 1 million nitrogen, and 450,000 chlorophyll a

measurements. Additionally, FDEP has collected 3,867 SCI samples to assess stream health, 

534 vegetation samples to assess lake health, 7,265 periphyton samples, and 7,897

phytoplankton samples. These biological samples allow FDEP to make connections between 

water chemistry and aquatic health to assist with determining protective values in a complex 

environment. 

Under FDEP’s watershed approach, the identification of data sources and development of tools 

to facilitate data entry and upload to the STOrage and RETrieval (STORET) Database have 

become high priorities for the agency. Florida’s IWR (Chapter 62-303, F.A.C.) designates 

STORET (and its successor database) as the primary data source to be used by FDEP to 

assess water quality under the watershed approach. Efforts to upload new and additional data 

of known and defensible quality, under FDEP’s Quality Assurance Rule (Chapter 62-160, 

F.A.C.) are ongoing and supported by a dedicated STORET group within FDEP. This group 

provides support to other state agencies, local governments, and various organizations in the 

transfer of data to Florida STORET. 

6.2 FDEP’s Ambient Monitoring Program

In 1996, FDEP redesigned its water resource monitoring programs to create an efficient, multiresource, comprehensive monitoring network. While the revised network, called the Integrated 

Water Resource Monitoring (IWRM) Network, was designed to fulfill many different monitoring 

needs, it includes two statewide monitoring programs (described below) that provide data that 

have proven invaluable in FDEP’s efforts to develop numeric nutrient criteria. It is anticipated 

that additional IWRM data will continue to be relied upon heavily for future nutrient evaluations.

The first IWRM program is a fixed-site statewide Trend Monitoring network. The objective of the 

Trend Monitoring program is to measure and estimate changes in the condition of water 

resources over time. FDEP’s Watershed Monitoring Section samples 75 rivers and streams 

monthly for chemical and field analytes. In addition, benthic community and habitat 

assessments are conducted annually. 

The second IWRM program, the Status Monitoring network, uses a stratified random sampling 

(probabilistic) design. The objective of the network is to broadly characterize the proportion of 

state water resources that meet or do not meet water quality standards. This statistical design 

was selected because sampling all water resources throughout the state would be cost and 

resource prohibitive. The Watershed Monitoring Section generates lists of representative 

surface and ground water sites, submits them to EPA for random selection, and samples 30 

sites per resource, by basin. As part of the design, the section samples 6 different resources, 

as follows: 4 surface water types (rivers, streams, small lakes of 4 to less than10 hectares, and 

large lakes of more than 10 hectares), and 2 ground water aquifer types (confined and 

unconfined). Samplers collect a standard suite of chemical, physical, and biological parameters 

to estimate the condition of the state’s water resources. Currently, the Watershed Monitoring 

Section collects 180 samples per resource in the state, or a total of 1,080 samples/year. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

47

Starting in 2009, the Watershed Monitoring Section will continue to collect Status Monitoring 

network samples from all 6 resource types, but the numbers collected and the sampling 

frequency will change. Sixty samples of each of the surface water types will be collected, with a 

repeat visit resulting in a total of 120 samples/surface water resource/year. The repeat visits 

are scheduled at opposite seasons and rainfall patterns during the calendar year, thus capturing 

potential differences in water quality. However, the 2 ground water resources will be sampled 

once per year, resulting in 120 samples of each type. The fixed-site, statewide Trend 

Monitoring network will remain the same.

FDEP’s watershed approach includes a strategic monitoring phase to gather new data within 

watersheds to supplement existing data. This monitoring is used to further characterize basin 

conditions, to investigate areas with identified or potential water quality problems, to evaluate 

the effectiveness of management actions, and for TMDL development. These activities, 

addressed in strategic monitoring plans, are intended to identify data gaps at the watershed 

level, to prioritize areas of data collection by FDEP or other partners, to establish a process for 

data dissemination, and to specify quality assurance/quality control (QA/QC) requirements. 

6.3 Requirements for New Data Collection

Although FDEP has invested significant resources in its efforts to assess the ecological health 

of the state’s waters, the process of developing numeric nutrient criteria has proven daunting. 

Most of the data described above were not originally collected for this purpose and thus have 

proven of limited value to derive protective response–based criteria. One of the greatest 

challenges is the fact that biological and water chemistry monitoring have been conducted on 

different temporal and spatial scales, making it difficult to appropriately pair nutrient and 

biological response data in a manner that can be used to link biological impairment to nutrient 

thresholds across a bioregion or ecoregion. As discussed previously, FDEP is currently 

conducting or initiating additional studies specifically aimed at making the necessary linkages 

for both streams and lakes.

FDEP is committed to pursuing additional grants and other funding opportunities to support 

specific projects directed toward establishing numeric nutrient criteria, including the collection of 

additional data. As the TAC identifies key parameters for criteria development, new data gaps 

may arise; therefore, it is not possible, at this time, to know how much data collection will be 

needed to propose ecoregional nutrient criteria.

7. Coordination with Bordering States

Florida shares some waterbodies with Alabama, Georgia, the Miccosukee Tribe, and the 

Seminole Tribe. Therefore, efforts will be made to coordinate with those states and tribes on

any nutrient criteria Florida is considering on shared lakes and streams, prior to submittal to the 

ERC for rule development. Additionally, FDEP will meet with other Gulf of Mexico states to 

discuss the adoption of nutrient criteria for Gulf estuaries.

8. Prioritization of Waters and Schedule for Development 

and Adoption

FDEP initially prioritized waters for the development and adoption of regional numeric nutrient 

criteria based on the availability of EPA guidance documents—i.e., lake and river stream 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

48

guidance were available first, followed by estuaries and coastal waters, and finally wetland 

guidance. However, the development of site-specific numeric nutrient targets has been driven 

by TMDL development schedules, including a number of nutrient TMDLs for specific 

waterbodies, to be completed in accordance with the consent decree between EPA Region 4 

and EarthJustice. Furthermore, FDEP will continue to identify (and prioritize for TMDL 

development) other waterbodies identified as potentially impaired by nutrients under Chapter 

62-303, F.A.C. 

These site-specific TMDL efforts are highly integrated with regional nutrient criteria development 

because information and experience gained in each effort has been and will continue to be used 

to refine the other. Methods originally developed by the TAC and FDEP to derive regional 

nutrient criteria have been used by FDEP to develop recommended TMDL thresholds for 

specific waterbodies. Conversely, site-specific targets developed via the TMDL process will be 

evaluated for potential regional application or possible consideration as site-specific nutrient 

criteria for given waterbodies, particularly for estuaries and coastal waters. 

FDEP has already made significant progress towards nutrient criteria development for streams 

and lakes, and anticipates continuing on a schedule consistent with EPA’s expectations for 

substantial progress towards criteria adoption (Grubbs, 2001). FDEP’s commitment to this 

nutrient criteria development process is demonstrated by the assignment of seven staff and a 

statistical consultant to work at least part-time on this project; FDEP’s continued consultation 

with its nutrient criteria development TAC; and FDEP staff participation in numerous regional 

and national nutrient criteria–related meetings, workshops, and conferences (e.g., Region 4 

Regional Technical Assistance Group [RTAG], 2006 All States Meeting, GOMA). 

As FDEP’s schedule follows the availability of EPA guidance documents, the state schedule is 

affected by the availability of those guidance documents and approaches. Continued progress 

on this schedule is also contingent on continued funding through state and federal programs to 

assist in completing the necessary research, developing appropriate assessment tools, and 

verifying the criteria. 

8.1 Lakes and Streams (1st Priority)

Florida identified lakes and streams as its first priority for the development and adoption of 

regional numeric nutrient criteria. FDEP has been meeting with the TAC and primarily 

discussing the development of nutrient criteria for these waters since January 2003. The TAC 

has held 16 meetings addressing various topics related to lake, stream, and canal nutrient 

criteria. Summaries of these meetings and meeting materials are provided on FDEP’s website 

(http://www.dep.state.fl.us/water/wqssp/nutrients/tac_archive.htm). FDEP currently anticipates

that the TAC process for lakes and streams will be concluded by December 2009, with numeric 

water quality criteria subsequently submitted to the ERC by 2011. 

FDEP currently plans to develop benchmark distributional approach–based criteria for lakes 

only as a backup, because it believes it is currently close to developing response-based criteria 

for lakes. However, FDEP may revisit the benchmark distributional approach for lakes if 

response-based approaches fail to identify significant relationships with nutrient enrichment. 

The schedule below provides additional detail on Florida’s progress to date and anticipated 

future activities. It should be noted that the projected future milestones are based on the 

assumption that FDEP’s current track and technical approaches are acceptable to EPA, and 

that there are no administrative challenges to adopting the criteria.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

49

It should also be noted that, while the schedule for criteria development does not make a 

specific distinction for south Florida streams/canals, criteria development for these systems may 

be unique because there currently are very limited bioassessment methods applicable to 

streams in Ecoregion XIII (Figure 1). As part of developing the stream criteria, FDEP plans to 

evaluate the nutrient criteria developed for peninsular Florida streams to determine whether 

they are adequately protective of south Florida streams. 

8.2 Estuaries (2nd Priority)

FDEP selected estuaries as the second priority because of the site-specific nature of nutrient 

response in estuaries and because there currently are very limited bioassessment tools 

available for estuaries. EPA’s (2001) nutrient criteria guidance for estuarine and coastal marine 

waters recognized the site-specific nature of nutrient response in estuaries, noting that 

“estuaries and coastal marine ecosystems tend to be relatively individualistic in their sensitivity 

and response to nutrient over enrichment.” The guidance further states that “the lack of 

physically similar waterbodies may severely limit grouping (classifying) waterbodies as 

recommended for lakes, reservoirs, rivers, and streams where frequency distributions are used 

to derive reference conditions.” FDEP concurs with these findings and anticipates that numeric 

nutrient criteria for Florida’s estuaries and coastal waters will rely on both site-specific efforts, 

including TMDL-related efforts, and the general approaches described below. 

EPA is assisting FDEP in the development of numeric nutrient criteria through the involvement 

of the EPA Office of Research and Development, Gulf Ecology Division, Gulf Breeze 

Laboratory. EPA/GED plans to focus on nutrient criteria development for estuaries over the 

next 12 to 24 months. There is likely to be uncertainty surrounding the observation of a single, 

comprehensive, statistically significant relationship between nutrient concentrations (or loads)

and observed biological responses for all of Florida’s estuaries due to their geological and 

ecological variability. The state recognizes that a one-size-fits-all approach to its estuaries may

yield limited results. However, if a strong enough relationship can be generated in some Florida

estuaries, and realistically applied to the remaining estuaries, the protection provided would 

serve as a solid foundation as more is learned about each estuary. 

8.3 Wetlands (3rd Priority)

Florida leads the nation in the development of protective nutrient criteria for wetlands, having 

adopted a numeric phosphorus criterion for the Everglades in 2004, well in advance of EPA’s 

draft wetland guidance. In fact, this guidance includes an appendix summarizing much of the 

research used to establish the Everglades phosphorus criterion of 10 μg/L. Furthermore, the 

state leads the nation in innovative treatment and best management practice (BMP)

technologies and research to achieve compliance with ultralow nutrient standards (e.g., Burns 

and McDonnell, 2003; Piccone, 2007). 

FDEP does not plan to initiate the development of regional wetland nutrient criteria until after the 

estuary nutrient criteria are into the rule development phase. EPA released draft wetland 

guidance for review in December 2006 (EPA, 2006), and specifically solicited information, data, 

and views on scientific issues pertaining to the information the agency used to develop the draft

document. Under this request, FDEP submitted review comments on the draft wetland 

guidance on February 15, 2007. EPA finalized its guidance in September 2007. FDEP is 

currently revaluating its statewide wetland strategy with the expectation that Florida’s next plan 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

50

update will include more specific strategies for wetland nutrient criteria development, including 

time frames and milestones.

The lower priority assigned to wetlands is based on an acknowledgment that wetlands are 

biologically very different from other waterbody types, that the state of the science on wetland 

nutrient dynamics is still evolving, that biological and water quality monitoring efforts for 

wetlands generally lag behind those of other waterbody types, and that with a few notable 

exceptions, wetlands tend to have a higher nutrient assimilative capacity. The implementation 

of nutrient threshold research or benchmark condition evaluations will take some time, given the 

current state of wetland science.

9. Florida’s Ongoing Investment in Nutrient Criteria 

Development 

Table 5 lists the funding Florida has provided for nutrient criteria development during the past 

several years, and includes studies planned for the next year.

10. Past, Current, and Future Schedule for Nutrient Criteria 

Development for Florida’s Waters

This section summarizes both previous efforts and planned activities for the development of 

numeric nutrient criteria for Florida’s waters. Previous efforts were specifically included 

because it is important to recognize the previous investments (in time and money) that have laid 

the groundwork for the establishment of biocriteria and numeric nutrient criteria. As evidenced 

throughout this document, FDEP strongly believes that scientifically defensible numeric nutrient 

criteria should be based on biological responses to nutrients. As such, it has invested 

significant resources in the development of biological assessment tools. This very complex 

process has required extensive methods development, staff training, and QA oversight to 

ensure the defensibility of the resulting products. The elements of this development and 

assessment process to date include habitat assessment for streams and lakes, benthic 

invertebrate indices for streams and lakes, a vegetation index for lakes, and a periphyton index 

for streams.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

51

Table 5. Recent and planned funding for nutrient criteria development in 

Florida

Project or Activity Cost to Date

SCI/BioRecon Development $3,737,500

LVI Development $358,750

LCI Development $1,180,000

SPI Development $1,020,000

Biocriteria Meetings and QA Activities $530,400

Stressor Identification Study $374,500

Nutrient Gradient Study $132,675

Stream Benchmark Site Determination $91,350

Longitudinal Study $38,400

Springs Nitrate Studies $384,000

Staff Technical Analysis and Coordination Time $292,000

Statistical Consultants $175,000

Nutrient Criteria Meeting Travel $33,200

Everglades TP Criterion Development $11,250,000

Total Numeric Nutrient Criteria Development Costs $19,597,775

FDEP also made major investments in the development of nutrient criteria for the Everglades, 

leading to the adoption of a phosphorus criterion. Although work on other wetlands has begun, 

additional validation and calibration of the wetland indices are needed prior to proceeding to 

nutrient criteria development for other wetlands. Because of their complexity and the 

confounding effects of salinity, FDEP currently has only limited bioassessment tools for 

estuaries and still needs to make significant progress in that area.

It should also be noted that this schedule and plan focus primarily on the scientific components 

of numeric nutrient criteria development. However, the successful adoption of numeric nutrient 

criteria also depends on the successful completion of the administrative rulemaking process, 

and it is very difficult to estimate the time frame for the rulemaking process, particularly given 

the potential for administrative challenges.

Past, current, and planned activities for the development of numeric nutrient criteria are as 

follows:

1992 To begin the phosphorus criterion development process in the Everglades, a 

research plan was developed to specifically determine the level of phosphorus 

necessary to prevent an imbalance in Everglades flora and fauna. This plan, 

the Everglades Nutrient Threshold Research Plan (Lean et al., 1992), was 

intended to provide appropriate data in support of a numerical interpretation of 

the existing state of Florida narrative nutrient criterion.

June 1995 FDEP formed the Everglades Technical Advisory Committee (ETAC) to review 

and comment to FDEP on Everglades research and monitoring in support of 

the process of developing a numeric phosphorus criterion for the Everglades.

Sept. 1999–Oct. 2001 FDEP staff published and revised three technical support documents in support 

of a numeric phosphorus criterion for the Everglades Protection Area (Payne et 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

52

al., 2000, 2001a, 2001b). These reports recommended a phosphorus criterion 

of 10 μg/L.

Dec. 2001 Based on the results of FDEP’s extensive analyses, the agency filed a notice of 

rulemaking and recommended a protective Everglades TP criterion of 10 μg/L 

for approval by the ERC.

FDEP conducted a statewide numeric nutrient criteria development “kickoff” 

meeting in Tallahassee.

March 2002 FDEP created a nutrient criteria website (accessible to the public at 

http://www.dep.state.fl.us/water/wqssp/nutrients/index.htm) to facilitate the 

dissemination of information about Florida’s nutrient criteria development 

process. The site includes agendas, minutes, and presentations from the 

Nutrient Criteria TAC meetings, copies of reports from the studies sponsored 

by FDEP on nutrient-related topics, links to federal nutrient websites, and other 

pertinent information.

FDEP established an electronic mail listserver to distribute information directly 

to interested parties.

April 2002 FDEP refined the first draft of Florida’s Numeric Nutrient Criteria Development 

Plan. 

FDEP identified potential Nutrient Criteria TAC members.

FDEP received a draft report from Tetra Tech, Inc. detailing efforts to date on 

the review of nutrient data and proposed potential nutrient criteria for Florida 

lakes. 

FDEP received a draft report from the University of Florida presenting 

paleolimnological characterization of predisturbance water quality conditions in 

Florida lake regions (Griffith et al., 1997).

FDEP hired a designated staff person to coordinate FDEP’s nutrient criteria 

development efforts. 

May 2002 FDEP submitted the Draft Numeric Nutrient Criteria Development Plan to EPA

Region 4 for review. 

An FDEP representative participated in the Region 4 RTAG and presented an 

overview of Florida’s Numeric Nutrient Criteria Plan for comment by RTAG 

members. 

FDEP solicited the participation of identified potential Nutrient Criteria TAC 

members.

June/July 2002 FDEP staff participated in the National Nutrient Team and the national 

stakeholders’ meetings in Washington, DC. 

Dec. 2002 The University of Florida completed a contract to conduct paleolimnological 

Cyanobacteria pigment studies to determine if past changes in the abundance 

of Cyanobacteria coincide with fossil diatom analysis in Florida lakes.

Jan. 2003 FDEP convened first meeting of the Nutrient Criteria TAC.

March–July 2003 The nutrient criteria coordinator position became vacant; therefore, no TAC 

meetings were held.

July 2003 The ERC approved the 10 μg/L TP criterion for the Everglades Protection Area 

during a July 8, 2003 hearing. Subsequent to the approval by ERC, both 

environmental and agricultural interest groups filed administrative challenges to 

the phosphorus criterion rule. Following discussions with FDEP concerning the 

application of the rule, all parties except the Miccosukee Tribe of Indians and 

the Friends of the Everglades withdrew their challenges.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

53

FDEP contracted a position to work with the TAC, to plan and

facilitate/coordinate TAC meetings.

Aug. 2003 FDEP held a second TAC meeting in Tallahassee; agenda items included

Florida water quality standards overview, existing narrative criteria, potential 

nutrient criteria tools, and nutrient criteria development approaches.

Oct. 2003 The University of Florida paleolimnological project was completed and the final 

report received.

The third TAC meeting was held in Orlando on Florida lake nutrient criteria and 

data availability.

Nov. 2003 FDEP representatives participated in the EPA Region 4 RTAG meeting in 

Atlanta.

Nov. 2003–Jan. 2004 An administrative hearing was held to resolve the remaining challenges to the 

Everglades phosphorus criterion rule.

Dec. 2003 FDEP submitted a revised FDEP Nutrient Criteria Development Plan to EPA.

Jan. 2004 FDEP held the fourth TAC meeting and started holding TAC meetings 

approximately every one and a half months. 

FDEP representatives participated in the EPA Region 4 RTAG meeting.

Feb. 2004 A designated FDEP staff position took over TAC facilitation/ coordination 

duties.

The fifth TAC meeting was held in West Palm Beach. The meeting focused

exclusively on canal nutrient criteria development.

April 2004 The sixth TAC meeting was held in Tallahassee.

The seventh TAC meeting (two days) was held in Fort Myers.

May 2004 The eighth TAC meeting was held in West Palm Beach.

June 2004 The final order filed by the Administrative Law Judge on June 17, 2004, upheld 

all parts of the proposed Everglades phosphorus criterion rule, finding that the 

rule “is not an invalid exercise of delegated legislative authority” by FDEP.

July 2004 EPA and the state reached mutual agreement on a Numeric Nutrient Criteria 

Development Plan for Florida.

Aug. 2004 The ninth TAC meeting (two days) was held in Tampa.

Nov. 2004 The tenth TAC meeting was held in Tallahassee.

Jan. 2005 EPA approved all portions of the Everglades phosphorus criterion rule, except 

the use of the assessment methodology specified in Appendix B of the 

Settlement Agreement in the Federal Everglades lawsuit, Case No. 88-1886-

CIV-Hoeveler, U.S., as modified by Omnibus Order entered in the case on April 

27, 2001.

Feb. 2005 The eleventh TAC meeting was held in Gainesville.

March 2005 Florida initiated the Dissolved Oxygen/Nutrient Study, an intensive one-year 

DO and nutrient study. Nutrient and biological data were collected in streams, 

canals, and lakes across the entire state. These data, in addition to other 

ambient data available in STORET, will be used to establish numeric nutrient 

criteria. Additionally, data will be used to help establish new bioassessment 

methods (phytoplankton and periphyton indices).

April 2005 A revised Everglades phosphorus criterion rule was presented to the ERC and 

received unanimous approval on April 7, 2005.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

54

June 2005 The Everglades phosphorus criterion rule was resubmitted to EPA for approval.

July 2005 The Everglades phosphorus criterion received final approval from EPA.

Aug. 2005 The twelfth TAC meeting (two days) was held in West Palm Beach.

Oct. 2005 FDEP representatives participated in the EPA Region 4 RTAG meeting in 

Atlanta and presented an overview of the status of Florida’s numeric nutrient 

criteria development. 

Feb. 2006 FDEP representatives participated in EPA’s All States Numeric Nutrient Criteria 

Meeting in Dallas.

The thirteenth TAC meeting was held at Wakulla Springs State Park, Wakulla.

May 2006 The fourteenth TAC meeting was held in Gainesville. 

DO and nutrient study data collection were completed. 

Oct. 2006 The fifteenth TAC meeting was held in Ponte Vedra Beach.

Dec. 2006 The sixteenth TAC meeting was held in Tallahassee.

Jan. 2007 FDEP established and SFWMD began monitoring an ambient monitoring 

network in the Everglades Protection Area designed to assess the 

achievement of the Everglades phosphorus criterion rule.

FDEP representatives participated in the GOMA Nutrient Criteria Conference in 

Gulf Breeze.

Feb. 2007 FDEP submitted a revised Numeric Nutrient Criteria Development Plan to EPA.

FDEP submitted review comments on EPA’s Draft Nutrient Criteria Technical 

Guidance Manual for Wetlands (EPA 823-F-05-015 – December 2006).

March 2007 FDEP representatives participated in the EPA Region 4 RTAG meeting in 

Decatur, GA.

May 2007 FDEP submitted to EPA Region 4 a pilot study application of its benchmark 

distributional approach as part of FDEP’s comments on EPA’s Proposed Total 

Maximum Daily Load (TMDL) for Biochemical Oxygen Demand, Dissolved 

Oxygen, Nutrients, and Unionized Ammonia In the Lake Okeechobee 

Tributaries.

Aug. 2007 All macroinvertebrate, periphyton, and phytoplankton data from the intensive 

one-year DO and nutrient study were marked complete and entered into 

Florida’s biological database.

Feb. 2008 The seventeenth TAC meeting was held in Tallahassee. FDEP received 

positive feedback from EPA on the application of the benchmark distributional

approach as utilized in FDEP’s pilot study for peninsula bioregion streams.

March 2008 The Nutrient Gradient Study sampling was initiated.

June 2008 FDEP held the estuaries and coastal waters numeric nutrient criteria kickoff 

meeting with the existing TAC and other experts, and provided training to 

GOMA staff on water quality sampling and QA.

Aug. 2008 FDEP analyzed algal response to nitrate concentrations in spring systems and 

proposed a criterion of 0.35 mg/L during the triennial review process.

Summer 2008 FDEP created a strategy for developing estuarine criteria and wrote scope of 

work for EPA assistance.

June 2008–Dec. 2009 FDEP continues data synthesis and analysis (e.g., biological indices, 

regionalization analyses) for lakes, streams, and canals, and meets with the 

TAC as needed.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

55

FDEP continues additional data collection as needed.

Summer/Fall 2008 FDEP gathered LVI readings from targeted lakes to be used to explore 

relationships with nutrient concentrations and conducted QA testing of all LVI 

teams to ensure data usability.

Sept. 2008 FDEP representatives participated in the planned EPA Region 4 RTAG 

meeting.

Nov. 2008 A contract to develop the stressor identification conceptual model was initiated 

and the contractor began reviewing data. An intensive kick-off meeting was

conducted in January 2009. 

Dec. 2008 FDEP completed fieldwork for the validation of peninsula, panhandle, and 

northeast bioregion benchmark streams.

Dec. 2008 FDEP staff met with EPA Headquarters and EPA GED staff to discuss the 

project to develop numeric nutrient criteria for estuaries.

Jan. 2009 FDEP to collect final data and information related to the Nutrient Gradient 

Study. Approximately 95% of these data were collected by December 2008. 

FDEP completed sampling for Longitudinal Study

Feb 2009 FDEP convened (with EPA support and participation) a panel of national 

experts to assist and advise FDEP in the calibration of a Stream Periphyton 

Index (SPI)

March–April 2009 FDEP plans to generate draft benchmark distributional approach–derived 

stream nitrogen and phosphorus thresholds as potential backup criteria. 

March–April 2009 FDEP to analyze data and information collected during the Nutrient Gradient 

Study and analyze nutrient statistics related to the LVI.

May 2009 FDEP to generate draft response–based nutrient criteria for streams, lakes, 

and estuaries if the statistical rigor of the results is sufficient (see Table 3 for 

specific causal and response variables).. If results are not sufficient, a six- to 

eight-month delay may occur to collect and analyze additional data.

July 2009 FDEP plans to gather data appropriate for nutrient criteria development in 

Ecoregion XIII streams/canals.

Dec. 2009 Conclude TAC process for lakes and streams, and potentially estuaries (if GED 

efforts are successful). Anticipated products include the recommended 

numeric nutrient criteria for Florida lakes, streams, and Ecoregion XIII 

streams/canals, and estuaries, and draft rule language to be incorporated into 

state water quality standards (see Table 3 for specific causal and response 

variables)..

Jan. 2010–Dec. 2010 DEP conducts formal rulemaking to incorporate nutrient criteria into Florida’s 

water quality standards (Chapters 62-302 and 62-303, F.A.C.). FDEP works to 

refine draft rule text, allowing time for draft rule review and public workshops on 

the proposed rule before the nutrient criteria rule language is submitted to the 

ERC. It is anticipated that the rulemaking process will take approximately 12 

months.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

56

References Consulted or Cited

Barbour, M., J. Gerritsen, and J. White. 1996. Development of the Stream Condition Index 

(SCI) for Florida. Owings Mills, MD: Tetra Tech, Inc.

Brown, M.T., and M.B. Vivas. 2005. Landscape Development Intensity Index. Environmental

Monitoring and Assessment 101:289–309

Brown, M.T., and K.C. Reiss. 2006. Proposed breakpoint of LDI < 2.0 for determining 

minimally affected reference conditions for water bodies. Gainesville, FL: Center for 

Environmental Policy, Department of Environmental Engineering Sciences, University of 

Florida. Technical report Submitted to the Florida Department of Environmental Protection.

Burns and McDonnell. October 2003. Everglades Protection Area tributary basins long-term 

plan for achieving water quality goals. Report prepared for the South Florida Water 

Management District, West Palm Beach, FL.

Davies, S.P., and S.K. Jackson. 2006. The biological condition gradient: a descriptive model 

for interpreting change in aquatic ecosystems. Ecological Applications 16(4):1251-1266.

Florida Department of Environmental Protection. 1998. 303(d) list of impaired waters. 

Tallahassee, FL: Florida Department of Environmental Protection. 

———. 2008. Florida Department of Environmental Protection standard operating procedures, 

Tallahassee, FL.

Fore. L.S. 2004. Development and testing of biomonitoring tools for macroinvertebrates in 

Florida streams. Final report to the Florida Department of Environmental Protection.

———. 2005. Assessing the biological condition of Florida lakes: Development of the Lake 

Vegetation Index (LVI). Final report to the Florida Department of Environmental Protection. 

Fore, L.S., R. Frydenborg, D. Miller, T. Frick, D. Whiting, J. Espy, and L. Wolfe. 2007a. 

Development and testing of biomonitoring tools for macroinvertebrates in Florida streams 

(Stream Condition Index and BioRecon). Final report to the Florida Department of 

Environmental Protection.

Fore, L.S. , R. Frydenborg, N. Wellendorf, J. Espy, T. Frick, D. Whiting, J. Jackson, and J. 

Patronis. 2007b. Assessing the biological condition of Florida lakes: Development of the 

Lake Vegetation Index (LVI). Final report to the Florida Department of Environmental 

Protection.

Gerritsen, J., B. Jessup, E.W. Leppo, and J. White. 2000. Development of Lake Condition 

Indices (LCI) for Florida. Final report to the Florida Department of Environmental 

Protection.

Griffith, G.E., D.E. Canfield, Jr., C.A. Horsburgh, and J.M. Omernik. 1997. Lake regions of 

Florida. Environmental Research Laboratory, Corvallis, OR: U.S. Environmental Protection 

Agency.

Griffith, G.E., J.M. Omernik, C.M. Rohm, and S.M. Pierson. 1994. Florida regionalization 

project. Corvallis, OR: Environmental Research Laboratory, U.S. Environmental Protection 

Agency.

Grubbs, G. November 14, 2001. Development and adoption of nutrient criteria into water 

quality standards. Memorandum to Water Directors, Regions I – X; Directors, State Water 

Programs; Directors, Great Water Body Programs; Directors, Authorized Tribal Water 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

57

Quality Standards Programs; State and Interstate Water Pollution Control Administrators. 

Washington, DC: WQSP-01-01. Washington, DC: U.S. Environmental Protection Agency, 

Office of Science and Technology. 

Hand, J., J. Col, D. Tterlikkis, J. Jackson, R. Odom, L. Lord, and L. Clemens. 2000. Florida 

water quality assessment 305(b) report. Tallahassee, FL: Florida Department of 

Environmental Protection.

Hendrickson, J.C., E.F. Lowe, D. Dobberfuhl and D. Campbell. 2003. Accelerated 

eutrophication in the Lower St. Johns River Estuary and recommendation of targets for the 

achievement of water quality goals to fulfill TMDL and PLRG objectives. Palatka, FL: 

Water Resources Department Technical Memorandum, St. Johns River Water Management 

District.

Jacobs, T.C., and J. W. Gilliam. 1985. Riparian losses of nitrate from agricultural drainage 

waters. Journal of Environmental Quality 14:472-478.

Jordan, T.E., D.L. Correll, and D.E. Weller. 1993. Nutrient interception by a riparian forest 

receiving inputs from adjacent cropland. Journal of Environmental Quality 22:467-473.

Lane, C.R., M.T. Brown, M. Murray-Hudson, and M. B. Vivas. 2003. Wetland Condition Index 

(WCI): Biological indicators of wetland condition for isolated depressional herbaceous 

wetlands in Florida. Gainesville, FL: Howard T. Odum Center for Wetlands, University of 

Florida. Report to the Florida Department of Environmental Protection. 

Lean, D., K. Reckhow. W. Walker, and R. Wetzel. 1992. Everglades nutrient threshold plan. 

Research and Monitoring Subcommittees of the Everglades Technical Oversight 

Committee.

Lowrance, R. 1997. Water quality functions of riparian forest buffers in Chesapeake Bay 

watersheds. Environmental Management 21:687–712.

———. 1992. Groundwater nitrate and denitrification in a coastal plain riparian soil. Journal of 

Environmental Quality 21:401-405.

Niu, X. 2004. Change point analysis of the chlorophyll-a and LDI data from the IWRM Status 

Network Cycle 1 lakes study. Tallahassee, FL: Department of Statistics, Florida State 

University. Technical report submitted to the Florida Department of Environmental 

Protection, Tallahassee, FL.

Niu, X, and X. Gau. 2007. Change point analysis of Suwannee River algal data. Technical 

report prepared for the Florida Department of Environmental Protection. Technical report 

submitted to the Florida Department of Environmental Protection, Tallahassee, FL.

Niu, X., P. Lin., and D. Meeter. 2000. Detecting change points in the species composition and 

water quality data of WCA2A. Tallahassee, FL: Department of Statistics, Florida State 

University. Technical report submitted to the Florida Department of Environmental 

Protection, Tallahassee, FL.

Payne, G., K. Weaver, T. Bennett, and F. Nearhoof. 2000. Everglades phosphorus criterion 

development support document, Part 1: Water Conservation Area 2. Tallahassee, FL: 

Everglades Technical Support Section, Division of Water Resource Management.

———. 2001a. Everglades phosphorus criterion development support document, Part 2: Water 

Conservation Area 1. Tallahassee, FL: Everglades Technical Support Section, Division of 

Water Resource Management. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

58

———. 2001b. Everglades phosphorus criterion development support document, Part 3: Water 

Conservation Area 3 and Everglades National Park. Tallahassee, FL: Everglades 

Technical Support Section, Division of Water Resource Management.

Peterjohn, W.T., and D.L. Corell. 1985. Nutrient dynamics in an agricultural watershed: 

Observations on the role of a riparian forest. Ecology 65:1466-1475.

Piccone, T. 2007. Implementation of the long-term plan for achieving water quality goals in the 

Everglades Protection Area. G. Redfield, ed. In: 2007 South Florida environmental report 

(West Palm Beach, FL: South Florida Water Management District).

Pinowska, A., R. J. Stevenson, J. O. Sickman, A. Albertin, and M. Anderson. 2007. Integrated 

interpretation of survey for determining nutrient thresholds for macroalgae in Florida 

Springs: Macroalgal relationships to water, sediment and macroalgae nutrients, diatom 

indicators and land use. Technical report submitted to the Florida Department of 

Environmental Protection, Tallahassee, FL.

Stevenson, R.J., A. Pinowska, A. Albertin, and J.O. Sickman. October 31, 2007. Ecological 

condition of algae and nutrients in Florida springs: The synthesis report. Final report to the 

Florida Department of Environmental Protection. East Lansing, MI: Department of Zoology, 

Michigan State University.

Stoddard, J.L., D.P. Larsen, C.P. Hawkins, R.K. Johnson and R.H. Norris. 2006. Setting 

expectations for the ecological condition of streams: The concept of reference condition.

Ecological Applications 16(4):1267-1276.

U.S. Environmental Protection Agency. 1991. The watershed protection approach: An 

overview. EPA 503/9-92-001. Washington, DC: Office of Water.

———. 1995. Watershed protection: A statewide approach. EPA 841-R-95-004. Washington, 

DC: Office of Water.

———. 1998. National strategy for the development of regional nutrient criteria. EPA 822-R98-002. Washington, DC: Office of Water.

———. 2000a. 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. Washington, DC: Office of Water.

———. 2000b. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Lakes and reservoirs in Nutrient Ecoregion 

XII. EPA 822-B-00-013. Washington, DC: Office of Water. 

———. 2000c. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Lakes and reservoirs in Nutrient Ecoregion 

XIII. EPA 822-B-00-014. Washington, DC: Office of Water. 

———. 2000d. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Rivers and streams in Nutrient Ecoregion 

IX. EPA 822-B-00-019. Washington, DC: Office of Water. 

______. 2000e. Nutrient criteria technical guidance manual: Rivers and streams. EPA 822-B00-002. Washington, DC: U.S. Environmental Protection Agency.

______. 2000f. Nutrient criteria technical guidance manual – Lakes and reservoirs. EPA 822-

B-00-001. Washington, DC: U.S. Environmental Protection Agency.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

59

———. 2000g. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Rivers and streams in Nutrient Ecoregion 

XII. EPA 822-B-00-021. Washington, DC: Office of Water.

———. 2001. Nutrient criteria technical guidance manual: Estuarine and coastal marine 

waters. EPA-822-B-01-003. Washington, DC: Office of Water. 

———. 2006. Draft nutrient criteria technical guidance manual: Wetlands. EPA-823-B-05-003. 

Washington, DC: Office of Water.

Valiela, I., and M.L. Cole. 2002. Comparative evidence that salt marshes and mangroves may 

protect seagrass meadows from land-derived nitrogen loads. Ecosystems 5:92-102.

Weaver, K. 2006a. Nutrient criteria development update. Presentation to the Florida Nutrient

Criteria Development TAC, February 22, 2006 meeting, Wakulla, FL. http://dep.state.fl.us/

water/wqssp/nutrients/docs/TAC/tac13_NutrientCriteriaDevelopmentUpdate.pdf.

———. 2006b. Nutrient criteria development update. Presentation to the Florida Nutrient 

Criteria Development TAC, February 22, 2006 meeting, Wakulla, FL. http://dep.state.fl.us/

water/wqssp/nutrients/docs/TAC/tac13_NutrientCriteriaDevelopmentUpdate.pdf.

———. 2006c. Derivation of numeric nutrient criteria. Presentation to the Florida Nutrient 

Criteria Development TAC, December 6, 2006 meeting, Tallahassee, FL. http://www.dep

.state.fl.us/water/wqssp/nutrients/docs/TAC/tac16_NumericNutrientCriteriaDerivation.pdf

Weaver, K., and R. Frydenborg. 2006. Evolving approach for nutrient criteria development. 

Presentation to the Florida Nutrient Criteria Development TAC, May 22, 2006 meeting. 

Gainesville, FL. 

.

http://www.dep.state.fl.us/water/wqssp/nutrients/docs/TAC/tac14_Evolving

ApproachNutrientCriteria.pdf.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

60
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

61

APPENDICES

Appendix A: FDEP’s Review of EPA’s Recommended Nutrient Criteria 

for Streams and Lakes

Prepared by the Florida Department of Environmental Protection, Bureau of 

Assessment and Restoration Support

Background

EPA’s Nutrient Criteria Technical Guidance Manual: Rivers and Streams (Buck et al., 2000) 

described three general approaches for the development of numeric nutrient criteria for streams. 

This appendix evaluates EPA’s third and least preferred approach, which involves establishing 

criteria using a lower distribution (e.g., 5th to 25th percentile) of a pool of sites of unknown 

ecological quality in a designated ecoregion. It is FDEP’s position that this approach is not 

scientifically defensible, since there is no connection between the resulting thresholds and any 

environmental measure. A general population of data contains an unknown mix of reference 

and nonreference sites with varying levels of impairment (i.e., unknown ecological quality), 

allowing no predetermined relationship between the nutrient concentrations in this “unknown” 

population and any valued ecological attribute. Since there is no predestined relationship 

between the 25th percentile nutrient concentration of a general population and any biological 

response variable, nothing can be predicted concerning the level of protection afforded by a 

criterion derived using this approach. 

EPA’s approach uses designated ecoregions (Figure A-1). Florida’s ecoregions are IX, XII, and 

XIII. These ecoregions cover a large area, and waterbodies within each of these areas can 

experience vastly different environmental circumstances. Note that Ecoregion IX starts in 

Pennsylvania, comes down to Florida, heads north to Illinois, heads west to Nebraska, and ends 

in Texas and Louisiana. EPA’s recommended nutrient criteria were derived based on data 

collected throughout this vast and heterogeneous region (Figure A-2) and therefore cannot be 

expected to accurately reflect conditions in any particular state, including Florida. 

The 25th percentile concentration of the general population is purely dependent on the number 

of sites and their level of enrichment. This fact is acknowledged in EPA guidance (EPA, 2000a, 

2000b, 2000c, 2000d, 2000e). If the general population of data were primarily composed of 

minimally disturbed “reference” sites, a 25th percentile criterion would result in these healthy 

sites being out of compliance. Even worse, if nutrients were actually reduced below those 

needed for the proper functioning of these reference systems, adverse harm would occur. On 

the other hand, if the general population were primarily composed of highly nutrient-enriched 

sites, a criterion derived in this way might be underprotective. It would be purely coincidence 

that a criterion developed in this manner would be appropriate. 

Therefore, any criterion derived based on the 25th percentile of data collected at a pool of 

random sites with unknown ecological quality is scientifically indefensible and unlikely to be 

upheld if challenged, due to the fundamental technical flaws associated with this approach. 

However, EPA has taken this method and recommended criteria for streams (Table A-1) and 

lakes/impoundments (Table A-2).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

62

Figure A-1. Aggregations of Level III ecoregions for national nutrient strategy
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

63

Figure A-2. Location of sampling stations used by EPA to derive Ecoregion IX 

recommended nutrient criteria for rivers and streams and lakes

Table A-1. EPA recommendations for streams using the lower 25th percentile 

approach of a dataset of unknown site quality

Region IX -

Southeastern 

Temperate

Forested Plains 

and Hills

Region XII -

Southern

Coastal Plain

Region XIII -

Southern Florida 

Coastal Plain ++

TP (μg/L) 36.56 40.00 N/A **

TN (mg/L) 0.69 0.9 N/A **

Chlorophyll a (μg/L) 0.93 0.40 N/A **

Periphyton Chlorophyll a

(mg/m3) 20.35 N/A * N/A **

Turbidity (NTU) 5.70 1.90 N/A **

N/A – Not available.

* Periphyton chlorophyll a (mg/m3

) criteria recommendations were not included in the EPA publication addressing 

ambient water quality criteria recommendations for rivers and streams in Region XII.

** EPA has not issued ambient water quality criteria recommendations for rivers and streams in Region XIII.

Rivers and Stream Lakes
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

64

Table A-2. EPA recommendations for lakes/impoundments using the lower 25th

percentile approach of a dataset of unknown site quality

Region IX -

Southeastern 

Temperate 

Forested 

Plains 

and Hills

Region XII -

Southern 

Coastal Plain

Region XIII -

Southern 

Florida 

Coastal Plain

TP (μg/L) 20.00 10.0 17.5

TN (mg/L) 0.36 0.52 1.27

Chlorophyll a (μg/L) 4.93 2.60 12.35

Secchi depth (m) 1.53 2.10 0.79

EPA notes in its national nutrient guidance documents that sampling protocols and analytical 

methods must demonstrate comparable data in order to compare data collected under different 

sampling programs or by different agencies, but EPA’s contractor did not perform such a review 

when assembling the national nutrient database. The review focused on the following: 

(1) Sample location verification; 

(2) The deletion of duplicate samples; 

(3) The deletion of samples downstream of effluent discharge points; 

(4) The verification of station identification numbers, HUC codes, county, and 

ecoregions; and 

(5) The verification of laboratory and sampling methods, where this information was 

available or in some cases when data generators responded to inquiries. 

Several of the datasets (Legacy STORET, National Water Quality Assessment [NAWQA], and 

National Stream Quality Accounting Network [NASQAN]) received minimal review by the 

contractor on the assumption that the review had previously been conducted by a previous 

contractor, or on the assumption that the source agency, the USGS, had reviewed the data for 

QA/QC.

In short, the database lacks sufficient supporting information to indicate that acceptable 

measurement procedures were used and that the results are reliable. This is inconsistent with 

the manner in which both aquatic criteria and human health criteria are established. EPA has 

very specific guidelines regarding the documentation of test controls, endpoints, and data 

quality for both criteria types (Stephen et al., 1985; EPA, 2000a, 2000b, 2000c, 2000d, 2000e). 

Equivalent scrutiny was not applied to the ecoregional numeric nutrient criteria 

recommendations. 

EPA’s handling of the national nutrient database also included a highly questionable data 

manipulation where values reported as less than the analytical detection limit were replaced 

with a value of zero. It is improbable if not impossible that the actual nutrient concentrations in 

the environment were zero. Additionally, values reported below the method quantitation limits 

were replaced with one-half the reported value. These decisions very likely caused EPA’s 

recommended criteria to be biased low.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

65

The method by which below detection and quantitation limit values are handled will bias low 25th

percentiles and medians, when 25 and 50%, respectively, of the values are below these limits. 

However, it is impossible to determine the actual degree to which EPA’s manipulations affected 

the final recommendations because (1) they do not document the percentage of altered values,

and (2) the detection and quantitation limits used by the various data generators are not 

documented. 

Method detection and quantitation vary among data generators depending on analytical 

procedures, which change over time, and organizational policies. However, the 

recommendations and data summaries can be compared with typical detection and quantitation 

limits used in Florida. For example, typical Florida chlorophyll a detection and quantitation limits 

are at or above 1 and 4 μg/L, respectively. The seasonal 25th percentile values used by EPA to 

derive the stream recommendations are all below the 1 μg/L detection limit, with one exception 

(Tables A-3 and A-4). Furthermore, the seasonal 25th percentiles and median values are all 

between the detection and quantitation limits. This strongly suggests that EPA’s data 

manipulations artificially biased its criteria recommendations. The recommendations reflect 

data manipulation artifacts rather than realistic or protective thresholds.

Table A-3. Summary of seasonal values chlorophyll a concentrations used by 

EPA to derive the recommended Ecoregion IX rivers and streams 

chlorophyll a criteria

The criterion was calculated as the median of seasonal 25th percentiles (P25).

Season N Mean Minimum Maximum P5 P25 Median P75

Fall 187 6.03 .000 78.60 0.25 0.9 2.85 7.50

Spring 206 6.54 .000 98.52 0.00 0.97 3.38 7.95

Summer 235 7.44 .000 79.20 0.00 1.03 3.48 9.00

Winter 178 3.13 .000 34.80 0.00 0.25 1.65 3.48

Table A-4. Summary of seasonal values chlorophyll a concentrations used by 

EPA to derive the recommended Ecoregion XII rivers and streams

chlorophyll a criteria

The criterion was calculated as the median of seasonal 25th percentiles (P25).

Season N Mean Minimum Maximum P5 P25 Median P75

Fall 146 6.40 0.00 87.94 0.00 0.38 1.07 5.25

Spring 171 7.86 0.00 100.25 0.00 0.39 1.71 8.04

Summer 171 8.93 0.00 62.40 0.00 0.53 3.21 11.6

Winter 159 4.98 0.00 96.20 0.00 0.41 1.38 5.85

While these recommendations appear on the surface to represent water quality criteria that can 

be set for waterbodies, they are both incomplete and illogical. They are incomplete in that they 

only represent the magnitude of a criterion and do not provide duration and frequency. Duration 

is the averaging period that a criterion represents in order to be protective (i.e., monthly 

average, annual average, instantaneous maximum, etc.). Frequency is the number of times the 

magnitude/duration expression can be violated and still protect the designated use (i.e., no 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

66

more than one exceedance per year, less than 10% exceedance over 5 years, etc.). Rarely 

does a single exceedance of a naturally occurring parameter impair the designated use. 

While these values are incomplete, assuming they were established as an annual average not 

to be exceeded for the purposes of comparison with actual environmental data proves useful in 

trying to determine the logic of applying them to Florida waterbodies. Furthermore, the criteria 

recommendations are illogical from the perspective of protecting designated uses. As 

previously stated, there is no predestined relationship between the 25th percentile nutrient 

concentration of a general population and any valued ecological attribute linked to the 

designated uses. There is nothing that can be predicted concerning the level of protection 

afforded by a criterion derived using this approach.

Application of EPA Criteria Recommendations

STREAMS

This section tests the application of the criteria to determine if they meet the CWA test in 

Section 303(b)(2)(A), “Such standards shall be such as to protect the public health or welfare, 

enhance the quality of water and serve the purposes of this Act.” The purposes of the CWA are 

defined in Section 101(a). The expectation of water quality standards to provide protection to 

waterbodies is further defined in federal regulation at 40 CFR Part 131.6 and Subpart B.

FDEP has identified a number of unimpacted reference streams in the central peninsula of the 

state, called the peninsula bioregion (Figure A-3). These streams represent conditions with 

minimal to no additional nutrient contribution from natural conditions. Therefore, one can 

conclude that the aquatic life in these waterbodies fully support the designated uses and are 

adapted to long-standing natural nutrient conditions. Figure A-4 shows the distribution of 

nitrogen, phosphorus, chlorophyll a, and turbidity concentrations associated with these 

reference streams and the associated EPA criteria recommendation values.

The implementation of the criteria that EPA has recommended would result in the identification 

of many natural streams as impaired, and with a strict application of the CWA, would result in 

TMDLs requiring reductions in nutrient availability to the aquatic life dependent on the stream for 

habitat. This reduction in nutrient availability is no different than reducing the food supply for the 

organisms, and will alter the biological integrity of the waterbody and limit the aquatic life 

contained in the waterbody. This is inconsistent with the goals of the CWA and federal 

regulations. Furthermore, the application of EPA’s recommendations would require the state to 

regulate and remediate nutrients below natural conditions in many streams throughout the state. 

This is illogical and would result in a waste of public and private resources that could otherwise 

be invested to address real societal problems, including valid nutrient impairments.

An additional complication is that monitoring the biological integrity of streams is an evolving 

science. EPA has recommended the use of chlorophyll a and turbidity (water clarity) as 

indicator tools for measuring biological response in streams. While chlorophyll a and turbidity 

are a way to measure algal mass buildup in waters, they are not the best tool for flowing 

waterbodies, where the excessive growth of algae due to elevated nutrients is often in the form 

of algae growth attached to physical objects in the stream (streambed, rocks, logs, etc.), not 

suspended and floating in the water column. EPA’s chlorophyll a criteria recommendation is for 

suspended growth (floating algae). A better measure that is evolving involves an analysis of the 

attached plant community, known as periphyton. Figures A-5 and A-6 show the relationship 

between excess nutrients and periphyton growth in the Suwannee River in Florida (one 

waterbody in Florida with extensive periphyton data).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

67

Figure A-3. Stream bioregions of Florida

 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

68

Figure A-4. Cumulative frequency distributions of (A) total phosphorus, (B) total 

nitrogen, (C) chlorophyll a, and (D) turbidity in confirmed peninsula 

bioregion reference streams

The vertical blue dash-dotted line indicates the EPA-recommended 25th percentile criterion for Ecoregion XII. The 

intersection between the curve and vertical lines demonstrates the percentage of biologically healthy streams (e.g., 

80% for TP) that would be falsely identified as impaired if the EPA recommendations were adopted. 

0

10

20

30

40

50

60

70

80

90

100

0 0.05 0.1 0.15 0.2 0.25

Total Phosphorus (mg/L)

Percentile

Peninsula Bioregion Reference

Region XII 25th Percentile

A.

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3

Total Nitrogen (mg/L)

Percentile

B.

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10

Turbidity (NTU)

Percentile

D.

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2

Chlorophyll (μg/L)

Percentile

C.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

69

Figure A-5. Adverse biomass changes in Suwannee River periphyton related to 

anthropogenic nitrate-nitrate levels

Phytoplankton chlorophyll is typically very low.

Figure A-6. Increases in Vaucheria sp. (nuisance algae) in Florida spring runs 

related to anthropogenic nitrate-nitrate levels (graph lists TN as axis, 

but this was predominantly nitrate-nitrate)

Phytoplankton chlorophyll in springs is typically very low.

Mean NOx (Mg/L)

AFDW (g/Square-Meter)

0.0 0.2 0.4 0.6 0.8

0 2 4 6

0.1 1 6

0

10

20

30

40

50

60

70

80

90

100

Total N (mg/L)

Vaucheria % cover
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

70

LAKES

FDEP has made very significant progress in the development of an LVI specifically designed to 

assess the health of aquatic biological communities in lakes. While FDEP intends to evaluate 

dose-effect relationships between the LVI and nutrients, the LVI may also be used to identify 

biologically healthy, reference lakes. Lakes with an LVI score of 37 or greater support healthy 

biological communities that fully support the designated uses and are adapted to long-standing 

natural nutrient conditions. Figure A-7 shows the distribution of nitrogen, phosphorus, and 

chlorophyll a concentrations associated with these reference lakes and the associated EPA 

criteria recommendation values. 

Figure A-7. Cumulative frequency distributions of (A) total phosphorus, (B) total 

nitrogen, and (C) chlorophyll a in Florida lakes with healthy aquatic 

plant communities (LVI ≥ 37)

The vertical green and blue dashed lines indicate the EPA-recommended 25th percentile criterion for Ecoregions XI 

and XII, respectively. The intersection between the curve and vertical lines demonstrates the percentage of 

biologically healthy lakes that would be falsely identified as impaired if the EPA recommendations were adopted.

0

10

20

30

40

50

60

70

80

90

100

0 0.05 0.1 0.15 0.2 0.25 0.3

Total Phosphorus (mg/L)

Percentile

Pass LVI

Region IX 25th Percentile

Region XII 25th Percentile

A.

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Total Nitrogen (mg/L)

Percentile

B.

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Chlorophyll a (μg/L)

Percentile

C.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

71

The implementation of the criteria that EPA has recommended would result in the identification 

of many reference lakes (LVI ≥ 37) as impaired and, with a strict application of the CWA, would 

result in TMDLs requiring significant reductions in nutrient availability to aquatic life. As noted 

for streams, reducing nutrient availability is no different than reducing the food supply for the 

organisms. This will alter the biological integrity of the waterbody and limit its aquatic life, which 

is inconsistent with the goals of the CWA and federal regulations.

ESTUARIES

EPA published the document Nutrient Criteria Technical Guidance Manual: Estuarine and 

Coastal Marine Waters in 2001. The guidance concluded that, because of differing geographic 

and climatic conditions among the East, Gulf, and West Coasts, uniform national criteria for 

estuarine and coastal waters are not appropriate, and that they should be developed at the 

state, regional, or individual waterbody levels. Therefore, EPA did not propose, nor is it 

currently in a position to propose, CWA Section 304(a) numeric nutrient criteria 

recommendations for estuaries. EPA currently has no basis upon which to promulgate nutrient 

criteria for Florida estuaries.

WETLANDS

EPA published a final document, Nutrient Criteria Technical Guidance Manual: Wetlands, in

2007. While the document provided technical guidance for developing numeric nutrient criteria 

for wetlands, EPA has not developed Section 304(a) recommendations upon which numeric 

nutrient criteria could be developed for Florida wetlands.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

72

Literature Cited

Buck, S., W. Dodds, J. Fisher, D. Hart, A. Parker, J. Stevenson, V. Watson, and E. Welch. 

2000. Nutrient criteria technical guidance manual: Rivers and streams. EPA 822-B-00-

002. Washington, DC: U.S. Environmental Protection Agency.

Stephen, C.D., D.I. Mount, D.J. Hansen, J.H. Gentile, G.A. Chapman, and W.A. Brungs. 1985. 

Guidelines for deriving numerical national water quality criteria for the protection of aquatic 

organisms and their uses. Duluth, MN: U.S. Environmental Protection Agency, Office of 

Research and Development, Environmental Research Laboratories.

U.S. Environmental Protection Agency. 2000a. 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. Washington, 

DC: Office of Water.

———. 2000b. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Lakes and reservoirs in Nutrient Ecoregion 

XII. EPA 822-B-00-013. Washington, DC: Office of Water. 

———. 2000c. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Lakes and reservoirs in Nutrient Ecoregion 

XIII. EPA 822-B-00-014. Washington, DC: Office of Water. 

———. 2000d. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Rivers and streams in Nutrient Ecoregion 

IX. EPA 822-B-00-019. Washington, DC: Office of Water. 

———. 2000e. Ambient water quality criteria recommendations, information supporting the 

development of state and tribal nutrient criteria: Rivers and streams in Nutrient Ecoregion 

XII. EPA 822-B-00-021. Washington, DC: Office of Water. 

———. 2001. Nutrient criteria technical guidance manual: Estuarine and coastal marine 

waters. EPA-822-B-01-003. Washington, DC: Office of Water.

———. 2007. Nutrient criteria technical guidance manual: Wetlands. EPA-822-R-07-004. 

Washington, DC: Office of Water.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

73

Appendix B: Selection of Benchmark Sites (Characterized by Low 

Levels of Human Disturbance) Using the LDI Index

Prepared by the Florida Department of Environmental Protection, Water Quality 

Standards and Special Projects Program

Brown and Vivas (2003) have developed an LDI to estimate the intensity of human land use 

based on nonrenewable energy flow. The application of the LDI is based on the ecological 

principle that the intensity of human-dominated land uses in a landscape affect ecological 

processes of natural communities. The more intense the activity, the greater the effect on 

ecological processes. Natural landscapes with little or no agricultural or urban development will 

likely have intact ecological systems and processes. The intended use of the LDI was as an 

index of the HDG.

The LDI is a land use–based index of potential human disturbance calculated using coefficients 

corresponding to specific land use categories within drainage basins. The LDI coefficients were 

quantified using emergy3

LDITotal = Σ (LDCi * %LUi)

use per unit area per time (Brown and Vivas, 2003). Brown and 

colleagues collected energy consumption data from billing records and literature sources, for 

energies such as electricity, fuels, fertilizers, pesticides, and water (both public water supply and 

irrigation). Because the LDI was meant to be a measure of human disturbance, only 

nonrenewable energies were used in the calculation. Natural systems were assigned a 

nonrenewable empowerment density of 0 sej/ha·yr.

1

 The LDI coefficients were calculated as 

the natural log of the empower densities normalized on a scale from 1 to 10. LDI coefficients for 

natural lands equal 1.0 and a LDI coefficient of 10.0 is associated with the highest intensity land

uses (e.g., central business district or power plant).

The LDI is calculated as the area-weighted value of the land uses within an area of influence. 

Using the land use coefficients and the percent area occupied by each land use as determined 

by GIS land use coverages, the LDI is calculated as follows:

Where,

LDITotal = LDI Index for the area of influence

%LUi

 = percent of total area of influence in land use i

LDCi = LDI coefficient for land use i

Brown and Vivas (2003) and Fore (2004) evaluated various methods for calculating the LDI, 

including distance weighting and the area of influence. Brown and Vivas (2003) evaluated the 

differences in LDIs calculated using 100, 200, and 500 m buffer differences around drainage 

basins for wetlands. They reported no significant difference between LDIs calculated using 

buffer distances of either 100 or 200 m; however, LDIs calculated using a 500 m buffer were 

different from those determined using either the 100 or 200 m distances in some cases. 

Additionally, they found that the LDIs determined using buffer distances of either 100 or 200 m 

were better able to predict the Wetland Biological Integrity (SFWMD’s Wetland Rapid 

Assessment Procedure [WRAP]). 

 3 “Emergy” is energy that has been corrected for different qualities. Its unit is expressed as the solar emergy joule (sej). The units

for quantifying the intensity of human activity are therefore sej/ha•yr-1 (empower density).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

74

Brown and Vivas (2003) also compared distance-weighted and area-weighted LDIs. They 

found no significant difference between the two methods and concluded that, since the time to 

calculate an area-weighted LDI was considerably less, the area-weighted method was the most 

efficient method to calculate an LDI. Fore (2004) evaluated the effect of upstream catchment 

distance on the LDI for streams, in order to determine which spatial scale was a better predictor 

of site condition. She compared a LDI calculated as 100 m buffers around the streams both 10 

km upstream of sampling points and for the entire upstream catchment area (watershed). The 

LDIs calculated using the two distances were both highly correlated with each other and almost 

equally correlated with Florida’s SCI of stream macroinvertebrate biological integrity. 

EPA guidance (2000a, 2000b, 2000c, 2000d, and 2000e) states that reference reaches are 

relatively undisturbed stream segments that can serve as examples of the natural biological 

integrity of a region. Because reference reaches should be both minimally disturbed by 

anthropogenic influences and support valued ecological attributes (healthy populations of flora 

and fauna), the metrics used to select reference reaches need to be correlated with both the 

degree of human disturbance influencing the reach as well the biological or ecological health of 

the system. As discussed above, the LDI was developed as a direct and objective measure of 

human disturbance. It has also been shown to be a reliable predictor of pollutant loading 

(Figure B-1). Furthermore, the LDI has been demonstrated in multiple cases and across 

multiple waterbody types to be an effective predictor of biological health. 

Brown and Reiss (2006) suggested an LDI breakpoint of less than or equal to 2.0 to identify 

minimally disturbed sites and an LDI of greater than 2.0 to designate areas with increasing 

levels of human disturbance based on an evaluation of diatom, macrophyte, and 

macroinvertebrate assemblages (i.e., Florida Wetland Condition Index [FWCI]) in 193 

depressional wetlands in Florida. The study divided wetlands into four groups for analysis 

(Group 1 – LDI = 1.0; Group 2 – 1.0 < LDI ≤ 2.0; Group 3 – 2.0 < LDI ≤ 3.0; and Group 4 – LDI > 

3.0). Statistical comparisons (2-sample t-test and Fisher’s one-way multiple comparison) 

showed that there were no significant differences in diatom, macrophyte, or macroinvertebrate 

FWCI scores for LDI Groups 1 and 2 (Table B-1 and Figure B-2). Additionally, Groups 3 and 4 

(LDI >2) were found to be significantly different from Groups 1 and 2 (LDI < 2). Brown and 

Reiss (2006) concluded that an LDI of 2.0 represented a very conservative breakpoint between 

potentially disturbed sites and reference conditions.

The LDI has been also shown to be an effective predictor of stream macroinvertebrate biological 

integrity. Fore (2004) demonstrated a strong correlation (Spearman’s r=-0.60, p<0.01) between 

the LDI and the SCI (Figure B-3). Furthermore, many of the 10 biological metrics that go into 

the SCI, particularly percent sensitive taxa, exhibit a strong correlation with the LDI (Figure 

B-4).

Niu (2004) provided another example of the relationship between LDI and biologic heath. He

evaluated breakpoints in lake chlorophyll a concentrations relative to LDI in 547 Florida lakes 

using change point analysis and found statistically significant change points in median lake 

chlorophyll a concentrations at LDI values of 1.9 and 6.3 (Figure B-5).

As discussed above, the LDI was specially designed as a metric of human disturbance. LDI 

values of less than 2.0 are indicative of areas with very minimal levels of human disturbance. 

Although it would be ideal to incorporate direct measures of biological health into the selection 

of benchmark sites, this is not currently possible given the paucity of paired nutrient and 

biological data for the Lake Okeechobee Tributaries TMDL, determined based on the selected 

analysis method. Since it has been demonstrated that the LDI is highly correlated with multiple 

measures of biological health, the use of the LDI alone is deemed appropriate and adequate for 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

75

the selection of benchmark sites. Further, across multiple waterbody types and multiple trophic 

levels, an LDI of 2.0 has been shown to be a biologically significant breakpoint that can be used 

to distinguish benchmark conditions from potentially disturbed areas. Therefore, an LDI of 2.0 

or less is a conservative criterion that can appropriately and reliably be used to identify 

minimally disturbed benchmark sites.

Table B-1. Comparison of FWCI scores using Fisher’s one-way multiple 

comparison test for three separate species assemblages (diatoms, 

macrophytes, and macroinvertebrates) for depressional palustrine 

wetlands

From Brown and Reiss (2006).

LDI Group Diatom FWCI Macrophyte FWCI Macroinvertebrate 

FWCI

Group 1 LDI = 1.0 84.9 (15.2) a 85.1 (9.1) a 66.8 (17.1) a

Group 2 1.0 < LDI ≤ 2.0 80.4 (17.8) a 80.3 (13.4) a 65.9 (18.0) a

Group 3 2.0 < LDI ≤ 3.0 64.4 (18.9) b 56.8 (20.3) b 44.3 (22.1) b

Group 4 LDI > 3.0 35.5 (25.9) c 26.5 (21.7) c 34.0 (18.4) b

Notes: 

Group values represent mean (standard deviation).

Means in the same column followed by the same letter are not significantly different at α = 0.05

using Fisher’s least significant difference (LSD) procedure. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

76

Figure B-1. Area-weighted LDI Index versus phosphorus pollutant load in 64

hydrologic units (subwatersheds) of the St. Marks River watershed.

Re-created from Brown and Vivas (2003).

Area Weighted LDI

0 1 2 3 4 5 6 7 8 9 10

Pollutant Load (kg P/ha·yr-1) 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

y=-0.49x-0.29

r

2=0.90
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

77

Figure B-2. Box plot comparison of macroinvertebrate FWCI scores among LDI 

groups, including Group 1 (LDI = 1.0), Group 2 (1.0 < LDI ≤ 2.0), Group 

3 (2.0 < LDI ≤ 3.0), and Group 4 (LDI > 3.0).

Boxes represent the 25th to 75th quartile range, circles represent group mean values, and horizontal lines represent 

median values (from Brown and Reiss, 2006).

Figure B-3. Box plot comparison of SCI scores and LDI values calculated based 

on a 100 m buffer area extending 10 km upstream of the sample point

Macroinvertebrate F

W

CI

1 2 3 4

100

80

60

40

20

0

LDI Range

1.0 - 1.9 2.0-3.9 4.0 - 5.9 >6

Stream Condition Index

0

20

40

60

80

100
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

78

Figure B-4. Comparison of average number of sensitive stream 

macroinvertebrate taxa for sites within different LDI groups

The number of sensitive taxa from streams with LDIs < 2.0 was significantly greater than for streams with higher LDIs 

(Kruskall-Wallis p<0.0001).

LDI Range

1.0-1.9 2.0-3.9 4.0-5.9 >6.0

Average Number of Sensitive Taxa (n)

0

2

4

6

8

10

12

14

16

LDI

0 2 4 6 8 10

Average Number of Sensitive Taxa (n)

0

2

4

6

8

10

12

14

16

(Spearman’s r=-0.50, p<0.001)
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

79

Figure B-5. Log of lake median chlorophyll a concentrations versus LDI

Two change points were detected. The first was detected at an LDI = 1.9 with about 80% confidence, and a second 

was detected at an LDI = 6.3 with about 95% confidence.

LDI

Log of Median of Chl-a

2 4 6 8

-1

0 1 2

3

4

5

 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

80

Literature Cited

Brown, M.T., and K.C. Reiss. 2006. Proposed breakpoint of LDI < 2.0 for determining 

minimally affected reference conditions for water bodies. Gainesville, FL: Center for 

Environmental Policy, Department of Environmental Engineering Sciences, University of 

Florida. Technical report submitted to the Florida Department of Environmental Protection.

Brown, M.T., and M.B. Vivas. 2003. A Landscape Development Intensity Index. Gainesville, 

FL: Center for Environmental Policy, Department of Environmental Engineering Sciences, 

University of Florida. Technical report submitted to the Florida Department of 

Environmental Protection.

Fore, L.S. 2004. Development and testing of biomonitoring tools for macroinvertebrates in 

Florida streams. Statistical Design, Seattle, WA. Final report submitted to the Florida 

Department of Environmental Protection

Niu, X. 2004. Change point analysis of the chlorophyll-a and LDI data from the IWRM Status 

Network Cycle 1 lakes study. Tallahassee, FL: Department of Statistics, Florida State 

University. Technical report submitted to the Florida Department of Environmental 

Protection.

Niu, X., P. Lin., and D. Meeter. 2000. Detecting change points in the species composition and 

water quality data of WCA2A. Tallahassee, FL: Department of Statistics, Florida State 

University. Technical report submitted to the Florida Department of Environmental 

Protection.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

81

Appendix C. Peninsular Nutrient Benchmark Summaries

Nutrient Benchmark Site Summary

Bee Branch

STORET Station 28020299FTM

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.64, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of citrus and field/pasture observed beyond the forested buffer zone. There are no point source 

discharges upstream of the site.

DOQQ 2004 aerial photograph of Bee Branch (Station 28020299FTM) showing watershed vicinity and land use. 

The headwaters drain an area dominated by pine flatwoods, prairie, and wetlands.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

82

DOQQ 2004 aerial l photograph of Bee Branch (Station 28020299FTM) showing close-up of sampling site. An 

extensive forested riparian zone was evident of both sides of the system.

Photographs of Bee Branch (Station 28020299FTM).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

83

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 147

Hydrologic Score 3

LDI Score 1.64

SCI Score 49 A

Total Phosphorus Geometric Mean (mg/L) 0.080

Total Nitrogen Geometric Mean (mg/L) 1.13

The habitat assessment scored in the “Optimal” range. The Stream Condition Index scored in the “Healthy” 

category, exhibiting a diverse assemblage of sensitive invertebrates and indicating the site is clearly meeting the 

Class III designated use.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 91.33

% Chlorophycota 2.67

% Euglenophycota 0.67

% Cyanophycota 4.67

Number of Taxa 60

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 60 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal community) at Bee Branch. Based on our analyses, the Department concluded that the site 

was influenced only by very low levels of anthropogenic stressors and that it clearly maintained healthy biological 

assemblages. Thus, not only are the nutrient concentrations reflective of minimally disturbed conditions, they are 

associated with biota which demonstrate full support of the most sensitive designated use (propagation and 

maintenance of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

84

Nutrient Reference Site Summary

Blackwater Creek at State Road 44A

STORET Station ALT_BWC44 (20010455)

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.09, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Blackwater Creek at State Road 44A (Station BWC44 or 20010455) showing 

watershed vicinity and land use. The system originates in Lake Norris, an undeveloped lake surrounded by wetland.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

85

DOQQ 2004 aerial photograph of Blackwater Creek at State Road 44A (Station BWC44 or 20010455) showing 

close-up of sampling site. An extensive forested riparian zone was evident on both sides of the system.

Photographs of Blackwater Creek at State Road 44A 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

86

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 125

Hydrologic Score 2

LDI Score 1.09

SCI Score 77 A

Total Phosphorus Geometric Mean (mg/L) 0.050

Total Nitrogen Geometric Mean (mg/L) 1.60

The habitat assessment scored in the “Optimal” range, and the Stream Condition Index scored in the “Exceptional” 

category, indicating an unusually diverse assemblage of sensitive invertebrates, definitively supporting the Class III 

designation.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 93.0

% Chlorophycota 0

% Cryptophycophyta 0

% Cyanophycota 7.0

Number of Taxa 45

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 45 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (hydrology, habitat assessment, 

local land use, algal and macroinvertebrate communities) at Blackwater Creek at State Road 44A. Based on our 

analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic stressors 

and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient concentrations 

reflective of minimally disturbed conditions, they are associated with biota which demonstrate full support of the 

most sensitive designated use (propagation and maintenance of a healthy, well-balanced population of fish and 

wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

87

Nutrient Benchmark Site Summary

Blackwater Creek upstream of Carter Prop Bridge

STORET Station BWCCPB / 20010536

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.31, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Blackwater Creek upstream of Carter Prop Bridge (Station BWCCPB) showing 

watershed vicinity and land use. The system originates in Lake Norris, an undeveloped lake surrounding by 

wetland.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

88

DOQQ aerial photograph of Blackwater Creek upstream of Carter Prop Bridge (Station BWCCPB) showing closeup of sampling site. An extensive forested riparian zone was evident of both sides of the system.

Photographs of Blackwater Creek upstream of Carter Prop Bridge 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

89

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 130

Hydrologic Score 2

LDI Score 1.31

Total Phosphorus Geometric Mean (mg/L) 0.054

Total Nitrogen Geometric Mean (mg/L) 1.28

The habitat assessment scored in the “Optimal” range. High water caused by recent rains made Stream Condition 

Index sampling inappropriate according to DEP standard operating procedures. Results from a Biorecon that was 

performed 2/7/2007 demonstrated that this site scored in the “healthy” range, indicating that the Class III 

designation is being fully supported. 

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 72.43

% Chlorophycota 15.28

% Cryptophycophyta 0.33

% Cyanophycota 7.31

% Euglenophycota 2.99

Number of Taxa 72

Very little periphyton was observed at the site, which would allow optimal substrate use by macroinvertebrates. No 

nuisance algal growth was found. Of the 72 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. 

. 

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (hydrology, local land use, and 

algal communities) at Blackwater Creek, upstream of Carter Prop Bridge. Based on our analyses, the Department 

concluded that the site was influenced only by very low levels of anthropogenic stressors and that it clearly 

maintained healthy biological assemblages. Thus, not only are the nutrient concentrations reflective of minimally 

disturbed conditions, they are associated with biota which demonstrate full support of the most sensitive designated 

use (propagation and maintenance of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

90

Nutrient Benchmark Site Summary

Cypress Branch above 78

STORET Station GLA630GS

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.21 suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

areas of citrus and field/pasture observed beyond an extensive forested riparian buffer zone. There are no point 

source discharges upstream of the site.

DOQQ 2004 aerial photograph of Cypress Branch (Station GLA630GS) showing watershed vicinity and land use. 

The stream originates in an area of prairie, flatwoods, and swamp.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

91

DOQQ 2004 aerial photograph of Cypress Branch (Station GLA630GS) showing close-up of sampling site. An 

extensive riparian forested zone is generally present on both sides of the system throughout the watershed, with a 

minimum of a 75-100 m buffer.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

92

Photograph of Cypress Branch (Station GLA630GS).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

93

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 134

Hydrologic Score 2

LDI Score 1.21

SCI Score 63 A

Total Phosphorus Geometric Mean (mg/L) 0.131

Total Nitrogen Geometric Mean (mg/L) 1.97

The habitat assessment scored in the “Optimal” range, and the Stream Condition Index scored in the “Healthy” 

category, indicating a diverse assemblage of sensitive invertebrates, and fully supporting the Class III designation.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 91.33

% Chlorophycota 0

% Cryptophycophyta 0

% Cyanophycota 8.67

Number of Taxa 48

Very little periphyton was observed at the site, which would allow optimal substrate use by macroinvertebrates. No 

nuisance algal growth was found. Of the 48 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. 

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

and local land use) at Cypress Branch. Based on our analyses, the Department concluded that the site was 

influenced only by very low levels of anthropogenic stressors and that it clearly maintained healthy biological 

assemblages. Thus, not only are the nutrient concentrations reflective of minimally disturbed conditions, they are 

associated with biota which demonstrate full support of the most sensitive designated use (propagation and 

maintenance of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

94

Nutrient Benchmark Site Summary

Econlockhatchee River at Snowhill Road

STORET Station ECH

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.14, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond the forested buffer zone. 

DOQQ 2004 aerial photograph of Econlockhatchee River at Snowhill Road (Station ECH) showing watershed 

vicinity and land use. The system originates in the Econlockhatchee River Swamp, an extensive wetland area.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

95

DOQQ 2004 aerial photograph of Econlockhatchee River at Snowhill Road (Station ECH) showing close-up of 

sampling site. An extensive forested riparian zone was evident of both sides of the system.

Photographs of Econlockhatchee River at Snowhill Road
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

96

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 106

Hydrologic Score 2

LDI Score 1.14

SCI Score 52 A

Total Phosphorus Geometric Mean (mg/L) 0.098

Total Nitrogen Geometric Mean (mg/L) 0.93

The habitat assessment score of 106 placed this site in the high “Suboptimal” range. The Stream Condition Index 

score of 52 was in the “Healthy” category, exhibiting a diverse assemblage of sensitive invertebrates and indicating 

the site is clearly meeting the Class III designated use.

Algal Community Structure

Periphyton Community Composition

% Composition

% Bacillariophyta 90.31

% Chlorophycota 1.38

% Cryptophycophyta 0

% Cyanophycota 8.3

Number of Taxa 53

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 53 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at Econlockhatchee River at Snowhill Road. Based on 

our analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic 

stressors and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient 

concentrations reflective of minimally disturbed conditions, they are associated with biota which demonstrate full 

support of the most sensitive designated use (propagation and maintenance of a healthy, well-balanced population of 

fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

97

Nutrient Benchmark Site Summary

Little Orange Creek below Cabbage Creek

STORET Station LOCBCC

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.54, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Little Orange Creek below Cabbage Creek (Station LOCBCC) showing watershed 

vicinity and land use. Little Orange Creek originates from Little Orange Lake, a completely undeveloped system 

surrounded by forest, and associated wetlands.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

98

DOQQ 2004 aerial photograph of Little Orange Creek below Cabbage Creek (Station LOCBCC) showing close-up 

of sampling site. An extensive riparian forested wetland buffer is present on both sides of the system.

Photographs of Little Orange Creek below Cabbage Creek
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

99

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 132

Hydrologic Score 2

LDI Score 1.54

SCI Score 89 A

Total Phosphorus Geometric Mean (mg/L) 0.067

Total Nitrogen Geometric Mean (mg/L) 0.70

The habitat assessment scored in the “Optimal” range, and the Stream Condition Index scored in the “Exceptional” 

category, indicating an unusually diverse assemblage of sensitive invertebrates, definitively supporting the Class III 

designation.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 84.52

% Chlorophycota 5.16

% Cryptophycophyta 0

% Cyanophycota 10.32

Number of Taxa 54

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 54 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at Little Orange Creek below Cabbage Creek. Based 

on our analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic 

stressors and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient 

concentrations reflective of minimally disturbed conditions, they are associated with biota which demonstrate full 

support of the most sensitive designated use (propagation and maintenance of a healthy, well-balanced population of 

fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

100

Nutrient Benchmark Site Summary

Little Orange Creek

STORET Station PUT308GS

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 2.01, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Little Orange Creek (Station PUT308GS) showing watershed vicinity and land 

use. The stream originates from Little Orange Lake, an undeveloped system surrounded by forest and swamp.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

101

DOQQ 2004 aerial photograph of Little Orange Creek (Station PUT308GS) showing close-up of sampling site. An 

extensive riparian forested buffer is generally present on both sides of the system throughout the watershed, with 

one small clear-cut area approaching within 75 m of the stream.

Photograph of Little Orange Creek 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

102

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 131

Hydrologic Score 2

LDI Score 2.01

SCI Score 75 A

Total Phosphorus Geometric Mean (mg/L) 0.201

Total Nitrogen Geometric Mean (mg/L) 1.13

The habitat assessment scored in the “Optimal” range, and the Stream Condition Index scored in the “Exceptional” 

category, indicating an unusually diverse assemblage of sensitive invertebrates, definitively supporting the Class III 

designated use. This is one of the few peninsular sites where Plecopterans (stoneflies, known to be extremely 

sensitive to stress) are routinely found.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 86.6

% Chlorophycota 5.7

% Cryptophycophyta 0

% Cyanophycota 7.4

Number of Taxa 48

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 48 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at Little Orange Creek. Based on our analyses, the 

Department concluded that the site was influenced only by very low levels of anthropogenic stressors and that it 

clearly maintained healthy biological assemblages. Thus, not only are the nutrient concentrations reflective of 

minimally disturbed conditions, they are associated with biota which demonstrate full support of the most sensitive 

designated use (propagation and maintenance of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

103

Nutrient Benchmark Site Summary

Moses Creek at US 1

STORET Station 27010050

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.24, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond the forested buffer zone. There are no point source 

discharges upstream of the site.

DOQQ 2004 aerial photograph of Moses Creek at US 1 (Station 27010050) showing watershed vicinity and land 

use.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

104

DOQQ 2004 aerial photograph of Moses Creek at US 1 (Station 27010050) showing close-up of sampling site. 

Moses Creek originates in an area of pine flatwoods and swamp. An extensive riparian forested buffer is present on 

both sides of the system.

Photograph of Moses Creek at US 1 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

105

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 138

Hydrologic Score 1

LDI Score 1.24

SCI Score 60 A

Total Phosphorus Geometric Mean (mg/L) 0.081

Total Nitrogen Geometric Mean (mg/L) 1.03

The habitat assessment scored in the “Optimal” range. The Stream Condition Index score of 60 was in the 

“Healthy” category, exhibiting a diverse assemblage of sensitive invertebrates and indicating the site is meeting the 

Class III designated use.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 14.33

% Chlorophycota 1.33

% Euglenophycota 1.67

% Cyanophycota 81.67

Number of Taxa 71

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 71algal taxa observed, including 66 diatom taxa, the majority of the 

periphyton community was composed of blue-green algae. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

and local land use) at Moses Creek at US 1. Based on our analyses, the Department concluded that the site was 

influenced only by very low levels of anthropogenic stressors and that it clearly maintained healthy biological 

assemblages. Thus, not only are the nutrient concentrations reflective of minimally disturbed conditions, they are 

associated with biota which demonstrate full support of the most sensitive designated use (propagation and 

maintenance of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

106

Nutrient Benchmark Site Summary

Orange Creek Upstream of Highway 21

STORET Station 21202

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.7, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture and field/pasture observed beyond a forested riparian buffer zone. There are no point 

source discharges upstream of the site.

DOQQ 2004 aerial photograph of Orange Creek upstream of Highway 21 (Station 21202) showing watershed 

vicinity and land use. The stream originates from Orange Lake, an Outstanding Florida Water.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

107

DOQQ 2004 aerial photograph of Orange Creek upstream of HWY 21 (Station 21202) showing close-up of 

sampling site. An extensive riparian forested wetland buffer is present on both sides of the system.

Photograph of Orange Creek upstream of Highway 21 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

108

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 121

Hydrologic Score 3

LDI Score 1.74

SCI Score 74 A

Total Phosphorus Geometric Mean (mg/L) 0.125

Total Nitrogen Geometric Mean (mg/L) 1.43

The habitat assessment scored in the “Optimal” range, and the Stream Condition Index scored in the “Exceptional” 

category, indicating an unusually diverse assemblage of sensitive invertebrates. This is one of the few peninsular 

sites where Plecopterans (stoneflies, known to be extremely sensitive to stress) are routinely found.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 90.38

% Chlorophycota 1.37

% Cryptophycophyta 0

% Cyanophycota 8.25

Number of Taxa 51

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 51 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at Orange Creek, upstream of Highway 21. Based on 

our analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic 

stressors and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient 

concentrations reflective of minimally disturbed conditions, they are associated with biota which demonstrate full 

support of the most sensitive designated use (propagation and maintenance of a healthy, well-balanced population of 

fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

109

Nutrient Benchmark Site Summary

St. Johns River Near DeLand

STORET Station 2236000

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.68, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond the forested buffer zone.

DOQQ 2004 aerial photograph of St. John’s River near DeLand (Station 2236000) showing watershed vicinity and 

land use. The system originates from Blue Cypress Lake, a completely undeveloped system surrounding by forest 

and wetlands.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

110

DOQQ 2004 aerial photograph of St. John’s River near DeLand (Station 2236000) showing close-up of sampling 

site. An extensive riparian forested wetland buffer is present on both sides of the system.

Photographs of St. John’s River near DeLand
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

111

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 128

Hydrologic Score 4

LDI Score 1.68

SCI Score NA

Total Phosphorus Geometric Mean (mg/L) 0.078

Total Nitrogen Geometric Mean (mg/L) 1.39

The habitat assessment scored in the “Optimal” range. This system is characterized by very low flow, therefore 

Stream Condition Index sampling was inappropriate according to DEP standard operating procedures. Aquatic 

vegetation present was typical of sluggish, open systems and there were no nuisance plant issues.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 88.2

% Chlorophycota 2.4

% Cryptophycophyta 0

% Cyanophycota 9.5

Number of Taxa 53

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 53 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal communities) at the St. Johns River near Deland. Based on our analyses, the Department 

concluded that the site was influenced only by very low levels of anthropogenic stressors and based upon 

observations during the site visit, that no adverse algal or aquatic plant issues were present. Thus, not only are the 

nutrient concentrations reflective of minimally disturbed conditions, they are associated with biota which suggest 

support of the most sensitive designated use (propagation and maintenance of a healthy, well-balanced population of 

fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

112

Nutrient Benchmark Site Summary

Steven’s Branch off CR 204

STORET Station 27010070

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.29, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Steven’s Branch off CR 204 (Station 27010070) showing watershed vicinity and 

land use. Steven’s Branch originates in an area of pine flatwoods, wetlands and prairie.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

113

DOQQ 2004 aerial photograph of Steven’s Branch off CR 204 (Station 27010070) showing close-up of sampling 

site. An extensive riparian forested buffer is present on both sides of the system.

Photographs of Steven’s Branch off CR 204 (Station 27010070)
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

114

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 128

Hydrologic Score 3

LDI Score 1.29

SCI Score 76 A

Total Phosphorus Geometric Mean (mg/L) 0.120

Total Nitrogen Geometric Mean (mg/L) 1.09

The habitat assessment scored in the “Optimal” range, and the Stream Condition Index scored in the “Exceptional” 

category, indicating an unusually diverse assemblage of sensitive invertebrates, definitively supporting the Class III 

designation.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 75.14

% Chlorophycota 3.39

% Cryptophycophyta 0

% Cyanophycota 21.47

Number of Taxa 66

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 66 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at Steven’s Branch off CR 204. Based on our 

analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic stressors 

and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient concentrations 

reflective of minimally disturbed conditions, they are associated with biota which demonstrate full support of the 

most sensitive designated use (propagation and maintenance of a healthy, well-balanced population of fish and 

wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

115

Nutrient Benchmark Site Summary

Tosohatchee Creek @ WMA

STORET Station ORA331LV

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.50, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Tosohatchee Creek (Station ORA331LV) showing watershed vicinity and land 

use. The stream originates in a swampy area adjacent to Tosohatchee Creek State Preserve.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

116

DOQQ 2004 aerial photograph of Tosohatchee Creek (Station ORA331LV) showing close-up of sampling site. An 

extensive riparian forested wetland buffer is present on both sides of the system.

Photograph of Tosohatchee Creek (Station ORA331LV).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

117

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 116

Hydrologic Score 1

LDI Score 1.50

SCI Score NA

Total Phosphorus Geometric Mean (mg/L) 0.034

Total Nitrogen Geometric Mean (mg/L) 0.77

The habitat assessment scored in the high “Suboptimal” range, with water velocity being the lowest scoring 

parameter. The site was deemed inappropriate for SCI sampling due to the swamp-like nature of the system and lack 

of water flow. Vegetation present was typical of minimally disturbed swamp systems.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 89.00

% Chlorophycota 0.33

% Euglenophycota 0.33

% Cyanophycota 10.33

Number of Taxa 56

Of the 56 algal taxa identified, the majority of the periphyton community was composed of diatoms. No problematic 

filamentous algae were observed.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

algal community, and local land use) at Tosohatchee Creek. Based on our analyses, the Department concluded that 

the site was influenced only by very low levels of anthropogenic stressors and that no adverse algal or aquatic plant 

issues were present. Thus, not only are the nutrient concentrations reflective of minimally disturbed conditions, they 

are associated with biota which suggest support of the most sensitive designated use (propagation and maintenance 

of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

118

Nutrient Benchmark Site Summary

Waccasassa River above SR 24

STORET Station LEV502GS

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.23, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, and field/pasture observed beyond the forested riparian buffer zone. There are no point 

source discharges upstream of the site.

DOQQ 2004 aerial photograph of the Waccasassa River (Station LEV502GS) showing watershed vicinity and land 

use. The Wacasassa River originates in an area of hardwood swamp known as Devils Hammock.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

119

DOQQ 2004 aerial photograph of the Waccasassa River (Station LEV502GS) showing close-up of sampling site. 

Although there was some encroachment from a clear cut area near the site, extensive riparian forested wetland 

buffer is present on both sides for the majority of the system. Note that the forested buffer still exceeded 

approximately 75 m at minimum, and was generally several hundred m wide.

Photographs of the Waccasassa River
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

120

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 138

Hydrologic Score 1

LDI Score 1.23

SCI Score 69 A

Total Phosphorus Geometric Mean (mg/L) 0.065

Total Nitrogen Geometric Mean (mg/L) 0.63

The habitat assessment scored in the high “Optimal” range, and the Stream Condition Index scored in the 

“Exceptional” category, indicating an unusually diverse assemblage of sensitive invertebrates, definitively 

supporting the Class III designation.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 84.24

% Chlorophycota 0.32

% Cryptophycophyta 0

% Cyanophycota 15.43

Number of Taxa 46

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 46 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. Although some filamentous algal growth was found in a few small areas, it did not affect 

habitat suitability, as evidenced by the very good SCI score.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at the Waccasassa River. Based on our analyses, the 

Department concluded that the site was influenced only by very low levels of anthropogenic stressors and that it 

clearly maintained healthy biological assemblages. Thus, not only are the nutrient concentrations reflective of 

minimally disturbed conditions, they are associated with biota demonstrated to be fully supportive of the designated 

use (healthy, well balanced populations of aquatic organisms).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

121

Nutrient Benchmark Site Summary

Withlacoochee River at Stokes Ferry

STORET Station 3513

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.82, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, field/pasture, and residential uses observed beyond a forested riparian buffer zone. There 

are no point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Withlacoochee River at Stokes Ferry (Station 3513) showing watershed vicinity 

and land use. The Withlacoochee River originates in the Green Swamp, a very large wetland with considerable

areas in public ownership.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

122

DOQQ 2004 aerial photograph of Withlacoochee River at Stokes Ferry (Station 3513) showing close-up of sampling 

site. An extensive riparian forested wetland buffer is present on both sides of the system.

Photographs of the Withlacoochee River at Stokes Ferry 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

123

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 153

Hydrologic Score 4

LDI Score 1.82

SCI Score 68 A

Total Phosphorus Geometric Mean (mg/L) 0.043

Total Nitrogen Geometric Mean (mg/L) 0.86

The habitat assessment scored in the high “Optimal” range, and the Stream Condition Index scored in the 

“Exceptional” category, indicating an unusually diverse assemblage of sensitive invertebrates, definitively 

supporting the Class III designated use.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 90.24

% Chlorophycota 0.7

% Cryptophycophyta 0

% Cyanophycota 9.06

Number of Taxa 40

Moderate periphyton growth was observed at the site; however, substrate availability for benthic invertebrates was 

not problematic, as evidenced by the “exceptional” SCI score. Of the 40 algal taxa observed, the majority of the 

periphyton community was composed of diatoms. No problematic filamentous algal growth was found, despite the 

relatively open, sunny conditions characteristic of the site.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) at Withlacoochee River at Stokes Ferry. Based on our 

analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic stressors 

and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient concentrations 

reflective of minimally disturbed conditions, they are associated with biota demonstrated to be fully supportive of 

the designated use (healthy, well balanced populations of aquatic organisms).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

124

Nutrient Benchmark Site Summary

Withlacoochee River at Trails End

STORET Station FL0052000087500

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.34, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture, field/pasture, and residential uses observed beyond the forested buffer zone. There are no 

point source discharges upstream of the site.

DOQQ 2004 aerial photograph of Withlacoochee River at Trails End (Station FL0052000087500) showing 

watershed vicinity and land use. The Withlacoochee River originates in the Green Swamp, a very large wetland 

with considerable areas in public ownership.
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

125

DOQQ 2004 aerial photograph of Withlacoochee River at Trails End (Station FL0052000087500) showing close-up 

of sampling site. An extensive riparian forested wetland buffer is present on both sides of the system.

Photographs of Withlacoochee River at Trails End
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

126

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 118

Hydrologic Score 2

LDI Score 1.34

SCI Score NA

Total Phosphorus Geometric Mean (mg/L) 0.059

Total Nitrogen Geometric Mean (mg/L) 1.01

The habitat assessment scored in the high “Suboptimal” range. The SCI was not performed due to the morphology 

of the system in this area (lake-like), which when coupled with low water levels, resulted in the system having no 

perceptible water velocity. Typical aquatic plants observed at the site included Taxodium distichum, Hydrocotyle 

sp., Panicum hemitomon, Myriophyllum heterophyllum, and Polygonum sp., indicating healthy conditions.

Qualitative Periphyton Sampling was not performed at this site, however minimal periphyton growth was observed, 

which would allow for optimal substrate use by benthic invertebrate and fish communities. No problematic 

filamentous algal growth was found, despite the relatively open, sunny conditions characteristic of the site.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology 

and local land use) at Withlacoochee River at Trails End. Based on our analyses, the Department concluded that the 

site was influenced only by very low levels of anthropogenic stressors and that no adverse algal or aquatic plant 

issues were present. Thus, not only are the nutrient concentrations reflective of minimally disturbed conditions, they 

are associated with biota which suggest support of the most sensitive designated use (propagation and maintenance 

of a healthy, well-balanced population of fish and wildlife).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

127

Nutrient Benchmark Site Summary

Withlacoochee River at SR 471

STORET Station WITHLACOORVR1

Land Use

This station was considered to be a candidate reference site based on the Landscape Development Intensity Index 

score of 1.45, suggesting benign human influences in the watershed. During the site visit, aerial photographs were 

examined and direct observations confirmed that the majority of the watershed land use was forest/natural, with 

small areas of silviculture and field/pasture observed beyond an extensive forested riparian buffer zone. There are 

no point source discharges upstream of the site.

Aerial photograph of Withlacoochee River at SR 471 (Station WITHLACOORVR1) showing watershed vicinity 

and landuse. The Withlacoochee River originates in the Green Swamp, an extensive wetland with considerable 

areas in public ownership. 
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

128

Aerial photograph of Withlacoochee River at SR 471 (Station WITHLACOORVR1) showing close-up of sampling 

site. An extensive riparian forested wetland buffer is present on both sides of the system.

Photograph of Withlacoochee River at SR 471 (Station WITHLACOORVR1).
State of Florida Numeric Nutrient Criteria Development Plan March 2009

Florida Department of Environmental Protection

129

Parameter

Habitat, Biological and Water Quality Data

Value

Habitat Assessment 119

Hydrologic Score 2

LDI Score 1.45

SCI Score 46 A

Total Phosphorus Geometric Mean (mg/L) 0.080

Total Nitrogen Geometric Mean (mg/L) 1.68

The habitat assessment scored in the high “suboptimal” range due to no water velocity. The Stream Condition Index 

was not performed during this site visit due to low water levels and minimal stream velocity. However, sites both 

upstream (station 33449) and downstream (station 34401) of the sampling location and within the same WBID 

received “healthy” SCI designations in 2007, (51 A and 40 A, respectively) indicating that the water quality is fully 

supporting the Class III designated use. These scores were averaged for the above table.

Algal Community Stricture

Periphyton Community Composition

% Composition

% Bacillariophyta 85.95

% Chlorophycota 1.3

% Cryptophycophyta 0

% Cyanophycota 12.1

% Euglenophycota 0.7

Number of Taxa 61

Minimal periphyton growth was observed at the site, which would allow for optimal substrate use by benthic 

invertebrate and fish communities. Of the 61 algal taxa observed, the majority of the periphyton community was 

composed of diatoms. No problematic filamentous algal growth was found.

Overall Reference Site Conclusion: 

Experienced FDEP scientists conducted a series of observations and measurements (habitat assessment, hydrology, 

local land use, and algal and macroinvertebrate communities) Withlacoochee River at SR 471. Based on our 

analyses, the Department concluded that the site was influenced only by very low levels of anthropogenic stressors 

and that it clearly maintained healthy biological assemblages. Thus, not only are the nutrient concentrations 

reflective of minimally disturbed conditions, they are associated with biota demonstrated to be fully supportive of 

the designated use (healthy, well balanced populations of aquatic organisms).