## Technical Support Document for U.S. EPA’s Proposed Rule for Numeric Nutrient Criteria for Florida’s Inland Surface Fresh WatersTSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

i 

## Disclaimer

This document is intended to provide technical support to EPA in developing and establishing numeric water quality criteria for nutrients under the Clean Water Act (CWA) pursuant to Section 303(c)(4), in order to pr otect aquatic life in the State of Florida from the effects of nutrient over-enrichment. This document constitutes scientific information regarding the development of numeric criteria for Florida’s inland fresh waters (lakes, streams, springs, and canals) reflecting ambient concentrations of nutri ents that are protective of aquatic life. The information provided herein does not substitute for the CWA or EPA’s regulations; nor is this document a regulation itself. Thus, this doc ument cannot and does not impose any legally binding requirements on EPA, States, Authorized tribes, the regulated co mmunity, or any other party, and might not apply to a particular situ ation or circumstance. This document does not constitute a determination by the Administrato r under CWA Section 303(c)(4)(B) that new or revised water quality standards are needed in the State of Florida.TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

ii 

## List of Contributing Authors Tiffany Crawford, U.S. Envi ronmental Protection Agency 1 Ed Decker, U.S. Environmental Protection Agency 1 Erica Fleisig, U.S. Environmental Protection Agency 1 Richard Greene, U.S. Environmental Protection Agency 1 James Hagy, U.S. Environmental Protection Agency 1 F. James Keating, U.S. Environmental Protection Agency 1 Jan Kurtz, U.S. Environmental Protection Agency Jacques Oliver, U.S. Environmental Protection Agency 1 Lauren Petter, U.S. Environmental Protection Agency 1 Danielle Salvaterra, U.S. Environmental Protection Agency 1 Dan Scheidt, U.S. Environmental Protection Agency 1 Dana Thomas, U.S. Environmental Protection Agency 1 Timothy Wool, U.S. Environmental Protection Agency 1 Lester Yuan, U.S. Environmental Protection Agency 1 Jeroen Gerritsen, Tetra Tech 1 Jon Harcum, Tetra Tech 1 Ann Lincoln, Tetra Tech Michael Paul, Tetra Tech 1 Lei Zhang, Tetra Tech Andrew Bartlett, Florida Departme nt of Environmental Protection Russel Frydenborg, Florida Departme nt of Environmental Protection Joy Jackson, Florida Departmentof Environmental Protection Daryll Joyner, Florida Department of Environmental Protection Denise Miller, Florida Departme nt of Environmental Protection Frank Nearhoof, Florida Departme nt of Environmental Protection Grover Payne, Florida Department of Environmental Protection Emily Peffer, Florida Department of Environmental Protection Kenneth Weaver, Florida Departme nt of Environmental Protection Nijole Wellendorf, Florida Department of Environmental Protection Leska Fore, Statistical Design Xu-Feng Niu, Florida State University

1 U.S. EPA Florida Nutrient Criteria Technical Workgroup for Inland WatersTSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

iii 

## Scope and Purpose of this Document

This document consists of scientific informa tion that EPA gathered and considered as it developed its proposed rule for numeric nutrient criteria for Class I and III surface freshwaters in the State of Florida. Specifically, this doc ument and the appendices consist of chemical, physical, and biological data, meta-data, methods and analyses considered in developing numeric nutrient criteria for specific inland surface waters in Florida (i.e., lakes, streams, springs, and canals). EPA used this information to devel op scientifically-defen sible proposed numeric nutrient criteria to protect designated uses in th ese waters. The designated uses for these waters are, “Recreation, Propagation and Maintenance of a Healthy, Well- Balanced Population of Fish and Wildlife” (F.A.C. 62-302.400). Portions of the information contai ned in this document were also considered by the Florida De partment of Environmental Protec tion as part of its process to develop numeric nutrient water qu ality criteria under state law.TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

iv 

## Foreword Excess nitrogen and phosphorus loadings, or nutri ent pollution, are a l eading cause of water quality degradation in the nation’s waters. Nutrie nt pollution may result in harmful algal blooms, reduced spawning grounds and nursery habitats, fish kills, oxygen-starved hypoxic or "dead" zones, and public health concerns related to impaired drinking water sources and increased exposure to toxic microbes such as cyanobacter ia. Nutrient problems can exhibit themselves locally or much further downstream , leading to degraded estuaries, lakes and reservoirs, and to hypoxic zones where fish and aquatic life can no longer survive.

EPA recommends that States a dopt numeric nutrient criteria for two causal parameters, such as total nitrogen (TN) and total phosphorus (TP), and two response parameters , such as chlorophyll

a (chl. a ) and clarity, into their water quality standard s to protect against the effects of nutrient pollution. State water quality standards are th e foundation for protecting the quality of the nation’s surface waters and are the cornerstone of the water quality-based control program mandated by the CWA. Standards describe the de sired condition of a waterbody and consist of three principal elements: (1) the “d esignated uses” of the state’s wa ters (e.g., fishing, aquatic life, drinking water); (2) “criter ia” specifying the amounts of various pollutants, in either numeric or narrative form, that may be pres ent in those waters without impairing the designated uses; and (3) anti-degradation policies pr oviding for protection of existi ng water uses and limitations on degradation of high quality waters . In the case of Flor ida lakes and flowing waters, the current relevant designated uses of these waters with regard to numeric nutrient criteria are “Recreation, Propagation and Maintenance of a Healthy, Well- Balanced Population of Fish and Wildlife” (F.A.C. 62-302.400). Numeric nutrient criteria must ensure that these uses ar e attained, and, that downstream uses are protected.
EPA recognizes that nutrients are es sential for life, and that some wa ters are naturallyenriched at high levels. It is the excess nutri ent levels, resulting from human disturbance and activities that lead to accelerated eutrophication that is the endpoint of concern in establishing protective numeric nutrient criteria.
Numeric nutrient water quality standards driv e water quality assessments and watershed protection management. They support improved development of National Pollution Discharge Elimination System (NPDES) permits and Tota l Maximum Daily Loads (TMDLs) for nutrients. They also create state- and community-developed environmental baselines that more effectively measure progress and support broader partnerships based on nutrient trading, best management practices (BMPs), land stewardship, wetlands protection, voluntary co llaboration, and urban storm water runoff control strategies.TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

v 

## Contents

Disclaimer ....................................................................................................................................... i List of Contributing Authors ....................................................................................................... ii Scope and Purpose of this Document......................................................................................... iii

Foreword....................................................................................................................................... iv Chapter 1: Methodology for Deriving U.S. EPA’s Proposed Criteria for Lakes ................ 1-1 1a. Methodology for Proposed Lake Classification............................................................. 1-1 i. Background

............................................................................................................. 1-1 ii. Data Used for Analysis.......................................................................................... 1-2 iii. Data Analysis for Classification........................................................................... 1-2 iv. Other Classifi cation Variables.............................................................................. 1-3 v. Color and Alkalinity/Specific Conductance Results.............................................. 1-3 1b. Methodology for Proposed Chlorophyll a Criteria......................................................... 1-4 i. Trophic State and Aquatic Life Use ....................................................................... 1-4 ii. Reference Condition .............................................................................................. 1-8 iii. Other Efforts to Establish Chlorophyll a Thresholds ........................................... 1-9 1c. Methodology for Proposed TP and TN Criteria in Lakes ............................................ 1-13 1d. Duration and Frequency for Proposed Lakes Criteria.................................................. 1-15 1e. Application of Lake-specific Ambient Calculation Provision for Alternative TP and TN Criteria............................................................................................................. 1-17 1f. Alternatives Considered by U.S. EPA.......................................................................... 1-18 i. Single Value Approach to Derive Lake s Criteria - Derive TN and TP Criteria Using Correlations Associated with th e Regression Line or Upper Bound of the 50 thPercentile Prediction Interval ................................................................. 1-18 ii. Additional Modification to Proposed Lakes Classification................................. 1-19 iii. Modif ication to Include Upper Percent ile Criteria with an Associated Ten Percent Exceedance Frequency ........................................................................... 1-20 Chapter 2: Methodology for Deriving U.S. EPA’s Proposed Criteria for Streams............. 2-1 2a. Methodology for Stream Classificati on: U.S. EPA’s Nutrient Wa tershed Regions (NWRs) ............................................................................................................ 2-1 i. Developing a Regionalization Schem e................................................................... 2-1 ii. Ecoregional and Biological Regi onalization Scheme s for Florida........................ 2-1 iii. Refinement of Regionalization for Nutrient Criteria Development ..................... 2-2 iv. Development of the Nutrient Watershed Regions ................................................ 2-2 2b. The Use of the Stream Condition Index as an Indicator for Establishing Biologically Healthy Conditions.................................................................................... 2-3TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

vi i. Development of the Stream Condition Index ......................................................... 2-4 ii. Establishing Healthy Biological C onditions in Streams––Stream Condition Index: Application of the Reference Site Approach ............................................. 2-5 iii. Bio logical Condition Gradient Approach............................................................. 2-5 iv. Evaluation of BCG Calibration Information ........................................................ 2-7 v. Selecting the Threshold between Healthy and Unhealthy Biological Conditions

............................................................................................................. 2-8 2c. Methodology for Calculating In-str eam Protection Values: T he Nutrient Watershed Region Distribution Approach ..................................................................... 2-8 i. Methods f or Calculating Attainin g Site Distributional Statistics ........................... 2-8 ii. SCI Data Preparation ............................................................................................. 2-8 iii. Site Average W ater Chemistry............................................................................. 2-9 iv. Identifying Impaired WBIDs................................................................................ 2-9 v. Identifying Biologically Unhealthy Site List....................................................... 2-10 vi. Removing Sites................................................................................................... 2-10 vii. Calculating Distributional Statistics .................................................................. 2-10 viii. 75 thPercentiles for Site Average Da ta – In-stream Protective Values............. 2-11 ix. Distribution of Nutrient Concen trations among Nutrient Regions..................... 2-11 2d. Duration and Frequency for Proposed Stream s Criteria .............................................. 2-12 2e. Protection of Downstr eam Estuaries and Lakes........................................................... 2-13 i. Downstream Protection of Lakes.......................................................................... 2-13 ii. Downstream Protect ion of Estuaries

................................................................... 2-17 iii. Delineation of Florida’s Estuaries and their Watershe ds ................................... 2-22 2f. Alternative Approach Considered by U.S. EPA .......................................................... 2-30 i. FDEP’s Benchmark Distribution Approach and the Calculation of Benchmark Distribution Approach and Selection of Percentiles from the Benchmark Distribution ...................................................................................... 2-30 ii. Identification of Least-Disturbed Streams........................................................... 2-31 iii. Verification Process for Se lection of Benchmark Sites...................................... 2-31 iv. LDI score of ≤ 2.................................................................................................. 2-32 v. Screening against the 303(d) List of I mpaired Waters ........................................ 2-33 vi. Screening against the 0.35 m g/L Pr oposed Nitrate-Nitrite Threshold................ 2-34 vii. Verification of Surrounding Land Use by Examining High-Resolution Aerial Photographs .............................................................................................. 2-34 viii. Obtaining Input fromFDEP District Biologists............................................... 2-34 ix. Field Evaluation Process, Including Watershed Assessme nt and Biological Appraisal of Benchmark Sites............................................................................. 2-35 x. Results of Benchmark Screening Process............................................................ 2-36 xi. Analysis of Nutrient Benc hmark Sites Biological Data ..................................... 2-36TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

vii xii. Calculation of Benchmar k Derived Nutrient Criteria........................................ 2-37 Chapter 3: Methodology for Derivi ng U. S. EPA's Proposed Criteria for Springs and Clear Streams.......................................................................................................... 3-1 3a. Basis for Nitrat e-Nitrite Criteria..................................................................................... 3-4 i. Criteria Developm ent Methods............................................................................... 3-6 ii. Laboratory Studies

................................................................................................. 3-6 iii. Field Surveys ........................................................................................................ 3-7 iv. TMDL Development Activities............................................................................ 3-8 v. Analysis of Nutrient Gradie nt Study Rapid Periphyton Data.............................. 3-10 vi. Summary and Conclusions

................................................................................. 3-10 3b. Duration and Frequency for Proposed Springs Criteria ............................................... 3-11 3c. Alternative Approach Considered by U.S. EPA .......................................................... 3-12 i. Nitrate-Nitrite Criteria for all Waters as an Independent Criterion...................... 3-12 Chapter 4: Methodology for Deriving U.S. EPA’s Proposed Criteria for Canals

............... 4-1 4a. Other Analyses Conducted and Consider ed by U.S. EPA in the Derivation of Proposed Nume ric NutrientCriteria for Canals ............................................................. 4-4 4b. Duration and Frequency for Proposed Canals Criteria .................................................. 4-5 4c. Alternative Approach Considered by U.S. EPA ............................................................ 4-6 i. Stressor-Response Approach .................................................................................. 4-6 ii. Calculation of TP Criteria for the EAA Using a Downstream Protection Approach ............................................................................................................... 4-8 iii. Upper Percentile Criterion with Low Exceedance Frequency ............................. 4-9TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

viii 

## Tables

Table 1-1. Warm-water TSI Categori es (after Salas and Martino 1991)................................... 1-22 Table 1-2. Relationship between Chl. a , TP, and TN, as Described by Florida’s TSI.............. 1-22
Table 1-3. Summ ary of the Linear Multiple Regression between Ln Transf ormed Chl. a and Ln Transformed TP and TN in Colored Florida Lakes................................................. 1-22 Table 1-4. TP and TN Criteria Ranges for Cl ear (< 40 PCU) and Colored Florida Lakes (> 40 PCU)........................................................................................................................... 1-23
Table 1-5. Su mmary Statistics (Mean and SD) of Nutrient Variables fo r Acidic, Alkaline Lakes, and Colored Lakes, Meeting Annual Criteria .......................................................... 1-23 Table 1-6. Single Observation Criteria for Nutr ient Variables Derived Using Both Mean Observed SD and Modeled SD, for Lakes Meeting Respective Criteria............................. 1-24
Table 2-1. Distributional Statistics of Str eam TP and TN by Estuarine W atershed and Aggregated by U.S. EPA NWR........................................................................................... 2-39 Table 2-2. Results of Interval and Equivale nce Tests Conducted on Reference Sites with 2 SCI Results........................................................................................................................... 2-40
Table 2-3. A verage Values for Metrics at an SCI Score Equivalent to BCG Category 2, and Average Values for Metrics Near the SCI score of Impairme nt.......................................... 2-40
Table 2-4. Distributional Statis tics of TN and TP Based on Site Average Values. The Instream Protective Criteria are the 75th Per centile Valu es (in mg/L). Note: The Mean and Standard Deviations are in Natural Logarithm Units.................................................... 2-40 Table 2-5. TP Thresholds for Lakes Used in Vollenweider Model Screening.......................... 2-41 Table 2-6. Summary of TN Load Estimates to Florida Estuaries, Normalized to Estu ary Area (g N m 2 /y; SE: Standard Error) ................................................................................... 2-41 Table 2-7. Application of Downstream Prot ection Methodology to Estim ate TN Criteria in Stream Reaches that Ensure Pr otection of Downstream Wa ters ......................................... 2-42
Table 2-8. Characteristics of Florida Estuaries and their Watersheds as De lineated by the NOAA CAF ......................................................................................................................... 2-43 Table 2-9. Average TN Loads to Flor ida Estuaries Normalized to 2002 .................................. 2-44
Table 2-10. Inform ation on Downstream River Gage Stations in Florida Estuarine Watersheds........................................................................................................................... 2-45
Table 2-11. Selected Results for Florida Estu aries from NEEA (Bri cker et al. 2007).............. 2-47 Table 2-12. Summary of Nutrient -related Listings for Estuar ine W aters on Florida’s 1998 303(d) List of Im paired Waters............................................................................................ 2-48
Table 2-13. Seasonal 90 thPercentile (P90) and Geometri c Mean Surface (depth < 1.5 m) Chl. a in Florida Estuaries ................................................................................................... 2-49TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

ix Table 2-14. FDEP TMDLs, Marine WBIDs Co nsidered, and the Date Completed or Drafted ................................................................................................................................. 2-50 Table 2-15. TMDL Thresholds, Chl. a , BOD, Nutrient Loads and Percent Reduction

............ 2-51 Table 2-16. Regional TP and TN Cr iteria for Florida Stream s.................................................. 2-52
Table 2-17. Parame ters Monitored Du ring the Benchmark Stream Survey .............................. 2-53
Table 2-18. Summ ary of Information Collected from Field-verified Nutrient Benchmark Sites...................................................................................................................................... 2-54 Table 2-19. Summary of the Regi onal Data Outlier Analysis and Exclusions for the Florida Stream Nutrient Benchmark Data Set.................................................................................. 2-55
Table 4-1. D istributional Statistics Computed from the Natural Logarithm Transformed Data at Sites Located in WBIDs notListed as Nutrient Impaired

....................................... 4-10 Table 4-2. Distributional Statistics Computed from the Natural Logarithm Transformed Data Using All Data............................................................................................................

. 4-11 Table 4-3. Q uantile Regression Results for Matched Annual Geometric Mean Chlorophyll and Nutrient Data................................................................................................................. 4-12
Table 4-4. R esults of “Not to Exceed” Criteria Computations.................................................. 4-12



## Figures

Figure 1-1. Relationship between Ln transformed chl. a and TP in clear lakes by nutrient region. Note, over the entire range of data, th at the lakes exhibit a similar chlorophyll response to TP indepe ndent of region.................................................................................. 1-24 Figure 1-2. Relationship between Ln transformed chl. a and TN in clear lakes by nutrient region. Note, over the entire range of data, th at the lakes exhibit a sim ilar chlorophyll response to TN independent of region................................................................................. 1-25 Figure 1-3. Box plots of chl. a by season in clear (left pane l) and colored (right panel) lakes. .................................................................................................................................... 1-25 Figure 1-4. Regression analyses of annual geometric m ean chl. a concentration and nutrients in colored and clear lakes, showi ng grouping of the two lake classes and the different regression lines.....................................................................................................

. 1-26 Figure 1-5. Scatter plot of annual geometric mean chl. a concentration and nutrients of clear lakes, showing acidic (< 50 m g/L CaCO 3 ) and alkaline lakes. Acidic and alkaline groups were combined in a single regression. ..................................................................... 1-27 Figure 1-6. The relationship between chl. a concentrations (note the log scale) and the percent cyanobacteria in 1,364 lake samp les collected for Florida’s statewide probabilistic monitoring program

. ....................................................................................... 1-28 Figure 1-7. Relationship between the residual error in the TP and TN chlorophyll model and (A) period of record geometric mean lake color and (B) annual geom etric mean lake color. Note that both relationshi ps exhibit a signifi cant negative slope....................... 1-28TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

x Figure 1-8. CART analysis, using a least-squa res fitting method, of th e residual erro r from the TP and TN model for chl. a response in colored Florida lakes. The analysis demonstrates that colored lakes can be spli t into two large groups, using the first CART split, where the chl. a response to TP and TN differs because of the confounding effect of color. *Proportion reduction in error............................................................................... 1-29 Figure 1-9. Relationship between Ln transformed chl. a and TP in moderately colored lakes by nutrient region. Note, over the entire range of data, that the lakes exhibit a sim ilar chlorophyll response to TP independent of region. ............................................................. 1-30 Figure 1-10. Relationship between Ln transformed chl. a and TN in mode rately colore d lakes by nutrient region. Note, over the entire range of data, that the lakes exhibit a similar chlorophyll response to TN independent of region. ................................................ 1-31 Figure 1-11. Regression analyses annual geometric m ean chl. a concentrations and annual geometric mean (A) TP and (B) TN concen trations in moderate ly colored (> 40–140 PCU) Florida lakes. Note that the x axis and y axis are both expr essed on a log-scale. ..... 1-32 Figure 1-12. Regression analyses annual geometric m ean chl. a concentrations and annual geometric mean (A) TP and (B) TN concentr ations in highly co lored (> 140 PCU) Florida lakes. Note that the x axis and y axis are both expressed on a log-scale. ............... 1-33 Figure 1-13. Regression analyses annual geometric m ean chl. a concentrations and annual geometric mean (A) TP and (B) TN concentrat ions in clear Florida lakes. Note that x axis and y axis are both expressed on a log-scale................................................................ 1-34 Figure 1-14. Variance in Lake Okeechobee color data from eight pelagic s tations, averaged over varying time periods. ................................................................................................... 1-35 Figure 1-15. Distribution of average log alka linity in clear Flor ida lakes (log scale). Alkalinities of 20 and 50 m g/L shown by arrows................................................................ 1-35 Figure 1-16. Scatterplots of mean TP, TN, Chl. a , and specific conductance on lake alkalinity. Vertical solid lines are the estimat ed change points, and vertical dashed lines denote th e 95% confidence intervals for th e change points. Wavy dashed lines are LOESS nonlinear regressions and confidence intervals. ..................................................... 1-36 Figure 1-17. Scatter plot of annual geometric mean chl. a concentration and nutrients of clear lakes, showing separa tion of acidic and alkaline lakes with classification breakpoint at 20 m g/L CaCO 3 . Compare to Figure 1-5. Acid ic and alkaline groups were combined in a single regression. a: TN; b: TP..................................................................... 1-37 Figure 1-18. Relationship between specific cond uctance and alkalinity in clear lakes. (a) The curve shows loess fi tted line, and the vertical line s show change point and its 90% con fi dence limits; (b) The curve shows median quantile fi t, and the red dot is the intercept of the quantile regression line with specific conductance = 200 μS/cm............... 1-38 Figure 1-19. Cumulative frequenc y distribution of mean TP c oncentration s in acidic and alkaline lakes that meet the annual averag e criteria. A specific conductance > or < 250 μS/cm is applied as a threshold for classifying high- or acidic lakes.................................. 1-38 Figure 1-20. Density distribution function of normal distribution for acidic (left) and alkaline lakes (right) .........................................................................................................

... 1-39TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

xi Figure 2-1. Level IV subecoregions fo r Florida’s small/wadeable st reams. ............................. 2-56 Figure 2-2. Stream bior egions of Florida................................................................................... 2-57 Figure 2-3. Location of the Peace River and B one Valley Member geologic formations......... 2-58 Figure 2-4. Box plots of stream TN, TP, and TN:TP molar ratio in Florida watersheds. ......... 2-59 Figure 2-5. NWRs in Florida. ...................................................................................................

. 2-60 Figure 2-6. Typical m acroinvertebrate response to organic load ing associated with primary wastewater treatment typical in the 1950s and 1960s.......................................................... 2-61 Figure 2-7. Photo of Hester-Dendy samplers used for determining the Shannon-Weaver diversity index................................................................................................................

...... 2-61 Figure 2-8. Factors affecting bi ological comm unity composition. To conclude that huma n factors are primarily responsible for biol ogical degradation, reas onable knowledge of the influence of natural factors is essential.......................................................................... 2-62 Figure 2-9. Sub-ecoregions of Florida, which we re aggregated into three bioregions, based on multivariate measures of taxonomic si milarity............................................................... 2-62 Figure 2-10. The BCG model (fro m Davies and Jackson 2006). .............................................. 2-63 Figure 2-11. Regression line wi th 90% confidence inte rval showing the relationship between the mean BCG score and SCI score....................................................................... 2-63 Figure 2-12. BCG tier assignments modeled with a proportional odds logistic regression. ..... 2-64 Figure 2-13. Plot of TP concentration of gr ab samples taken at all sites sampled f or biological condition (SCI sites). Concentr ations are in milligrams per liter. ...................... 2-65 Figure 2-14. Plot of TP concentration of grab samples taken from sites sampled for biological condition (SCI site s) that me t the SCI thresh old of 40. Map symbols and units as in Figure 2-13. Also shown are histograms of TP concentrations and cumulative (hatched line) and empirical (solid line) percen t frequencies of TP concentrations in biologically healthy sites by nutrient region. .......................................... 2-66 Figure 2-15. Plot of TN con centration of grab samples taken at all sites sampled for biological condition (SCI sites). Concentr ation s are in milligrams per liter. ...................... 2-67 Figure 2-16. Plot of TN con centration of grab samples taken from sites sampled for biological condition (SCI sites) that me t the SCI threshol d of 40. Map symbols as in Figure 2-15. Also shown are histograms of TN concentrations and cumulative (hatched line) and empirical (solid line) percent frequencies of TN concentration in biologically healthy sites by nutrient region............................................................................................ 2-68 Figure 2-17. Critical stream TP concentration for inflows into clear, low-conductivity lakes to meet lake criterion of 0.010 mg/L TP. Area below the curve results in lake TP below the lake criterion. Streamflow is 100% of inflow into lake. Dashed line: Panhandle 75th percentile proposed instream pr otective value. For residence tim es less than 11 years, stream TP concentration of 0.042 mg/L will result in lake TP > 0.010 mg/L (shaded area)...................................................................................................................................... 2-69TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

xii Figure 2-18. Critical stream TP concentrati ons for stream inflows into clear, lowconductivity lakes. Blue (lower curve): streamflow is 100% of lake water input; this is the same curve shown in Figure 2-17. Red (m iddle curve): streamflow is 50% of lake water input. Green (upper curv e): streamflow is 10% of lake water input. Horizontal dashed lines: 75 thpercentile proposed instream prot ective values for TP regions. ............. 2-69 Figure 2-19. Critical stream TP concentrati ons for stream i nflows into clear, highconductivity lakes. Blue (lower curve): st reamflow is 100% of lake water input. Red (middle curve): streamflow is 50% of lake water input. Gr een (upper curve): streamflow is 10% of lake water input. Horizontal da shed lines: 75th percentile proposed instream protective values for TP regions. .......................................................................................... 2-70 Figure 2-20. Critical stream TP concentrations for stream inflows into colored lakes. Blue (lower curve): streamflow is 100% of lake water input. Red (middle curve): streamflow is 50% of lake water input. Green (upper curv e): stream flow is 10% of lake water input. Horizontal dashed lines: 75t h percentile proposed instream protective values for TP regions.................................................................................................................................. 2-70 Figure 2-21. Summary of TN load estimates fromwatersheds to estuaries in Florida (kg/y). Current TN load and the background TN lo ad were derived from the USGS regional SPARROW model for the SAGT basins. Protective loads were com puted by reducing the anthropogenic contribution of the current load by 50%. ............................................... 2-71 Figure 2-22. Map showing the sp atial distributio n of the fr action of TN delivered to estuarine waters in watersheds of Florida’s estuaries. The map is based on a spatial join of incremental watersheds within the ERF1 stream network and Florida’s waterbodies (WBIDs)............................................................................................................................... 2-72 Figure 2-23. Map showing Florida estuaries and their watersheds as delineated by the NOAA CAF. ........................................................................................................................ 2-73 Figure 2-24. Land use characteri stics of Florida es tuarine wa tersheds as reported by N EEA (Bricker et al. 2007). .........................................................................................................

... 2-74 Figure 2-25. Fraction of delivered anthropogenic TN load (i.e., TN loading delivered to estuaries attributed to pointsources, fertilizer, manure, and urban land use) resulting from each of those sources. Point source loads include those discharging directly to estuaries. Data are from the SAGT regional SPARROW model (Hoos and McMahon 2009) and McMahon et al. (2007). ...................................................................................... 2-74 Figure 2-26. Time series of atmospheric wet deposition of nitrogen at three NADP monitoring sites in Florida................................................................................................... 2-75 Figure 2-27. TN yield (i.e., per km 2 of watershed area) from atmospheric sources (left axis) and the fraction of loads from all sources co ntributing to watershed loading contributed by atmospheric deposition (right axis). All data were derived from the SAGT regional SPARROW watershed model (Hoos and McMahon 2009). ............................................... 2-75 Figure 2-28. Area of estuarine watershed area (%) accounted for and that unaccounted for by river gage stations in Fl orida estuarine watershed.......................................................... 2-76TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

xiii Figure 2-29. LDI results for 5570 stations by s ub-ecoregion for initial candidate reference site evaluation. Sites scoring above 2 on the LDI were eliminated from further consideration (excep t for a single site in the Bone Valley Region that, due to the sparseness of reference sites, wa s accepted at an LDI of 2.2). ............................................ 2-76 Figure 2-30. Relationship between nutrient lo ading (nitrogen in panel (a), phosphorus in panel (b)) and the LDI in th e St. Marks watershed, Florid a (after Brown and Vivas 2003). The arrow is the LDI value at 2.0, the benchm ark site threshold............................. 2-77 Figure 2-31. Depiction of land use area (light yellow) included in an LDI calculation............ 2-78 Figure 2-32. Relationship between the LDI and Stream Condition Index across the entire range of LDI......................................................................................................................... 2-78 Figure 2-33. Benchmark site LDI vs. Average SC I score. In contrast to Figure 2-32, note the lack of correlation between SCI and LDI values of m inimally disturbed sites (LDI ≤ 2, with one exception where LDI was 2.2)....................................................................... 2-79 Figure 2-34. Benchm ark site SCI vs. TN. Note the lack of correlation between SCI and TN throughout the range of benchmark sites. This indicates that there are no adverse effects from establishing nutrient criteria at the upper 90th percentile of the benchmark distribution. Sites scoring less than 40 on the SCI (after QA review) were excluded from the benchmark data set for calculat ion of the final nutrient distribution. ................... 2-79 Figure 2-35. Benchmark site SCI vs. TP. Note the lack of correlation between SCI and TP throughout the range of benchmark sites. This indicates that there are no adverse effects from establishing nutrient criteria at the upper 90th percentile of the benchm ark distribution. Sites scoring less than 40 on the SCI (after QA review) were excluded from the benchmark data set for calculat ion of the final nutrient distribution. ................... 2-80 Figure 3-1. Changes in NO 3 concentration in Weeki Wachee Spring discharge and population of Hernando County, Florida. Note that NO 3 concentrations follow a pattern very similar to the population curv e with a 10- to 15-year lag............................................ 3-13 Figure 3-2. Increased NO 3 concentrations in discharges from 13 selected first-magnitude springs (Alexander, Chassahowitzka Main, Fanning, Ichetucknee Main, Jackson Blue, Madison Blue, Manatee, Rainbow Group compos ite, Silver Main, Silver Glen, Volusia Blue, Wakulla, and Wacissa #2 Springs) between the 1970s an d the early 2000s. Source: Scott et al. 2004. ..................................................................................................... 3-13 Figure 3-3. Relationship betweenmean nitrate/nitrite (NO x ) concentration and mean periphyton cell density from sampling s ites on the Suwannee, Santa Fe, and Withlacoochee rivers. Source: Mattson et al. 2006. ............................................................ 3-14 Figure 3-4. Relationship betweenmean nitrate/nitrite (NO x ) concentration and mean periphyton biomass from sampling si tes on the Suwannee, Santa Fe, and Withlacoochee Rivers. Source: Mattson et al. 2006............................................................ 3-14 Figure 3-5. Change point analysis for data from the 13 stations at the Suwannee River System (m ean cell density vs. mean NO x ). Change point = 0.44 mg/L. The 95% confidence interval for the change point based on 1000 bootstrapping samples is 0.378 to 0.629. ............................................................................................................................... 3-15TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

xiv Figure 3-6. Change point analysis for data from the 13 stations At the Suwannee River System (m ean biomass vs. mean NO x ). Change point = 0.44. The 95% confidence interval for the change point based on 1000 bootstrapping samples is 0.441 to 0.584 μg/L...................................................................................................................................... 3-15 Figure 3-7. Relationship between mean nitrat e plus nitrite con centration and m ean periphyton abundance for sampling sites on the Suwannee, Santa Fe, and Withlacoochee rivers. Values with NO 3 concentrations above and below 0.35 mg/L are shown in different colors. Red dotted lines are at 0.23 mg/L and 0.44 mg/L, representing results from lab and field................................................................................. 3-16 Figure 3-8. Relationship between mean nitrat e plus nitrite and m ean periphyton biomass for sampling sites on the Suwannee, Santa Fe , an d Withlacoochee Rivers. Values with nitrate concentrations above and below 0.35 mg N/L are shown in different colors. Red dotted lines are at 0.23 mg N/L and 0.44 mg N/L, representing results from lab and field studies, respectively..................................................................................................... 3-16 Figure 3-9. The mean cell density of Van Dam eutrophic indicator diatoms increases with increasing nitrate plus nitrite concentrations . The red dotted lines are at 0.23 mg/L and 0.44 m g/L, representing results from la b and field studies, respectively. ........................... 3-17 Figure 3-10. An example of the full-range c onfidence interval procedure to develop a nitrate plus nitrite criterion. The full c onfidence interval procedure resulted in a protective threshold of 0. 33 mg/L. The upper half of confidence interval method yielded a protective thres hold of 0.38 m g/L. The average of these complementary methods resulted in the final protective threshold of 0.35 mg/L. ........................................ 3-17 Figure 4-1a. Location of EAA and EvPA.................................................................................. 4-12 Figure 4-1b. STATSGO soil orde rs for southern Florida.......................................................... 4-12 Figure 4-2. Site locations ( n =513) w ith canal water quality data evaluated in this document.

. 4-13 Figure 4-3. Site locations ( n =72) with chlorophyll data ev aluated in this document................ 4-14 Figure 4-4. Site locations ( n =72) with chlorophyll data evalua ted in this document together with Florida WB IDs that FDEP has identified as nutrient-impaired................................... 4-15 Figure 4-5. Sites located within WBID s not listed as nutrient-impaired................................... 4-16 Figure 4-6. a) Bivariate plot of annual geometric mean chlo rophyll as a function of TP by canal region, b) bivari ate plot with fitted linear regr ession and 90% prediction interval, c) regression analysis statistics, and d) residual plots from regression analysis.................. 4-17 Figure 4-7. a) Bivariate plot of annual geometric mean chlo rophyll as a function of TP by canal region excluding the EvPA , b) bivariate plot with fi tted linear regression and 90% prediction interval, c) regression analysis statistics, and d) residual plots from regression analysis. ...........................................................................................................

... 4-18 Figure 4-8. Bivariate plot of annual geometric mean chlorophy ll as a function of TP with fitted linear regression and 90% prediction interval for a) EAA (not statistically significant), b) EvPA, c) West Coast, and d) East Coast. (Residual plots for the EvPA, West Coast, and East Coast were visua lly examined and found to have constant variance, independence, and normal distribution.) .............................................................. 4-19TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

xv Figure 4-9. EvPA regression analys is statistics for annual geometric m ean chlorophyll as a function of TP and residual plots......................................................................................... 4-20 Figure 4-10. West Coast regression analysis statistics for annual geometric mean chlorophyll as a function of TP and residual plots. ............................................................. 4-20 Figure 4-11. East Coast regression analysis statistics for annual geom etric mean chlorophyll as a function of TP and residual plots.

............................................................. 4-21 Figure 4-12. a) Bivariate plot of annual geometric mean chlo rophyll as a function of TN by canal region, b) bivari ate plot with fitted linear regr ession and 90% prediction interval, c) regression analysis statistics, and d) residual plots from regression analysis.................. 4-22 Figure 4-13. Bivariate plot of annual geometric mean chlorophy ll as a function of TN with fitted linear regression and 90% prediction interval for a) EAA (not statistically significant), b) EvPA (not sta tistically significant), c) West Coast, and d) East Coast. (Residual plots for the West and East Coasts were visually examined and found to have independence and normal distribution. The variance associated with the West Coast residuals did show a tendency to increase as a f unction of TN.)......................................... 4-23 Figure 4-14. West Coast regression analysis statistics for annual geometric mean chlorophyll as a function of TN and re sidual plots.............................................................. 4-24 Figure 4-15. East Coast regression analysis statistics for annual geometric mean chlorophyll as a function of TN and r esidual plots.............................................................. 4-24 Figure 4-16. Bivariate plot of annual geometric mean chlorop hyll as a function of TN and TP across all regions tog ether with Spearman’s rho correlation coefficient, LOESS smoother (black line, f=0.7), and quantile regr ession results (blue line and blue text)....... 4-25 Figure 4-17. Bivariate plot of annual geometric mean chlorop hyll as a function of TP for the EvPA together with Spearman’s rho correlation coefficient, LOESS smoother (black line, f =0.7), and quantile regre ssion results (blue line and blue text)....................... 4-26 Figure 4-18. Bivariate plot of annual geometric mean chlorop hyll as a function of TN and TP for the West Coast together with Spear ma n’s rho correlation coefficient, LOESS smoother (black line, f=0.7), and quantile regr ession results (blue line and blue text)....... 4-27 Figure 4-19. Bivariate plot of annual geometric mean chlorop hyll as a function of TN and TP for the East Coast to gether with Spear man’s rho correlation coefficient, LOESS smoother (black line, f=0.7), and quantile regr ession results (blue line and blue text)....... 4-28