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



## Appendix A-1: Lake Nutrient, Chl. a , and Clarity Distributional Statistics by Lake ClassTSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

A1-1 

### Appendix A-1. Lake Nutrient, Chl. a , and Clarity Distributional Statistics by

Lake Class

One of the principal approaches for deriving candi date nutrient criteria is the exploration of

distributional statistics associated with differe nt waterbody classes. I ndeed, original U.S. Environmental Protection Agency (U.S. EPA) nutrient guidance was based upon such an approach, whereby the 25 th percentile of all site values within a class or the 75 th percentile of

reference site values within a class was recommended for deriving criteria, although other percentiles could be used by st ates/tribes as long as defensible reasons were used (USEPA 2000a, b, c, d; USEPA 2001; USEPA 2007). Florid a Department of Envi ronmental Protection (FDEP) has decided to pursue such an appr oach for their stream criteria using the 90 th percentile of reference or “benchmark” sites, but similar analysis has not been av ailable for lakes. We conducted an analysis of distributional statistics for all lakes and referenc e lakes within the two lake color classes identified by FDEP, namely clear lakes (color < 40 platinum-cobalt units (PCU)) and colored lakes (color > 40 PCU). This approach is ofte n referred to as the “all sites” approach, and usually involve s establishing crite ria using a lower distribution (e.g., 25 th
percentile) of a pool of site s of undetermined ecological qu ality, 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 a nd the availability of data at the time of publication, U.S. EPA used this method to develop and publish under the Clean Water Act (CWA) section 304(a)

recommended nutrient criteria for streams and la kes in nutrient ecoregions IX, XII, and XIII. While an “all sites data distribution approach” does not directly link nutrie nt concentrations to valued ecological attributes (healthy, well-balanced populations of flora or fauna), it does make the presumption that the 25 th percentile will closely approxima te a reference condition for that geographic location. Several examples with data fr om actual reference site s have validated this assumption.



### Methods

Impaired Waters Rule (IWR) data were r eceived in MS Access 2003® format, and were

maintained in that format for data selection. Se parate lakes data sets were created in Access® (using VBA code) and exported as te xt for statistical analysis. Th ese files were all lakes (annual average by station), and subsets for each Weav er nutrient region (Bone Valley, North Central, Northeast, Panhandle, and Peninsula for phosphor us; Panhandle and all else for nitrogen).



### Selection Criteria

Any lake station was removed if it:

1) Occurred in southern Florida (based on Weav er Regions and determined via geographic
information system (GIS) analysis)
2) Had a maximum measured salinity >=0.5 ppt
3) Had a maximum conductivity >= 3,000 μS/cm
4) Did not originate from any of the following organizations (exactly as listed in the Organizations table):TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

A1-2 a. Unnamed agency (21FLCOT) b. Unnamed agency (21FLWQSP) c. Unnamed agency (21FLLEON) d. Unnamed agency (21FLBRA) e. Alachua County (21FLACEP)

f. Choctawhatchee Ba sin Alliance (21FLCBA) g. City of Lakeland, Florida (LAKELAND) h. City of Orlando, Florida (21FLORL) i. Collier County Pollution Control, Florida (21FLCOLL) j. Environmental Research and Design, Inc (21FLERDI) k. FDEP Water Quality A ssessment Section (21FLWQA) l. FDEP Central District (21FLCEN) m. FDEP Charlotte Harbor Aquatic/Buffer Preserves (21FLCHAR) n. FDEP Northwest District (21FLPNS) o. FDEP Rookery Bay National Estuarine Reserve (21FLROOK) p. FDEP South District (21FLFTM) q. FDEP Southeast District (21FLWPB) r. FDEP Southwest District (21FLTPA) s. FDEP/FDEP Northeast District (21FLA) t. Florida Game and Freshwater Fish Commission (21FLGFWF) u. FDEP - OCEC (21FLCMP) v. FDEP (21FLGW) w. Hillsboro County (21FLHILL) x. Lake County Water Resource Management (21FLLCPC) y. Northwest Florida Water Mana gement District (21FLNWFD) z. Orange County Environm ental Protection (21FLORAN) aa. Palm Beach County Department of Environmental Resource Management (21FLPBCH) bb. Pinellas County Department of Environmental Management (21FLPDEM) cc. Polk County Natural Resources Division (21FLPOLK) dd. Seminole County Public Works Roads/Stormwater (21FLSEM)

ee. South Florida Water Mana gement District (21FLSFWM)

ff. Southwest Florida Water Ma nagement District (21FLSWFD) gg. St. Johns River Water Mana gement District (21FLSJWM) hh. FDEP (21FLDEP)

ii. Suwannee River Water Mana gement District (21FLSUW) jj. Volusia County Environmental Health Lab (21VEMD)

Lakes were identified as any station with a value of “Lake” for the BODY field, PLUS any stations verified as a reference lake (see be low). In some cases, the station “BODY” type

conflicted with elements of the station name. For example, some stations with the “BODY” type “stream” had names that suggested that they were lakes or intake or discharge canals. The lake data set was likewise limited by excluding stations with names like “borrow pit,” “canal,” or “ditch.” However, not all stati ons with conflicting names and BO DY types could be identified without reviewing every stati on name individually (and even that would not guarantee 100%TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

A1-3 success). Therefore, despite the appl ication of these selection criteria , it is possible that the lake data sets contain incorrect data types.



### Reference Lakes

Reference reaches were mapped to individual stations, which contai ned both reach IDs and

station IDs. These reference stati ons were annotated as reference in the complete lakes data set (as described above). Stations that were not mark ed as references in th e combined excel files

were marked as not referen ce in the lakes data set.



### Outliers and Invalid Data

Additionally, individual sample s were evaluated for potentiall y erroneous data. Individual samples were removed if they met any of the following criteria:

1) Salinity < 0 ppt 2) Conductivity <20 μS/cm 3) pH <3 or >10 4) Dissolved Oxygen (DO) >15 mg/L 5) Nitrate plus Nitrite (NO 3 +NO 2 ) > 75 mg/L 6) Total Nitrogen (TN) > 20 mg/L 7) Total Phosphorus (TP) > 15 mg/L 8) Chl. a > 1,000 μg/L 9) Color > 1,000 PCU 10) Secchi depth ≥ 50 meters

Zero values were eliminated for al l nitrogen and phosphorus parameters.



### Detection Limits

Detection limits were not reliably reported, a nd in some cases, reported results fell below detection limits. Therefore, we did not adjust reported “below det ection limits” results. Additionally, we did not alter or eliminate any data based on remark codes. Descriptions were not available for all remark codes, and theref ore they could not reliably be interpreted. Consequently, some data that should be ex cluded (e.g., results flagged for samples being analyzed outside holding time limits) could not be identified and may appear in the data set.



### Station Averages and Data Transformations

Chlorophyll a (chl. a ), color (COLOR), conducti vity (COND), ammonia (NH 4 ), nitrate plus nitrite (NO 3 + NO 2 ), total nitrogen (TN), and total phosphor us (TP) values were natural-log transformed prior to proceeding. Tr ansformed values were used to create scatter plots, and native values were used to genera te descriptive statistics.

Annual averages were determined for individual stat ions, using all available data for that station in a given year. The final data sets therefore co ntain one record for each year that a station was sampled, with the parameter resu lts equal to the arithmetic mean (average) for non-transformed data (DO, pH, salinity, Secchi depth, and temperatur e) or the geometric mean for ln-transformedTSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

A1-4 data (chl. a , color, conductivity, and nutrien ts) over all samples availabl e for that station in that

year.



### Color Groups

Color groups were assigned to stations based on the geometric mean color value. Therefore, a station could be assigned to different color groups in different years, based on the average color observed in those years. Lakes with average annual color values less than or equal to 40 PCU are

considered clear lakes and values greater than 40 PCU considered colored lakes, consistent with

FDEP definitions.



### Final Data Sets

Annotating the lakes stations by reference class and color group yielded the possible datasets shown in Table A1-1 for further analysis.



### Analyses

Descriptive statistics (minimum, mean, maximum, standard deviation, and selected percentiles) were calculated for each parameter using arithmetic means, standard deviations, and standard errors for each data set in the table above (when sufficient data were available). We also calculated natural log means and standard deviations which were used to estimate theoretical percentiles as well, consistent with FDEP approaches for the stream analysis.



### Results

Distributional statistics for clear and colored la ke classes varied between the classes and there

were marked differences between the reference s ite and entire site popula tion within each class (Table A1-2). For clear and colored lakes, the 25 th percentile of all lake sites was lower for every constituent (and higher for Secchi depth) than either the 75 th or 90 th percentile of reference lakes whether the empirical or theore tical percentiles are used.

Considering both reference and all sites and empi rical and theoretical percentiles, the ranges of variables can be reported. Fo r clear lakes, the chl. a values range from 4-18  g/L and Secchi depth from 0.2-2.9 m. Ammonium (NH 3 + ), NO 3 /NO 2 , and TN ranged from 10-33  g/L, 7-32

 g/L and 0.6-1.0 mg/L respectively. Finally, TP ranged from 13-52  g/L.

For colored lakes, the ranges were larger, driven mostly by higher reference site 90 th percentile values based on both empirical and theore tical calculations. The range of chl. a was 6-30  g/L and 0.2-1.3 meters for Secchi depth. NH 3 + , NO 3 /NO 2 , and TN ranged from 11-61  g/L,

7-109  g/L, and 0.9-2.0 mg/L respectively. Lastly, TP ranged from 32-162  g/L.TSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh Waters

A1-5 Table A1-1. Possible Datase ts for Further Analysis

Reference

Class Weaver Region Color Group

Set Ref NonRef Bone Valley North Central Northeast Panhandle Peninsula Low Med. High

All X X X X X X X X X X

AllRef X X X X X X X X X

AllClear X X X X X X X X

RefClear X X X X X X X

AllColor X X X X X X X X

RefColor X X X X X X XTSD for U.S. EPA’s Proposed Numeric Nutrient Criteria for FL Inland Surface Fresh WatersA1-6Table A1-2. Distributional Statistics for Clear lakes (< 40 PCU) and Colored Lakes (>40 PCU)based on Reference (Ref) andReference and Non-reference Sites Combined within Each ClassDataset Variable N Min Mean Max SD SE 25th75th90thCVLnMeanLnSDTheor10thTheor25thTheor75thTheor90thClearRef Chl.a21 1 8 22 6 1 41217 70 1.85 0.82 2 41118ClearRef NH443 8 17 40 9 1 102133 57 -4.22 0.49 8 112027ClearRef NO3/NO245 4 13 50 12 2 61432 90 -4.63 0.75 4 61626ClearRef TN 55 0.1 0.5 1.4 0.3 0.0 0.30.70.8 54 -0.83 0.64 0.2 0.30.71.0ClearRef TP 52 4 24 120 21 3 103150 89 -4.07 0.87 6 103152ClearRef Secchi 41 0.3 1.6 5.2 1.0 0.20.8 2.1 2.4 67 1.55 1.030.20.9 2.2 2.9Clear Chl.a2437 1 25 846 39 14 30 65 154 2.45 1.29 25 28 61Clear NH43008 1 30 10913 232 410 23 42 772 -4.10 0.77 610 28 45Clear NO3/NO22817 1 36 7925 206 47 20 46 576 -4.34 1.01 47 26 48Clear TN 4107 0.0 1.1 12.3 0.9 0.00.6 1.2 2.1 85 -0.17 0.68 0.40.5 1.3 2.0Clear TP 3889 1 46 8935 160 313 45 82 349 -3.67 0.96 713 49 88Clear Secchi 3676 0.0 1.4 10.3 1.1 0.0 0.62.02.9 75 1.44 1.07 0.1 0.72.22.8ColoredRef Chl.a137 1 17 846 72 6 31130 429 1.90 1.07 2 31426ColoredRef NH4262 6 33 361 44 3 123460 132 -3.79 0.78 8 133861ColoredRef NO3/NO2267 4 41 432 51 3 750109 124 -3.83 1.17 5 104897ColoredRef TN 274 0.3 1.2 5.4 0.6 0.0 0.71.51.9 50 0.06 0.49 0.6 0.81.52.0ColoredRef TP 275 8 79 705 78 5 33106141 98 -2.87 0.82 20 3399162ColoredRef Secchi 233 0.1 0.6 1.7 0.3 0.00.5 0.8 1.0 45 0.60 0.300.20.4 0.8 1.0Colored Chl.a1424 1 38 846 63 26 36 110 168 2.76 1.28 37 38 82Colored NH42696 1 38 3254 131 311 32 60 342 -3.86 0.83 712 37 61Colored NO3/NO22921 1 44 7389 184 37 33 93 423 -4.08 1.18 48 38 77Colored TN 3300 0.1 1.6 13.3 1.2 0.00.9 2.0 3.3 73 0.30 0.61 0.60.9 2.0 3.0Colored TP 3202 2 115 14880 310 632 120 262 268 -2.74 1.02 1732 128 238Colored Secchi 2896 0.0 0.7 3.9 0.4 0.0 0.40.91.3 64 0.70 0.40 0.2 0.41.01.2Note: Most statistics are based on untransformed values except the natural log-transformed (Ln)mean and standard deviation (SD) used to estimate thetheoretical percentiles (Theor). All units are in μg/L, except TN in mg/L and Secchidepth in m. SE = standard error, CV = coefficient of variation, N= sample size.