# Site

- Specific Information in Support of Establishing Numeric Nutrient Criteria in the Halifax River Estuary

Florida Department of Environmental Protection Tallahassee, FL 32399

August 23, 2010Draft ii August 2010 Table of Contents Executive Summary

............................................................................................................................ 1 Geographic and Physical Description

.................................................................................................. 4
Sources of Nutrients

........................................................................................................................... 6 Biological Summary

........................................................................................................................... 7 Oyster Reefs

................................................................................................ .............................................. 7
Salt Marsh

................................................................................................ ................................................. 7
Plankton

................................................................................................ .................................................... 8 Water Quality Data Sources and Studies

............................................................................................. 8 Temporal Considerations and the Reference Period Method

................................................................ . 12 Waters on the 303(d) List

................................................................................................................. 14
Numeric Nutrient Criteria Recommendation

..................................................................................... 20 Reference Period

................................................................................................ ..................................... 20 Chlorophyll a/[TN] or [TP] Regression Models

........................................................................................ 20
General Models

................................................................................................ ....................................... 21
Results and Discus sion

..................................................................................................................... 21 Spatial Considerations and Segmentation

.............................................................................................. 21
General Models

................................................................................................ ....................................... 28 Proposed Numeric Nutrient Targets

................................................................................................ . 31 Methodology

................................................................................................ ........................................... 31 Magnitude

................................................................................................ ............................................... 32 Summary and Conclusions

................................................................................................................ 33
References

................................................................................................ ....................................... 35Draft iii August 2010 

### List of Tables Table 1a. Summary of lines

- of

- evidence results: loading and concentration limits for the north HRE.

................................................................................................ ............................................. 1 Table 1b. Summary of lines

- of

- evidence results: loading and concentration limits for the south HRE.

................................................................................................ ............................................. 2 Table 2. Checklist of nutrient enrichment symptoms in the HRE.

................................................................ 3 Table 3. Land uses in the HRE and watershed (SJRWMD 2004).

.................................................................. 4 Table 4a. Estimates of current (circa 2004) external loadings of TN and TP to the north HRE.

.................. 6 Table 4b. Estimates of current (circa 2004) external loadings of TN and TP to the south HRE.

.................. 7 Table 5. Waterbodies on the 2010 Verified List for impairments in the Halifax River Planning Unit (FDEP).

................................................................................................ ...................................... 14 Table 6. Estuarine waterbodies in the Halifax River Planning U nit that are proposed for delisting 14 Table 7 a. HRE reference period results

— first line of evidence: Annual median, 2000

– 08

....................... 25 Table 7 b. HRE reference period results

— first line of evidence: Maximum wet

- season median, 2000

– 08 (July

–

September)

...................................................................................................... 26 Table 8 a. HRE linear regression results

– second line of evidence: Annual median (1992

– 2008; annual average data)

............................................................................................................... 27 Table 8 b. HRE linear regression results

– second line of evidence: Maximum wet

- season median (1992

– 2008; average monthly; July

–

September only fo r TN; all months for TP)

..................... 27 Table 9 a. Estimates of current (circa 2004) external loadings of TN and TP to the north HRE.

................ 28 Table 9 b. Estimates of current (circa 2004) external loadings of TN and TP to the south HRE.

................ 29 Table 10 a. North HRE current loading (loading limits) for TN and TP with the model

- predicted concentrations.

......................................................................................................................... 31 Table 10 b. South HRE current loading (loading limits) for TN and TP with the model

- predicted concentrations.

......................................................................................................................... 31 Table 1 1 a. Summary of lines

- of

- evidence results: Loading and concentration limits for the north HRE.

................................................................................................ ........................................... 34 Table 1 1 b. Summary of lines

- of

- evidence results: Loading and concentration limits for the south HRE.

................................................................................................ ........................................... 34



### List of Figures Figure 1. Halifax River Planning Unit, Including the 1998 303(d) list and Planning List waters.

................. 5 Figure 2. Spatial distribution of salinity and turbidity (mean and standard deviation) by sampling site.

................................................................................................ ............................................. 9 Figure 3. Spatial distribution of TSS (mean and standard deviation) by sampling site.

............................. 10 Figure 4. Spatial distribution of chlorophyll a, TN, and TP (mean and standard deviation) by sampling site.

............................................................................................................................ 11 Figure 5. Spatial distribution of TSI values (means) for two periods, 1992

– 2000 and 2000

– 08.

.............. 12 Figure 6. Temporal trends in TN, TP, and chlorophyll a for the HRE overall, 1992

– 2008.

......................... 13 Figure 7. Percent composition of major land uses in the south and north HRE (based on 2004 i magery).

................................................................................................ ................................... 22Draft iv August 2010 Figure 8a. Location of tidal node at boundary between the north and south HRE.

................................... 22 Figure 8b. Location of tidal node at boundary between the HRE and Matanzas River Estuary near High Bridge.

.............................................................................................................................. 23 Figure 9. Distribution of oyster and other significant habitat communities in the HRE.

........................... 24 Figure 10. VCEMD water quality sampling sites.

....................................................................................... 25 Figure 11. Average monthly TN, chlorophyll a, and TP in the HRE overall. Monthly rainfall data are shown for comparison. The 1992

– 2008 period was used for both water quality and rainfall data.

...................................................................................................................... 26 Figure 12. Mean turbidity by year (1992

– 2008) for the north and south HRE compared with the IRL.

................................................................................................ ............................................ 28 Figure 13. The log

- linear plot of TN and TP load limits (g/m 2 /yr) vs. hydraulic loading (q s ). A point lying above the 95% confidence interval for the line

- of

- best

- fit (= upper mestrophy) is considered eutrophic; below the lower mesotrop hic line (LML) is considered oligotrophic (based on Steward and Lowe 2010).

.................................................. 30Draft 1 August 2010 

### Executive Summary
This report was prepared by the Florida Department of Environmental Protection (FDEP), in cooperation with local scientists, to support the development of numeric nutrient criteria for the Halifax River Estuary (HRE)

. The primary purpose of the p roposed numeric nutrient criteria is to protect healthy
, well

- balanced natural populations of flora and fauna from the effects of excess nutrient enrichment.

The Halifax River is a 40

- kilometer

- long tidal estuary located on the Atlantic coast near Daytona Beach
, with its major ocean connection situated at Ponce de Leon Inlet (Figure 1). The basin morphology is typical of the Florida east coast
, with a series of flat, low

- gradient terraces separated by ancient barrier beaches (Scholl et al. 1980). The Hal ifax River drains approximately 963 square kilometers (km 2 ), of which roughly 18% is urbanized (S t. Johns River Water Management District [S JRWMD ] 20 04 Land Use ). From 1990 to 2006, t he population i n Volusia County grew approximately 34 % ( http://www protectourwaters.org/ ).

Nutrient s to the H RE originate from stormwater runoff
, agriculture, silvicultur e, urban/suburban land uses, atmospheric deposition, sediment loading and turbidity from shoreli ne erosion, septic tanks
, and wastewater treatment facilities (WWTFs)

.
Oys ter beds are the primary sensitive aquatic resource in the H RE , roughly analogous in form and function to seagrasses in other estuaries throughout Florida . Unfortunately, there is no functional relationship between nutrient levels and oysters (as there is with seagrasses) that would be useful for setting nutrient limits in the estuary

. In fact, additional nutrient load s may actually increase oyster production. Therefore, FDEP has evaluat ed multiple lines of evidence associated with the trophic state/ chlorophyll a / nutrient relationship in the HRE to develop nutrient criteria that would maintain designated uses

. The evidence presented in this document shows that aquatic life designa ted use in the H RE is fully supported. FDEP therefore proposes that the numeric nutrient criteria be crafted to maintain the existing nutrient regime

.

N umeric nutrient criteria were developed from data collected at 20 stations by the Volusia County Enviro nmental Management Department (VCEMD) from 1992 to 2008. For the data analysis, t he H RE was divided into a northern and a southern segment based on local land uses and hydrodynamic properties, particular ly water residence time, which greatly influences wa ter quality and trophic response (Steward and Lowe 2010). T he HRE system appears to be nitrogen (N) limited
, with a total nitrogen:total phosphorus ( TN:TP ) ratio of less than 5 (by weight).

C hlorophyll a concentrations in the HRE tend to correlate better to TN than to TP (Steward and Lowe 2010)

. Additional d ata from the University of Florida suggest N limitation (E

. Phlips, pers. comm.)

. TN has generally declined in the HRE since the 1990s , correspond ing to reductions in chlorophyll a and trophic status (Steward and Lowe 2010).

Three lines of evidence were used in developing numeric nutrient criteri a for the H RE : a r eference period method, c hlorophyll a
– nutrient regression analyses , and t wo estuary empirical models (Steward and Lowe 2010; Dettman 2001 ). Table s 1 a and 1b summarize the three lines of evidence and the proposed loading and concentration limits for the north and south segments , respectively

.

Table 1a. Summary of lines

- of

- evidence results: loading and concentration limits for the north HRE

.Draft 2 August 2010 Target condition is mesotrophy ( c hlorophyll a targets are an annual median of 4.5 micrograms per liter [ μg/L ] and a seasonal median of 7.9 μg/L for Jul y through Sep tember )

- = Empty cell/no data kg/yr = Kilograms per year mg/L = Milligr ams per liter N/A = Not applicable

a 0.62 mg/L TN and 0.2 mg/L TP are predicted concentrations based on current loadings (c irca 2004)

.

- TN (k g/yr ) TN ( k g/yr ) TP ( k g/yr ) TP ( k g/yr ) Loading Limit (current loading) 257,832 257,832 43,494 43,494

- Median (mg/L) Annual Median (mg/L) July

– September Median (mg/L) Annual Median (mg/L) July

– September Reference Period (2000

– 08) 0.61 0.90 0.12 0.18 Regressions (1992

– 2008 data) 0.58 0.90 N ot sign ificant 0.17 General Models 0.62 N/A 0.2 N/A

Table 1b . Summary of lines

- of

- evidence results: loading and concentration limits for the south HRE. Target condition is oligo

- mesotrophy (chlorophyll a targets are an annual median of 3.5 μg/L and a seasonal median of 5.8 μg/L for July through September)

- = Empty cell/no data N/A = Not applicable

a The midpoint between the two values in parentheses = 0.135 mg/L TP. The two [TP] values reported in parentheses are the results from the lower mesotrophic and oligotrophic [TP] model equations applied to the south HRE (see the section on General Considerations and Methods).

- TN (kg/yr) TN (kg/yr) TP (kg/yr) TP (kg/yr) Loading L imit (current loading) 222,000 222,000 38,000 38,000

- Median (mg/L) Annual Median (mg/L) July

– September Median (mg/L) Annual Median (mg/L) July

– September Reference Period ( 2000

– 08) 0.39 0.51 0.12 0.19 Regressions ( 1992

– 08 data) 0.30 0.41 N ot sign ificant 0.15 General Models 0.42 N/A 0.135 (0.09, 0.18) a N/ADraft 3 August 2010 Table 2. Checklist of nutrient enrichment symptoms in the HRE.

- = Empty cell/no data N/A = Not applicable Response V ariable Observed H istorically? Observed C urrently? Explanation Source

Low dissolved oxygen ( DO ) (hypoxia/anoxia) Yes Yes There are naturally low DO levels in some of the tidal creeks and in Rose Bay. FDEP 200 8

Reduced clarity Yes Yes Naturally occur r ing high turbidities with potential exacerbation by human activities. Steward et al. 2010 Increased chlorophyll a concentrations Yes No No annual average exceeds the 11 μg/L threshold for estuaries. General decreasing trend in chlorophyll a and Trophic State Index ( TSI ) from 1992 to 2008. FDEP 200 8; Steward et al. 2010 Phytoplankton blooms No No - Steward et al. 2010 Problematic epiphyte growth N/A N/A - Steward et al. 2010 Problematic macroalgal growth No No - Steward et al. 2010
S ubmerged aquatic vegetation (S AV ) community changes or loss N/A N/A Naturally high turbidities and high flushing rates have prevented SAV establishment. Steward et al. 2010 Emergent or shoreline vegetation community changes or loss Yes Yes Roughly 50% and 75% of the shoreline hardened in south HRE and north HRE, respectively. Dredge

- and -f ill activities primarily responsible for the disappearance of shoreline vegetation, not nutrients. Steward et al. 2010

Oyster reef community changes or loss Yes Yes Roughly 50% and 75% of the shoreline hardened in the south and north HRE, respectively. Dredge

- and -f ill activities primarily responsible for the disappearance of oyster reefs, not nutrients. Steward et al. 2010

Impacts to benthic community Yes No A 1979 assessment of the benthic macroinvertebrate community found an extremely depauperate fauna with a total of 36 species present and only one mollusk was found in appreciable numbers. Diaz et al. 1980 Magley 1990

Fish kills No No - F lorida Fish and Wildlife Conservation Commission ( FWCC ) 2010 Other N/A N/A -Draft 4 August 2010 

### Geographic and Physical Description

The H RE is l ocated in the Upper East Coa st Drainage Basin ( Figure 1) and consists of 53 segments with waterbody identification (WBID) numbers (FDEP 200 8) . It includes portions of Flagler and Volusia C ounties and
encompa sses an area of nearly 87 , 986 hectares (ha) ( 208,000 acres ). M ajor sources of fresh water to the estuary include B ulow Creek, the Tomoka River, and Spruce Creek, and their natural tributaries. Both the Tomoka River and Spruce Creek are designated as O utstanding F lorida W ater s (OFWs)

.
The H RE is 37.5 kilometers long and 914 meters wide on average, and has a total area of 35.8 km 2 (Steward et al. 2010). The average slack tide depth is 1.1 meters (m) (Scholl et al. 1980). Rainfall has averaged 50 inch es pe r year over the past 30 years
, with a rainy season occurring from June through September (SJRWMD 1998). Six causeways cross the HRE and inhibit circulation in the area (SJRWMD 2003)

. The Intracoastal Waterway intersects the Halifax River and is freq uently used by large vessels transiting north and south. The watershed area ( 87 , 986 ha) to estuary area ( 3, 581 ha ) ratio is approximately 24 to 1
, indicative of a potentially large volume of runoff into a comparatively small estuarine system (Steward et al. 2010). Table 3 lists the major land uses and their associated percentages in the Halifax watershed, the majority of which (70%) is a combination of water, wetlands, range land, and forested lands.

Mosquito impoundments, residential development, and sil viculture h ave altered a majority of the estuary’s historical watershed drainage. Ormond Beach, Holly Hill, Daytona Beach, and Bethune Point are all relatively densely populated residential areas in the watershed

. Some salient physical characterist ics of the HRE are as follows :
Length of system

— ~23 miles (mi) (37.5 km), wholly within Volusia County; Average width of estuary

— 0.56 mi (0.9 km); Area of estuary

— ~13.8 square miles (mi 2 ) (35.8 km 2 ); Mean depth

— 1.4 m from High Bridge near Bulow Creek to south Daytona, 1.7 m from south Daytona to Ponce De Leon Inlet; Tidal amplitude

— 0.7 m; Area of catchment

— ~340 mi 2 (~880 km 2 ); Catchment area:Estuary area ratio

— ~24:1; and Average annual rainfall

— ~50 inches/year over last 30 years

.

Ta ble 3. L and uses in the H RE and w atershed (SJRWMD 2004 ). Land Use % Source Water/Wetland 36% Steward et al. 2010 Range/Forest 34% Steward et al. 2010
Urban 22% Steward et al. 2010 Agriculture 5% Steward et al. 2010
Other 3% Steward et al. 2010Draft 5 August 2010 Figure 1. Halifax River Planning Unit, Including the 1998 303(d) list and Planning List waters.Draft 6 August 2010 

### Sources of Nutrients

Potential sources of nutrients in the watershed include stormwater runoff
, agriculture
, silviculture
, urban/suburban land uses, atmospheric deposition, sediment loading and t urbidity from shoreline erosion, and septic tanks.

Septic tanks have been identified as a potential source of nutrients ( N and P ), pathogens, and other pollutants that can pose a threat to public health (SJRW MD 2003)

. Surface waters can be adversely affected by the direct or indirect runoff of septic system leachate

. Areas in the Halifax River watershed that have been identified by the Volusia County Health Department as having potential septic tank problems include the town of Ormond by the Sea, neighborhoods around Ormond Beach along the Tomoka River, Port Orange, Rose Bay, and the

area along Spruce Creek. Septic tank failure rates in Flagler, St. Johns, and Volusia C ounties exceed state failure rates (SJRWMD 200 3 ).

A wasteload allocation was established for all the major surface water dischargers in to the north Halifax River Estuary based on a number of water quality studies th at identified significant nutrient problems (Magley 1990). It was determined that existing point sources of nitrogen and phosphorus were approximately 1.5 to 2.4 times the nonpoint load. In addition, there were violations of the Class II I DO criteria, ele vated nutrients and chlorophyll a levels, depressed invertebreate populations, and sediments enriched with metals. When compared to other estuaries in Florida, the overall trophic state index was considered fair to poor. Based upon the potential impacts of further loads, an advanced wastewater treatment (AWT) was implemented for all the major dischargers (Magley 1990).

F ive permi t ted domestic WWTFs discharge into the H RE (Figure 1; Table 4 ): Daytona Beach/Bethune Point (13 million gallons per day [ MGD ] ), city of Holly Hill (2.4 MGD), Ormond Beach (6 MGD), Port Orange (6 MGD)
, and New Smyrna Beach (6 MGD) drain into the H RE watershed (SJRWMD 2006).

Table s 4 a and 4b show sources of nutrients and loads in the north and south H RE, respectively, using a Pollut ion Load S creening Model (PLSM) (Adamus and Bergman 1995). The model’s input requirements are

s patial d ata l ayers ( drainage boundary, land use, soil type, and annual rainfall ), r unoff c oefficients ( volumetric ratio of runoff to total rainfall derived from the literature ), the ratio of pervious to impervious surface area for a particular land use group , r unoff c oncentrations ( literature values derived from field studies ), and best management practice ( BMP ) t reatment e fficiencie s ( literature values applied to development occurring after stormwater rule implementation ). E stimated loads from 1983

- 1986 are included in Table 4a. A comparison of 2004 WWTF loads to those of 1986 show remarkable dec lines in TN and TP loads in to the nor th HRE.

Table 4a. Estimates of current (c irca 2004) external loadings of TN and TP to the north HRE. g/m 2 /yr = Grams per square meter of estuary area per year *SJRWMD PLSM

- estimated surface water loadings based on 2004 land use and 2001

– 08 av erage annual rainfall, which is nearly equivalent to 30 -y ear
av erage annual rainfall. Major tributary streams are the Tomoka R iver , Bulow Cr eek , 11 th St. Canal, and Reed Canal in the north HRE; Spruce Cr eek
, Turnbull Cr eek
, and Halifax Canal in the south HRE. ** Domestic WWTF s : Daytona/Westside, Holly Hill, Ormond Beach in north HRE; Port Orange, New Smyrna Beach (@27% of annual discharge) in south HRE. WWTF loading estimates calculated from data obtained from FDEP, Tallahassee.

. ***1983

- 1986 values adapted from Magley 1990. North HRE Sources TN (kg/yr) TP (kg/yr) Surface Water Drainage* 207,906 34,088 Atmospheric Deposition 8,911 203 WWTFs ** ( 1983

- 1986 ) ** * 41,015 ( 317,621) 9,203 (110,750) Ground Water Unquantified; assumed negligible by Scholl et al. 1980 Unquantified; assumed negligible by Scholl et al. 1980 Total Loading: 257,832 (13.26 g/m 2 /yr) 43,494 (2.24 g/m 2 /yr)Draft 7 August 2010 Table 4b. Estimates of current (c irca 2004) external loadings of TN and TP to the south HRE.
*SJRWMD PLSM

- estimated surface water loadings based on 2004 land use and 2001

– 08 av erage annual rainfall, which is nearly equivalent to 30 -y ear
av erage annual rainfall. Major tributary streams are the Tomoka R iver , Bulow Cr eek , 11 th St. Canal, Reed Canal in the north HRE; Spruce Cr eek
, Turnbull Cr eek
, and Halifax Canal in the south HRE. ** Domestic WWTF s : Daytona/Westside, Holly Hill, Ormond Beach in north HRE; Port Orange, New Smyrna Beach (@27% of annual discharge) in south HRE. WWTF loading estimates calculated from data obtained from FDEP, Tallahassee. South HRE Sources TN (kg/yr) TP (kg/yr)
Surface W ater D rainage * 196,284 32,927 Atmospheric Deposition 7,516 171 WWTF s ** 17,335 4,492 Ground W ater Unquantified; assumed negligible by Scholl et al. 1980 Unquantified; assumed negligible by Scholl et al. 1980 Total Loading: 221,135 (13.04 g/m 2 /yr) 37,590 (2.22 g/m 2 /yr)



### Biological Summary
The biological communities that characterize the vast majority of the aquatic habitat in the H RE are tidal marshes and oyster reefs (Steward et al. 2010)

. A large portion of the north HRE has been affected by historical dredge and fill activities that has limited the extent of the biological communities in this area. In addition, t here is anecdota l information from District biologists that the few oysters or oyster reefs present in the N. HRE do not appear healthy. There are a disproportionate number of undersized or small individuals per reef population. There is no evidence to suggest that nutr ients are involved in the apparent differences between oysters in the north HRE compared to those in the south HRE (Steward pers onal comm unication
, August 2010 ).

Oyster Reefs

Oyster reefs are a major aquatic community in the H RE and locally decrease turbid ity by trapping sediment. They present a dynamic
, community

- forming refugia, nursery grounds, and feeding areas for a variety of other estuarine organisms. Oysters provide hard substrate and habitat for many other species
, including mud crabs ( Rhithropanopeus harrisii ), blue crabs ( Callinectes sapidus ), and amphipods.

Oyster density diminishes considerably near south Daytona and do es not increase substantially until the Tomoka River area (Steward et al. 2010). Habitat maps suggest a spatial d ivide in the oyster population abundance between Port Orange and Daytona Beach, and between Daytona Beach and Ormond Beach, caused primarily by historic al dredge

- and

- fill activities

. Approximately 75% of the shoreline in the north HRE is hardened
, and app rox imately 50% of the main east and west shorelines in the south HRE are hardened. Dredge

- and -f ill activities are primarily responsible for the disappearance of oyster s , not altered wa t er quality
, including increased nutrients (Steward et al. 2010).

A three

- year study conducted in the nearby Guana Tolomato Matanzas (GTM) Estuary that looked at oyster growth rates at two sites with different nutrient loading scenarios found that density, length, and biomass increased in oyster communities with higher nut rient loads . This finding suggest ed that the oyster communities were capable of assimilating current nutrient loads and responded positively to increases in nutrient loads ( at least to concentrations within the range of current levels ) (Dix
, 2010).

Salt Marsh

Salt marshes are a nother common community type in the HRE . D ominant plants include saltmarsh cordgrass ( Spartina alterniflora ), black needlerush ( Juncus roemerianus ), g lasswort ( Salicornia spp.), and saltwort ( BatisDraft 8 August 2010 maritima ). This habitat supports a large population of infaunal organisms as well as a variety of transient fish and wildlife.

McFarlin and Brewer (2008) assessed the effect of fertilization on food webs in 19 coastal estuaries in Georgia and found that fertilization increased the cover, height, and biomass of Spartina and the height of Juncus , but decreased Juncus cover and biomass. The study also showed increases in herbivores (grasshoppers) with fertilization, but little to no effect on decomposers (fungi) or detritivores (snails). In comparisons between fertilized plots and control plots, variation among control sites was typically greater than the effects of fertilization. These results suggest that the effects of increase d nutrients at any particular site wou ld be difficult to distinguish from the natural variability among sites
, and that increased nutrients (within the range tested) are likely to have a stimulatory effect on beneficial plants and herbivores.

Plankton

There have been occasional algal blooms on the east coast of Florida, with a 

### Karenia brevis bloom occurring in the nearby GTM Estuary in October 2007

. The bloom began in Atlantic coastal waters between the mouths of the St. Johns and Nassau Rivers. It was transported south by winds and currents, entering both the St. Augustine and Matanzas Inlets. Cell counts as high as 5 million cells per liter were recorded in the Matanzas River south of the 206 bridge (Hitchcock and Frazel, unpublished raw data). N o evidence suggests that nearshore nutrients were responsible for the origination or persistence of the bloom.


### Water Quality Data Sources and Studies
According to the STORET Watershed Summary for the Upper East Coast
, including the Halifax Planning Unit
, t he organizations listed below conduct water quality monitoring

. A complete list of monitoring stations is available at : http://cfpub.epa.gov/surf/huc.cfm?huc_code=03080201

.

21FLA – F lorida Department of Environmental Protection 21FLCEN - Florida Department of Environmental Protection 21FLDOH – Florida Department of Health, Division of Environmental Health, Bureau of Water (Florida) 21FLFMRI - Florida Fish and Wildlife C onservation Commission / Florida Marin e Research Institute 21FLGTM - Guana Tolomato Matanzas (GTM) Estu a rine (National Estuarine Research Reserve

– Florida) 21FLGW - Florida Dep artme nt of Environmental Protection 21FLKWAT - Florida LakeWatch 21FLMRC - Marine Resources Council of East Florida 21FLSEAS - Florida Department of Environmental Protection 21FLSJWM - St. Johns River Water Management District (Florida) 21FLVEMD - Volus i a County Environmental Health Lab (Florida) 21FLWPB - Florida Department of Environmental Protection

Water quality conditions from 1992 to 2008 suggest a division of the HRE system into two or potentially three segments. S patial trends for selected water quality parameters are shown in the following graphs

. Clear shifts in spatial gradients f or salinity and turbidity exist ( Figure 2 ); one shift occurs from the Matanzas system ( S ites MAT and JXTR26) into the north HRE and the other from the north HRE into the south HRE.

The spatial breakpoints, particularly b etween the north and south HRE, occur at tida l null point locations, which is indicative of the strong influence of hydrodynamics and the full extent of the daily ocean/estuary exchange on the region’s salinity and turbidity. There is no obvious breakpoint between the Tomoka and Daytona areas of the north HRE segment.Draft 9 August 2010 A similar spatial pattern exists for total suspended solids (TSS)
, as lower levels are consistent throughout the south HRE compared with the north HRE ( Figure 3) . However, there is no spatial difference in TSS concentrations between the Tomoka and Daytona areas of the north HRE , and between the north HRE and the south Matanzas sites (MAT and JXTR26).

Figure 2 . Spatial distribution of salinity and turbidity ( mean and standard deviation) by sampling site. 0 5 10 15 20 25Turbidity (ntu)

Site 

### Turbidity

Dry Season Wet Season Mean 1992

- 2008 +Std Dev

JXTR26 1997

- 2008 0 5 10 15 20 25 30 35 40 45Salinity (ppt)

Site 

### Salinity

Dry Season Wet Season Mean 1992

- 2008 +Std Dev

JXTR26 1997

- 2008 

## Tidal null point

N. HRE Tomoka N. HRE Daytona S. HREDraft 10 August 2010 Figure 3 . Spatial distribution of TSS (mean and standard deviation) by sampling site.

Chlor o phyll a , TN, and TP concentrations are clearly higher throughout most of the HRE compared with levels in south Matanzas ( Figure 4) , with mean values 7.9 μg/L, 0.9 mg/L, and 0.17 mg/L, respectively . Within the HRE system, spatial differences are not readily apparent ( Figure 4 ); however, nonparametric analyses indicate a significant difference between the north and south HRE for chlorophyll a and TN, not for TP (Kruskal

- Wallis and Mann

- Whitney; family α = 0.15 for the 3 segments; individual α = 0.05 for pairs of segments).

Higher TSI values 1

The information above regarding the spatial distribution of physical properties, habitat, a nd water quality support s a recommendation for dividing the HRE into two segments, south HRE and north HRE (Tomoka and Daytona areas combined), for the development of segment

- specific nutrient criteria. were calculated for the north HRE than for the south HRE ( Figure 4)
, reflec t ing differences in chlorophyll a and nutrient levels. Similarly , TSI values in the south HRE continue to decline as the distance to Ponce De Leon Inlet shortens.

1 TSI values were calculated using the equation specified in FDEP (1996), and the value ranges for estuaries, as specified by F DEP (1996), are as follows: 0– 49, good; 50

– 59, fair; and 60

– 100, poor. 0 10 20 30 40 50 60 70TSS (mg/l)

Site Total Suspended Solids

Dry Season Wet Season Mean 1992

- 2008 +Std Dev

JXTR26 1997

- 2008 N. HRE Tomoka N. HRE Daytona S. HRE 

### Tidal null pointDraft 11 August 2010 Figure 4 . Spatial distribution of chlorophyll a, TN, and TP (mean and standard deviation) by sampling site. 0 5 10 15 20 25Chl a Corr (μg/L)

Site Chlorophyll a Corrected

Dry Season Wet Season Mean 1992

- 2008 +Std Dev

JXTR26 1997

- 2008

0 0.5

1 1.5

2 2.5TN (mg/l)

Site Total Nitrogen

Dry Season Wet Season

JXTR26 1997

- 2008

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7TP (mg/l)

Site Total Phosphorus

Dry Season Wet Season Mean 1992

- 2008 +Std Dev

JXTR26 1997

- 2008 

### N. HRE Tomoka N. HRE Daytona S. HRE 

# Tidal null point



# ---- N. HRE

---- ---- S. HRE

----Draft 12 August 2010 TSI values throughout the HRE have decreased over time
, as shown in the comparison of mean TSI values between the 1992

– 2000 and 2000

– 08 periods ( Figure 5 ). The more recent TSI values strongly suggest upper mesotrophic conditions throughout the north HRE, and lower mesotrophic to oligotrophic conditions in the south HRE.

Figure 5 . Spatial distribution of TSI values (means) for two periods, 1992

– 2000 and 2000

– 08.

Tempora l C onsiderations and the R eference P eriod M ethod

The decrease in trophic state from one decade to the next is a consequence of general reductions in chlorophyll a s ince 2000, a likely response to the precipitous decline in TN over the same period ( Figure 6 ). TN started to decline in the early 1990s, reaching much lower and more stable levels from 1996 to 2008. While other unknown factors may have contributed to the reduction in TN concentrations, reductions in effluent loadings from domestic WWTF s occurr ed during the same period (D

. Judy, FDEP Central District, pers. com., March 2010).

TP does not follow a similar trend. T he temporal trend in TP is flat over the full period of record. It is likely that nonpoint sources and internal processes are more i nfluential in controlling TP than WWTF loadings. 0 10 20 30 40 50 60TSI 

## Trophic State Index 1992

- 2000

0 5 10 15 20 25 30 35 40 45 50 

## 2000

- 2008TSI 

### N. HRE

Tomoka N. HRE Daytona S. HREDraft 13 August 2010 Because TN:TP (and dissolved inorganic nitrogen:dissolved inorganic phosphorus [ DIN:DIP ] ) ratios are less than 5 (by weight) and chlorophyll a appears to be more responsive to TN than to TP, the HRE syste m overall may be N limited. Data collected by the University of Florida also support N limitation, but this characterization should be treated with caution because no bioassay analys e s ha ve been performed for verification (E

. Phlips, U niversity of Florida, pers. com., February 2010).

Figure 6 . Temporal trends in TN, TP, and chlorophyll a for the HRE overall, 1992

– 2008. 0 0.5

1 1.5

2 2.5

3TN (mg/l)

Year Total Nitrogen

Dry Season Wet Season

HL01

- HL04 

### Low and stable in HRE overall since 1996 However, [TP ] trend was flat: 0.14

– 0.17 mg/L long

- term avg.

0 2 4 6 8 10 12 14 16 18 20Chl a corr (μg/l)

Year 

### Chlorophyll a Corrected

Dry Season Wet Season

HL12

- HL20 

### Possible response in Chla to TN reduction since wet season 2000 Wet season spikes >11 μg/L persist; concurrent with [TN] & [TP] increases, esp. in Aug.

– Sept.Draft 14 August 2010 

### Waters on the 303(d) List
Table 5 provides the complete list of waters that are verified impaired in the Upper East Coast

– Halifax River Planning Unit , and Table 6 identifies the waters that are proposed for delisting.

Table 5. Waterbodies on the 2010 Verified List for impairment s in the Halifax River Planning Unit (FDEP).
3M = Class III Marine Basin Group Name Planning Unit Waterbody ID (WBID) Waterbody Segment Waterbody Type Waterbody Class 1 Parameters Assessed Using 2001 IWR Concentration Causing Impairment 2 Priority for TMDL Development 3 Comments (# Exceedances/# Samples) PP = Planning Period VP = Verified Period 4

Upper East Coast Halifax River Unit 8117B Dunlawton Beach 3M Coliforms (Beach Advisory) > 21 days of advisories in a
year High Beach advisories posted for a total of 36 days in 2003.

Upper East Coast Halifax River Unit 8117C Hilton Beach 3M Coliforms (Beach Advisory) > 21 days of advisories in a
year High Beach advisories posted for a total of 73 days in 2003 and 23 days in 2004.

Upper East Coast Halifax River Unit 8117D Silver Beach Beach 3M Coliforms (Beach Advisory) > 21 days of advisories in a
year High Beach advisories posted for a total of 33 days in 2003.

Upper East Coast Halifax River Unit 2363A Halifax River Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2363B Halifax River Estuary 3M Copper >3.7 μg/L High pp = 22/48; vp = 9/50

Upper East Coast Halifax River Unit 2363B Halifax River Estuary 3M Iron > 0.3 mg/L High PP - 39/51 VP - 46/65 May be due to high iron concentrations in groundwater. Prelimary investigation reveals that much of the data from surrounding monitoring wells significantly exceed the 0.3 mg/L c riterion (see the groundwater chapter in the "Upper East Coast Basin Status Report"). Will be investigated further.Draft 15 August 2010 Basin Group Name Planning Unit Waterbody ID (WBID) Waterbody Segment Waterbody Type Waterbody Class 1 Parameters Assessed Using 2001 IWR Concentration Causing Impairment 2 Priority for TMDL Development 3 Comments (# Exceedances/# Samples) PP = Planning Period VP = Verified Period 4

Upper East Coast Halifax River Unit 2363B Halifax River Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2363J Palm Coast Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2672 Rose Bay Estuary 3M Dissolved Oxygen < 4.0 mg/L High PP - 1/49 VP

- 13/43 DO met verification threshold of IWR, and TN was identifed as a causative pollutant. PP median TN = 0.66 mg/L (n=153); median TP = 0.13 mg/L (n=154); no BOD data. VP median TN = 1.115 mg/L (n=17); median TP =0.14 mg/L (n=17); BO D = 2.05 (n=16).

Upper East Coast Halifax River Unit 2672 Rose Bay Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2674A Spruce Creek Estuary 3M Copper > 3.7 μg/L Medium pp = 6/9; vp = 6/20

Upper East Coast Halifax River Unit 2674A Spruce Creek Estuary 3M Dissolved Oxygen < 4.0 mg/L High pp = 96/285; vp = 40/137 DO met verification threshold of IWR and linked to nutrients,Draft 16 August 2010 Basin Group Name Planning Unit Waterbody ID (WBID) Waterbody Segment Waterbody Type Waterbody Class 1 Parameters Assessed Using 2001 IWR Concentration Causing Impairment 2 Priority for TMDL Development 3 Comments (# Exceedances/# Samples) PP = Planning Period VP = Verified Period 4

Upper East Coast Halifax River Unit 2674A Spruce Creek Estuary 3M Fecal Coliform > 400 Colonies/100 mL Low pp = 69/305; vp = 33/123

Upper East Coast Halifax River Unit 2674A Spruce Creek Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2674A Spruce Creek Estuary 3M Nutrients (Chla) Median TN = 0.85 mg/L Median TP = 0.150 mg/L High Annual averages for 1996 and 2003 exceed the threshold of 11 μg/L for estuaries. Annual averages: 1994 - 6.04 μg/L; 1995 - 5.46 μg/L; 1996 - 11.74 μg/L; 1997 - 4 .16 μg/L; 1998 - 9.80 μg/L; 1999 - 5.30 μg/L; 2000 - 3.82 μg/L; 2001 - 5.96 μg/L; 2003 - 12.05 μg/L; 2005 - 2.95 μg/L. Nutrients (Chla) Nitrogen was identified as the limiting nutrient based on 80% of the TN/TP ratios were less than 10.

Upper East Coast Halifax River Unit 2674B Strickland Bay At Us1 Estuary 3M Fecal Coliform > 400 mg/L Low pp = 0/1; vp = 9/24

Upper East Coast Halifax River Unit 2674B Strickland Bay At Us1 Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2363C Tomoka Basin Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.Draft 17 August 2010 Basin Group Name Planning Unit Waterbody ID (WBID) Waterbody Segment Waterbody Type Waterbody Class 1 Parameters Assessed Using 2001 IWR Concentration Causing Impairment 2 Priority for TMDL Development 3 Comments (# Exceedances/# Samples) PP = Planning Period VP = Verified Period 4

Upper East Coast Halifax River Unit 2634A Tomoka River Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2678 Turnbull Bay Estuary 3M Dissolved Oxygen < 4.0 mg/L Medium PP - 10/13 VP - 12/45 DO met verification threshold of IWR, TN and BOD were identified as causative pollutants. PP median TN = 0.996 mg/L (n=8), median TP = 0.1925 mg/L (n=12), no BOD data. VP median TN = 1.295 mg/L (n=12), median TP = 0.1755 mg/L ( n=16), median BOD = 2.5 mg/L (n=25).

Upper East Coast Halifax River Unit 2678 Turnbull Bay Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.

Upper East Coast Halifax River Unit 2678 Turnbull Bay Estuary 3M Nutrients (Chla) Median TN = 1.00 mg/L Median TP = 0.192 mg/L Medium Annual average for 2003 exceeds the 11 μg/L threshold for estuaries. Only annual average is from 2003

- 17.17 μg/L . Nitrogen identified as the limiting nutrient based on all the TN/TP ratios less than 10.

Upper East Coast Halifax River Unit 2642 Unnamed Branch Estuary 3M Mercury (In Fish Tissue) > 0.43 mg/kg in Fish tissue High Listed based on king mackerel and bull shark concentrations exceeding 0.43 mg/kg; collected in 2002

- 2004.Draft 18 August 2010 Table 6. Estuarine waterbodies in the Halifax River Planning Unit that are proposed for delisting (FDEP).
3M = Class III Marine Basin Group Name Planning Unit WBID Waterbody Segment Waterbody Type Waterbody Class 1998 303(D) Parameters of Concern Parameters Evaluated Using IWR Comments (with # of Exceedances/# of Samples)

Upper East Coast Halifax River 2363A Halifax River Estuary 3M Coliforms Fecal Coliform PP - 3/532 VP - 0/202

Upper East Coast Halifax River 2363B Halifax River Estuary 3M Lead Lead PP

- 2/47 VP - 4/31

Upper East Coast Halifax River 2363B Halifax River Estuary 3M Nutrients Nutrients (Chla) No annual average exceeds the 11 μg/L threshold for estuaries. Annual averages: 1994 - 10.30 μg/L, 1995 - 5.94 μg/L, 1996

- 6.45 μg/L, 1997 - 6.84 μg/L, 1998 - 7.07 μg/L, 1999 - 9.40 μg/L, 2000 - 7.72 μg/L, 2001 - 5.68 μg/L, 2002 - 8.01 μg/L, 2003 - 5.36 μg/L, 2004 - 5.74 μg/L, 2005 - 3.79 μg/L. Assessment category will be 3b because biology or site

- specific data is needed to validate non

- impairment assessment.
Upper East Coast Halifax River 2672 Rose Bay Estuary 3M Coliforms Fecal Coliform PP

- 8/57 VP - 1/39

Upper East Coast Halifax River 2674A Spruce Creek Estuary 3M Iron Iron PP - 0/0 VP - 22/22 A document has been prepared that supports that elevated iron concentrations are a natural condition. Consequently, it has been assigned an EPA Integrated Report Category 4C. Upper East Coast Halifax River 2634A Tomoka River Estuary 3M Nutrients Nutrients (Chla) No annual average exceeds the 11 μg/L threshold for estuaries. Annual averages: 1994 - 9.50 μg/L, 1995 - 8.26 μg/L, 1996 - 5.79 μg/L, 1997 - 4.30 μg/L, 1998 - 5.41 μg/L, 1999 - 6.34 μg/L, 2000 - 7.41 μg/L, 2001 - 7.96 μg/L, 2002 - 4.47 μg/L, 2003 - 7.91 μg/L, 2004 - 7.15 μg/L, 2005 - 4.38 μg/L. Upper East Coast Halifax River 2634A Tomoka River Estuary 3M Iron Iron PP - 43/54 . VP - 53/62 A document has been prepared that supports that elevated iron concentrations are a natural condition. Consequently, it has been assigned an EPA Integrated Report Category 4C.Draft 19 August 2010 Basin Group Name Planning Unit WBID Waterbody Segment Waterbody Type Waterbody Class 1998 303(D) Parameters of Concern Parameters Evaluated Using IWR Comments (with # of Exceedances/# of Samples)

Upper East Coast Halifax River 2674 Spruce Creek Stream 3F Dissolved Oxygen Dissolved Oxygen PP - 9/52 VP - 9/59

Upper East Coast Halifax River 2674 Spruce Creek Stream 3F Nutrients Nutrients (Chla and Histchla) Annual average for 1997 exceeds the threshold of 20 μg/L for streams. Annual averages: 1995 - 8.48 ug/L; 1996 - 1.08 μg/L, 1997 - 21.22 ug/L; 1998 - 9.06 ug/L; 1999 - 1.57 μg/L, 2000 - 2.82 μg/L, 2001 - 7.56 ug/L; 2002 - 1.25 μg/L; 2003 - 2.19 μg/L; 2005 - 2.80 μg/L. Nutrients (Chla) Delist since the annual for every year after 1997 has been less than the threshold. The historic minimum annual chlorophy ll average of 10.19 ug/L was not exceeded by more than 50% for two consecutive years.

Upper East Coast Halifax River 2674 Spruce Creek Stream 3F Iron Iron PP - 45/52 . VP - 51/57 A document has been prepared that supports that elevated iron concentrations are a natural condition. Consequently, it has been assigned an EPA Integrated Report Category 4C.

Upper East Coast Halifax River 2634 Tomoka River Stream 3F Coliforms Fecal Coliform PP - 41/267 VP - 20/150

Upper East Coast Halifax River 2634 Tomoka River Stream 3F Iron Iron PP - 13/31 . VP - 2/21

Upper East Coast Halifax River 2634 Tomoka River Stream 3F Nutrients Nutrients (Chla) No annual average exceeds the 20 μg/L threshold for streams. Annual averages are: 1994 - 4.25 μg/L,1995 - 3.34, 1996 - 2.32 μg/L, 1997 - 2.26 μg/L, 1998 - 2.49 μg/L, 1999 - 3.69 μg/L, 2000 - 2.65 μg/L, 2001 - 1.78 μg/L, 2002 - 1.88 μg/L, 2003 - 2.20 μg/L, 2004 - 1.55 μg/L . Assessment category will be 3b because biology or site

- specific data is needed to validate

non

- impairment assessment.Draft 20 August 2010 

### Numeric Nutrient Criteria Recommendation
The analyses presented in this report are based on ambient data collected as part of long

- term, routine monitoring networks designed to address basic status and trend quest ions relat ed to trophic state and site

specific nutrient targets. Therefore, short

- term, high

- frequency data (event or experimental data), permit d ata, episodic data, permit compliance data, facility status or compliance data, volunteer network data , or data of unknown quality were not included ( J. Steward
, pers. comm. , 2010).

With respect to the HRE, as well as the other bar

- built
, lagoonal estuaries oriented linearly along Florida’s east coast, the development of nutrient criteria should consider at least three points:

1. Spatial heterogeneity within the system, segmenting the system accordingly for the purpose of setting segment

- specific criteria;

2. Tem poral shifts in water quality by which a certain period of record representing desirable trophic water quality conditions (when designated uses are fully met) can be selected to develop protective criteria; and

3. Multiple lines of evidence, helping to ensure a high level of certainty or confidence associated with the nutrient criteria derived from any one or all lines of evidence.

The following lines of evidence are used for the HRE :

**•** A reference period method;

**•** C hlorophyll a

– nu trient regression analyses; a nd

**•** T wo empirical models that pertain to estuaries in general.

The primary source for the site

- specific data required by these methods is the VCEMD, and the full period of record for these data extends from 1992 to 2008.

Reference P eriod

For the reference period method, a reference period (preferably 5 consecutive years as a minimum) within the full period of record that provide d the lowest chlorophyll a and nutrient levels along with a desirable trophic state was selected to calculate annual an d wet

- season median concentration s of chlorophyll a , TN, and TP. A trophic condition was considered desirable for a given segment if the average of TSI values, as applied to estuaries (FDEP 1996), was less than 50. Note that this target has not been full y evaluated for all estuary systems, and it may need to be shifted depe nding on the biological communities in a given estuary. Because nutrient loadings and concentrations (and presumably chlorophyll a and TSI) in the HRE are largely a function of watershed rainfall

– runoff, the selected reference period should not be a drought period but
, rather
, one that approximates the 30

- year annual average rainfall for the region.
Chlorophyll a/[TN] or [TP] R egression M odels

All data from the full period of record wer e reduced and organized into annual average, average monthly, and average monthly wet

- season (peak production months of July through September only) datasets. Simple linear regression models were developed per segment from these reduced datasets: [ chloro phyll a ] regressed against [TN] and against [TP]. If the regressions had moderate to strong correlation ( r ) and significance ( p ) statistics, they were used to predict median concentration limits based on reference period [ chlorophyll a ] medians (the de facto chlorophyll a target levels). M ultivariate regression analysis was also performed toDraft 21 August 2010 identify major variables that may regulate algal production (i.e., chlorophyll a levels) in the HRE and, if statistically feasible, could be used as a complementary line of evidence to help set nutrient criteria.

General M odels

Two general nutrient models were applied to the HRE to predict the limits or acceptable ranges of nutrient loadings and concentrations related to a desirable trophic state ( e.g., mesotrophy or oligotrophy). TP limits were derived by the Florida model
, an empirically defined relationship between hydraulic loading (mean depth/water residence time) and nutrient loading limits for mesotrophic Florida systems (Steward and Lowe 2010). Because the F lorida TP loading limit model (Steward and Lowe 2010) is consistent with the Vollenweider (1976) TP critical loading model, the Vollenweider model equation was adjusted (specifically the

τ

w exponent) to fit the Florida m odel (Steward and Lowe 2010) , which was used to predict both the upper and lower mesotrophic [TP] and an oligotrophic level of [TP]:

U pper mesotrophic [TP] = L M (P) X τ w 0.847 /z(1 + τ w 0.5 ), which was empirically derived;

L ower mesotrophic [TP] = L M (P) X τ w 0.7 /z(1 + τ w 0.5 ) as a theoretical derivation;

O ligotrophic [TP] = L O (P) X τ w 0.5 /z(1 + τ w 0.5 ) as a theoretical derivation; whereby L M , L O = mesotrophic,

o ligotrophic loads (g/m 2 /yr); τ w = water residence time; z= mean depth (m).

The N

- analog of the Vollenweider (1976) model was not equiva lent to or consistent with the Florida TN trophic loading model (Steward and Lowe 2010)
, and thus the Vollenweider model could not be used to predict [TN]. Therefore, a second model (Dettmann 2001) for estuaries was selected to predict [TN] based on a tro phically desirable TN loading limit as determined by the prior application of the Florida model. The Dettmann (2001) model equation is:

[TN] = (L N X τ w / V + [TN] s )(1/1 + ατ w ); whereby L N = TN loading (g/yr), τ w = freshwater residence time (yr), V = volume of estuary (liters, L) segment, [TN] s = average [TN] at segment boundaries (g/L), α = 1 st order rate coefficient for N loss (3.6 yr -1 ).

Among the three lines of evidence, the reference period provides the primary line of evidence because it constitutes the most direct analysis of site

- specific data that represents a time when trophic state was desirable. The other two lines of evidence are model predictions (incorporating site

- specific data) and regarded a s supporting evidence.



### Results and Discussion

Spatial C onsiderations and S egmentation

The northern half of the HRE system, including the estuary and catchment, is distinct from the southern half based on a number of characteristics. For example, even though the percent proportion s of land uses in the area are nearly equivalent between the south HRE (S. HRE) and north HRE (N. HRE) (Fig ure 7; SJRWMD geographic information system [ GIS ] file data on 2004 land use), their population densities are quite diff erent. The municipal population density in the north HRE, about 3,300 people/mi 2 , is about 1.7 times greater than in the south HRE , with about 2, 000 people/mi 2 (Volusia County Dep artment of Economic Development 2009).Draft 22 August 2010 Figure 7 . Percent composition of major land uses in the south and north HRE (based on 2004 imagery).

Hydrodynamic properties probably best describe the estuarine di fferences between the north and south HRE

. John and Morris (1999) conducted a tracer study with a calibrated RMA2 model (U.S. Army Corps of Engineers) to determine two tidal null or node points within the HRE. A tidal node point is a general location within the estuary where there is no net water flow in either direction ( in this case, north or sout h). One node point is located between s outh Daytona and Daytona Beach (Figure 8a ), and the other is located just south of High Bridge and east of the lower reach of Bulow Creek ( Figure 8b ).

Figure 8a. Location of tidal node at boundary between the nor th and south HRE. Agriculture
Other Range/Forest

Residential
Urban Water/Wetlands 7% 2%

33%

14% 10% 35%

3% 3%

36%

11% 11% 37% 

## N. HRE (S . Daytona to Bulow) 

## S . HRE (Ponce De Leon Inlet to S. Daytona)



## N. HRE Tidal nodeDraft 23 August 2010 Figure 8b . Location of tidal node at boundary between the HRE and Matanzas River Estuary near High Bridge.

The Daytona tidal node point marks the initial delineation between the south HRE and north HRE segments. The High Bridge node point generally marks the divide between the HRE and Matanzas River E stuary systems. The south HRE and north HRE share the same tidal height or amplitude of about 0.7 m and are only slightly different in mean depth: 1.7 m and 1.4 m, respectively. However, the flushing rates or water residence times between the 2 segments are very different. The north HRE has an approximate freshwater residence time of 14 days
, 2

The s patial distributions of major habitat communities in the HRE estuary and catchment appear to support the deline ation between the south and north HRE , as described above. Two biological resource maps are shown ( Figure 9 ) as evidence of this support. One map shows the distribution of oyster reefs (SJRWMD 2006)
, and the other shows the distribution of aquatic and te rrestrial habitat deemed regionally significant (Johnson et al. 1998). Oyster reef abundance in the south HRE is clearly contrasted with the near absence of oyster reefs in the north HRE (primarily due to dredge

- and

- fill development during the first 60 ye ars of the 20 th century). The presence of regionally significant habitat is comparatively sparse in the north HRE, especially along the estuary, compared with more the intact and contiguous habitats found in the south HRE and in the southern portion of th e Matanzas River estuary. while the freshwater residence in the south HRE is 3 days (derived from Sheng et al. 2008), attributable to that segment’s proximity to Ponce De Leon Inlet. As shown below , water residence tim e is an important factor that influences the critical nutrient loading limit required to achieve or maintain a desired trophic condition.

2 Revised estimate that replaces the 20

- day residence time presented at the March 2010 FDEP workshop 

### Tidal node

Bulow Cr.

Google Earth High Bridge



## N. HREDraft 24 August 2010 Figure 9 . Distribution of oyster and other significant habitat communities in the HRE.

Water quality conditions over the period of record also suggest a division of the HRE system into two or potentially three segments. The network of VCEMD water quality sites, and their respective data, were spatially aggregated into three segments
, with t he first two segments divided at the north HRE and south HRE boundary, as previously described
, and a third segment consisting of sites selected to represent the northernmost Tomoka area of the north HRE ( Figure 10 ). With an emphasis on those three segmen ts, the following graphs show spatial trends for selected water quality parameters

.
The 2000 through 2008 period 3

3 The reference period changed to 2000

– 08 from 1996

– 2008. The latter period was presented as the reference period, along with related results, at the March 2010 FDEP workshop. wa s selected as a reference period for nutrient criteria development because ( 1) TN levels were about half the levels measured during the early 1990s; ( 2) chlorophyll a levels dropped since the late 1990s, probably in response to the TN reduction, and are consistent with the TMDL

- related chlorophyll a targets established for other Florida estuaries (typically ≤7 μg/L annual average; Steward and Lowe 2010); and ( 3) trophic status was “good”

— upper mesotrophic in the north HRE, and mesotrophic tending toward oligotrophic in the south HRE. The TP trend was stable throughout the full p eriod of record (1992

– 2008) and likely inconsequential with respect to the estuary’s trophic condition. 

### SJRWMD Oyster Reef Imagery (2006) SJRWMD NCB Recon Report (Johnson et al. 1998) Regionally Significant

Habitat (includes salt marsh, oyster habitat as

well as Fw and upland habitats) 

### Oyster reefs

Port Orange Daytona Beach

S. HRE

N. HRE

N. HRE

S. HREDraft 25 August 2010 Figure 10 . VCEMD water quality sampling sites. Only data from sites HL01 through HL20 were analyzed for development of estuarine nutrient criteria for the Halifax River Estuary.

The reference period results for chlorophyll a , TN, and TP are reported as annual median concentrations and maximum wet

- season median concentrations (based on the highest monthly values, typically observed in July, August, and September). The se results (Table s 7a and 7b ) constitute the first and primary line of evidence in the development of nutrient criteria for the north and south HRE

.
Table 7a

. H RE r

eference period r esults

— first line of evidence : Annual median, 2000

– 08 Segment Chlorophyll a (μg/L) TN (mg/L) TP (mg/L) North HRE 4.5 0.61 0.12 South HRE 3.5 0.39 0.12 Sites Segment HL01-04 N. HRE/Tomoka HL05-11 N. HRE/Daytona HL12-20 S. HREDraft 26 August 2010 Table 7b

. H RE r

eference period r esults

— first line of evidence : Maximum wet

- season median, 2000

– 08 (July

–

September) Segment Chlorophyll a (μg/L) TN (mg/L) TP (mg/L) North HRE 7.9 0.90 0.18 South HRE 5.8 0.51 0.19

The maximum wet

- season medians for chlorophyll a (7.9 and 5.8 μg/L for the north HRE and south HRE, respectively ) are well below the tentative indicator level of 12 μg/L that corresponds to dinoflagellate blooms or dominance as indicated by analysis of a U.F., Edward Phlips 2000

– 01 dataset for the HRE (Steward et al. 2010) . One of the dominant dinoflagellate species in the HRE is Prorocentrum minimum , which, in high bloom concentrations, was responsible for oyster mortality in the Chesapeake Bay (N ational Oceanic and Atmospheric Administration [N OAA ] 2007). It is not known whet her P. minimum densities have reached lethal levels in the HRE, and archived samples remain to be analyzed (E

. Phlips, U niversity of Florida , pers. com., February 2010).

Chlorophyll a

– [TN], [TP] R egression M odels

A covariant trend among average monthly TN, TP, and chlorophyll a was apparent ( Figure 11 ) and prompted the development of simple regression models
, as described in the section on General Considerations and Methods

.

Figure 11. Average monthly TN, c hlorophyll a , and TP in the HRE overall. Monthly rainfall data are shown for comparison. The 1992

– 2008 period was used for both water quality and rainfall data.

I f any of the regressions proved statistically significant, they were applied toward setting median TN and TP based on chlorophyll a “targets” predetermined by the reference period method. The annual average regressions were used to predict annual median concentrations. The average monthly regressions were used to predict max imum wet

- season med ian limits us ing either the average July

– September datasets or the all

months datasets, depending on which datasets yielded the better statistical result ( r and p values)

. The r esults of the simple linear regressions are the second line of evidence (Table s 8 a and 8b ). 

### TP, mg/L x 10 TN, mg/L x 10 2 4 6 8 10 12 14



### Chl a, μg/L 0


### Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month 2.5” 2.6” 

### 4.3” 1.7” 1.8” 

### 6.9” 6.2” 7.0” 7.7” 5.1” 2.9” 2.6” 

### rainfallDraft 27 August 2010 Table 8a. HRE linear regression results

– second line of evidence: Annual median (1992

– 2008; annual average data) Segment Target Chlorophyll a (μg/L) TN (mg/L) r p TP (mg/L) r p

North HRE 4.5 0.58 0.62 .008 Not significant Not significant Not significant South HRE 3.5 0.30 0.74 .0008 Not significant Not significant Not significant

Table 8b. HRE linear regression results

– second line of evidence: Maximum wet

- season median (1992

– 2008; average monthly; July

–

September only for TN; all months for TP) Segment Target Chlorophyll a (μg/L) TN (mg/L) r p TP (mg/L) r p

North HRE 7.9 0.90 0.69 .004 0.17 0.87 .0002
South HRE 5.8 0.41 0.76 .001 0.15 0.86 .0003

Multivariate analysi s (stepwise regression) revealed that the major factor regulating chlorophyll a is water temperature, reflecting elevated chlorophyll a in summer ( wet

- season) months. Incorporating TN and TP together or separately did not strengthen the multivariate model. This lack of an enhanced rela tionship by nutrients does not necessarily reflect the system’s nutrient or trophic state (Borum 1996; Cloern 1982 ). Even if a system is nutrient over enriched, its trophic response could be limited by other factors. Given that the HRE system has relative ly low chlorophyll a and trophic state, other factors controlling chlorophyll a may be involved besides nutrients and water temperature. Metrics related to water transparency or light availability

— Secchi depth and turbidity

— do not improve the multivariate relationship either
, but that is more a consequence of low temporal variability, not magnitude. In fact, turbidities are comparatively and persistently high in the south and north HRE. HRE turbidities are typically over twice those observed in the I ndian R iver L agoon (IRL) system ( Figure 12 ).

High turbidities in the HRE are probably a natural condition. The HRE is similar to many well

- flushed, yet naturally turbid estuaries in the South Atlantic Bight region ( northeast Florida through South Carolina) t hat are dominated ecologically by oyster and marsh communities. A high level of turbidity or tripton is one major factor (short water residence time, appreciable tidal amplitude
, and tidal current being others) that constrains phytoplankton and submersed macrophyte production in favor of marsh production in the estuaries of northeast Florida, Georgia, and South Carolina (Lee and Jones 1981; Dame et al. 2000; Roman et al. 2000; R. Virnstein, Seagrass Ecosystems Analyst, pers. com., April 2010; E

. Phlips, U niversity of Florida , pers. com., 2010).Draft 28 August 2010 Figure 12

. Mean turbidity by year (1992

– 2008) for the north and south H RE compared with the IRL.

General M odels

Both models (Steward and Lowe 2010; Dettmann 2001) require estimates of water residence time and external nutrient loadings to predict trophic state, loading limits
, and complementary concentrations of TN and TP. Table s 9 a and 9 b present e stimates of external nutrient loadings for the north and south HRE , respectively

.

Table 9 a. Estimates of current (c irca 2004) external loadings of TN and TP to the north HRE. g/m 2 /yr = Grams per square meter per year *SJRWMD PLSM

- estimated surface water loadings based on 2004 land use and 2001

– 08 av erage annual rainfall, which is nearly equivalent to 30 -y ear
av erage annual rainfall. Major tributary streams are the Tomoka R iver , Bulow Cr eek , 11 th St. Canal, and Reed Canal in the north HRE; Spruce Cr eek
, Turnbull Cr eek
, and Halifax Canal in the south HRE. ** Domestic WWTF s : Daytona/Westside, Holly Hill, Ormond B ea ch in north HRE; Port Orange, New Smyrna Beach (@27% of annual discharge) in the

s outh HRE. WWTF loading estimates calculated from data obtained from FDEP, Tallahassee. North HRE Sources TN (kg/yr) TP (kg/yr) Surface Water Drainage* 207,906 34,088 Atmospheric Deposition 8,911 203 WWTFs** 41,015 9,203 Ground Water Unquantified; assumed negligible by Scholl et al. 1980 Unquantified; assumed negligible by Scholl et al. 1980 Total Loading: 257,832 (13.26 g/m 2 /yr) 43,494 (2.24 g/m 2 /yr) 0 2 4 6 8 10 12 14 16 18Turbidity (ntu)



### Year 

## Mean Turbidity in the HRE and IRL

Mean Turb.

- N. HRE Mean Turb.

- S.HRE Mean Turb.

- IRL

N. HRE

S. HRE

IRLDraft 29 August 2010 Table 9 b. Estimates of current (c irca 2004) external loadings of TN and TP to the south HRE.
*SJRWMD PLSM

- estimated surface water loadings based on 2004 land use and 2001

– 08 av erage annual rainfall, which is nearly equivalent to 30 -y ear
av erage annual rainfall. Major tributary streams are the Tomoka R iver , Bulow Cr eek , 11 th St. Canal, and Reed Canal in the north HRE; Spruce Cr eek
, Turnbull Cr eek
, and Halifax Canal in the south HRE. ** Domestic WWTF s : Daytona/Westside, Holly Hill, Ormond B ea ch in the north HRE; Port Orange, New Smyrna Beach (@27% of annual discharge) in the south HRE. WWTF loading estimates calculated from data obtained from FDEP, Tallahassee. South HRE Sources TN (kg/yr) TP (kg/yr) Surface W ater Drainage* 196,284 32,927 Atmospheric Deposition 7,516 171 WWTF s ** 17,335 4,492 Ground W ater Unquantified; assumed negligible by Scholl et al. 1980 Unquantified; assumed negligible by Scholl et al. 1980 Total Loading: 221,135 (13.04 g/m 2 /yr) 37,590 (2.22 g/m 2 /yr)

Nonpoint surface water drainage conveys the largest percentage of the total external nutrient loading to the HRE (78% to 89%), followed by WWTFs (8% to 21%). Atmospheric loading estimates, based on areal loading estimates for the n orth I RL (Gao 2009), constitute about 3% of the total TN loading and less than 1% of TP loading.

Ground water nutrient loading to the HRE was considered negligible by Scholl e t al. (1980), possibly because the majority of the population in the HRE catchment is served by centralized WWTFs , not septic tanks
, and there are large withdrawals from both the surficial and Floridan aquifers for water supply (Rutledge 1985).

Despite the conclusion reached by Scholl et al. (1980), the Floridan aquifer may be a significant, albeit unquantified, source of TP to the HRE. A geologic confining layer, the Hawthorn Formation, ordinarily restricts water movement between the Floridan and surfi cial aquifers. That layer is nearly absent in the HRE catchment (Toth 1987)
, and what remains is a thin, discontinuous clay strata with slags of apatite (ferric 4

Estimating annual TP loading from the upper Floridan is difficult at best. The interannual variability of the Floridan potentiometric surface elevation in coastal Volusia County is so large, approximately between +10 f ee t to - 10 f ee t from mean sea level per year over the last 10 years (D

. Toth, SJRWMD, pers. com., May 2010)
, that any estimate of upwelled TP loading in 1 year can easily be offset by zero loading in another year. Nonetheless, over the long term, the contributi on from the Floridan via upwelling or pumped withdrawal for surface irrigation may be partly responsible for maintaining high TP in HRE waters. phosphate) (J

. Martin, U niversity of Florida Geology Dep artment , April 2010). Consequently, some degree of hydrologic connection exists between the aquifers, potentially allowing the artesian upwelling of phosphorus

- rich ground water into the HRE (~0.1 mg/L TP near the HRE vs. 0.03 mg/L TP near Mosquito Lagoon; SJRWM D upper Floridan well data).

The total external TN and TP loading estimates for the north and south HRE were normalized to estuarine surface water area (g/m 2 /yr) for input to the Steward and Lowe (2010) model. The north and south HRE areal loading estimates were then paired with their respective hydraulic loadings (mean depth/residence time) and plotted on a graph that describes TN or TP areal loading limit (published TMDLs or pollutant load reduction goals [ PLRGs ] ) as a function of estuarine hydraulic loading ( Figure 13 ). The line of best fit in the graph represents upper mesotrophy (UML) for Florida estuaries (ba sed on Steward and Lowe 2010)

. The line in the plot representing lower mesotrophy (LML) was constructed using TN and TP limits for lower mesotrophy established by Steward and Lowe (2010), Smith (1998), and Baker et al. (1981)(further explanation provided in Steward and Lowe 2010).

4 FDEP determined that iron ( Fe ) in the HRE exceeds the standard and commented that ground water may be the major source (FDEP 2008).Draft 30 August 2010 The plotted points for TN and TP are located on or just below the lower mesotrophic line (LML) for the south HRE, indicating lower mesotrophy or oligo

- mesotrophy; and just above the upper mesotrophic line (UML) for the north HRE, indicating eutrophy ( Figur e 13 ). Alternatively, the TSI values and chlorophyll a in the north HRE indicate (upper) mesotrophy. The inconsistency between these sets of results for the north HRE may be explained by high levels of tripton in the north HRE that attenuate the trophic response, as indicated by the low TSI, but this phenomenon can not accounted for in the Steward and Lowe (2010) model. The same phenomenon may exist in the south HRE, but its current nutrient loading rates are sufficiently low to maintain oligo

- mesotrophic conditions.

Figure 13. The log

- linear plot of TN and TP load limits (g/m 2 /yr) vs. hydraulic loading (q s ). A point lying above the 95% confidence interval for the line

- of

- best

- fit (= upper mestrophy) is considered eutrophic; below the lower mesotrophic line (LML) is considered oligotrophic (based on Steward and Lowe 2010).

The plotted positions of the TN and TP points on the Florida trophic models (Fig. 13) suggest that the current external nutrient loa dings ( ca 2004) to S. HRE can serve as the loading limits that should maintain that segment’s current trophic state (oligo

- mesotrophy). The positions of the N. HRE points suggest that current 

### N. HRE S. HRE

- 

### 0.5 0.5

1 1.5

2 2.5

- 

### 0.5 0 0.5 1 1.5 2 2.5 3 

### log q s 

### (z/ τ w 

### ; m/yr)log TN load limit (g/m2/yr) 

### 95% upper CI

LML

- 2.0 - 1.5 - 1.0 - 0.5 0.0 0.5 1.0 1.5

- 0.5 0.0 0.5 1.0 2.0 2.5 3.0

log q s (z/ τ w ; m/yr)log TP load limit (g/m2/yr)

S. HRE N. HRE 2.0 95% upper CI

LML 

# TN

TP UML

UML log TN Load Limit ( ≈UML) = 0.83(log q s ) – 0.018 ; R 2 = 0.96, p < 0.001

log T P Load Limit ( ≈UML) = 0. 92 (log q s ) – 0. 95; R 2 = 0.97, p < 0.001 

# TP log T P Load Limit ( ≈UML) = 0. 92 (log q s ) – 0. 95; R 2 = 0.97, p < 0.001Draft 31 August 2010 nutrient loadings may promote eutrophy in that segment; however , there is other evidence ( mean TSI < 50; and the lack of impairment symptoms as described in Table 2) that indicate mesotrophy. It is likely that other factors (possibly including tripton) may be attenuating the trophic response in N. HRE. Without defin itive evidence of eutrophy or eutrophic symptoms, the current nutrient loadings to N. HRE are regarded as the loading limits sufficient to maintain mesotrophy in that segment.

Finally, the Dettmann (2001) and Steward and Lowe (2010) models were used to predict TN and TP concentrations in the north and south HRE that correspond to their respective current loading s or loading limits

. The TN and TP loading limits (current loadings ) and their predicted concentrations are presented as the third line of eviden ce (Table s 10a and 1 0 b, respectively ).

Table 10a

. North H RE current loading ( loading limits ) for TN and TP with the model

- predicted concentrations

. * The Dettmann (2001) TN model equation was applied ( Steward et al. 2010 ).

** The upper mesotrophic [TP] model equation was applied to the north HRE ( Steward et al. 2010 ). North HRE TN (kg/yr) TN (mg/L)* TP (kg/yr) TP (mg/L)** Current loading (circa 2004) 257,832 0.62 43,494 0.20

Table 1 0b

. South H RE current loading ( loading limits ) for TN and TP with the model

- predicted concentrations

. * The Dettmann (2001) TN model equation was applied ( Steward et al. 2010 ).

** Midpoint between the two [TP] values reported in the parentheses. Two [TP] values are reported because both the lower mesotrophic and oligotrophic [TP] model equations were applied to the south HRE ( Steward et al. 2010 ). South HRE TN (kg/yr) TN (mg/L)* TP (kg/yr) TP (mg/L)** Current loading (circa 2004) 221,135 0.42 37,590 0.135 (0.09, 0.18 )



### Proposed Numeric Nutrient Targets

Methodology

For consistent application and for providing an appropriate level of protection, water quality criteria need to include magnitude, frequency, and duration components. The magnitude is a measure of how much of a pollutant may be present in the water without an unacceptable adv erse effect. Duration is a measure of how long the pollutant may be above the magnitude, and frequency relates to how often the magnitude may be exceeded without adverse effects. It is preferred to derive the ma gnitude component of a criterion through a

cause

- effect relationship (such as those meas ured through toxicity testing). The magnitude would then be set at a level that would protect a majority of the sensitive aquatic organisms inhabiting the system. Abs ent a demonstrated cause

- effect relationship, the magnitude may be set at a level designed to maintain the current data distribution, accounting for natural temporal variability, when the current conditions are protective of the de signated uses of the wate rbody. Since a criterion derived based on the existing data distribution has no direct link to any observed cause and effect relationship, it is assumed that maintaining the current data distribution will preserve the uses associated with that distributio n.
The frequency and duration components of the criteria are best established as additional descriptors of the referen ce condition data distribution. Specifically, these components should be part of a statistical test designed to determine whether the lo ng

- term distribution of data has shifted upward (or in some cases, downward) f rom the reference distribution. This test would then be used to determine whether futureDraft 32 August 2010 monitoring data are consistent with the magnitude (long

- term average) de fined by the ref erence dataset. It is critical to account for the natural variability surrounding the magnitude expression and to control for statistical

errors.
The derivation of the magnitude, frequency and duration components of the numeric nutrient criteria for Pensa cola Bay is described briefly below. More details concerning the statistical approaches used can be found in the document “Overview of FDEP Approaches for Nutrient Criteria Development in Marine Waters” (FDEP 2010).

Magnitude

The magnitude component can be set at a variety of values based on the frequency and duration that will b e used to determine compliance. For the “healthy existing conditions” approach, FDEP established the magnitude at: a) an adjusted long

- term central tendency (geometric mean) of the distribution, expressed as a long

- term geometric mean never to be exceeded; and b) an annual geometric mean, not to be exceeded more than two times over a five - year period. The long

- term average condition was adjusted to a level that represents an insignificant increase from the baseline

. Allowing for an insignificant increase accounts for uncertainty in the estimate of the mean and partially addresses the fact that the reference based approach fails to identify a threshold of imbalance, and thus is highly prone to excessive Type I error

. For the purpose of antidegradation evaluations, EPA has established that a ten percent change in a water quality parameter represents an insignificant departure from the historical condition, known as a de minimus c hange (US Sixth Circuit Court 2008). Therefore, the proposed thresholds allow for up to a ten percent increase in the long

- term geometric mean, which was calculated as the geometric mean of the annual geometric means of the long

- term dataset for each segm ent of the waterbody.

Because it is not always practical to assess compliance with the criteria on the same long

- term basis, FDEP also developed criteria expressed as an annual geometric mean so that estuaries could be assessed on an annual basis. It shou ld be noted that the duration and frequency components of the criteria must be linked to the response timeframe of the sensitive endpoint. Short

- term averaging periods (e.g., 1 to 30 days) might be appropriate for nutrient criteria where a sufficiently ro bust cause

- effect relationship has demonstrated that a eutrophic response occurs over such timeframes. If however, such a short

- term response cannot be demonstrated, or there is no indication of use impairment, longer averaging periods should be used.

Since the duration and frequency components of the criteria must be consistent with the derivation of the magnitude component, the long

- term geometric mean target cannot simpl y be applied as an annual mean. Doing so would result in an unacceptability high Type I failure rate (identifying a healthy system as being impaired) since approximately 50 percent of the individual yearly means are expected to be above the long

term mean. Therefore, the long

- term target must be adjusted to allow for the application to a shorter duration with an acceptable Type I error rate of no more than a 10 percent.

An annual criterion with an approximate 10 percent Type I error rate for a given frequency was derived by appropriately accounting for the annual variability above the mean. This annual target concentration was derived as an upper percentile of the distribution of the annual geometric mean concentrations. Previous proposals by EPA have utilized three

- year assessment periods to express the duration nutrient criteria

co mponents. Although it is possible to construct a test that achieves the 10 percent Type I error rate target over a 3

- year period, a slightly longer period (5 years) will provide better control for Type II error and will more fully capture climatic cycles ( e.g ., el nino, la nina), which tend to be longer than three years in Florida (and may actually be on a multi

- decadal scale). Furthermore, a five year period is more consistent with both the State’s five year 303(d) assessment and NPDES permit renewal cyc les.Draft 33 August 2010 Given a five year assessment period, FDEP derived criteria expressed as an annual geometric mean by using the 75 th percentile of the annual geometric means from the long

- term dataset. FDEP demonstrated that setting the criteria at this percentile res ults in a magnitude that, when expressed as an annual geometric mean not to be exceeded more than twice during a five

- year period, will achieve the targeted 10 percent error rate. The magnitude component of the criteria (not to be exceeded more than twice in a 5 year period) was established to allow for two separate assessments:

As an annual geometric mean for a network of stations in a specified segment of the waterbody; and

As an annual geometric mean for a single station in a given segment.

The two ex pressions of magnitude differ in the handling of within

- segment spatial variability. The network average magnitude was calculated based on the distribution of spatially averaged annual geometric means, while the single site magnitude was calculated using the distribution of station annual geometric means. Use of the network average magnitude is appropriate for assessing overall segment status. However, a network average is only representative of overall segment status if it is relatively homogeneous. If the segment is not well mixed, is very large, or contains localized nutrient sources, then there is a potential that isolated areas of enrichment may be masked in the network spatial average. Therefore, the single station annual geometric mean has the be nefit of assessing localized enrichment patterns. DEP has not decided whether both expressions of magnitude are needed in all cases, and we are seeking additional feedback from local experts and stakeholders.


### Summary and Conclusions

The r esults from the t hree lines of evidence are tabulated for ease of comparison (Table s 11a and 11b ). Overall, the results from the HRE

- specific regression models and the general models compare well with the reference period results, increasing the level of confidence that numeric nutrient criteria for the north and south HRE can be based on the 2000

– 08 period of record. For the south HRE, the results of the TN regression model do not compare well with those of the reference period method. This inconsistency cannot be explained, but it is the exception in an otherwise solid, weight

- of

- evidence case for the HRE.

For the north HRE, the potential for current (c irca 2004) nutrient loadings to induce eutrophy ha s possibly been mitigated by the estuary’s turbidity ( more specifically, tripton or non

- algal turbidity) , suggesting that
current nutrient loadings can serve as the loading limits protective of the system’s current trophic state (mesotrophy to oligo

- mesotrophy)

. In addition, t he three l ines of evidence for the north HRE produced a tight range of annual and wet

- season median concentration s (Table s 11a ). Therefore , the north HRE current loading estimates ( ca 2004) and reference period results are proposed as that segment’s nutrient criter ia: 257,832 kg/yr TN and 43,494 kg/yr TP; 0. 61 mg/L TN and 0.12 mg/L TP as annual medians; and 0. 90 mg/L TN and 0.1 8 mg/L TP as Jul y– Sep tember medians (Table 11a)

.Draft 34 August 2010 Table 1 1 a. Summary of lines

- of

- evidence results: L oading and concentration limits for the north HRE

. Target condition is mesotrophy ( c hlorophyll a targets are an annual median of 4.5 μg/L and a seasonal median of 7.9 μg/L for Jul y through Sep tember )

- = Empty cell/no data kg/yr = Kilograms per year mg/L = Milligrams per liter N/A = Not app licable

a 0.62 mg/L TN and 0.2 mg/L TP are predicted concentrations based on current loadings (ca. 2004)

.

- TN ( k g/yr ) TN ( k g/yr ) TP ( k g/yr ) TP ( k g/yr ) Loading Limit (current loading) 257,832 257,832 43,494 43,494

- Median (mg/L) Annual Median (mg/L) July

– September Median (mg/L) Annual Median (mg/L) July

– September Reference Period (2000

– 08) 0.61 0.90 0.12 0.18 Regressions (1992

– 2008 data) 0.58 0.90 N ot sign ificant 0.17 General Models 0.62, a N/A 0.2, a N/A

Table 11b . Summary of lines

- of

- evidence results: L oading and concentration limits for the south HRE

. Target condition is oligo

- mesotrophy (chlorophyll a targets are an annual median of 3.5 μg/L and a seasonal median of 5.8 μg/L for July through September)

- = Empty cell/no data N/A = Not applicable

a The midpoint between the two values in parentheses = 0.135 mg/L TP. The two [TP] values reported in parentheses are the results from the lower mesotrophic and oligotrophic [TP] model equations applied to the sou th HRE (see the section on General Considerations and Methods).

- TN ( kg/yr ) TN ( kg/yr ) TP ( kg/yr ) TP ( kg/yr ) Loading L imit (current loading) 222,000 222,000 38,000 38,000

- Median (mg/L) Annual Median (mg/L) July

– September Median (mg/L) Annual Median (mg/L) July

– September Reference Period ( 2000

– 08) 0.39 0.51 0.12 0.19 Regressions ( 1992

– 08 data) 0.30 0.41 N ot sign ificant 0.15 General Models 0.42 N/A 0.135 (0.09, 0.18) a N/A

For the south HRE, the current (c irca 2004) loadings of TN and TP are proposed as loading limits. Current TN and TP loadings should maintain the oligo

- mesotrophic condition in the south HRE. The predicted trophic state and concentration limits from the regression analysis and the general mo dels support that conclusion and are generally consistent with the 2000

– 08 reference period results (Table 11b) . Consequently, the south HRE current loadings ( ca 2004) and reference period results are proposed as that segment’s nutrient criteria: 222,000 kg/yr TN and 38,000 kg/yr TP; 0.39 mg/L TN and 0.12 mg/L TP as annual medians; and 0.51 mg/L TN and 0.19 mg/L TP as the Jul y through September medians (Table 11b)

.Draft 35 August 2010 

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