## SARASOTA BAY TMDL SUPPORT

Prepared for

Sarasota Bay Estuary Program 111 S. Orange Avenue, Suite 200W Sarasota, Florida 34236

Prepared by

5300 West Cypress Street Suite 200 Tampa, FL 33607-1768

DRAFT August 2007i Sarasota Bay TMDL Support DRAFT August 2007 

## Table of Contents

1.0 Introduction ................................................................................................................... ..................1 1.1 Approach 1 – Acceptance of existi ng standards for ch lorophyll-a.....................................3 1.2 Approach 2 – Establish site-specific and re source-linked targets for chlorophyll-a ..........3

2.0 Materials a nd Methods.......................................................................................................... ..........4 2.1 Site Identif ication............................................................................................................ ....5 2.1.1 Segments 7, 8 10 and 11 (Sarasota Bay).............................................................5 2.1.2 Segments 1, 3, 13, 14 and 16...............................................................................6 2.2 Seagrass Co verage ...........................................................................................................7 2.3 Depth Measur ements.........................................................................................................8 2.4 NOAA NOS Bath ymetry...................................................................................................10 2.5 Depth Comp arison ...........................................................................................................11 2.6 Chlorophyll-a and K Data.................................................................................................11 2.7 Chlorophyll- a Tar get.........................................................................................................11

3.0 Results ........................................................................................................................ ..................13 3.1 Water Depth Co mparison ................................................................................................13 3.2 Chlorophyll-a Target s.......................................................................................................15

4.0 Discussion..................................................................................................................... ................31

5.0 References..................................................................................................................... ...............34

LIST OF TABLES

Table 1. Verified Impaired Waterbodies in Sarasota Bay (from FDEP Group 3 Verified Impaired List (6/ 20/2005)).............................................................................................................. ...........2 Table 2. Common names for portions of Sarasota Bay and corresponding SBEP bay segments. ...................................................................................................................... ............4 Table 3. Braun-Blanquet s eagrass coverage method. ............................................................................7 Table 4. Segment and referenc e tidal station for fiel d data................................................................... ..9 Table 5. Results of Linear Model Regression between chlorophyll-a and K for each Bay Segment........................................................................................................................ ...........12 Table 6. Average Corrected chlorophyll-a, Li ght Attenuation Coefficient, and PAR for each segment. ....................................................................................................................... ...........17 Table 7. Segment 7 current and proposed water depth, K and target chlo rophyll-a.............................17 Table 8. Segment 8 current and proposed water depth, K and target chlo rophyll-a.............................20 Table 9. Segment 10 current and proposed wa ter depth, K and target chlorophyll-a..........................21 Table 10. Segment 11 current and proposed wa ter depth, K and target chlorophyll-a..........................23 Table 11. Segment 13 current and proposed wa ter depth, K and tar get chlor ophyll-a. ..........................25 Table 12. Segment 14 current and proposed wa ter depth, K and tar get chlor ophyll-a. ..........................27 Table 13. Segment 16 current and proposed wa ter depth, K and tar get chlor ophyll-a. ..........................29 Table 14. PBSJ Proposed chlorophy ll-a targets for all segments and percent reduction required to reach the propose d 2050 target...........................................................................................32

### Table of Contents

ii Sarasota Bay TMDL Support DRAFT August 2007 LIST OF FIGURES

Figure 1. Site location in Segments 7,8,10 and 11. ............................................................................. .....5 Figure 2. Site location in Segments 13, 14 and 16. ............................................................................. .....6 Figure 3. Site Locati on in Segment s 1 and 3.................................................................................... ........6 Figure 4. Seagrass identifica tion and cover age estima tion ...................................................................... 7 Figure 5. Customized staff gauge us ed to measure wa ter depth. ............................................................8 Figure 6. 1950’s NOS NOAA bathymetr y data for Sara sota Bay. ..........................................................10 Figure 7. Average Water Depth at the 1950’s NOS and 2007 field si tes. ..............................................13 Figure 8. Average water depth using both 1950’ s bathymetry data and surveyed mapped and deep-edges..................................................................................................................... .........14 Figure 9. Distance from the mapped deep-e dge to the field ve rified deep- edge....................................14 Figure 10. Correlation between Light attenuation and chlorophyll-a for Segment 1 (August 2001- February 2006). ................................................................................................................ .......15 Figure 11. Correlation between Light attenuation and chlorophyll-a for Segment 3 (August 2001- February 2006). ................................................................................................................ .......16 Figure 12. Correlation between Light attenuation and chlorophyll-a for Segment 7 (August 2001- February 2006). ................................................................................................................ .......18 Figure 13. Current and future target chlo rophyll-a concentration s for Segm ent 7....................................18 Figure 14. Correlation between Light attenuation and chlorophyll-a for Segment 8 (August 2001- February 2006). ................................................................................................................ .......19 Figure 15. Current and future target chlo rophyll-a concentration s for Segm ent 8....................................20 Figure 16. Correlation between Light attenuati on and chlorophyll-a for Segment 10 (August 2001-Februar y 2006). ........................................................................................................... ...21 Figure 17. Current and Future target chloro phyll-a concentrations for Segm ent 10. ...............................22 Figure 18. Correlation between Light attenuati on and chlorophyll-a for Segment 11 (August 2001-Februar y 2006). ........................................................................................................... ...23 Figure 19. Current and Future target chloro phyll-a concentrations for Segm ent 11. ...............................24 Figure 20. Correlation between Light attenuati on and chlorophyll-a for Segment 13 (August 2001-Februar y 2006). ........................................................................................................... ...25 Figure 21. Current and Future target chloro phyll-a concentrations for Segm ent 13. ...............................26 Figure 22. Correlation between Light attenuati on and chlorophyll-a for Segment 14 (August 2001-Februar y 2006). ........................................................................................................... ...27 Figure 23. Current and Future target chloro phyll-a concentrations for Segm ent 14. ...............................28 Figure 24. Correlation between Light attenuati on and chlorophyll-a for Segment 14 (August 2001-Februar y 2006). ........................................................................................................... ...29 Figure 25. Current and Future target chloro phyll-a concentrations for Segm ent 16. ...............................301 Sarasota Bay TMDL Support DRAFT August 2007 

## 1.0 Introduction

In Southwest Florida, a substant ial amount of research has focuse d on the relati onships between population growth, changing land us e patterns, pollutant loads, estuarine water quality, and seagrass health. In Tampa Bay, historical losses of seagrass coverage have been linked to both direct and indirect impacts (i.e., Lewis et al., 1985; Lewis, 1989; Ha ddad, 1989). In contrast, recent (1982–1996) increases in seagrass coverage in Tampa Bay have been linked to improved water quality (i.e., Johansson, 1991; Johansson and Ries, 1997; Lewis et al., 1998; Johansson and Greening, 1999). Improvements in water quality have in turn been attributed mostly to improvements in the treatment and disposal of wastewater discharges by the Cities of Tampa, St. Petersburg and Clearwater since the mid to late 1980s (Johansson and Greening, 1999).

A similar situation exists in Sarasota Bay, where recent increases in seagrass coverage were related to reductions in anthropoge nic nitrogen loads to the bay by the City of Sarasota and Manatee and Sarasota Coun ties (Kurz et al., 1999; Tomasko et al. 2005).

Nitrogen loads into Tampa Bay and Sarasota Bay (generated primarily by domestic wastewater treatment facilities) were reduced by 57% and 46%, respectively, dur ing the 1980s and 1990s (Tomasko et al. 2005). In response, both Tampa Ba y and Sarasota Bay have lower phytoplankton concentrations, greater water clarity and more exte nsive seagrass coverage in recent years than in the early 1980s (Johansson and Greening, 1999; Kurz et al., 1999; Tomasko et al. 2005). As there is no evidence of a concurrent and explan atory trend in rainfall during this same time period, it was concluded that variation in rain fall could not account for the observed increase in seagrass coverage in these two bays (Tomasko et al. 2005).

The following is the conceptual framework within which the topic of “impairment” should be considered regarding issues relating to the to pic of Total Maximum Daily Loads (TMDLs) for Sarasota Bay. The bay itself is characterized as having stable or incr easing seagrass coverage bay-wide, yet portions of the ba y are characterized as “impaire d” via the state of Florida’s Impaired Waters Rule (IWR).

In Florida, the IWR (Chapter 62-303, Florida Administrative Code [FAC ]) includes guidelines for chlorophyll-a in surface water bodies. Estu aries or estuary segments are included on the “planning list” for nutrients if their annual mean chlorophyll-a for any year is greater than 11 μg / liter or if annual mean chlorophyll-a va lues have increased by more than 50% over historical values for at least two consecutive years. When comparing changes in chlorophyll-a to historical levels, historical levels are based on the lowest five-year average for the period of record. To calculate a five-year average, there mu st be annual means from at least three years of that five-year period.

Waterbodies are placed on the verified list for impai rment due to nutrients if there are sufficient data from the last five years preceding the pl anning list assessment, combined with historical data (if needed to establish historical chlorophyll-a levels or historical TSIs), to meet the data sufficiency requirements spel led out in FAC 62-303.350(2).

### Introduction

Portions of Sarasota Bay have chlorophyll-A concentrations that are near the thresholds described in the IWR; and therefore, may have required pollutant load reductions assigned to them through the state’s Total Maximu m Daily Load (TMDL) Program.

Portions of Sarasota Bay that are currently lis ted as impaired are shown in Table 1. Also included is the bay segment that correlates with the Waterbody Identification number (WBID) of concern, as outlined in both the Sarasota Bay Estuary Program’s (SBEP) Framework for Action (1992) and also the SBEP’s Comprehensive Conservation and Manage ment Plan (1995).

Table 1. Verified Impaired Waterbodi es in Sarasota Bay (from FDEP Group 3 Verified Impaired List (6/20/2005)).

Waterbody Name WBID SBNEP Segment Parameter of Concern

Palma Sola Bay 1883 2 and 3 Nutrients (chlorophyll-a > 11 μg / liter) Palma Sola Bay North 1883 B 3 Bacteria (exceeds DOH thresholds)
Palma Sola South 1883 C 3 Bacteria (exceeds DOH thresholds)
Bowlees Creek 1896 NA Fecal Coliform Bacteria
Bowlees Creek 1896 NA Total Coliform Bacteria
Bowlees Creek 1896 NA Nutrients (chlorophyll-a) Philippi Creek 1937 NA Fecal Coliform Bacteria Philippi Creek 1937 NA Total Coliform Bacteria Roberts Bay 1968 D 13 Nutrients (Historic chlorophyll-a) Blackburn Bay 1968 F 16 Nutrients (Historic chlorophyll-a)
Clark Lake 1971 NA Nutrients (TSI > 60)
Clowers Creek Tidal 1975 AA NA Nutrients (chlorophyll-a)

This report focuses on the review of current listing criteria for Sarasota Bay, and the development of potential alternative criteria for the water quality goal development for Sarasota Bay.

While chlorophyll-a can be a useful indicator of impaired conditions in an estuary, interpreting the causes and effects of varyi ng chlorophyll-a concentrations is challenging. Chlorophyll-a is known to be highly variable and responsive to a variety of factors, in cluding nutrient loads, rainfall, salinity, residence time, season, and even th e time of day. In addi tion, factors other than chlorophyll, such as turb idity and color, may also affect wa ter transparency. If those factors affect water clarity to such a degree that they may also affect phytoplankton growth rates, than issues other than nutrient availability alone may need to be accounted for to develop potential nutrient limits for water quality protection and/ or restoration.

For Sarasota Bay, there appear to be two main c ourses of action that could be pursued, as relates to the issue of potentially biologi cally relevant values of chlorophyll-a, as summarized below.

2 Sarasota Bay TMDL Support DRAFT August 2007

### Introduction

3 Sarasota Bay TMDL Support DRAFT August 2007 1.1 Approach 1 – Acceptance of exi sting standards for chlorophyll-a

This approach would be to accept the state’s determination that a chlorophyll-a concentration of 11 μg / liter, and the water clarity that accompanies such conditions, is an appropriate target. Or, that a 50 percent increase in leve ls of chlorophyll-a over “historical” levels is an indication of an impaired condition. If this approach is view ed as satisfactory, then Clowers Creek would be impaired for exceeding the 11 μg / liter st andard, and Bowlees Creek, Roberts Bay and Blackburn Bay would be impaired for increases ov er historical levels of chlorophyll-a.

1.2 Approach 2 – Establish site-sp ecific and resource-linked targets for chlorophyll-a

A second approach would be to develop site-speci fic and scientifically-d efensible water clarity and chlorophyll-a goals that could be linked to a living resource. An approach such as this, using science-based management to protect the health of living resources, is similar to that currently being used by the Tampa Bay Estuary Program.

This report summarizes efforts conducted in Sarasota Bay related to Approach 2, the development of site-specific and reso urce-linked targets for chlorophyll-a.

In addition, this report also addresses the issu e of whether or not “o ffshore” or “deep” edges from seagrass mapping efforts are the same as a “deep ” edge that would be found from site visits and careful depth measurements.

Finally, this report focuses on the potentially important issue of sea level rise, as it relates to the development of resource-based water clarity and chlorophyll-a target s for Sarasota Bay.4 Sarasota Bay TMDL Support DRAFT August 2007 

## 2.0 Materials and Methods

The techniques used in this re port involved the following steps: 1) identification of “mapped” deep edges of seagrass meadows, 2) determin ing the “surveyed” deep edges of seagrass meadows, 3) assessing the percent coverage of seagrasses at these two depths , 4) determining the depths at these two potentially different locations, 5) determining the light levels at these depths, and 6) determining the levels of chlorophyll-a that would allow for adequate light penetration to target depths, and 7) determining the implicatio ns of sea level rise on potential chlorophyll-a targets.

For this effort, the original Sarasota Bay segm entation scheme used in the SBEP’s Framework for Action (1992) and the Comprehensive Conser vation and Management Plan (SBEP 1995) was utilized. Table 2 contains information on the re lationship between portions of Sarasota Bay and the corresponding SBNEP bay segment numbers used in this report.

Table 2. Common names for portions of Sarasota Bay and corresponding SBEP bay segments.

Common Name for Waterbody SBEP Segment Numbers
Anna Maria Sound 1 Western Palma Sola Bay 2 Eastern Palma Sola Bay 3 Longboat Pass 4 Western Upper Sarasota Bay – Manatee County 5 Eastern Upper Sarasota Bay – Manatee County 6
Western Upper Sarasota Bay – Sarasota County 7 Eastern Upper Sarasota Bay – Sarasota County 8
New Pass 9 East of New Pass / Big Pass 10
Offshore of Downtown Sarasota 11 Big Pass 12 Roberts Bay 13 Little Sarasota Bay 14 “Midnight Pass” 15 Blackburn Bay 16
Nearshore Gulf of Mexico 17

### Materials and Methods

In greater detail, these steps are outlined below:

2.1 Site Identification

2.1.1 Segments 7, 8 10 and 11 (Sarasota Bay)

PBS&J, working in concert with Janicki Enviro nmental, verified seagrass coverage and water depth information along the mapped deep-edge of the seagrass beds within Sarasota Bay. As such, Janicki Environmental crea ted a “Universe” of sampling st ations along the deep-edge of the consistently mapped seagra ss beds performed by the Southw est Florida Water Management District (SWFWMD). Twenty randomly sele cted stations were provided by Janicki Environmental for each of the segments in Sa rasota Bay (7, 8, 10 and 11). PBS&J randomly selected eight sites for field verification of both seagrass c overage and water depth in each segment (Figure 1). The sites were visi ted on two calm weather days, February 20 th and 21 st

, 2007. All sites were QA/QC for site accuracy; four sites were removed from analysis based on their proximity to the target site location.

Figure 1. Site location in Segments 7,8,10 and 11.

5 Sarasota Bay TMDL Support DRAFT August 2007

### Materials and Methods

2.1.2 Segments 1, 3, 13, 14 and 16

PBS&J identified 7-9 mapped deep-edge sampling points based upon the 2006 SWFMWD seagrass coverage maps. Four sites were randomly selected to verify both seagrass coverage and water depth in segments 13, 14 and16 (Figure 2). This data was collected on May 4, 2007 during calm weather conditions. Five sites were randomly selected to verify both seagrass coverage and water depth in segments 1 and 3 (Figure 3). These data were collected on May 14, 2007 during calm weather conditions.

Figure 2. Site location in Segments 13, 14 and 16.

Figure 3. Site Location in Segments 1 and 3.

6 Sarasota Bay TMDL Support DRAFT August 2007

### Materials and Methods

2.2 Seagrass Coverage

At all mapped deep-edge sites, a modified Braun-Blanquet method was used to determine seagrass coverage (Figure 4; Table 3). Three assessments of seagrass coverage and species diversity were recorded at each site using a 1m 2 quadrant. Each site was evaluated to determine if it satisfied the Virnst ein et al. 2000 method for classificati on of the deep-edge of a seagrass bed, <10% seagrass coverage (Virns tein et al. 2000). If it was determined that the site had >10% seagrass coverage, PBS&J located the deep-edge. The location and water depth of the surveyed deep-edge were recorded.

Figure 4. Seagrass identificat ion and coverage estimation

Table 3. Braun-Blanquet seagrass coverage method.

Assessed Value Percent Seagrass Coverage

0 No coverage
0.1 Solitary short shoot
0.5 Sparse of <1% coverage

1 1-5% coverage
2 6-25% coverage
3 26-50% coverage
4 51-75% coverage
5 76-100% coverage
6 Coverage outside of m 2 placement

7 Sarasota Bay TMDL Support DRAFT August 2007

### Materials and Methods

2.3 Depth Measurements

Water depth information was collected at a tota l of 89 sampling sites throughout all Segments. A total of 39 water depth measurements were reco rded at the mapped deep-edge and an additional 50 measurements were made at the surveyed d eep-edge. Eleven of the 50 surveyed deep-edge sites were consistent with the mapped deep-edge. Three depths were recorded at each site using a customized staff gauge designed to reduce errors associated with the soft substrate (Figure 5). The weather condition was observed to reduce error associated with fetch and chop. All data were collected during calm bay conditions. The GPS coordinates were recorded for each station using a WAAS (Wide Area Augmentation System) enabled Garmin GPSmap 60CSx.

Figure 5. Customized staff gauge used to measure water depth.

All of the data were co rrected for tide and referenced to Mean Low Water (MLW) (Table 4). The 6-minute verified water level data from the St. Petersburg, Fl ( 8726520) tide station was used to model the tide for the Cortez, Sa rasota and Venice tide stations ( tidesandcurrents.noaa.gov ). The tidal prediction for each station was used to modify the St. Petersburg data. The St. Petersburg tide was adjusted for high and low tide and a time shift was applied for each station.

8 Sarasota Bay TMDL Support DRAFT August 2007

### Materials and Methods

9 Sarasota Bay TMDL Support DRAFT August 2007 Table 4. Segment and reference tidal station for field data.

Segment Bay Tide Station

1 Anna Maria Sound Cortez
3 Palma Sola Bay Cortez
7 NW Sarasota Bay Cortez
8 NE Sarasota Bay Cortez
10 SW Sarasota Bay Sarasota
11 SE Sarasota Bay Sarasota
13 Roberts Bay Sarasota
14 Little Sarasota Bay Sarasota
16 Blackburn Bay Venice

### Materials and Methods

2.4 NOAA NOS Bathymetry

Bathymetry data was collected in Sarasota Bay by the U.S. Coast and Geodetic Survey between 1953 and 1955 (Figure 6; www.estuarinebathym etry.noaa.gov). The majority of depth soundings were completed in 1954. Six survey s were completed collecting approximately 52,299 depth values using a portable depth recorder. The average distance between readings was 51 meters. The vertical datum was referenced to Mean Low Water. The horizontal datum was referenced to NAD83. The data provided bathym etry information for all Segments listed in Table 2.

Figure 6. 1950’s NOS NOAA bathymetry data for Sarasota Bay.

10 Sarasota Bay TMDL Support DRAFT August 2007

### Materials and Methods

11 Sarasota Bay TMDL Support DRAFT August 2007 2.5 Depth Comparison

Using GIS, the closest NOS water depth point to each field site was selected and paired. The distance between the 1950’s NOS station and 2007 field site wa s determined. The 1950’s NOS and 2007 surveyed water depths of all 89 sites we re statistically compared using a two-sample comparison with StatGraphics. Additionally, the water depth at the 2007 mapped deep-edge and the 2007 surveyed deep-edge sites were compared using a two-sample comparison. Again, the distance between the mapped deep-edge and surveyed deep-edge was determined.

2.6 Chlorophyll-a and K Data

Chlorophyll-a and the light attenuation coefficien t (K) data for each segment were downloaded from the Florida STORET database –( www.dep.state.fl.us/water/storet ).

These data were available for all segments between August 2001 and February 2006. Light attenuation coefficients (K / meter) in Segmen t 1 and 3 were calculated from the raw underwater incident light readings where z=0.5m (persona l communication, Greg Blanchard). Additionally, only uncorrected chlorophyll-a values were available for Segment 1 and 3. Corrected chlorophyll-a was available for all other segments. Statistical significance was determined based on the R 2 and sample size (Schefler 1979).

The average K was determined for each segmen t based on the monthly averages from August 2001 to February 2006. Percent Sub-surface Irra diance was calculated for each location at 4 corresponding depths (Mapped Deep-Edge (1 950’s), Mapped Deep-Edge (2007); Surveyed Deep-Edge (1950’s) and Surveyed Deep- Edge ( 2007); Formula 1), and then the average percent sub-surface irradiance (or PAR – photosynthetically active radia tion) for each segment at each depth was determined.

Formula 1: Percent PAR = +exp (-k*z)*100

Where k=average light attenuation coefficien t and z =water depth in meters at MLW

2.7 Chlorophyll-a Target

The chlorophyll-a target for segments 7, 8, 10, 11, 13, 14 and 16 were determined based on the average percent sub-surface irradiance at the Surveyed Deep-Edge (2007). The light attenuation coefficient was calculated based on PAR and the water depth at wh ich light readings were made (Formula 2).

Formula 2: K= -1/z * ln(Iz / Io)

Where Iz = PAR at depth z (in meters ) and Io = directly sub-surface PAR

### Materials and Methods

12 Sarasota Bay TMDL Support DRAFT August 2007 The current target chlorophyll- a concentration was calculated based upon the linear model relating K and chlorophyll-a for each segment (T able 5). A target chlo rophyll-a concentration was also calculated based upon anti cipated sea-level rise in Sara sota Bay for the years 2020 and 2050 (after Clark 1992). Using th e measured rate of sea-level rise between 1954 and 2007, sealevel rise was simulated for the next 13 and 43 y ears. The modified water levels were used to recalculate the new (lower) K value required to keep the same percent PAR at a location with additional water depths (due to sea level rise) an d the revised chlorophyll-a target was calculated based on the new estimate of K.

Table 5. Results of Linear Model Re gression between chlorophyll-a and K for each Bay Segment.

Segment No. Segment Name Chl- A significant? Linear Model

1 Anna Maria Sound No

3 Palma Sola Bay No

7 Upper Big SB – West Side Yes – posit ive K = 0.5342 + 0.0241(chlorophyll-a)

8 Upper Big SB – East Side Yes – positive K = 0.5408+ 0.0238 (chlorophyll-a)

10 Lower Big SB – West Side Yes – posit ive K = 0.5628 + 0.0205 (chlorophyll-a)

11 Lower Big SB – East Side Yes – posit ive K = 0.5025 + 0.0403(chlorophyll-a)

13 Roberts Bay Yes – positive K = 0.7263 + 0.0364(chlorophyll-a)

14 Little Sarasota Bay Yes – positive K = 0.7078 + 0.0404 (chlorophyll-a)

16 Blackburn Bay Yes – positive K = 0.592 + 0.0564 (chlorophyll-a)

## 3.0 Results

3.1 Water Depth Comparison

Tide-corrected water depth measurements from 89 sites were compared to the water depth estimates for these same locations using th e bathymetry data compiled in 1953-1955 by the USGCS. The average (n = 89) water depth for s ites visited in Sarasota Bay, based on the 1950’s bathymetry data, was 1.09 m at MLW compared to 1.26 m at MLW water depth for those same locations, but with directly meas ured water depths recorded in 2007 (Figure 7). The change in water depth was 0.17 m which is equivalent to 3.2 cm/decade. There was a highly significant difference between the 2007 water depths and the 1950’s data (N=89; p=0.01). This difference in water depths is within the range of documented rates of sea level rise in St. Petersburg during 1950 to 1990 (2.4 cm/decade), and estimated rates of future sea level rise of approximately 5.2 cm/decade, as outlined in Clark (1992)

Additionally, the mapped deep-edg e (2007) sites were compared to the surveyed deep-edge (2007) sites; the average water depth was 1.16 m at MLW and 1.34 m at MLW, respectively (Figure 8), but this difference was not sta tistically signi ficant (N=39; p= 0.09).

The average distance between the mapped deep-e dge (2007) and the surv eyed deep-edge (2007) was 42 m (Figure 9).

Figure 7. Average Water Depth at the 1950’s NOS and 2007 field sites.

13 Sarasota Bay TMDL Support DRAFT August 2007

### Results

Mapped DeepEdge (1950’s) Mapped DeepEdge (2007) Surveyed DeepEdge (1950’s) Surveyed Deep-Edge

Figure 8. Average water de pth using both 1950’s bathymetry data and surveyed mapped and deep-edges.

0 50 100 150 200 250PS-17PS-16PS-15PS-14PS-13AM-9AM-8AM-7AM-6BB-39BB-37BB-36BB-35LSB-31LSB-30LSB-29LSB-28RB-25RB-23RB-2111-NE16-NE17-NE19-NE20-NE03-NW04-NW05-NW20-NW07-SE10-SE15-SE16-SE17-SE18-SE08-SW17-SW18-SW20-SWDistance (m) Distance

Figure 9. Distance from the mapped deep-e dge to the field verified deep-edge.

14 Sarasota Bay TMDL Support DRAFT August 2007

### Results

3.2 Chlorophyll-a Targets

Segments 1 and 3

A significant correlation between chlorophyll-a a nd light attenuation was not found for Segments 1 and 3 (Figures 10 and 11). In these parts of Sarasota Bay, prior stud ies concluded that nonchlorophyll suspended material (NCSM) was th e dominant attenuator of light in the water column (Dixon and Kirkpatrick 1995). On aver age, NCSM explained 77% of the partitioned non-water attenuation for diffuse light in segmen t 1 and 58% in segment 3. Consequently, a chlorophyll-a target was not cal culated for these segments.

0.0 1.0 2.0 3.0 4.0 5.0 6.0

0 2 0 4 0 6 0 8 Uncorrected Chlorophyll a (ug/l)Light attenuation coefficient (K per m)

0

Figure 10. Correlation between Light atte nuation and chlorophyll-a for Segment 1 (August 2001-February 2006).

15 Sarasota Bay TMDL Support DRAFT August 2007

### Results

0.0 1.0 2.0 3.0 4.0 5.0 6.0

0 5 10 15 20 25 Uncorrected Chlorophyll a (ug/l)Light attenuation coefficient (K per m)

Figure 11. Correlation between Light atte nuation and chlorophyll-a for Segment 3 (August 2001-February 2006).

Segment 7

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 5.4 μ g/l and 0.6681 K per m, respectively (Table 6). Figure 12 shows the statistically significant relationship between chlorophyll-a and light attenuation for Segment 7. The linear model (Tab le 5) was used to produce target chlorophyll-a values for Segment 7 (Table 3). Based on th e Surveyed Deep-Edge water depth and percent PAR, a chlorophyll-a target of 5.3 μ g/l was calculated to maintain deep edge light requirements (Figure 14; Table 7). A potential IWR target was calculated based upon the chlorophyll a value which exceeds the historic value by 50% for WBID 1968B (Sarasota Bay; 5.5 μ g/l ). The 2020 and 2050 target chlorophyll-a concentrations were calculated based on anticipated sea-level rise. A projected water depth of 1.63m in 2020 and 1.76 m in 2050 was used. To maintain current water clarity conditions with in creased water depth, a target ch lorophyll-a concen tration of 4.6
μ g/l is proposed for 2020. The proposed target chlorophyll-a concen tration for 2050 is 2.6 μ g/l.

16 Sarasota Bay TMDL Support DRAFT August 2007

### Results

17 Sarasota Bay TMDL Support DRAFT August 2007 Table 6. Average Corrected chlorophyll-a, Light Attenuation Coefficient, and PAR for each segment.

Segment Average Chl- a (μg / liter) Average Light Attenuation Coefficient (K per m) Percent PAR at the Surveyed Deep-Edge (2007)

7 5.4 0.6681 35
8 5.4 0.6681 36
10 3.8 0.6372 34
11 4.5 0.6837 47
13 7.7 0.9993 31
14 7.7 1.0180 37
16 5.6 0.9105 46

Table 7. Segment 7 current and proposed wa ter depth, K and target chlorophyll-a.

Segment 7 PBSJ Proposed

Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 1.58 1.63 1.76 K (per m) 0.662 0.645 0.596 Chl a ( μ g/l) 5.3 4.6 2.6

### Results

y = 0.0241x + 0.5342
R 2 = 0.2191

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0 1 0 2 0 3 0 4 Corrected Chlorophyll a (ug/l)Light attenuation coefficient (K perm)

0

Figure 12. Correlation between Light atte nuation and chlorophyll-a for Segment 7 (August 2001-February 2006).

5.5 4.6

2.6 5.3 5.4

0.0 2.0 4.0 6.0 8.0 10.0 12.0

Average 2001- 2006 Potential IWR Target PBSJ Proposed Target 2020 target 2050 targetCorrected Chloropyll a (ug

Figure 13. Current and future target chlo rophyll-a concentrations for Segment 7

18 Sarasota Bay TMDL Support DRAFT August 2007

### Results

Segment 8

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 5.4 μ g/l and 0.6681 K per m, respectively (Table 6). Figure 14 shows the statistically significant relationship between chlorophyll-a and light attenuation for Segment 8. The linear model (Tab le 5) was used to produce target chlorophyll-a values for Segment 8. Based on the Surveyed Deep-Edge water depth and K, a chlorophyll-a target of 5.0 μ g/l was calculated to maintain current de ep edge light requirements (Figure 15; Table 8). A potential IWR ta rget was calculated based upon the chlorophyll a value which exceeds the historic value by 50% fo r WBID 1968B (Sarasota Bay; 5.5 μ g/l ). The 2020 and 2050 target chlorophyll-a concentrations were calculated based on antic ipated sea-level rise based on projected water depths of 1.61m and 1.74m, respect ively. To maintain current water clarity conditions with increased water dept h, a chlorophyll-a concentration of 4.3 μ g/l is proposed for 2020. The proposed target chlorophy ll-a concentration for 2050 is 2.2 μ g/l.

y = 0.0238x + 0.5408
R 2 = 0.181

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

0 5 10 15 20 25 30 Corrected Chlorophyll a (ug/l)Light attenuation coefficient (K per m)

Figure 14. Correlation between Light atte nuation and chlorophyll-a for Segment 8 (August 2001-February 2006).

19 Sarasota Bay TMDL Support DRAFT August 2007

### Results

Table 8. Segment 8 current and proposed wa ter depth, K and target chlorophyll-a.

Segment 8 PBSJ Proposed Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 1.56 1.61 1.74 K (per m) 0.660 0.643 0.594 Chl a ( μ g/l) 5.0 4.3 2.2

5.5

4.3

2.2 5.0 5.4

0.0 2.0 4.0 6.0 8.0 10.0 12.0

Average 2001- 2006 Potential IWR Target PBSJ Proposed Target 2020 target 2050 targetCorrected Chloropyll a (ug/l)

Figure 15. Current and future target chlo rophyll-a concentrations for Segment 8.

Segment 10

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 3.8 μ g/l and 0.6372 K per m, respectively (Table 6). Figure 16 shows the statistically significant relationship between chlorophyll-a and light attenuation for Segment 10. The linear model (T able 5) was used to produce target chlorophylla values for Segment 10. Based on the Surveyed Deep-Edge water depth and K, a chlorophyll-a target of 1.9 μ g/l was calculated to maintain current de ep edge light requirements (Figure 17; Table 9). A potential IWR ta rget was calculated based upon the chlorophyll a value which exceeds the historic value by 50% fo r WBID 1968B (Sarasota Bay; 5.5 μ g/l ). The 2020 and 2050 target chlorophyll-a concentrations were calculated based on anticipated sea-level rise, therefore, projected water depths of 1.85m and 1.98m were used, respectively. To maintain current water clarity conditions with increas ed water depth, a target chlo rophyll-a concentration of 1.2 μ g/l is proposed for 2020. Due to further increases in wa ter depth, a target chlorophyll-a concentration could not be derived for Segment 10 for 2050 conditions.

20 Sarasota Bay TMDL Support DRAFT August 2007

### Results

y = 0.0205x + 0.5628
R 2 = 0.0609

0 0.5 1 1.5

2 2.5 3 3.5

0 5 10 15 20 25 30 35 40 Corrected Chlorophyll a (ug/l)Light attenuation coefficient (K per m)

Figure 16. Correlation between Light atte nuation and chlorophyll-a for Segment 10 (August 2001-February 2006).

Table 9. Segment 10 current and propos ed water depth, K and target chlorophyll-a.

Segment 10 PBSJ Proposed Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 1.81 1.85 1.98 K (per m) 0.602 0.588 0.549 Chl a ( μ g/l) 1.9 1.2 N/A

21 Sarasota Bay TMDL Support DRAFT August 2007

### Results

1.9 5.5

N/A 3.8

1.2

0.0 2.0 4.0 6.0 8.0

Average 2001- 2006 Potential IWR Target PBSJ Proposed Target 2020 target 2050 targetCorrected Chloropyll a (ug/l)

Figure 17. Current and Future target chlor ophyll-a concentrations for Segment 10.

Segment 11

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 4.5 μ g/l and 0.6837 K per m, respectively (Table 6). Figure 18 shows the statistically significant relationship between chlorophyll-a and light attenuation. The linear model (Table 5) was used to pro duce target chlor ophyll-a values for Segment 11 (Table 10). Based on the Surveyed Deep-Edge water depth and K, a chlorophyll-a target of 6.4 μ g/l was calculated to maintain current de ep edge light requirements (Figure 19; Table 10). A potential IWR targ et was calculated based upon the chlorophyll a value which exceeds the historic value by 50% fo r WBID 1968B (Sarasota Bay; 5.5 μ g/l ). The 2020 and 2050 target chlorophyll-a concentr ations were calculated based on anticipated sea-level rise using projected water depths of 1.19m and 1.32m, respectively. To maintain current water clarity conditions with increase water depth, a target chlorophyll-a concentration of 3.3 μ g/l is proposed for 2020. The proposed chlorophyll-a c oncentration for 2050 is 1.7 μg / liter.

22 Sarasota Bay TMDL Support DRAFT August 2007

### Results

y = 0.0403x + 0.5025
R 2 = 0.3239

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0 10 20 30 40 Corrected Chlorophyll a (ug/l)Light attenuation coefficient (K per m)

50

Figure 18. Correlation between Light atte nuation and chlorophyll-a for Segment 11 (August 2001-February 2006).

Table 10. Segment 11 current and proposed water depth, K and target chlorophyll-a.

Segment 11 PBSJ Proposed

Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 1.14 1.19 1.32 K (per m) 0.659 0.635 0.571 Chl a ( μ g/l) 3.9 3.3 1.7

23 Sarasota Bay TMDL Support DRAFT August 2007

### Results

5.5

3.9 3.3

1.7 4.5

0.0 3.0 6.0 9.0

Average 2001- 2006 Potential IWR Target PBSJ Proposed Target 2020 target 2050 targetChloropyll a (ug/l)

Figure 19. Current and Future target chlor ophyll-a concentrations for Segment 11.

Segment 13

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 7.7 μ g/l and 0.9993 K per m, respectively (Table 6). Figure 20 shows the statistically significant relationship between chlorophyll-a and light attenuation. The linear model (Table 5) was used to pro duce target chlor ophyll-a values for Segment 13. Based on the Surveyed Deep-Edge wate r depth and K, a chlorophyll-a target of 3.9
μ g/l was calculated to maintain current deep edge light requirements (Figure 21; Table 11). A TMDL target was developed based upon the chlorophyll a value which exceeds the historic value by 50% for WBID 1968D (Roberts Bay; 7.2 μ g/l ). The 2020 and 20 50 target chlorophyll-a concentrations were calculated based on anticipated sea-level rise and projected water depths of 1.26m and 1.39m, respectively. To maintain curre nt water clarity conditions with increased water depth, a target chlo rophyll-a concentration of 5.5 μ g/l is proposed for 2020. The proposed chlorophyll-a concentration for 2050 is 3.1 μ g/l.

24 Sarasota Bay TMDL Support DRAFT August 2007

### Results

y = 0.0364x + 0.7263
R 2 = 0.4233

0.0 1.0 2.0 3.0 4.0

0 10 20 30 40 50 6 Corrected chlorophyll a (ug/l)Light attenuation coefficient (K per

0m

Figure 20. Correlation between Light atte nuation and chlorophyll-a for Segment 13 (August 2001-February 2006).

Table 11. Segment 13 current and pr oposed water depth, K and target chlorophyll-a.

Segment 13 PBSJ Proposed

Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 1.21 1.26 1.39 K (per m) 0.959 0.927 0.838 Chl a ( μ g/l) 6.4 5.5 3.1

25 Sarasota Bay TMDL Support DRAFT August 2007

### Results

5.5

3.1 7.2 6.4 7.7

0.0 3.0 6.0 9.0 12.0 15.0 18.0

Average 2001- 2006 TMDL Target PBSJ Proposed Target 2020 target 2050 targetCorrected Chloropyll a (ug/

Figure 21. Current and Fuure target chlor ophyll-a concentrations for Segment 13.

Segment 14

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 7.7 μ g/l and 0.9105 K per m, respectively (Table 6). Figure 22 shows the statistically significant relationship between chlorophyll-a and light attenuation. The linear model (Table 5) was used to pro duce target chlor ophyll-a values for Segment 14. Based on the Surveyed Deep-Edge wate r depth and K, a chlorophyll-a target of 7.7
μ g/l was calculated to maintain current deep e dge light requirements (F igure 23; Table 12). A potential IWR target was calculated based u pon the chlorophyll a value which exceeds the historic value by 50% for WBID 1968E (Little Sarasota Bay; 8.6 μ g/l ). In comparison, the TMDL target derived by the Florida Department of Environmental Protection and adopted for the improvement of water quality in Segment 14 is 8.6 μ g/l.The 2020 and 2050 target chlorophyll-a concentrations were calculated ba sed on anticipated sea-level rise and projected water depths of 1.01m and 1.14m, respectively. To maintain current water clarity conditions with increased water depth, a target chlorophyll-a concentration of 6.6 μ g/l is proposed for 2020. The proposed chlorophyll-a concentration for 2050 is 3.8 μ g/l.

26 Sarasota Bay TMDL Support DRAFT August 2007

### Results

y = 0.0404x + 0.7078
R 2 = 0.4422

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0 10 20 30 40 5 Corrected Chlorophyll a (ug/l)Light Attenuation Coefficient (K per m)

0

Figure 22. Correlation between Light atte nuation and chlorophyll-a for Segment 14 (August 2001-February 2006).

Table 12. Segment 14 current and pr oposed water depth, K and target chlorophyll-a.

Segment 14 PBSJ Proposed

Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 0.97 1.01 1.14 K (per m) 1.017 0.975 0.861 Chl a ( μ g/l) 7.7 6.6 3.8

27 Sarasota Bay TMDL Support DRAFT August 2007

### Results

7.7 6.6

3.8 7.7 8.6

0.0 4.0 8.0 12.0 16.0

Average 2001- 2006 Potential IWR Target PBSJ Proposed Target 2020 target 2050 targetCorrected Chloropyll a (ug/l)

Figure 23. Current and Future target chlor ophyll-a concentrations for Segment 14.

Segment 16

Based on the data from August 2001 to February 2006, the average chlorophyll-a concentration and light attenuation coefficient were 5.6 μ g/l and 0.9105 K per m, respectively (Table 6). Figure 24 shows the statistically significant relationship between chlorophyll-a and light attenuation for Segment 16. The linear model (T able 5) was used to produce target chlorophylla values for Segment 16. Based on the Surveyed Deep-Edge water depth and K, a chlorophyll-a target of 4.7 μ g/l was calculated to maintain current de ep edge light requirements (Figure 25; Table 13). An IWR target was calculated based upon the chlorophyll a value which exceeds the historic value by 50% for WBID 1968F (Blackburn Bay; 5.5 μ g/l ). The 2020 and 2050 target chlorophyll-a concentrations were calculated ba sed on anticipated sea-level rise and projected water depths of 0.94 m and 1.08 m, respectively. To maintain current water clarity conditions with increased water depth, a target chlorophyll-a concentration of 4.0 μ g/l is proposed for 2020. The proposed chlorophyll-a concentration for 2050 is 2.2 μ g/l.

28 Sarasota Bay TMDL Support DRAFT August 2007

### Results

y = 0.0564x + 0.592
R 2 = 0.3536

0.0 1.0 2.0 3.0 4.0 5.0

0 1 0 2 0 3 0 4 Corrected Chlorophyll a (ug/l)Light attenuation coefficient (K per m)

0

Figure 24. Correlation between Light atte nuation and chlorophyll-a for Segment 14 (August 2001-February 2006).

Table 13. Segment 16 current and pr oposed water depth, K and target chlorophyll-a.

Segment 16 PBSJ Proposed

Target PBSJ Proposed 2020 PBSJ Proposed 2050 Depth (m at MLW) 0.90 0.94 1.08 K (per m) 0.858 0.820 0.718 Chl a ( μ g/l) 4.7 4.0 2.2

29 Sarasota Bay TMDL Support DRAFT August 2007

### Results

4.7 4.0

2.2 5.5 5.6

0.0 3.0 6.0 9.0 12.0

Average 2001- 2006 IWR Target PBSJ Proposed Target 2020 target 2050 targetCorrected Chloropyll a (ug/l)

Figure 25. Current and Future target chlor ophyll-a concentrations for Segment 16.

30 Sarasota Bay TMDL Support DRAFT August 200731 Sarasota Bay TMDL Support DRAFT August 2007 

## 4.0 Discussion

The results of this project can be summarized as follows:



##  For much of the bay, correlations between ch lorophyll-a and water clarity allow for the development of potential wate r clarity goals or “targets”



##  For much of the bay, Chlorophyll-a targets could be developed to protect seagrass resources as a “bio-indicator” of system health



##  However, Chlorophyll-a and water clarity does no t appear to be correla ted in either Palma Sola Bay or Anna Maria Sound



##  Detailed surveying of the “deep edge” of s eagrass meadows results in a multi-year annual average light requirement of approximately 31 to 46 percent of sub-surface irradiance (at MLW)



##  Surveyed deep edges are typically 17 cm deeper than “deep edges” delimited by mapping techniques



##  Surveyed deep edges typically extend 30 to 40 meters farther offshore than edges delimited by mapping techniques



##  Based on a comparison between predicted dept hs from a 1950s-era bathymetric map and current depth measurements, it appears that th e waters of Sarasota Bay are approximately 17 cm deeper now (2007) than was the case in the 1950s



##  The rate of sea level rise (SLR) that appears to have been documented in Sarasota Bay is in line with estimates of the degree of SLR expected over a 50 year timeline



##  If future SLR occurs at a similar rate, water clarity would have to be improved, to allow the same light level to penetrate to the offshor e edges of future seagrass meadows at their current locations



##  To maintain the same light penetration to future, deeper waters, chlorophyll-a levels would have to decrease by 51 to 56 percent by the year 2050, to allow seagrasses to maintain their present coverage (Table 14).

### Discussion

32 Sarasota Bay TMDL Support DRAFT August 2007 Table 14. PBSJ Proposed chlorophyll- a targets for all segments and percent reduction required to reach the proposed 2050 target.

Segment PBSJ Proposed

Target PBSJ 2020 target PBSJ 2050 target % decrease (current to 2050)

7 5.3 4.6 2.6 52
8 5.0 4.3 2.2 56
10 1.9 1.2 N/A N/A
11 3.9 3.3 1.7 56
13 6.4 5.5 3.1 52
14 7.7 6.6 3.8 51
16 4.7 4.0 2.2 53

It is not surprising that surv eyed offshore edges of seagrass meadows, delimited via snorkeling, extend farther offshore and into deep waters than offshore edges delimited via aerial photography and photointerpretation. It would be difficult to believe that aerial imagery, regardless of the technique used, would be suffici ent to pick up all the se agrass resources found in any particular area. However, the more rele vant implication of this finding is that “edges” found by snorkeling would have deep er depths, and would have diffe rent light levels at those depths than locations depicted by a map as being a “deep edge.” Fo r this reason, it is important that the type of “edge” is consistent with the literature, for de veloping minimum light requirement targets for seagrasses. For example, estimates of minimum light requirements for seagrasses determined in Tampa Bay (Dixon 199 9), Sarasota Bay (Di xon and Kirkpatrick 1995), and Lemon Bay (Tomasko et al. 2001) range as hi gh as 42 percent of immediately sub-surface irradiance. In all three of these locations, the “deep edge” used for estimating light requirements was defined by field surveying the site, and not by photointerpretation of aerial photography and mapping techniques. The choice of what “target” light level to use for maintaining seagrass coverage is an important one fo r setting water clarity targets, and thus for setting possible chlorophyll-a targets.

An additional consideration for TMDL development in Sarasota Bay is whether or not there is evidence of system-wide improvements or degrad ation in water quality, based on ambient water quality monitoring programs or other objective a ssessments. That is, is “impairment” status derived from the rules and regula tions outlined in the Impaired Waters Rule (IWR) consistent with more locally-collected data on trends in appropriate bio-indicators of system health?

In the SBEP’s document “Framework for Action”, Lowrey (1992) concluded that of the 16 baywide segments (plus the nearshore waters of th e Gulf of Mexico) in Sarasota Bay, roughly twothirds of those segments had trends in chlorophyll-a. Of those segments with trends, 93 percent of them had trends of decreasing values of ch lorophyll-a, while only one segment had a trend of increasing values. Likewise, trends for TN were found in 43 percent of SBNEP segments, with twice as many having decreasing trends as in creasing trends. For TP, 48 percent of bay

### Discussion

33 Sarasota Bay TMDL Support DRAFT August 2007 segments had significant trends, with only 10 percent of those segments showing signs of degradation over time (i.e., increasing values of TP).

For water clarity (measured as Secchi disk dept hs) 29 percent of bay segments had trends over time – all of those trends were of improving water clarity (i.e., none showed evidence of degrading water clarity).

In a later assessment of status and trends in water quality, Dixon and Heyl (1999) found that recent (1989 to 1998) trends of declining concentr ations of total nitrogen and total phosphorus (9 of 12 bay segments) were not accompanied by concurrent decreases in phytoplankton abundance, as no bay segments showed trends of decreasing chlorophyll-a concentrations during that same time period. The basis for this po tential disconnect between declining nutrient concentrations and further decreases in phytoplankton abundance (between 1989 and 1998) merits further investigation, especi ally as it relates to the finding (discussed below) of continued increases in seagrass coverage in Sarasota Bay (i.e., Kurz et al. 1999, Tomasko et al. 2005).

In the SBEP’s Framework for Action, the tech nical synthesis chapte r (Tomasko et al. 1992) outlined the finding that seagrass biomass and pr oductivity was a better indicator of segmentspecific nitrogen loads than eith er chlorophyll-a or Total Kjel dahl Nitrogen (TKN). A key finding of Tomasko et al. (1996) was that the status and trends of seagrass coverage in Sarasota Bay would be a better indicator of system “hea lth” than traditional wa ter quality monitoring
programs.
As seagrass coverage has been found to be increasi ng in Sarasota Bay in recent years (Kurz et al. 1999, Tomasko et al., 2005), these results would in dicate that findings of “impairment” for nutrients in various Sarasota Bay segments (e.g., Palma Sola Bay, Roberts Bay, Blackburn Bay) might be more a function of a po tentially locally inadequate list ing criteria via the IWR than a true indicator of a stressed ecosystem.

However, results of the depth measurements, comparing 1950’s bathymetry estimates vs. field survey estimates from 2007 suggest that sea level ri se could be an important factor to consider, when developing water quality goals for Sarasota Bay. The average increase in water depth of 17 cm, comparing 1950’s depths to 2007 estimates , calculates out to a sea level rise of approximately 3.2 cm/decade. This difference in wa ter depths is within the range of rates of measured sea level rise in St. Petersburg dur ing 1950 to 1990 (ca. 2.4 cm/decade), and estimated rates of future sea level rise (ca. 5.2 cm/decade) as outlined in Clark (1992). Should these estimates of future sea level ri se prove accurate, chlorophyll-a c oncentrations in Sarasota Bay would have to be reduced by 51 to 56 percent, to allow for the present-day light levels to penetrate to the same, but deeper, offshore e dges of future seagrass meadows in the bay.34 Sarasota Bay TMDL Support DRAFT August 2007 

## 5.0 References

Clark P. 1992. Implications of a sea-level ri se on the Sarasota Bay region. PP. 7.1-7.24. In : Sarasota Bay National Estuary Pr ogram. 1992 Framework for Action.

Dixon, L.K. 1999. Establishing light requirements for the seagrass Thalassia testudinum : an example for Tampa Bay, Florida. Pp. 9-31, In : Bortone, S.A. (ed.). Seagrasses: Monitoring, Ecology, Physiology and Management . CRC Press, Boca Raton, Florida.

Dixon, L. K. and M. Heyl (1999). Trend Analysis of Water Quality Data for the Sarasota Bay National Estuary Program. Sarasota, FL, Mote Marine Laboratory Technical Report No. 645. 61 pp. plus Appendices.

Dixon, L. K. and G. Kirkpatrick (1995). Light Attenuation with Respec t to Seagrasses in Sarasota Bay, Florida. Sarasota, FL, Mote Marine Laboratory Technical Report No.407. 53
pp.
Haddad, K.D., 1989. Habitat trends and fisheries in Tampa and Sarasota Bays. In: Estevez, E. (Ed.), Tampa and Sarasota Bays: Issues, Resources, Status, a nd Management, NOAA Estuary-of the-month Seminar Series No. 11. National Oceanic and Atmospheric Administration, Washington, DC, pp. 113–128.

Johansson, J.O.R., 1991. Long-term trends in ni trogen loading, water quality and biological indicators in Hillsborough Bay, Florida. In: Treat, S.F., Clark, P.A. (Eds.), Proceedings, Tampa Bay Area Scientific Information Sy mposium 2. Tampa Bay Regional Planning Council, St. Petersburg, Florida, pp. 157–176.

Johansson, J., Ries, T., 1997. Seagrass in Tampa Bay: historic trends and fu ture expectations. In: Treat, S. (Ed.), Proceedings, Tampa Bay Area Scientific Information Symposium 3. Tampa Bay Regional Planning Council, St . Petersburg, Florida, pp. 139–150.

Johansson, J.O.R., Greening, H., 1999. Seagrass re storation in Tampa Ba y: a resource-based approach to estuarine management. In: Bortone, S. (Ed.), Subtropical and Tropical Seagrass Management Ecology. CRC Press, Boca Raton, FL, pp. 279–293.

Kurz, R. C., D. A. Tomasko, D. Burdick, T. F. Ries, K. Patterson, a nd R. Finck. 1999. Recent trends in seagrass distributions in southw est Florida coastal waters. In: Seagrasses: monitoring, ecology, physiology, and management . Edited by: S. A. Bortone. CRC Press LLC, Boca Raton, Florida.

Lewis III, R.R., 1989. Biology and eutrophication of Tampa Bay. In: Estevez, E. (Ed.), Tampa and Sarasota Bays: Issues, Resources, Stat us, and Management, N OAA Estuary-of-themonth Seminar Series No. 11. National O ceanic and Atmospheric Administration, Washington, DC, pp. 89–112.

### References

35 Sarasota Bay TMDL Support DRAFT August 2007 Lewis, R.R., Durako, M.J., Moffler, M.D., Ph illips, R.C., 1985.Seagrass meadows of Tampa Bay—a review. In: Treat, S.F., Simon, J.L. , Lewis, R.R., Whitman, R.L. (Eds.), Proceedings, Tampa Bay Area Scientific In formation Symposium. Florida Sea Grant Publication 65, Burgess, Minneapolis, pp. 210–246.

Lewis, R.R., Clark, P.A., Fehring, W.K., Green ing, H.S., Johansson, R.O., Paul, R.T. 1998. The rehabilitation of the Tampa Bay Estuary, Fl orida, USA, as an example of successful integrated coastal management. Marine Pollution Bulleting 37, 468-473.

Lowrey, S. S., L. K. Dixon, et al. (1993). Water and Sediment Qu ality: Trends and Status for Sarasota Bay. Sarasota, Mote Marine La boratory Technical Report No. 254. 108 pp. plus Appendices.

SBEP 1992. Sarasota Bay Framework for Acti on. Sarasota Bay National Estuary Program, Sarasota, Fl.

SBEP 1995. Sarasota Bay: The Voyage to Paradise Reclaimed, 1995. The Comprehensive Conservation and Management Plan for Sa rasota Bay. Sarasota Bay National Estuary Program, Sarasota, Fl.

Schefler, William C. 1979. Statistics for th e Biological Sciences Second Edition, pp 25-A7.

Tomasko, D., M. Alderson, P. Clark, J. Culter, K. Dixon, R. Edward s, E. Estevez, M. Heyl, S. Lowrey, Y. Sheng, and J. Stevely. 1992. Technical Synthesis of Sarasota Bay. Pp. 14.1- 14.16. In : Sarasota Bay National Estuary Program. 1992 Framework for Action.

Tomasko, D.A., C.J. Dawes, and M.O. Hall . 1996. The effects of anthropogenic nutrient enrichment on turtle grass ( Thalassia testudinum ) in Sarasota Bay, Florida. Estuaries. 22: 592-602.

Tomasko, D.A. , D.L. Bristol, and J.A. Ott. 2001. Assessment of present and future nitrogen loads, water quality, and seagrass ( Thalassia testudinum ) depth distribution in Lemon Bay, Florida. Estuaries. 24: 926-938.

Tomasko, D.A., Corbett, C.A., Greening, H.S., and G.E. Raulerson. 2005. Spatial and temporal variation in seagrass coverage in Southwest Florida: assessing the relative effects of anthropogenic nutrient load reductions and rain fall in four contiguou s estuaries. Marine Pollution Bulletin . 50: 797-805.

Virnstein, R. W., Avery, W. and Johansson, J. O.R. 2000. On Defining the “Edge” of a Seagrass Bed. Pp. 169-170. In Proceedings of a Symposium: Seagrass Management: It’s Not Just Nutrients! St. Petersburg, Florida.