# Tampa Bay Estuary Program Tracking Progress Toward Its Nitrogen Management Goals:

Fifth-Year Assessment of Bay Water Quality Indicators and Models

Prepared for:



# Tampa Bay Estuary Program

Mail Station I-1/NEP

100 8 th 

## Avenue SE St. Petersburg, FL 33701

Prepared by:

1155 Eden Isle Drive NE St. Petersburg, FL 33704

July 2001

## FOREWORD

This report was prepared by Janicki Envir onmental, Inc. under the direction of Mr. Dick Eckenrod and Ms. Holly Greening of the Tampa Bay Estuary Program. This work was performed under Contract No . T-98-06 for the Tampa Bay Estuary
Program.

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## ACKNOWLEDGMENTS

We thank Mr. Dick Eckenrod and Ms. Holly Greening of the TBEP for their helpful

comments and direction in the course of this work. We also thank the TBEP/SWFWMD Joint Water Quality Subc ommittee for its review, insight, and assistance in the evaluations performed. Special thanks are directed to Mr. Roger Johansson, City of Tampa Department of Sanitary Sewers Bay Study Group, for sharing his knowledge of Tampa Bay gained from years of monitoring in its waters, and providing data for this project. Specia l thanks are also directed to Mr. Craig Kovach, CF Industries, for his assistance in obtaining data necessary for the completion of this work and his helpfu l comments. We also thank Mr. Tom

Cardinale and Mr. Richard Boler of th e Environmental Protection Commission of Hillsborough County, Mr. Andy Squires and his staff at the Pinellas County Department of Environmental Managemen t, Mr. Rob Brown and his staff at the Manatee County Environmental Management Department, and Mr. Charles Kovach and his staff at the Florida Department of Environmental Protection for their assistance in obtaining data for this project.

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## BACKGROUND

The Tampa Bay National Estuary Progra m (TBNEP) developed a Comprehensive Conservation & Management Plan (CCMP), entitled Charting the Course, which was the culmination of five years of effort aimed at bringing together the participants of the TBNEP to address the key environmenta l issues affecting Tampa Bay. In February 1998 the Tampa Bay National Estuar y Program Interlocal Agreement was executed by the following entities:

• City of Clearwater

• City of St. Petersburg

• City of Tampa

• Florida Department of Environmental Protection

• Florida Marine Research Institute

• Florida Game and Freshwater Fish Commission

• Hillsborough County

• Hillsborough County Environmen tal Protection Commission

• Manatee County

• Pinellas County

• Southwest Florida Water Management District

• Tampa Port Authority

• Tampa Bay Regional Planning Council

These parties and the U.S. Environmenta l Protection Agency and the U.S. Army Corps of Engineers have approved and adopt ed the goals set forth in the CCMP. These goals address such issues as water & sediment quality, fish & wildlife habitats, spill prevention & response, a nd dredging and dredged material management. The Interlocal Agreement requires the parties to make their best effort s to meet the goals

within the time frames defined in the CCMP. Generally, these goals are to be met in a cooperative fashion with attempts to achieve all goals in a cost-efficient manner. The Tampa Bay Nitrogen Management Cons ortium represents the only efforts to meet a goal where the individual par ties have specific responsibilities. The Interlocal Agreement also requires the par ties to review progre ss toward these goals at least every five (5) years.

The Interlocal Agreement also provided for the creation of th e Tampa Bay Estuary Program (TBEP). The TBEP is comprised of a Policy Board, Management Board, Technical Advisory Committee (TAC), and Citizens Advisory Committee (CAC). In simple terms, the TBEP was established to oversee and assist in the implementation of the CCMP. TBEP has no regulatory or taxation powers.

The implementation of the CCMP will genera lly be achieved by implementation of the Action Plans set forth in that document. In 1998, the TBEP published Partnership for Progress , an action plan for the Tampa Bay Nitrogen Management

1Consortium. This plan was the culminati on of about two years of planning. The plan defined nitrogen load reduction target s, by bay segment, and specific projects and their expected nitrogen load reducti on to which the consortium partners are committed. The plan also sets out an element for tracking pr ogress toward load reduction targets. Another basic tenet of th e plan is that tracking will be reviewed every five years.

The objective of this report is to summarize the results from a series of investigations whose purpose was to assess the progress to ward meeting the nitrogen management goals of the Tampa Bay Estuary CCMP. Sp ecifically, the status of a number of bay

indicators is assessed relative to histori cal conditions and desired bay management targets. Also, the models employed to develop the nitrogen management strategy are reviewed, using data collected sinc e 1994, to determine if model refinements and ultimately modifications to the load management strategy may be necessary.



## Tampa Bay Nitrogen Management Strategy Paradigm

The CCMP specifically addressed several ma jor issues, including water quality and habitat loss. The loss of seagrasses in Ta mpa Bay drew particular interest, given their important role in the ecological f unctioning of the bay. Seagrasses provide critical habitat for recreationally and co mmercially important fish and invertebrate species. Seagrasses in Florida provide ju venile nursery and adult feeding areas for red drum, spotted seatrout, spot, silver perch, sheepshead, snook, shrimp, and the bay scallop (Zieman and Zieman, 1989). Seagrass meadows are also important feeding areas for the Florida manatee. Sea grasses serve to impr ove water quality by reducing nutrients in the water column and are an important component of the energy and nutrient cycles in coastal environments.

Seagrass extent and condition can be impacted by many factors, including water quality, physical factors such as prop scarri ng and currents, seagrass disease, and location of seagrass beds in relation to offshore transverse sandbars. The TBNEP Technical Advisory Committee (TAC) recogn izes that these and other factors may affect progress towards reaching adopted seag rass restoration goals, and is currently initiating actions which will assist with addre ssing factors in addition to water clarity and quality (including the initiation of meas uring the depth of water at various seagrass beds around the bay, and the mon itoring of potential seagrass disease).

Actions needed to address additional factor s, such as the bay-wide effects of prop scarring or the location of various seagra ss beds, will be included in discussions of future monitoring needs.

In Tampa Bay, seagrasses typically grow at depths no deeper than six to eight feet. Light is one of the limiting factors on the depth at which seagrasses can be found. Light requirements for growth vary by se agrass species. Turtle grass, the most common seagrass species in Tampa Bay, ha s an estimated light requirement of

220.5% of the incident subsurface light (Dixon and Leverone, 1995). For the purposes of seagrass restoration target settin g, this was assumed to be the minimum light requirement for seagrasses in Tampa Bay (Janicki and Wade, 1996).

To address the issue of se agrass habitat loss, recommended seagrass protection and restoration targets were developed (Janicki et al., 1995). Seagrass restoration targets were determined by comparing 1990 seag rass extent to that observed in 1950. Seagrass targets were defined as those porti ons of Tampa Bay that had seagrasses in 1950, did not have seagrasses in 1990, and had not been permanently altered to preclude restoration of seagrasses.

As discussed above, the TBNEP developed the Nitrogen Management Strategy to strive toward the seagrass restoration goal s. The Strategy seeks to prevent future impacts due to excessive nitrogen loadin gs to Tampa Bay. Excessive nitrogen loading can fuel algal growth to the point where the phytoplankt on standing stock is sufficiently large to impair water clarity . Such conditions can stress submerged seagrasses that are intolerant of low light conditions. Such was the case prior to the early 1980s, and seagrass loss was significant, particularly along the deep edge of the seagrass beds. Physical alteration through dredging and filling activities has also

contributed to some of the losses since the early 1980s. The restoration of lost seagrasses and protection of existing beds, th erefore, depends at least in part on the maintenance of a light environment conducive to seagrass growth and reproduction.

A paradigm that relates nitr ogen loading to chlorophyll and seagrass was utilized, as shown in Figure 1.

Figure 1. The TBEP Nitrogen Management Strategy Paradigm.

An empirical modeling approach was taken to define quantitatively the relationships between TN loads and chlorophyll a conc entrations and between chlorophyll a concentrations and light attenuation (Jani cki and Wade, 1996). These relationships were defined for those bay segments (Fig ure 2) for which sufficient data existed.

3Figure 2. Bay segments of Tampa Bay.

4A corollary to the paradigm deals with the relationship between nutrient loading and dissolved oxygen (DO) concentrations in the estuary. Nutr ient over-enrichment clearly can lead to excessive algal grow th and biomass. The organic matter generated can support rates of oxygen c onsumption that exceed rates of oxygen production and mixing, leading to the esta blishment of hypoxia (DO < 2 mg/L) in productive estuarine waters. The northern Gulf of Mexico near the mouth of the Mississippi River is a notable example of such a condition (NRC, 2000). Hypoxic conditions can significantly influence the distribution and abundance of benthic

macroinvertebrates and fishes and ultimatel y the trophic dynamics of a water body. Given the potential for significant impacts on important bay resources, tracking the response of DO concentrati ons in Tampa Bay to changes in nitrogen loading is another critical component of this assessment.



## STATUS OF BAY INDICATORS

To satisfy the objective of tracking progre ss toward the goals of the TBEP, four critical bay indicators were examined:

• Seagrass areal extent

• Chlorophyll a concentrations

• Nitrogen loading, and

• DO concentrations.

Generally, the status of these indicator s of bay health as of 1998 has been examined. In some cases, data colle cted in 1999 have been included in the analyses.

SEAGRASS EXTENT

The status of seagrass areal extent in Tampa Bay has been reviewed by Pribble et al. (2000) and Tomasko (2000). Several conclusions were drawn:

• From 1990 to 1996, seagrass acreage show ed a net increase of 1,690 acres in the bay;

• More than half of the increa se observed between 1990 and 1996, approximately 900 acres, occurred in Boca Ciega Bay;

• The rate of increase in bay-wide seagrass acreage slowed from 1994 to 1996, when seagrass acreage increased by a pproximately 400 acres, compared to

the increases observed between 1992 and 1994 (700 acres) and between 1990 and 1992 (600 acres);

5• Between 1994 and 1996, seagrass acreage declined by 150 acres in Old Tampa Bay and by 240 acres in Middle Tampa Bay;

• Results from the 1999 areal survey indicat e that as much as 2,000 acres of seagrasses (representing an 8% declin e) were lost since 1996. The losses were most notable in Old Tampa Bay, especially along its western shore.

The loss of seagrass in Tampa Bay be tween 1996 and 1999 was similar to that found in other regional estuaries, ranging fr om 7% in Charlotte Harbor to 10% in Sarasota Bay. These losses are notab le but perhaps understandable given the extremely unusual meteorological conditions due to the El Niño – La Niña effects

observed in 1997 and 1998.

Recent observations also led to concerns that seagrass goals may not be achieved solely by nitrogen load management. Between the early 1980s and 1996, seagrass acreage in Tampa Bay showed a relativel y continuous increase, although varying

rates of increase were found between monitoring periods. However, there

continued to be areas that did not support seagrass into which seagrass was expected to expand. These expectations were based on considerations including water quality, water column depth, and the pr esence of seagrass in the 1950 period.

The possible reasons for the continued abse nce of seagrass in these areas include those associated with physical impacts and those associated with water quality impacts. Physical impacts may include changes in wave energy and loss or

movement of transverse sandbars. Wate r quality impacts may include relatively poorer water quality in near-shore shallo w areas than observed in the deeper offshore areas by the ambient monitoring pr ograms in the bay. These alternative hypotheses were investigated at a symposiu m sponsored by TBEP in 2000. A TBEP seagrass working group was established follo wing the symposium, and this working group is further examining these hypotheses.

Along these lines, an investigation of spa tial differences in water quality resulted from the finding of appreciable reductions in seagrass in Old Tampa Bay between 1996 and 1999, especially along the western shoreline. Statistically significant differences were found in chlorophyll and clarity, with the western shore water quality poorer than that along the eastern shore. The TBEP seagrass working group is examining both additional physical and wate r quality factors and their influences on

seagrass recovery.

6CHLOROPHYLL a CONCENTRATIONS

Chlorophyll a targets that were consistent with light requirement s of seagrasses were previously established (Janicki and Wade, 1996). These targets were:

• Old Tampa Bay – 8.5 μ g/L

• Hillsborough Bay – 13.2 μ g/L

• Middle Tampa Bay – 7.4 μ g/L

• Lower Tampa Bay – 4.7 μ g/L

Two studies were completed in 2000 to asse ss the status of Tampa Bay relative to these targets.

Janicki et al. (1999) and Janicki and Pribble (2000) evaluat ed and applied a methodological framework for assessing ambient conditions and identifying commensurate management responses to devi ations from the desired conditions. The method was developed with the assist ance of the TBEP/SWFWMD Joint Water Quality Subcommittee to determine if a dopted seagrass acreage goals and water quality targets are being achieved. Thi s method employed a matrix that incorporated the magnitude and dura tion of chlorophyll and light target exceedances from target levels. Additiona lly, consideration of changes in seagrass extent are included in a separate decision tree, and in the event of no increase in seagrass extent, more severe management responses may be examined.

The decision matrix of the st atus tracking process identifies appropriate categories of management actions in response to various outcomes of the chlorophyll a and light

attenuation decision formulations.

Decision matrix identifying appropriate categories of management actions in response to various outcomes of the moni toring and assessment of chlorophyll a and light attenuation data.

LIGHT ATTENUATION CHLOROPHYLL Outcome 0 Outcome 1 Outcome 2 Outcome 3

Outcome 0 GREEN YELLOW YELLOW RED

Outcome 1 YELLOW YELLOW YELLOW RED

Outcome 2 YELLOW YELLOW RED RED

Outcome 3 YELLOW RED RED RED

7The recommended management actions resu lting from the decision matrix are classified by color into three categories, as follows:

• GREEN

- “Stay the course”; partners continue with planned projects to implement the CCMP. Data summa ry and reporting via the Baywide Environmental Monitoring Report and annual assessment and progress

reports.

• YELLOW

- TAC and Management Board on cauti on alert; review monitoring data and loading estimates; attempt to identify causes of target exceedances; TAC report to Management Board on findings and recommended responses

if needed.

• RED - TAC, Management and Policy Boar ds on alert; review and report by TAC to Management Board on reco mmended types of responses. Management and Policy Boards take appr opriate actions to get the program

back on track.

The decision matrix was applied to the ch lorophyll a concentration and water clarity data collected in 1995 through 1999 and th e following results were obtained:

Decision matrix results for the period 1995 through 1999.

BAY SEGMENT

YEAR Old Tampa
Bay Hillsborough
Bay Middle Tampa Bay Lower Tampa Bay

1995 RED YELLOW RED YELLOW

1996 YELLOW GREEN YELLOW GREEN

1997 YELLOW GREEN RED YELLOW

1998 RED RED RED RED

1999 YELLOW GREEN YELLOW YELLOW

Clearly, the increased nitrogen loading due to the higher than normal rainfall during 1997 and 1998 (discussed below) resulted in less than desired conditions in Tampa Bay during that period. Elevated chlor ophyll a concentrations and reduced light penetration were found during this period. However, the bay responded favorably to the apparent reduction in loading during 1999.

8A second assessment approach entailed exami nation of long-term trends in water quality in Tampa Bay (Janicki et al., 2000a). The long-term record of water quality in Tampa Bay points to three distinctive periods of water quality conditions in the bay. Relatively poor conditions existed from the mid-1970s to the early 1980s, a transitional period to improved cond itions followed until the mid-1980s, and a period of relatively good water quality cond itions has persisted since. Thus, longterm improvements in the trophic st atus of the bay have been observed.

These improvements have occurred despite continuing urbanization and growth in the watershed since the early 1980s. The relatively good water quality conditions persisting since the mid-1980s support the contention that nitrogen management activities are working, precluding increa sing nitrogen loads in the watershed typically considered concomitant with increasing development.

Throughout the period of record, Hillsboroug h Bay has reflected the poorest water quality conditions of the mainstem bay segm ents. The best water quality conditions are typically observed in Lower Tampa Ba y. Comparison with the other five bay segments shows intermediate water quality conditions between those in Hillsborough Bay and Lower Tampa Bay. Long-term declines in nutrient concentrations have also occurred in tributaries to the bay.

As noted above, concern about the lack of seagrass response to apparently improved water quality conditions led to a comparison of water quality between the

western and eastern shore areas of Old Ta mpa Bay. Chlorophyll a concentrations were greater and Secchi disc depths were shallower in sites along the western shore than in sites along the eastern shore. The differences were grea test in the western

sites that are located in areas where expected seagrass growth has not been

observed in the 1990s.

NITROGEN LOADING

Examination of the nitrogen loading is also a critical component of this assessment. To this end, nitrogen loading estimates were updated through 1998 (Pribble et al., 2001) and the predicted nitrogen loadin g estimates for 2010 were also refined based on the most recent knowledge of land use change and anticipated changes in point source discharges a nd atmospheric nitrogen emi ssions from both stationary and mobile sources (Janicki et al., 2001b).

1995-1998 Loading Estimates - Annual loadings in 1995, 1997, and 1998 were generally higher than those observed dur ing the 1985-1994 period. Specifically, the loadings during these three years exceeded the “hold the line” loadings established by the Nitrogen Management Consortium, which were based on the average TN loadings of the 1992-1994 period.

9Examination of the TN loadings data sugges ts that much of the increase in TN loadings could be explained by the higher rainfall and resultant hydrologic loadings observed in 1995, 1997, and 1998. Most noticeably, the El Niño event of 1997- 1998 resulted in relatively higher rainfalls and loadings compared to observations from the period of record. Increases in nonpoint source loadings were the primary

contributors to the increased annual load ings. It should be noted, however, that nitrogen management actions being practiced in the watershed likely mitigated the impacts of the high rainfall period with re spect to nitrogen loadings to the bay.

2010 Loading Estimates – The future loading estimates for industrial point sources are approximately half of the current cond ition loading estimates (1998) from these sources. This is largely the result of the unusually high discharges during the current period in response to the high rainfall experienced during that the period. Future loading estimates for domestic point source facilities are very similar to the estimates for the current period. The futu re loading estimates from material losses are approximately 13% higher than for th e current period, reflecting the expected industry growth rate of 1% annually.

As a result of planned decreases in nitr ogen emissions from the TECO facilities, future atmospheric deposition loading estimat es may be as much as approximately

50% less than the current condition loading from this source.

The future nonpoint source loading estimat es are not appreciably different from those for the current condition, despite the future land use having a larger proportion of urban land use than the cu rrent period. This is likely due to differences in typical nutrient concentrati ons in runoff from agricultural and urban land uses and the expected load attenuation from any newly developed urban area.

In summary, the total annual nitrogen lo ading estimates for 2010 are approximately 700 tons less than for the current condition, largely due to the predicted declines in atmospheric deposition and industr ial point source loadings.

HYPOXIA

As discussed above, reductions in bottom DO concentrations are a typical response

to nutrient over-enrichment of estuarine waters. Thus, as n itrogen loading in particular changes then changes in bo ttom DO concentrations should result. If these changes are severe enough, stressful and potentially lethal conditions can

result.

To address the concerns about the extent of hypoxia (DO < 2 mg/L) in Tampa Bay, Janicki et al. (2001c) examined the spatial and temporal nature of hypoxia in the bottom waters of the bay. Hypoxic cond itions are typically found in late summer, primarily in Hillsborough Bay and less freque ntly in Old Tampa Bay. In September

101998, for example, hypoxic conditions extended over approximately 19 km 2 ; most of this area of hypoxia was found in H illsborough Bay. The frequency of hypoxic conditions observed during the study period in each bay segment is as follows:

• Hillsborough Bay – 26%

• Old Tampa Bay – 1%

• Middle Tampa Bay – <1%

• Lower Tampa Bay - < 1%

• Boca Ciega Bay - 0%

• Terra Ceia Bay and Manatee River – 0%

No significant temporal trends in the areal extent of hypoxic conditions were found. The year-to-year variation in the extent of hypoxia is significan tly correlated with rainfall, river flow, the degree of stratifica tion, and nitrogen loads to Hillsborough Bay. Monthly monitoring data reveal that the duration of hypoxia is typically two months or less, while diel monitoring data reveal that at an hour ly temporal scale, the duration of hypoxia is typically six hours or less.

Bottom DO concentration declined in Hillsborough Bay and Old Tampa Bay from 1976 through 1998, although the rate of de cline was small. These results were largely due to the difference in relatively high bottom DO values between the late 1970s and early 1980s period and during the period since 1985. No change in the bottom DO values in the lower portion of the observed range of concentrations was apparent during the early part of the reco rd. Thus, while a statistically significant trend was detected, more stressful c onditions have not necessarily resulted.

Another note of interest emerged from this investigation. Mid-day DO measurements comprise the majority of the data available to assess hypoxia in Tampa Bay. Comparison of these mid-day data to minimum DO data derived from a series of diel DO surveys indicates th at the mid-day data correctly reflect the occurrence of hypoxia approximately 75% of the time. There also appears to be a relationship between mid-day and mini mum DO; however, more data will allow improvement in the quantification of this relationship.



## MODEL REVIEW AND UPDATES

The second major element of this assessmen t of progress toward bay quality targets is the review of the models that provide the basis of the nitrogen loading strategy paradigm described above. An empirical modeling approach was taken to define quantitatively the relationships between TN loads and chlorophyll a concentrations and between chlorophyll a concentrations and light attenuation (Janicki and Wade,

1996).

11Chlorophyll a – Light Attenuation Model - A review of the chlorophyll a – light attenuation regression model which entaile d application of the ambient data collected from 1995 through 1998 to the mode l derived from data collected during the 1986-1994 period has been completed (Jani cki et al., 2001d). In general, the chlorophyll a – light model explains the obser ved variation in light attenuation as a function of chlorophyll a concentrations. Ho wever, there appears to be a small bias in the predicted Z values (dep ths to which 20.5% of the incident light penetrates) at low chlorophyll a concentrations. Spec ifically, the Z values were somewhat shallower during the 1995-1998 period than had been predicted by the model

based on the 1986-1994 data. The bias is expressed at both monthly and annual time scales. A regression model based on data from the extended time period of 1986 through 1998 was examined and the regr ession coefficients from this model were compared to those from the orig inal model based on 1986-1994 data. Neither the monthly-specific intercept estimates nor the slope estimates from these two models were sign ificantly different.

Several hypotheses emerged that might exp lain the observed bias. Initially, the residuals (the differences between the predicted and observed Z values) were plotted against turbidity and color to exami ne whether the variation in either of

these variables was related to the residuals. No significant relationships were found. A second hypothesis was that differences in solar radiation might exist between the two periods of interest. No significan t differences between periods in solar

radiation estimates were detected. A third hypothesis entailed changes in the methods employed to collect and/or an alyze the chlorophyll samples between the two periods. No relevant differences in either field or laboratory methods were reported.

Another hypothesis that might explain the observed bias is a change in phytoplankton community structure that coul d result in changes in light attenuation per unit of algal biomass. Phytoplankt on community composition data have been collected by the City of Tampa Bay Study Group since 1978, and can be used to test this hypothesis. Preliminary indicati ons point toward a shift in community dominance in Hillsborough Bay from blue-g reen algae prior to 1995 to diatoms in the succeeding period.

Nitrogen Loading – Chlorophyll a Model – A Vollenweider-type regression model

that relates nutrient load ing to phytoplankton biomass was developed for Old Tampa Bay, Hillsborough Bay, and Middl e Tampa Bay (Janicki and Wade, 1996). The model included both external nitrogen loading estimates to each segment and the flux of nitrogen between bay segmen ts (for example, between Hillsborough Bay and Middle Tampa Bay). The inclusion of the inter-segment fluxes greatly improved

the model since this source of nitrogen may be significantly greater than the external load to a given bay segment. The general form of the model was:

12Chlorophyll a = f {(external load+inter nal flux), monthly-specific intercept}

The monthly loading estimates from th e period of 1995-1998 and the chlorophyll a

concentration data were used to test the model developed on data collected during the 1986-1994 period (Janicki et al., 2001e). The results from this analysis reflect very good correspondence between pred icted and observed chlorophyll a concentrations. Thus, the relationship betw een nitrogen loading and algal biomass has been relatively consistent dur ing the period of 1986 through 1998.

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## CONCLUSIONS AND RECOMMENDATIONS

Several conclusions and recommendations can be drawn from this assessment:

• Nitrogen loading to Tampa Bay was greater during the 1995-1998 period than during the 1992-1994 period due to higher than normal rainfall.

• Generally, water quality has improved significantly in Tampa Bay since the mid-1980s, especially with respect to those water quality constituents related to the productivity of the estuary – chlorophyll a concentrations, nutrient concentrations, water clarity, and disso lved oxygen. However, “hot spots”

do exist where localized occurrences of degraded water quality are found (western shore of Old Tampa Bay, McKay Bay) and should be closely

monitored.

• Undesired water quality responses to higher than normal rainfall do occur but the bay also displays an ability to respond favorably to reduced nutrient loading.

• While seagrasses declined between 1996 and 1999, the decline was within the range of that noted in other estu arine systems in the region, and was perhaps understandable given the extreme rainfall in 1997-1998.

• Areas where seagrass growth should be expected based on apparent ambient water clarity but has not been observed exist. The seagrass working group is examining factors other than water clar ity alone that may be more important

in these areas. These factors shoul d be examined in the next five-year period.

• The models that comprise the TBEP Nitrogen Loading Paradigm reflected different degrees of similarity to the or iginal model constructs. Output from the loading-chlorophyll a model showed close agreement between observed and predicted chlorophyll a concentrati ons. There was a small bias in the light attenuation values predicted by the chlorophyll a – light attenuation model. No readily apparent cause for th is bias could be found, but it may be that changes in phytoplankton commun ity composition have contributed to this bias. Continued monitoring and analysis of the ambient chlorophyll a concentrations and water clarity is need ed to ensure factor s other than algal biomass are not contributing significan tly to water clarity in the bay.

• Given the observed responses to changes in nutrient loading and the current status of bay indicators associated with its trophic state, there does not appear to be compelling evidence to deviate from the current nitrogen

management strategy.

14• Appropriate management actions should be identified and applied to address additional factors that are influencing the restoration of seagrasses. Continued seagrass monitoring should occur to support the efforts of the seagrass working group examining these additional factors.

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Janicki, A. and D. Wade. 1996. Estimatin g Critical External Nitrogen Loads for the Tampa Bay Estuary: An Empirically Based Approach to Setting Management Targets. Prepared for: Tampa Bay National Estu ary Program. Prepared by: Coastal Environmental, Inc. Tampa Bay Nationa l Estuary Program Technical Publication

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Janicki, A.J., and J.R. Pribble. 2000. Establishing a Process for Tracking Chlorophyll-a Concentrations and Light Atte nuation in Tampa Bay. Prepared for: Tampa Bay Estuary Program. Prepared by: Janicki Environmental, Inc.

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Janicki, A.J., J.R. Pribble, H. Zarbock, S. Janicki, and M. Winowitch. 2001b. Model-Based Estimates of Total Nitrogen Loading to Tampa Bay: Updated Current and 2010 Conditions. Prepared for: Tamp a Bay Estuary Program. Prepared by: Janicki Environmental, Inc.

Janicki, A.J., J.R. Pribble, and M. Winowitc h. 2001c. Examination of the Spatial and Temporal Nature of Hypoxia in Tampa Ba y, Florida. Prepared for: Tampa Bay Estuary Program. Prepared by: Janicki Environmental, Inc.

Janicki, A.J., J.R. Pribble, and S. Janicki. 2001d. Tampa Bay Es tuary Program Model Evaluation and Update: Chlorophyll a – Li ght Attenuation Relationship. Prepared for: Tampa Bay Estuary Program. Pr epared by: Janicki Environmental, Inc.

Janicki, A.J., J.R. Pribble, and S. Janicki. 2001e. Tampa Bay Estuary Program Model Evaluation and Update: Nitrogen Load - Ch lorophyll a Relationship. Prepared for:
Tampa Bay Estuary Program. Prepar ed by: Janicki Environmental, Inc.

16National Research Council (NRC). 2000. Clean Coastal Waters . National Academy Press. Washington, D.C.

Pribble, J.R., A.J. Janicki, and M. Winow itch. 2000. A Summary of Seagrass Coverage Data for Tampa Bay: Data Report 1997. Prepared for: Tampa Bay Estuary Program. Prepared by: Janicki Environmental, Inc.

Pribble, R., A. Janicki, H. Zarbock, S. Janicki, and M. Winowitch. 2001. Estimates of Total Nitrogen, Total Phosphorus, Total Suspended Solids, and Biochemical Oxygen Demand Loadings to Tampa Bay, Florida: 1995-1998. Prepared for: Tampa Bay Estuary Program. Prepared by: Janicki Environmental, Inc.

Tampa Bay National Estuary Program (TBNEP). 1996. Charting the Course: The Comprehensive Conservation and Management Plan for Tampa Bay . Tampa Bay National Estuary Program in cooperation w ith the U.S. Environmental Protection Agency, Region IV.

Tampa Bay Estuary Prog ram (TBEP). 1999. Partnership for Progress, the Tampa Bay Nitrogen Management Cons ortium Action Plan 1995-1999 . Tampa Bay Estuary Program, St. Petersburg, FL.

Tomasko, D. 2000. Presentation of Octobe r 20, 2000, to TBEP Technical Advisory Committee. Dr. David Tomasko, Southwes t Florida Water Management District SWIM Department.

Zieman, R.C. and R.T. Zieman. 1989. The Ecology of the Seagrass Meadows of the West Coast of Florida: A Community Profile . U.S. Fish. Wildl. Serv. Biol. Rep. 85(7-

2 5 )

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