### Executive Summary

This report was prepared by the Tampa Bay Estuary Program (TBEP), in cooperation with local scientists and the Florida Department of Environmental Protection (FDEP) , to support the development of numeric nutrient criteria for Tampa Bay. The primary purpose of the proposed numeric nutrient criteria is to protect healthy, well

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

The Tampa Bay estuary is located on the eastern shore of the Gulf of Mexico in Florida. At 882 km 2 

### , it is Florida’s largest open water estuary. More than 2 million people live in the 5700 km 2 

### watershed, with the population projected to double by 2050. Land use in the watershed is mixed, with about 40% of the watershe d undeveloped, 35% agricultural, 16% residential, and the remaining commercial and mining. Major habitats in the Tampa Bay estuary include mangroves, salt marshes
, and submerged aquatic vegetation.

Between 1950 and 1990, an estimated 40

- 50% of the seagras s acreage in Tampa Bay was lost due to excess nitrogen loading and related i ncreases in algae concentration which caused light limitation detrimental to seagrass survival and growth. In 1980, all municipal wastewater treatment plants were required to prov ide Advanced Wastewater Treatment (AWT) for discharges directly to the bay and its tributaries. In addition to the significant reductions in nitrogen loadings from municipal wastewater treatment plants, stormwater regulations enacted in the 1980s also res ulted in reduced nitrogen loads to the bay. Estimates for average annual total nitrogen loadings to Tampa Bay for 1976 are more than 2 times as high as current (2003

- 2007) estimates.

A key focus of local resource managers has been to establish nitrogen loading targets for Tampa Bay to
encourage seagrass recovery. A number of studies in the 1990s clearly established that nitrogen was the limiting nutrient in the Tampa Bay estuary and that phosphorus loadings to the bay from the enriched Bone Valley region were not controlling estuarine production. In 1996, local government and agency partners of the Tampa Bay Estuary Program ( TBEP ) approved a long

- term goal to restore 95% of the seagrass coverage observed in 1950. Also in 1996, the Tampa Bay Nitrogen Man agement Consortium ( TB NMC), a public

- private partnership convened by the TBEP, was formed. In 2009, the
TB NMC collaboratively defined nitrogen load allocations for all major sources to Tampa Bay in order to support the seagrass restoration goals.

Both phosphorus and nitrogen (N) levels have been stable and/or declining in the major bay segments of Tampa Bay over recent decades . Additionally, as supported through the TB NMC’s process to develop N load allocations for Tampa Bay, the N delivery (i.e. N load per unit hydrologic input) from the watershed to the major bay segments of the estuary has been declining since 1985. With implementation of the adaptive nutrient management plan adopted by the TB NMC and FDEP through its Reasonable Assurance process, the maintenance of full aquatic life support within the Tampa Bay estuary has been evidenced by stable water quality conditions (chlorophyll a thresholds achieved >85% of the time since 1996), the expansion of seagrass resources (>3,200 ha since 1982), and a stable, well

- balanced population of benthic and nekton species

. As such, the nutrie nt regime of the recent record is protective of full aquatic life support, and the goals of the TB NMC to maintain N loads at levels consistent with the 2003

- 2007 period wil l ensure that the recovery of Tampa Bay is sustained.

Contributors

Dr. Tony Janicki (Janicki Environmental, Inc.); Holly Greening and Ed Sherwood (Tampa Bay Estuary Program); Tampa Bay Nitrogen Management Consortium; FDEP

### Nutrient Criteria Technical Support Document Tampa Bay

Draft 2 August 2010 Table 1a. Checklist of nutrient enrichment symptoms in Tampa Bay

- = Empty cell/no data; N/A = Not available Response Variable Observed Historically or Currently? Explanation Source

Low dissolved oxygen (DO) (hypoxia/anoxia) Yes, limited in space and time Typically, the lowest dissolved oxygen conditions occur during the summer months in Hillsborough Bay; however, no apparent increasing trends have been detected for the areal extent of hypoxia during these months in this bay segment . Hypoxic events in this bay segment appear to be largely driven by physical processes rather than nutrient effects. Janicki et al. 2001; Poe 2006.

Reduced clarity No. Long

- term monitoring of bay water clarity via secchi disk depths by the EPCHC has indicated a significant improvement. Sherwood 2010.

Increased chlorophyll

a concentrations No. Long

- term monitoring of bay chlorophyll

- a concentrations by the EPCHC has indicated a significant decline. Sherwood 2010.

Phytoplankton blooms (nuisance or toxic) Yes, limited in space and time Red tide blooms originating in the Gulf of Mexico have occasionally entered the lower bay. Most recently in upper Tampa Bay, nuisance blooms of Pyrodinium bahamense have occurred as a result of anomalous spring/summer rainfall events in 2008 and 2009. Blooms have not reoccurred in 2010. Phlips et al. 2006; Badylak et al. 2007; Heil et al. 2007. Problematic epiphyte growth No No significant trends in epiphyte growth have been reported as result of monitoring conducted by the Tampa Bay Interagency Seagrass Monitoring Program. Avery and Johansson 2010. Problematic macroalgal growth No Macroalgal blooms have been reported and observed in the past; however, nuisance blooms have not occurred over the recent period or have only been associated with distinct events and restricted to minor embayments (e.g. in 2003 in Bishop Harbor from FDEP

- endorsed Piney Point controlled releases). Johansson 1991; Johansson and Lewis 1992.

Submerged aquatic vegetation (SAV) community changes or loss Yes, historically.

Currently increasing. The Tampa Bay estuary is one of only a few estuaries worldwide that has shown recovery of seagrass resources despite continuing population growth and urbanization within the watershed

. Seagrass coverage has increased by approximately 3,200 ha since 1982. Greening and Janicki 2006; Bricker et al. 2008; Waycott et al. 2009. Emergent or shoreline vegetation community changes or loss Yes, historically.

Currently increasing. The 2010 Tampa Bay Habitat Master Plan Update has identified restoration and protection goals for critical coastal habitats in the Tampa Bay watershed

. The TBEP and its partners have adopted a strategy to “restore the balance” of coastal habitats to levels commensurate to the 1950s. Significant progress has been made in restoring and protecting coastal habitats in Tampa Bay since 1996. Robison 2010.

Coral/hardbottom community changes or loss Unknown No information on change or loss h as been developed

. Current h ardbottom communities within Tampa Bay have been tentatively identified , but no historical reference exists for comparison. Robison 2010.

Impacts to benthic community No Benthic communities have been monitored since 1993 in Tampa Bay and have shown stable populations as evidenced by the Tampa Bay Benthic Index

. Karlen et al. 2008.

Fish kills Yes, limited in space and time Periodic fish kills have occurred as a result of red tide blooms entering the lower bay and cold

- water induced shock; however, no significant kills have been reported as a direct result of nutrient inputs into the estuary. -

### Nutrient Criteria Technical Support Document Tampa Bay

Draft 3 August 2010 Table 1b. Checklist of additional factors in Tampa Bay

- = Empty cell/no data Nutrient Factors Observed? Explanation Source Increased nutrient loading or concentrations No Phosphorus and nitrogen levels have been stable and/or declining in the major bay segments of Tampa Bay over recent decades. N itrogen delivery (i.e. N load per unit hydrologic input) from the watershed to the major bay segments of the estuary has been declining since 1985 TBNMC 2009.

Mitigating factors that could prevent nutrient expression Yes Bay hydrologic residence times and circulation; highly

- colored seasonal, freshwater inflows. -

Other significant
stressors to biological communities No - -

Natural high

nutrient episodes (e.g., seasonal or event driven) Yes During periods of extreme ly high rainfall (e.g., the El Niño event in 1998), other storm events (hurricanes), and/or domestic/industrial spills elevated nutrient and/or chlorophyll

- a concentrations have been observed

. -

Poe, A., ed. 2006. Baywide Environmental Monitoring Report, 2002

- 2005. TBEP Technical Publication #06

- 06. 202pp.

Tampa Bay Nitrogen Management Consortium. 2009. 2009 Reasonable Assurance Addendum: Allocation and Assessment Report. Prepared by the Tampa Bay Estuary Program. 89pp.+appendices.

### Nutrient Criteria Technical Support Document Tampa Bay

Draft 4 REFERENCES

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Johansson, J.O.R. 1991 . Long

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. Sherwood, E.T. 2010. 2009 Tampa Bay Water Quality Assessment. 2010. Technical Report #02

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Waycott, M. & 13 others. 2009. Accelerating loss of seagrass across the globe threatens coastal ecosystems. Proceedings of th e National Academy of Science. 106(30):12377

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