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 km2

, it is 

Florida’s largest open water estuary. More than 2 million people live in the 5700 km2 watershed, with 

the population projected to double by 2050. Land use in the watershed is mixed, with about 40% of the 

watershed 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 seagrass acreage in Tampa Bay was lost due to 

excess nitrogen loading and related increases in algae concentration which caused light limitation 

detrimental to seagrass survival and growth. In 1980, all municipal wastewater treatment plants were 

required to provide 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 resulted 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 Management 

Consortium (TBNMC), a public-private partnership convened by the TBEP, was formed. In 2009, the 

TBNMC 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 TBNMC’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 TBNMC 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 nutrient regime of the recent record is protective of full 

aquatic life support, and the goals of the TBNMC to maintain N loads at levels consistent with the 2003-

2007 period will 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 has been developed. Current hardbottom 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. Nitrogen 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 highnutrient episodes 

(e.g., seasonal or 

event driven)

Yes During periods of extremely 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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Waycott, M. & 13 others. 2009. Accelerating loss of seagrass across the globe threatens coastal ecosystems. Proceedings of the 

National Academy of Science. 106(30):12377-12381