TBNMC Recommendation for Tampa Bay Numeric Nutrient Criteria

In March 2010, the TBNMC provided comments and requests regarding the development by EPA of protective loads for the Tampa Bay Estuary as it relates to establishing numeric nutrient criteria for inland waters and estuaries in Florida.  As part of this effort, the TBNMC provided recommended protective nutrient loads for the Tampa Bay Estuary.  The TBNMC proposed TN and TP loading criteria for the four mainstem segments of Tampa Bay as follows:

Proposed TN and TP loading criteria for the segments of Tampa Bay. 
Segment TN Load (tons/year) TP Load (tons/year)
Old Tampa Bay 486 104
Hillsborough Bay 1451 1093
Middle Tampa Bay 799 140
Lower Tampa Bay 349 52

EPA expectations are for both total nitrogen (TN) and total phosphorus (TP) protective loads.  The recommended protective TN loads for the segments of Tampa Bay are those from the 1992-1994 period, as utilized in the Final 2009 Reasonable Assurance Addendum: Allocation & Assessment Report and in the federally-recognized Tampa Bay TMDL.  The TBNMC recommended protective TP loads from the same time period in its comments and requests to the EPA in March 2010.

The TBNMC approach that has established state and federally-approved nitrogen loading targets for the estuary follows EPA’s technical guidance that quantitative stressor-response relationships are the most preferred methodology in establishing numeric nutrient criteria.  Multiple lines of empirical evidence justify maintaining existing TN and TP loads to the Tampa Bay Estuary.  Water quality and clarity in the Bay has improved tremendously since significant management actions were initiated starting in the 1980s, seagrass acreage has increased to the highest levels observed since the 1950s and continues to increase, and economically important fish and wildlife populations have been maintained since routine monitoring programs began in the 1990s.

Continuing TBEP Input to EPA Regarding Numeric Nutrient Criteria

The TBEP, in cooperation with the Sarasota Bay Estuary Program and Charlotte Harbor National Estuary Program, supported the development of a document that identified the potential methods for the estimation of numeric nutrient criteria for southwest Florida estuaries (Janicki Environmental, 2010).· This document identified several methods currently being considered by both EPA (EPA, 2010) and FDEP (2010) to establish numeric nutrient criteria for Florida estuarine waters.

In addition to the methods document, the TBEP has addressed several other issues associated with the establishment of numeric nutrient criteria for the Tampa Bay Estuary.  These include:

  • Expression of recommended TN and TP criteria as concentrations.
  • Demonstration that the proposed criteria provide full aquatic life support, especially achievement of dissolved oxygen (DO) standards.
  • The need for establishment of downstream protective values (DPVs) for terminal reaches that drain directly into Tampa Bay.
  • Consideration of the influence of infrequent non-anthropogenic events, such as hurricanes and El Niño conditions, on implementation of the proposed criteria.

The following PDFs summarize the TBEP recommendations regarding these issues.  Detailed evaluations for each issue can be found in the full PDF document listed below with all letter memos attached.

File Description File size
Download this file (TBEP_NNC_Final_Executive_Summary_22Feb2011.pdf)Executive Summary + All Letter Memos Attached (Large Document)   15425 kB
Download this file (TBEP_NNC_Final_Executive_Summary_22Feb2011.pdf)Executive Summary Only   1931 kB