# Numeric Nutrient Criteria Recommendations
for the Tampa Bay Estuary

SUMMARY AND TECHNICAL SUPPORT

DOCUMENTS

Prepared for:

Tampa Bay Estuary Program

Prepared by:

Janicki Environmental, Inc.

22 February 20111



### Objective

The objective of this document is to provide a summary of the rece nt work conducted by the Tampa Bay Estuary Program (TBEP) to provide the U.S. Environmental Protection Agency (EPA) and the Florida Department of Environmental Protection (FDEP) recommen dations regarding the establishment of numeric nutrient criteria for the Tampa Bay Estu ary. For reference, the following map of Tampa Bay depicts the four major bay segments referred to in this summary and the

attached technical documents.



### Old Tampa

Bay

Hillsborough

Bay

Middle Tampa

Bay

Lower
Tampa
Bay

Gulf

of

Mexico2



### The Need for Numeric Nutrient Criteria

The FDEP began development of numeric nutrient standards in December 2001. The FDEP formed a technical advisory committee and an agency work group to assist in identifying appropriate

nutrient standards. FDEP has conducted a number of worksh ops and meetings as well as several

studies since 2002.

In 2008, several environmental groups filed suit against EPA in Fed eral Court alleging that EPA had

determined in 1998 that Florida’s current narrative nutrient standard did not comply with the Clean

Water Act and that EPA had not established numeric nutrient standards pursuant to Section 303(c)(4)(B) of the Clean Water Act. As a consequence of t his lawsuit, EPA sent FDEP a letter on January 14, 2009 finding that FDEP’s narrative nutrient stan dard did not comply with the Clean Water Act and directing the State of Florida to develop numeri c nutrient standards for rivers and lakes by January 2010 and estuarine and coastal waters by Janua ry 2011. EPA stated that it would adopt its own nutrient standards if FDEP could not meet these deadlines. In August 2009, the suit plaintiffs and EPA agreed to a Consent Decree formally establi shing the deadlines and determined that EPA would be responsible for establishing numeric criteri a for Florida waters.



### Management of the Tampa Bay Estuary

The Tampa Bay Comprehensive Conservation and Management Plan (TBNEP, 1996) established the restoration of seagrass in the bay to levels estimated in the 1950 s as a primary goal for overall bay restoration. In establishing and addressing this goal, a conc eptual paradigm was developed to identify the primary, manageable factors thought to influence th e recovery and sustainability of seagrass resources within the bay. Reduced water clarity as a result of excessive nitrogen loads to the bay and resulting light attenuation by phytoplankton resp onding to these loadings were the key water quality indicators by which seagrass recovery could be managed. A number of studies in the 1990s clearly established that nitrogen was the limiting nutri ent in the Tampa Bay estuary and that phosphorus loadings to the bay from the enriched Bone Valley re gion were not controlling estuarine production.

In November 2002, the Florida Department of Environmental Protec tion (FDEP) concluded that the Tampa Bay Nitrogen Management Consortium’s (TBNMC) nitrogen manage ment strategy provided reasonable assurance that the state water quality criteria for nutrients would be met in Tampa Bay. Prior to this state determination, the U.S. Environmental Pr otection Agency (EPA) recognized a 1998 action by FDEP that proposed a total maximum load (“fed erally-recognized TMDL”) of nitrogen that could be discharged to the bay annually and still meet state water quality standards

related to nutrients. Both FDEP’s reasonable assurance determi nation and the total maximum nitrogen loading recognized by EPA are based on statistical model ing and data analyses peerreviewed by the TBEP, its partners, and state and federal regul ators. Thus, the TBNMC’s nitrogen loading targets developed for the major bay segments of Tampa Bay have b een acknowledged by both FDEP and EPA as protective nutrient loads for this estuar y. A five-year renewal of the Tampa Bay Reasonable Assurance (RA) was recently approved by order of the FDEP Secretary.

The Southwest Florida Water Management District recently reported on the seagrass acreage in Tampa Bay from its survey conducted in 2010. The results fro m this survey show an increase of approximately 3,250 acres since the 2008 survey (Figure 1). Theref ore, there is tangible evidence3

that the TBNMC nitrogen loading strategy continues to suppor t seagrass recovery in the Tampa Bay
Estuary.

Figure 1. Tampa Bay seagrass coverage. Data sourc e: Southwest Florida Water Management District.

Recent results from the Environmental Protection Commission of Hil lsborough County ambient monitoring program indicate that the chlorophyll targets wer e achieved in all four bay segments of Tampa Bay in 2010 (Figure 2). Therefore, there is tangible evidenc e that the TBNMC nitrogen loading strategy continues to achieve water quality targets in the Tampa Bay Estuary.

Figure 2. Tampa Bay mean annual chlorophyll a concentrations for each of the four major bay segm ents,
1974-2010. Data source: Environmental Protection C ommission of Hillsborough County.4



### TBNMC Recommendation for Tampa Bay Numeric Nutrient Criteria

In March 2010, the TBNMC provided comments and requests regar ding the development by EPA of protective loads for the Tampa Bay Estuary as it relates to est ablishing numeric nutrient criteria for inland waters and estuaries in Florida. As part of th is 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 Ad dendum: 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-ap proved 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 criter ia (EPA, 2010). Multiple lines of empirical evidence justify maintaining existing TN and TP loads t o the Tampa Bay Estuary. Water quality and clarity in the Bay has improved tremendously since signif icant management actions were initiated starting in the 1980s, seagrass acreage has increase d to the highest levels observed since the 1950s and continues to increase, and economically i mportant fish and wildlife populations have been maintained since routine monitoring pro grams began in the 1990s.



### Continuing TBEP Input to EPA Regarding Numeric Nutrient Criteri a

The TBEP, in cooperation with the Sarasota Bay Estuary Progra m and Charlotte Harbor National Estuary Program, supported the development of a document that i dentified 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 criter ia 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 aquat ic 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-anthropo genic events, such as hurricanes
and El Niño conditions, on implementation of the proposed c riteria.5

The following summarizes the TBEP recommendations regarding these issu es. Detailed evaluations

for each issue can be found in the attached documents.

- Concentration-based Criteria

Previous efforts by the TBEP have developed strong relationships betw een nutrient supply to Tampa Bay and resultant chlorophyll a concentrations in the bay, and between chlorophyll a concentrations and light availability for seagrasses. Thus, management actions have focused on controlling nitrogen loads to Tampa Bay, with measureable succ ess as expressed by increases in a biological endpoint, seagrass acreage. The relationships are bet ween nitrogen loads and chlorophyll a , however, not nitrogen concentrations in the bay and chlor ophyll a

.

TBEP recognizes that EPA intends to establish criteria for TN a nd TP and that these criteria may be expressed as ambient concentrations. Although the TBEP recommendat ions for TN and TP criteria remain the TN and TP loads reported above, recommendations f or concentration-based numeric nutrient criteria consistent with the TN and TP loading rec ommendations have been developed and are being provided by the TBEP (Janicki Environmental, 2011a), in the event that EPA determines that loadings cannot be used as numeric nutrient criteria.

The Reference Period approach was selected to establish the prop osed concentration-based

numeric criteria for TN and TP. Based on a 1992-1994 ref erence period, segment-specific chlorophyll a targets have been identified and implemented as part of the Tamp a Bay Nitrogen Management Strategy since 2000 (Janicki and Wade, 1996; Janic ki, Wade, and Pribble, 2000). Using this similar and consistent approach, segment-specific annu al geometric mean TN and TP concentrations from the 1992-1994 period were derived for t his current effort. TN and TP concentration thresholds, as were developed for established, regu latory-recognized chlorophyll a thresholds, account for the inter-annual variability in the TN and TP concentrations observed from

1992-2009.

Application of the Reference Period approach resulted in t he following recommendations for concentration-based TN and TP criteria for Tampa Bay. Th ese criteria are:

 Old Tampa Bay TN=0.93 mg/L TP=0.31 mg/L

 Hillsborough Bay TN=1.01 mg/L TP=0.45 mg/L

 Middle Tampa Bay TN=0.87 mg/L TP=0.29 mg/L

 Lower Tampa Bay TN=0.74 mg/L TP=0.10 mg/L.

The criteria referenced above should be assessed as an annual geo metric mean from long-term
monthly water quality monitoring stations currently used in th e state’s chlorophyll a threshold
assessments under the Tampa Bay RA determination. The assessment of TN and TP concentrations
attainment should only occur when chlorophyll a thresholds are exceeded within a bay segment,
and should coordinate with current regulatory assessments un der the FDEP RA determination and
EPA TMDL for TN loads in Tampa Bay. Further, compliance assessm ents should be conducted
over five-year time frames, with no more than two consecutive years being greater than these
established criteria if chlorophyll a thresholds are also exceeded during the same time period. This6

approach is analogous to the chlorophyll a threshold assessments currently being conducted under
the regulatory requirements for the FDEP RA determination and EPA TMDL for Tampa Bay.

- Aquatic Life Support - Dissolved Oxygen

The numeric nutrient criteria to be promulgated will need t o provide full aquatic life support in each estuary. The aquatic life forms specifically influenced b y excessive nutrient loadings to estuaries include seagrasses (affected by reduced water clarity d ue to excessive chlorophyll a concentrations) and fish and benthic communities (affected by reduced DO conditions). Seagrass support is provided by maintenance of appropriate nutrient co nditions and the resulting chlorophyll

a concentrations as discussed above. Support of fish and benth ic communities is provided by maintenance of appropriate nutrient conditions and the resul ting DO conditions.

The spatial and temporal distributions of DO concentratio ns in Tampa Bay’s major bay segments have been characterized, the principal drivers of low DO con ditions in Tampa Bay have been investigated, and the relevance of the empirical distribution o f DO concentrations to the FDEP’s Impaired Water Rule standard for DO have been evaluated with respect to the proposed numeric nutrient criteria for the Tampa Bay Estuary (Janicki Environment al, 2011b). The following

conclusions can be drawn from these efforts:

• A descriptive characterization of the spatial and temporal attributes of observed DO concentrations used over 30 years of data, collected by 4 dif ferent sampling agencies. Examination of the spatial distribution of DO samples shows that DO exceedances < 4 mg/L were always less than 10% of the samples in all segments except Hillsb orough Bay, never exceeded 15% of the samples in Hillsborough Bay, and are most likely to occur in Hillsborough Bay near the mouths of the Hillsborough River and A lafia River and along the western half of Hillsborough Bay. These are deeper areas, more likel y to be stratified due to freshwater inputs, and have high organic sediment content.

• The principal factor affecting DO in Tampa Bay is temperature. That is evident in both the descriptive temporal plots and in the generalized linear model asse ssed in the quantitative assessment of those factors affecting the probability of DO being less than 4 mg/L. The model results indicate that stratification, bottom type, and sample depth were other factors that contributed to the probability of low DO conditio ns (i.e., < 4 mg/L). Furthermore, it was determined that chlorophyll a concentrations were not a significant factor contributin g to the probability of low DO conditions in Tampa Bay. In other words, the occurrence of DO values below 4 mg/L were not significantly related to observed chlorophyll a concentrations at the time of sampling.

• Based on the weight-of-evidence presented here, it is reasonable to c onclude that the proposed numeric nutrient criteria are protective of full a quatic life uses with respect to DO.

- Downstream Protection Values

Downstream Protection Values (DPVs) are defined by EPA as those wa ter quality criteria in flowing waters that ensure protection of designated uses in the downstrea m estuarine waters as required by the Clean Water Act under 40 CFR 131.10(b). For freshwater lakes, EPA has determined that a7

DPV for stream tributaries that flow into a downstream lake is either the allowable concentration or the allowable loading of TN and/or TP applied at the poi nt of entry into the downstream waterbody (EPA Freshwater Rule, finalized December 2010). Either expression ( concentration or loading) may be used for assessment and source control allocation purpose s, such as TMDLs.

Based on input garnered from a January 28 th , 2011, joint TBEP Technical Advisory Committee and TBNMC meeting and the adopted logic approved by EPA for DPVs f or freshwater lakes, the TBEP staff contends that the existing federally-approved TMDL TN loa ding limits and the recommended TP loading limits meet the intent of DPVs for Tampa Bay major b ay segments. Continued attainment of chlorophyll a thresholds in the major bay segments of Tampa Bay should provide

sufficient evidence that the TN and TP contributions of tri butaries draining to Tampa Bay are protective of the estuary. Therefore, the protective TN and TP l oads recommended by the TBNMC in March 2010 to the EPA are sufficiently protective to att ain in-bay chlorophyll a thresholds for
Tampa Bay.

- Recommendation for Consideration of Tidal Creeks as Unique Entities

Questions have been raised as to whether the numeric nutrient cr iteria proposed for the estuary proper should apply to tidal creeks that drain to the estua ry. Tidal creeks play an integral role in the ecological function of coastal estuaries (summarized in Ja nicki Environmental, 2011d). The treatment of tidal creeks in the implementation of the estuarine nu meric nutrient criteria is, therefore, a significant issue. A thorough understanding of t he ecological elements (e.g., faunal and floral species and communities), processes (e.g., primary productivi ty, nutrient cycling, secondary production), dynamics of tidal creeks (e.g., temporal fluctuat ions in dissolved oxygen) and function in exporting energy to estuarine and coastal ecotones is paramou nt to the establishment of ecologically appropriate nutrient criteria. Numeric nutrien t criteria established for tidal creeks must consider the different ecological processes and functions tha t distinguish them from both from the freshwater systems upstream and the open estuary downstream. Only wi th careful consideration of these attributes can criteria be developed that will maintain t he function of tidal creeks in support of the greater estuarine ecosystem. Recently, EPA’s SAB (SAB Draft Panel Discussion, Jan. 25, 2011) concurred that tidal creeks warrant development of d istinct criteria relative to the estuary

proper.

Studies of Tampa Bay tidal creeks have revealed compelling evidence that these systems represent unique ecotones within the greater Tampa Bay estuary. Tidal creeks play an integral role in the ecological function of coastal estuaries as sites of high primar y and secondary production, nursery and refuge habitat for several species of economically importan t fish and decapod crustaceans, and foraging areas for large-bodied fishes, wading birds, and other piscivorous species. Higher nutrient concentrations in tidal creeks relative to the greater estuary may b e required to support the higher levels of primary and secondary production in these systems.

Analysis of fish collections in tidal creeks suggests that fishes inh abiting tidal creeks appear to be very tolerant to the typical DO conditions found in these systems. Both fish abundance and species richness data indicate that fish communities are relatively inva riant to DO levels between 2-10 mg/L. There are indications that at DO concentrations below 2 mg/L, both fish abundance and species richness decline. Species richness of fish and decapod c rustaceans may be a more sensitive indicator of the aquatic-life support function of tida l creeks; however, these need further8

quantification to eliminate the possibility that seasonal rec ruitment patterns of estuarine-dependent

fishes are not correlated with seasonal variation in DO concen trations due to temperature.

The most desirable approach to establish numeric nutrient cri teria for these systems would be to develop stressor-response models. Stressor-response models require the i dentification of an

indicator variable that can be used to evaluate the conditio n of the tidal creek. Moreover, stressorresponse models require identification of a threshold value abo ve (or below) which the system would no longer fully support its designated use. It is impo rtant that the established criteria for tidal creeks also account for the fact that these systems by nature are mo re variable than their upstream or downstream counterparts. This variability is in part wh at makes these systems so productive and also so difficult to generalize. The timing and volume of freshw ater inflows are physical drivers that exert a great deal of control on tidal creeks. Inflows are det erministic of salinity regimes, nutrient delivery, water depths, temperatures and the potential for salini ty stratification in these systems. Inflows also may control access to these systems for both small recr uit species looking for refuge and for large-bodied predators. Therefore, the quantifica tion of the effects on inflows on these systems will be necessary both to determine appropriate criteria and in the evaluation process. The extent of tidal creeks in the Tampa Bay watershed to which these rec ommendations pertain include, but may not be limited to, the systems identified in the ma ps provided in Figure 3a,b

below.

Based on the recognized need to define distinct biological endpoi nts for tidal tributaries and water quality criteria to support them, TBEP staff recommends the foll owing:

• Recognize tidal tributaries as a separate waterbody class; and

• Consider setting a schedule (i.e., within 3 years) by which ti me endpoints and criteria will be proposed, but do not attempt to set interi m or final criteria with

insufficient data.

TBEP has dedicated funds to continue work in tidal tributa ries in Tampa Bay and will commit to work with EPA to develop recommendations by September 2014.9 Figure 3. a) Named tidal creeks within the Tampa B ay watershed.10 Figure 3. b) Approximate location of the upstream limit of tidal creeks and rivers as defined by empirical salinity data analysis of data from tribu taries within the Tampa Bay watershed.

- Implementation Considerations

TBEP has addressed two key issues identified by the EPA regarding suc cessful implementation of the proposed numeric nutrient criteria in Tampa Bay, namely t he method to account for nonanthropogenic events, such as El Niño and hurricanes, and t he allowable exceedance criteria (how often criteria may be exceeded before non-compliance is observed). Analyses were performed to direct input on these subjects (Janicki Environmental, 2011c) , with the following conclusions:

• The annual response time to recover from the maximum monthly chloro phyll a concentration during a year is relatively short. Median annu al response times are two11

months or less in all segments, and average annual response times are three months or less in all segments. This indicates that the bay recovers very quickly fr om normal loading

events.

• The typical response times to unusual events, such as El Niño, are longer and, depending upon the timing of such events, can span over parts of two successive years.

• Comparison of the two temporal assessment schemes (1 in 3 years) v s (2 in 5 years) suggested that the 2 in 5 rule was less likely to result in a viol ation due solely to natural variability.

- Final Implementation and Assessment Recommendations

It is recommended that the assessment of compliance with the propo sed numeric nutrient criteria be performed in a manner similar to that which has been propo sed by TBEP for compliance with both the Tampa Bay RA determination and EPA TMDL. The goal of the estuarine numeric nutrient criteria is to provide full aquatic-life support within t he estuary. The TBEP has determined that seagrasses are important indicators of desirable conditions i n the bay and has defined the waterquality conditions (i.e., chlorophyll a concentrations) that allow for the maintenance and growth of seagrass beds in Tampa Bay. Therefore, TBEP bases its compliance a ssessment on the comparison of both observed chlorophyll a concentrations and seagrass extent to the goals that have been established. To date, this has proven to be a successful adap tive management approach for abating nutrient eutrophication in the Tampa Bay Estuary.



### References

U.S. Environmental Protection Agency (EPA). 2010. Methods a nd Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in Flori da’s Estuaries, Coastal Waters, and Southern Inland Flowing Waters.

Florida Department of Environmental Protetion (FDEP). 2010. DRAFT Overview of Approaches for Numeric Nutrient Criteria Development in Marine Waters. Divisi on of Environmental Assessment and Restoration, Standards and Assessment Section, Florida Depar tment of Environmental Protection, Tallahassee, FL

Hagy, J.D. 2010. Chapter 6: Numeric Nutrient Criteria D evelopment for Protection of Downstream Estuaries. Presentation to EPA Science Advisory Board, D ec 13-14, 2010, Washington, D.C.

Janicki, A., and D. Wade. 1996. Estimating critical extern al nitrogen loads for the Tampa Bay Estuary: An empirically based approach to setting management target s. Tampa Bay National Estuary Program Technical Publication #06-96. http://www.tbeptech.org/TBEP_TECH_PUBS/1996/TBEP_06_96ExternalTN Loads.pdf12

Janicki, A., D. Wade, and J.R. Pribble. 2000. Developing and Establishing a Process to Track the Status of Chlorophyll-a Concentrations and Light Attenuatio n to Support Seagrass Restoration Goals in Tampa Bay. Tampa Bay Estuary Program Technical Report #04-00. http://www.tbeptech.org/TBEP_TECH_PUBS/2000/TBEP_04_00Chlor-A. pdf

Janicki Environmental, Inc. 2010. Empirical Approaches to Establishing Numeric Nutrient Criteria for Southwest Florida Estuaries. Report prepared for the Tamp a Bay Estuary Program, Sarasota Bay Estuary Program, and Charlotte Harbor National Estuary Progr am by Janicki Environmental, Inc. http://www.tbeptech.org/TBEP_TECH_PUBS/2010/TBEP_05_10_SW_Florida _NEP_NNC_MethodsJuly_14_2010.pdf

Janicki Environmental, Inc. 2011a. Tampa Bay Numeric Nutri ent Criteria: Task 1 – TN and TP Concentrations. Letter Memorandum. Prepared for Tampa Bay Estu ary Program. http://www.tbeptech.org/NitrogenMgmtConsort/NNC/TBEP_NNC_TN_TP_ Letter_Memo_16Feb201 1.pdf

Janicki Environmental, Inc. 2011b. Tampa Bay Numeric Nutri ent Criteria: Task 3 – Dissolved Oxygen. Letter Memorandum. Prepared for Tampa Bay Estuary Program. http://www.tbeptech.org/NitrogenMgmtConsort/NNC/TBEP_NNC_DO_Letter_M emo_16Feb2011.p

df

Janicki Environmental, Inc. 2011c. Tampa Bay Numeric Nutri ent Criteria: Task 4 – Implementation Issues. Letter Memorandum. Prepared for Tampa Bay Estuary Program. http://www.tbeptech.org/NitrogenMgmtConsort/NNC/TBEP_NNC_Implement ation_Letter_Memo_1 6Feb2011.pdf

Janicki Environmental, Inc. 2011d. Tampa Bay Numeric Nutr ient Criteria: Tidal Creeks. Letter Memorandum. Prepared for Tampa Bay Estuary Program. http://www.tbeptech.org/NitrogenMgmtConsort/NNC/TBEP_NNC_Tidal_C reeks_Letter_Memo_16F eb2011.pdf

Tampa Bay National Estuary Program (TBNEP). 1996. Charting the Course. The Comprehensive Conservation and Management Plan for Tampa Bay. Published by t he Tampa Bay National Estuary Program in cooperation with the U.S. Environmental Protectio n Agency, Region IV. http://www.tbep.org/tbep/download_charting_the_course.html