# PROPOSED

NUMERIC NUTRIENT CRITERIA

FOR TAMPA BAY

Prepared for:

Tampa Bay Estuary Program

110 – 8 th 

## Ave. S.E. St. Petersburg, Florida 33701

Prepared by:

Janicki Environmental, Inc.

1155 Eden Isle Drive NE St. Petersburg, Florida 33704

September, 20111 

## EXECUTIVE SUMMARY

FDEP is developing a rule to establish numeric nu trient criteria for a number of water body types. The overarching FDEP goal is to “manage nutrien ts in surface (and groundwater) at loadings or concentrations that result in protection and maintenance of healthy, well-balanced aquatic communities”. Absent site-specific analyses, cr iteria should be based on a quantifiable linkage between anthropogenic nutrient enrichment and a bi ological response. FDEP recognizes the role of site-specific factors that affect numeric responses and proposes to base new standards on establishing a systematic numeric interpretation of the existing narrative criteria. Nutrient TMDLs, Site Specific Alternative Criteria (SSAC), and ot her site-specific actions written to achieve the narrative nutrient criteria should be given preference over more broadly applicable interpretations.

The TBEP and the Tampa Bay Nitrogen Mana gement Consortium (TBNMC) have developed a nitrogen management strategy linking seagrass growth to external nitrogen loadings. FDEP has accepted this strategy as providing reasonable assu rance that the state water quality criteria would be met in Tampa Bay. In addition, the EPA has recognized the TN loadin g targets developed as part of the strategy as the TMDL for Tamp a Bay. The TBEP and TBNMC have previously

recommended to EPA numeric nutrient criteria as segment-specific annual TN loads.

The recommended TN loads followed development of seagrass targets and corresponding water quality targets and thresholds for Tampa Bay. Ex tensive empirical evaluations found strong links between TN loads, resultant chlorophyll and lig ht attenuation, and seagrass response. Water quality has been improving since the mid-80s, a nd corresponding responses in seagrass acreage have occurred. During this same period, howe ver, TN loads often exceeded the TMDL targets.

The TBNMC further investigated relationships be tween TN loads and water quality, and found that

residence time should be accounted for. As resi dence time shortens when freshwater inputs are greater, loadings move through the system more quickly and thus biological processes have less time to convert nutrients to chlorophyll. Given th at both TN loads and hydrologic loads affect the chlorophyll within the bay, the annual hydrologic loads are considered along with the annual TN loads when assessing target compliance.

A more appropriate predictor of the likelihood of good water quality, as defined by meeting the FDEP-approved chlorophyll a thresholds, is expected to be the amount of TN delivered per unit water. This is denoted as the Nitrogen Deliv ery Ratio, and is defined as the amount of TN delivered, in tons, per million cubic meters of freshwater delivered. The proposed criteria are expressed as the segment-specific Nitrogen Delivery Ratios observed during the 1992-1994 reference period, provided in the table below. TBEP has also developed alternative criteria, specifically concentration-based TN criteria and both loading and concentration-based TP criteria for each bay segment.

TBEP estuarine numeric nutrient criteria expressed as Nitrogen Delivery Ratio (tons TN per

million m 3 hydrologic load) based on 1992-1994 conditions.

Segment Nitrogen Delivery Ratio Threshold (tons/million m 3 ) Old Tampa Bay 1.08 Hillsborough Bay 1.62 Middle Tampa Bay 1.24
Lower Tampa Bay 0.972 

## 1.0 Introduction

The Florida Department of Environmental Protec tion (FDEP) is currently developing a rule to

establish numeric nutrient criteria for a number of water body types. The following summarizes FDEP’s view on the development of numeric nut rient criteria in Florida (FDEP website, 2011).

The overarching FDEP goal is to “manage nutrient s in surface water (and groundwater) at loadings or concentrations that result in protection a nd maintenance of healthy, well-balanced aquatic communities”. Absent site-specific analyses , water quality criteria should be based on a quantifiable linkage between anthropogenic nutrient en richment and a biological response (such as seagrass growth) that can be used to numerically in terpret the narrative nutrient criteria. There is value in knowing whether nutrient concentrati ons are elevated to potentially environmentally harmful levels, but, conversely, it is equally impo rtant to identify adverse biological effects and determine if they are linked to nutrients before deci ding that nutrient reduction strategies should be pursued.

The Department recognizes the role of site-spe cific factors that affect nutrient responses and proposes to base new standards on establishing a systematic numeric interpretation of the existing narrative criteria. This concept is intended to implement Rule 62-302.530 (47)(b), FAC, which states, “in no case shall nutrient concentrations of a body of water be altered so as to cause an imbalance in natural populations of aquatic flora or fauna.”

As envisioned by FDEP, the narrative nutrient crite ria would continue to apply to all waterbodies, and numeric interpretations would be applied when adequate scientific information is available. The narrative criteria would be implemented usin g a hierarchical approach that numerically interprets the narrative nutrien t criteria for each waterbody.

Numeric interpretations are most accurate when determined as a s ite-specific function. Therefore, nutrient Total Maximum Daily Loads (TMDLs), Site Specific Alternative Criteria (SSAC), and other site-specific actions written to achieve the narra tive nutrient criteria should be given preference over more broadly applicable interpretations.

The first tier of the hierarchical approach entails an evaluation of previously established site-specific numeric interpretations of the narrative criteria (in cluding TMDLs, SSACs, and other interpretations embodied in an official Department action) as the primary interpretation of the narrative nutrient criteria. Currently, Tampa Bay has an FDEP-a pproved Reasonable Assurance and Water Quality Based Effluent Limitation (WQBEL) in addition to an EPA-recognized TMDL. Therefore, Tampa Bay would be included in this first tier of the hierarchical approach.

FDEP has also stated that if nutrient TMDLs are expressed as loads instead of concentrations, the

loads do not have to be translated into concentra tions to be deemed the numeric interpretation of the narrative nutrient criteria. This document pres ents loading-based numeric nutrient criteria for the four mainstem bay segments of Tampa Bay.

Finally, FDEP recognizes that futu re TMDL rules may include a resp onse target (chlorophyll a, for example) designed to implement the narrative nutrient criterion. Currently, the recommended assessment of the proposed numeric nutrient cr iteria for Tampa Bay is built on assessing the achievement of a series of segment-specific chlorophyll a targets.3 In November 2002, FDEP concluded that the ni trogen management strategy developed by the Tampa Bay Estuary Program (TBEP) and Tampa Bay Nitrogen Management Consortium (TBNMC) provided reasonable assurance that the state wate r quality criteria for nutrients would be met in Tampa Bay. Prior to this state determination, the U.S. Environmental Protection Agency (EPA) recognized a 1998 action by FDEP that proposed a total maximum load (“federally-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 determination and the total maximum nitrogen loading recognized by EPA are based on statistical modeling and data analyses peer-reviewed by the TBEP, its partners, and state and federal regulators. Thus, the TBNMC’s nitrogen loading targets developed for the major bay segments of Tampa Bay have been acknowledged by both FDEP and EPA as protective nutrient loads for this estuary. A five-year renewal of the Tampa Bay Reasonable Assurance (RA) was recently approved by order of the FDEP Secretary.

The TBEP and TBNMC have previously recommende d to EPA numeric nutrient criteria for the Tampa Bay estuary as segment-specific annual tota l nitrogen (TN) loads (TBNMC, 2010a). These recommendations were based on the previous work to develop a Reasonable Assurance (RA) plan and eventual nitrogen load allocations (TBNMC, 2010b).

This document provides background information concerning the Tampa Bay estuarine system, including a brief physical characterization of the system and a summary of previous work completed with respect to Tampa Bay estuarine tar gets. In addition, this document provides the data and methodology utilized for developing estuarine numeric nutrient criteria for Tampa Bay, the targets resulting from application of the method ology, the proposed crite ria, and the proposed methodology for implementation and compliance of the Tampa Bay estuarine numeric nutrient

criteria.



## 1.1 Tampa Bay and Its Watershed

Tampa Bay is on the west central coast of Florida, and has been divided into seven bay segments for purposes of management activities. The bay covers approximately 1,030 km 2 , extends approximately 56 km inland from the Gulf of Mexico, is 8-16 km wide along most of its length, and is the largest open water estuary in Florida (Figure 1-1). Tampa Bay is crossed by four major causeways, and has about 42 nautical miles of dr edged channels with designed mean low water depths of 6-13 meters. The major shipping channe l has been dredged from the mouth of the bay to the port facilities near Tampa. The average depth of the bay is approximately 4 meters.

The four mainstem segments of the bay include Lower Tampa Bay, Middle Tampa Bay, Hillsborough Bay, and Old Tampa Bay (Figure 1-1 ). Lower Tampa Bay connects the mouth of the bay to the Gulf of Mexico, and is joined on the southeast by the Manatee River and Terra Ceia Bay segments and on the north by the Boca Ciega Bay segment. Middle Tampa Bay is northeast of Lower Tampa Bay, and connects to the Hillsboroug h Bay segment to the northeast and the Old Tampa Bay segment to the north.Moveme n inflows.

freshwat e Alafia Ri v the Man a contribut n t of water i Average tid a

e r inflow to

v er discharg

a tee River t
es about 15

- Figu

n the bay is

a l range in t

the bay, w

i ng to Hills b

t o Lower T a

- 30% of the t re 1-1. Tam p

controlled b he bay is a b

ith the Hill s b orough Bay

,

a mpa Bay.

t otal. p a Bay mainst e

b y tidal proc e b out 0.7 m ( P

s borough Ri v

, the Little M

Runoff to t e m segments

.

e sses, winds

P ribble, 200 6

v er/Tampa B

M anatee Riv e

t he bay oth .

, morpholo g
6 ). Four m a
B ypass Can a

e r to Middl e h er than tha t g y, and fresh w

a jor rivers pr

a l system an

e Tampa Ba y

t from the

4 water
ovide

d the

y , and

rivers5 The Tampa Bay watershed covers approximately 5,700 km 2 , and includes all or parts of Pasco, Pinellas, Hillsborough, Polk, Manatee, and Saraso ta counties, with more than 2 million current residents and a projected population doubling by 2050. Land use is mixed, with about 40% of the watershed undeveloped, 35% agricultural, 16% re sidential, and the remaining commercial and mining. Major habitats in the Tampa Bay estuar y include mangroves, salt marshes, and submerged aquatic vegetation.

The watershed is divided into seven drainage ba sins, corresponding to the seven bay segments. The watershed contains various source types supp lying freshwater runoff and associated nutrients and other pollutants to Tampa Bay (Greening and Janicki, 2006). These sources have been categorized as nonpoint sources (representative of runoff), atmospheric deposition (directly to the open water of the estuary), point sources (domestic and industrial wastewater facilities), springs, and groundwater. An additional source of nutrien t loadings to the bay is loss from fertilizer handling operations at the two port facilities, in Hillsborough Bay and Lower Tampa Bay.

The TBEP, in cooperation with local scientists and FDEP, has developed a tabular listing of symptoms of nutrient enrichment in Tampa Ba y, along with potential explanations of these expressions, to aid in development of numeric nutrie nt criteria for the bay. This listing is provided in Tables 1-1 and 1-2 below. These tables prov ide a summary of potential responses expressed in the bay related to nutrient loads, and notes whethe r these responses are currently or historically found in the bay.6Table 1-1. Checklist of nutrient enrichment symptoms in Tampa Bay.Response VariableObservedHistoricallyorCurrently?ExplanationSourceLow dissolvedoxygen (DO)(hypoxia/anoxia)Yes, limitedin space andtimeTypically, the lowest dissolved oxygen conditions occur during the summer months inHillsborough Bay; however, no apparent increasing trends have been detected for the arealextent of hypoxia during these months in this bay segment . Hypoxic events in this bay segmentappear to be largely driven by physical processes rather than nutrient effects.Janicki et al. 2001;Poe 2006.Reduced clarityNo. Long-term monitoring of bay water clarity via Secchi disk depths by the EPCHC has indicated asignificant improvement.Sherwood 2010.IncreasedchlorophyllaconcentrationsNo.Long-term monitoring of bay chlorophyll-a concentrations by the EPCHC has indicated asignificant decline.Sherwood 2010.Phytoplanktonblooms (nuisance ortoxic)Yes, limitedin space andtimeRed tide blooms originating in the Gulf of Mexico have occasionally entered the lower bay.Most recently in Old Tampa Bay, nuisance blooms ofPyrodinium bahamensehave occurred asa result of anomalous spring/summer rainfall events in 2008 and 2009. Blooms did not reoccurin 2010, but did occur in late summer 2011.Phlips et al. 2006;Badylak et al. 2007;Heil et al. 2007.Problematicepiphyte growthNoNo significant trends in epiphyte growth have been reported as result of monitoring conductedby the Tampa Bay Interagency Seagrass Monitoring Program.Avery and Johansson2010.Problematicmacroalgal growthYes(historical),No (current)Macroalgal blooms have been reported and observed in the past; however, nuisance bloomshave not occurred over the recent period or haveonly been associated with distinct events andrestricted to minor embayments (e.g. in 2003 in Bishop Harbor from FDEP-endorsed Piney Pointcontrolled releases).Johansson 1991;Johansson and Lewis1992.Submerged aquaticvegetation (SAV)community changesor lossYes,historically.Currentlyincreasing.The Tampa Bay estuary is one of only a few estuaries worldwide that has shown recovery ofseagrass resources despite continuing population growth and urbanization within the watershed.Seagrass coverage has increased by approximately 3,200 ha since 1982.Greening and Janicki2006; Bricker et al.2008; Waycott et al.2009.Emergent orshoreline vegetationcommunity changesor lossYes,historically.Currentlyincreasing.The 2010 Tampa Bay Habitat Master Plan Update has identified restoration and protection goalsfor critical coastal habitats in the Tampa Bay watershed. The TBEP and its partners have adopteda 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 Baysince 1996.Robison 2010.Coral/hardbottomcommunity changesor lossUnknownNo information on change or loss has been developed. Current hardbottom communities withinTampa Bay have been tentatively identified, but no historical reference exists for comparison.Robison 2010.Impacts to benthiccommunityNo Benthic communities have been monitored since 1993 in Tampa Bay and have shown stablepopulations as evidenced by the Tampa Bay Benthic Index.Karlen et al. 2008.Fish killsYes, limitedin space andtimePeriodic fish kills have occurred as a result ofred tide blooms entering the lower bay and coldwater induced shock; however, no significant kills have been reported as a direct result ofnutrient inputs into the estuary.-7Table 1-2. Checklist of additional factors in Tampa Bay.Nutrient FactorsObserved?ExplanationSourceIncreased nutrientloading orconcentrationsNoPhosphorus and nitrogen levels have been stable and/or declining in the major bay segmentsof Tampa Bay over recent decades. Nitrogen delivery (i.e. N load per unit hydrologic input)from the watershed to the major bay segmentsof the estuary has been declining since 1985TBNMC 2010b.Mitigating factorsthat couldprevent nutrientexpressionYesBay hydrologic residence times and circulation;highly-colored seasonal, freshwater inflows.-Other significantstressorsto biologicalcommunitiesNo --Natural highnutrient episodes(e.g., seasonal orevent driven)YesDuring periods of extremely high rainfall (e.g., the El Niño event in 1998), other storm events(hurricanes), and/or domestic/industrial spillselevated nutrient and/or chlorophyll-aconcentrations have been observed.-8 

## 2.0 Objective

The objective of this document is to propose estuarine numeric nutri ent criteria specific to the four mainstem segments of Tampa Bay: Old Tampa Bay, Hillsborough Bay, Middle Tampa Bay, and Lower Tampa Bay. The remaining three segments (Boca Ciega Bay, Terra Ceia Bay, and Manatee River) will be addressed in a separate document. The criteria are expressed as TN and TP loadings to the bay. The proposed TN lo ading criteria for the four mainst em segments were based on the nitrogen management strategy developed by the TBNMC.



## 3.0 Development of Seagrass, Ligh t Attenuation, Chlorophyll a, and Nitrogen Loading Targets

This section provides detailed summary of work previously completed by the TBEP and TBNMC in establishment of the seagrass target, the associated water quality (light attenuation and chlorophyll) targets, and TN loading targets to each segment. An assessment of the se agrass, water quality, and TN loading data utilized in this effort is provided in Appendix A. Appendix B contains a description of the derivation of the recently proposed TP loading targets and TN and TP concentration thresholds which may be utilized as criteria if necessary.



## 3.1 Background and Rationale

Between 1950 and 1990, an estimated 40-50% of the seagrass acreage in Tampa Bay was lost due to excess nitrogen loading and related increase s in algae concentration which caused light limitation detrimental to seagrass survival and grow th, in addition to shoreline modifications. 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 wa stewater treatment plants, stormwater regulations

enacted in the 1980s also resulted in reduced nitro gen loads to the bay. Estimated TN loads in 1976 are more than twice recent (2003-2007) estimates.

The Comprehensive Conservation and Management Plan (CCMP) of the TBEP (TBEP, 1996a) established the restoration of seagrass in the bay to levels estimated in the 1950s as a primary goal for overall bay restoration. In establishing and addressing this goal, a conceptual paradigm was developed to identify the primary, manageable factors thought to influence the recovery and sustainability of seagrass resources within the bay (Figure 3-1). As depicted in the TBEP’s nitrogen management paradigm, reduced water clarity as a re sult of excessive nitrogen loads to the bay and resulting light attenuation by phytoplankton respon ding to these loadings were the key water quality indicators by which seagra ss recovery could be managed.

A number of studies since the 1990s clearly esta blished that nitrogen loads were 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 (Johansson, 1991, 2009; Janicki Environmental, 2011a).Figure 3



## 3.2 D

Detailed al. (199 5 develop m Bay was
dataset d

Service c supporti n

seagrass

seagrass e areas wh

that the Physical potential

restorati o

The sea g describe d

seagrass target w a -1. Concept u Estuary Prog r



## D evelopm e

explanation

5 ). The cir c

m ent of resto

available fo eveloped fo

c ooperative s

n g seagrasse s

coverage w

e s in 1950 b

ich had bee n areas could
Impacts Pr o restoration a

o n areas (are a

g rass targets
d in Janicki a

a creage res u

a s 38,000 ac r

Fig u u al paradigm d

r am partners



## e nt of Sea g

of the deriv a

c a 1950 ti m ration target s r that perio d

r a Florida D

s tudy (TBRP

s in 1990 w e ith the 195 0
b ut not in 1 9

n physically

support se a

o ject (TBEP

,

a reas, result i

a s with seag r

(Figure 3-2)

a nd Wade (1

u lting from s

r es baywide.

u re 3-2. Seag r d escribing th e to relate nitr o



## g rass Tar g

a tion of the s

m e period w

s , as a datas e d . A GIS c o
D epartment C, 1986). T

e re identifie d

0 s-era cove r
9 90, provid i

altered sinc e

a grasses we r 1994). T

i ng in seagr a

r ass in 1950

were devel 996). The s e umming the

r ass acreage e e nitrogen m a

o gen loading t



## g ets

s eagrass tar g

w as selected

e t providing

o verage of s e

of Natural R

T o develop

d as resourc

r age provid e
i ng potentia

e the 1950s s

r e identified

hese non-r e

a ss protectio
but not in 1 9

oped from t

e agrass targ e

restoration

e stimates for T a nagement str

t o seagrass r e

g et for Tamp a

as the hist

estimation o

e agrass in t h

R esources a n the seagras s

c e protectio n

e d an estim a

l restoration

s o that there

using map p

e storable ar e n areas (are a
9 90 less any

t hese prote c

e t for the ba y

and protecti

T ampa Bay f o r ategy emplo y

e sponse in Ta m

a Bay is pro v

t orical benc h

o f seagrass c o h e bay was d

n d the U.S.

s target for T

n areas. Co m

a te of those

areas for s e

was no reas

p ing compl e

e as were r e

a s with seag

non-restora b

c tion and re s

y was set ba s

on areas, s o

o r 1950-2010. y ed by Tampa

m pa Bay.

v ided in Jani

h mark peri o

o verage in T

d eveloped f r Fish and W i

T ampa Bay,

m bining the

areas supp o

e agrasses. T onable poss i

e ted for the

e moved fro m

rass in 199 0
b le areas).

s toration ar e

s ed on 95% o

o that the se a

9 Bay

cki et

o d for

ampa

r om a
i ldlife

areas
1990

o rting

T hose

i bility

TBEP

m the

0 ) and

e as as

o f the

a grass10 The segment-specific seagrass targets for the four mainstem bay segments were established as:

 Old Tampa Bay 10,545 acres,

 Hillsborough Bay 1,663 acres,

 Middle Tampa Bay 8,930 acres, and

 Lower Tampa Bay 7,030 acres.



## 3.3 Development of Chlorophyll a , Light Attenuation, and Nitrogen Loading
Targets

The TBEP developed targets for light and chlorophyll a in support of the seagrass target for the bay, based on a specified percentage of incident light reaching segment-specific depths as determined from historical (1950s) seagrass distribution. Ta rget depths were chosen based on conservative estimates of the deepest edges of seagrass meadow s in the 1950s period (Janicki et al., 1995). The minimum light requirement at these targets depths was established as 22.5% of incident light, based on data obtained during a SWFWMD study conducted by Mote Marine Laboratory (Dixon and Leverone, 1995). Further eva luation included accounting for bottom reflectance, resulting in the light requirement target being adjusted to 20. 5% of incident light (Janicki and Wade, 1996).

Following establishment of depth and light tar gets, relationships were developed between water quality and light attenuation. Least squares regre ssion methods were used to estimate parameters relating average monthly chlorophyll a concentrations to light availability (Janicki and Wade, 1996). Chlorophyll a levels were related to light attenuation (via estimates derived from Secchi disk depths) using a functional form of Beers’ law in a linear regression and served as a proxy for light availability to seagrass in the bay (Figure 3- 3). Given the minimum light requirement of 20.5% of incident light, predictions of chlorophyll a levels and Secchi disk depths (light penetration) necessary to restore seagrass to average depths obs erved in each of the major bay segments during the 1950s were used to assess the development of annual targets for these parameters (Janicki and Wade, 1996; Greening and Janicki, 2006).

Figure 3-3. Relationship between chlorophyll a and depth of 20.5% light attenuation



### .11 The next step in the TBEP paradigm (Figure 3-1) was linking chlorophyll a concentrations to loadings. As described in Janicki and Wade (1 996), the net flux of water and nitrogen between segments must be considered. First, a series of dilution equations were written for the four mainstem segments of the bay, and fit to observe d salinity and freshwater inflow data. Next, the dilution equations were used to predict nitrogen concentrations, and a regression parameter was used to relate the observed and predicted nitrogen concentrations to account for the net of all nonconservative processes affecting nitrogen (such as sediment uptake or release) (Figure 3-4).

The chlorophyll a targets developed from this effort we re segment-specific. Potential chlorophyll a targets were developed utilizing two methods: the TN loading-chlorophyll a model described above, and annual average values from the 19 92-1994 period. The TN loading-chlorophyll a model was used to identify the chlorophyll a needed for sufficient light to reach depths in each segment corresponding to recovery to seagrass tar get. Recall from above that the seagrass target was set as 95% of the sum of the protection and re storation areas. Based on improving seagrass coverage and water quality seen over the 1990–19 96 period, secondary targets were developed from the average annual chlorophyll a levels seen during 1992-1994 (a period of time with high and low rainfall during which seagrass was expa nding). The ultimate selection of bay segmentspecific chlorophyll a targets was determined as the average annual levels developed from the empirical model predictions (Janicki and Wade, 1996) or the 1992-1994 average annual levels – which ever were lower (TBEP, 1996b and 2001).

The TBEP TAC further recognized that there may be years in which these targets may be exceeded without causing significant reductions in seagrass cover. This means that there is some allowable amount of variation that should not elicit a sign ificant degradation in water quality and therefore seagrass coverage. This level of variation was defin ed as two standard errors around the period of record mean annual chlorophyll a concentrations in each segment. Therefore, a distinction is made

between a target , i.e., a desired chlorophyll a concentration and a threshold , i.e., a chlorophyll a concentration above which undesirable chlorophyll a concentrations exist. The chlorophyll a threshold for each segment is the sum of the tar get and two standard errors around the mean annual chlorophyll a concentrations in each segment. These thresholds have been recognized both in the recent WQBEL and RA documents (FDEP, 2010; TBNMC, 2010b). The chlorophyll a targets and

thresholds are shown in Table 3-1.

Table 3 1. Tampa Bay chlorophyll a targets and thresholds.

Segment Chlorophyll a Target
(μg/L) Chlorophyll a Threshold
(μg/L)
Old Tampa Bay 8.5 9.3
Hillsborough Bay 13.2 15.0
Middle Tampa Bay 7.4 8.5

Lower Tampa Bay 4.6 5.1

Finally, TN loads from both external sources and intersegment transport were related to the observed chlorophyll a using a regression model (Figure 3-4) (Janicki and Wade, 1996). During this same time, the 1992-1994 average annual total nitr ogen loads were established as the appropriate nitrogen load management targets by TBEP partners (Table 3-2) in order to support the maintenance of the chlorophyll a and light attenuation targets developed for each of Tampa Bay’s major bay segments. These targets have subsequently been adopted by EPA as the federally-recognized nitrogen TMDL for Tampa Bay.12 Figure 3-4. Comparison of observed chlorophyll a and that predicted from the TN load – chlorophyll a relationships, all four mainstem bay segments, for 1986-1998 and 1999-2007



### .

Table 3 2. Tampa Bay TN loading targets.

Segment TN Load Target
(tons/year)
Old Tampa Bay 486
Hillsborough Bay 1,451
Middle Tampa Bay 799

Lower Tampa Bay 349



## 4.0 Proposed Criteria

The TBNMC annual assessment of the water quality conditions in the four mainstem segments of the bay is accomplished by completion of the previously developed Decision Matrix, which compares annual average chlorophyll a and light conditions to targets (Janicki et al., 2000). The Decision Matrix results through 2010 are provided in Figure 4-1. Chlorophyll a values were less than the thresholds in most segments for most yea rs following the 1992-1994 period (see Appendix A). Exceptions were linked either to excessive ra infall conditions or to an emergency action taken associated with the closure of an industrial point source (TBNMC, 2010b).13 Figure 4-1. Decision Matrix results through 2010 showing assessment of chlorophyll a threshold values. Year OTB HB MTB LTB

1975 No No No Yes

1976 No No No Yes

1977 No No No No

1978 No No No Yes

1979 No No No No

1980 No No No No

1981 No No No No

1982 No No No No

1983 No No No No

1984 Yes Yes No Yes

1985 No No No Yes

1986 No No Yes Yes

1987 No Yes No Yes

1988 Yes Yes Yes Yes

1989 No Yes Yes Yes

1990 No Yes Yes Yes

1991 Yes Yes Yes Yes

1992 Yes Yes Yes Yes

1993 Yes Yes Yes Yes

1994 No No No No

1995 No No No Yes

1996 Yes Yes Yes Yes

1997 Yes Yes Yes Yes

1998 No No No No

1999 Yes Yes Yes Yes

2000 Yes Yes Yes Yes

2001 Yes Yes Yes Yes

2002 Yes Yes Yes Yes

2003 No Yes Yes Yes

2004 No Yes Yes Yes

2005 Yes Yes Yes No

2006 Yes Yes Yes Yes

2007 Yes Yes Yes Yes

2008 Yes Yes Yes Yes

2009 No Yes Yes Yes

2010 Yes Yes Yes Yes14 During the development of the 2009 Reasonable Assurance (TBNMC, 2010b), the TBNMC investigated the temporal trends in TN loading. While the chlorophyll a thresholds were being met, the TN loading targets were exceeded in so me years (Figure 4-2). The TBNMC investigated the relationships between TN loads and chlorophyll a to better understand how the bay responds to varying nitrogen loads. Non- anthropogenic factors can signifi cantly influence the relationship between chlorophyll a and TN loadings. One such factor is rainfall and its role in determining estuarine residence time, which in turn has been s hown to influence this relationship in many lakes

and other estuaries. As residence time shorte ns, and loadings move more quickly out of the estuary, biological processes have less time to co nvert nutrients to chloro phyll. As residence time lengthens, loadings remain within the system longer, and thus more nutrients can be converted to chlorophyll. Given the same nutrie nt loads, different residence tim es within the system can result in very different expressions in water quality constitu ents. Given this paradigm, that both TN loads and hydrologic loads affect the chlorophyll a within the systems, the annual hydrologic loads to each of the segments must be considered alon g with the annual TN loads to establish loading thresholds for each segment. Figure 4-3 pr ovides a schematic of these influences.

Figure 4-2. Comparison of annual loading to the four mainstem segments to the segment-specific targets.Figur e

Given th appropri a

approve d

delivere d

of TN d e compari s segment. Nitrogen
four mai hydrolog

presents Nitrogen

Figure 4

- e 4-3. Schem a

e combined

a te predicto r d chlorophyl

d to the bay.

e livered, in t
on of the o b

These da t Delivery R a

n stem bay s ic normaliz a the relation s Delivery Ra

- 4. Comparis a tic of the eff e

influence o

r of the likeli

l a threshol d

This is den o

t ons, per mi
b served ann u

t a agree wit

a tios are a m

s egments wi

a tion agreed

s hip betwee n tio from the

on of annual e cts of TN an

o f both TN l

hood of ad e d s, is expec t

o ted as the N
llion cubic m

u al Nitrogen

h the obser v

ore appropr i thin Tampa upon durin g

n TN and h y

1992-1994 r

Nitrogen Del

by the 1992 d freshwater

oads and h y

e quate water

t ed to be th e
N itrogen De

m eters of fr e Delivery R a

v ed chloro p
i ate expressi

Bay. Conc e

g the RA de v

y drologic lo a

r eference pe r

ivery Ratios t o -1994 averag e loadings on c

y drologic lo a

quality, as d

e amount o f livery Ratio,

e shwater de l

a tios to the 1

p hyll a con c

on of the n u

e ptually, the

v elopment ( T

a ds in each s riod.

o the segmen

e ratios. c hlorophyll a c

a ds on wat e d efined by m f TN deliver e and is defi n l ivered. Fig u
1992-1994 r

c entrations a

u meric nutri e

e se ratios ar e

T BNMC, 20

s egment and

t-specific thr e c oncentratio n

e r quality, a

m eeting the F

e d per unit

n ed as the a m

u re 4-4 pres e

r atios in eac h

a nd therefor e

e nt criteria f o

e identical t 09). Appen compared t

e sholds as de f

15 n s.

more
F DEPwater

m ount

e nts a
h bay

e , the

o r the

o the

dix C

t o the

f ined16 Given the critical contributions of both TN load and hydrologic load to chlorophyll a concentrations, the proposed criteria are expresse d as the segment-specific Nitrogen Delivery Ratios observed during the 1992-1994 reference period. The proposed criteria for the four mainstem segments are provided in Table 4-1 below.

Table 4-1. TBEP estuarine numeric nutrient crit eria expressed as Nitrogen Delivery Ratio (tons
TN per million m 3 hydrologic load) based on 1992-1994 conditions.

Segment Nitrogen Delivery Ratio Threshold

(tons/million m 3 )
Old Tampa Bay 1.08
Hillsborough Bay 1.62
Middle Tampa Bay 1.24

Lower Tampa Bay 0.97



## 5.0 Implementation

The TBNMC and TBEP have recommended that FDEP and EPA compliance assessments should first consider whether the mean annual bay segment chlorophyll a concentration is above the FDEPapproved threshold, and as a result, whether seag rass resources within the bay segment have been or are likely to be impacted (TBNMC, 2010b). The RA defines a series of management actions to be taken in response to various threshold exceedances. The following assessment strategy builds on that approved by FDEP for the Tampa Bay RA.

The proposed compliance assessmen t strategy involves two steps. The initial step is the comparison of the mean annual chlorophyll a concentrations in each bay segment to the established chlorophyll a thresholds . Compliance is achieved if the thre shold is met in that year. If the chlorophyll a threshold is exceeded in more than two years during any five-year period, an assessment of nitrogen loading (relative to the hydr ologic loads, i.e., the Nitrogen Delivery Ratios) during that period will be completed. The justifi cation for this “2-in-5 year” compliance assessment has been developed (Janicki Environmental, 2010b) and summarized in Appendix D.

The recommendation for compliance assessment also hinges on the av ailability of the appropriate data for a defensible assessment. Thus, how the sp ecific spatial and temporal averaging has been conducted in the development of the targets and th resholds as well as the compliance assessment is critical. The following discusses this aspect of the implementation of the proposed numeric nutrient criteria for Tampa Bay.

From the initial efforts to establish defensible water quality targets throug h the development of the RA, the primary data source has been the En vironmental Protection Commission of Hillsborough County (EPC). The EPC has monitored water quality at more than 50 sites on a monthly basis since 1974. Investigation of the available data resulte d in the identification of 46 sites for use in the establishment of water quality targets in Tampa Bay. The suite of segment-specific EPCHC sites utilized for establishment of segment-specific chlorophyll a targets and thresholds, and for the annual assessment, and location maps for each segm ent are provided in Appendix E. Defensible assessment will depend upon conti nued monitoring at these sites to ensure that the annual assessment for attainment of the FDEP-adopted chlorophyll a thresholds, implementation of the FDEP-approved Reasonable Assurance Plan, a nd implementation of the proposed TN loading criteria presented here.17 

## 6.0 References

Avery, W. and J.O.R. Johansson. 2010. Data Su mmary from the Tampa Bay Interagency Seagrass Monitoring Program through year 2008. Tech nical Report #01-10 of the Tampa Bay Estuary Program. Prepared by the City of Tampa Bay Study Group.

Badylak, S., E.J. Phlips, P. Baker, J. Fajans, and R. Boler. 2007. Distributi ons of Phytoplankton in Tampa Bay Estuary, U.S.A. 2002–2003. Bulle tin of Marine Science, 80(2): 295–317.

Bricker, S.B. & 6 others. 2008. Effects of nutrient enrichment in the nation’s estuaries: A decade of change. Harmful Algae. 8:21-32.

Dixon, L.K., and J.R. Leverone. 1995. Light requirements of Thalassia testudinum in Tampa Bay Florida. Submitted to: Surface Water Improvem ent and Management Progra m, Southwest Florida Water Management District. Submitted by: Mote Marine Laboratory, Sarasota, Florida.

Florida Department of Environmenta l Protection (FDEP) website. 2011. http://www.dep.state.fl.us/water/wqssp/nutrients/index.htm

Florida Department of Environmental Protecti on (FDEP). 2010. Final Order Adopting Water Quality Based Effluent Limits for Point Source Discharges to the Tampa Bay Watershed.

Greening, H. and A. Janicki. 2006. Toward r eversal of eutrophic conditions in a subtropical estuary: water quality and seagrass response to nitr ogen loading reductions in Tampa Bay, Florida, USA. Environmental Management Vol. 38, No. 2, pp. 163-178.

Heil, C.H., M. Revilla, P.M. Gilbert and S. Murask o. 2007. Nutrient quality drives differential phytoplankton community composition on the s outhwest Florida shelf. Limnol. Oceanogr.,

52(3):1067–1078.

Janicki, A.J., D.L. Wade, and D.E. Robison. 1995. Habitat protection and restoration targets for Tampa Bay. Tech. Pub #07-93, Tampa Bay Nationa l Estuary Program. Prepared by Coastal Environmental, Inc.

Janicki, A.J. and D.L. Wade. 1996. Estimating Cri tical Nitrogen Loads for the Tampa Bay Estuary: An Empirically Based Approach to Setting Managem ent Targets. Technical Publication #06-96 of the Tampa Bay National Estuary Program. Pr epared by Coastal Environmental, Inc.

Janicki, A., D. Wade, and R. Pribble. 2000. D eveloping and Establishing a Process to Track the Status of Chlorophyll-a Concentrations and Ligh t Attenuation to Support Seagrass Restoration Goals in Tampa Bay. Technical Report #04-00 of the Ta mpa Bay Estuary Program. Prepared by Janicki Environmental, Inc.

Janicki, A.J., R. Pribble and M. Winowitch. 2001. Es timation of the Spatial and Temporal Nature of Hypoxia in Tampa Bay, Florida. 2001.Technical Re port #09-01 of the Tampa Bay Estuary Program. Prepared by Janicki Environmental, Inc.18 Janicki Environmental, Inc. 2010a. Sarasota Ba y Numeric Nutrient Criteria: Implementation Issues. Letter Memorandum Prepared for Sara sota Bay Estuary Program. Sarasota, Florida

Janicki Environmental, Inc. 2010b. Charlotte Ha rbor Numeric Nutrient Criteria: Implementation Issues. Letter Memorandum Prepared for Charlott e Harbor Estuary Program. Ft. Myers, Florida

Janicki Environmental, Inc. 2011a. Tampa Bay Nume ric Nutrient Criteria: Task 1 – TN and TP Concentrations. Letter Memorandum. Prep ared for: Tampa Bay Estuary Program.

Janicki Environmental, Inc. 2011b. Tampa Ba y Numeric Nutrient Criteria: Task 4 – Implementation Issues. Letter Memorandum. Prepared for: Tampa Bay Estuary Program.

Johansson, J.O.R. 1991. Long-term trends of nitrogen loading, water quality and biological indicators in Hillsborough Bay, Florida in Treat, S.F. and P. Clark, ed s. Proceedings, Tampa Bay Area Scientific Information Symposium 2. Feb. 27 – Mar. 1, 1992, Tampa, FL. 528pp.

Johansson, J.O.R. 2009. Nutrient enrichment studies of natural phytoplankton populations in Tampa Bay: A summary of results June 1993 to August 2009. City of Tampa Wastewater Department Bay Study Group.

Johansson, J.O.R. and R.R. Lewis. 1992. Recent improvements of water quality and biological indicators in Hillsborough Bay, a highly impact ed subdivision of Tampa Bay, Florida, USA
pp.1199-1215 in R.A. Vollenwedier et al., eds. Marine Coastal Eutrophication: The Response of Marine Transitional Systems to Human Impact: Problems and Perspectives for Restoration. Proceedings of an International Confer ence, Bologna, Italy, 21-24 March 1990.

Karlen, D., T. Dix, B. Goetting, S. Markham, C. Meyer, M. Flock and G. Blanchard. 2008. Tampa Bay Benthic Interpretive Report: 1993-2004 Bay Wide Report. 2008. Technical Report #05-08 of the Tampa Bay Estuary Program. Prepared by the Environmental Protection Commission of Hillsborough County.

Lewis, R.R. III, R.G. Gilmore, Jr., D.W. Crewz, and W.E. Odum. 1985a. Mangrove habitat and fishery resources of Florida. In: W. Seaman, Jr. (Ed.). Florida Aquatic Habitat and Fishery Resources. Florida Chapter of the American Fisheries Society.

Morrison, G., E.T. Sherwood, R. Boler, and J. Barron. 2006. Variations in water clarity and chlorophyll a in Tampa Bay, Florida, in response to annual rainfall, 1985-2004. Estuaries and

Coasts. 29:926-931.

Phlips, E.J., S. Badylak, E. Bledsoe and M. Ci chra. 2006. Factors affecting the distribution of Pyrodinium bahamense var. bahamense in coastal waters of Florida. Marine Ecology Progress
Series, 322:99-115.

Poe, A., ed. 2006. Baywide Environmental M onitoring Report, 2002-2005. TBEP Technical Publication #06-06. 202pp.

Pribble, R. 2006. Bay Characteristics. In “Baywide Environmental Monitoring Report, 2002-2005. Tampa Bay, Florida.” Eds. A. Poe, A.J. Janicki, and H. Greening. Tampa Bay Estuary Program Technical Publication

#06-06.19 Robison, D. 2010. Tampa Bay Estuary Program Ha bitat Master Plan Update. Technical Report #06- 09 of the Tampa Bay Estuary Program. Prepared by PBS&J.

Sherwood, E.T. 2010. 2009 Tamp a Bay Water Quality Assessment. 2010. Technical Report #02-10 of the Tampa Bay Estuary Program. Prepared by the Tampa Bay Estuary Program.

Tampa Bay Estuary Program (TBEP). 1994. Physical impacts to bottom habitats in Tampa Bay. Prepared for the Tampa Bay Estuary Program. Prepared by Coastal Environmental, Inc.

Tampa Bay Estuary Program (TBEP). 1996a. Charting the Course. The Comprehensive Conservation and Management Plan for Tampa Bay. Published by the Tampa Bay National Estuary Program in cooperation with the U.S. Envi ronmental Protection Agency, Region IV.

Tampa Bay Estuary Program (TBEP). 1996b. Fi nal Action taken by TBNEP Management and Policy Committees, adopting goals for seagrass acreage, targets for segment specific chlorophyll-a concentrations, and a five-year nitrogen manage ment strategy to “hold the line” on nitrogen loadings for each bay segment. June 14, 1996.

Tampa Bay Estuary Program (TBEP). 2001. Fina l Action taken by TBEP Management and Policy Boards, extending through 2005 the previously adopted chlorophyll a concentrations for each bay segment, and the nitrogen management strategy to “hold the line.” May 11, 2001.

Tampa Bay Nitrogen Management Consor tium (TBNMC). 2009. Decision Memo #11. Incorporation of hydrological normalization into Tampa Bay Nitrogen TMDLs. Appendix A in: 2009 Reasonable Assurance Addendum: Allocation and Assessment Report.

Tampa Bay Nitrogen Management Consortium (TBNMC). 2010a. Tampa Bay Nitrogen Management Consortium Comments and Request Rega rding the Development of Protective Loads for the Tampa Bay Estuary as It Relates to Establis hing Numeric Nutrient Cr iteria for Lakes, Flowing

Waters and Estuaries in Florida. Attachment to Letter from TBNMC to EPA, March 8, 2010.

Tampa Bay Nitrogen Management Consortium (TBN MC). 2010b. 2009 Reasonable Assurance Addendum: Allocation and Assessment Report. TBEP Technical Publication #03-10.

Tampa Bay Regional Planning Council (TBRPC). 1986. Habitat restoration study for the Tampa Bay Region. Prepared by TBRPC, St. Petersburg, FL.

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

Wolter, K., and M.S. Timlin, 1993: Monitoring ENSO in COADS with a seasonally adjusted principal component index. Proc. of the 17th Climate Diagnostics Workshop , Norman, OK, NOAA/NMC/CAC, NSSL, Oklahoma Clim. Survey, CIMMS and the School of Meteor., Univ. of Oklahoma, 52-57.

Download PDF

. http://www.esrl.noaa.gov/psd/pe ople/klaus.wolter/MEI/#ref_wt1

## APPENDIX A

. Data Description and

Assessment of S eagrass, W ater Q uality, and TN Loading



## 1.0 Data Description

This section provides identification and description of the data utilized for developing relationships between seagrass extent, water quality, and loadings.



## 1.1 Seagrasses

An estimate of seagrass extent is available for 1950 (Figure 1

- 1). The areal covera ge of the 1950 seagrass beds was developed using data collected by the Florida Department of Natural Resources (FDNR) and the U.S. Fish and Wildlife Service (USFWS). Seagrass meadows were mapped from
1:24,000

- scale color photography, and obtained in digit al form from the FDNR. A GIS coverage of the data was created, and horizontally rectified to geographically coincide with mapped data for the time period (Janicki et al., 1995).

Aerial photography of seagrasses in the bay has been gathered approximately every two years since 1988 by the Southwest Florida Water Management District (SWFWMD), resulting in seagrass coverages for 1988, 1990, 1992, 1994, 1996, 1999, 2001, 2004, 2006, 2008, and 2010. Some of the 1988 areas mapped as seagrasses were later found to actually represent attached macro

- algae. From 1990 on, the aerial photography was field checked to verify presence of seagrasses (Figures 1

- 1, 1

- 2, and 1

- 3).

Additional aerial photography exists for 1982, as described in Lewis et al. (1985a). The methodology used in developing the 1982 seagrass coverage was different than that employed by the SWFWMD, so that it should be understood that direct comparisons of specific seagrass areas between the 1982 coverage and later coverages are not appropriate. However, the 1982 coverage does provide some measure of the baywide extent of seagrasses, and is useful for tracking seagrass changes on a baywide basis.Figure 1

- 1 . Tampa Bay seagrass, 1950 (FDNR and USFWS); 1990

- 1994 (SWFWMD) , with four mainstem segments identified.Figure 1

- 2 . Tampa Bay seagrass, 1996

- 2004 (SWFWMD), with four mainstem segments identified.Figure 1

- 3 . Tampa Bay seagrass, 2006

- 2010 (SWFWMD), with four mainstem segments identified.

## 1.2 Water Quality and Loadings

Water quality data utilized previously for establishment of targets in Tampa Bay, and here for developing numeric nutrient criteria in the bay, are those collected by the Environmental Protection Commission of Hillsborough County (EPCHC). The EPCHC has conducted monthly monitoring of ambient water quality in Tampa Bay since 1972, with complete records for most statio ns since 1974. Monitoring is performed at 52 fixed stations in Old Tampa Bay, Hillsborough Bay, Middle Tampa Bay, and Lower Tampa Bay. Monitoring is also performed in several bay tributaries. Water quality samples are collected at mid

- depth, and are ana lyzed for nutrients, chlorophyll, and biochemical oxygen demand (BOD). Hydrolab measurements are taken of dissolved oxygen (DO), specific conductivity, temperature, and pH at the surface, mid

- depth, and bottom. Water clarity is measured using a Secchi di sc. Full descriptions of the EPCHC water quality monitoring program and data summaries are found in Boler (1998), including the methods employed for sampling and analysis. The selected sites displayed in Figure 1

- 4 are those utilized for target setting e fforts in the past, and used for developing estuarine numeric nutrient criteria for the four mainstem segments.

Figure 1

- 4 . Locations of EPCHC water quality monitoring sites used in analyses.

## 2.0 Assessmen t of Conditions

Evaluation of the success of the TBNMC nitrogen management strategy is accomplished by an annual review of water quality data and biannual review of baywide seagrass extent. The following sections provide segment

- specific comparisons of o bserved conditions to the seagrass targets, chlorophyll a targets and regulatory thresholds, and TN loading targets. For reference, segment

specific t able s at the end of this appendix contains the annual mean chlorophyll a concentrations
utilized in the D ecision Matrix tool, the geometric mean annual TN and TP concentrations, and the annual hydrologic, TN, and TP loads for each of the four mainstem segments.



## 2.1 Old Tampa Bay

Time series plots of seagrass acreages, mean annual chlorophyll a concentrations, mean annual light attenuation and nutrient concentrations

, and annual TN loadings are provided in Figures 2

- 1 through 2

- 6 , respectively. Seagrasses in Old Tampa Bay have increased since 1990, with the exception of the period following the 1997

- 1998 El Niñ o event and during 2004 (Figure 2

- 1) . The TBEP has funded several studies in Old Tampa Bay to evaluate the potential cause of the less rapid increase in seagrass acreage here as compared to the bay as a whole, and is initiating additional

studies in the n ear future. As seen from the time series of annual chlorophyll a concentrations (Figure 2

- 2) , the regulatory threshold has been met in most years, indicating that light should be sufficient for seagrass recovery , with observed improvements in the availabl e light (Figure 2

- 3)

. Improvements in TN and TP concentrations have also occurred (Figures 2

- 4 and 2

- 5, respectively). Evaluation of the external TN load to the segment, which has been related to chlorophyll a concentrations via the empirical modeling ef fort (Janicki and Wade, 1996), shows that the target TN

loads have been exceeded in some years since 1994, even in years when chlorophyll a targets and

thresholds were met (Figure 2

- 6) . The apparent contradiction in meeting chlorophyll a targets and

thres holds while not meeting external TN loading targets has been related to the effects of varying hydrologic loading rates and residence time.Figure 2

- 1 . Comparison of observed Old Tampa Bay seagrass acreage to target.

Figure 2

- 2 . Comparison of observed Old Tampa Bay chlorophyll a concentrations to target and regulatory threshold.Figure 2

- 3

. Time series of Old Tampa Bay annual mean light attenuation, 1980

- 2010.

Figure 2

- 4 . Time series of Old Tampa Bay annual geometric mean TN concentrations, 1981

- 2009.Figure 2

- 5 . Time series of Old Tampa Bay annual geometric mean TP concentrations, 1980

- 2009.

Figure 2

- 6

. Comparison of observed Old Tampa Bay TN loadings to target.

## 2.2 Hillsborough Bay

Time series plots of seagrass acreages, mean annual chlorophyll a concentrations, mean annual light attenuation and nutrient concentrations, and annual TN loadings are provided in Figures 2

- 7 through 2

- 12 , respectively

, for Hillsborough Bay. Seagrasses in this segment have increased considerably since 1990 (Figure 2

- 7) . As seen from the time series of annual chlorophyll a concentrations, the regulatory threshold has been met in most years since 1994, and continuously for more than a decade, so that wate r quality conditions are appropriate for the observed increase in seagrasses (Figure 2

- 8)

. This is reinforced by the time series of light attenuation (Figure 2

- 9), with improved light availability. Nutrient concentrations have declined as well (Figures 2

- 10 and 2

- 11), especially TP. As in Old Tampa Bay, evaluation of the external TN load to the segment shows that the target TN loads have been exceeded several times since 1994, during the same period in which the segment was meeting chlorophyll a targets and thresholds. This has been related to the effects of varying hydrologic loading rates and residence time.

Figure 2

- 7

. Comparison of observed Hillsborough Bay seagrass acreage to target.Figure 2

- 8 . Comparison of observed Hillsborough Bay chlorophyll a concentrations to target and regulatory threshold.

Figure 2

- 9

. Time series of Hillsborough Bay annual mean light attenuation, 1980

- 2010.Figure 2

- 10 . Time series of Hillsborough Bay annual geometric mean TN concentrations, 1981

- 2009.

Figure 2

- 11 . Time series of Hillsborough Bay annual geometric mean TP concentrations, 1980

- 2009.Figure 2

- 12 . Comparison of observed Hillsborough Bay TN loadings to target.



## 2.3 Middle Tampa Bay

Time series plots of seagrass acreages, mean annual chlorophyll a concentrations, mean annual light attenuation and nutrient concentrations, and annual TN loadings are provided in Figures 2

- 13 through 2

- 18 , respectively , for Middle Tampa Bay. S eagrasses in this segment have increased by almost 3,000 acres since 1990 (Figure 2

- 13) . As seen from the time series of annual chlorophyll a concentrations, the regulatory threshold has been met in most years since 1994, and continuously

for more than a decade, so that water quality conditions are appropriate for the observed increase in seagrasses (Figure 2

- 14)

. This is supported by the time series of light attenuation (Figure 2

- 15), with improved light availability. Nutrient concentrations have declin ed as well (Figures 2

- 16 and 2

- 17), especially TP. As in Old Tampa Bay and Hillsborough Bay, evaluation of the external TN load to the segment shows that the target TN loads have been exceeded many times 1994, during the same period in which the segment w as meeting chlorophyll a targets and thresholds (Figure 2

- 18)

. This has been related to the effects of varying hydrologic loading rates and residence time.Figure 2

- 13 . Comparison of observed Middle Tampa Bay seagrass acreage to target.

Figure 2

- 14 . Comparison of observed Middle Tampa Bay chlorophyll a concentrations to target and regulatory threshold.Figure 2

- 15 . Time series of Middle Tampa Bay annual mean light attenuation, 1980

- 2010.

Figure 2

- 16 . Time series of Middle Tampa Bay annual geometric mean TN concentrations, 1981

- 2009

.Figure 2

- 17 . Time series of Middle Tampa Bay annual geometric mean TP concentrations, 1980

- 2009.

Figure 2

- 18 . Comparison of observed Middle Tampa Bay TN loadings to target.

## 2.4 Lower Tampa Bay

Time series plots of seagrass acreages, mean annual chlorophyll a concentrations, mean annual light attenuation and nutrient concentrations, and annual TN loadings are provided in Figures 2

- 1 9 through 2

- 24 , respecti vely, for Lower Tampa Bay. Seagrass acreages in this segment have remained more or less steady since 1990, with an increase during the last decade to nearly the segment target (Figure 2

- 19). As seen from the time series of annual chlorophyll a concentrat ions, the regulatory threshold has been exceeded only twice since 1994, so that water quality conditions are appropriate for the observed increase in seagrasses (Figure 2

- 20)

. This is supported by the time series of light attenuation (Figure 2

- 21), with i mproved light availability. Nutrient concentrations have declined as well (Figures 2

- 22 and 2

- 23). Evaluation of the external TN load to the segment shows that the target TN loads have been exceeded only three times since 1994 (Figure 2

- 24) . As for the other segments, exceedance of target load while attaining chlorophyll a targets and thresholds has been related to the effects of varying hydrologic loading rates and residence time.

Figure 2

- 19 . Comparison of observed Lower Tampa Bay seagrass acreage to target.Figure 2

- 20 . Comparison of observed Lower Tampa Bay chlorophyll a concentrations to target and regulatory threshold.

Figure 2

- 21 . Time series of Lower Tampa Bay annual mean light attenuation, 1980

- 2010.Figure 2

- 22 . Time series of Lower Tampa Bay annual geometric mean TN concentrations, 1981

- 2009.

Figure 2

- 23 . Time series of Lower Tampa Bay annual geometric mean TP concentrations, 1980

- 2009.Figure 2

- 24 . Comparison of ob served Lower Tampa Bay TN loadings to target.Old Tampa Bay mean annual chlorophyll a , geometric mean annual TN and TP concentrations,

and annual hydrologic, TN, and TP loads.

Year Chl a

(μg/L) TN Conc

(mg/L) TP Conc

(mg/L) TN Load

(tons/yr) TP Load

(tons/yr) Hydrologic Load

(10 6 m3/yr)

1980 13.87 0.64

1981 12.03 0.56 0.43

1982 12.99 0.59 0.30

1983 17.54 0.86 0.41

1984 9.16 1.05 0.41

1985 11.16 0.70 0.39 419 114 513

1986 10.59 0.58 0.43 478 111 515

1987 9.30 0.89 0.40 607 131 594

1988 8.16 0.58 0.37 685 187 695

1989 9.35 0.73 0.39 493 96 459

1990 9.34 0.52 0.40 386 88 395

1991 8.29 0.52 0.30 519 109 518

1992 7.88 0.62 0.27 444 105 441

1993 7.59 0.73 0.25 453 97 420

1994 9.43 0.92 0.25 562 109 488

1995 11.52 0.81 0.26 653 276 687

1996 6.85 0.83 0.19 475 191 514

1997 8.36 0.70 0.18 758 158 780

1998 11.23 0.78 0.24 811 179 789

1999 8.13 0.62 0.12 394 146 446

2000 7.17 0.92 0.09 396 106 413

2001 8.60 0.89 0.13 444 107 507

2002 7.83 0.82 0.14 615 134 688

2003 11.72 0.52 0.16 841 185 784

2004 11.81 0.56 0.12 855 190 910

2005 8.40 0.47 0.13 470 119 544

2006 6.28 0.45 0.14 515 116 604

2007 8.64 0.41 0.14 390 91 484

2008 9.27 0.44 0.13

2009 12.12 0.49 0.14Hillsborough Bay mean annual chlorophyll a , geometric mean annual TN and TP concentrations,

and annual hydrologic, TN, and TP loads.

Year Chl a

(μg/L) TN Conc

(mg/L) TP Conc

(mg/L) TN Load

(tons/yr) TP Load

(tons/yr) Hydrologic Load

(10 6 m3/yr)

1980 22.64 0.94

1981 30.98 1.09 0.74

1982 35.95 1.02 0.63

1983 25.86 1.10 0.67

1984 13.05 1.04 0.68

1985 19.27 0.85 0.63 1321 1474 707

1986 16.78 0.64 0.60 1516 1384 880

1987 14.23 1.03 0.66 2454 1862 1087

1988 13.04 0.70 0.65 2101 2006 1177

1989 14.18 0.75 0.56 1236 1352 642

1990 12.78 0.62 0.47 1010 1149 499

1991 14.10 0.59 0.45 1731 1603 921

1992 11.09 0.73 0.38 1240 1102 717

1993 9.84 0.71 0.34 1206 1166 804

1994 18.65 1.05 0.38 1911 1019 1192

1995 18.70 0.90 0.40 2163 1782 1447

1996 9.63 0.75 0.30 1459 991 1000

1997 11.99 0.73 0.30 2012 2507 1270

1998 20.74 0.85 0.43 3023 1910 1933

1999 10.29 0.64 0.24 1204 838 743

2000 8.83 0.88 0.20 799 584 490

2001 10.10 0.86 0.23 1499 1071 941

2002 13.69 0.77 0.23 1723 1193 1159

2003 12.40 0.56 0.26 2922 2055 1873

2004 11.93 0.57 0.28 3359 3929 1774

2005 13.12 0.51 0.26 1540 1128 1035

2006 10.95 0.46 0.24 1337 757 697

2007 8.34 0.42 0.20 741 550 565

2008 11.58 0.47 0.23

2009 14.63 0.46 0.23Middle Tampa Bay mean annual chlorophyll a , geometric mean annual TN and TP concentrations,

and annual hydrologic, TN, and TP loads.

Year Chl a

(μg/L) TN Conc

(mg/L) TP Conc

(mg/L) TN Load

(tons/yr) TP Load

(tons/yr) Hydrologic Load

(10 6 m3/yr)

1980 14.67 0.61

1981 14.21 0.58 0.37

1982 18.78 0.63 0.30

1983 19.33 0.81 0.43

1984 8.80 0.82 0.39

1985 13.00 0.65 0.37 461 92 565

1986 8.18 0.49 0.37 679 117 671

1987 8.56 0.75 0.42 859 140 690

1988 7.65 0.53 0.38 1215 249 1048

1989 8.38 0.59 0.36 694 109 572

1990 8.35 0.49 0.34 546 77 458

1991 7.88 0.45 0.28 674 130 610

1992 6.47 0.57 0.25 808 164 663

1993 6.57 0.61 0.23 560 87 524

1994 11.03 0.94 0.25 1036 221 751

1995 10.28 0.73 0.25 985 378 912

1996 5.35 0.63 0.16 484 177 509

1997 7.96 0.66 0.18 936 157 875

1998 12.24 0.75 0.27 944 201 869

1999 7.23 0.56 0.14 498 75 521

2000 6.07 0.81 0.11 493 66 475

2001 7.73 0.77 0.13 877 203 823

2002 6.14 0.68 0.14 649 103 673

2003 7.76 0.46 0.16 1230 246 1037

2004 6.58 0.42 0.14 854 213 842

2005 7.66 0.39 0.15 519 121 574

2006 5.13 0.34 0.14 468 89 502

2007 5.54 0.35 0.13 427 58 466

2008 5.75 0.38 0.14

2009 6.47 0.40 0.14Lower Tampa Bay mean annual chlorophyll a , geometric mean annual TN and TP concentrations,

and annual hydrologic, TN, and TP loads.

Year Chl a

(μg/L) TN Conc

(mg/L) TP Conc

(mg/L) TN Load

(tons/yr) TP Load

(tons/yr) Hydrologic Load

(10 6 m3/yr)

1980 6.13 0.27

1981 6.15 0.34 0.12

1982 6.14 0.38 0.12

1983 7.48 0.54 0.19

1984 3.94 0.57 0.13

1985 4.91 0.47 0.12 293 141 359

1986 3.56 0.37 0.15 379 128 399

1987 3.51 0.54 0.17 379 76 403

1988 3.39 0.42 0.15 369 119 499

1989 5.09 0.48 0.14 444 81 362

1990 4.06 0.34 0.12 318 53 293

1991 3.61 0.31 0.09 331 59 343

1992 4.04 0.46 0.08 341 63 393

1993 3.56 0.50 0.07 323 39 324

1994 5.49 0.80 0.08 386 55 367

1995 4.52 0.54 0.09 314 180 469

1996 2.21 0.44 0.06 211 95 321

1997 4.59 0.46 0.10 458 41 531

1998 5.81 0.54 0.14 457 57 437

1999 4.23 0.46 0.09 222 13 317

2000 4.49 0.80 0.06 217 13 286

2001 4.76 0.73 0.07 270 30 428

2002 3.82 0.59 0.11 247 16 406

2003 3.41 0.37 0.11 490 41 547

2004 4.89 0.32 0.07 285 35 438

2005 6.15 0.34 0.07 213 22 343

2006 3.64 0.29 0.08 195 18 330

2007 3.11 0.25 0.08 179 12 288

2008 2.85 0.27 0.08

2009 4.42 0.31 0.08

## APPENDIX B

.

Alternative Criteria Expressed as TN Concentrations, and as

TP Loads and Concentrations



## 1.0 TN Concentrations

T he TBEP has developed recommended segment

- specific numeric nutrient criteria in terms of TN

concentrations should these be necessary for Tampa Bay (Janicki Environmental, 2011 a ). The development of these criteria is described below.

Multiple analyses were completed in the evaluation of potential TN criteria expressed as in

- bay

concentrations , as described in Janicki Environmental (2011a) . These included:

 examination of the relationships between TN loadings and in

- bay TN concentrations;

 examination of relationships between monthly TN concentrations and chlorophyll a concentrations;

 examination of relationships between annual TN concentrations and chlorop hyll a concentrations; and

 application of a reference period approach to establishing TN concentration

- based criteria.

Since the previously proposed TN criteria are expressed as loads, the simplest method to propose criteria expressed as in

- bay concentrat ions would be based on the potential relationships between

in

- bay TN concentrations and TN loads delivered to each segment. All four mainstem segments

have annual TMDL TN target loads recognized by both EPA and DEP. If significant relationships

were foun d between the nutrient loads and their respective in

- bay concentrations, then the proposed numeric nutrient criteria could be expressed as concentrations.

Monthly segment

- specific TN concentrations were merged with monthly segment

- specific TN loads

res ulting in a dataset of monthly values of TN concentrations and loads. Plots of these data were inspected, with TN concentrations as functions of TN loads, including various lag and cumulative

load effects.

No relationships were found between TN concentrations and potential TN load explanatory variables that explained more than 20% of the variation in TN concentrations in Hillsborough Bay

or more than 10% of the variation in concentrations in the other three bay segments. This suggests

that there are some in

- bay processes (e.g., sedimentation, denitrification, and transport within the bay and exchange with the Gulf of Mexico) that affect the relationship between the TN loads and

the resultant in

- bay TN concen trations.

The results of these analyses did not provide adequate evidence to support recommendations for TN concentration criteria based on the relationships between the in

- bay nutrient concentrations and the nutrient loads to those segments.

The ne xt method used in evaluation of potential TN concentration criteria was to examine potential relationships between monthly TN concentrations and monthly chlorophyll a concentrations in each segment. Given the existing chlorophyll a targets and associated FDEP chlorophyll athresholds in each segment, sufficiently predictive relationships between nutrient and chlorophyll a

concentrations would allow derivation of TN concentration criteria commensurate with the

threshold values.

No relationships were found between chlorophyll a and TN concentrations that explained more than 24% of the variation in chlorophyll a concentrations.

The third method evaluated was to examine relationships between annual mean chlorophyll a and annual mean TN concentrations as a potential means of developing nutrient criteria. The annual mean TN concentrations were classified according to whether the annual chlorophyll a threshold in a given segment was met or not. Based on this classifica tion, the TN concentrations for those years in which the threshold was met could be compared to those TN concentrations for those years

when the threshold was exceeded.

The results of this analysis indicated that on an annual basis, there are apparent differences in the

in

- bay TN concentrations during years in which the threshold chlorophyll a targets are met and those in which they are not met. This is particularly the case in Hillsborough Bay and Middle Tampa Bay. These findings indicate that establishment of n utrient criteria should be linked to the annual chlorophyll a and loading targets already established for Tampa Bay.

The fourth approach to developing concentration

- based numeric nutrient criteria was the reference period approach. Segment

- specific chlor ophyll a targets (values at this level or below indicate desirable conditions) have been previously established (Janicki and Wade, 1996). These targets

were based on the 1992

- 1994 reference period. In 2000, a protocol for assessing whether the
Tampa Bay segments were achieving these targets was developed (Janicki et al., 2000). This protocol, referred to as the Decision Matrix approach, considered the year

- to

- year variability in chlorophyll a concentrations and arrived at segment

- specific chlorophyll a t hresholds (values above this level indicate undesirable conditions). The threshold was the sum of the chlorophyll a target and 2X the standard error of the long

- term chlorophyll a concentrations. FDEP has adopted these thresholds to assess compliance wit h the Tampa Bay Reasonable Assurance.

Applying the reference period approach to deriving concentration

- based numeric nutrient criteria also considered the effects of year

- to

- year variability, similar to that included in the development of the segment

- spec ific chlorophyll a targets and thresholds discussed above.

The 1992

- 1994 segment

- specific annual geometric mean TN concentrations are provided below,

with the standard deviation based on the 1992

- 2009 period :

Segment Geometric Mean Standard Deviation

 O ld Tampa Bay 0.75 mg/L 0.18 mg/L

 Hillsborough Bay 0 .82 mg/L 0.19 mg/L

 Middle Tampa Bay 0 .69 mg/L 0.18 mg/L

 Lower Tampa Bay 0.57 mg/L 0.17 mg/L

The proposed alternative concentration

- based TN criteria (Table 1

- 1) are defined as the sum of the annual geometric mean concentration and the standard deviation of the long

- term mean annual TN

concentrations.Table 1

- 1 . TBEP estuarine numeric nutrient criteria for TN expressed as concentrations.
Segment TN Concentration (mg/L) Old Tampa Bay 0.93 Hillsborough Bay 1.01 Middle Tampa Bay 0.87 Lower Tampa Bay 0.74

The proposed TN concentration criteria are compared to the observed geometric mean annual TN

concentrations in Figures 1

- 1 through 1

- 4 . The green horizontal lines represent the proposed

alternative criteria; the data to the right of the vertical lines depict the TN concentrations since the reference period (1992

- 1994).

Figure 1

- 1 . Comparison of proposed alternative TN concentration criterion for Old Tampa Bay to the

annual geometric mean TN concentrations from 1981 through 2009.Figure 1

- 2 . Comparison of proposed alternative TN concentration criterion for Hillsborough Bay to the annual geometric mean TN concentrations from 1981 through 2009.

Figure 1

- 3 . Comparison of proposed alternative TN concentration criterion for Middle Tampa Bay to the

annual geometric mean TN concentrations from 1980 through 2009.Figure 1

- 4 . Comparison of proposed alternative TN concentration criterion for Lower Tampa Bay to the annual geometric mean TN concentrations from 1980 through 2009.



## 2.0 TP Load and Concentration Alternative / Supplem en tary
Criteria

T he 1992

- 1994 average annual total nitrogen loads were established as the appropriate nitrogen load management targets by TBEP partners in order to support the maintenance of the chlorophyll a and light attenuation targets developed for each of Tampa Bay’ s major bay segments. The TN loading threshold criteria were defined as the segment

- specific Nitrogen Delivery Ratio based on

the mean 1992

- 1994 conditions. In keeping with this approach, the TP loading target and TP loading threshold criteria are define d as the segment

- specific Phosphorus Delivery Ratio based on

the mean 1992

- 1994 conditions. The TP loading targets and loading threshold criteria expressed as the Phosphorus Delivery Ratio are provided in Table 2

- 1. Time series plots of annual Phosphorus Deliver Ratio to the threshold are provided in Figures 1

- 5 through 1

- 8, indicating that the threshold value has been exceeded infrequently during the recent (2000 on) period.

Table 2

- 1 . TBEP estuarine numer ic nutrient criteria for TP target loads and threshold criteria expressed as the Phosphorus Delivery Ratio

.

Segment TP Load Target
(tons/yr) TP Load Threshold Expressed as Phosphorus
Delivery Ratio (tons/million m 3 )
Old Tampa Bay 104 0.23
Hillsborough Bay 1093 1.28
Middle Tampa Bay 140 0.24

Lower Tampa Bay 112 0.14Figure 2

- 1 . Comparison of annual Phosphorus Delivery Ratio to proposed T P loading threshold criteria for

Old Tampa Bay.

Figure 2

- 2 . Comparison of annual Phosphorus Delivery Ratio to proposed T P loading threshold criteria for Hillsborough Bay.Figure 2

- 3 . Comparison of annual Phospho rus Delivery Ratio to proposed T P loading threshold criteria for

Middle Tampa Bay.

Figure 2

- 4 . Comparison of annual Phosphorus Delivery Ratio to proposed T P loading threshold criteria for

Lower Tampa Bay.In the same manner as described above for development of the TN criteria in terms of

concentrations, evaluation of TP concentration criteria was completed. As for the TN concentration methodology, the most appropriate method was determined to be the Reference Period approach, in keeping with the existing TN loading targets and proposed threshold criteria, the proposed TN concentration criteria, and the proposed TP loading targets and threshold criteria.

The 1992

- 1994 segment

- specific annual geometric mean TP concentrations are provided below,

with the standard deviation based on the 1992

- 2009 period :

Segment Geometric Mean Standard Deviation

 Old Tampa Bay 0. 2 5 mg/L 0.06 mg/L

 Hillsborough Bay 0

. 37 mg/L 0.08 mg/L

 Middle Tampa Bay 0

. 24 mg/L 0.05 mg/L

 Lower Tampa Bay 0. 08 mg/L 0.02 mg/L

The proposed alternative concentration

- based T P criteria (Table 2

- 2) are defined as the sum of the annual geometric mean concentration and the standard deviation of the long

- term mean annual T P

concentrations.

Table 2

- 2 . TBEP estuarine numeric nutrient criteria for T P

expressed as concentrations.
Segment T P Concentration (mg/L) Old Tampa Bay 0. 31 Hillsborough Bay 0

. 45 Middle Tampa Bay 0. 29 Lower Tampa Bay 0. 10

The proposed T P concentration criteria are compared to the observed geometric mean annual T P concentrations in Figures 2

- 5 through 2

- 8 . The green horizontal lines represent the proposed

criteria . As seen in these graphics, the proposed TP concentration criteria have been met in most years in all segments since the early 1990s.Figure 2

- 5

. Comparison of proposed TP concentration criterion for Old Tampa Bay to the annual
geometric mean TP concentrations from 1980 through 2009.

Figure 2

- 6 . Comparison of proposed TP concentration criterion for Hillsborough Bay to the annual

geometric mean TP concentrations from 1980 through 2009.Figure 2

- 7 . Comparison of proposed TP concentration criterion for Middle Tampa Bay to the annual
geometric mean TP concentrations from 1980 through 2009.

Figure 2

- 8 . Comparison of proposed TP concentration criterion for Lower Tampa Bay to the annual

geometric mean TP concentrations from 1980 through 2009.

## APPENDIX C

.

Comparison of Annual TN Loads to Annual Hydrologic Loads:

Nitrogen Delivery Ratio

A comparison of the annual TN loads to annual hydrologic loads for each bay segment between 1995 and 2007 is shown graphically in Figures 1

- 4 below. The vertical axis is the annual TN load, and the horizontal axis is the annual hydrologic load. The slanted blue line represents the loads corresponding to those expected using the 1994

- 1994 Nitrogen Delivery Ratio, in terms of tons TN/year per million m 3 hyd rologic load/year. Points falling below the line represent those years when the Nitrogen Delivery Ratio was less than that observ ed during the 1992

- 1994 period. Points above the blue line in each graphic denote years when the loads would be in excess of the

thresholds . The Hillsborough Bay threshold as denoted by the Nitrogen Delivery Ratio was exceeded in 2004 and 2006, and the Lower Tampa Bay threshold was exceeded in 1998. In all the remaining years for those bay segments, and in all years during t he 1995

- 2007 period for Middle Tampa Bay and Old Tampa Bay, the Nitrogen Delivery Ratios were below the threshold.

Figure 1. Relationship between annual TN load and annual hydrologic load in Old Tampa Bay for 1995

- 2007. The slanted blue line is what the expected relationship would be given the Nitrogen Delivery Ratio

of 1.08 tons TN load/million m 3 hydrologic load from the 1992

- 1994 period.Figure 2

. Relationship between annual TN load and annual hydrologic load in Hillsborough Bay for 1995

-

2007. The slanted blue line is what the expected relationship would be given the Nitrogen Delivery Ratio

of 1.62 tons TN load/million m 3 hydrologic load from the 1992

- 1994 period.

Figure 3

. Relationship between annual TN load and annual hydrologic load in Middle Tampa Bay for 1995

- 2007. The slanted blue line is what the expected relationship would be given the Nitrogen Delivery Ratio

of 1.24 tons TN load/million m 3 hydrologic load from the 1992

- 1994 period.Figure 4

. Relationship between annual TN l oad and annual hydrologic load in Lower Tampa Bay for 1995

-

2007. The slanted blue line is what the expected relationship would be given the Nitrogen Delivery Ratio

of 0.97 tons TN load/million m 3 hydrologic load from the 1992

- 1994 period.

## APPENDIX D

. Implementation Issues and Compliance Assessment

Background

As part of this document, s ite specific numeric nutrient criteria are being proposed as alternatives to the application of regional or state wide model based standards

. The se site specific criteria rely on the identification of a response endpoint which has been defined for Tampa Bay as chlorophyll a concentration s and their effect on light attenuation to seagrass es . The temporal scale has been

defined as annually

. The implementation of the Florida numeric nutrient criteria proposed by EPA will require the definition of an implementation and assessment cycle. Consideration of the potential ramifications of an assessment that is either too lenient or too strident is a cr itical element of the evaluation of alternative assessment cycles. Both EPA and FDEP are considering allowances of criteria exceedance due to natural variability. The draft freshwater numeric nutrient criteria proposed by EPA identified a 3

- year as sessment cycle which incorporates a “1 in 3” rule to allow

one exceedance in a three

- year assessment cycle to account for natural variability. The Florida Department of Environmental Protection (FDEP) currently uses a 5

- year assessment cycle for

evaluati on of impairment in waterbodies, as well as NPDES, MS4, and other regulatory permitting cycles. FDEP was initially considering a “2 in 5” rule for compliance but has since proposed “1 in 5” as the allowable exceedance frequency.

Climate anomalies and c riteria exce e d a nces

Janicki Environmental (2011 a,b,c ) examine d the effects of these different temporal assessment schemes on the likelihood of concluding that a waterbody was in exceedance based solely on natural meteorological variability and concluded that the 2 in 5 rule would be most appropriate to allow for natural variability due to climatological anomalies and yet remain sensitive to detecting a deviation in water quality due to anthropogenic activities. Th e investigation wa s based on a conceptual mode l expressed by the EPA that the regul atory compliance assessment cycle should allow for natural disturbance patterns resulting from episodic events in Florida . These events could

include h urricanes and ENSO

- related droughts and floods that influence water quality independent of anthropogenic effects. T he relationship between these events and water quality has been substantiated in several southwest Florida estuaries. (e.g. Morrison et al.

, 2006; Sherwood, 2010).

Janicki Environmental (2011 c ) used long

- ter m stream flow records to characterize natural vari ability in the hydrologic conditions in Tampa Bay since the 1930s. T his estimate of natural variability was then used to test two potential temporal assessment schemes with respect to their ability to acco unt for natural variability and identify exceedance s relate d to anthropogenic activities. Since the objective of the rule is to account for exceedances due to natural environmental variability, th e analysis suggest ed that a “ 2 in 5 ” rule is more likely to absorb natural variability than the “ 1 in 3 ”

rule . Based on the s e analyses , the “ 1 in 3 ” rule would result in more exceedance s due to natural variability alone and

, therefore

, be overly sensitive to non

- anthropogenic variability co mpared to

the “ 2 in 5 ” rule. For example, i t is easy to see in Figure 1 that when El Niño or La Niña events occur they tend to last more than a single year. In fact, it’s quite possible for many of the single events to cross a calendar year. Further inform ation on the frequency and duration of ENSO events

can be found at: http://www.esrl.noaa.gov/psd/enso/mei/Figure 1

. Classification of El Niño and La Niña events as described in Janicki Environmental 201 1 a.

FDEP is also considering allowances for the misclassification of an impairment due to sampling variability. This type of misclassification is called the “ Type 1 er ror ” of “False Positive Rate” . The type 1 error rate is defined when establishing targets and threshold values using any estimate of a population of water quality data with variability. Such is the case with many of the estuaries that are developing crite ria based on the reference period approach. An example of that discussion follows.

Type 1 Error and the Reference Period Approach

To begin this example, a hypothetical reference period distribution of chlorophyll a concentrations

was generated. Chlorophyll a concentrations in estuaries typically exhibit “lognormal” distribution characteristics. This implies that when a natural log transformation is applied to the distribution, it becomes normally distributed which conforms to most pa rametric statistical tests. Therefore, a lognormal distribution of chlorophyll a concentrations was simulated using a mean of 6.75 μg/L

and a standard deviation of 4.49 μg/L. This distribution composed of 10000 observations is shown in Figure 2 . Once the d ata are natural log transformed, the distribution becomes bell shaped corresponding to the normal distribution (Figure 2). Since FDEP and EPA have proposed using

ann ual geometric means as regulatory statistics for parameters with lognormal distributions such as chlorophyll a, we now consider the log transformed values to represent the data underlying this hypothetical evaluation and back transform the averages to obta in the geometric means.Given the theoretical distribution of Figure 3 , we can generate annual averages to simulate the

product of a typical monitoring program. For example, we can randomly select 12 observations

from the distribution of log values, and calculate an average and back transform that average to obtain the geometric mean. Further, we can repeat this experiment many times, each time selecting 12 samples and calculating the average of the log values. We expect each average to be close to the overall average of the reference period since it is a random sub

- sample, however, we know that variability will exist due to sampling. For example, in Figure 4 , we have generated 100 annual averages from the reference period distributio n. As can be seen in Figure 4 , the distribution of annual averages is centered on a value very close to the overall average in Figure 3 which is expected.

Figure 2 . Simulated distribution of chlorophyll a concentrations.Figure 3 . Distribution of the natural log transformed values of the simulated distribution above.

Figure 4 . Distribution of 100 annual averages of the log transformed chlorophyll values using 12 samples per year.To derive the geometric annual averages, we simply back transf orm the annual averages of Figure

3. This distribution is shown in Figure 5

.

Figure 5 . Geometric means taken from the simulated chlorophyll concentrations above.

Targets and Thresholds

Once the geometric means have been calculated we have all the information necessary to develop
targets and thresholds for this theoretical reference period distribution.

The reference period target for this distribution can be defined as the overall average of all the geometric means. Th at is, 5.947 μg/L is our goal for the water body to ensure that it remains similar to the reference period condition we identified as being indicative of full aquatic life support. However, it can be seen from Figure 4 that the distribution of annual geome tric means for this population ranges between 3.9 μg/L and 8.3 μg/L . Therefore, the distribution of geometric means can be considered a population of values that represent the expected distribution of annual averages of the reference period. Based on normal distribution theory, we can assign a threshold value to represen t an annual average above which we would reject the hypothesis that the value was from the same population as the reference period distribution of annual geometric means. Using the z table of standard statistical tests, only 5% of a normal distribution wit h a mean and standard deviation of the distribution in Figure 4 would lie above the mean+1.65*the standard deviation of the population of geometric means. Therefore, a threshold can be constructed for this

distribution that defines with 95% confidence wha t value a given geometric mean would need to exceed to reject the hypothesis that it belonged to the reference period distribution. For this

distribution that threshold value equals 7.59 μg/L

.The threshold value provides a level of certainty that a fut ure single geometric mean value (i.e. a

sample) is not declared to exceed the reference distribution simply due to sampling. As was demonstrated above, we know that some portion of the reference distribution values will be above

the target value. In fact, nearly 50% of the annual geometric means will be higher than the target

. However, only 5% of the values will be higher than the threshold value of 7.59 μg/L due to

chance. This construct defines what is known as the Type I error rate or False Positive ra te

. That
is, we are willing to accept that 1 in 20 times we may get a value that is higher than 7.59 μg/L that still belongs to the reference period distribution. As was seen in Figure 5 , 5% of the values did

exceed 7.59 μg/L even though we know the enti re population of values.

Therefore, the type I error rate is a value that is selected based on judgment and while 5% is typically used, there is no definitive rationale for 5% versus 1% or 10%. If we wish to be more conservative, we would select a lower type I error rate by choosing a larger value (e.g., 1.96) to multiple against the standard deviation to minimize the potential for falsely declaring that a value

was different from the reference distribution. If we have reason to believe that the water bod y may not fully meet its designated use at values at the higher end of the reference distribution, one could select a higher type I error rate which in turn would equate to a smaller z score to multiply by the standard deviation (e.g., 1). For example, sel ecting 1 standard deviation equates to a type 1 error

rate of 16%. Therefore , the type 1 error rate does obviously have implications on the compliance

assessment that also need to be accounted for

.

Recommendations

Based on this analysis, it makes sense to allow for the potential that an anomalous event could result in higher annual geometric average than the reference period threshold value in more than one year in a 5 year cycle as is currently proposed by FDEP.

Therefore

, the recommended allowance as an exceedance frequency in a five year assessment cycle is to allow for no more than 2 exceedances in a 5 year assessment cycle.

It is possible that the type I error rate and the probability of an anomalous event c ould be est imated such that both the probability of an exceedance occurring by chance and the probability that an exceedance occurs due to anomalous conditions could be integrated. That is, over a 5 year cycle one might calculate the probability of either an exceedan ce due to chance or an exceedance due to a natural anomaly. This was beyond the scope of this memorandum but one that might be pursued as the implementation process is refined. Because the proposed criteria are based on threshold values with known type 1 e rror rates, the criteria and the 2 in 5 year implementation criteria are inextricably linked and should not be separated. Further information supporting the use of the 2 in 5 implementation rule is provided in Janicki Environmental (2011 a,b,c ).

### References

Janicki Environmental, Inc. 201 1 a. Sarasota Bay Numeric Nutrient Criteria: T
ask 4

- Implementation Issues. Letter Memorandum Prepared for Sarasota Bay Estuary Program. Sarasota, Florida

Janicki Environmental, Inc. 201 1 b. Charlotte Harbor Numeric Nu trient Criteria: Implementation Issues. Letter Memorandum Prepared for Charlotte Harbor Estuary Program. Ft. Myers, Florida

Janicki Environmental, Inc. 2011 c . Tampa Bay Numeric Nutrient Criteria: Task 4

– Implementation Issues. Letter Memorandum. P repared for: Tampa Bay Estuary Program.

Morrison, G., E.T. Sherwood, R. Boler, and J. Barron. 2006. Variations in water clarity and chlorophyll a in Tampa Bay, Florida, in response to annual rainfall, 1985

- 2004. Estuaries and

Coasts. 29:926

- 931.

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

- 10 of the Tampa Bay Estuary Program. Prepared by the Tampa Bay Estuary Program.

Wolter, K., and M.S. Timlin, 1993: Monitoring ENSO in COADS with a seasonally adjusted principal component index. Proc. of the 17th Climate Diagnostics Workshop , Norman, OK, NOAA/NMC/CAC, NSSL, Oklahoma Clim. Survey, CIMMS and the School of Meteor., Univ. of Oklahoma, 52

- 57.
Download PDF

. http://www.esrl.noaa.gov/psd/people/klaus.wolter/MEI/#ref_wt1

## APPENDIX E

. Maps of EPCHC Monitoring Sites
Utilized for Water Quality Assessment in

Each SegmentFigure 1. EPCHC sites used for assessment of water quality conditions in Old Tampa Bay.Figure 2. EPCHC sites used for assessment of water quality conditions in Hillsborough Bay.Figure 3. EPCHC sites used for assessment of water quality conditions in Middle Tampa Bay.Figure 4. EPCHC sites used for assessment of water quality conditions in Lower Tampa Bay.