from nitrogen and phosphorus pollution in Florida include monetary
losses due to depressed fisheries, tourism and property values, and
elevated costs to address nutrient impacts (e.g., beach cleanup costs,
HAB monitoring).
---------------------------------------------------------------------------

    \128\ Anderson, D.M.. 2008. Hearing on ``Harmful Algal Blooms:
The Challenges on the Nation's Coastlines''. Woods Hole
Oceanographic Institution. http://www.whoi.edu/page.do?pid=8916&tid=282&cid=46007. Accessed December 2011.
---------------------------------------------------------------------------

    Seagrass habitats are valuable components of Florida's estuarine
and coastal waters. FDEP has estimated that each acre of seagrass is
worth $20,255 per year, which would translate to a benefit of $44.6
billion statewide.\129\

The nearly 2.2 million acres of seagrass beds in Florida's nearshore
waters support fish and shellfish that are economically vital to
commercial and recreational businesses in Florida.\130\ Some estuary
experts have attempted to quantify the overall value of individual
estuaries in Florida. For example, the Indian River Lagoon National
Estuary Program estimated the total value of the Indian River Lagoon at
$3.7 billion (2009 dollars). In the study, recreational and non-use
values of the lagoon were estimated to increase by nearly $80 million
per year (2009 dollars) if there were a significant increase in the
amount and diversity of wildlife in the lagoon, as well as increased
water quality throughout the system from restoration and water quality
improvement projects.\131\
---------------------------------------------------------------------------

    \129\ USGS. 2001. Seagrass Habitat In the Northern Gulf of
Mexico: Degradation, Conservation, and Restoration of a Valuable
Resource. U.S. Geological Survey, Gulf of Mexico Habitat Program
Team,
    855-R-04-001. http://gulfsci.usgs.gov/gom_ims/pdf/pubs_gom.pdf. Accessed July 2011.
    Burkholder, J.M., D.A. Tomasko, and B.W. Touchette. 2007.
Seagrasses and eutrophication. Journal of Experimental Marine
Biology and Ecology 350:46-72.
    Waycott, M., C.M. Duarte, T.J.B. Carruthers, R.J. Orth, W.C.
Dennison, S. Olyarnik, A. Calladine, J.W. Fourqurean, K.L. Heck,
Jr., A.R. Hughes, G.A. Kendrick, W.J. Kenworthy, F.T. Short, and
S.L. Williams. 2009. Accelerating loss of seagrasses across the
globe threatens coastal ecosystems. Proceedings of the National
Academy of Sciences of the United States of America 106(30):12377-
12381.
    Short, F.T., B. Polidoro, S.R. Livingstone, K.E. Carpenter, S.
Bandeira, J.S. Bujang, H.P. Calumpong, T.J.B. Carruthers, R.G.
Coles, W.C. Dennison, P.L.A. Erftemeijer, M.D. Fortes, A.S. Freeman,
T.G. Jagtap, A.H.M. Kamal, G.A. Kendrick, W.J. Kenworthy, Y.A. La
Nafie, I.M. Nasution, R.J. Orth, A. Prathep, J.C. Sanciangco, B. van
Tussenbroek, S.G. Vergara, M. Waycott, and J.C. Zieman. 2011.
Extinction risk assessment of the world's seagrass species.
Biological Conservation144:1963-1971.
    Watson R.A., R.G. Coles, and W.J. Lee Long. 1993. Simulation
estimates of annual yield and landed value for commercial penaeid
prawns from a tropical seagrass habitat, Northern Queensland,
Australia. Australian Journal of Marine and Freshwater Research
44:211-219.
    Carlson, P., and L. Yarbro. 2008. Seagrass Mapping and
Monitoring: Big Bend and Beyond. Presented at Florida Water
Resources Monitoring Council Meeting, St. Petersburg, FL, September
24-25, 2008.
    Costanza, R., R. d'Arge, R. de Groot, S. Farber, M. Grasso, B.
Hannon, K. Limburg, S. Naeem, R.V. Neill, J. Paruelo, R.G. Raskin,
P. Sutton, and M. van den Belt. 1997. The value of the world's
ecosystem services and natural capital. Nature 387:253-260.
    \130\ FDEP. 2011. Celebrate Seagrass Awareness Month. Florida
Department of Environmental Protection. http://www.dep.state.fl.us/coastal/news/articles/2011/1103_Seagrass.htm. Accessed June 2011.
    Scott, R. 2011. Seagrass Awareness Month. Proclamation by
Governor Rick Scott of the State of Florida. Florida Department of
Environmental Protection. http://www.dep.state.fl.us/coastal/habitats/seagrass/awareness/Proclamation_2011.pdf. Accessed June
2011.
    \131\ USEPA. 2009. Determining an Estuary's Economic Value. EPA-
842F09001. U.S. Environmental Protection Agency, National Estuary
Program, Washington, DC. http://water.epa.gov/type/oceb/nep/upload/2009_05_28_estuaries_inaction_Efficient_IndianRiver.pdf.
Accessed July 2011.
---------------------------------------------------------------------------

    According to a study on the impacts of HABs on beachfront tourism-
dependent businesses in the Ft. Walton Beach and Destin areas of
Florida, HABs reduced restaurant and lodging revenues by $2.8 million
and $3.7 million per month, respectively, representing a 29 percent to
35 percent decline in average monthly revenues.\132\
---------------------------------------------------------------------------

    \132\ Larkin, S.L., and C.M. Adams. 2007. Harmful algal blooms
and coastal business: economic consequences in Florida. Society &
Natural Resources 20(9):849-859.
---------------------------------------------------------------------------

    A study by Mather Economics estimated the effects of water quality
on real estate value in the South Florida Water Management District.
The aggregate owner-occupied residential real estate value in the 16-
county South Florida Water Management District is approximately $976
billion. If water quality (measured by dissolved oxygen levels) can be
returned to 1970 levels as a result of restoring the Everglades (a
potential 23.4 percent improvement in water quality), the study found
that real estate values would increase by $16 billion.\133\
---------------------------------------------------------------------------

    \133\ McCormick, B., R. Clement, D. Fischer, M. Lindsay, R.
Watson. 2010. Measuring the Economic Benefits of America's
Everglades Restoration: An Economic Evaluation of Ecosystem Services
Affiliated with the World's Largest Ecosystem Restoration Project.
Prepared for the Everglades Foundation, Palmetto Bay, FL, by Mather
Economics, Roswell, GA.
---------------------------------------------------------------------------

    In addition to negatively impacting Florida businesses, nitrogen
and phosphorus pollution increases costs for beach cleanup, HAB
monitoring, and wastewater treatment. For example, approximately
$63,000 was spent annually from 1995-1997 to dispose of red seaweed and
fish killed by HAB events that littered 17.5 miles of beach in Sarasota
County.\134\
---------------------------------------------------------------------------

    \134\ Hoagland, P., D.M. Anderson, Y. Kaoru, and A.W. White.
2002. The economic effects of harmful algal blooms in the United
States: estimates, assessment issues, and information needs.
Estuaries 25:819-837.
---------------------------------------------------------------------------

    In addition, there are increased costs due to the need to treat
polluted sources of drinking water. As an example of increased costs
for drinking water treatment, in 1991, Des Moines (Iowa) Water Works
constructed a $4 million ion exchange facility to remove nitrate from
its drinking water supply. This facility was designed to be used an
average of 35-40 days per year to remove excess nitrate levels at a
cost of nearly $3,000 per day.\135\ In another example, Fremont, Ohio
(a city of approximately 20,000) has experienced high levels of nitrate
from its drinking water source, the Sandusky River, resulting in
numerous drinking water use advisories. An estimated $15 million is
needed to build a reservoir (and associated piping) that will allow for
selective withdrawal from the river to avoid elevated levels of nitrate
and provide storage.\136\ By regulating allowable levels of chlorophyll
a in Oklahoma drinking water reservoirs, the Oklahoma Water Resources
Board estimated that the long-term cost savings in averted drinking
water treatment for 86 systems would range between $106 million and
$615 million if such regulations were implemented.\137\ These
statistics are illustrative of what treatment to address nitrates and
nitrites can cost. Any impacts in Florida would be site-specific and
might or might not be comparable to these numbers.
---------------------------------------------------------------------------

    \135\ Jones, C.S., D. Hill, and G. Brand. 2007. Use a
multifaceted approach to manage high sourcewater nitrate. Opflow
June:20-22.
    \136\ Taft, Jim, Association of State Drinking Water
Administrators (ASDWA). 2009. Personal Communication.
    \137\ Moershel, Philip, Oklahoma Water Resources Board (OWRB)
and Mark Derischweiler, Oklahoma Department of Environmental Quality
(ODEQ). 2009. Personal Communication.
---------------------------------------------------------------------------

B. Statutory and Regulatory Background

    Section 303(c) of the CWA (33 U.S.C. 1313(c)) directs states to
adopt WQS for their navigable waters. CWA Section 303(c)(2)(A) and
EPA's implementing regulations at 40 CFR 131 require, among other
things, that state WQS include the designated use and criteria that
protect those uses. EPA regulations at 40 CFR 131.11(a)(1) provide that
states shall ``adopt those water quality criteria that protect the
designated use'' and that such criteria ``must be based on sound
scientific rationale and must contain sufficient parameters or
constituents to protect the designated use.'' In addition, 40 CFR
131.10(b) provides that ``[i]n designating uses of a water body and the
appropriate criteria for those uses, the state shall take into
consideration the water quality standards of downstream waters and
ensure that its water quality standards provide for the attainment and
maintenance of the water quality standards of downstream waters.''
    States are also required to review their water quality standards at
least once every three years and, if appropriate, revise or adopt new
standards (CWA section 303(c)(1)). Any new or revised water quality
standards must be submitted to EPA for review and approval or
disapproval (CWA section 303(c)(2)(A) and (c)(3)). In addition, CWA
section 303(c)(4)(B) authorizes the Administrator to determine, even in
the absence of a state submission, that a new or revised standard is
needed to meet CWA requirements. The EPA approved the State of
Florida's rules (which include criteria for certain estuaries and
coastal marine waters) on November 30, 2012. The criteria proposed in
this rulemaking protect the uses designated by the State of Florida and
implement Florida's narrative nutrient provision at Subsection 62-
302.530(47)(b), F.A.C. for the purposes of the CWA. These criteria
include numeric values that apply to Florida's

estuaries and coastal waters not covered by the newly-approved State
WQS, south Florida inland flowing waters, and DPVs to ensure the
attainment and maintenance of the water quality standards of downstream
estuaries.\138\ As explained more fully in Section I.A, EPA does not
intend to finalize these DPVs if the district court modifies the
Consent Decree consistent with EPA's amended determination that numeric
DPVs are not necessary to meet CWA requirements in Florida.
---------------------------------------------------------------------------

    \138\ The criteria proposed in this rulemaking do not address or
implement Florida's narrative nutrient provision at Subsection 62-
302.530(47)(a), F.A.C. Subsection 62-302.530(47)(a), F.A.C. remains
in place as an applicable water quality standard for CWA purposes.
---------------------------------------------------------------------------

C. Water Quality Criteria

    Water quality criteria include three components. The first
component is ``magnitude,'' the concentration of a pollutant that can
be maintained over time in the ambient receiving water without
adversely affecting the designated use that the criteria is intended to
support. The second component is ``duration,'' or the time period over
which exposure is averaged (i.e., the averaging period) to limit the
time of exposure to elevated concentrations. This accounts for the
variability in the quality of the ambient water due to variations of
constituent inputs, flow, and other factors. The third component is
``frequency,'' or how often the magnitude/duration condition may be
exceeded and still protect the designated use. Combining the criterion-
magnitude with the duration and frequency prevents harmful effects from
infrequent exceedances of the criterion-magnitude by ensuring
compensating periods of time during which the concentration is below
the criterion-magnitude. When criterion-magnitudes are exceeded for
short periods of time or infrequently, aquatic life can typically
recover; that is, the designated uses of the water body are typically
protected. Designated uses are typically not protected when criterion-
magnitudes are exceeded for longer periods of time (i.e., for longer
than the specified duration) or more frequently (i.e., more often than
the allowed frequency).\139\ Use of this magnitude-duration-frequency
format allows for some exceedances of the criterion-magnitude
concentrations while still protecting applicable designated uses, which
is important for pollutants such as nitrogen and phosphorus because
their concentrations can vary naturally in the environment.
---------------------------------------------------------------------------

    \139\ USEPA. 1994. Water Quality Standards Handbook: Second
Edition, Chapter 3--Water Quality Criteria. EPA-823-B-94-005a. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
    USEPA 1991. Technical Support Document for Water Quality-based
Toxics Control. Appendix D--Duration and Frequency. EPA/505/2-90-
001. U.S. Environmental Protection Agency, Office of Water,
Washington, DC.
---------------------------------------------------------------------------

    Under CWA section 304(a), EPA periodically publishes criteria
recommendations for use by states in setting water quality criteria for
particular parameters to protect recreational and aquatic life uses of
waters. Where EPA has published recommended criteria, states have the
option of adopting water quality criteria based on EPA's CWA section
304(a) criteria guidance, section 304(a) criteria guidance modified to
reflect site-specific conditions, or other scientifically defensible
methods (40 CFR 131.11(b)(1)).
    For nitrogen and phosphorus pollution, EPA has published under CWA
section 304(a) a series of peer-reviewed, national technical approaches
and methods for the development of numeric nutrient criteria for lakes
and reservoirs,\140\ rivers and streams,\141\ and estuarine and coastal
marine waters.\142\ EPA based the methodologies used to develop numeric
nutrient criteria for Florida in this proposed regulation on these
published guidance documents, which identify three scientifically
defensible approaches for deriving nutrient criteria: (1) The reference
condition approach derives criteria from observations collected in
reference water bodies or during reference time periods; (2) the
mechanistic modeling approach represents contaminant loadings,
hydrodynamics, and impacts in aquatic systems using equations that
represent physical and ecological processes, calibrated using site-
specific data; and (3) the stressor-response approach estimates the
relationship between nutrient concentrations and response measures
related to a designated use of the water body. These three analytical
approaches have been independently peer-reviewed and are appropriate
for deriving scientifically defensible numeric nutrient criteria,
taking into consideration the method-specific data needs and available
data. In addition to these approaches, consideration of established
(e.g., published and peer-reviewed) nutrient response thresholds is
also an acceptable approach for deriving criteria.\143\
---------------------------------------------------------------------------

    \140\ USEPA. 2000a. Nutrient Criteria Technical Guidance Manual:
Lakes and Reservoirs. EPA-822-B-00-001. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
    \141\ USEPA. 2000b. Nutrient Criteria Technical Guidance Manual:
Rivers and Streams. EPA-822-B-00-002. U.S. Environmental Protection
Agency, Office of Water, Washington, DC.
    \142\ USEPA. 2001. Nutrient Criteria Technical Manual: Estuarine
and Coastal Marine Waters. EPA-822-B-01-003. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
    \143\ USEPA. 2000a. Nutrient Criteria Technical Guidance Manual:
Lakes and Reservoirs. EPA-822-B-00-001. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
---------------------------------------------------------------------------

    The criteria proposed in this rulemaking implement Florida's
narrative nutrient provision at Subsection 62-302.530(47)(b), F.A.C.,
for the purposes of the CWA as numeric values that apply to, and
protect, Class I, II, and III estuaries and coastal waters in Florida
and south Florida inland flowing waters. In Florida, water quality
criteria established for Class I, II, and III surface waters must
protect ``fish consumption, recreation and the propagation and
maintenance of a healthy, well-balanced population of fish and
wildlife.'' \144\ Florida's existing narrative nutrient provision
serves to protect Class I, II, and III waters from nitrogen and
phosphorus pollution by requiring that ``[i]n no case shall nutrient
concentration of a body of water be altered so as to cause an imbalance
in natural populations of aquatic flora or fauna.''
---------------------------------------------------------------------------

    \144\ Pursuant to Subsection 62-302.400(4), F.A.C.
---------------------------------------------------------------------------

    After an extensive review of the latest scientific knowledge
relating to the impacts of nutrient pollution on aquatic systems, EPA
is proposing the use of three biological endpoints--maintenance of
seagrasses, maintenance of balanced algal populations, and maintenance
of aquatic life (fauna)--as the most sensitive to effectively derive
numeric nutrient criteria that will protect Class I, II, and III
designated uses from the harmful, adverse effects of nutrient
pollution. The endpoint measures that EPA is proposing to use to
determine the nutrient concentrations to protect these biological
endpoints are light levels to maintain historic depth of seagrass
colonization, chlorophyll a concentrations associated with balanced
phytoplankton biomass, and sufficient DO to maintain aquatic life. Fish
consumption relies on the presence of fish and aquatic life as well as
the habitat that supports them, which in turn relies on seagrasses and
limited occurrence of nuisance algal blooms. The protection of
recreation (both fishing and swimming related uses) relies on the
presence of fish and aquatic life as well as limited occurrence of
nuisance algal blooms. Lastly, the protection of propagation and
maintenance of a healthy, well-balanced population of fish and wildlife
relies on the presence of fish and

aquatic life as well as the habitat that supports them.
    EPA's January 14, 2009 determination addressed Florida's narrative
nutrient provision at Subsection 62-302.530(47)(b), F.A.C. As discussed
earlier, EPA has proposed and promulgated criteria, in this and other
proposals, to implement that provision, which provides that ``[i]n 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.
The criteria proposed in this rulemaking do not address or implement
Florida's narrative nutrient provision at Subsection 62-302.530(47)(a),
F.A.C. which provides that ``[t]he discharge of nutrients shall
continue to be limited as needed to prevent violations of other
standards contained in this chapter. Human-induced nutrient enrichment
(total nitrogen or total phosphorus) shall be considered degradation in
relation to the provisions of Sections 62-302.300, 62-302.700, and 62-
4.242, F.A.C.'' Subsection 62-302.530(47)(a), F.A.C. remains in place
as an applicable WQS for CWA purposes and could result in more
stringent nitrogen and phosphorus limits than those proposed in this
rule, where necessary to protect other applicable water quality
standards in Florida.

D. EPA Determination Regarding Florida and Consent Decree

    On January 14, 2009, EPA determined under CWA section 303(c)(4)(B)
that new or revised water quality standards in the form of numeric
water quality criteria for nitrogen and phosphorus pollution are
necessary to meet the requirements of the CWA in the State of Florida.
EPA's determination is available at the following Web site: http://water.epa.gov/lawsregs/rulesregs/florida_consent.cfm.
    Subsequently, EPA entered into a Consent Decree with Florida
Wildlife Federation, Sierra Club, Conservancy of Southwest Florida,
Environmental Confederation of Southwest Florida, and St. Johns
Riverkeeper, effective on December 30, 2009, which established a
schedule for EPA to propose and promulgate numeric nutrient criteria
for Florida's lakes, springs, flowing waters, estuaries, and coastal
waters, as well as downstream protection values (DPVs) to protect
downstream lakes and estuaries. The Consent Decree provided that if
Florida submitted and EPA approved numeric nutrient criteria for the
relevant water bodies before the dates outlined in the schedule, EPA
would no longer be obligated to propose or promulgate criteria for
those water bodies.

E. EPA's Rulemaking and Subsequent Litigation

    On December 6, 2010, EPA published a rule finalizing numeric
nutrient criteria for Florida's lakes, springs, and flowing waters
outside of the South Florida Nutrient Watershed Region (40 CFR 131.43).
The 2010 ``inland waters rule'' was previously scheduled to take effect
on March 6, 2012, with the exception of one provision that allowed
entities to submit Site-Specific Alternative Criteria (SSAC) effective
February 4, 2011. The March 6, 2012 effective date was subsequently
extended on two occasions (77 FR 13497 and 77 FR 39949) such that the
current effective date of the rule is January 6, 2013. Concurrently
with this proposal, EPA is issuing a separate proposed rule to stay the
inland waters rule until November 15, 2013. For more information on the
proposed stay rule, see http://water.epa.gov/lawsregs/rulesregs/florida_inland.cfm.
    Following the publication of the inland waters rule, 12 cases were
filed in the U.S. District Court for the Northern District of Florida
challenging the rule. The cases, consolidated before Judge Robert
Hinkle in the Tallahassee Division of the Northern District, were filed
by environmental groups, Florida's State Department of Agriculture, the
South Florida Water Management District, and various industry/
discharger groups. The challenges alleged that EPA's determination and
final inland waters rule were arbitrary, capricious, an abuse of
discretion, and not in accordance with the law for a variety of
reasons. Oral argument in the case was held on January 9, 2012 before
Judge Hinkle.
    On February 18, 2012, the Court upheld EPA's January 2009
determination and the final numeric nutrient criteria for Florida's
lakes and springs, as well as the site-specific alternative criteria
(SSAC) provisions and the provisions for calculating DPVs using either
modeling or a default option for an impaired lake that is not attaining
its numeric nutrient criteria.\145\ With regard to EPA's numeric
nutrient criteria for flowing waters (i.e., streams) and the default
option to calculate DPVs for unimpaired lakes based on ambient stream
nutrient concentrations at the point of entry to the lake, the Court
found that EPA had not provided sufficient information in its final
rule explaining why or how the criteria or DPV protect against harmful
increases, as opposed to any increase, in nutrients. The Court observed
that EPA's scientific approach to deriving stream criteria (i.e., the
reference condition approach), including the criteria's duration and
frequency components, ``are matters of scientific judgment on which the
rule would survive arbitrary-or-capricious review.'' The Court also
found, however, that EPA had not explained in sufficient detail how the
stream criteria would prevent a ``harmful increase in a nutrient
level''. In addition, the Court found that EPA had not explained in
sufficient detail how exceedances of the default DPV for unimpaired
lakes would lead to ``harmful effects'' in the downstream lake. Thus,
the Court invalidated these two aspects of EPA's final rule and
remanded them to the Agency for further action. Concurrently with this
proposal, EPA is issuing a separate proposed rule for Florida's streams
and DPVs for unimpaired lakes (Water Quality Standards for the State of
Florida's Streams and Downstream Protection Values for Lakes: Remanded
Provisions). For more information on the proposed rule for the remanded
provisions, see http://water.epa.gov/lawsregs/rulesregs/florida_inland.cfm.
---------------------------------------------------------------------------

    \145\ Case 4:08-cv-00324-RH-WCS, February 18, 2012.
---------------------------------------------------------------------------

    On several occasions, the court granted EPA's request to modify the
deadlines in the December 2009 Consent Decree.\146\ Under the revised
Consent Decree, EPA is required to propose criteria for Florida's
estuaries, coastal waters, and south Florida inland flowing waters by
November 30, 2012 and to finalize such criteria by September 30, 2013.
---------------------------------------------------------------------------

    \146\ http://water.epa.gov/lawsregs/rulesregs/florida_consent.cfm.
---------------------------------------------------------------------------

    In accordance with the January 14, 2009 determination, the December
30, 2009 Consent Decree, and the subsequent modifications to the
deadlines in the December 30, 2009 Consent Decree, EPA is proposing in
this notice numeric nutrient criteria for estuaries and coastal waters
in the State of Florida, and south Florida inland flowing waters. This
proposed rule satisfies EPA's requirement to propose criteria for these
three categories of Florida waters by November 30, 2012.

F. Florida Adoption of Numeric Nutrient Criteria and EPA Approval

    On June 13, 2012, FDEP submitted new and revised WQS for review by
the EPA pursuant to section 303(c) of the CWA. These new and revised
WQS are set out primarily in Rule 62-302 of the F.A.C. [Surface Water
Quality Standards]. FDEP also submitted amendments to Rule 62-303,
F.A.C. [Identification of Impaired Surface Waters], which sets out
Florida's methodology for assessing whether

waters are attaining State WQS. On November 30, 2012, EPA approved the
provisions of these rules submitted for review that constitute new or
revised WQS (referred to in this preamble as the ``newly-approved State
WQS'').
    Among the newly-approved State WQS are numeric criteria for
nutrients that apply to a set of estuaries and coastal marine waters in
Florida. Specifically, these newly-approved State WQS apply to
Clearwater Harbor/St. Joseph Sound, Tampa Bay, Sarasota Bay, Charlotte
Harbor/Estero Bay, Clam Bay, Tidal Cocohatchee River/Ten Thousand
Islands, Florida Bay, Florida Keys, and Biscayne Bay. Under the Consent
Decree, EPA is relieved of its obligation to propose numeric criteria
for these waters.

III. Proposed Numeric Criteria for Florida's Estuaries, Coastal Waters,
and South Florida Inland Flowing Waters

    In this notice of proposed rulemaking, EPA is proposing numeric
nutrient criteria to protect against harmful increases in nutrients,
and therefore, protect the designated uses of the State of Florida's
Class I, II, and III waters, specifically Florida's estuaries and
coastal waters (excluding those contained in Florida's newly-approved
State WQS), and south Florida inland flowing waters. This proposed rule
also includes downstream protection values (DPVs) to ensure the
attainment and maintenance of WQS in downstream estuarine and south
Florida marine waters. The proposed criteria and related provisions in
this rule reflect a detailed consideration of the best available
scientific research, data, and analyses related to the specific
circumstances for deriving numeric nutrient criteria in the State of
Florida. EPA's actions are consistent with and support existing Florida
WQS regulations.
    EPA proposes developing numeric nutrient criteria to restore and
maintain the balance of natural populations of aquatic flora and fauna
in Florida waters. The analytical process that EPA used to derive the
proposed criteria consisted of several steps that included (1)
classification of the water body systems, (2) subdividing water body
systems into smaller segments that have similar chemical, physical, and
biological features, (3) review and analysis of biological endpoints,
and (4) application of one or more analytical methodologies.
    After accounting for the spatial coverage of Florida's newly-
approved State WQS, EPA grouped Florida's remaining estuarine and
coastal waters according to the natural geographic features of
estuarine basins and their associated watersheds (classification). This
resulted in 19 estuarine systems and three coastal systems. Next, EPA
divided each resulting estuary and coastal system into segments on the
basis of similar biological, chemical, and physical attributes
(segmentation). Segmentation resulted in 89 estuarine segments among
the 19 estuarine systems and 71 coastal segments among the three
coastal systems. In the Big Bend region (Ochlockonee Bay to Springs
Coast) EPA combined coastal waters with estuarine waters for analysis.
The classification serves as an organizing framework for analyses, and
the segmentation delineates areas in each estuary or coastal system
where the numeric nutrient criteria apply.
    EPA is proposing to develop numeric nutrient criteria for Florida's
estuarine and coastal waters based on three biological endpoints that
are sensitive to changes in nitrogen and phosphorus concentrations.
These biological endpoints reflect the water quality conditions
necessary to ensure protection of balanced populations of aquatic flora
and fauna: (1) Maintenance of seagrasses (as measured by water clarity
sufficient to maintain historic depth of seagrass colonization), (2)
maintenance of balanced algal populations (as measured by chlorophyll a
concentrations associated with balanced phytoplankton biomass), and (3)
maintenance of aquatic life (as measured by levels of dissolved oxygen
sufficient to maintain aquatic life). For each water body, EPA derived
numeric nutrient criteria based on the most nutrient sensitive of the
three endpoints and the sufficiency of data available in each segment.
    For each estuary and coastal system, one of three analytical
approaches was used to derive numeric nutrient criteria--reference
condition, stressor-response (statistical modeling), and mechanistic
modeling. In some cases, a secondary approach provided corroborating
evidence for the results of the primary analytical methodology. EPA
evaluated multiple lines of evidence to determine the analytical
approach that was best suited for derivation of numeric nutrient
criteria in each estuarine or coastal system. In general, and as
discussed in more detail in later Sections of this proposed rule, the
reference condition approach was applied when there were sufficient
data available to characterize conditions that were representative of
and protective of designated uses, the stressor-response approach was
applied when there were sufficient data available to statistically
quantify relationships between nutrient concentrations and the
biological endpoints, and lastly, the mechanistic modeling approach was
applied when there were sufficient data and information available to
quantify the relationships between nutrient loads and the biological
endpoints.
    For calculating DPVs for estuaries and south Florida marine waters,
EPA is proposing four approaches for setting nitrogen and phosphorus
protective levels in a hierarchy that reflects the data and scientific
information available, including (1) water quality simulation modeling,
(2) reference condition approach, (3) dilution models, and (4) the
numeric nutrient criteria in the estuarine segment to which a
freshwater stream or canal discharges.
    For south Florida EPA is proposing the use of downstream protection
values (DPVs) to manage nitrogen and phosphorus pollution in the inland
flowing waters and protect the water quality of estuaries and coastal
waters downstream. As in estuarine and coastal systems, EPA followed a
series of steps to derive criteria in south Florida inland flowing
waters, including classification of water bodies, segmentation, review
and analysis of biological endpoints, application of analytical
methodologies, and development of DPVs. EPA defined south Florida
inland flowing waters as inland predominantly fresh surface waters that
have been classified as Class I or Class III, which encompasses the
waters south of Lake Okeechobee, the Caloosahatchee River (including
Estero Bay) watershed, and the St. Lucie watershed. EPA segmented south
Florida waters by identifying 22 canal pour points that drain
freshwater to each marine segment. To manage nitrogen and phosphorus
pollution in the inland flowing waters and protect the water quality of
estuaries and coastal waters downstream EPA then screened water quality
data at each pour point to prevent the use of upstream water quality
data that coincided with a documented downstream impact. EPA then
calculated DPVs using the reference condition approach.
    In deriving scientifically sound numeric nutrient criteria for this
proposed rulemaking, EPA relied on the local technical expertise of
various scientific experts in Florida. EPA met and consulted with
FDEP's scientific and technical experts during the development of these
numeric nutrient criteria as part of an ongoing collaborative process
to analyze, evaluate, and interpret a substantial amount of Florida-
specific data. EPA carefully evaluated the technical approaches and
scientific analyses that FDEP presented as part of their draft

approaches to develop numeric nutrient criteria for estuaries within
the State. Finally, EPA also carefully considered substantial
stakeholder input from twelve public hearings conducted by FDEP during
2010, in addition to working with scientists from several Florida
National Estuary Programs (NEPs), Water Management Districts,
universities, and other government agencies in Florida.
    To further ensure the best use of available data and scientific
analyses for deriving criteria, the Agency submitted its potential
methods and approaches for an independent, scientific peer review by
EPA's Science Advisory Board (SAB) in November 2010. The SAB reviewed
the document entitled, Methods and Approaches for Numeric Nutrient
Criteria for Nitrogen/Phosphorus Pollution in Florida's Estuaries,
Coastal Waters, and Southern Inland Flowing Waters, and submitted their
final recommendations to EPA in July 2011.\147\ The SAB agreed that a
dual nutrient strategy to derive criteria for both nitrogen and
phosphorus is warranted. The SAB also found that all of the approaches
that EPA proposed for use in this rulemaking (i.e., reference
condition, stressor-response, and mechanistic modeling) have utility
and recommended that a combination of approaches be used where data and
models are available. The SAB provided numerous recommendations to
strengthen the application of the approaches to develop numeric
nutrient criteria for Florida waters that EPA has used to refine the
methods and approaches for deriving the criteria proposed in this
rulemaking.\148\
---------------------------------------------------------------------------

    \147\ USEPA-SAB. 2011. Review of EPA's Draft Approaches for
Deriving Numeric Nutrient Criteria for Florida's Estuaries, Coastal
Waters, and Southern Inland Flowing Waters. EPA-SAB-11-010. U.S.
Environmental Protection Agency, Science Advisory Board, Washington,
DC.
    USEPA. 2010. Methods and Approaches for Deriving Numeric
Criteria for Nitrogen/Phosphorus Pollution in Florida's Estuaries,
Coastal Waters, and Southern Inland Flowing Waters. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
    \148\ EPA response letter to SAB. http://yosemite.epa.gov/sab/
sabproduct.nsf/fedrgstr--activites/DCC3488B67473BDA852578D20058F3C9/
$File/EPA-SAB-11-010--Response--10-26-2011.pdf. Accessed May 2012.
---------------------------------------------------------------------------

    Section III.A provides an overview of the technical elements used
to support derivation of the numeric nutrient criteria proposed in this
rulemaking for estuaries and coastal waters.\149\ The remainder of
Section III specifically describes EPA's proposed numeric nutrient
criteria for estuaries (Section III.B), coastal waters (Section III.C),
and south Florida inland flowing waters (Section III.D). Also included
are proposed DPVs for estuaries (Section III.B) and south Florida
marine waters (Section III.D).
---------------------------------------------------------------------------

    \149\ Additional details are provided in a separate document,
the Technical Support Document for U.S. EPA's Proposed Rule for
Numeric Nutrient Criteria for Florida's Estuaries, Coastal Waters,
and Southern Inland Flowing Waters (TSD); located at
www.regulations.gov, Docket ID No. EPA-HQ-OW-2010-0222.
---------------------------------------------------------------------------

A. General Information and Approaches

    For each group of waters addressed in Section III, EPA is proposing
to use system-specific approaches based on the classification and
segmentation results for each system (described in detail in Sections
III.B, III.C, and III.D) for the derivation of numeric nutrient
criteria to ensure that the diversity of unique ecosystems found in
each type of water body is taken into consideration. This system-
specific approach allows the Agency to consider the physical, chemical,
and biological characteristics of a particular water body and to select
a scientifically defensible approach, considering the data and
information available for each system. This section describes the
technical approaches EPA employed to derive the proposed criteria and
DPVs, including (1) data and segmentation, (2) biological endpoints,
and (3) analytical methodologies.
1. Data Sources and Segmentation
(a) Estuaries
    Florida's estuarine areas encompass approximately 1,950 square
miles. EPA used the IWR Run 40 database \150\ to identify available
data from a range of sampling sites in Florida's estuaries. To compute
relationships between nutrient concentrations and chlorophyll a, EPA
relied on measurements of Total Kjeldahl Nitrogen (TKN), TN, Nitrate-
Nitrite (NO3-NO2), TP, and chlorophyll a from the
IWR Run 40 database. The resulting dataset included 180,814 water
quality samples, collected at 13,648 sites. The Agency also analyzed
additional data submitted by local experts and organizations.
---------------------------------------------------------------------------

    \150\ Florida's IWR data are the chemical, physical and
biological water quality data that FDEP uses to create its
integrated reports. IWR Run 40. Updated through February 2010. FL
IWR and STORET can be found at: http://www.dep.state.fl.us/WATER/STORET/INDEX.HTM.
---------------------------------------------------------------------------

    The water quality and biological communities of an estuary are
affected by multiple factors related to the shape and size of the
estuary, its connections to the ocean, geology, climate, and watershed
characteristics (e.g., watershed area and land use). Because each of
these factors can vary from one system to another, causing the water
quality and aquatic populations of flora and fauna in each estuary to
be distinct, EPA proposes to classify 19 individual estuarine systems
based on the natural geographic features of estuarine basins and their
associated watersheds. This approach has been utilized previously in
development of the NOAA Coastal Assessment Framework.\151\ This
approach is also consistent with a watershed approach to water quality
management, which EPA encourages as a way to integrate and coordinate
efforts within a watershed in order to most effectively and efficiently
assess conditions and implement controls.\152\
---------------------------------------------------------------------------

    \151\ NOAA. 2007. NOAA's Coastal Geospatial Data Project,
Coastal Assessment Framework (CAF). NOAA/NOS Special Projects
Office--Coastal Geospatial Data Project. Silver Spring, MD. http://coastalgeospatial.noaa.gov/. Accessed May 2012.
    \152\ USEPA. 2008. Handbook for Developing Watershed Plans to
Restore and Protect Our Waters. EPA 841-B-08-002. U.S. Environmental
Protection Agency, Office of Water, Washington DC.
---------------------------------------------------------------------------

    EPA is proposing to sub-divide each estuarine system into segments
based on physical factors and long-term average salinity gradients.
Estuaries are complex and dynamic systems that reflect the mixing of
fresh and marine water, and different ecological zones correspond to
differences in salinity within each estuary. The estuary segments are
expected to have unique physical, chemical, and biological
characteristics that may respond differently to nutrient inputs than
other segments within the same estuary.\153\ EPA is proposing numeric
nutrient criteria for 89 individual segments in 19 estuaries. A
detailed description and detailed maps of EPA's proposed within-estuary
segments are provided in the TSD (Volume 1: Estuaries, Section 1.3 and
for each estuarine system in Section 2).
---------------------------------------------------------------------------

    \153\ Telesh, I.V., and V.V. Khlebovich. 2010. Principal
processes within the estuarine salinity gradient: A review. Marine
Pollution Bulletin 61(4-6):149-155.
---------------------------------------------------------------------------

(b) Coastal Waters
    There are substantial data available from satellite remote sensing
that can be used in a scientifically defensible and reliable way in
conjunction with available field monitoring data to derive numeric
chlorophyll a criteria for coastal waters. Satellite remote sensing
technologies have been widely used \154\ to measure chlorophyll a in
approximately 3,865 square miles of coastal waters in Florida. These
technologies allow consistent and

reliable monitoring of expansive areas of Florida's coastline.
---------------------------------------------------------------------------

    \154\ Gregg, W.W., and NW. Casey. 2004. Global and regional
evaluation of the SeaWiFS chlorophyll data set. Remote Sensing of
Environment 93(4):463-479.
---------------------------------------------------------------------------

    The data EPA used to derive numeric chlorophyll a criteria for
Florida's coastal waters encompass a twelve year period of record
(1998-2009). The length of this data record captures the long-term
variability that has been observed in water quality within Florida's
coastal waters and allows EPA to take advantage of the available remote
sensing data. To obtain chlorophyll a measurements from satellite
remote sensing (chlRS-a), EPA processed data from over 1,000
8-day composites of remotely sensed images from satellite ocean color
data. The eight-day binning period is a standard approach based on the
satellite orbit repeat period of 16 days for the Sea-viewing Wide
Field-of-view Sensor (SeaWiFS) satellite.\155\ EPA also obtained field
monitoring TN, TP, and chlorophyll a data from FDEP IWR Run 40, the
Northeastern Gulf of Mexico Chemical Oceanography and Hydrography Study
(NEGOM), the Ecology and Oceanography of Harmful Algal Blooms Research
Program (ECOHAB), the Florida Fish and Wildlife Conservation Commission
Fish and Wildlife Research Institute (FWRI), NOAA Oceanographic Data
Center (NODC), Mote Marine Laboratory, and the SeaWiFS Bio-optical
Archive and Storage System (SeaBASS). Field monitoring data included
over 5,500 chlorophyll a measurements, which were reduced to 1,947
measurements after screening for data quality, as described later in
this proposed rule.
---------------------------------------------------------------------------

    \155\ Campbell, J.W., J.M. Blaisdell, and M. Darzi. 1995. Volume
32, Level-3 SeaWiFS Data Products: Spatial and Temporal Binning
Algorithms. In: SeaWiFS Technical Report Series. eds. Hooker, S.B.,
E.R. Firestone, and J.G. Acker. NASA Technical Memorandum 104566,
Vol. 32. National Aeronautics and Space Administration. Greenbelt,
MD.
---------------------------------------------------------------------------

    EPA is not proposing to derive TN and TP criteria for Florida's
coastal waters due to lack of sufficient field monitoring data for TN
and TP. Although it would be a more reliable indicator to include TN
and TP in combination with chlorophyll a, EPA believes that the
chlorophyll a criteria should protect these Florida waters because
chlorophyll a can be a sensitive biological parameter that would serve
as a signal to the State that nutrient pollution is creating an
imbalance in the natural populations of aquatic flora and fauna in
Florida's coastal waters. Where EPA has not derived criteria for
certain parameters in this proposed rule, due to insufficient
scientific evidence to support a protective threshold for numeric
nutrient criteria (e.g., TN and TP for the majority of Florida's
coastal waters), EPA or the State may consider deriving criteria in the
future for those parameters.
    To ensure data quality, EPA screened available field monitoring
data to find samples with, at a minimum, metadata for date, time,
latitude, longitude, and chlorophyll a or light attenuation
information. Where multiple samples of chlorophyll a at different
depths existed, EPA selected the sample closest to the surface in order
to provide a better comparison to the remotely sensed data. The
monitoring sampling times were also compared to the satellite overpass
times. EPA used samples falling within a plus or minus three hour time
window to minimize variability between the sample time and satellite
overpass time. EPA then compared the satellite chlRS-a data
to the field monitored chlorophyll a data. From this assessment EPA
determined that chlRS-a accurately represents chlorophyll a
in coastal waters.
    For the purposes of deriving criteria for coastal waters using
remote sensing data, EPA is proposing to exclude chlRS-a
measurements taken during known bloom events of Karenia brevis from the
statistical distribution of coastal data. K. brevis is a dinoflagellate
responsible for red tide. Satellites can detect K. brevis blooms when
cell counts are above 50,000 cells/L. EPA flagged coastal segments with
cell counts greater than 50,000 cells/L during an 8-day composite and
did not include them in the chlRS-a distributions used in
criteria derivation.\156\ In addition, the same segment was flagged one
week prior to and after a bloom detection to provide a temporal buffer
as blooms are transported along the coast. This proposed approach is
consistent with recommendations from the Agency's Science Advisory
Board, which recommended EPA screen out these data points, as they are
likely not representative of reference conditions.\157\ Analyses of
cumulative distributions of chlRS-a show they are minimally
affected by inclusion or removal of observations affected by K. brevis.
---------------------------------------------------------------------------

    \156\ Heil, C.A., and K.A. Steidinger. 2009. Monitoring,
management, and mitigation of Karenia blooms in the Eastern Gulf of
Mexico. Harmful Algae 8:611-617.
    \157\ USEPA-SAB. 2011. Review of EPA's draft Approaches for
Deriving Numeric Nutrient Criteria for Florida's Estuaries, Coastal
Waters, and Southern Inland Flowing Waters. EPA-SAB-11-010. U.S.
Environmental Protection Agency, Science Advisory Board, Washington,
DC.
---------------------------------------------------------------------------

    EPA classified Florida's coastal waters into three main areas: The
Florida Panhandle, West Florida Shelf, and Atlantic Coast. These three
coastal areas were subdivided into a total of 71 segments based on
FDEP's Water Body Identification System (WBIDs), physical factors, the
optical properties of the coastal areas, water quality characteristics,
and the jurisdictional limits of the Clean Water Act (i.e., three
nautical mile seaward limit). A detailed description of EPA's data
screening process and a map of the coastal waters are provided in the
TSD (Volume 2: Coastal Waters, Section 1.3).
(c) Request for Comment on Data and Segmentation
    EPA believes the proposed data and segmentation approaches provide
a strong foundation for the derivation of numeric nutrient criteria
that will protect the designated uses in Florida's estuaries and
coastal waters. EPA requests comment on all aspects of these
approaches. Additionally, the Agency is soliciting additional relevant
data and information to assist in the derivation of numeric nutrient
criteria. Relevant data and information includes, but is not limited
to: Monitoring data for DO, chlorophyll a, TN, TP, TKN, dissolved
organic nitrogen, dissolved organic phosphorus, dissolved inorganic
nitrogen, dissolved inorganic phosphorus, and NO3-
NO2. EPA also invites comment on the timeframe of the data
used to derive criteria for each of the water body types. In addition,
EPA requests comment on excluding chlRS-a measurements taken
during known bloom events of K. brevis from the statistical
distribution of coastal data. EPA also solicits additional available
scientific data and information that could be used in the derivation of
numeric criteria for nitrogen and phosphorus in coastal waters.
    Even though waters were assigned to segments to ensure homogeneity
of water quality across different locations within a segment, EPA
recognizes that limited variability may still exist across locations
within a given segment. EPA also solicits comment on and requests any
additional available information regarding the ability of the proposed
segmentation approaches to account for the unique water quality
conditions that can be found in estuarine and coastal waters throughout
the State. Finally, EPA is proposing to derive numeric nutrient
criteria using a system-specific approach. EPA requests comment on the
spatial scale of the proposed criteria and whether a broader spatial
approach would be more appropriate.
2. Biological Endpoints
    When deriving numeric nutrient criteria, it is important to
identify nutrient-sensitive biological endpoints

relevant to particular estuarine and coastal systems. These biological
endpoints serve as sensitive measures to identify protective
concentrations of TN, TP, and chlorophyll a that, in turn, will support
balanced natural populations of aquatic flora and fauna and protect the
State's designated uses. EPA conducted an extensive evaluation of
available scientific literature to select appropriate biological
endpoints, reviewing over 800 documents. From this review of the latest
scientific knowledge, EPA has determined that maintenance of
seagrasses, maintenance of balanced algal populations, and maintenance
of aquatic life are three sensitive biological endpoints, which can be
measured by water clarity (as it relates to light levels sufficient to
maintain historic depth of seagrass colonization), chlorophyll a, and
DO, respectively, and appropriately used in derivation of numeric
nutrient criteria that protect the State's designated uses from harmful
increases in nitrogen and phosphorus concentrations. The selection of
these biological endpoints was based upon their scientific
defensibility; sensitivity to harmful, adverse effects caused by the
pollutants nitrogen and phosphorus; and the sufficiency of data
available for each.
    EPA derived TN, TP, and chlorophyll a criteria to: (1) Maintain
water clarity to achieve seagrass depth of colonization targets, (2)
reduce the risk of phytoplankton blooms, and (3) maintain dissolved
oxygen concentrations sufficient for balanced, natural aquatic life in
Florida's estuaries and coastal waters. As set out more fully in the
following discussion, these three biological endpoints provide a
scientifically defensible basis upon which to derive numeric nutrient
criteria that protect balanced natural populations of aquatic flora and
fauna over the full range of estuarine and coastal conditions across
Florida; waters that achieve these endpoints support designated uses.
(a) Maintenance of Seagrasses
    EPA selected the maintenance of seagrasses, as measured by water
clarity to maintain historic depth of seagrass colonization, as one
biological endpoint and corresponding endpoint measure to derive
numeric nutrient criteria for estuaries. Healthy populations of
seagrasses serve as widely recognized indicators of biological
integrity in estuarine systems and, in turn, of balanced natural
populations of aquatic flora and fauna.\158\
---------------------------------------------------------------------------

    \158\ Ferdie, M., and J.W. Fourqurean. 2004. Responses of
seagrass communities to fertilization along a gradient of relative
availability of nitrogen and phosphorus in a carbonate environment.
Limnology and Oceanography 49(6):2082-2094.
    Orth, R.J., T.J.B. Carruthers, W.C. Dennison, C.M. Duarte, J.W.
Fourqurean, K.L. Heck, A.R. Hughes, G.A. Kendrick, W.J. Kenworthy,
S. Olyarnik, F.T. Short, M. Waycott, and S.L. Williams. 2006. A
global crisis for seagrass ecosystems. BioScience 56(12):987-996.
    Doren, R.F., J.C. Trexler, A.D. Gottlieb, and M.C. Harwell.
2009. Ecological indicators for system-wide assessment of the
greater everglades ecosystem restoration program. Ecological
Indicators 9:S2-S16.
    Gibson, G.R., M.L. Bowman, J. Gerritsen, and B.D. Snyder. 2000.
Estuarine and Coastal Marine Waters: Bioassessment and Biocriteria
Technical Guidance. EPA 822-B-00-024. U.S. Environmental Protection
Agency, Office of Water, Washington, DC. http://water.epa.gov/scitech/swguidance/standards/criteria/aqlife/biocriteria/upload/2009_04_22_biocriteria_States_estuaries_estuaries.pdf.
Accessed November 2011.
---------------------------------------------------------------------------

    Because of the unique conditions that are created within seagrass
communities, populations of other aquatic floral and faunal species
benefit from the presence and abundance of seagrasses.\159\ For
example, seagrasses act as nurseries for many species by providing
refuge from predators. Seagrasses also improve water quality by
trapping suspended sediments, preventing sediment resuspension, and
retaining nutrients. Florida's NEPs and FDEP have also used endpoints
based on seagrasses to derive their recommended estuarine criteria
because of seagrass sensitivity to nutrient pollution.
---------------------------------------------------------------------------

    \159\ Orth, R.J., T.J.B. Carruthers, W.C. Dennison, C.M. Duarte,
J.W. Fourqurean, K.L. Heck Jr., A.R. Hughes, G.A. Kendrick, W.J.
Kenworthy, S. Olyarnik, F.T. Short, M. Waycott, and S.L. Williams.
2006. A global crisis for seagrass ecosystems. Bioscience
56(12):987-996.
---------------------------------------------------------------------------

    Seagrass communities depend on a variety of physical, chemical, and
biological conditions to thrive. Among these, adequate underwater light
availability (as measured by water clarity) is one critical factor for
seagrass health. The relationship between water clarity and the depth
to which seagrasses grow, known as the depth of colonization, has been
well-documented.\160\ When seagrasses receive sufficient sunlight,
seagrass biomass remains constant or increases over time. Conversely,
when incoming light is blocked by substances in the water column, such
as phytoplankton, suspended solids, or color, seagrass growth slows or
stops. Studies on seagrasses have documented the relationship of
nutrient pollution-related accelerated algal growth to declines in
available light and subsequent declines in seagrass communities.\161\
Since the area within an estuary available for seagrass growth is
partially a function of the total area with enough sunlight at
sufficient depths to sustain growth, as water clarity decreases and
reduces the amount of sunlight that can reach the seagrasses, the
available area for seagrass growth also decreases. Hence, the greater
the water clarity (and associated available light), the deeper the
water that can support seagrass communities and, therefore, the greater
the extent of seagrass coverage.
---------------------------------------------------------------------------

    \160\ Dennison, W.C. 1987. Effects of light on seagrass
photosynthesis, growth, and depth distribution. Aquatic Botany
27:15-26.
    Dennison, W.C., R.J. Orth, K.A. Moore, J.C. Stevenson, V.
Carter, S. Kollar, P.W. Bergstrom, and R.A. Batiuk. 1993. Assessing
water quality with submersed aquatic vegetation. BioScience
43(2):86-94.
    Duarte, C.M. 1991. Seagrass depth limits. Aquatic Botany
40(4):363-377.
    Gallegos, C.L. 1994. Refining habitat requirements of submersed
aquatic vegetation: Role of optical models. Estuaries 17(1):187-199.
    Gallegos, C.L., and W.J. Kenworthy. 1996. Seagrass depth limits
in the Indian River Lagoon (Florida, USA): Application of an optical
water quality model. Estuarine, Coastal and Shelf Science 42(3):267-
288.
    Gallegos, C.L. 2005. Optical water quality of a blackwater river
estuary: the Lower St. Johns River, Florida, USA. Estuarine, Coastal
and Shelf Science 63(1-2):57-72.
    Steward, J.S., R.W. Virnstein, L.J. Morris, and E.F. Lowe. 2005.
Setting seagrass depth, coverage, and light targets for the Indian
River Lagoon system, Florida. Estuaries and Coasts 28(6):923-935.
    \161\ Ferdie, M., and J.W. Fourqurean. 2004. Responses of
seagrass communities to fertilization along a gradient of relative
availability of nitrogen and phosphorus in a carbonate environment.
Limnology and Oceanography 49(6):2082-2094.
    Orth, R.J., T.J.B. Carruthers, W.C. Dennison, C.M. Duarte, J.W.
Fourqurean, K.L. Heck, A.R. Hughes, G.A. Kendrick, W.J. Kenworthy,
S. Olyarnik, F.T. Short, M. Waycott, and S.L. Williams. 2006. A
global crisis for seagrass ecosystems. BioScience 56(12):987-996.
---------------------------------------------------------------------------

    EPA reviewed studies that empirically assessed the relationship
between seagrass growth and available light \162\ and is proposing
that, for Florida, when an average value of 20 percent of the sunlight
that strikes the water's surface (incident light) reaches the bottom of
the water column (to the depth of seagrass colonization), sufficient
light is available to maintain seagrasses. A similar value has been
used in previous nutrient management efforts in Florida.\163\
---------------------------------------------------------------------------

    \162\ Dennison, W.C., R.J. Orth, K.A. Moore, J.C. Stevenson, V.
Carter, S. Kollar, P.W. Bergstrom, and R.A. Batiuk. 1993. Assessing
water quality with submersed aquatic vegetation. BioScience
43(2):86-94.
    Duarte, C.M. 1991. Seagrass depth limits. Aquatic Botany
40(4):363-377.
    Gallegos, C.L. 1994. Refining habitat requirements of submersed
aquatic vegetation: Role of optical models. Estuaries 17(1):187-199.
    Steward, J.S., R.W. Virnstein, L.J. Morris, and E.F. Lowe. 2005.
Setting seagrass depth, coverage, and light targets for the Indian
River Lagoon system, Florida. Estuaries and Coasts 28(6):923-935.
    \163\ Janicki, A.J., and D.L. Wade. 1996. Estimating critical
external nitrogen loads for the Tampa Bay estuary: An empirically
based approach to setting management targets. Technical Publication
06-96. Prepared for Tampa Bay National Estuary Program, St.
Petersburg, FL, by Coastal Environmental, Inc., St. Petersburg, FL.

---------------------------------------------------------------------------

    EPA is also proposing that protecting and maintaining water clarity
sufficient to support an appropriate depth of colonization provides the
greatest protection of balanced natural populations of aquatic flora
and fauna since maintenance of seagrass habitat is critical to
ecosystem conditions. EPA used available historical seagrass coverage
data (including the earliest available, generally 1940-1960, or more
recent, 1992) to compute the historical maximum depth of seagrass
colonization as a reference. In all cases the most recent (2000-2010)
seagrass coverage was also evaluated to determine existing depth of
colonization, and to relate this value to existing water quality. To
compute seagrass depth of colonization, EPA overlaid seagrass coverage
data and bathymetric data compiled by NOAA using a Geographic
Information System.\164\ EPA then used the data on seagrass coverage to
determine the maximum depths that seagrasses have been able to grow in
each estuary, where applicable (this approach was not used in some
estuaries in Florida that do not have historical evidence of seagrass
colonization), in order to identify a reference point for a healthy
level of seagrass colonization. Because seagrass habitats support a
rich array of biological uses,\165\ EPA is proposing to derive numeric
nutrient criteria to maintain a comparable depth of seagrass
colonization to the reference level (i.e. seagrasses growing at the
deepest observed depth of colonization) to ensure protection of
balanced natural populations of aquatic flora and fauna. EPA chose to
use the historical maximum observed depth, and resulting areal
coverage, because increasing nutrients beyond the point that is
protective of maximum coverage of seagrass is likely to cause a decline
in seagrass coverage. Because a wide variety of organisms rely on
healthy seagrass communities, a decrease in seagrass coverage to levels
below the maximum observed depth will result in a decline in overall
system health and biodiversity.\166\ EPA calculated a water clarity
target that would ensure 20% percent of incident light at the surface
would be able to reach the reference depth of colonization. Finally,
EPA used this water clarity target to derive numeric criteria for TN,
TP, and chlorophyll a to support balanced natural populations of
aquatic flora and fauna. (More detail on the importance of seagrass can
be found in the TSD, Volume 1: Estuaries, Section 1.2.1).
---------------------------------------------------------------------------

    \165\ Hughes, A.R., S.L. Williams, C.M. Duarte, K.L. Heck, Jr.,
and M. Waycott. 2009. Associations of concern: declining seagrasses
and threatened dependent species. Frontiers in Ecology and the
Environment 7(5):242-246.
    \166\ Hughes, A.R., S.L. Williams, C.M. Duarte, K.L. Heck, Jr.,
and M. Waycott. 2009. Associations of concern: declining seagrasses
and threatened dependent species. Frontiers in Ecology and the
Environment 7(5):242-246.
    Orth, R.J., T.J.B. Carruthers, W.C. Dennison, C.M. Duarte, J.W.
Fourqurean, K.L. Heck, A.R. Hughes, G.A. Kendrick, W.J. Kenworthy,
S. Olyarnik, F.T. Short, M. Waycott, and S.L. Williams. 2006. A
global crisis for seagrass ecosystems. BioScience 56(12):987-996.
    FFWCC. 2003. Conserving Florida's Seagrass Resources: Developing
a Coordinated Statewide Management Program. Florida Fish and
Wildlife Conservation Commission, Florida Marine Research Institute.
St. Petersburg, FL.
---------------------------------------------------------------------------

    (b) Maintenance of Balanced Algal Populations
    Based upon EPA's extensive review of current scientific literature,
EPA selected maintenance of balanced algal populations, as measured by
the chlorophyll a concentrations associated with balanced phytoplankton
biomass, as the second biological endpoint and corresponding endpoint
measure to derive numeric nutrient criteria for estuaries and coastal
waters. The maintenance of balanced algal populations is an important
sensitive biological endpoint because of its responsiveness to nutrient
enrichment, integral role in aquatic food webs, well-established use as
an integrative measure of aquatic ecosystem condition, and correlation
with changes in floral composition and subsequent faunal response.\167\
Chlorophyll a is the endpoint measure of balanced algal populations,
and has a long history of use in aquatic ecology as a measure of
phytoplankton biomass and production.\168\ Elevated chlorophyll a
concentrations resulting from nutrient pollution-enhanced algal growth
and accumulation are a well-documented symptom of eutrophication and
the harmful, adverse impacts of nitrogen and phosphorus pollution
across the nation, and specifically in Florida (refer to Section II.A
for additional information).\169\ In most of Florida's coastal and
estuarine waters, healthy biological communities depend on balanced
natural populations of algae because algae are integral components of
aquatic food webs and aquatic nutrient cycling.\170\
---------------------------------------------------------------------------

    \167\ Boyer, J.N., C.R. Kelble, P.B. Ortner, and D.T. Rudnick.
2009. Phytoplankton bloom status: Chlorophyll a biomass as an
indicator of water quality condition in the southern estuaries of
Florida, USA. Ecological Indicators 9s:S56-S67.
    Hagy, J.D., J.C. Kurtz, and R.M. Greene. 2008. An approach for
developing numeric nutrient criteria for a Gulf coast estuary. EPA
600R-08/004. U.S. Environmental Protection Agency, Office of
Research and Development, National Health and Environmental Effects
Research Laboratory, Gulf Breeze, FL.
    Bricker, S.B., C.G. Clement, D.E. Pirhalla, S.P. Orlando, and
D.R.G. Farrow. 1999. National Estuarine Eutrophication Assessment.
Effects of Nutrient Enrichment in the Nation's Estuaries. National
Oceanic and Atmospheric Administration, National Ocean Service,
Special Projects Office and the National Centers for Coastal Ocean
Science, Silver Spring, MD.
    See Section B.3 in Appendix B of USEPA. 2010. Methods and
Approaches for Deriving Numeric Criteria for Nitrogen/Phosphorus
Pollution in Florida's Estuaries, Coastal Waters, and Southern
Inland Flowing Waters. U.S. Environmental Protection Agency, Office
of Water, Washington, DC.
    \168\ Wetzel, R.G. 2001. Limnology: Lakes and River Ecosystems.
3rd ed. Academic Press, San Diego, CA.
    Kalff, J. 2002. Limnology: Inland Water Ecosystems. Prentice-
Hall, Inc., Upper Saddle River, New Jersey.
    \169\ Elser, J.J., M.E.S. Bracken, E.E. Cleland, D.S. Gruner,
W.S. Harpole, H. Hillebrand, J.T. Ngai, E.W. Seabloom, J.B. Shurin,
and J.E. Smith. 2007. Global analysis of nitrogen and phosphorus
limitation of primary production in freshwater, marine, and
terrestrial ecosystems. Ecology Letters 10:1135-1142.
    Smith, V.H. 2006. Responses of estuarine and coastal marine
phytoplankton to nitrogen and phosphorus enrichment. Limnology and
Oceanography 51(1 part 2):377-384
    \170\ Hauxwell, J., C. Jacoby, T. Frazer, and J. Stevely. 2001.
Nutrients and Florida's Coastal Waters: The Links Between People,
Increased Nutrients and Changes to Coastal Aquatic Systems. Florida
Sea Grant Report No. SGEB-55. Florida Sea Grant College Program,
University of Florida, Gainesville, FL. http://edis.ifas.ufl.edu/pdffiles/SG/SG06100.pdf. Accessed June 2011.
    NOAA. 2011. Overview of Harmful Algal Blooms. National Oceanic
and Atmospheric Administration, Center for Sponsored Coastal
Research. http://www.cop.noaa.gov/stressors/extremeevents/hab/default.aspx. Accessed June 2011.
---------------------------------------------------------------------------

    Elevated chlorophyll a concentrations resulting from nitrogen and
phosphorus pollution alter the trophic state of estuarine and coastal
waters and increase the frequency and magnitude of algal blooms. EPA
evaluated the available scientific literature to determine chlorophyll
a concentrations indicative of phytoplankton blooms associated with
imbalance in natural populations of aquatic flora and fauna. Published
reports on chlorophyll a concentrations in estuarine waters across the
nation, including Florida estuaries, reflect the range of natural
trophic states and enrichment. These studies suggest that low algal
bloom conditions are defined as maximum chlorophyll a concentrations
less than or equal to 5 [micro]g/L, medium bloom conditions are defined
as maximum chlorophyll a concentrations from greater than 5 to 20
[micro]g/L, high bloom conditions are defined as maximum chlorophyll a
concentrations from greater than 20 to 60 [micro]g/L, and
hypereutrophic conditions are defined by maximum bloom concentrations

above 60 [micro]g/L.\171\ Two Florida estuaries, Florida Bay and
Pensacola Bay, were analyzed as a part of a larger NOAA national survey
of estuaries. The authors reported the average chlorophyll a
concentrations were 20 [micro]g/L or less for seven of ten large
estuaries nationally, and were especially low for Florida Bay (8
[micro]g/L) and Pensacola Bay (10 [micro]g/L).\172\ Other literature
regarding phytoplankton blooms indicated similar results.\173\
---------------------------------------------------------------------------

    \171\ Bricker, S.B., J.G. Ferreira, and T. Simas. 2003. An
integrated methodology for assessment of estuarine trophic status.
Ecological Modelling 169(1):39-60.
    \172\ Glibert, P.M., C.J. Madden, W. Boynton, D. Flemer, C.
Heil, and J. Sharp, eds. 2010. Nutrients in Estuaries: A Summary
Report of the National Estuarine Experts Workgroup, 2005-2007.
Report to U.S. Environmental Protection Agency, Office of Water,
Washington DC.
    \173\ OECD. 1982. Eutrophication of Waters: Monitoring,
Assessment and Control. Organisation for Economic Cooperation and
Development, Paris, France.
    Painting, S.J., M.J. Devlin, S.J. Malcolm, E.R. Parker, D.K.
Mills, C. Mills, P. Tett, A. Wither, J. Burt, R. Jones, and K.
Winpenny. 2007. Assessing the impact of nutrient enrichment in
estuaries: susceptibility to eutrophication. Marine Pollution
Bulletin 55:74-90.
    Painting, S.J., M.J. Devlin, S.I. Rogers, D.K. Mills, E.R.
Parker, and H.L. Rees. 2005. Assessing the suitability of OSPAR
EcoQOs for eutrophication vs. ICES criteria for England and Wales.
Marine Pollution Bulletin 50:1569-1584.
    Tett, P., R. Gowen, D. Mills, T. Fernandes, L. Gilpin, M.
Huxham, K. Kennington, P. Read, M. Service, M. Wilkinson, and S.
Malcolm. 2007. Defining and detecting undesirable disturbance in the
context of marine eutrophication. Marine Pollution Bulletin 55:282-
297.
---------------------------------------------------------------------------

    Chlorophyll a concentrations associated with hypereutrophic
conditions (>60 [micro]g/L) reflect a trophic state that is unnatural
for Florida estuaries. While some estuaries in the State are more
productive than others, high chlorophyll a concentrations (20 to 60
[micro]g/L) also do not appear to reflect balanced conditions in
Florida, especially given observed ranges in Florida. Concentrations of
chlorophyll a in this high range are associated more frequently with
loss of seagrass and a shift of algal populations to monoculture or, in
other words, a loss in the balance of diverse populations of aquatic
flora.\174\ Moreover, this concentration range was also associated with
conditions where other uses, including recreation, are adversely
affected. Based on the range of chlorophyll a concentrations indicative
of natural algal bloom conditions characteristic of Florida estuaries,
as well as the literature on concentrations associated with harmful,
adverse conditions for estuarine biota and other use support, EPA is
proposing a chlorophyll a concentration of 20 [micro]g/L as the water
quality target to define a nuisance algal bloom. Thus, estuarine waters
with chlorophyll a concentrations that exceed this water quality target
threshold are indicative of imbalanced populations of aquatic flora and
fauna (More detail regarding EPA's analysis can be found in the TSD,
Volume 1: Estuaries, Section 1.2.2).
---------------------------------------------------------------------------

    \174\ Bricker, S.B., J.G. Ferreira, and T. Simas. 2003. An
integrated methodology for assessment of estuarine trophic status.
Ecological Modelling 169(1):39-60.
---------------------------------------------------------------------------

    EPA also considered the available scientific research described in
this section to establish an allowable frequency of occurrence of
phytoplankton blooms, represented by chlorophyll a levels greater than
20 [mu]g/L, to further define this endpoint measure. EPA is proposing a
value of 10% as an allowable frequency of occurrence of phytoplankton
blooms, that is, chlorophyll a measurements may not exceed 20 [mu]g/L
more than 10% of the time. This frequency is also consistent with
current nutrient management practices in Florida, such as those
utilized in approved Florida TMDLs.
(c) Maintenance of Aquatic Life
    EPA selected maintenance of aquatic life, as measured by the
sufficiency of dissolved oxygen (DO) to maintain aquatic life, as a
third biological endpoint and corresponding endpoint measure to derive
numeric nutrient criteria for estuaries. DO concentrations are a well-
known indicator of the health of estuarine and coastal biological
communities. Aquatic animals including fish, benthic
macroinvertebrates, and zooplankton depend on adequate levels of DO to
survive and grow. These levels may differ depending on the species and
life stage of the organism (e.g., larval, juvenile, and adult).\175\
---------------------------------------------------------------------------

    \175\ Diaz, R.J. 2001. Overview of hypoxia around the world.
Journal of Environmental Quality 30(2):275-281.
    Diaz, R.J., and R. Rosenberg. 2008. Spreading dead zones and
consequences for marine ecosystems. Science 321(5891):926-929.
---------------------------------------------------------------------------

    To derive the DO endpoint, EPA conducted an analysis of the
dissolved oxygen requirements of sensitive species in Florida using the
Virginian Province dissolved oxygen evaluation procedure.\176\ This
analysis derives DO levels that protect both larval recruitment and
growth for aquatic organisms. EPA used the results of this analysis to
determine the dissolved oxygen water quality targets considered for
numeric nutrient criteria development that would protect sensitive
aquatic species in Florida estuaries. EPA is proposing that satisfying
three different DO requirements in Florida's estuarine waters would
meet the needs of resident sensitive aquatic species, and thus support
the maintenance of aquatic life. These requirements are an
instantaneous DO concentration of 4.0 mg/L, a daily average DO
concentration of 5.0 mg/L, and a bottom water average DO concentration
of 1.5 mg/L. Both the instantaneous minimum of 4.0 mg/L and the daily
average of 5.0 mg/L are spatial averages over the water column for each
estuarine segment. These values and interpretations are consistent with
existing Florida DO criteria (Subsection 62-302.530(30), F.A.C.) and
FDEP's assessment procedures (Subsection 62-303.320(5), F.A.C.). (More
detail on both the existing Florida DO criteria and EPA's analysis can
be found in the TSD, Volume 1: Estuaries, Sections 1.2.3 and 1.4.1).
---------------------------------------------------------------------------

    \176\ Vincent, A.M., J. Flippin, E. Leppo, and J.D. Hagy III.
Dissolved oxygen requirements of Florida-resident saltwater species
applied to water quality criteria development. In review.
    USEPA. 2000. Ambient Aquatic Life Water Quality Criteria for
Dissolved Oxygen (Saltwater): Cape Cod to Cape Hatteras. EPA-822-R-
00-012. U.S. Environmental Protection Agency, Office of Water,
Washington DC.
---------------------------------------------------------------------------

(d) Other Endpoints Considered by EPA
    EPA considered, but is not proposing to use, the following
nutrient-sensitive biological endpoints: (1) Harmful algal blooms
(HABs), (2) coral, (3) epiphytes, (4) macroinvertebrate and fish
indices, (5) macroalgae, (6) Spartina marshes (salt-marshes), and (7)
the Eastern oyster (Crassostrea virginica). EPA did not select these
biological endpoints because there was an absence of sufficient data to
quantify the link between measurements of these endpoints and nitrogen
and phosphorus concentrations. Additional details on these alternative
endpoints are provided in Appendix B in the Methods and Approaches for
Deriving Numeric Criteria for Nitrogen/Phosphorus Pollution in
Florida's Estuaries, Coastal Waters, and Southern Inland Flowing
Waters.\177\
---------------------------------------------------------------------------

    \177\ USEPA. 2010. Methods and Approaches for Deriving Numeric
Criteria for Nitrogen/Phosphorus Pollution in Florida's Estuaries,
Coastal Waters, and Southern Inland Flowing Waters. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
---------------------------------------------------------------------------

(e) Request for Commerce on Endpoints
    EPA believes that maintenance of seagrasses, maintenance of
balanced algal populations, and maintenance of aquatic life are the
three most appropriate nutrient-sensitive biological endpoints to use
to derive numeric nutrient criteria to ensure that nutrient
concentrations in a body of water

protect balanced natural populations of aquatic flora and fauna, and in
turn support designated uses. EPA requests comment regarding the
biological endpoints and endpoint measures selected. EPA also solicits
additional scientific information on other appropriate endpoints that
can be used to protect fish consumption, recreation, and the
propagation and maintenance of a healthy, well-balanced population of
fish and wildlife in Florida's Class II and III estuarine and coastal
waters.
3. Analytical Methodologies
    EPA used three analytical approaches to derive TN, TP, and
chlorophyll a numeric nutrient criteria for different types of waters
in Florida. In most of Florida coastal waters, EPA is proposing to use
a reference condition approach that utilizes data from waters that
support balanced natural populations of aquatic flora and fauna to
derive numeric nutrient criteria. In Florida estuaries (including some
coastal waters in the Big Bend Coastal region), EPA is proposing to use
statistical and mechanistic models to determine protective
concentrations of TN, TP, and chlorophyll a linked to biological
endpoints. Where sufficient data were not available to apply
statistical models (i.e., stressor-response approach) in all segments
in an estuary, EPA used mechanistic model predictions to derive
criteria. In these instances, EPA analyzed the available stressor-
response analysis as a second line of evidence, in segments where the
data were available.
(a) Reference Condition Approach
    EPA is proposing to use the reference condition approach to derive
numeric nutrient criteria in coastal waters that support balanced
natural populations of aquatic flora and fauna. EPA is proposing this
approach to derive numeric chlorophyll a criteria for Florida's coastal
waters because the scientific data and information available were
insufficient to establish accurate quantifiable relationships between
TN and TP concentrations and harmful, adverse effects due to the
limited TN and TP data available. Therefore, EPA is proposing to rely
upon the reference condition approach to identify numeric chlorophyll a
criteria concentrations that protect the designated uses, and avoid any
adverse change in natural populations of aquatic flora or fauna in
Florida's coastal waters.
    The reference condition approach, which has been well documented,
peer reviewed, and developed in a number of different contexts,\178\ is
used to derive numeric nutrient criteria that are protective of
applicable designated uses by identifying numeric nutrient criteria
concentrations occurring in least-disturbed, healthy coastal waters
that are supporting designated uses.
---------------------------------------------------------------------------

    \178\ USEPA. 2000a. Nutrient Criteria Technical Guidance Manual:
Lakes and Reservoirs. EPA-822-B-00-001. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
    USEPA. 2000b. Nutrient Criteria Technical Guidance Manual:
Rivers and Streams. EPA-822-B-00-002. U.S. Environmental Protection
Agency, Office of Water, Washington, DC.
    Stoddard, J.L., D.P. Larsen, C.P. Hawkins, R.K. Johnson, and
R.H. Norris. 2006. Setting expectations for the ecological condition
of streams: The concept of reference condition. Ecological
Applications 16:1267-1276.
    Herlihy, A.T., S.G. Paulsen, J. Van Sickle, J.L. Stoddard, C.P.
Hawkins, L.L. Yuan. 2008. Striving for consistency in a national
assessment: The challenges of applying a reference-condition
approach at a continental scale. Journal of the North American
Benthological Society 27:860-877.
    USEPA. 2001. Nutrient Criteria Technical Manual: Estuarine and
Coastal Marine Waters. EPA-822-B-01-003. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
    USEPA-SAB. 2011. Review of EPA's draft Approaches for Deriving
Numeric Nutrient Criteria for Florida's Estuaries, Coastal Waters,
and Southern Inland Flowing Waters. EPA-SAB-11-010. U.S.
Environmental Protection Agency, Science Advisory Board, Washington,
DC.
---------------------------------------------------------------------------

    To derive the proposed numeric nutrient criteria using the
reference condition approach, EPA first selected reference conditions
in Florida's coastal waters where the Agency was confident that
designated uses are protected. EPA reviewed available monitoring
information, peer-reviewed literature, and technical reports to ensure
that, where applicable, seagrass beds are healthy, DO is adequate for
sensitive species, phytoplankton biomass is balanced, and that any
other information relating to the ecosystem indicates that the waters
are supporting balanced natural populations of aquatic flora and fauna.
EPA also removed data during periods of temporary known human
disturbances (e.g., bridge and roadway construction) where natural
populations were temporarily affected. Finally, EPA reviewed CWA
section 303(d) listings, and removed data associated with impairment
listings for chlorophyll a, dissolved oxygen, and nutrients, as well as
data from coastal segments adjacent to CWA section 303(d) impaired
estuary waters, such that the resulting data would reflect unimpaired
conditions. EPA only removed data from the period of impairment. The
result of this rigorous analysis was a set of reference waters that,
although not pristine, reflected healthy conditions that were
supporting designated uses, and thus free from harmful, adverse effects
on natural populations of aquatic flora and fauna due to nutrient
pollution. EPA has confidence that these reference waters are
supporting designated uses and balanced natural populations of flora
and fauna, and has confidence that if the criteria are attained or
maintained at the concentrations that are among the highest observed in
these waters, then designated uses and natural populations of aquatic
flora and fauna will be protected in coastal waters. Further details
regarding data screening can be found in the TSD (Volume 2: Coastal
Waters, Section 1.4).
    After selecting the reference waters, EPA calculated the annual
geometric mean concentrations of chlorophyll a for each year of the
data record and for each segment.\179\ EPA then calculated a normal
distribution based on the annual geometric mean chlorophyll a
concentrations. From this distribution, which represents the population
of water quality observations in each segment, EPA selected the 90th
percentile as the applicable criteria for each segment. EPA selected
the 90th percentile as an appropriate concentration to specify the
criterion-magnitude because the Agency is confident that the
distribution reflects minimally-impacted, biologically healthy
reference conditions, which support the State's Class II and III
designated uses. The use of the 90th percentile of chlorophyll a is
also supported by several eutrophication assessment frameworks in
Europe and the U.S, such as the Oslo-Paris Commission ``Common
Procedure'' (OSPAR), Water Framework Directive of the EU, Assessment of
Estuarine Trophic Status in the US, and the Marine Strategy Framework
Directive used by the European Commission, which identify the 90th
percentile as representative of a chlorophyll a concentration above
which eutrophication is considered ecologically problematic or where an
undesirable disturbance to aquatic life and water quality from
eutrophication are highly likely to appear.\180\ For

further information on the use of the reference approach see the TSD
(Volume 2, Coastal Waters, Section 1.5.1).
---------------------------------------------------------------------------

    \179\ Geometric means were used for averages in the reference
condition, statistical modeling, and mechanistic modeling approaches
because concentrations were log-normally distributed.
    \180\ OSPAR Commission. 2005. Common Procedure for the
Identification of the Eutrophication Status of the OSPAR Maritime
Area (Reference Number: 2005-3). OSPAR Commission, London.
    Ferreira, J.G., J.H. Andersen, A. Borja, S.B. Bricker, J. Camp,
M.C. da Silva, E. Garc[eacute]s, A-S. Heiskanen, C. Humborg, L.
Ignatiades, C. Lancelot, A. Menesguen, P. Tett, N. Hoepffner, and U.
Claussen. 2011. Overview of eutrophication indicators to assess
environmental status within the European Marine Strategy Framework
Directive. Estuarine, Coastal and Shelf Science 93(2):117-131.
    Bricker, S.B., J.G. Ferreira, and T. Simas. 2003. An integrated
methodology for assessment of estuarine trophic status. Ecological
Modelling 169:39-60.
    European Commission. 2003. Common Implementation Strategy for
the Water Framework Directive (2000/60/EC): Guidance Document No. 5,
Transitional and Coastal Waters-Typology, Reference Conditions and
Classification Systems. European Commission, Working Group 2.4--
COAST, Office for Official Publications of the European Communities,
Luxembourg.
---------------------------------------------------------------------------

    EPA chose not to select the extreme upper end of the distribution
(95th or 100th percentile). This is because these highest observed
annual average concentrations (i.e., 95th or 100th percentile) have
rarely been observed at any reference site and are most likely to be
heavily influenced by extreme event factors (e.g., hurricanes,
droughts). Thus these highest observed concentrations could be outliers
that are not representative of conditions that would typically support
designated uses and natural populations of aquatic flora and fauna.
Therefore, EPA has less confidence that such highest observed
concentrations would continue to be supportive of designated uses and
natural populations of aquatic flora and fauna if maintained in all
coastal waters at all times.
    Alternatively, the selection of a much lower percentile, such as a
representation of the central tendency of the distribution (i.e., 50th
percentile), would not be appropriate because it would imply that half
of the conditions observed at reference sites would not support
designated uses and natural populations of aquatic flora and fauna,
when EPA's analysis indicates that they do. By setting the criteria at
the 90th percentile of the reference condition distribution, EPA
believes the designated uses, i.e., natural populations of aquatic
flora and fauna, will be protected when these concentrations are
attained for the majority of coastal water segments. For those coastal
water segments that are shown to accommodate or require higher or lower
concentrations, the SSAC provision is provided in EPA's proposed rule
as discussed in Section V.C.
(b) Statistical Modeling
    EPA evaluated the data available for each estuary segment in terms
of temporal and spatial representativeness to establish whether there
were sufficient data to use a statistical model. Where enough
monitoring data in estuaries were available, EPA developed statistical
models (i.e., stressor-response relationships) \181\ that quantified
relationships between TN, TP, chlorophyll a, and the selected endpoint
measures (i.e., water clarity to maintain maximum depth of seagrass
colonization and chlorophyll a concentrations associated with balanced
phytoplankton biomass). There were not enough temporally-resolved DO
monitoring data, particularly in pre-dawn hours when dissolved oxygen
concentrations are typically lower than during that day,\182\ in any of
the estuaries to permit the use of statistical models to derive
criterion values associated with sufficient DO to support aquatic life.
Where the available endpoints were shown to be sufficiently sensitive,
EPA used these relationships to calculate TN, TP, and chlorophyll a
concentrations that achieved the selected water quality targets for
these endpoints, which serve as measures of balanced natural
populations of aquatic flora and fauna.
---------------------------------------------------------------------------

    \181\ USEPA. 2010. Using stressor-response relationships to
derive numeric nutrient criteria. EPA-820-S-10-001. U.S.
Environmental Protection Agency, Office of Water, Office of Science
and Technology, Washington, DC.
    \182\ D'Avanzo, C., and J.N. Kremer. 1994. Diel Oxygen Dynamics
and Anoxic Events in an Eutrophic Estuary of Waquoit Bay,
Massachusetts. Estuaries and Coasts 17(1B):131-139.
---------------------------------------------------------------------------

    To determine chlorophyll a concentrations supportive of the water
clarity depth target to achieve the healthy seagrass endpoint in a
segment, EPA estimated the relationship between annual geometric mean
chlorophyll a concentrations and annual geometric mean water clarity
for each segment. Then, EPA computed the chlorophyll a criterion as the
chlorophyll a concentration that was associated with the water clarity
target. In other words, the chlorophyll a criterion was determined such
that the water quality target for water clarity was achieved on an
annual average basis.\183\ In some segments, increased annual geometric
mean chlorophyll a concentrations were not associated with decreased
annual geometric mean water clarity, possibly because other factors,
such as suspended sediment or colored dissolved organic material, more
strongly affected water clarity.\184\ In these segments, EPA determined
that the water clarity endpoint was not sufficiently sensitive to
increased chlorophyll a, and therefore, this endpoint was not used to
derive a chlorophyll a criterion, and associated TN and TP criteria in
that segment.
---------------------------------------------------------------------------

    \183\ Dennison, W.C. 1987. Effects of light on seagrass
photosynthesis, growth, and depth distribution. Aquatic Botany
27:15-26.
    \184\ Gallegos, C.L. 2005. Optical water quality of a blackwater
river estuary: the Lower St. Johns River, Florida, USA. Estuarine,
Coastal and Shelf Science 63(1-2):57-72.
---------------------------------------------------------------------------

    EPA also used stressor-response relationships to derive chlorophyll
a criteria to maintain balanced algal populations. To this end, EPA
used logistic regression to estimate the relationship between annual
geometric mean chlorophyll a concentrations and the probability of any
single chlorophyll a measurement exceeding EPA's proposed water quality
target of 20 [micro]g/L during the year. Then, EPA derived a
chlorophyll a criterion from this relationship by selecting the annual
geometric mean chlorophyll a concentration that ensured that any single
chlorophyll a measurement would not exceed 20 [micro]g/L more than 10%
of the time.
    After calculating chlorophyll a candidate criteria values necessary
to meet the water quality targets for the two biological endpoints for
which data were available (maintenance of seagrasses and maintenance of
balanced algal populations), in each water body segment, EPA selected
the more stringent of the two as the proposed criterion for that
segment to ensure that the proposed chlorophyll a criterion would
protect both endpoints.
    To calculate TN and TP criteria associated with the chlorophyll a
criterion, EPA estimated the relationship between annual geometric mean
TN and TP concentrations and annual geometric mean chlorophyll a
concentrations for each segment. EPA then used these relationships to
compute the TN and TP concentrations that were required to maintain
average chlorophyll a concentrations at the chlorophyll a criterion. In
some estuary segments, increased TN or TP concentrations were not
associated with increased chlorophyll a concentrations, possibly
because of differences in the proportion of TP or TN that was composed
of biologically unavailable forms of phosphorus or nitrogen, or because
of unique physical or hydrological characteristics of the estuary
segment.\185\ In these segments, EPA determined that chlorophyll a
concentrations were not sufficiently sensitive to increases in TN or TP
concentrations, and therefore, this approach was not used to derive
criteria for these segments.
---------------------------------------------------------------------------

    \185\ USEPA. 2001. Nutrient Criteria Technical Manual: Estuarine
and Coastal Marine Waters. EPA-822-B-01-003. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.

---------------------------------------------------------------------------

    In instances where one of the endpoints was not sufficiently
sensitive to increases in TN or TP concentrations the relationship of
the other endpoint to TN or TP was examined. If both endpoints were
insensitive to TN or TP, then the statistical models were not used to
derive candidate criteria for the particular nutrient.
    In a limited number of estuary segments, EPA found that the TN, TP,
or chlorophyll a concentrations that were associated with achieving the
water quality targets for the biological endpoints were outside
(greater than or less than) the range of TN, TP, or chlorophyll a
concentrations observed in the available data for the estuary. In other
words, in these situations, using statistical models to derive numeric
nutrient criteria would require EPA to extrapolate the TN, TP, and
chlorophyll a relationships beyond the range of available data. Because
of the uncertainty inherent in conducting such extrapolations, EPA is
proposing instead to set numeric nutrient criteria derived from these
statistically modeled relationships at the 90th percentile or 10th
percentile limit of the distribution of available data instead of
deriving criteria outside the range of data observations.\186\ For
example, if the statistically modeled value for TP associated with
achieving all water quality targets to meet the biological endpoints in
an estuary segment was less than the 10th percentile of annual average
values of TP observed in that segment, EPA is proposing to set the
criterion value at the 10th percentile of annual average values of TP.
This approach defines criterion values that maintain balanced natural
populations of aquatic flora and fauna within the limits of available
data and is consistent with EPA's reasoning for the selection of the
90th percentile when using the reference condition approach. EPA
requests comment on whether to extrapolate stressor-response
relationships beyond the range of available data. For further
information on the use of statistical modeling approach, see the TSD
(Volume 1: Estuaries, Section 1.4.2 and Appendix B).
---------------------------------------------------------------------------

    \186\ USEPA. 2010. Using Stressor-response Relationships to
Derive Numeric Nutrient Criteria. EPA-820-S-10-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
---------------------------------------------------------------------------

(c) Mechanistic Modeling
    EPA also quantified relationships between nitrogen and phosphorus
loads and the three biological endpoints using a coupled system of
watershed models and estuarine hydrodynamic and water quality models.
These models simulated the physical, chemical, and biological processes
in a watershed-estuarine system. EPA first used the watershed models to
develop estimates of TN, TP, and freshwater inputs to the estuary.
Next, EPA used the estuarine hydrodynamic and water quality models to
simulate estuarine water quality responses to the watershed inputs,
including changes in estuarine TN, TP, and chlorophyll a
concentrations, water clarity, and DO. Then, EPA utilized these models
to determine concentrations of TN and TP that would protect the most
nutrient-sensitive biological endpoint to derive the numeric nutrient
criteria.
    To select the appropriate models, EPA developed an inventory of
watershed and estuary models that have been applied previously to
estuaries in Florida, including models developed by FDEP.\187\ Based on
the results of the review, EPA selected the Loading Simulation Program
in C++ (LSPC) \188\ to simulate freshwater flows and nutrient loading
from watersheds, the Environmental Fluid Dynamics Code (EFDC) \189\ to
simulate estuarine hydrodynamics, and the Water Quality Analysis
Simulation Program (WASP) \190\ to simulate estuarine water
quality.\191\
---------------------------------------------------------------------------

    \187\ Wolfe, S.H. 2007. An Inventory of Hydrodynamic, Water
Quality, and Ecosystem Models of Florida Coastal and Ocean Waters.
Florida Department of Environmental Protection, Tallahassee,
Florida.
    \188\ USEPA. 2011. Loading Simulation Program in C++ (LSPC).
http://www.epa.gov/athens/wwqtsc/html/lspc.html. Accessed December
2011.
    \189\ USEPA. 2011. Environmental Fluid Dynamics Code (EFDC).
http://www.epa.gov/athens/wwqtsc/html/efdc.html. Accessed December
2011.
    \190\ USEPA. 2011. Water Quality Analysis Simulation Program
(WASP). http://www.epa.gov/athens/wwqtsc/html/wasp.html. Accessed
December 2011.
    \191\ USEPA. 2010. Methods and Approaches for Deriving Numeric
Criteria for Nitrogen/Phosphorus Pollution in Florida's Estuaries,
Coastal Waters, and Southern Inland Flowing Waters. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
---------------------------------------------------------------------------

    LSPC can continuously simulate the hydrologic and water quality
processes on pervious and impervious land surfaces, in streams, and in
well-mixed impoundments throughout the watershed and can provide daily
estimates of stream flow, TN, and TP concentrations entering the
estuary. In addition, LSPC is publicly available and has been peer
reviewed.\192\ LSPC has been successfully applied for water quality
management purposes to many watersheds throughout the southeastern
United States and Florida. Therefore, EPA is proposing to apply the
LSPC model to the watersheds in Florida outside of the South Florida
Nutrient Watershed Region.
---------------------------------------------------------------------------

    \192\ USEPA-SAB. 2011. Review of EPA's draft Approaches for
Deriving Numeric Nutrient Criteria for Florida's Estuaries, Coastal
Waters, and Southern Inland Flowing Waters. EPA-SAB-11-010. U.S.
Environmental Protection Agency, Science Advisory Board, Washington,
DC.
---------------------------------------------------------------------------

    EFDC and WASP have been applied in conjunction to simulate
hydrodynamics and water quality (respectively) for many water quality
management projects throughout the southeastern United States and
Florida. EFDC and WASP are also publicly available and have undergone
peer review.\193\ Based on the extensive use of these models for
similar applications and their acceptance in the scientific community,
EPA is proposing to use the EFDC and WASP models to derive numeric
nutrient criteria for Florida's estuaries.
---------------------------------------------------------------------------

    \193\ USEPA-SAB. 2011. Review of EPA's draft Approaches for
Deriving Numeric Nutrient Criteria for Florida's Estuaries, Coastal
Waters, and Southern Inland Flowing Waters. EPA-SAB-11-010. U.S.
Environmental Protection Agency, Science Advisory Board, Washington,
DC.
---------------------------------------------------------------------------

    For estuaries where monitoring data were insufficient to calculate
criteria using the statistical models, EPA mechanistically modeled the
conditions in each system and corresponding watershed that occurred
from 2002-2009 using all available, screened data. EPA evaluated data
over the historic period of record and is proposing to use 2002 through
2009 as a representative modeling period because complete, continuous
flow and water quality data were available. This period also reflects
the range of hydrology and meteorology observed over the historic
period of record across the Florida estuaries.
    EPA then used relationships between TN, TP, and biological
endpoints quantified by the mechanistic models to derive numeric
nutrient criteria. That is, EPA determined the concentrations of TN and
TP that were associated with meeting all biological endpoints in each
segment.
    Because estuaries differ in their physical, chemical, and
hydrological characteristics, EPA expected that differences would exist
in the degree to which different biological endpoints respond to
changes in nutrient concentration. For example, in certain estuaries,
high concentrations of colored dissolved organic material (CDOM) occur
naturally and reduce water clarity. Because of the influence of CDOM in
these estuarine systems, changes in TN, TP, and chlorophyll a are not
strongly associated with changes in water clarity. In these systems,
the water clarity endpoint does not appear to be sensitive to changes
in nutrients,

and therefore, the water clarity endpoint does not provide useful
information for the purposes of deriving numeric nutrient criteria in
these systems. In each estuarine system, EPA used output from
mechanistic models and available monitoring data to evaluate the
sensitivity of each endpoint measure to changes in nutrients. This
analysis was used to determine which endpoints were most critical to
determine protective nutrient concentrations. Endpoints that were found
to be insensitive to changes in nutrient concentrations in a particular
estuarine system were not considered further in deriving numeric
nutrient criteria for a system. Numeric nutrient criteria for each
system were based on the modeled scenario in which the remaining
endpoint measures were met during the modeled period, calculated as
annual geometric means for each year during the modeled period.
Criteria were calculated using the 90th percentile of the annual
geometric means from the modeled years for the model scenario meeting
all appropriate endpoints. EPA selected the 90th percentile to account
for natural variability in the data to represent the upper bound of
conditions supporting designated uses. The selection of the 90th
percentile is appropriate for the same reasons as when using the
reference condition approach. For further information on the use of the
mechanistic modeling approach, see the TSD (Volume 1: Estuaries,
Section 1.4.1).
(d) Request for Comment on Analytical Methodologies
    EPA believes that the three proposed analytical methodologies used
in combination result in numeric nutrient criteria that are supportive
of balanced natural populations of aquatic flora and fauna, and thus
protect Class II and III estuarine and coastal waters in the State of
Florida from nutrient pollution. These analytical methodologies
utilized the latest scientific knowledge, nutrient sensitive endpoints,
and the best available data. The Agency requests comment on the
application of the proposed methodologies and whether these
methodologies are appropriate to derive criteria protective of
designated uses in Florida's estuaries and coastal waters.
Specifically, EPA is soliciting comment and any scientific information
on the use of these approaches in areas where there may be other
factors present in addition to nutrients that may also affect the three
biological endpoints by attenuating light in similar ways as
chlorophyll a (e.g., colored dissolved organic matter (CDOM) or
suspended sediments). EPA is also requesting comment on the procedures
used to screen data to identify reference conditions that are
supporting balanced natural populations of aquatic flora and fauna.

B. Proposed Numeric Criteria for Estuaries

1. Introduction
    EPA is proposing to use a system-specific approach to derive
numeric nutrient criteria for estuaries to ensure that the unique
physical, chemical, and biological characteristics of each estuarine
ecosystem are taken into consideration.\194\
---------------------------------------------------------------------------

    \194\ USEPA. 2001. Nutrient Criteria Technical Manual: Estuarine
and Coastal Marine Waters. EPA-822-B-01-003. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. Glibert, P.M.,
C.J. Madden, W. Boynton, D. Flemer, C. Heil, and J. Sharp, eds.
2010. Nutrients in Estuaries: A Summary Report of the National
Estuarine Experts Workgroup, 2005-2007. Report to U.S. Environmental
Protection Agency, Office of Water, Washington DC.
---------------------------------------------------------------------------

2. Proposed Numeric Criteria (Estuaries)
    EPA is proposing numeric TN, TP, and chlorophyll a criteria for 89
discrete segments within 19 estuarine systems in Florida (Table III.B-
1). These include Class II and III waters under Florida law (Section
62-302.400, F.A.C.); EPA did not find any Class I estuarine waters in
Florida. The 19 estuaries include seven systems in the Florida
Panhandle region, four systems in the Big Bend region, and eight
systems along the Atlantic coast. Maps showing the locations of these
estuarine systems and EPA's proposed within-estuary segments are
provided in the TSD (Volume 1: Estuaries, Section 1.3 and Section 2).
    In some areas a gap may exist between maps used by Florida and EPA
to show where criteria apply. In areas where a gap exists between EPA's
proposed criteria and Florida's numeric criteria, EPA proposes that
Florida's numeric criteria from the adjacent estuary or marine segment
apply (see Section 62-302.532, F.A.C. for values). EPA proposes that
Florida's criteria from the northernmost segment of Clearwater Harbor/
St Joseph Sound (Subsection 62-302.532(a)1., F.A.C.) apply to the
waters between that segment and the southernmost segment of EPA's
Springs Coast estuary system. EPA proposes that Florida's numeric
criteria from the northernmost segment of Biscayne Bay (Subsection 62-
302.532(h)5., F.A.C.) apply to the waters of the intercoastal waterway
between that segment and the southernmost segment of EPA's Lake Worth
Lagoon estuary system.
    In other areas a gap may exist within estuaries covered by
Florida's numeric criteria. In these areas, EPA proposes that Florida's
criteria from the adjacent estuary or marine segment to the south apply
to that gap. EPA proposes that Florida's criteria from (1) the upper
Lemon Bay segment (Subsection 62-302.532(d)2., F.A.C.) apply to the
segment between the upper Lemon Bay segment and the Dona/Roberts Bay
segment (Subsection 62-302.532(d)1., F.A.C.), (2) the Tidal Cocohatchee
River segment (Subsection 62-302.532(e)1., F.A.C.) apply to the waters
between the Tidal Cocohatchee River segment and the Estero Bay segment
(Subsection 62-302.532(d)9., F.A.C.), (3) the Clam Bay segment
(Subsection 62-302.532(j)., F.A.C.) apply between the Clam Bay segment
and the Tidal Cocohatchee River segment (Subsection 62-302.532(e)1.,
F.A.C.), and (4) the Naples Bay segment (Subsection 62-302.532(e)4.,
F.A.C.) apply to the segment between the Naples Bay segment and the
Clam Bay Segment (Subsection 62-302.532(j)., F.A.C.). For further
information regarding the derivation and protectiveness of Florida's
criteria, see http://water.epa.gov/lawsregs/rulesregs/florida_index.cfm.

                     Table III.B-1--EPA's Proposed Numeric Criteria for Florida's Estuaries
                                [In geographic order from northwest to northeast]
----------------------------------------------------------------------------------------------------------------
                                                                                Proposed Criteria
                                                                 -----------------------------------------------
                     Segment                        Segment ID                                    Chl-a*  ([mu]g/
                                                                    TN*  (mg/L)     TP*  (mg/L)         L)
----------------------------------------------------------------------------------------------------------------
Perdido Bay:
    Upper Perdido Bay...........................            0101            0.59           0.042             5.2

    Big Lagoon..................................            0102            0.26           0.019             4.9
    Central Perdido Bay.........................            0103            0.47           0.031             5.8
    Lower Perdido Bay...........................            0104            0.34           0.023             5.8
Pensacola Bay:
    Blackwater Bay..............................            0201            0.53           0.022             3.9
    Upper Escambia Bay..........................            0202            0.43           0.025             3.7
    East Bay....................................            0203            0.50           0.021             4.2
    Santa Rosa Sound............................            0204            0.34           0.018             4.1
    Lower Escambia Bay..........................            0205            0.44           0.023             4.0
    Upper Pensacola Bay.........................            0206            0.40           0.021             3.9
    Lower Pensacola Bay.........................            0207            0.34           0.020             3.6
    Santa Rosa Sound............................            0208            0.33           0.020             3.9
    Santa Rosa Sound............................            0209            0.36           0.020             4.9
Choctawhatchee Bay:
    Eastern Choctawhatchee Bay..................            0301            0.47           0.025             8.1
    Central Choctawhatchee Bay..................            0302            0.36           0.019             3.8
    Western Choctawhatchee Bay..................            0303            0.21           0.012             2.4
St. Andrews Bay:
    East Bay....................................            0401            0.31           0.014             4.6
    St. Andrews Sound...........................            0402            0.14           0.009             2.3
    Eastern St. Andrews Bay.....................            0403            0.24           0.021             3.9
    Western St. Andrews Bay.....................            0404            0.19           0.016             3.1
    Southern St. Andrews Bay....................            0405            0.15           0.013             2.6
    North Bay 1.................................            0406            0.22           0.012             3.7
    North Bay 2.................................            0407            0.22           0.014             3.7
    North Bay 3.................................            0408            0.21           0.016             3.4
    West Bay....................................            0409            0.23           0.022             3.8
St. Joseph Bay:
    St. Joseph Bay..............................            0501            0.25           0.018             3.8
Apalachicola Bay:
    St. George Sound............................            0601            0.53           0.019             3.6
    Apalachicola Bay............................            0602            0.51           0.019             2.7
    East Bay....................................            0603            0.76           0.034             1.7
    St. Vincent Sound...........................            0605            0.52           0.016            11.9
    Apalachicola Offshore.......................            0606            0.30           0.008             2.3
Alligator Harbor:
    Alligator Harbor............................            0701            0.36           0.011             2.8
    Alligator Offshore..........................            0702            0.33           0.009             3.1
    Alligator Offshore..........................            0703            0.33           0.009             2.9
Ochlockonee Bay\+\:
    Ochlockonee-St. Marks Offshore..............            0825            0.79           0.033             2.7
    Ochlockonee Offshore........................            0829            0.47           0.019             1.9
    Ochlockonee Bay.............................            0830            0.66           0.037             1.8
    St. Marks River Offshore....................            0827            0.51           0.022             1.7
    St. Marks River.............................            0828            0.55           0.030             1.2
Big Bend/Apalachee Bay\+\:
    Econfina Offshore...........................            0824            0.59           0.028             4.6
    Econfina....................................            0832            0.55           0.032             4.4
    Fenholloway.................................            0822            1.15           0.444             1.9
    Fenholloway Offshore........................            0823            0.48           0.034            10.3
    Steinhatchee-Fenholloway Offshore...........            0821            0.40           0.023             4.1
    Steinhatchee River..........................            0819            0.67           0.077             1.0
    Steinhatchee Offshore.......................            0820            0.34           0.018             3.5
    Steinhatchee Offshore.......................            0818            0.39           0.032             4.8
Suwannee River\+\:
    Suwannee Offshore...........................            0817            0.78           0.049             5.2
Springs Coast\+\:
    Waccasassa River Offshore...................            0814            0.38           0.019             3.9
    Cedar Keys..................................            0815            0.32           0.019             4.1
    Crystal River...............................            0812            0.35           0.013             1.3
    Crystal-Homosassa Offshore..................            0813            0.36           0.013             2.1
    Homosassa River.............................            0833            0.47           0.032             1.9
    Chassahowitzka River........................            0810            0.32           0.010             0.7
    Chassahowitzka River Offshore...............            0811            0.29           0.009             1.7
    Weeki Wachee River..........................            0808            0.32           0.010             1.6
    Weeki Wachee Offshore.......................            0809            0.30           0.009             2.1
    Pithlachascotee River.......................            0806            0.50           0.022             2.4
    Pithlachascotee Offshore....................            0807            0.32           0.011             2.5

    Anclote River...............................            0804            0.48           0.037             4.7
    Anclote Offshore............................            0805            0.31           0.011             3.2
    Anclote Offshore South......................            0803            0.29           0.008             2.6
----------------------------------------------------------------------------------------------------------------
Clearwater Harbor/St. Joseph Sound:                             See Section 62-302.532(1)(a) F.A.C.
----------------------------------------------------------------------------------------------------------------
Tampa Bay:                                                      See Section 62-302.532(1)(b) F.A.C.
----------------------------------------------------------------------------------------------------------------
Sarasota Bay:                                                   See Section 62-302.532(1)(c) F.A.C.
----------------------------------------------------------------------------------------------------------------
Charlotte Harbor/Lemon Bay:                                     See Section 62-302.532(1)(d) F.A.C.
----------------------------------------------------------------------------------------------------------------
Lake Worth Lagoon/Loxahatchee:
    North Lake Worth Lagoon.....................            1201            0.55           0.067             4.7
    Central Lake Worth Lagoon...................            1202            0.57           0.089             5.3
    South Lake Worth Lagoon.....................            1203            0.48           0.034             3.6
    Lower Loxahatchee...........................            1301            0.68           0.028             2.7
    Middle Loxahatchee..........................            1302            0.98           0.044             3.9
    Upper Loxahatchee...........................            1303            1.25           0.072             3.6
St. Lucie:
    Lower St. Lucie.............................            1401            0.58           0.045             5.3
    Middle St. Lucie............................            1402            0.90           0.120             8.4
    Upper St. Lucie.............................            1403            1.22           0.197             8.9
Indian River Lagoon:
    Mosquito Lagoon.............................            1501            1.18           0.078             7.5
    Banana River................................            1502            1.17           0.036             5.7
    Upper Indian River Lagoon...................            1503            1.63           0.074             9.2
    Upper Central Indian River Lagoon...........            1504            1.33           0.076             9.2
    Lower Central Indian River Lagoon...........            1505            1.12           0.117             8.7
    Lower Indian River Lagoon...................            1506            0.49           0.037             4.0
Halifax River:
    Upper Halifax River.........................            1601            0.75           0.243             9.4
    Lower Halifax River.........................            1602            0.63           0.167             9.6
Guana, Tolomato, Matanzas, Pellicer:
    Upper GTMP..................................            1701            0.77           0.144             9.5
    Lower GTMP..................................            1702            0.53           0.108             6.1
Lower St. Johns River:
    Lower St. Johns River.......................            1801            0.75           0.095             2.5
    Trout River.................................            1802            1.09           0.108             3.6
    Trout River.................................            1803            1.15           0.074             7.7
Nassau River:
    Lower Nassau................................            1901            0.33           0.113             3.2
    Middle Nassau...............................            1902            0.40           0.120             2.4
    Upper Nassau................................            1903            0.75           0.125             3.4
St. Marys River:
    Lower St. Marys River.......................            2002            0.27           0.045             3.0
    Middle St. Marys River......................            2003            0.44           0.036             2.7
----------------------------------------------------------------------------------------------------------------
\1\ Chlorophyll a is defined as corrected chlorophyll, or the concentration of chlorophyll a remaining after the
  chlorophyll degradation product, phaeophytin a, has been subtracted from the uncorrected chlorophyll a
  measurement.
* For a given water body, the annual geometric mean of TN, TP, or chlorophyll a, concentrations shall not exceed
  the applicable criterion concentration more than once in a three-year period.
\+\ In these four areas (collectively referred to as the ``Big Bend region''), coastal and estuarine waters are
  combined. Criteria for the Big Bend region apply to the coastal and estuarine waters in that region.

(a) Summary of Approaches (Estuaries)
(1) Proposed Approach (Estuaries)
    In estuaries where sufficient monitoring data were available to
statistically quantify relationships between TN, TP, chlorophyll a, and
biological endpoints, and the endpoints available to derive criteria
were shown to be sufficiently sensitive (i.e., Choctawhatchee Bay; St.
Joseph Bay; Suwannee River; Indian River Lagoon; Halifax River; and the
Guana, Tolomato, Matanzas, and Pellicer (GTMP) estuarine system),
statistical models were used to derive the proposed numeric nutrient
criteria. In three of the estuaries, Choctawhatchee Bay, St. Joseph
Bay, and Indian River Lagoon, there were sufficient available data for
water clarity associated with historic depth of seagrasses, and
chlorophyll a concentrations associated with balanced phytoplankton
biomass targets, and these biological endpoints were sensitive to
changes in nutrients in most segments, so proposed criteria were
derived that were protective of these endpoints. In the Suwannee River,
the water clarity endpoint was not sensitive to changes in nutrients,
so proposed criteria were derived that were protective of the
chlorophyll a target

associated with balanced phytoplankton biomass. In the Halifax River
and GTMP, seagrass has not been historically present, so the proposed
criteria were derived that are protective of the chlorophyll a target
associated with balanced phytoplankton biomass.
    In all other estuaries mechanistic models were used to quantify the
relationship between nutrient loads and biological endpoints. EPA then
used the models to derive proposed numeric nutrient criteria that
protect the endpoints. For each estuary, the endpoints that were shown
to be sufficiently sensitive to nutrient changes above non-
anthropogenic nutrient levels were used, as described in Section
III.A.3.c. The endpoints for each of the estuaries where mechanistic
models were used to derive criteria are noted in the following
discussion.
    In Perdido Bay, Apalachicola Bay, three segments in Lake Worth
Lagoon/Loxahatchee (Lake Worth Lagoon, segments 1201, 1202, and 1203),
and St. Lucie, all three biological endpoints were found to be
sensitive to changes to nutrients, and so proposed criteria were
derived that were protective of historic depth of seagrasses (water
clarity), chlorophyll a concentrations associated with balanced
phytoplankton biomass, and dissolved oxygen concentrations sufficient
to maintain aquatic life.
    In St. Andrews Bay, 2 segments in the Springs Coast (Anclote River/
Anclote Offshore, segments 0804 and 0805) and 3 segments in Lake Worth
Lagoon/Loxahatchee (Lower, Middle, and Upper Loxahatchee, segments
1301, 1302, and 1303), dissolved oxygen concentrations were found to be
insensitive to changes in nutrients. Proposed criteria were derived
that were protective of historic depth of seagrasses (water clarity)
and chlorophyll a concentrations associated with balanced phytoplankton
biomass.
    In Pensacola Bay, 3 segments in Ochlockonee Bay (Ochlockonee-St.
Marks Offshore/Ochlockonee Offshore/Ochlockonee Bay, segments 0825,
0829, and 0830), and 4 segments in Big Bend/Apalachee Bay (Econfina/
Econfina Offshore, segments 0824, 0832; Steinhatchee-Fenholloway
Offshore, segment 0821; Steinhatchee Offshore, segment 0818), and 1
segment in Springs Coast (Anclote Offshore South, segment 0803), water
clarity was found to be insensitive to changes in nutrients. In
Alligator Harbor and 2 segments in Springs Coast (Waccasassa River
Offshore/Cedar Keys, segments 0814, 0815), there was not enough
available information to derive seagrass depth targets. As a result,
the proposed criteria were derived to be protective of water quality
targets for chlorophyll a concentrations associated with balanced
phytoplankton biomass and dissolved oxygen concentrations sufficient to
maintain aquatic life.
    In 2 segments in Ochlockonee Bay (St. Marks Offshore/St. Marks
River, segments 0827, 0828), 2 segments in Big Bend/Apalachee Bay
(Steinhatchee River/Steinhatchee Offshore, segments 0819, 0820), and 2
segments in Springs Coast (Pithlachascotee River/Pithlachascotee