Another technical concern is that there may be a time lag between
the presence of high nutrients and the biological response. In a study
of numerous lakes, researchers found that there was often a lag period
of a few years in chlorophyll a response to changes in nutrient
loading, but that there was correlation between chlorophyll a and
nutrient concentrations on an annual basis.\57\ The difference between
nutrient loading and nutrient concentration as a function of time is
related to the hydraulic retention time of a lake. EPA proposed TN and
TP criteria as concentration values with an annual averaging period, so
any time lag in response would not be expected to confound the
derivation of modified criteria. Furthermore, EPA is proposing to
require three years worth of data, which would reflect any short time
lag in response.
---------------------------------------------------------------------------

    \57\ Jeppeson et al. 2005. Lake responses to reduced nutrient
loading--an analysis of contemporary long-term data from 35 case
studies. Freshwater Biology 50: 1747-1771.
---------------------------------------------------------------------------

    A third technical concern is the presence of temporary or long-term
site-specific factors that may suppress biological response, such as
the presence of grazing zooplankton, excess sedimentation that blocks
light penetration, extensive canopy cover, or seasonal herbicide use
that impedes proliferation of algae. If any of these suppressing
factors are removed, then nutrient levels may result in a spike in
algal production above protective levels.

    EPA is proposing to require that the ambient calculation for
modified TP and TN criteria be based on at least a three-year record of
observation, and be based on representative sampling (i.e., four
samples per year with at least one between May and September and one
between October and April) during each year. These requirements will
minimize the influence of long-term site-specific factors and ensure
longer-term stable conditions. EPA selected three years as a reasonable
minimum length of time to appropriately account for anomalous
conditions in any given year that could lead to erroneous conclusions
regarding the true relationship between nutrient levels in a lake and
chlorophyll a levels. EPA anticipates that the State would use all
recent consecutive years of data on record (i.e., it would not be
appropriate to select three random years within a complete record over
the past seven years). EPA is requiring four measurements within a year
to provide seasonal representation (i.e., May-September and October-
April). Providing seasonal representation is important because nutrient
levels can vary by season. In addition, this minimum sample size is
conducive to the derivation of central tendency measurements, such as a
geometric mean, with an acceptable degree of confidence. EPA is
proposing that the chlorophyll a criterion must be met in each of the
three or more years of ambient monitoring that define the record of
observation for the lake to be eligible for the ambient calculation
modified provision for TN and TP. EPA requests comment on whether three
years of data is sufficient to establish for a particular lake that
there is a fundamentally different relationship between chlorophyll a
levels and TN and TP levels. EPA also requests comment on whether less
data or a different specification would be sufficient to establish this
different relationship in a particular lake, e.g. whether revised TN
and TP ambient criteria should be allowed when the chlorophyll a
criterion concentration has been exceeded once in three years.
    Application of the ambient calculation provision has implications
for assessment and permitting because the outcome of applying this
provision is to establish alternate numeric TN and TP values as the
applicable numeric nutrient criteria for TN and TP. For accountability
and tracking purposes, the State would need to document in a publicly
available and accessible manner, such as on an official State Web site,
the result of the ambient calculation for any given lake. The State may
wish to issue a public notification, with an opportunity to submit
additional data and check calculations, to ensure an appropriate value
is determined. The State may wish to publicly certify the outcome via a
Secretarial order or some other official statement of intent and
applicability. EPA's preference is that once modified criteria are
developed, they remain the applicable criteria for the long-term. The
State has the flexibility to revise the criteria, but the expectation
is that they will not be a continuously moving target for
implementation purposes. As an example of how the lakes criteria might
work in practice, consider a colored lake which meets the chlorophyll a
criterion. If FDEP established a modified TP criterion of 0.110 mg/L
and subsequent monitoring showed levels at 0.136 mg/L, that lake would
not be considered attaining the applicable criteria for CWA purposes
(unless the State goes through the process of establishing a revised
modified criterion).
    The permitting authority would use publicly certified modified TN
or TP criteria to develop water quality-based effluent limits (WQBELs)
that derive from and comply with applicable WQS. In this application,
the permit writer would use the modified ambient criterion, computed as
described above, as the basis for any reasonable potential analysis or
permit limit derivation. In this case, as in any other case, EPA
expects the details to be fully documented in the permit fact sheet.
    This type of ambient calculation provision based on meeting
response criteria applicable to the assessed water may not be
appropriate when the established TN and TP criteria are serving to
maintain and protect waters downstream. To address this concern, EPA
proposes that calculated TP and TN values in a lake that discharges to
a stream may not exceed criteria applicable to the stream to which a
lake discharges. EPA requests comment on this provision.
(3) Request for Comment and Data on Proposed Approach
    EPA is soliciting comment on the approaches described in this
proposal, the data underlying those approaches, and the proposed
criteria. EPA will evaluate all data and information submitted by the
close of the public comment period for this rulemaking with regard to
nutrient criteria for Florida's lakes. For the application of the
modified ambient calculation provision, EPA is seeking comment on
allowing the calculation to occur one time only, based on an adequate
period of record, and then holding that value as the protective TP or
TN criteria for future assessment and implementation purposes. EPA is
also seeking comment on whether to require an ambient chlorophyll a
level demonstrated to be below the chlorophyll a threshold criterion
for at least three years become the protective chlorophyll a criterion
for a lake subject to the modified ambient calculation provision (i.e.,
whether to require a more stringent chlorophyll a criterion if three
years of data show that the more stringent level reflects current
conditions in the lake). EPA also requests comment on whether an
additional condition for being able to apply a modified criterion
include continued ambient monitoring and verification that chlorophyll
a levels remain below the protective criterion. EPA could specify that
modified criteria remain in effect as long as FDEP subsequently
conducts monthly (or some other periodic) monitoring of the lake to
ensure that chlorophyll a levels continue to meet the protective
criterion. If this monitoring is not conducted and documented, EPA
could specify that the baseline criterion would become the applicable
criterion. Among others, this provision may address concerns about
whether the modified criterion adequately represents long-term
hydrologic variability. Finally, EPA requests comment on the
appropriate procedure for documenting and tracking the results of
modified criteria that allows transparency, public access, and
accountability.
(4) Alternatives Considered by EPA
    During EPA's review of the available data and information for
development of numeric nutrient criteria for Florida's lakes, EPA
considered and is soliciting comment on an alternative approach to
deriving lakes criteria from the statistical correlation plots and
regression analysis. The alternative approach would use either the
central tendency values or the lower values associated with the 50th
percentile prediction interval for TN and TP criteria and would not
include the framework to calculate modified TP and TN criteria when the
chlorophyll a criterion is met. EPA is also seeking comments on the
following two supplementary modifications that EPA considered but did
not include in this proposal: (1) the use of a modified categorization
of lakes in Florida; and (2) the addition of upper percentile criteria
with a different exceedance frequency.

(a) Single Value Approach To Derive Lakes Criteria--Derive TN and TP
Criteria Using Correlations Associated With the Regression Line or
Lower Value of the 50th Percentile Prediction Interval
    One alternative means of selecting TN and TP criteria is to use the
regression line (central tendency) to calculate TP and TN
concentrations that correlate to the proposed chlorophyll a criteria
for each lake class. A second alternative is to use the lower value of
the 50th percentile prediction interval to calculate TP and TN
concentrations. Establishing TP and TN criteria using the central
tendency of the regression line represents the best estimate of TN and
TP associated with a protective chlorophyll a criterion across all
lakes, but carries some risk of being overprotective for some
individual lakes and under-protective for others because of the
demonstrated variability of the data. On the other hand, establishing
TP and TN criteria using the lower value of the 50th percentile
prediction interval will likely be protective in most cases, but could
be overprotective for a greater number of lakes because the data
demonstrate that many lakes achieve the protective chlorophyll a
criterion with higher levels of TN and TP. Neither approach accounts
for lake-specific natural variability, apart from that accounted for by
color and alkalinity classification. However, the correlated TP and TN
concentrations within each lake class at these alternative statistical
boundaries would result in single criteria values for TN and TP, which
is an approach that water quality program managers will have more
familiarity. EPA's rationale for proposing a framework that uses both
the upper and lower values of the 50th percentile prediction interval
to allow the derivation of modified TN and TP lake-specific criteria
rather than either of these single values was to account for the
natural variability in the relationship between chlorophyll a and TN
and TP that may exist in lakes. EPA solicits comment, however, on this
alternative approach of using single values for TN and TP criteria in
Florida's lakes.
(b) Modification to Proposed Lakes Classification
    As discussed in Section III.B(2)(a), EPA used available data to
determine a classification scheme for Florida's lakes, based on a color
threshold of 40 PCU and a threshold of 50 mg/L alkalinity as
CaCO3. In its July 2009 numeric nutrient criteria proposal,
Florida considered a similar classification approach based on color and
alkalinity but proposed a chlorophyll a criterion of 9 [micro]g/L to
protect aquatic life in clear, acidic lakes. As discussed above, EPA
believes that the scientific evidence more strongly supports a
chlorophyll a criterion of 6 [micro]g/L to protect Florida's clear,
acidic lakes that include the very oligotrophic lakes found in
Florida's sandhills, principally in three areas: the Newhope Ridge/
Greenhead slope north of Panama City (locally called the Sandhill Lakes
region); the Norfleet/Springhill Ridge just west of Tallahassee, and
Trail Ridge northeast of Gainesville.\58\ However, some stakeholders
have suggested that many lakes in the clear, acidic class (as currently
defined) might be sufficiently protected with a chlorophyll a criterion
of 9 [micro]g/L. EPA believes the scientific basis for a 9 [micro]g/L
chlorophyll a value may be more applicable to clear acidic lakes other
than those in Florida's sandhills (i.e., other than those in the
Sandhill Lakes region, the Norfleet/Springhill Ridge just west of
Tallahassee and Trail Ridge northeast of Gainesville). To address this,
EPA could separate clear, acidic lakes into two categories: one
category for clear, acidic lakes in sandhill regions of Florida, and a
second category for clear, acidic lakes in other areas of the State.
EPA could assign the first category (clear, acidic sandhill lakes) a
chlorophyll a criterion of 6 [micro]g/L and the second category (clear,
acidic non-sandhill lakes) a chlorophyll a criterion of 9 [micro]g/L.
---------------------------------------------------------------------------

    \58\ Griffith, G.E., D.E. Canfield, Jr., C.A. Horsburgh, J.M.
Omernik, and S.H. Azevedo. 1997. Florida lake regions. U.S. EPA,
Corvallis, OR. http://www.epa.gov/wed/pages/ecoregions/fl_eco.htm.
---------------------------------------------------------------------------

    Alternatively, EPA could lower the defining alkalinity threshold to
20 mg/L CaCO3 so that the clear, acidic lakes category would
only include lakes with very acidic values and correspondingly low
chlorophyll a, TN, and TP values. EPA's analysis of a distribution of
alkalinity data from Florida's clear lakes found that lakes with
alkalinity values >= 20 mg/L CaCO3 had higher levels of
nutrients and nutrient response parameters than lakes with alkalinity
values < 20 mg/L CaCO3. By adjusting the alkalinity
threshold to 20 mg/L CaCO3, EPA would be creating a smaller
group of clear, acidic lakes that may be more representative of
naturally more acidic, oligotrophic conditions than the proposed
alkalinity threshold of 50 mg/L CaCO3. EPA opted to propose
a threshold of 50 mg/L CaCO3 because it represents a more
comprehensive group of lakes that may be naturally oligotrophic (i.e.,
ensures protection where there may be some uncertainty). EPA solicits
comment on these alternative approaches to classifying Florida's lakes.
EPA also notes, as discussed previously, that FDEP recommended a
criterion of 9 [mu]g/L as being protective of all clear acidic lakes,
including sandhill lakes and that the Nutrient Criteria TAC supported
``less than 10 [mu]g/L'' as protective. EPA also requests comment on 9
[mu]g/L chlorophyll a as being protective of all clear acidic lakes,
including sandhill lakes.
(c) Modification To Include Upper Percentile Criteria
    EPA is considering promulgating upper percentile criteria for
chlorophyll a, TN, and TP in colored, clear alkaline, and clear acidic
lakes to provide additional aquatic life protection. Accordingly, EPA
could add that the instantaneous concentration in the lake not surpass
these criterion-magnitude concentrations more than 10% of the time
(criterion-duration: instant; criterion-frequency: 10% of the time).
EPA derived example upper percentile criteria using the observed
standard deviation from the mean of lake samples meeting the respective
criteria (lower values of the TN and TP ranges) within each lake class.
Using this example, the calculated criteria-magnitude concentrations
for chlorophyll a, TN, and TP respectively by lake class are: 63 [mu]g/
L, 1.5 mg/L and 0.09 mg/L for colored lakes; 48 [mu]g/L, 1.8 mg/L and
0.05 mg/L for clear, alkaline lakes; and 15 [mu]g/L, 0.6 mg/L and 0.02
mg/L for clear, acidic lakes.
    These criteria would provide the means to protect lakes from
episodic events that increase loadings for significant periods of time
during the year, but are balanced out by lower levels in other parts of
the year such that the annual geometric mean value is met. EPA chose
not to propose such criteria because of the significant variability of
chlorophyll a, TN, and TP, the variety of other factors that may
influence levels of these parameters in the short-term, and that
significant environmental damage from eutrophication is more likely
when levels are elevated for longer periods of time. However, EPA
solicits comment on this additional approach of promulgating upper
percentile criteria for chlorophyll a, TN, and TP.
(5) Request for Comment and Data on Alternative Approaches
    EPA is soliciting comment on the Agency's proposed approach, as
well as the alternative approach to deriving numeric nutrient criteria
for Florida's lakes and the supplemental modifications as described in
Section III.B(4). EPA will evaluate all data and

information submitted by the close of the public comment period for
this rulemaking with regard to nutrient criteria for Florida's lakes.

C. Proposed Numeric Nutrient Criteria for the State of Florida's Rivers
and Streams

(1) Proposed Numeric Nutrient Criteria for Rivers and Streams
    EPA is proposing numeric nutrient criteria for TN and TP in four
geographically distinct watershed regions of Florida's rivers and
streams (hereafter, streams) classified as Class I or III waters under
Florida law (Rule 62-302.400, F.A.C.).

------------------------------------------------------------------------
                                             Instream protection value
                                                     criteria
        Nutrient watershed region        -------------------------------
                                           TN (mg/L) \a\   TP (mg/L) \a\
------------------------------------------------------------------------
Panhandle \b\...........................           0.824           0.043
Bone Valley \c\.........................           1.798           0.739
Peninsula \d\...........................           1.205           0.107
North Central \e\.......................           1.479           0.359
------------------------------------------------------------------------
\a\ Concentration values are based on annual geometric mean not to be
  surpassed more than once in a three-year period. In addition, the long-
  term average of annual geometric mean values shall not surpass the
  listed concentration values. (Duration = annual; Frequency = not to be
  surpassed more than once in a three-year period or as a long-term
  average).
\b\ Panhandle region includes the following watersheds: Perdido Bay
  Watershed, Pensacola Bay Watershed, Choctawhatchee Bay Watershed, St.
  Andrew Bay Watershed, Apalachicola Bay Watershed, Apalachee Bay
  Watershed, and Econfina/Steinhatchee Coastal Drainage Area.
\c\ Bone Valley region includes the following watersheds: Tampa Bay
  Watershed, Sarasota Bay Watershed, and Charlotte Harbor Watershed.
\d\ Peninsula region includes the following watersheds: Waccasassa
  Coastal Drainage Area, Withlacoochee Coastal Drainage Area, Crystal/
  Pithlachascotee Coastal Drainage Area, Indian River Watershed,
  Caloosahatchee River Watershed, St. Lucie Watershed, Kissimmee River
  Watershed, St. John's River Watershed, Daytona/St. Augustine Coastal
  Drainage Area, Nassau Coastal Drainage Area, and St. Mary's River
  Watershed.
\e\ North Central region includes the Suwannee River Watershed.

    The following section describes the methodology used to derive the
proposed numeric nutrient criteria for streams. EPA is soliciting
comments and scientific data and information regarding these proposed
criteria and their derivation.
(2) Methodology for Deriving EPA's Proposed Criteria for Streams
    Like other aquatic ecosystems, excess nutrients in streams
increases vegetative growth (plants and algae), and changes the
assemblage of plant and algal species present in the system. These
changes can affect the organisms that are consumers of algae and plants
in many ways. For example, these changes can alter the available food
resources by providing more dead plant material versus live plant
material, or providing algae with a different cell size for filter
feeders. These changes can also alter the habitat structure by covering
the stream or river bed with periphyton (attached algae) rather than
submerged aquatic plants, or clogging the water column with
phytoplankton (floating algae). In addition, these changes can lead to
the production of algal toxins that can be toxic to fish,
invertebrates, and humans. Chemical characteristics of the water, such
as pH and concentrations of dissolved oxygen, can also be affected by
excess nutrients. Each of these changes can, in turn, lead to other
changes in the stream community and, ultimately, to the stream ecology
that supports the overall function of the linked aquatic ecosystem.
    Although the general types of adverse effects can be described, not
all of these effects will occur in every stream at all times. For
example, some streams are well shaded, which would tend to reduce the
near-field effect of excess nutrients on primary production because
light, which is essential for plant or algae growth, does not reach the
water surface. Some streams are fast moving and pulses of nutrients are
swiftly carried away before any effect can be observed. However, if the
same stream widens and slows downstream or the canopy that provided
shading opens up, then the nutrients present may accelerate plant and
algal biomass production. As another example, the material on the
bottom of some streams, referred to as substrate, is frequently scoured
from intense rain storms. These streams may lack a natural grazing
community to consume excess plant growth and may be susceptible to
phytoplankton algae blooms during periods when water velocity is slower
and water residence time is longer. The effects of excess nutrients may
be subtle or dramatic, easily captured by measures of plant and algal
response (such as chlorophyll a) or not, and may occur in some
locations along a stream but not others.
    Notwithstanding natural environmental variability, there are well
understood and documented analyses and principles about the underlying
biological effects of TN and TP on an aquatic ecosystem. There is a
substantial and compelling scientific basis for the conclusion that
excess TN and TP will have adverse effects; however, it is often
unclear where precisely the impacts will occur. The value of regional
numeric nutrient criteria for streams is that the substantial
expenditure of time and scarce public resources to document and
interpret inevitable and expected stream variability on a site-by-site,
segment-by-segment basis (i.e., as in the course of interpreting a
narrative WQS for WQBELs and TMDL estimations) is no longer necessary.
Rather, regional numeric nutrient criteria for streams allows an
expedited and expanded level of aquatic protection across watersheds
and greatly strengthens local and regional capacity to support and
maintain State designated uses throughout aquatic ecosystems. In terms
of environmental outcomes, the result is a framework of expectations
and standards that is able to extend the protection needed to restore
and maintain valuable aquatic resources to entire watersheds and
associated aquatic ecosystems. At the same time, the ability to
promulgate SSAC, as well as other flexibilities discussed in this
proposal, allows the State to continue to address water bodies where
substantial data and analyses show that the regional criteria may be
either more stringent than necessary or not stringent enough to protect
designated uses.
    As mentioned earlier, to effectively apply this well understood and
documented science, EPA has recommended that nutrient criteria

include both causal (e.g., TN and TP) and response variables (e.g.,
chlorophyll a and some measure of clarity) for water bodies.\59\ EPA
recommends causal variables, in part, to have the means to develop
source control targets and, in part, to have the means to assess stream
condition with knowledge that responses can be variable, suppressed,
delayed, or expressed at different locations. EPA recommends response
variables, in part, to have a means to assess stream condition that
synthesizes the effect of causal variables over time, recognizing the
daily, seasonal, and annual variability in measured nutrient
levels.\60\
---------------------------------------------------------------------------

    \59\ U.S. EPA. 1998. National Strategy for the Development of
Regional Nutrient Criteria. Office of Water, Washington, DC. EPA
822-R-98-002; Grubbs, G. 2001. U.S. EPA. (Memorandum to Directors of
State Water Programs, Directors of Great Water Body Programs,
Directors of Authorized Tribal Water Quality Standards Programs and
State and Interstate Water Pollution Control Administrators on
Development and Adoption of Nutrient Criteria into Water Quality
Standards. November 14, 2001); Grumbles, B.H. 2007. U.S. EPA.
(Memorandum to Directors of State Water Programs, Directors of Great
Water Body Programs, Directors of Authorized Tribal Water Quality
Standards Programs and State and Interstate Water Pollution Control
Administrators on Nutrient Pollution and Numeric Water Quality
Standards. May 25, 2007).
    \60\ U.S. EPA. 2000. Nutrient Criteria Technical Guidance
Manual: Rivers and Streams. Office of Water, Washington, DC. EPA-
822-B-00-002.
---------------------------------------------------------------------------

    The ability to establish protective criteria for both causal and
response variables depends on available data and scientific approaches
to evaluate these data. Whereas, there are data available for water
column chlorophyll a (phytoplankton) and algal thickness on various
substrates (periphyton) for certain types of streams in Florida, there
are currently no available approaches to interpret these data to infer
scientifically supported thresholds for these nutrient-specific
response variables in Florida streams. Additionally, in previously
published guidance,\61\ EPA has recommended water clarity as a response
variable for numeric nutrient criteria because algal density in a water
column results in turbidity, and thus a related decrease in water
clarity can serve as an indicator of excess algal growth. For water
clarity, Florida has criteria for transparency and turbidity,
applicable to all Class I and III waters, expressed in terms of a
measurable deviation from natural background (32-302.530(67) and (69),
F.A.C.). Therefore, EPA is not proposing criteria for any response
variable in Florida's streams at this time, however, EPA will consider
additional data that becomes available during the comment period. One
approach for deriving criteria for water quality variables such as a
measure for water clarity or chlorophyll a, could be to apply a
statistical distribution approach to a population of streams for each
of the proposed NWRs. This approach is further described in previous
EPA guidance.\62\
---------------------------------------------------------------------------

    \61\ U.S. EPA. 2000. Nutrient Criteria Technical Guidance
Manual: Lakes and Reservoirs. Office of Water, Washington, DC. EPA-
822-B-00-001; U.S. EPA. 2000. Nutrient Criteria Technical Guidance
Manual: Rivers and Streams. Office of Water, Washington, DC. EPA-
822-B-00-002; U.S. EPA. 2001. Nutrient Criteria Technical Manual:
Estuarine and Coastal Marine Waters. Office of Water, Washington,
DC. EPA-822-B-01-003.
    \62\ U.S. EPA. 2000. Nutrient Criteria Technical Guidance
Manual: Rivers and Streams. Office of Water. 4304. EPA-822-B-00-002.
---------------------------------------------------------------------------

    For Florida streams, EPA has determined that there are sufficient
available data on TN and TP concentrations with corresponding
information on biological condition for a wide variety of stream types
that can be used to derive numeric nutrient criteria for those causal
variables. EPA used multiple measures of stream condition (or metrics)
that describe the biological condition of the benthic invertebrate
community. EPA then coupled the stream condition metrics with
associated measurements of TN and TP concentrations to provide the
basis for deriving causal variable numeric nutrient criteria.
    EPA's proposed instream numeric nutrient criteria for Florida's
streams are based upon EPA's evaluation of data on TN and TP levels in
rivers and streams that have been carefully evaluated by FDEP, and
subsequently by EPA, on a site-specific basis and identified as
biologically healthy. EPA's approach results in numeric criteria that
are protective of the streams themselves. EPA has determined, however,
that these instream values may not always be protective of the
designated uses in downstream lakes and estuaries. Therefore, EPA has
also developed an approach for deriving TN and TP values for rivers and
streams to ensure the protection of downstream lakes and estuaries.
This approach is discussed in Section III.C(6).
(a) Methodology for Stream Classification: EPA's Nutrient Watershed
Regions (NWRs)
    EPA classified Florida's streams north of Lake Okeechobee by
separating watersheds with a substantially different ratio of TN and TP
export into Nutrient Watershed Regions (NWR). The resulting regions
reflect the inherent differences in the natural factors that contribute
to nutrient concentrations in streams (e.g., geology, soil composition,
and/or hydrology). Reliance on a watershed-based classification
approach reflects the understanding that upstream water quality affects
downstream water quality. This watershed classification also
facilitates the ability to address the effects of TN and TP from
streams to downstream lakes or estuaries in the same watershed.
    EPA's classification approach results in four watershed regions:
the Panhandle, the Bone Valley, the Peninsula, and the North Central
(for a map of these regions, refer to the EPA TSD for Florida's Inland
Waters or the list of watersheds in the table above). These four
regions do not include the south Florida region (corresponding to
FDEP's Everglades Bioregion) that is addressed separately in Section
III.E which sets out EPA's proposed numeric nutrient criteria for
canals in south Florida. All flowing waters in this region are either a
canal or a wetland.
    When classifying Florida's streams, EPA identified geographic areas
of the State as having phosphorus-rich soils and geology, such as the
Bone Valley and the northern Suwannee River watershed. As indicated
above, the Bone Valley region and the Suwannee River watersheds are
classified in this proposal as separate NWRs because it is well
established that the naturally phosphorus-rich soils in these areas
significantly influence stream phosphorus concentrations in these
watersheds. EPA would expect from a general ecological standpoint that
the associated aquatic life uses, under these naturally-occurring,
nutrient-rich conditions, would be supported. The Agency requests
comment on this particular classification decision (regions based on
phosphorus-rich soils), as well as an alternate classification approach
that would not separate out the phosphorus-rich watersheds described in
this notice. The latter approach is similar to the approach proposed by
EPA, but would not result in separate NWRs for the Bone Valley and/or
North Central. Rather these NWRs would be integrated within the other
NWRs.
(b) The Use of the Stream Condition Index as an Indicator of
Biologically Healthy Conditions
    For EPA's proposed approach, the Agency utilized a multi-metric
index of benthic macroinvertebrate community composition and taxonomic
data known as the Stream Condition Index (SCI) developed by FDEP to
assess the

biological health of Florida's streams.\63\ Of the metrics that
comprise the SCI, some decrease in response to human disturbance-based
stressors, such as excess nutrients; for example, (1) total taxa
richness, (2) richness of Ephemeroptera (mayflies), (3) richness of
Plecoptera (stoneflies), (4) percentage of sensitive taxa, and (5)
percentage of filterers and suspension feeders. Other metrics increase
in response to human disturbance-based stressors; for example, percent
of very tolerant taxa (e.g., Genera Prostoma, Lumbriculus) and percent
of the dominant taxa (i.e., numerical abundance of the most dominant
taxon divided by the total abundance of all taxa).
---------------------------------------------------------------------------

    \63\ The SCI method was developed and calibrated by FDEP. See
``Fore et al. 2007. Development and testing biomonitoring tools for
macroinvertebrates in Florida streams (Stream Condition Index and
BioRecon). Final report to Florida Department of Environmental
Protection'' and the EPA TSD for Florida's Inland Waters for more
information on the SCI.
---------------------------------------------------------------------------

    The SCI was developed by FDEP in 2004, with subsequent revisions in
2007 to reduce the variability of results. In order to ensure that data
are produced with the highest quality, field biologists and lab
technicians must follow detailed Standard Operating Procedures (SOPs)
and additional guidance for sampling and data use provided through a
FDEP document entitled ``Sampling and Use of the Stream Condition Index
(SCI) for Assessing Flowing Waters: A Primer (DEP-SAS-001/09).'' Field
biologists must pass a rigorous audit with FDEP, and laboratory
taxonomists are regularly tested and must maintain greater than 95%
identification accuracy.
    EPA considered two lines of evidence in determining the SCI range
of scores that would indicate biologically healthy systems. The first
line of evidence was an evaluation of SCI scores in streams considered
by FDEP to be least-disturbed streams in Florida. A statistical
analysis balanced the probability of a stream being included in this
reference set with the probability of a stream not being included in
this reference set, and indicated that an SCI score of 40 was an
appropriate threshold. SCI scores range from 1 to 100 with higher
scores indicating healthier biology.
    A second line of evidence was the result of an expert workshop
convened by FDEP in October 2006. The workshop included scientists with
specific knowledge and expertise in stream macroinvertebrates. These
experts were asked to individually and collectively evaluate a range of
SCI data (i.e., macroinvertebrate composition and taxonomic data) and
then assign those data into one of the six Biological Condition
Gradient (BCG) \64\ categories, ranging from highly disturbed (Category
6) to pristine (Category 1). EPA analyzed the results of these
categorical assignments using a proportional odds regression model \65\
that predicts the probability of an SCI score occurring within one of
the BCG categories by overlapping the ranges of SCI scores associated
with each category from the individual expert assignment. The results
of the analysis provided support for identifying a range of SCI scores
that minimized the probability of incorrectly assigning a low quality
site to a high quality category, and incorrectly assigning a high
quality site to a low quality category, using the collective judgment
of expert opinion. The results indicated a range of SCI scores of 40-44
to represent an appropriate threshold of healthy biological condition.
Please refer to the EPA TSD for Florida's Inland Waters for more
information on such topics as EPA's estimates of the Type I and Type II
error associated with various threshold values. Thus, two very
different approaches yielded comparable results. A subsequent EPA
statistical analysis indicated that nutrient conditions in Florida
streams within different regions remain essentially constant within an
SCI score range of 40-50 providing further support for a selection of
40 as a threshold that is sufficiently protective for this application.
The resulting TN and TP concentrations associated with a SCI score of
40 versus 50 did not represent a statistical difference and 40 was more
in line with other lines of evidence for a SCI score threshold.
---------------------------------------------------------------------------

    \64\ Appendix H in ``Fore et al. 2007. Development and testing
biomonitoring tools for macroinvertebrates in Florida streams
(Stream Condition Index and BioRecon). Final report to Florida
Department of Environmental Protection''.
    \65\ See the EPA TSD for Florida's Inland Waters for more
information on the proportional odds regression model.
---------------------------------------------------------------------------

(c) Methodology for Calculating Instream Protection Values: The
Nutrient Watershed Region Distribution Approach
    EPA evaluated several methodologies, including reference conditions
and stressor-response relationships, to develop values that protect
designated uses of Florida streams instream. EPA analyzed stressor-
response relationships in Florida streams based on available data, but,
as mentioned above, did not find sufficient scientific support for
their use in the derivation of numeric nutrient criteria for Florida
streams. More specifically, EPA was not able to demonstrate a
sufficiently strong correlation between the biological response
indicators (e.g., chlorophyll a, periphyton biomass, or SCI) and TN or
TP concentrations. Thus, the Agency could not confidently predict a
specific biological response (such as an SCI score) for an individual
stream solely from the associated stream measurements of TN or TP
concentrations.
    There may be several reasons why empirical relationships between
field-derived data of nutrient stressor and biological response
variables show a relatively weak correlation. First, the relationship
between nutrient concentrations and a biological response, such as
algal growth, can be confounded by the presence of other stressors. For
example, other stressors, such as excessive scour could cause low
benthic invertebrate diversity, as measured by the SCI, even where
nutrients are low. Excessive scour could also suppress a biological
response (such as chlorophyll a or periphyton biomass) when nutrients
are high. Another reason for stressor-response relationships with low
correlations is that algal biomass accumulation is difficult to
characterize because dynamic conditions in an individual stream can
allow algae to accumulate and be removed rapidly, which is difficult to
capture with periodic monitoring programs.
    As an alternative to the stressor-response approach, EPA analyzed
the TN and TP concentrations associated with a healthy biological
condition in streams, and examined the statistical distributions of
these data in order to identify an appropriate threshold for providing
protection of aquatic life designated uses. To derive the instream
protection values under this approach, EPA first assembled the
available nutrient concentrations and biological response data for
streams in Florida. EPA used FDEP's data from the IWR and STORET \66\
databases and identified sites where SCI scores were 40 and higher. EPA
further screened these sites by cross-referencing them with Florida's
CWA section 303(d) list for Florida and excluded sites with identified
nutrient impairments or dissolved oxygen impairments associated with
elevated nutrients. EPA grouped the remaining sites (hereafter,
biologically healthy sites) according to its nutrient watershed regions
(Panhandle, Bone Valley, Peninsula, and North Central). For each
nutrient watershed region, EPA compiled nutrient data (TN and TP

concentrations) associated with the biologically healthy sites, and
calculated distributional statistics for annual average TN and TP
concentrations.
---------------------------------------------------------------------------

    \66\ FL IWR and STORET can be found at: http://
www.dep.state.fl.us/WATER/STORET/INDEX.HTM.
---------------------------------------------------------------------------

    The second step in deriving instream protection values was to
further characterize the distribution of TN and TP among biologically
healthy sites. Specifically, EPA calculated the number of biologically
healthy sites within integer log-scale ranges of TN and TP
concentrations, as well as the cumulative distribution. These nutrient
distributions from biologically healthy sites in each nutrient
watershed region are represented on a log-scale because concentration
data are typically log-normally distributed. A log-normal distribution
is skewed, with a mode near the geometric mean rather than the
arithmetic mean.
    The third step in deriving instream protection values was to
determine appropriate thresholds from these distributions for providing
protection of aquatic life designated uses. Selection of a central
tendency of the distribution (i.e., the median or geometric mean of a
log-normal distribution) would imply that half of the biologically
healthy sites are not attaining their uses. In contrast, an extreme
upper end of the distribution (e.g., the 90th or 95th percentile) may
be the most likely to be heavily influenced by extreme event factors
that are not representative of typically biologically healthy sites.
This might be the case because the upper tail of the distribution might
reflect a high loading year (landscape and/or atmospheric), and/or lack
of nutrient uptake by algae (in turn due to a myriad of physical and
biological factors like scour, grazing, light limitation, other
pollutants). Thus, this tail of the distribution may just represent the
most nutrient ``tolerant'' among the sites. Another possibility is that
these streams may experience adverse effects from nutrient enrichment
that are not yet reflected in the SCI score. A reasonable choice for a
threshold is one which lies just above the vast majority of the
population of healthy streams. This choice is reasonable because it
reflects a point where most biologically healthy sites will still be
identified as attaining uses, but avoids extrapolations into areas of
the distribution characterized by only a few data points (as would be
the case for the 90th or 95th percentile). When a threshold is
established as a water quality criterion, sites well below that
threshold might be allowed to experience an increase in nutrient levels
up to the threshold level. There is little assurance that biologically
healthy sites with nutrient concentrations well below the 90th or 95th
percentile would remain biologically healthy if nutrient concentrations
increased to those levels because relatively few sites with nutrient
concentrations as high as those at the 90th or 95th percentile are
demonstrated to be biologically healthy.
    The range between the 25th and 75th percentiles, or inter-quartile
range, is a common descriptive statistic used to characterize a
distribution of values. For example, statistical software packages
typically include the capability to display distributions as ``box and
whisker'' plots, which very prominently identify the inter-quartile
range. The inter-quartile range of a log normal distribution spans a
smaller range of values than the inter-quartile range of a distribution
of the data evenly spread across the entire range of values. This means
that the further a value goes past the 75th percentile of a log normal
distribution, the less representative it is of the majority of data (in
this case, less representative of biologically healthy sites). Within
the inter-quartile range of a log normal distribution, the slope of the
cumulative frequency distribution will be the greatest. The 75th
percentile represents a reasonable upper bound of where there is the
greatest confidence that biologically healthy sites will be
represented. Beyond the inter-quartile range (i.e., below the 25th
percentile and above the 75th percentile), there is a greater chance
that measurements may represent anomalies that would not correspond to
long-term healthy conditions in the majority of streams. Based on this
analysis, EPA concluded that the 75th percentile represents an
appropriate and well-founded protective threshold derived from a
distribution of nutrient concentrations from biologically healthy
sites. EPA solicits comment on its analysis of what constitutes a
protective threshold.
(d) Proposed Criteria: Duration and Frequency
    Aquatic life water quality criteria contain three components:
Magnitude, duration, and frequency. For the TN and TP numeric criteria
for streams, the derivation of the criterion-magnitude values is
described above and these values are provided in the table in Section
III.C(1). The criterion-duration of this magnitude is specified in
footnote a of the streams criteria table as an annual geometric mean.
EPA is proposing two expressions of allowable frequency, both of which
are to be met. First, EPA proposes a no-more-than-one-in-three-years
excursion frequency for the annual geometric mean criteria for lakes.
Second, EPA proposes that the long-term arithmetic average of annual
geometric means not to exceed the criterion-magnitude concentration.
EPA anticipates that Florida will use their standard assessment periods
as specified in Rule 62-303, F.A.C. (Impaired Waters Rule) to implement
this second provision. These proposed duration and frequency components
of the criteria are consistent with the data set used to derive these
criteria, which applied distributional statistics to measures of annual
geometric mean values from multiple years of record. EPA has determined
that this frequency of excursions will not result in unacceptable
effects on aquatic life as it will allow the stream ecosystem enough
time to recover from an occasionally elevated year of nutrient
loadings. The Agency requests comment on these proposed duration and
frequency components of the stream numeric nutrient criteria.
    EPA notes that some scientists and resource managers have suggested
that nutrient criteria duration and frequency expressions should be
more restrictive to avoid seasonal or annual ``spikes'' from which the
aquatic system cannot easily recover, whereas others have suggested
that criteria expressed as simply a long-term average of annual
geometric means, consistent with data used in criteria derivation, and
would still be protective. EPA requests comment on alternative duration
and frequency expressions that might be considered protective,
including (1) a criterion-duration expressed as a monthly average or
geometric mean, (2) a criterion-frequency expressed as meeting
allowable magnitude and duration every year, (3) a criterion-frequency
expressed as meeting allowable magnitude and duration in more than half
the years of a given assessment period, and (4) a criterion-frequency
expressed as meeting allowable magnitude and duration as a long-term
average only. EPA further requests comment on whether an expression of
the criteria in terms of an arithmetic average of annual geometric mean
values based on rolling three-year periods of time would also be
protective of the designated use.
 (3) Request for Comment and Data on Proposed Approach
    EPA is soliciting comments on the approaches taken by the Agency to
derive these proposed criteria, the data underlying those approaches,
and the proposed criteria specifically. EPA is requesting that the
public submit any other scientific data and information that may be
available related to nutrient concentrations and associated biological
responses in Florida's streams. EPA is

soliciting comment specifically on the selection of criteria parameters
for TN and TP; the proposed classification of streams into four regions
based on aggregated watersheds; and the conclusion that the proposed
criteria for streams are protective of designated uses and adequately
account for the spatial and temporal variability of nutrients. In
addition, EPA requests comment on folding the Suwannee River watershed
in north central Florida into the larger Peninsula NWR (i.e., not
having a separate North Central region) or, alternatively, making a
smaller North Central region within Hamilton County alone where the
highest phosphorus-rich soils are located, with the remainder of the
North Central becoming part of the Peninsula Region.
(4) Alternative Approaches Considered by EPA
    During EPA's review of the available data and information for
derivation of numeric nutrient criteria for Florida's streams, EPA also
considered an alternative approach for criteria derivation. EPA is
specifically requesting comment on a modified reference condition
approach called the benchmark distribution approach, as described
below.
(a) Benchmark Distribution Approach
    EPA's previously published guidance has recommended a variety of
methods to derive numeric nutrient criteria.\67\ One method, the
reference condition approach, relies on the identification of reference
waters that exhibit minimal impacts from anthropogenic disturbance and
are known to support designated uses. The thresholds of nutrient
concentrations where designated uses are in attainment are calculated
from a distribution of the available associated measurements of ambient
nutrient concentrations at these reference condition sites.
---------------------------------------------------------------------------

    \67\ U.S. EPA. 2000. Nutrient Criteria Technical Guidance
Manual: Rivers and Streams. Office of Water. 4304. EPA-822-B-00-002.
---------------------------------------------------------------------------

    EPA is seeking comment on a modified reference condition approach,
which was developed by FDEP and is referred to as the benchmark
distribution approach. The benchmark approach relies on least-disturbed
sites rather than true reference, or minimally-impacted, sites. The
benchmark distribution is a step-wise procedure used to calculate
distributional statistics of TN and TP from identified least-disturbed
streams.
(i) Identification of Least-Disturbed Streams
    FDEP identified benchmark stream sites in the following step-wise
manner (1) compiled a list of sites with low landscape development
intensity using FDEP's Landscape Development Intensity Index,\68\ (2)
eliminated any sites on Florida's CWA section 303(d) list of impaired
waters due to nutrients, as well as certain sites impaired for
dissolved oxygen, where the State determined the dissolved oxygen
impairment was caused by nutrients, (3) eliminated any sites with
nitrate concentrations greater than FDEP's 0.35 mg/L proposed nitrate-
nitrite criterion in order to reduce the possibility of including sites
with far-field human disturbance from groundwater impacts, (4)
eliminated sites known by FDEP district scientists to be disturbed, (5)
eliminated potentially erroneous data through outlier analysis, (6)
verified sites using high resolution aerial photographs, and (7)
verified a random sample of the sites in the field.
---------------------------------------------------------------------------

    \68\ A quantitative, integrated measure of the degree of human
landscape disturbance within 100 meters on either side of a
specified stream reach and extending to 10 kilometers upstream of
the same stream reach.
---------------------------------------------------------------------------

(ii) Calculation of Benchmark Distribution Approach and Selection of
Percentiles From the Benchmark Distribution
    FDEP selected either the 75th or 90th percentile of the benchmark
distribution approach from FDEP's proposed nutrient regions (75th
percentile--Bone Valley; 90th percentile--Panhandle, North Central,
Northeast, and Peninsula). FDEP's rationale for selecting either the
75th or 90th percentiles was based on the degree of certainty regarding
the benchmark sites reflecting least-disturbed conditions and a
probability (10% for the 90th percentile) of falsely identifying a
least-disturbed site as being impaired for nutrients.
    With this approach, the distribution of available annual geometric
means of nutrient concentrations for the benchmark sites within the
regional classes of streams is calculated. To compute the numeric
criteria for the causal variables, TN, and TP, EPA is seeking comment
on whether the 75th or 90th percentile of the benchmark distribution
for each nutrient stream region should be selected. As mentioned above,
the rationale for selecting either the 75th or 90th percentiles is
based on the degree of certainty regarding the benchmark sites
reflecting least-disturbed conditions and a probability of falsely
identifying a least-disturbed site as being impaired for nutrients or
vice-versa. In cases where data are more limited for a given nutrient
region (i.e., in the Bone Valley there were only four sites), the 75th
percentile may be more appropriate because the 90th percentile may not
be sufficiently robust (i.e., may be highly sensitive to a few data
points). In other cases, the 90th percentile may be more appropriate
when there is a more extensive data set. For further information,
please refer to EPA's TSD for Florida's Inland Waters, Chapter 2:
Methodology for Deriving U.S. EPA's Proposed Criteria for Streams.
    In evaluating whether to propose this approach, EPA determined that
a considerable amount of uncertainty remained whether this approach
would result in a list of benchmark sites that represented truly least-
disturbed conditions. Specifically, EPA is concerned that nutrient
concentrations at these sites may reflect anthropogenic sources (e.g.,
sources more than 100 meters away from and/or 10 kms upstream of the
segment), even if the sites appear least-disturbed on a local basis.
EPA is particularly concerned that several benchmark sites in the FDEP
dataset appear to have a high potential to be affected by
fertilizations associated with forestry activities. FDEP provided an
analysis in which FDEP concluded that this is not likely.\69\ EPA
solicits comment on this issue and more generally on whether the
benchmark sites identified by FDEP in its July 2009 proposal are an
appropriate set of least-disturbed sites on which to base the criteria
calculations.
---------------------------------------------------------------------------

    \69\ FDEP document titled, ``Responses to Earthjustice's
Comments on the Department's Reference Sites.'' Draft October 2,
2009. Located in the docket ID EPA-HQ-OW-2009-0596.
---------------------------------------------------------------------------

(5) Request for Comment and Data on Alternative Approach
    EPA is soliciting comment on the alternative to deriving numeric
nutrient criteria for Florida's streams as described in Section
III.C(4).
(6) Protection of Downstream Lakes and Estuaries
    Two key objectives of WQS are: First, to protect the immediate
water body to which a criterion initially applies and, second, to
ensure that criteria provide for protection of downstream WQS affected
by flow of pollutants from the upstream water body. See 40 CFR 131.11
and 131.10(b). EPA WQS regulations reflect the importance of protecting
downstream waters by requiring that upstream WQS ``provide for the
attainment and maintenance of the water quality standards of

downstream waters.'' 40 CFR 131.10(b). Thus, in developing numeric
nutrient criteria for Florida, EPA considered both instream aquatic
conditions and downstream aquatic ecosystem needs. In addressing the
issue of how, if at all, instream criteria values need to be adjusted
to assure attainment of downstream standards, EPA necessarily examined
the WQS for downstream lakes and estuaries. For lakes, this analysis
starts with the numeric nutrient criteria proposed in this notice. For
estuaries, this notice proposes an analytical approach to determine the
loadings that a particular estuary can receive and still assure
attainment and maintenance of the State's WQS for the estuary (i.e., a
protective load). An approach is then proposed for translating those
downstream loading values into criteria levels in the contributing
watershed stream reaches in a manner that ensures that the protective
downstream loadings are not exceeded.
    In connection with both lakes and estuaries, EPA fully recognizes
that there are a range of important technical questions and related
significant issues raised by this proposed approach for developing
instream water quality criteria that are protective of downstream
designated uses. With regard, in particular, to the protection of
estuaries, the Agency is working closely with FDEP to derive estuarine
numeric nutrient criteria for proposal and publication in 2011. Even
though estuarine numeric nutrient criteria will be developed in 2011,
there is already a substantial body of information, science, and
analysis that presently exists that should be considered in determining
flowing water criteria that are protective of downstream water quality.
    The substantial data, peer-reviewed methodologies, and extensive
scientific analyses available to and conducted by the Agency to date
indicate that numeric nutrient criteria for estuaries, when proposed
and finalized in 2011, may result in the need for more stringent rivers
and streams criteria to ensure protection of downstream water quality,
particularly for the nitrogen component of nutrient pollution.
Therefore, considering the numerous requests for the Agency to share
its analysis and scientific and technical conclusions at the earliest
possible opportunity to allow for full review and comment, EPA is
including downstream protection values for TN as proposed criteria for
rivers and streams to protect the State's estuaries in this notice.
    As described in more detail below and in EPA's TSD for Florida's
Inland Waters accompanying this notice, these proposed nitrogen
downstream protection values are based on substantial data, thorough
scientific analysis, and extensive technical evaluation. However, EPA
recognizes that additional data and analysis may be available for
particular estuaries to help inform what water quality criteria are
necessary to protect these waters. EPA also recognizes that substantial
site-specific work (including some very sophisticated analyses in the
context of certain TMDLs) has been completed for a number of these
estuaries. This notice and the proposed downstream protection values
are not intended to address or be interpreted as calling into question
the utility and protectiveness of these site-specific analyses. Rather,
the proposed values represent the output of a systematic and scientific
approach that may be generally applicable to all flowing waters in
Florida that terminate in estuaries for the purpose of ensuring the
protection of downstream estuaries. EPA is interested in obtaining
feedback at this time on this systematic and scientific approach. The
Agency further recognizes that the proposed values in this notice will
need to be considered in the context of the Agency's numeric nutrient
criteria for estuaries scheduled for proposal in January of 2011. At
this time, EPA plans to finalize any necessary downstream protection
values for nitrogen in flowing waters as part of the second phase of
this rulemaking process in coordination with the proposal and
finalization of numeric criteria for estuarine and coastal waters in
2011. However, if comments, data and analyses submitted as a result of
this proposal support finalizing such values sooner, by October 2010,
EPA may choose to proceed in this manner. To facilitate this process,
EPA requests comments and welcomes thorough evaluation on the need for
and the technical and scientific basis of these proposed downstream
protection values as part of the broader comment and evaluation process
that this proposal initiates.
    EPA believes that a detailed consideration and related proposed
approach to address protection of downstream water quality in this
proposal is necessary for several reasons, including (1) water quality
standards are required to protect downstream uses under Federal
regulations at 40 CFR 131.10(b), meaning also for prevention of
impairment; (2) it may be a relevant consideration in the development
of any TMDLs, NPDES permits, and Florida BMAPs that the State completes
in the interim period between the final rule for Florida lakes and
flowing waters in October 2010 and a final rule for Florida estuarine
and coastal waters in October of 2011; and (3) perhaps most
importantly, it is essential for informing and supporting a transparent
and engaged public consideration, evaluation, and discussion on the
question of what existing information, tools, and analyses suggest
regarding the need to ensure protection of downstream waters. The
Agency continues to emphasize its interest in and request for
additional information, further analysis, and any alternative
technically-based approaches that may be available to address
protection of downstream water quality. EPA also reiterates its
commitment to a full evaluation of all comments received and notes the
ability to issue a NODA to allow a full public review should
significant new additional information and analysis become available as
part of the comment period.
    In deriving criteria to protect designated uses, as noted above,
Federal WQS regulations established to implement the CWA provide WQS
must provide for the protection of designated uses in downstream
waters. In the case of deriving numeric nutrient criteria for streams
in Florida, EPA's analyses reflected in this notice indicate that the
proposed criteria values for instream protection of streams may not
fully protect downstream lakes and downstream estuaries. EPA's proposed
criteria for lakes are, in some cases, more stringent than the proposed
criteria for streams that flow into the lakes. For estuaries, EPA's
analyses of protective loads delivered to a specific estuary, and the
corresponding expected concentration values for streams that flow into
that estuary, indicate the proposed criteria for instream protection
may not always be sufficient to provide for the attainment and
maintenance of the estuarine WQS. For more detailed information, please
consult EPA's TSD for Florida's Inland Waters, Chapter 2: Methodology
for Deriving U.S. EPA's Proposed Criteria for Streams.
    To address each of these issues, EPA is proposing first, for lakes,
an equation that allows for input of lake characteristics to determine
the concentration in flowing streams that is needed to attain and
maintain the receiving lake's designated use and protective criteria.
Second, for estuaries, EPA is proposing an approach for identifying the
total nutrient loads a particular estuary can receive and still attain
and maintain the State's designated use for the water body.

Third, also for estuaries, the Agency is proposing a methodology to
derive protective concentration values for the instream criteria where
necessary to assure that downstream estuarine loads are not exceeded.
The following sections provide a more detailed explanation of the
proposed downstream protective approach for lakes and then for
estuaries.
(a) Downstream Protection of Lakes
    EPA is proposing an equation to relate a lake TP concentration
criterion to the concentration needed to be met in incoming streams to
support the lake criterion. EPA proposes to apply the resulting stream
concentration as the applicable criterion for all stream segments
upstream of the lake. EPA used a mathematical modeling approach to
derive this equation, with allowable input of lake-specific
characteristics, to calculate protective criteria necessary to assure
attainment and maintenance of the numeric lake nutrient criteria in
this proposal. More specifically, EPA started with a phosphorus loading
model equation first developed by Vollenweider.\70\ EPA assumed that
rainfall exceeds evaporation in Florida lakes and that all external
phosphorus loading comes from streams. EPA considers the first
assumption reasonable given the rainfall frequency and volume in
Florida. The second assumption is reasonable to the extent that surface
runoff contributions are far greater than groundwater or atmospheric
sources of TP in Florida lakes. EPA requests comment on both these
assumptions. After expressing these assumptions in terms of the
mathematical relationships among loading rates, stream flow, and lake
and stream concentrations, EPA derived the following equation to relate
a protective lake criterion to a corresponding protective stream
concentration:
---------------------------------------------------------------------------

    \70\ Vollenweider, R.A. 1975. Input-output models with special
reference to the phosphorus loading concept in limnology.
Schweizerische Zeitschrift fur Hydrologie. 37: 53-84; Vollenweider,
R.A. 1976. Advances in differing critical loading levels for
phosphorus in lake eutrophication. Mem. Ist. Ital. Idrobid.
33:53:83.
[GRAPHIC] [TIFF OMITTED] TP26JA10.000

---------------------------------------------------------------------------
where:

[TP]S is the total phosphorus (TP) downstream lake
protection value, mg/L
[TP]L is applicable TP lake criterion, mg/L
cf is the fraction of inflow due to all stream flow, 0 <=
cf <= 1
[tau]w is lake's hydraulic retention time (water volume
divided by annual flow rate)
The term
[GRAPHIC] [TIFF OMITTED] TP26JA10.005

expresses the net phosphorus loss from the water column (e.g. via
settling of sediment-sorbed phosphorus) as a function of the lake's
retention time

    This model equation requires input of two lake-specific
characteristics: The fraction of inflow due to stream flow and the
hydraulic retention time. Water in a lake can come from a combination
of groundwater sources, rainfall, and streams that flow into it. Using
the model equation above, the calculated stream TP criterion to protect
a downstream lake will be more stringent for lakes where the portion of
its volume coming from streams flowing into it is the greatest. In
addition, the calculated stream TP criterion to protect a downstream
lake will be more stringent for lakes with short hydraulic retention
times (how long water stays in a lake) because the longer the water
stays in the lake, the more phosphorus will settle out in the
underlying lake sediment.
    Because lake-specific input values may not always be readily
available, EPA is providing preset values for percent contribution from
stream flow and hydraulic retention time. In Florida lakes, rainfall
and groundwater sources tend to contribute a large portion of the total
volume of lake water. In fact, only about 20% of the more than 7,000
Florida lakes have a stream flowing into them,\71\ with the rest
entirely comprised of groundwater and rainwater sources. EPA evaluated
representative values for percent contribution from stream flow \72\
and hydraulic retention time,\73\ and selected 50% stream flow
contribution and 0.2 years (about two and a half months) retention time
as realistic and representative preset values to provide a protective
outcome for Florida lakes, in the absence of site-specific data. Using
these preset values, streams that flow into colored lakes would have a
TP criterion of 0.12 mg/L, and streams that flow into clear, alkaline
lakes would have a TP criterion of 0.073 mg/L, with respect to
downstream lake protection. In the Peninsula NWR, this compares to a
0.107 mg/L TP stream criterion protective of instream designated uses.
EPA's proposed rule does offer the flexibility to use site-specific
inputs to the Vollenweider equation for fraction of inflow from
streamflow and hydraulic retention time, as long as data supporting
such inputs are sufficiently robust and well-documented.
---------------------------------------------------------------------------

    \71\ Fernald, E.A. and E.D. Purdum. 1998. Water Resources Atlas
of Florida. Tallahassee: Institute of Science and Public Affairs,
Florida State University.
    \72\ Gao, X. 2006. Nutrient and Unionized Ammonia TMDLs for Lake
Jesup, WBIDs 2981 and 2981A. Prepared by Florida Department of
Environmental Protection, Division of Water Resource Management,
Bureau of Watershed Management, Tallahassee, FL.
    \73\ Steward, J.S. and E.F. Lowe. In Press. General empirical
models for estimating nutrient load limits for Florida's estuaries
and inland waters. Limnol. Oceanogr. 55: (in press).
---------------------------------------------------------------------------

    EPA carefully evaluated use of a settling/loss term for phosphorus
in the model equation. Florida lakes tend to be shallow, and internal
loadings to the lake water (e.g. from re-suspension of settled
phosphorus after storms that stir up lake sediment) may be substantial.
A more detailed model might be able to simulate this phenomenon
mechanistically, but would likely require substantial site-specific
data for calibration. For this reason, EPA chose to use the model
formulation above. EPA considered a simpler alternative to exclude the
settling/loss term from the above equation, or even to reverse the sign
on the settling/loss term so that it becomes a net source term, perhaps
with the inclusion of a default multiplier. However, EPA did not have
sufficient information to conclude that such a conservative approach
was necessary as a general application to all Florida lakes. EPA
remains open and receptive to comment on these alternatives or other
technically sound and protective approaches. EPA's supporting analyses
and detailed information on this downstream lake protection methodology
are provided in the accompanying TSD for Florida's Inland Waters,
Chapter 2: Methodology for Deriving U.S. EPA's Proposed Criteria for
Streams.
    The same processes that occur in lakes and affect lake water
phosphorus concentration may also occur in streams that feed lakes and
affect stream water phosphorus concentrations. These processes include
sorption to stream bed sediments, uptake into biota, and release into
the water column from decaying vegetation. EPA took into consideration
these processes when deciding whether it would be appropriate to add a
term to the model equation to account for phosphorus loss or uptake
within the streams in deriving stream criteria for downstream lake
protection. However, the net result of these processes is nutrient
spiraling, whereby nutrients released upstream gradually propagate
downstream at a rate slower than that of the moving water, and cycle
into and out of the food chain in the process. Over the short term, the
result may be water concentrations that decrease in the downstream
direction. However, unlike for nitrogen, there are no long-term
phosphorus net removal processes at work in streams. Phosphorus
adsorbed to sediment particles is eventually

carried downstream with the sediment, and phosphorus taken up by plants
is eventually returned to the flowing water. Over the long term,
upstream phosphorus inputs are in equilibrium with downstream
phosphorus outputs. Recognizing this feature of stream systems and the
conservative nature of phosphorus in aquatic environments, EPA
concluded that it was not appropriate to include a phosphorus loss term
that would apply to streams as they progress toward a downstream lake.
For further information, please refer to EPA's TSD for Florida's Inland
Waters, Chapter 2: Methodology for Deriving U.S. EPA's Proposed
Criteria for Streams.
    EPA requests comment on the need for additional instream criteria
to protect uses in downstream lakes. EPA further requests comment on
the model equation approach presented here to protect downstream lakes,
and also requests comment on use of an alternative model such as one
with a negative or zero settling term (i.e., set (1+
[radic][tau]w) in the equation above either equal to zero or
with the plus sign switched to a minus sign). EPA also requests comment
on whether and how to address direct surface runoff into the lake.
Where this input is substantial and land use around the lake indicates
that phosphorus input is likely, EPA believes it may be appropriate to
include this water volume contribution as part of the fraction of
inflow considered to be streamflow to be protective and consistent with
the assumption of no loading from sources other than streamflow. EPA
specifically requests comment on use of the Land Development Index
(LDI) as an indicator of how to treat this inflow, examination of
regional groundwater phosphorus levels to see if a zero TP input from
this source is appropriate, and potential development of regionally-
specific preset values as inputs to the equation. In addition, EPA
requests comment on the potential to develop a corollary approach for
nitrogen.
    EPA is open to alternative technically-supported approaches based
on best available data that offer the ability to address lake-specific
circumstances. The Agency recognizes that more specific information may
be readily available for individual lakes which could allow the use of
alternative approaches such as the BATHTUB model.\74\ The Agency
welcomes comment and technical analysis on the availability and
application of these models. In this regard, EPA requests comment on
whether there should be a specific allowance for use of alternative
lake-specific models where demonstrated to be protective and
scientifically defensible based upon readily and currently available
data, and whether use of such alternatives should best be facilitated
through use of the SSAC procedure described in Section V.C.
---------------------------------------------------------------------------

    \74\ Kennedy, R.H., 1995. Application of the BATHTUB Model to
Selected Southeastern Reservoirs. Technical Report EL-95-14, U.S.
Army Engineer Waterways Experiment Station, Vicksburg, MS. Walker,
W.W., 1985. Empirical Methods for Predicting Eutrophication in
Impoundments; Report 3, Phase II: Model Refinements. Technical
Report E-81-9, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
    Walker, W.W., 1987. Empirical Methods for Predicting
Eutrophication in Impoundments; Report 4, Phase III: Applications
Manual. Technical Report E-81-9, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, MS.
---------------------------------------------------------------------------

(b) Downstream Protection of Estuaries
(i) Overview
    EPA is proposing a methodology for calculation of applicable
criteria for streams that flow into estuaries and provide for their
protection. The proposed methodology would allow the State to utilize
either (1) EPA's downstream protection values (DPVs), or (2) the EPA
DPV methodology utilizing EPA's estimates of protective loading to
estuaries but with the load re-distributed among the tributaries to
each estuary, or (3) an alternative quantitative methodology, based on
scientifically defensible approaches, to derive and quantify the
protective load to each estuary and the associated protective stream
concentrations. The DPV methodology with a re-distributed load may be
used if the State provides public notice and opportunity for comment.
To use an alternative technical approach, based on scientifically
defensible methods to derive and quantify the protective load to each
estuary and the associated protective stream concentrations, the State
must go through the process for a Federal SSAC as described in Section
V.C. In some cases, the substantial and sophisticated analyses and
scientific effort already completed in the context of the TMDL process
may provide sufficient support for a SSAC. In such circumstances, EPA
encourages FDEP to submit these through the SSAC process and EPA looks
forward to working with FDEP in this process.
    EPA's approach to developing nutrient criteria for streams to
protect downstream estuaries in Florida involves two separate steps.
The first step is determining the average annual nutrient load that can
be delivered to an estuary without impairing designated uses. This is
the protective load. The second step is determining nutrient
concentrations throughout the network of streams and rivers that
discharge into an estuary that, if achieved, are expected to result in
nutrient loading to estuaries that do not exceed the protective load.
These concentrations, called ``downstream protection values'' or DPVs,
depend on the protective load for the receiving estuary and account for
nutrient losses within streams from natural biological processes. In
this way, higher DPVs may be appropriate in stream reaches where a
significant fraction of either TN or TP is permanently removed within
the reach before delivery to downstream receiving waters. EPA's
approach utilizes results obtained from a watershed modeling approach
called SPAtially Referenced Regressions on Watershed attributes, or
SPARROW.\75\ The specific model that was used is the South Atlantic,
Gulf and Tennessee (SAGT) regional SPARROW model.\76\ EPA selected this
model because it provided the information that was needed at the
appropriate temporal and spatial scales and it applies to all waters
that flow to Florida's estuaries.\77\ SPARROW was developed by the
United States Geological Survey (USGS) and has been reviewed,
published, updated and widely applied over the last two decades. It has
been used to address a variety of scientific applications, including
management and regulatory applications.\78\ In order to fully
understand EPA's methodology for developing DPVs, it is useful to
understand how the approach utilizes results from SPARROW, as well some
aspects of how SPARROW works.
---------------------------------------------------------------------------

    \75\ http://water.usgs.gov/nawqa/sparrow.
    \76\ Hoos, A.B., and G. McMahon. 2009. Spatial analysis of
instream nitrogen loads and factors controlling nitrogen delivery to
stream in the southeastern United Sates using spatially referenced
regression on watershed attributes (SPARROW) and regional
classification frameworks. Hydrological Processes. DOI: 10.1002/
hyp.7323.
    \77\ Hoos, A.B., S. Terziotti,, G. McMahon, K. Savvas, K.C.
Tighe, and R. Alkons-Wolinsky. 2008. Data to support statistical
modeling of instream nutrient load based on watershed attributes,
southeastern United States, 2002: U.S. Geological Survey Open-File
Report 2008-1163, 50 p.
    \78\ USGS SPARROW publications Web site: http://water.usgs.gov/
nawqa/sparrow/intro/pubs.html.

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

[GRAPHIC] [TIFF OMITTED] TP26JA10.001

    The remaining discussion focuses on TN, for which EPA has already
computed DPVs. The approach for computing DPVs for TP from estimates of
the protective TP load is expected to be essentially the same as for
TN. However, there is some question as to whether the same approach
used to determine the protective TN load will also apply to TP. EPA
requests comment on this issue.
(ii) EPA Approach to Estimating Protective Nitrogen Loads for Estuaries
    The first step in EPA's approach is to narrow the range of possible
values. The protective TN load is expected to vary widely among Florida
estuaries because they differ significantly in their size and physical
and biological attributes. For example, well flushed estuaries are able
to receive higher TN loading without adverse effect compared to poorly
flushed estuaries. EPA recognized that it may be possible to narrow
this initially very broad range of possible protective loads using one
consistent approach, and then consider whether additional information
might enable a further reduction in uncertainty. EPA is soliciting
credible scientific evidence that may improve these estimates and
further reduce uncertainty surrounding the proposed protective loads.
The most useful evidence would provide a scientific rationale, an
alternative estimate of the protective load, and an associated
confidence interval for the estimate. For further information, please
refer to EPA's TSD for Florida's Inland Waters, Chapter 2: Methodology
for Deriving U.S. EPA's Proposed Criteria for Streams.
    EPA first narrowed the range of possible protective loads by
establishing an estimate of current loading as an upper bound. Most of
Florida's estuaries are listed as impaired to some extent by nutrients
or nutrient-related causes. Florida's 1998 CWA section 303(d) verified
list of impaired waters under the Impaired Waters Rule (FAC 62-303)
identify many estuaries or estuary segments that are impaired by
nutrients, chlorophyll a, or low dissolved oxygen. Many or most
estuaries have reduced water clarity and substantial loss of seagrass
habitats. The National Estuarine Eutrophication Assessment \79\ reports
that current conditions are poor for many estuaries in Florida. This
information implies that current levels of TN loading are at least an
upper limit for the protective load and likely exceed the protective
load in many estuaries.
---------------------------------------------------------------------------

    \79\ Bricker, S., B. Longstaff, W. Dennison, A. Jones, K.
Boicourt, C. Wicks and J. Woerner, 2007. Effects of nutrient
enrichment in the Nation's estuaries: A decade of change. NOAA
Coastal Ocean Program Decision Analysis Series No. 26. National
Centers for Coastal Ocean Science, Silver Spring, MD 322.
---------------------------------------------------------------------------

    EPA used the SAGT-SPARROW regional watershed model to estimate
current loading to each estuary in Florida. While nitrogen loads have
been estimated from monitored gauge stations in many stream and rivers,
a large fraction of Florida streams and watersheds are not gauged and
thus load estimates were not previously available. An approach was
needed to spatially extrapolate the available measurements of loading
to obtain estimates of loading for all streams including those in
unmonitored watersheds or portions of watersheds. The SAGT SPARROW
model provided these estimates for all Florida estuarine watersheds.
The SPARROW modeling approach utilizes a multiple regression equation
to describe the relationship between watershed attributes (i.e., the
predictors) and measured instream nutrient loads (i.e., the responses).
The statistical methods incorporated into SPARROW help explain instream
nutrient water quality data (i.e., the mass flux of nitrogen) as a
function of upstream sources and watershed attributes. The SAGT-SPARROW
model utilized period of record monitored streamflow and nutrient water
quality data from Florida and across the SAGT region for load
estimation. SAGT-SPARROW also used extensive geospatial data sets
describing topography, land-use, climate, and soil characteristics,
nitrogen loading for point sources in Florida obtained from EPA's
permit compliance system, and estimates of nitrogen in fertilizer and
manure from county-level fertilizer sales, census of agriculture, and
population estimates. TN load estimates explain 96% of the variation in
observed loads from monitoring sites across the region with no spatial
bias at Florida sites.\80\ A more thorough description of the SAGT-
SPARROW model, the data sources, and analyses are found in the EPA TSD
for Florida's Inland Waters and in USGS publications.\81\
---------------------------------------------------------------------------

    \80\ Hoos, A.B., and G. McMahon. 2009. Spatial analysis of
instream nitrogen loads and factors controlling nitrogen delivery to
stream in the southeastern United Sates using spatially referenced
regression on watershed attributes (SPARROW) and regional
classification frameworks. Hydrological Processes. DOI: 10.1002/
hyp.7323.
    \81\ Hoos, A.B., S. Terziotti,, G. McMahon, K. Savvas, K.C.
Tighe, and R. Alkons-Wolinsky. 2008. Data to support statistical
modeling of instream nutrient load based on watershed attributes,
southeastern United States, 2002: U.S. Geological Survey Open-File
Report 2008-1163, 50 p.
---------------------------------------------------------------------------

    EPA further narrowed the range of possible protective loads by
establishing the background load as a lower bound. EPA recognizes that
a measure of natural background TN loading is the true lower limit, yet
EPA recognizes also that some level of anthropogenic nutrient loading
is acceptable, difficult to avoid, and unlikely to cause adverse
biological responses. The current TN load minus the fraction of TN
loading estimated to result from anthropogenic sources is used as an
estimate of the background TN load. EPA used the SAGT-SPARROW regional
watershed model to estimate background loading. SAGT-SPARROW
empirically associates 100% of the measured nutrient loading into one
of five classes (fertilizer, manure, urban, point sources, and
atmospheric). EPA recognizes that some watershed models define more
types of sources, according to their modeling objectives; however, it
is important to recognize that these are

source classes, not sources, and that 100% of the measured loading is
accounted for explicitly or implicitly by SPARROW in terms of these
source classes.
    The class termed ``atmospheric'' reflects all loading that cannot
be empirically attributed to causal variables associated with the other
classes. EPA used the estimate for this class of loading as the
background TN load. EPA recognizes that the SPARROW-estimated
``atmospheric'' load includes anthropogenic contributions associated
with regional-scale nitrogen emissions and does not represent pre-
industrial or true ``natural'' background loading. The ``atmospheric''
source term from SPARROW is also not equal to atmospheric nitrogen
deposition as measured by the National Atmospheric Deposition Program
(NADP). To properly interpret the TN load attributed to the
``atmospheric'' source term in SPARROW, it is useful to recognize that
SPARROW is a nonlinear regression model that seeks to explain measured
TN loads in streams and rivers in terms of a series of explanatory
variables. The atmospheric term is in all cases less, and often much
less, than the measured deposition because not all the nitrogen
deposited to the landscape is transported to streams, and not all of
the nitrogen transported in streams reaches estuaries. The atmospheric
source term from SPARROW excludes all the loading associated with both
local anthropogenic nitrogen sources and factors contributing to
increased transport of nitrogen from all sources (e.g., impervious
surfaces). Therefore, EPA expects that reasonable values for the
protective TN load are not likely to be less than these values.
    The protective TN load should be less than the current load and
greater than the background load. Although this recognition may appear
to be trivial, it is important. EPA estimates that TN loads to
estuaries across Florida vary approximately 25-fold (~2 to 50 grams of
nitrogen per square meter of estuary area). However, the ratio of the
current load to the background load varies only between 1.7 and 5; for
most estuaries, the range is between 2 and 4. Alternatively stated,
current TN loads, which include local anthropogenic nitrogen sources,
are two to four-fold higher than the background loads which do not
include those sources. Thus, for any specific estuary, there is a
relatively narrow range between the upper and lower bounds of potential
protective loads.
    EPA acknowledges that not all the TN entering estuaries comes
directly from the streams within its watershed. In some estuaries,
direct atmospheric nitrogen deposition to the estuary surface may be an
important source of TN loading to the estuary. Similarly, point sources
such as industrial or wastewater treatment plant discharges directly to
the estuary can be significant. In general, these sources are most
significant when the ratio of watershed area to estuary area is
relatively small compared to other estuaries (e.g., St. Andrew Bay,
Sarasota Bay). In a few cases in Florida, point source loads directly
to the estuary account for a large fraction of the aggregate load from
all sources.
    As a second step, EPA sought to further reduce the range of
possible protective loading values by considering additional evidence.
One line of evidence EPA considered is previous estimates of protective
loads. These have been developed as part of TMDLs for Florida estuaries
or as part of Florida's Pollutant Load Reduction Goal or PLRG program.
The scientific approaches utilized for TMDLs and PLRGs vary from simple
to sophisticated and have recommended TN loading reductions between 3%
and 63%, with a median of 38%. Higher reductions are typically
associated with portions of estuaries currently receiving higher
anthropogenic loading. Unfortunately, these analyses have not been
completed for all of Florida's estuaries. Steward and Lowe (2009) \82\
showed that the TN loading limits suggested by TMDLs and PLRGs for a
variety of aquatic ecosystems in Florida, including estuaries, could be
statistically related to water residence time for the receiving water.
EPA evaluated these relationships as an additional line of evidence for
estimating protective TN loads for estuaries. EPA found these
relationships to confirm in most cases, but not all, that the loading
limits were likely between the bounds EPA previously established using
SPARROW. However, the limits of uncertainty associated with the
relationship were nearly as large as those already established.
Nonetheless, the models provide additional support for EPA's estimates
of protective estuary loads, but no further refinement of the
estimates.
---------------------------------------------------------------------------

    \82\ Steward, J.S. and E.F. Lowe. 2010. General empirical models
for estimating nutrient load limits for Florida's estuaries and
inland waters. Limnology and Oceanography 55(1):433-445.
---------------------------------------------------------------------------

    Another approach to considering existing TMDLs and PLRGs is to
consider directly the loading rate reductions recommended from those
efforts, the median of which is 38% in Florida. This percent TN
reduction is similar to the scientific consensus for several well-
studied coastal systems elsewhere (e.g., Chesapeake Bay, northern Gulf
of Mexico) which have been subjected to increased TN loads from known
anthropogenic sources. EPA recognizes that the magnitude of
anthropogenic TN loads varies across Florida estuaries and that
applying a uniform percent reduction across all estuaries does not
account for the variable extent of anthropogenic loads and could lead
to estimates below background load. An alternative approach is to
assume that the appropriate loading reduction is proportional to the
magnitude of anthropogenic enrichment. Thus, EPA suggests that
protective TN loading may be estimated by assuming that the
anthropogenic component of TN loading should be reduced by a constant
fraction.
    As a result, EPA computed the protective TN load by reducing the
current TN load by one half of the anthropogenic contribution to that
load. EPA's protective load estimates are on average 25% less than
current TN loading (range = 5 to 40%), consistent with most TMDLs and
PLRGs for Florida estuaries.
    EPA developed protective TN loads for 16 estuarine water bodies in
Florida for the purpose of computing DPVs for streams that are
protective of uses in the estuarine receiving waters. EPA did not
develop loading targets for the seven estuarine water bodies in south
Florida (Caloosahatchee, St. Lucie, Biscayne Bay, Florida Bay, North
and South Ten Thousand Islands, and Rookery Bay), because requisite
information related to TN loading from the highly managed canals and
waterways cannot be derived from SAGT-SPARROW and were not available
otherwise, and three in central Florida (coastal drainage areas of the
Withlacoochee River, Crystal-Pithlachascotee River and Daytona-St.
Augustine) because EPA is still evaluating appropriate protective loads
and the flows necessary to derive DPVs.
    EPA notes that some stakeholders, including FDEP staff,\83\ have
raised

concerns about the suitability of the SAGT SPARROW to address
downstream protection of estuaries and have suggested alternative
models and approaches that have been applied for several of Florida's
larger estuaries and their watersheds. These concerns include known
limitations of the SPARROW model, particularly related to inadequate
resolution of complex hydrology in several parts of the State. EPA also
recognizes this limitation and as a result, has not used SAGT SPARROW
to propose protective loads and associated downstream protection values
for ten estuaries and their watersheds in Florida. EPA acknowledges
that other approaches and models may also provide defensible estimates
of protective loads.
---------------------------------------------------------------------------

    \83\ For further information on concerns raised by FDEP
regarding the use of SPARROW, refer to ``Florida Department of
Environmental Protection Review of SPARROW: How useful is it for the
purposes of supporting water quality standards development?,''
``Assessment of FDEP Panhandle Stream proposed benchmark numeric
nutrient criteria for downstream protection of Apalachicola Bay,''
and ``Analysis of Proposed Freshwater Stream Criteria's Relationship
to Protective Levels in the Lower St. Johns River Based on the Lower
St. Johns River Nutrient TMDL.'' located in EPA's docket ID No. EPA-
HQ-OW-2009-0596.
---------------------------------------------------------------------------

    Among the technical concerns that stakeholders including FDEP staff
have raised are that: (1) SPARROW is useful for general pattern, but
the large scale calibration lead to large errors for specific areas,
(2) SPARROW only utilizes four source inputs, and (3) SPARROW was
calibrated to only one year's worth of data. As presented in the above
sections, but to briefly reiterate here: (1) SPARROW is calibrated
across a larger area, but it utilizes a large amount of Florida site-
specific data and it explains 96% of the variation in observed loads
from monitoring sites, (2) SPARROW accounts for all sources, but groups
them into four general categories, and (3) SPARROW uses available data
from the 1975-2004 period at monitored sites. This last concern may be
confused with the technical procedure of presenting loading estimates
as ``detrended to 2002''. This procedure accounts for long-term, inter-
annual variability to ensure that long-term conditions and trends are
represented. The year 2002 was selected as a baseline because it has
the best available land use/land cover information available, but the
loading estimates, in fact, represent a long-term condition
representative of many years of record. EPA encourages technical
reviewers to consult with the technical references cited in this
section for the complete explanations of technical procedures.
    EPA requests comment on its use of the SPARROW model to derive
protective loads for downstream estuaries, as well as data and analyses
that would support alternate methods of deriving downstream loads, or
alternate methods of ensuring protection of designated uses in
estuaries. For estuaries where sophisticated scientific analyses have
been completed, relying on ample site-specific data to derive
protective loads in the context of TMDLs, EPA encourages FDEP to submit
resulting alternative DPVs under the SSAC process.
(iii) Computing Downstream Protection Values (DPVs)
    Once an estimate of protective TN loads is derived, EPA developed a
methodology for computing DPVs, for streams that, if achieved, are
expected to result in an average TN loading rate that does not exceed
the protective load. EPA's methodology, which is used as the narrative
translator, allows for the fraction of the protective TN loading
contributed from each tributary within the watershed of an estuary to
be determined by the fraction of the total freshwater flow contributed
by that tributary. The DPV is specified as an average TN concentration,
which is computed by dividing the protective TN load by the aggregate
average freshwater inflow from the watershed. This approach results in
the same DPV for each stream or river reach that terminates into a
given estuary.
    EPA's methodology accounts for instream losses of TN. EPA
recognizes that not all the TN transported within a stream network will
ultimately reach estuaries. Rather, some TN is permanently lost from
streams. This is not the same as reversible transformations of TN, such
as algal uptake. Losses of TN are primarily associated with
bacterially-mediated processes in stream sediments that convert
biologically available nitrogen into inert N2 gas, which
enters the atmosphere (a process called denitrification). This occurs
more rapidly in shallow streams and at almost negligible rates in
deeper streams and rivers. EPA refers to the fraction of nitrogen
transported in streams that ultimately reaches estuaries as the
``fraction delivered.'' Estimates of the fraction delivered in Florida
are less than 50% in streams very distant from the coast, but is
between 80 and 100% in approximately half the stream reaches in
Florida's estuarine watersheds.
    EPA's approach relies on estimating the fraction of TN delivered to
downstream estuaries. Measuring instream loss rates at the appropriate
time and space scale is exceedingly difficult, and it is not possible
to do State-wide. EPA is not aware of other models or data suitable to
estimating nitrogen losses in streams across the State of Florida. EPA
obtained estimates from the SAGT-SPARROW model,\84\ which is possibly
the best generally applicable approach to obtaining these estimates.
One reason is that SPARROW estimates watershed-scale instream losses at
the annual time scales across the entire region. Estimates of instream
losses are modeled in SPARROW using a first-order decay rate as a
function of time-of-travel in the reach. The inverse exponential
relationship is consistent with scientific understanding that nitrogen
losses decrease with increasing stream size and with results from
experimental reach-scale studies using a variety of methods.\85\ EPA
recognizes that stream attributes other than reach time-of-travel or
size may influence instream loss rates and though the SPARROW model did
not include these, the lack of spatial bias in model residuals suggests
that inclusion of other potential subregional-scale or State-wide
stream attributes may not improve modeled instream loss estimates.
---------------------------------------------------------------------------

    \84\ Hoos, A.B., and G. McMahon. 2009. Spatial analysis of
instream nitrogen loads and factors controlling nitrogen delivery to
streams in the southeastern United States using spatially referenced
regression on watershed attributes (SPARROW) and regional
classification frameworks. Hydrological Processes. DOI: 10.1002/
hyp.7323.
    \85\ Bohlke, J.K., R.C. Antweiler, J.W. Harvey, A.E. Laursen,
L.K. Smith, R.L. Smith, and M.A. Voytek. 2009. Multi-scale
measurements and modeling of Denitrification in streams with varying
flow and nitrate concentration in the upper Mississippi River basin,
USA. Biogeochemistry 93: 117-141. DOI 10.1007/s10533-008-9282-8.
---------------------------------------------------------------------------

    EPA developed and applied this methodology to compute DPVs for
every stream reach in each of 16 estuarine watersheds starting with
estuarine-specific estimates of the protective load. These estuarine
watersheds align with the Nutrient Watershed Regions (NWR) used to
derive instream protection values (IPVs). It is important to note that
the scale at which protective loads and DPVs were derived is smaller
than for IPVs (i.e., 16 estuarine watersheds vs. 4 nutrient watershed
regions). EPA's recognition that some fraction of nitrogen transported
in streams is retained or assimilated before reaching estuarine waters
help ensure that the DPVs are not overprotective of downstream use in
any particular estuary.
    In determining TN DPVs, EPA considered the contribution of TN
inputs from wastewater discharged in shoreline catchments directly to
the estuary. EPA found these point source inputs to be significant (>
5% of total loading) in three (St. Andrew's Bay, St. Marys, St. John's)
of the 16 estuaries. However, for the purpose of computing stream reach
DPVs for a given estuarine watershed, EPA considered only those TN
loads delivered from the estuarine watershed stream network and did not

include TN inputs from wastewater discharged in shoreline catchments
directly to an estuary because these loads do not originate from
upstream sources. However, point sources loads directly to the estuary
would need to be considered in developing TMDLs based on estuary-
specific criteria.
    EPA's computation of DPVs using estimates of protective loading for
each estuary and the fraction-delivered to estuaries is shown by
equation (1):
[GRAPHIC] [TIFF OMITTED] TP26JA10.002

where the terms are defined as follows for a specific or (ith)
stream reach:

Ci maximum flow-averaged nutrient concentration for a specific (the
ith) stream reach consistent with downstream use protection (i.e.,
the DPV)
k fraction of all loading to the estuary that comes from the stream
network resolved by SPARROW
Lest protective loading rate for the estuary, from all sources
QW combined average freshwater discharged into the estuary from the
portion of the watershed resolved by the SPARROW stream network
Fi fraction of the flux at the downstream node of the specific (ith)
reach that is transported through the stream network and ultimately
delivered to estuarine receiving waters (i.e., Fraction Delivered).

    Note that the quantity kLest is equal to the loading to the estuary
from sources resolved by SPARROW. For the purposes of practical
implementation, EPA classified each stream water body (i.e., Water Body
Identification or ``WBID'' using the FDEP term) according to the
estuarine receiving water and one of six categories based on the
fraction of TN delivered (0 to 50%, 51-60%, 61-70%, 71-80%, 81-90%, and
91-100%). For each category, the upper end of the range was utilized to
compute the applicable DPV for streams in the category, resulting in a
value that will be protective. This approach reduces the number of
unique DPVs from thousands to less than 100. Because the stream network
utilized by the SAGT-SPARROW watershed model (ERF1) does not recognize
all of the smaller streams in Florida (i.e., it is on a larger scale),
EPA mapped WBIDs to the applicable watershed-scale unit, or
``incremental watersheds,'' of the ERF1 reaches, assigning to each WBID
the fraction of TN delivered estimated for the ERF1 reach whose
incremental watershed includes the WBID. Where the WBID includes
portions of the incremental watersheds of more than one ERF1 reach, EPA
computed a weighted-average based on the proportion of WBID area in the
watershed of each ERF1 reach.
    Given an even distribution of reaches within each 10% interval,
EPA's ``binning'' approach to the fraction-delivered estimates results
in a 5% to 10% margin of safety for the average reach in each range
(closer to 10% for the lower fraction-delivered ranges). Potentially
larger margins are possible within the 0 to 50% range, where the
fraction delivered might be 20%, but the DPV would be computed assuming
a fraction delivered of 50%. However, only one watershed in Florida for
which EPA is proposing DPVs, the St. Johns River, has a substantial
number of reaches estimated to have less than 50% TN delivered to
estuarine waters. The SAGT-SPARROW watershed model estimates that 17%
of the stream reaches in the St. Johns watershed are in this category,
with about half the reaches delivering nearly 50% of TN and a
substantial number delivering only 20% of TN. Given EPA's DPV for
terminal reaches in the St. Johns watershed, however, the DPV for
reaches with a fraction delivered less than 50% will be higher than the
IPV, and therefore, will not apply. EPA requests comment on the binning
approach for calculating DPVs, which allows for a relatively simple
table of DPVs to be presented as compared to using the actual estimate
of fraction TN delivered to calculate a DPV unique to each WBID using
formula (1), above.
    At this time, EPA has not calculated protective TP loads for
Florida's estuaries or DPVs for TP. However, advances in the
application of regional watershed models, such as SPARROW, that address
the sources and terrestrial and aquatic processes that influence the
supply and transport of TP in the watershed and delivery to estuaries
are currently in advanced stages of development.\86\ EPA anticipates
obtaining the necessary data and information to compute TP loads for
the estuarine water bodies in Florida in 2010 and could make this
additional information available by issuing a supplemental Federal
Register Notice of Data Availability (NODA), which would also be posted
in the public docket for this proposed rule. EPA intends to derive
proposed protective loads and DPVs for TP using an analogous approach
as used for TN DPVs. EPA expects the approach will recognize that TP,
like TN, is essential for estuarine processes but in excess will
adversely impact aquatic life uses.
---------------------------------------------------------------------------

    \86\ Hoos, A.B., S. Terziotti, G. McMahon, K. Savvas, K.C.
Tighe, and R. Alkons-Wolinsky. 2008. Data to support statistical
modeling of instream nutrient load based on watershed attributes,
southeastern United States, 2002: U.S. Geological Survey Open-File
Report 2008--1163, 50 p.
---------------------------------------------------------------------------

(iv) EPA Downstream Protection Values (DPVs)
    The following criteria tables and corresponding DPVs for a given
stream reach category have been geo-referenced to specific WBIDs which
are managed by FDEP as the principal assessment unit for Florida's
surface waters. To see where the criteria are geographically
applicable, refer to EPA's TSD for Florida's Inland Waters, Appendix B-
18: In-Stream and Downstream Protection Value (IPV/DPV) Tables with DPV
Geo-Reference Table to Florida WBIDs.

----------------------------------------------------------------------------------------------------------------
                                                          (mg L-1)                         TP (mg L-1)
    River/stream reach category--percent     -------------------------------------------------------------------
          delivered to estuary \4\               TN IPV \5\       TN DPV \6\       TP IPV \7\       TP DPV \8\
----------------------------------------------------------------------------------------------------------------
                                Perdido Bay Watershed \PH\ (EDA Code: \1\ G140x)
                            Protective TN Load for the Estuary: \2\: 847,520 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................              NR               NR            0.043              TBD
70.1-80.0%..................................              NR               NR            0.043              TBD
80.1-90.0%..................................           0.824             0.34            0.043              TBD
90.1-100%...................................           0.824             0.30            0.043              TBD
----------------------------------------------------------------------------------------------------------------

                               Pensacola Bay Watershed \PH\ (EDA Code: \1\ G130x)
                           Protective TN Load for the Estuary: \2\ 4,388,478 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................              NR               NR            0.043              TBD
70.1-80.0%..................................              NR               NR            0.043              TBD
80.1-90.0%..................................           0.824             0.48            0.043              TBD
90.1-100%...................................           0.824             0.43            0.043              TBD
----------------------------------------------------------------------------------------------------------------
                             Choctawhatchee Bay Watershed \PH\ (EDA Code: \1\ G120x)
                           Protective TN Load for the Estuary: \2\ 2,875,861 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................              NR               NR            0.043              TBD
70.1-80.0%..................................           0.824             0.48            0.043              TBD
80.1-90.0%..................................           0.824             0.43            0.043              TBD
90.1-100%...................................           0.824             0.39            0.043              TBD
----------------------------------------------------------------------------------------------------------------
                               St. Andrew Bay Watershed \PH\ (EDA Code: \1\ G110x)
                            Protective TN Load for the Estuary: \2\ 310,322 kg y-\1\
                                  Protective TP Load for the Estuary: \3\ TBDK
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           0.824             0.48            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................              NR               NR            0.043              TBD
70.1-80.0%..................................           0.824             0.30            0.043              TBD
80.1-90.0%..................................           0.824             0.27            0.043              TBD
90.1-100%...................................           0.824             0.24            0.043              TBD
----------------------------------------------------------------------------------------------------------------
                              Apalachicola Bay Watershed \PH\ (EDA Code: \1\ G100x)
                           Protective TN Load for the Estuary: \2\ 10,971,582 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           0.824             0.91            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................           0.824             0.65            0.043              TBD
70.1-80.0%..................................           0.824             0.57            0.043              TBD
80.1-90.0%..................................           0.824             0.51            0.043              TBD
90.1-100%...................................           0.824             0.46            0.043              TBD
----------------------------------------------------------------------------------------------------------------
                               Apalachee Bay Watershed \PH\ (EDA Code: \1\ G090x)
                           Protective TN Load for the Estuary: \2\ 2,539,883 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................              NR               NR            0.043              TBD
70.1-80.0%..................................           0.824             0.67            0.043              TBD
80.1-90.0%..................................           0.824             0.59            0.043              TBD
90.1-100%...................................           0.824             0.53            0.043              TBD
----------------------------------------------------------------------------------------------------------------
                     Econfina/Steinhatchee Coastal Drainage Area \PH\ (CDA Code: \1\ G086x)
                            Protective TN Load for the Estuary: \2\ 185,301 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.043              TBD
50.1-60.0%..................................              NR               NR            0.043              TBD
60.1-70.0%..................................              NR               NR            0.043              TBD
70.1-80.0%..................................              NR               NR            0.043              TBD
80.1-90.0%..................................           0.824             0.41            0.043              TBD
90.1-100%...................................           0.824             0.37            0.043              TBD
----------------------------------------------------------------------------------------------------------------
                                Suwannee River Watershed\NC\ (EDA Code: \1\G080x)
                           Protective TN Load for the Estuary: \2\ 5,421,050 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.359              TBD
50.1-60.0%..................................              NR               NR            0.359              TBD
60.1-70.0%..................................           1.479             0.78            0.359              TBD

70.1-80.0%..................................           1.479             0.69            0.359              TBD
80.1-90.0%..................................           1.479             0.61            0.359              TBD
90.1-100%...................................           1.479             0.55            0.359              TBD
----------------------------------------------------------------------------------------------------------------
                           Waccasassa Coastal Drainage Area \PN\ (CDA Code: \1\ 078x)
                            Protective TN Load for the Estuary: \2\ 433,756 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.107              TBD
50.1-60.0%..................................              NR               NR            0.107              TBD
60.1-70.0%..................................              NR               NR            0.107              TBD
70.1-80.0%..................................              NR               NR            0.107              TBD
80.1-90.0%..................................           1.205             0.45            0.107              TBD
90.1-100%...................................           1.205             0.40            0.107              TBD
----------------------------------------------------------------------------------------------------------------
                         Withlacoochee Coastal Drainage Area \PN\ (CDA Code: \1\ G076x)
                                   Protective TN Load for the Estuary: \2\ TBD
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           1.205              TBD            0.107              TBD
50.1-60.0%..................................           1.205              TBD            0.107              TBD
60.1-70.0%..................................           1.205              TBD            0.107              TBD
70.1-80.0%..................................           1.205              TBD            0.107              TBD
80.1-90.0%..................................           1.205              TBD            0.107              TBD
90.1-100%...................................           1.205              TBD            0.107              TBD
----------------------------------------------------------------------------------------------------------------
                    Crystal/Pithlachascotee Coastal Drainage Area \PN\ (CDA Code: \1\ G074x)
                                   Protective TN Load for the Estuary: \2\ TBD
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           1.205              TBD            0.107              TBD
50.1-60.0%..................................              NR              TBD            0.107              TBD
60.1-70.0%..................................              NR              TBD            0.107              TBD
70.1-80.0%..................................              NR              TBD            0.107              TBD
80.1-90.0%..................................           1.205              TBD            0.107              TBD
90.1-100%...................................           1.205              TBD            0.107              TBD
----------------------------------------------------------------------------------------------------------------
                                 Tampa Bay Watershed \BV\ (EDA Code: \1\ G070x)
                           Protective TN Load for the Estuary: \2\ 1,289,671 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           1.798             1.11            0.739              TBD
50.1-60.0%..................................           1.798             0.93            0.739              TBD
60.1-70.0%..................................           1.798             0.80            0.739              TBD
70.1-80.0%..................................           1.798             0.70            0.739              TBD
80.1-90.0%..................................           1.798             0.62            0.739              TBD
90.1-100%...................................           1.798             0.56            0.739              TBD
----------------------------------------------------------------------------------------------------------------
                                Sarasota Bay Watershed \BV\ (EDA Code: \1\ G060x)
                            Protective TN Load for the Estuary: \2\ 155,576 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.739              TBD
50.1-60.0%..................................              NR               NR            0.739              TBD
60.1-70.0%..................................              NR               NR            0.739              TBD
70.1-80.0%..................................              NR               NR            0.739              TBD
80.1-90.0%..................................              NR               NR            0.739              TBD
90.1-100%...................................           1.798             0.54            0.739              TBD
----------------------------------------------------------------------------------------------------------------
                              Charlotte Harbor Watershed \BV\ (EDA Code: \1\ G050w)
                           Protective TN Load for the Estuary: \2\ 2,710,107 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.739              TBD
50.1-60.0%..................................           1.798             1.58            0.739              TBD
60.1-70.0%..................................           1.798             1.35            0.739              TBD
70.1-80.0%..................................           1.798             1.18            0.739              TBD
80.1-90.0%..................................           1.798             1.05            0.739              TBD
90.1-100%...................................           1.798             0.95            0.739              TBD
----------------------------------------------------------------------------------------------------------------

                                Indian River Watershed \PN\ (EDA Code: \1\ S190x)
                            Protective TN Load for the Estuary: \2\ 463,724 kg y-\1\
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................              NR               NR            0.107              TBD
50.1-60.0%..................................              NR               NR            0.107              TBD
60.1-70.0%..................................              NR               NR            0.107              TBD
70.1-80.0%..................................           1.205             0.87            0.107              TBD
80.1-90.0%..................................           1.205             0.77            0.107              TBD
90.1-100%...................................           1.205             0.69            0.107              TBD
----------------------------------------------------------------------------------------------------------------
                            Caloosahatchee River Watershed PN,# (EDA Code: \1\ G050a)
                                   Protective TN Load for the Estuary: \2\ TBD
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           1.205              TBD            0.107              TBD
50.1-60.0%..................................           1.205              TBD            0.107              TBD
60.1-70.0%..................................           1.205              TBD            0.107              TBD
70.1-80.0%..................................           1.205              TBD            0.107              TBD
80.1-90.0%..................................           1.205              TBD            0.107              TBD
90.1-100%...................................           1.205              TBD            0.107              TBD
----------------------------------------------------------------------------------------------------------------
                              St. Lucie River Watershed PN,# (EDA Code: \1\ S190x)
                                   Protective TN Load for the Estuary: \2\ TBD
                                   Protective TP Load for the Estuary: \3\ TBD
----------------------------------------------------------------------------------------------------------------
Less than 50%...............................           1.205              TBD            0.107              TBD
50.1-60.0%..................................           1.205              TBD            0.107              TBD
60.1-70.0%..................................           1.205              TBD            0.107              TBD
70.1-80.0%..................................           1.205              TBD            0.107              TBD
80.1-90.0%..................................           1.205              TBD            0.107              TBD
90.1-100%...................................           1.205              TBD            0.107              TBD
----------------------------------------------------------------------------------------------------------------
                                      Kissimmee River Watershed PN,[caret]