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.

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.  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).

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)
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 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.

(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 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.

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.

he 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.

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.  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.

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, 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.

(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
(ie, 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.  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.

 (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.  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:

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

w is lake’s hydraulic retention time (water volume divided by
annual flow rate)

  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, with the rest entirely
comprised of groundwater and rainwater sources.  EPA evaluated
representative values for percent contribution from stream flow and
hydraulic retention time, 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.

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.

  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.  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.

(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.  The specific model
that was used is the South Atlantic, Gulf and Tennessee (SAGT) regional
SPARROW model.  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.
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.  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.

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 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.

hile 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.  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.

PA 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) 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.

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.

PA notes that some stakeholders, including FDEP staff, 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.

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.

stimates 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.  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.

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):

 ,							(1)

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

 		maximum flow-averaged nutrient concentration for a specific (the ith
) stream reach consistent with downstream use protection (i.e., the DPV)

 		fraction of all loading to the estuary that comes from the stream
network resolved by SPARROW

 	protective loading rate for the estuary, from all sources

 	combined average freshwater discharged into the estuary from the
portion of the watershed resolved by the SPARROW stream network

 		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.

iven 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.  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.

(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.

Perdido Bay WatershedPH (EDA Code1: G140x)

Protective TN Load for the Estuary2: 847,520 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPH (EDA Code1: G130x)

Protective TN Load for the Estuary2: 4,388,478 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPH (EDA Code1: G120x)

Protective TN Load for the Estuary2: 2,875,861 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPH (EDA Code1: G110x)

Protective TN Load for the Estuary2: 310,322 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPH (EDA Code1: G100x)

Protective TN Load for the Estuary2: 10,971,582 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPH (EDA Code1: G090x)

Protective TN Load for the Estuary2: 2,539,883 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 AreaPH (CDA Code1: G086x)

Protective TN Load for the Estuary2: 185,301 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Fraction Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedNC (EDA Code1:G080x)

Protective TN Load for the Estuary2: 5,421,050 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 AreaPN (CDA Code1: 078x)

Protective TN Load for the Estuary2:  433,756 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 AreaPN (CDA Code1: G076x)

Protective TN Load for the Estuary2:  TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 AreaPN (CDA Code1: G074x)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedBV (EDA Code1: G070x)

Protective TN Load for the Estuary2: 1,289,671 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedBV (EDA Code1: G060x)

Protective TN Load for the Estuary2: 155,576 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedBV (EDA Code1: G050w)

Protective TN Load for the Estuary2: 2,710,107 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 Code1: S190x)

Protective TN Load for the Estuary2: 463,724 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPN, # (EDA Code1: G050a)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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 WatershedPN, # (EDA Code1: S190x)

Protective TN Load for the Estuary2: TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

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, ^

Protective TN Load for the Estuary2:  TBD

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6, LO	TP IPV7	TP DPV8, LO

Less than 50%	1.205	TBD9	0.107	TBD9

50.1 – 60.0%	1.205	TBD9	0.107	TBD9

60.1 – 70.0%	1.205	TBD9	0.107	TBD9

70.1 – 80.0%	1.205	TBD9	0.107	TBD9

80.1 – 90.0%	1.205	TBD9	0.107	TBD9

90.1 – 100%	1.205	TBD9	0.107	TBD9

St. John’s River Watershed PN (EDA Code1: S180x)

Protective TN Load for the Estuary2: 4,954,662 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

Less than 50%	1.205	1.41	0.107	TBD

50.1 – 60.0%	1.205	1.17	0.107	TBD

60.1 – 70.0%	1.205	1.00	0.107	TBD

70.1 – 80.0%	1.205	0.88	0.107	TBD

80.1 – 90.0%	1.205	0.78	0.107	TBD

90.1 – 100%	1.205	0.70	0.107	TBD

Daytona/St. Augustine Coastal Drainage AreaPN (CDA Code1: S183x)

Protective TN Load for the Estuary2:  TBD

Protective TP Load for the Estuary3:  TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

Less than 50%	NR	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

Nassau Coastal Drainage AreaPN (CDA Code1: S175x)

Protective TN Load for the Estuary2: 131,389 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV5	TN DPV6	TP IPV7	TP DPV8

Less than 50%	1.205	0.59	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	0.33	0.107	TBD

90.1 – 100%	1.205	0.30	0.107	TBD

St. Mary’s River WatershedPN (EDA Code1: S170x)

Protective TN Load for the Estuary2: 562,644 kg y-1

Protective TP Load for the Estuary3: TBD

River/Stream Reach Category -

Percent Delivered to Estuary4	TN (mg L-1)	TP (mg L-1)

	TN IPV 5	TN DPV6	TP IPV 7	TP DPV8

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	0.43	0.107	TBD

80.1 – 90.0%	1.205	0.38	0.107	TBD

90.1 – 100%	1.205	0.34	0.107	TBD

Footnotes associated with this table:

1 Watershed delineated by NOAA’s Coastal Assessment Framework and
associated Florida Department of Environmental Protection’s estuarine
and coastal water body identifier (WBID).

2 Estimated TN load delivered to the estuary protective of aquatic life
use.  These estimates may be revised pursuant to the EPA final rule for
numeric nutrient criteria for Florida’s estuaries and coastal waters
(October 2011).

3 Estimated TP load delivered to the estuary protective of aquatic life
use.  These estimates are currently under development.  Preliminary
estimates may be revised pursuant to the EPA final rule for numeric
nutrient criteria for Florida’s estuaries and coastal waters (October
2011).

4 River/Stream reach categories within each estuarine watershed are
linked spatially to a specific FDEP water body identifier (WBID). See
Appendix B-18 of the "Technical Support Document for EPA's Proposed Rule
for Numeric Nutrient Criteria for Florida's Inland Surface Fresh
Waters.”

5 Instream Protection Value (IPV) is the TN concentration protective of
instream aquatic life use.

6 Downstream protection values (DPVs) are estimated TN concentrations in
the river/stream reach that meet the estimated TN load, protective of
aquatic life use, delivered to the estuarine waters.  These estimates
may be revised pursuant to the EPA final rule for numeric nutrient
criteria for Florida’s estuaries and coastal waters (October 2011).

7 Instream Protection Value (IPV) is the TP concentration protective of
instream aquatic life use.

8 Downstream protection values (DPVs) are estimated TP concentrations in
the river/stream reach that meet the estimated TP load, protective of
aquatic life use, delivered to the estuarine waters.  These estimates
are currently under development.  Preliminary estimates may be revised
pursuant to the EPA final rule for numeric nutrient criteria for
Florida’s estuaries and coastal waters (October 2011).

9 EPA’s proposed TN and TP criteria for colored lakes (> 40 PCU) are
1.2 and 0.050 mg L-1, respectively.

# Estimated TN and TP loads protective of aquatic life in the
Caloosahatchee and St. Lucie River estuaries, and in turn estimated TN
and TP concentrations that would meet those protective loads, could not
be calculated using EPA’s downstream protection approach. An
alternative downstream protection approach will be proposed in EPA’s
proposed rule for FL estuaries (January 2011).

^ Kissimmee River watershed does not have an EDA or CDA code because it
does not drain directly to an estuary or coastal area, but rather
indirectly through Lake Okeechobee and the south Florida canal system.
A protective TN and TP load for Lake Okeechobee has not been calculated,
however, a TMDL is in effect for TP.  EPA’s proposed colored lake
criteria (> 40 PCU) could be used to develop DPVs for TN and TP for the
Kissimmee watershed (see footnote 9).

LO DPVs to be based on protective TN and TP loads for Lake Okeechobee.
EPA’s proposed colored lake criteria (> 40 PCU) could be used to
develop DPVs for TN and TP for the Kissimmee watershed (see footnote 9).

NR There are no stream reaches present in this watershed that have a
percent-delivered within this range and thus criteria are not
applicable..

PH Panhandle Nutrient Watershed Region.

BV Bone Valley Nutrient Watershed Region.

PN Peninsula Nutrient Watershed Region.

NC North Central Nutrient Watershed Region

TBD To be determined.

(v)  Application of DPVs for Downstream Estuary Protection

The following discussion further explains the conceptual relationship
between IPVs and DPVs for stream criteria.  EPA developed IPVs to
protect the uses that occur within the stream itself at the point of
application, such as protection of the benthic invertebrate community
and maintenance of a healthy balance of phytoplankton species.  In
contrast, EPA developed DPVs for streams to protect WQS of downstream
waters.  EPA derived DPVs in Florida streams by distributing the
protective load from the aggregate stream network identified for each
downstream estuary (that is protective of estuarine conditions) across
the watershed in proportion to the amount of flow contributed by each
stream reach.  EPA’s approach also accounts for attenuation of
nutrients (or loss from the system) as water travels from locations
upstream in the watershed to locations near the mouth of the estuary.

When comparing an IPV and DPV that are each deemed to apply to a
particular stream segment, the more stringent of the two values is the
numeric nutrient criterion that would need to be met when implementing
CWA programs.  Water bodies can differ significantly in their
sensitivity to nutrients in general and to TN specifically.  Although
not universally true, freshwaters are generally phosphorus-limited and
thus more sensitive to phosphorus enrichment because nitrogen is present
in excess.  Enriching freshwaters with phosphorus does not usually drive
these systems into nitrogen limitation but can simply encourage growth
of nitrogen-fixing algal species which can convert atmospheric nitrogen
into ammonia.  Conversely, estuaries are more often nitrogen limited and
thus more sensitive to adverse impacts from nitrogen enrichment.  As a
result, it is not at all surprising that DPVs for TN in Florida are
often less than the corresponding IPVs.

Adjustments to DPVs are possible with a redistribution approach, which
revises the original uniform assignment of protective downstream
estuarine loadings across the estuarine drainage area using the DPV
methodology, or by revising either the protective load delivered to the
downstream estuary and/or the equivalent DPVs using a technical approach
of comparable scientific rigor and the Federal SSAC procedure described
in section V.C of this notice.

nlike re-allocation of an even distribution of loading, these types of
adjustments, as well as other site-specific information on alternative
fractions delivered, would require use of the SSAC procedure under this
proposal.  EPA requests comment on whether these adjustments should be
allowed to occur in the implementation of the re-allocation process
rather than as a SSAC.

A technical approach of comparable scientific rigor will include a
systematic data driven evaluation and accompanying analysis of relevant
factors to identify a protective load delivered to the estuary.  An
acceptable alternate numeric approach also includes a method to
distribute and apply the load to streams and other waters within the
estuarine drainage area in a manner that recognizes conservation of mass
and makes use of a peer-reviewed model (empirical or mechanistic) of
comparable or greater rigor and scientific defensibility than the USGS
SPARROW model.  To use an alternative technical approach, the State must
go through the process for a Federal SSAC procedure as described in
Section V.C.

EPA requests comment on the DPV approach, the technical merit of the
estimated protective loadings, and the technical merit of the method for
calculating stream reach values.  EPA also requests comment on other
scientifically defensible approaches for ensuring protection of
designated uses in estuaries.  At this time, EPA plans to take final
action with respect to downstream protection values for nitrogen as part
of the second phase of this rulemaking process in coordination with the
proposal and finalization of numeric standards for estuarine and coastal
waters in 2011.  However, if comments, data and analyses submitted as a
result of this proposal support finalizing these 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 technical and scientific basis of these proposed downstream
protection values as part of the broader comment and evaluation process
that this proposal initiates.

D.  Proposed Numeric Nutrient Criteria for the State of Florida’s
Springs and Clear Streams

(1)  Proposed Numeric Nutrient Criteria for Springs and Clear Streams

	Springs and their associated spring runs in Florida are a unique class
of aquatic ecosystem, highly treasured for their biological, economic,
aesthetic, and recreational value.  Globally, the largest number of
springs (per unit of area), occur in Florida; Florida has over 700
springs and associated spring runs.  Many of the larger spring
ecosystems in Florida have likely been in existence since the end of the
last major ice age

 (approximately 15,000 to 30,000 years ago).  The productivity of the
diverse assemblage of aquatic flora and fauna in Florida springs is
primarily determined by the naturally high amount of light availability
of these waters (naturally high clarity).  As recently as 50 years ago,
these waters were considered by naturalists and scientists to be some of
the most unique and exceptional waters in the State of Florida and the
Nation as a whole.

	In Florida, springs are also highly valued as a water resource for
human use: people use springs for a variety of recreational purposes and
are interested in the intrinsic aesthetics of clear, cool water
emanating vigorously from beneath the ground.  A good example of the
value of springs in Florida is the use of the spring boil areas that
have sometimes been modified to encourage human recreation (bathing or
swimming).

	Over the past two decades, scientists have identified two significant
anthropogenic factors linked to adverse changes in spring ecosystems
that have the potential to permanently alter Florida’s spring
ecosystems.  These are:  1) pollution of groundwater, principally with
nitrate-nitrite, resulting from human land use changes, cultural
practices, and explosive population growth; and 2) simultaneous
reductions in groundwater supply from human withdrawals.  Pollution
associated with human activities is one of the most critical issues
affecting the health of Florida’s springs.

	Excess nutrients, in particular excess nitrogen, seep into the soils
and move to groundwater.  When in excess, nutrients lead to
eutrophication of groundwater-fed springs, allowing algae and invasive
plant species to displace native plants, which in turn results in an
ecological imbalance.  Excessive growth of nuisance algae and noxious
plant species in turn result in reduced habitat and food sources for
native wildlife, excess organic carbon production, accelerated
decomposition, and lowered quality of the floor or “bottom” of
springs and spring runs, all of which adversely impact the overall
health and aesthetics of Florida’s springs.

	Adverse impacts on the overall health of Florida’s springs have been
evident over the past several decades.  Within the last 20-30 years,
observations at several of Florida’s springs suggest that nuisance
algae species have proliferated, and are now out-competing and replacing
native submerged vegetation.  Numerous biological studies have
documented excessive algal growth at many major springs.  In some of the
more extreme examples, such as Silver Springs and Weeki Wachee Springs,
algal mat accumulations have become over three feet thick.,

	As a result of human-induced land use changes, cultural practices, and
explosive population growth, there has been an increase in the level of
pollutants, especially nitrate, in groundwater over the past decades.
Because there is no geologic source of nitrogen in springs, all of the
nitrogen emerging in spring vents originates from that which is
deposited on the land.  Historically, nitrate concentrations in
Florida’s spring discharges were thought to have been around 0.05 mg/L
or less, which is sufficiently low to restrict growth of algae and
vegetation under “natural” conditions.

	Regions where springs emanate in Florida have experienced unprecedented
population growth and changes in land use over the past several decades.
 With these changes in population and growth came a transfer of
nutrients, particularly nitrate, to groundwater.  Of 125 spring vents
sampled by the Florida Geological Survey in 2001-2002, 42% had nitrate
concentrations exceeding 0.50 mg/L and 24% had concentrations greater
than 1.0 mg/L.  Similarly, a recent evaluation of water quality in 13
springs shows that mean nitrate-nitrite levels have increased from 0.05
mg/L to 0.9 mg/L between 1970 and 2002.  Overall, data suggest that
nitrate-nitrite concentrations in many spring discharges have increased
from 10 to 350 fold over the past 50 years, with the level of increase
closely correlated with anthropogenic activity and land use changes
within the karst regions of Florida where springs predominate.

	As nitrate-nitrite concentrations have increased during the past 20 to
50 years, many Florida springs have undergone adverse environmental and
biological changes.  According to FDEP, there is a general consensus in
the scientific community that nitrate is an important factor leading to
the observed changes in spring ecosystems, and their associated
biological communities.  Nitrogen, particularly nitrate-nitrite, appears
to be the most problematic nutrient problem in Florida’s karst region.

	Because nitrate-nitrite has been linked to many of the observed
detrimental impacts in spring ecosystems, there is an immediate need to
reduce nitrate-nitrite concentrations in spring vents and groundwater.
A critical step in achieving reductions in nitrate-nitrite is to develop
a numeric nitrate-nitrite criterion for spring systems that will be
protective of these unique and treasured resources.

	To protect springs and clear streams and to provide assessment levels
and restoration goals for those that have already been impaired by
nutrients, EPA is proposing numeric nutrient criteria for the following
parameter for Florida’s springs and clear streams (< 40 PCU)
classified as Class I or III waters under Florida law (Rule 62-302.400,
F.A.C.):

Nitrate (NO3-)+Nitrite (NO2-) shall not surpass a concentration of 0.35
mg/L as an annual geometric mean more than once in a three-year period,
nor surpassed as a long-term average of annual geometric mean values.

In addition to the nitrate-nitrite criterion, TN and TP criteria
developed for streams on a watershed basis are also applicable to clear
streams.  See Section III.C(1) “Proposed Numeric Nutrient Criteria for
the State of Florida’s Rivers and Streams” for the table of proposed
TN and TP criteria that would apply to clear streams located within
specific watersheds.

(2)  Methodology for Deriving EPA’s Proposed Criteria for Springs and
Clear Streams

EPA’s proposed nitrate-nitrite criterion for springs and clear streams
are derived from a combination of FDEP laboratory data, field surveys,
and analyses which include analyses conducted to determine the stressor
response-based thresholds that link nitrate-nitrite levels to biological
risk in springs and clear streams.  These data document the response of
nuisance algae, Lyngbya wollei and Vaucheria sp., and periphyton to
nitrate-nitrite concentrations.  Please refer to EPA’s TSD for
Florida’s Inland Waters, Chapter 3: Methodology for Deriving U.S.
EPA’s Proposed Criteria for Springs and Clear Streams.

As described in Section III.C(2), the ability to establish protective
criteria for both causal and response variables depends on available
data and scientific approaches to evaluate these data.  EPA has not
undertaken the development of TP criteria for springs because phosphorus
has historically been present in Florida’s springs, given the
State’s naturally phosphorus-rich geology, and the lack of an
increasing trend of phosphorus concentrations in most spring discharges.
 EPA is not proposing chlorophyll a and clarity criteria due to the lack
of available data for these response variables in spring systems.
Furthermore, scientific evidence examining the strong relationship
between rapid periphyton survey data (measurements of the thickness of
algal biomass attached to substrate rather than free-floating) and
nutrients in clear streams (those with color <40 PCU and canopy cover
≤ 40% which are comparable to most waters found in springs and spring
runs) show that benthic algal thickness is highly dependent on nitrogen
parameters (TN and total inorganic nitrogen), as opposed to phosphorus.
In addition, EPA is proposing to apply the nitrate-nitrite criteria
derived for springs to clear streams as a measure to gauge anthropogenic
contributions to TN.  EPA is not currently proposing criteria for
clarity and chlorophyll a for clear streams due to the lack of
scientific evidence supporting the relationship between these response
variables and nutrients.  Clear streams show weak relationships between
nutrients and chlorophyll a, as opposed to color streams where
phytoplankton responses occur more readily than periphyton growth.
Please refer to EPA’s TSD for Florida’s Inland Waters, Chapter 3:
Methodology for Deriving U.S. EPA’s Proposed Criteria for Springs and
Clear Streams.

	(a)  Derivation of Proposed Nitrate-Nitrite Criteria

EPA’s goal in deriving nitrate-nitrite criteria for Florida springs
and clear streams is to ensure that the criteria will preserve the
ecosystem structure and function of Florida’s springs and clear
streams.  EPA reviewed Florida data, FDEP’s approach and analyses, and
FDEP’s proposed nitrate-nitrite criterion for springs and clear
streams and has concluded that the FDEP approach and the values FDEP
derived represent a scientifically sound basis for the derivation of
these criteria.  FDEP evaluated results from laboratory scale dosing
studies, data from in-situ algal monitoring, real-world surveys of
biological communities and nutrient levels in Florida springs, and data
on nitrate-nitrite concentrations found in minimally-impacted reference
locations.

FDEP analyzed laboratory data that evaluated the growth response of
nuisance algae to nitrate addition.  FDEP’s analysis showed that
Lyngbya wollei and Vaucheria sp. reached 90% of their maximum growth at
0.230 mg/L and 0.261 mg/L nitrate-nitrite, respectively.  FDEP also
reviewed long-term field surveys that examined the response of nuisance
algae, periphyton, and eutrophic indicator diatoms to nitrate-nitrite
concentration.  The results showed a sharp increase in abundance and/or
biomass of the nuisance algae, periphyton, and diatoms at 0.44 mg/L
nitrate-nitrite.

FDED also reviewed the field surveys used to develop TMDLs for Wekiva
River and Rock Spring Run to evaluate the relationship between the
observed excessive algal growth and imbalance in aquatic flora with
measurements of nutrients in these particular systems.  FDEP found that
taxa indicative of eutrophic conditions increased significantly with
increasing nitrate-nitrite concentrations above approximately 0.35 mg/L.

Based on its review of a combination of this laboratory and field data,
FDEP concluded that significant alterations in community composition
(eutrophic indicator diatoms), in combination with an increase in
periphyton cell density and biomass, clearly demonstrate that a
nitrate-nitrite level in the range between 0.23 mg/L (the laboratory
threshold) and 0.44 mg/L (the field study derived value associated with
the upper bound nitrate-nitrite concentration where substantial observed
biological changes were apparent) is the amount of nitrate-nitrite
associated with an imbalance of aquatic flora in spring systems.

FDEP conducted further statistical analyses of the available data from
the multiple lines of evidence, applied an appropriate safety factor to
ensure that waters would not reach the nitrate-nitrite levels associated
with “substantial observed biological changes,” and averaged the
results to arrive at a final protective threshold value for
nitrate-nitrite in springs and clear streams of 0.35 mg/L.  Based on the
discussion above and corresponding analysis in the TSD for Florida’s
Inland Waters, EPA has concluded that this value was derived in a
scientifically sound manner, appropriately considering the available
data, and appropriately interpreting the multiple lines of evidence.
Accordingly, EPA is proposing 0.35 mg/L nitrate-nitrite as a protective
criterion for aquatic life in Florida’s springs and clear streams.

(b)  Proposed Criteria:  Duration and Frequency

EPA is proposing a duration and frequency expression of an annual
geometric mean not to be surpassed more than once in a three-year period
to be consistent with the expressions of duration and frequency for
other water body types (e.g., lakes, streams, canals) for TN and TP and
for the same reasons EPA selected a three-year period for those waters.
Second, EPA proposes that the long-term arithmetic average of annual
geometric means not exceed the criterion-magnitude concentration.  EPA
anticipates that Florida will use its standard assessment periods as
specified in Rule 62-303, F.A.C. (Impaired Waters Rule) to implement
this second provision.   EPA has determined that this frequency of
excursions should not result in unacceptable effects on aquatic life as
it will allow the springs and clear streams aquatic systems enough time
to recover from an occasionally elevated year of nutrient loadings.  The
Agency requests comment on these proposed duration and frequency
expressions of the springs and clear streams numeric nutrient criteria.

EPA also considered as an alternative, expressing the criterion as a
monthly median not to be surpassed more than 10% of the time.  Stated
another way, the median value over any given calendar month shall not be
higher than the criterion-magnitude value in more than one out of every
ten months.  It is appropriate to express a monthly criterion as a
median because the median is less susceptible to outliers than the
geometric mean.  This is particularly important when dealing with small
sample sizes.  This alternative is consistent with the expression that
FDEP proposed in July 2009 for its State rule and the expression in the
TSD for Florida’s Inland Waters that EPA sent out for external
scientific peer review in July 2009.  The rationale for this alternative
is that field data indicate that the response in springs is correlated
to monthly exposure at the criterion-magnitude concentration value and a
10% frequency of excursions is a reasonable and fully protective
allowance given small sample sizes in any given month (i.e., the
anticipated amount of data that will be available for assessment
purposes in the future).  The clear streams nitrate-nitrite criterion
was derived by FDEP based on multiple lines of evidence, with the
primary lines of evidence being mesocosm dosing experiments and field
studies.  These two main studies were conducted by FDEP over very
different time frames.  One set of mesocosm studies was conducted by
FDEP for periods just under one month (i.e., 21 to 28 days), while
another, the algal biomass field survey, was conducted over an 18-year
period and was analyzed using four to five year averaging periods.
While lab studies indicate that algal communities can respond to excess
nitrate-nitrite over a short period of time, the mesocosm and other
dosing studies indicate that this response occurs on the order of a
month, which might support a monthly expression of the criterion.
However, there is no evidence to suggest that the responses observed
within a month under controlled lab settings equate to impairment of the
designated use in conditions experienced in State waters.  Please refer
to EPA’s TSD for Florida’s Inland Waters, Chapter 3: Methodology for
Deriving U.S. EPA’s Proposed Criteria for Springs and Clear Streams.

The 10% excursion frequency would recognize that in most cases the
monthly “median” would actually be based on a single sample, given
that most springs are only sampled monthly at the most.  A 10% excursion
frequency may be considered a reasonable and fully protective allowance
given small sample sizes in any given month, essentially requiring that
the monthly median nitrate-nitrate concentrations thought to be fully
supportive of relevant designated uses be met 90% of the time.

) a criterion-frequency expressed as meeting the 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 believes the proposed nutrient criterion for springs and clear
streams in this rule are protective of the designated aquatic life use
of these waters in Florida.  EPA is soliciting comment on the approach
FDEP used and EPA adopted to derive nitrate-nitrite criterion for
springs and clear streams, including the data and analyses underlying
the proposed criterion.  EPA is seeking additional, readily-available,
pertinent data and information related to nutrient concentrations or
nutrient responses in springs and clear streams in Florida.  EPA is also
soliciting views on other potential, scientifically sound approaches to
deriving protective nitrate-nitrite criterion for springs and clear
streams in Florida.

	(4)  Alternative Approaches:  Nitrate-Nitrite Criterion for All Waters
as an Independent Criterion

EPA is soliciting comment on the environmental benefits associated with
deriving a nitrate-nitrite criterion for all waters covered by this
proposal (i.e., all streams, lakes, and canals), in addition to the
other proposed nutrient criteria for those water bodies.  Adoption of a
nitrate-nitrite criterion for waters other than springs and clear
streams could be useful from an assessment and management perspective.
Florida could use nitrate-nitrite data to identify increasing trends
that may indicate the need for more specific controls of certain
nitrogen enrichment sources.  In cases where waters are impaired for
either TN, nitrate-nitrite, or both TN and nitrate-nitrite, FDEP could
use the nitrate-nitrite data to potentially target discharges of
anthropogenic origin given their relative source contribution to
nitrogen enrichment.

This alternative approach, which would involve EPA deriving
nitrate-nitrite criteria for all waters or alternatively applying 0.35
mg/L nitrate-nitrite to all waters, could provide additional protection
for aquatic life designated uses.  The alternative approach would also
eliminate the need for FDEP to characterize streams as clear or not.
Deriving and applying a nitrate-nitrite criterion to all waters would
reduce the likelihood of excess loading of the specific anthropogenic
components of TN to colored waters.  However, these colored streams may
be less likely to show an observed response to nitrate-nitrite due to
the presence of tannins that block light penetration.  Thus, the
presence of color in streams may confound the relationship that produced
the 0.35 mg/L nitrate-nitrite criterion.

E.  Proposed Numeric Nutrient Criteria for South Florida Canals

(1)  Proposed Numeric Nutrient Criteria for South Florida Canals

There are thousands of miles of canals in Florida, particularly in the
southeastern part of the State.  Canals are artificial waterways that
are either the result of modifications to existing rivers or streams, or
waters that have been created for various purposes, including drainage
and flood control (stormwater management), irrigation, navigation, and
recreation.  These canals also allow for the creation of many waterfront
home sites in Florida.  Ecosystems that existed in rivers and streams
prior to their modification into canals are altered.  These changes can
affect fish and wildlife and plant growth, as further explained in the
following paragraphs.  Newly created canals may have a tendency to fill
with aquatic plants.  Canals in south Florida vary greatly in size and
depth.  They can be anywhere from a few feet wide and a few feet deep to
hundreds of feet wide and as deep as 30-35 feet.

South Florida canals vary in their hydrology and behavior due to their
size, function, and seasonality.  Shallow canals with slow water flow
have poor turnover of water and little flushing.  Large canals also may
have low flow and turnover during the dry season.  In contrast, during
the wet season these same large canals are flowing systems that quickly
move large volumes of water, as they were designed to accomplish.
Excess nutrients in canals in combination with poor water circulation
and decreased levels of dissolved oxygen, can lead to accelerated
eutrophication and adverse impacts on other forms of aquatic life such
as fish and other aquatic animals.  In these canals, the accumulation of
decaying organic matter on the canal bottom can also adversely impact
healthy aquatic ecosystems.

South Florida canals are highly managed waterways.  Some canals are
prone to an over-abundance of aquatic plants.  Without regular and
frequent management, dense vegetation can clog the waterways making
navigation difficult and slowing the movement of water through the canal
system.  This can interfere with flood control, boating, and fishing.
Aquatic plants (like plants in the terrestrial environment) respond and
grow when fertilized with nutrients such as phosphorus and nitrogen, and
thus nutrient runoff into canals is likely a significant contributor to
both nuisance algal blooms and clogging of canal systems by aquatic
plants.

  EPA is proposing numeric nutrient criteria for the following
parameters and geographic classifications in south Florida, for canals
classified as Class III waters under Florida law (Rule 62-302.400,
F.A.C.).  The proposed and alternative approaches described herein would
not apply for TP in canals within the Everglades Protection Area (EvPA)
since there is an existing TP criterion of 0.010 mg/L that currently
applies to the marshes and adjacent canals within the EvPA (Rule
62-302.540, F.A.C.).

	Chlorophyll a

(µg/L) a	Total Phosphorus (TP)

(mg/L) a, b	Total Nitrogen (TN)

(mg/L) a

Canals	4.0 	0.042 	1.6

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 Applies to all canals within the Florida Department of Environmental
Protection’s South Florida bioregion, with the exception of canals
within the Everglades Protection Area (EvPA) where the TP criterion of
0.010 mg/L currently applies.

The following sections detail the methodology EPA used to develop the
proposed numeric nutrient criteria for canals in south Florida, and
request comment on the proposed criteria and their derivation.  In
addition, EPA is providing details of two alternative options for
deriving canal criteria values that EPA considered and is soliciting
comments on these alternatives.

(2)  Methodology for Deriving EPA’s Proposed Criteria for South
Florida Canals

	Based on the available information for canals, EPA determined that the
most scientifically sound way to derive protective numeric nutrient
criteria for south Florida’s canals is to use a similar approach to
what EPA used to derive numeric nutrient criteria for streams.  That is,
EPA chose a nutrient concentration distribution-based approach using
data from only those canals that have been determined to support the
applicable designated use.  EPA used existing water quality assessments
and identified canals that have been determined to be impaired for
nutrients.  Data for those canals were excluded from the larger data set
in order to create a set of data representing canals attaining the
designated use of aquatic life, according to FDEP’s assessment
decisions.  For further information, please refer to EPA’s TSD for
Florida’s Inland Waters, Chapter 4:  Methodology for Deriving U.S.
EPA’s Proposed Criteria for Canals.

	(a)  Derivation of Proposed Numeric Nutrient Criteria for South Florida
Canals

EPA derived numeric nutrient criteria for south Florida canals for two
causal variables, TN and TP, and one response variable, chlorophyll a.
In contrast to EPA’s proposed criteria for Florida’s streams, EPA
concluded that there was a sufficient scientific basis for a chlorophyll
a criterion for south Florida canals.  EPA considered chlorophyll a to
be an appropriate indicator of nutrient impairment in canals on the
basis of the observed seasonal flow regimes, particularly during the
relatively drier winter months when flows are relatively lower and canal
water residence time is relatively higher (as compared to wetter, summer
months).  Furthermore, EPA found evidence that canals are susceptible to
impairment due to excessive chlorophyll a based on the number of canals
on Florida’s CWA section 303(d) list with chlorophyll a cited as the
parameter of concern.  EPA analyzed the range of chlorophyll a
concentrations in canals and found that 12% of chlorophyll a
concentration observations occurred at 10 g/L or higher and 5% of
chlorophyll a concentration observations occurred at 20 g/L or
higher.  As a point of reference, Florida has chlorophyll a thresholds
of 20 as the numeric interpretations of its narrative nutrient criteria
for streams and 11 g/L for estuaries/open coastal waters,
respectively, in its Impaired Waters Rule (IWR) (Rules 62-303.351 and
62-303.353, F.A.C.).  Thus, EPA included chlorophyll a as a nutrient
criterion to protect canal aquatic life designated uses from an
unacceptable biological response to excess nutrients.

	EPA employed a statistical distribution approach for deriving numeric
nutrient criteria for south Florida canals.  Specifically, EPA computed
statistical distributions and descriptive statistics (e.g., quartiles,
mean, standard deviation) of TN, TP, and chlorophyll a concentrations
from data derived at canal sites across south Florida that are not on
the impaired waters list for Florida.  EPA has determined that the
criteria derived from a distribution of canal data from canals with no
evidence of nutrient impairment are appropriate and protective of
designated uses.

	 As described in detail in Section III.C(2)(c), EPA concluded that the
75th percentiles of the respective TN, TP, and chlorophyll a
distributions would yield values that would ensure that aquatic life
designated uses would be protected in south Florida canals.  A
reasonable choice is one that lies just above the vast majority of the
population.  The 75th percentile represents such a point on the
distribution of TN, TP, and chlorophyll a values.

	(b)  Other Data and Analyses Conducted and Considered by EPA in the
Derivation of Proposed Numeric Nutrient Criteria for South Florida
Canals

EPA undertook extensive analyses and considered a variety of data and
methods for deriving numeric nutrient criteria for Florida’s canals.
Although EPA derived the proposed values based on the approach outlined
in the section above, EPA also factored into its decision-making process
the results of these other analyses as additional lines of evidence.

One line of additional evidence is based on an evaluation of the
stressor-response relationship between chlorophyll a levels in canals
and TN and TP levels using a variety of statistical tools.  A second
line of evidence is based on a consideration of the distribution of
chlorophyll a measurements, TN measurements, and TP measurements from
all canals, impaired and not impaired.  Nutrient concentrations at the
lower end of these distributions were compared to the concentration that
the stressor-response analysis determined to be associated with canals
with no evidence of nutrient impairment.  The third line of evidence is
based on a consideration of the distribution of chlorophyll a, TN, and
TP values from only those canals considered to be minimally impacted by
nutrient-related pollution.  EPA considered each of these lines of
evidence in deriving the numeric nutrient criteria for canals.

Because soil or substrate type at the bottom of a canal can influence
the nutrient cycling and relationships between the observed biological
response and the TP and TN levels in canals, EPA used data on soil types
in south Florida along with knowledge of the Everglades Agricultural
Area (EAA) and the Everglades Protection Area (EvPA) to subdivide the
canal areas for criteria derivation.  Thus the first step in these other
analyses was to group canals and canal data by soil type.  The four
groupings consist of histosol and entisol soils of the EAA; histosol and
entisol soils of the EvPA; spodosol and alfisol soils and areas west of
the EvPA and EAA (hereafter, West Coast); and spodosol, entisol and
alfisol soils and areas east of the EvPA and EAA (hereafter East Coast).

EPA then sorted canal data (provided by FDEP, Miami-Dade County, and the
South Florida Water Management District) into the four canal groupings.
EPA screened the data to ensure the exclusion of the following: 1) sites
without relevant data (e.g., nitrogen, phosphorus, chlorophyll a), 2)
sites influenced by marine waters, 3) sites within Class IV canals or
Lake Okeechobee, 4) data not originating within a canal,  5) data with
questionable units, and 6) outlier data.  Data were organized by canal
regions and year.  Each site occurring near the border of a region
and/or WBID was visually inspected using geographic information system
(GIS) tools to ensure the correct placement of those sites.  Local
experts were also consulted by EPA.  EPA analyzed the resulting
regionalized data using statistical distribution and regression
analyses.  EPA undertook its additional analyses using these canal (and
data) groupings.

EPA’s analysis of the distribution of chlorophyll a values in each of
the four groupings of canals (using data from impaired and unimpaired
sites) indicated that the lower percentile (i.e., 25th percentile)
ranged from 1.9 to 2.2 µg/L for chlorophyll a in the EvPA, West Coast,
and East Coast, and was 6.3 µg/L for the EAA.  EPA’s analysis of the
distribution of TN values in each of the four groupings of canals
indicated that the lower percentile (i.e., 25th percentile) ranged from
0.8 to 1.4 mg/L for the EvPA, West Coast, and East Coast and was 2.1mg/L
for the EAA.  EPA’s analysis of the distribution of TP values in each
of the four groupings of canals indicated that the lower percentile
(i.e., 25th percentile) ranged from 0.013 to 0.023 mg/L for the EvPA,
West Coast, and East Coast and was 0.048 mg/L for the EAA canals.

In an effort to consider chlorophyll a, TN, and TP values in canals
minimally impacted by nutrient pollution, EPA identified canal sites
surrounded by the EvPA in the east and the Big Cypress National Preserve
in the west and considered the distribution of chlorophyll a, TN and TP
values for these sites.  Although EPA acknowledges that these sites have
not been thoroughly vetted for biological condition, EPA believes that
because they are remote and surrounded by wetlands, that these canal
sites represent sites with the lowest impact from human activities.  The
upper percentile values (i.e., the 75th percentile) from the
distributions of chlorophyll a, TN and TP values for these lower impact
sites are 3.4 µg/L for chlorophyll a, 1.3 mg/L for TN and 0.018 mg/L
for TP.

	When considering the results of these additional analyses and comparing
these results to the outcome of EPA’s analysis of TN, TP, and
chlorophyll a concentrations from data derived at canal sites across
south Florida that are not on the impaired waters list for Florida, it
is clear that EPA’s proposed criteria for canals are similar to those
derived from alternative approaches and therefore, represent a
reasonable integration of these multiple lines of evidence.  For further
information, please refer to EPA’s TSD for Florida’s Inland Waters,
Chapter 4:  Methodology for Deriving U.S. EPA’s Proposed Criteria for
Canals.

(c)  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
canals, the derivation of the criterion-magnitude values is described
above and these values are provided in the table in Section III.E(1).
The criterion-duration for this magnitude (or averaging period) is
specified in footnote a of the canals 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 canals.  Second, EPA proposes that the
long-term arithmetic average of annual geometric means not 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 the criteria that contained
data from multiple years of record, all seasons, and a variety of
hydrologic conditions.  EPA has determined that this frequency of
excursions should not result in unacceptable effects on aquatic life as
it will allow the canal aquatic system enough time to recover from an
occasionally elevated year of nutrient loadings.  The Agency requests
comment on these proposed duration and frequency expressions of the
canal numeric nutrient criteria.

) a criterion-frequency expressed as meeting the 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 believes the proposed numeric nutrient criteria for south Florida
canals in this rule are protective of the designated uses, consistent
with CWA section 303(c)(2)(A) and 40 CFR 131.11(a)(1).  EPA solicits
comment on the approaches taken by the Agency in this proposal, the data
underlying those approaches, and the proposed criteria.  EPA is seeking
other pertinent scientific data and information that are readily
available related to nutrient concentrations or nutrient responses in
Class III canals in south Florida.

EPA is soliciting comment specifically on the selection of criteria
parameters for TN, TP, and chlorophyll a; development of criteria for
Class III canals across south Florida; and the conclusion that the
proposed criteria for Class III canals are protective of designated uses
and adequately account for the spatial and temporal variability of
nutrients.

(4)  Alternative Approaches for Comment

EPA is requesting comments and views on the advantages and disadvantages
of alternative approaches to deriving protective criteria for south
Florida canals.  These approaches include: 1) a stressor-response
approach (based on data from all canals or canals grouped by soil type),
and 2) methodologies that have been employed to develop nutrient targets
in an EPA-proposed TMDL for dissolved oxygen and nutrients.

As previously described in Section III.E(2)(b), EPA considered the
underlying soil type of south Florida canals as a possible basis for
geographic classification.  Analysis of the underlying soil types,
indicated by STATSGO, led EPA to identify the following four canal
regions: Everglades Agricultural Area (EAA) comprised of histosol and
entisol soils, EvPA comprised of histosol and entisol soils, areas west
of the EvPA and EAA, or West Coast, comprised of spodosol and alfisol
soils, and areas east of the EvPA and EAA, or East Coast, comprised of
spodosol, entisol, and alfisol soils.

Subsequent to classification, the proposed statistical
distribution-based approach  or the alternatives to the proposed
approach described in the following sections could be used to derive
numeric nutrient criteria by canal region for any or all of the proposed
criteria (i.e., TN, TP, and chlorophyll a) provided that sufficient data
are available.

	(a)  Stressor-Response Approach

	EPA considered two statistical analyses for assessing the
stressor-response relationship between nutrients and biological
response.  In contrast to the proposed option, which included only data
from sites with no evidence of nutrient impairment, the
stressor-response analyses included all data regardless of whether sites
were associated with WBIDs that have been determined to be impaired.
EPA conducted linear and quantile regression analyses between
chlorophyll a, TP, and TN on a regional and aggregated regional basis.
EPA used the linear regression model as a statistical tool to predict
the chlorophyll a response based on matched chlorophyll a and TN and TP
data.  Similarly, quantile regression was used to analyze the matched
nutrient and chlorophyll a data.  In this application, quantile
regression was used to predict the 90th percentile of the distribution
of chlorophyll a concentration at a given concentration of TN or TP.

	To apply either statistical approach for developing numeric nutrient
criteria for TP or TN, EPA would need to identify the concentration of
chlorophyll a that would be protective of the designated use for these
canal systems.  One approach would be to use EPA’s proposed
chlorophyll a criterion of 4.0 µg/L for canals to derive the TN and TP
criteria from stressor-response relationships.

(b)  Calculation of TP Criteria for the Everglades Agricultural Area
(EAA) Using a Downstream Protection Approach

EPA considered using the methodologies described in the EPA-proposed
TMDL for dissolved oxygen and nutrients to develop numeric nutrient
criteria, specifically TP, for portions of the EAA.  These methodologies
are described in the TMDL in Section <IP_ADDRESS> of the TMDL document,
“Approach #1: Estimate STA inflow loads resulting in WQS in downstream
waters”, and Section <IP_ADDRESS> of the TMDL document, “Approach #2:
Simple modeling approach.”  The first approach takes into account the
downstream criterion of the EvPA and the performance of the stormwater
treatment areas (STAs).  Based on these considerations, inflowing TP
concentrations within the EAA to the STAs were derived to meet the
downstream EvPA TP criterion of 0.010 mg/L.  The second approach used a
model that extrapolated natural background TP concentrations, based on
land use changes, for specific WBIDs within the EAA.  These approaches
could support the derivation of numeric nutrient criteria for TP within
the EAA region.  Approach #1 would result in a TP concentration of 0.10
mg/L, while Approach #2 would result in a TP concentration of 0.087
mg/L.

(5)  Request for Comment and Data on Alternative Approaches

	The alternatives for Class III south Florida canal criteria in this
proposed rule represent alternative approaches given the availability of
data in the State of Florida to date and are consistent with the
requirements of both the CWA and EPA’s implementing regulations.  EPA
is soliciting comment on the alternative approaches considered by the
Agency in this proposal, the data underlying those approaches, and the
proposed alternatives themselves, including criteria expressed as an
upper percentile maxima not to be exceeded more than 10% of the time in
one year, similar to those discussed for lakes.  For further information
on the upper percentile criteria for canals, refer to EPA’s TSD on
Florida’s Inland Waters, Chapter 4:  Methodology for Deriving U.S.
EPA’s Proposed Criteria for Canals.  EPA is seeking other pertinent
data and information related to nutrient concentrations or nutrient
responses in Class III canals in south Florida.

F.  Comparison Between EPA’s and Florida DEP’s Proposed Numeric
Nutrient Criteria for Florida’s Lakes and Flowing Waters

To date, Florida has invested significant resources in its statewide
nutrient criteria effort, and has made substantial progress toward
developing numeric nutrient criteria.  For several years, FDEP has been
actively working with EPA on the development of numeric nutrient
criteria and EPA has worked extensively with FDEP on data interpretation
and technical analyses for developing EPA’s recommended numeric
nutrient criteria proposed in this rulemaking.

On January 14, 2009, EPA formally determined that numeric nutrient
criteria were necessary to protect Florida’s lakes and flowing waters
and should be developed by January 14, 2010.  FDEP, independently from
EPA, initiated its own State rulemaking process to adopt numeric
nutrient water quality criteria protective of Florida’s lakes and
flowing waters.  According to FDEP, the State initiated its rulemaking
process to facilitate the assessment of designated use attainment for
Florida’s waters and to provide a better means to protect its waters
from the adverse effects of nutrient over-enrichment.  Florida
established a technical advisory committee, which met over a number of
years, to help develop its proposed numeric nutrient criteria.  The
State also held several public workshops to solicit comment on the draft
WQS.  While FDEP was progressing with its State rulemaking, EPA moved
forward to develop Federal numeric nutrient criteria for Florida’s
lakes and flowing waters, consistent with EPA’s January 14, 2009
determination and based on the best available science.

Most recently, in July 2009, FDEP solicited public comment on its
proposed numeric nutrient criteria for lakes and flowing waters.  In