Nutrient Panel Review

SAB Panel Recommendations and EPA Response

Based on feedback in the 2nd draft report 4.8.11

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RESPONSE MATRIX

SAB Comment EPA Response

Conceptual Approach

Conceptual Model (Charge Question 1(a)):

“EPA has introduced a general conceptual model in Chapter 2, including the selection of assessment endpoints and indicator variables. What is your

perspective of the general conceptual model?”

1. We recommend the terminology that implies TN and TP are causal

variables be dropped in favor of terms such as driver variables.

Under the paradigm of the National Nutrient Criteria program, causal

variables and drivers are synonymous. The term “causal variable” has been

used in the program since its inception and EPA disagrees that it is beneficial

to change to a different term.

2. TN and TP loadings are likely to be better predictors of Chlorophyll-a,

hypoxia and seagrass loss than TN and TP concentrations.

Studies in Florida have shown that nutrient loadings are not always better

predictors of these ecosystem responses than nutrient concentrations.

However, EPA has considered both types of relationships in its regression

and simulation modeling.

3. TN and TP concentrations also can be considered response variables in

that they reflect long-term loading rates; the temporal and spatial scales

over which they would be measured should be clarified.

EPA acknowledges that TN and TP concentrations in estuaries reflect the net

result of TN and TP loading, flushing processes, and TN and TP processing

within estuaries. Thus, TN and TP concentrations are both a response to

loading and a cause of ecological effects. Numeric criteria for TN and TP

concentrations would therefore protect water quality in more than one way.

4. Biological endpoints and objectives are not discussed in sufficient detail Additional background information on the objectives and the application of

the biological assessment endpoints are discussed in the proposed rule TSD

and preamble.

5. The endpoints need to be much better defined and, in some cases, more

clearly connected to the explanatory variables that would be the basis for

setting numeric criteria.

Additional background information on the objectives and the application of

the biological assessment endpoints are discussed in the proposed rule TSD

and preamble.

6. It is critical that EPA define “balanced” for each of the three biological

endpoints, preferably in quantitative terms. Simply relying on the state’s

assessment of whether or not waters are “healthy” is not an adequate

definition.

EPA defines “balanced flora” in terms of seagrass community condition as a

state, providing a reasonable expectation that the ecological integrity of the

seagrass-based community would be not be impacted by pollution. In the

context of nutrient pollution, anthropogenic nutrient loading should not

cause reduced transmission of light through the water to a degree that the
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SAB Panel Recommendations and EPA Response

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SAB Comment EPA Response

historically-attained depth of colonization of seagrasses could no longer be

attained, as this would be expected to decrease the ecological function

associated with the habitat. In this context, “historically attained” means a

depth of colonization that may be inferred from a map of seagrass extent at

a time when nutrient impacts are believed to have been minimal. Where

suitable historical data are not available, historically-attained depth targets

could be estimated by considering historically-attained depth of colonization

in nearby estuarine areas that have a similar level of light attenuation

associated with natural causes, principally colored dissolved organic matter

(CDOM).

EPA is developing definitions relative to these endpoints and will include

them in the proposed rule TSD and preamble.

7. Although the panel believes that Chlorophyll-a concentration in the water

column is a reasonable endpoint, Chlorophyll-a alone (which measures

phytoplankton biomass) cannot be used to infer anything about primary

productivity or whether phytoplankton populations are “balanced’’ in terms

of species composition or relative abundance/dominance. While we support

the using Chlorophyll-a as an endpoint, its limitation need to be explicitly

recognized.

In acknowledgment of your comment, EPA is proposing more than one

biological endpoint (seagrass, DO) where the data will allow ensuring the

protection of aquatic life. The use of chlorophyll-a as a biological indicator is

consistent with multiple water quality and eutrophication frameworks used

in Europe in the USA that consider chlorophyll a as a statistic that can

effectively signify changes in primary production, and serve as an indication

of ecological state.

8. The Panel is concerned about relying upon Chlorophyll-a as the sole

criterion to protect seagrass communities even as water-column

Chlorophyll-a levels remain low.

For estuaries where seagrass is present, EPA evaluated chlorophyll-a as an

indicator of nutrient pollution, and TN and TP criteria were derived to

protect seagrass communities. There are several mechanisms whereby

nutrients could impact seagrass communities. One of these is by increasing

phytoplankton abundance, as indicated by chlorophyll-a, which is expected

to decrease light available to seagrasses. Two other mechanisms are

stimulating growth of epiphytic microalgae and stimulating growth of

macroalgae in seagrass beds. Both of these can also impact seagrasses,

however, data does not currently exist to address these alternative

mechanisms. The panel suggests a “stressor response” approach (item 9),

which could conceivably relate seagrass extent to changes in loading.
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SAB Comment EPA Response

Sufficient data were not available to implement this approach. Instead, EPA

considered field studies indicating the light requirements for seagrasses,

then related nutrients to attainment of the light requirement.

9. EPA should consider a stressor-response approach to link nutrient loading

with seagrass areal extent for protecting seagrass communities.

EPA does not believe this is a reasonable approach for the estuaries in

Florida, as many estuaries have significant gradients in water quality

(incomplete horizontal mixing) such that exposure resulting in one particular

location is not expected to relate directly to loading into the estuary as a

whole. This contrasts with the large number of small, well-mixed

embayments in southern New England.

10. The Panel recommends that EPA consider this approach [Tampa Bay

approach] and also ways to back-calculate concentrations from specific

loadings that impair seagrasses.

EPA has worked with Tampa Bay NEP to better understand the underlying

science and assumptions used to develop their approach. EPA is considering

Tampa Bay NEP’s technical approach as an alternative in the Agency’s

proposed rule.

11. The panel is concerned that no direct measures of faunal community are

proposed to define whether a balanced community is being protected and

maintained.

The state of Florida does not currently have data to support the use of direct

measures of faunal communities in estuarine, coastal, and southern inland

waters. In response, EPA is using the best available data on water quality

indicators needed to support a balanced faunal community.

12. The panel is concerned with the absence of any reference whatsoever to

explicit faunal metrics.

The state of Florida does not currently have data to support the

development of a faunal metrics in estuarine, coastal, and southern inland

waters. EPA's approach reflects the tested relationship between oxygen

requirements and survival of marine faunal species. Also, protection of

seagrass habitats also related to protection of fauna that utilize these

habitats.

13. The Panel suggests that EPA alter the diagram or include an explanation

on how numeric criteria for Chlorophyll-a will be linked to balanced faunal

communities.

The linkage between the biological assessment endpoints and the numeric

criteria is further explained in the proposed rule TSD.

Conceptual Approach

Categories of Florida Waters (Charge Question 1(b)):

“EPA has delineated the State of Florida into 4 general categories of waters—Florida estuaries, Florida coastal waters, South Florida inland flowing waters,

and South Florida marine waters—for purposes of considering approaches to numeric nutrient criteria development. Are these categories appropriate and

scientifically defensible?”
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SAB Comment EPA Response

1. The panel recommends that the term [South Florida] “marine waters” be

replaced with “estuarine and coastal waters”.

EPA appreciates the panel’s feedback; nevertheless EPA has chosen to

maintain the “marine waters” term because this term "marine" is widely

accepted as applicable to salt water. For the waters in question, the

distinction between "estuarine" and "coastal" is not relevant as elsewhere in

the State, so this change would not be helpful. Language has been added to

the proposed rule preamble and TSD to clearly indicate that South Florida

marine waters include waters that are "estuarine" or "coastal" in character.

2. South Florida inland flowing waters appears to be a default category

without strong scientific rationale for this classification; for purposes of

criteria development, these waters should be subdivided into managed

canals and natural streams.

EPA established this region of flowing freshwaters in its final rule as the

South Florida Nutrient Watershed Region (NWR) in November 2010. The

basis for regionalizing the flowing waters is described in EPA’s final rule TSD.

Briefly, EPA identified stream regions on the basis of underlying phosphorus

geology and coincident downstream receiving estuary watersheds. EPA

delineated the South Florida NWR on this basis and noted the unique

hydrology of this region as further evidence for its separation from other

flowing freshwaters in the state.

Since the SAB’s review, EPA has further subdivided the South Florida NWR

into five subregions based on information related to vegetation, soil type

and geomorphology. EPA also considered whether to subdivide south

Florida inland flowing into managed canals and natural streams. In an

exploration of SAB’s recommendation, EPA found that most streams that

might be considered natural are located near the coast and are, at least

partially, tidal in nature and therefore outside the scope of the south Florida

inland analyses. Further, EPA found that some streams are a mixture of

natural and hydrologically modified segments, and that some natural

streams segments are downstream of managed canals. Ultimately, EPA

determined that there was insufficient data to separate natural streams

from managed canals and to develop separate criteria for just natural

streams in south Florida.

Florida Estuaries

Delineation and Data Sources (Charge Question 2(a)):

“Are the data sources identified appropriate for use in deriving numeric criteria in Florida’s estuaries (as discussed in Sections 2.4 and 3.2)? Is the SAB aware

of additional available, reliable data that EPA should consider in delineating estuaries or deriving criteria for estuarine waters? Please identify the
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SAB Comment EPA Response

additional data sources.”

1. Geographic delineations of estuaries seem appropriate although it is not

clear why a salinity of 2.7 psu rather than 0.5 psu was used to delineate the

upper reaches of these systems. A finer classification based on degree of

impact may be useful.

As discussed further in our next response, EPA acknowledges tidal waters

represent a transition between estuaries and freshwater systems. EPA

utilizes a salinity of 2.7 psu because Florida’s state regulations (Rule 62–

302.200, F.A.C.) are clear with respect to what the state considers

freshwater and non-freshwater: “predominantly fresh waters shall mean

surface waters in which the chloride concentration at the surface is less than

1,500 milligrams per liter,” which corresponds to 2.7 psu.

2. EPA should consider adding tidal creeks as a separate ecosystem type

because they have different characteristics than the open estuaries and

therefore may require different nutrient criteria.

EPA agrees with the SAB that tidal creeks are a separate ecosystem from

estuaries. Tidal creeks are a transition between estuaries and freshwater

systems and are essentially small sub-estuaries that are dominated by twicedaily tidal flow. Tidal creeks may be fed by an upland freshwater stream,

but in extensive salt marsh and mangrove areas, many smaller tidal creeks

have no freshwater stream input and are simply conduits for tidal water. In

the absence of upland streams, many tidal creeks may still receive fresh

groundwater input. The tidal action results in extreme changes in salinity at

any one place on the creek. As a result, tidal creeks are clearly different from

the main body of an estuary and may have different expectations relative to

adjacent open waters. EPA is proposing to apply the TN and TP criteria

developed for either the adjacent freshwater or estuarine segments to each

tidal creek in Florida, depending on the tidal creek’s salinity levels. EPA is

alternatively proposing that TN and TP criteria for tidal creeks can be

computed using mean salinity to interpolate between the adjoining

freshwater and estuary criteria.

3. We encourage continued searching for appropriate data. In public

comments to the Panel, one researcher (Dr. Tom Frazer, University of

Florida) indicated that additional data are available for some estuarine areas

and have yet to be utilized.

EPA agrees with the SAB and has since reached out to several organizations

for additional data for estuarine waters during the rulemaking process,

including the National Estuarine Programs and State University research

programs, among others.

4. Panel encourages EPA to continue consultations with state and local

agencies and researchers to access additional data and local knowledge

where possible.

EPA engaged in local scientific consultation with key stakeholders in the

State of Florida including the National Estuary Programs (NEPs), county

technical staff, and the Water Management Districts prior to the proposal of
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SAB Comment EPA Response

numeric nutrient criteria.

Florida Estuaries

Assessment Endpoints (Charge Question 2(b)):

“Are the assessment endpoints identified in Sections 2.3 and 3.2 (healthy seagrass communities; balanced phytoplankton biomass and production; and

balanced faunal communities) appropriate to translate Florida’s narrative nutrient criterion into numeric criteria for Florida’s estuaries, given currently

available data? Does the SAB suggest modification or addition to these assessment endpoints?”

5. To protect seagrass communities, EPA should consider a measure of

epiphyte abundance in addition to the proposed determination of

Chlorophyll-a in the waters column.

Measures of epiphyte abundance were considered as an additional line of

evidence to support balanced seagrass communities. However, there is not

enough State data to determine a protective water quality target at this

time. In addition, it is unclear at this time whether nutrients alone can lead

to overgrowth of seagrasses by epiphytes --removal of predators by fishing

has been suggested by some to have caused a trophic cascade resulting in

reduced populations of “mesograzers,” small organisms that could maintain

top-down control, preventing epiphyte overgrowth of seagrasses.

6. The Panel recommends that EPA provide a more quantitative description

of the concept of balanced phytoplankton and faunal communities, and

remove the word “production” in the description of phytoplankton unless

measures of production are added.

See EPA answer to #6 under charge question 1(a).

7. Whether Chlorophyll-a is an appropriate endpoint for assessing

“balanced” phytoplankton communities, depends on how EPA defines

“balanced”, which has not been done.

See EPA answer to SAB comment #6 under charge question 1(a).

8. Direct indicators of faunal community balance should be considered in

addition to DO. When hypoxic conditions are observed, impacts on the

biota usually have already occurred. It is preferable to identify indicators

that show stress on the faunal community before such degraded

conditions develop.

See EPA answer to SAB comment #11 and #12 under charge question 1(a).

9. Diel variability needs to be considered when establishing DO water quality

targets.

EPA recognizes that diel variability in DO can result from nutrient pollution.

However, there is not sufficient data available at this time for most locations

in the State, to address this issue with empirical observations.

Florida Estuaries
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SAB Panel Recommendations and EPA Response

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SAB Comment EPA Response

Approaches (Charge Question 2(c)):

“EPA describes potential approaches in Section 3.3 (reference conditions, stressor response relationships, and water quality simulation models) for deriving

numeric criteria in Florida’s estuaries. Compare and contrast the ability of each approach to ensure the attainment and maintenance of natural populations

of aquatic flora and fauna for different types of estuaries, given currently available data?”

10. The Panel emphasizes that there is no single approach that is ideal for

developing nutrient criteria. This being the case, we support using multiple

approaches where possible.

EPA appreciates the panel’s feedback and has used a combination of

reference condition, stressor-response, and water quality simulation

modeling where the data will allow.

11. We encourage EPA to give thorough consideration to the stressorresponse approach when developing criteria for Florida waters.EPA appreciates the panel’s feedback and has evaluated the use of stressorresponse relationships in combination with reference condition and water

quality simulation modeling where the data will allow.

12. We urge caution in EPA’s apparent emphasis on water quality modeling

approaches; if this approach is selected, a reasonable representation of

internal nutrient cycling needs to be included. In light of climate-related

effects on hydrology and temperature regimes, as well as increases in

freshwater withdrawals for human use, the panel recommends that EPA

consider the possibility that thresholds could be crossed, fundamentally

changing these systems.

EPA water quality models (WASP) reflect many of the dynamics cited by the

SAB. EPA refers to the WASP model manual as well as the Agency’s

proposed rule TSD for further information on the details of how certain

dynamics are represented in the models. EPA took into account variability in

hydrology and temperature in its watershed (LSPC) and hydrodynamic

(EFDC) models. However, EPA did not explicitly consider freshwater

withdrawals on changes to estuarine water quality due to the inability to

predict such withdrawals with the available scientific information.

13. When setting nutrient criteria, the Panel recommends that EPA

recognize that threshold changes could occur in these systems. These

changes will in part be a result of changing nutrient loading and freshwater

discharge dynamics due to changing anthropogenic activities in watersheds

and air sheds. They will also be modulated by climatic changes, including

changes in rainfall (and conversely drought) intensities, frequencies and

geographic patterns, as well as temperature changes (i.e., warming, which

will favor the growth and proliferation of nuisance taxa such as

cyanobacteria).

See EPA answer to SAB comment #12 under charge question 2(c).

Florida Coastal Waters

Delineation and Data Sources (Charge Question 3(a)):

“Are the data sources identified in Sections 2.4, 4.1.1 and 4.2 appropriate for use in deriving numeric criteria in Florida’s coastal waters? Is the SAB aware of

additional available, reliable data that EPA should consider in delineating coastal waters or deriving criteria for coastal waters? Please identify the
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SAB Comment EPA Response

additional data sources.”

1. The Panel recommends that a preliminary assessment of nutrient inputs

be undertaken to better understand chlorophyll levels in the coastal zone

(i.e., to relate observed chlorophyll levels in coastal waters to TN/TP

concentrations or loadings from land). A first pass calculation might consist

of an estimate of the total nitrogen and total phosphorus released into the

coastal zones from all sources.

EPA currently believes the best scientific approach is to not derive separate

TN and TP criteria for Florida’s coastal waters due to the present lack of

available data for calculating TN and TP criteria. Due to this concern, coastal

criteria will focus on ChlRS-a.

2. Panel recommends that EPA consider remote-sensed chlorophyll in

waters beyond the 3-mile zone because some blooms observed in coastal

waters may form further offshore.

EPA incorporated additional data beyond 3 nautical miles for satellite

validation. Additionally, each coastal segment was extended to 4 nautical

miles to ensure satellite data bins that approached the 3 nautical mile limit

were included in the criteria analysis. This comment is further addressed in

the proposed rule TSD and preamble.

3. Data from the shelf should be used to improve the calibration of remotely

sensed and field-measured (in situ) chlorophyll.

EPA utilized the available field data that coincide with ChlRS-a data. EPA

followed the SAB’s recommendation to further illustrate the correlation

between ChlRS-a and field-based measures by considering data from

offshore.

4. EPA might consider using anomalies relative to either seasonal or annual

means, rather than absolute Chlorophyll-a concentrations, in their estimates

(see Stumpf et al. 2003, 2009; Tomlinson et al. 2004).

The SAB suggests using an anomaly approach to mitigate problems such as

bottom reflectance in the satellite estimates of chlorophyll. EPA believes

the approach presented in the proposed rule TSD provides similar mitigation

of such problems. Interferences such as CDOM and bottom reflectance

were additive to the ChlRS-a value within each coastal segment and set the

lower limit for the ChlRS-a response. The proposed approach used nonparametric statistics and focused on the 90th percentile, so the interferences

by bottom reflectance and CDOM were minimized. To further protect

against anomalies, EPA recommends that compliance with ChlRS-a reference

condition criteria values be assessed using similar satellite data and

algorithms. This will mitigate problems associated with using the OC4 close

to the coast, as interferences and overestimations are expected to be

constant.

5. The panel further notes that the proposed coastal segments are a result

of historical precedence, and EPA may wish to consider segments defined in

EPA appreciates the panel’s feedback. However, given the proximity to the

shore in which ChlRS-a will be use, incorporating bathymetry to will not
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SAB Comment EPA Response

terms of bathymetry. refine the current delineation of coastal waters.

6. Because available satellite-based sensors will change over time, as some

platforms are retired and others are launched, the Panel recommends that

EPA cross-calibrate data from existing sensors with future sensors as they

become available.

EPA has set criteria that are based on SeaWiFS, but also has provided an

additional method for future assessment/analysis of coastal criteria using

other operational satellites, such as MODIS. EPA has discussed in its

proposed rule TSD a process of normalizing the magnitude of the response

from MODIS and MERIS on the basis of SeaWiFS. The adjusted and then

normalized value could be compared against the set criteria numbers from

SeaWiFS. This method could be applied using other future satellites, in

addition to MODIS. Despite the loss of SeaWiFS and MERIS, other satellites

will continue to be available. The Visible Infrared Imager Radiometer Suite

(VIIRS) was launched on October 28, 2011, and has similar wavebands as

MODIS. For MERIS, the ESA Sentinel 3 is scheduled to launch in 2013.

Florida Coastal Waters

Assessment Endpoints (Charge Question 3(b)):

“Is the assessment endpoint identified in Section 4.2 (chlorophyll-a to measure balanced phytoplankton biomass and production) appropriate to translate

Florida’s narrative nutrient criteria (described above) into numeric criteria for Florida’s coastal waters, given currently available data? Does the SAB suggest

modification or addition to this assessment endpoint?”

7. While acknowledging that ChlRS-a is the most feasible indicator of nutrient

status for coastal waters, given available data and the lack of a better

alternative, the Panel has several concerns:

(1) there is a causal relationship between ChlRS- a and nutrient loads but a

number of other factors also influence ChlRS-a levels;

(2) few in situ Chlorophyll-a data are available for calibration;

(3) the ten-year remote-sensing dataset may not constitute an adequate

baseline, given decadal-scale variability; and

(4) the future availability of ChlRS-a data is in doubt, particularly given the

loss of the SeaWiFS sensor.

EPA acknowledges coastal chlorophyll does change due to factors other than

anthropogenic nutrient pollution, such as coastal upwelling. However this

method still provides a fixed quantitative baseline and an efficient

procedure for detecting change.

Satellites do not provide direct measurements of chlorophyll-a as do bottle

samples, which are commonly considered acceptable across many

laboratories and agencies. However, Florida's coastal waters have not been

monitored comprehensively, and the current limited data available will not

effectively support numeric criteria development for all coastal waters

based on field-sampling. EPA conducted an analysis of both field

observations and remotely sensed chlorophyll data, which provided strong

evidence that remotely sensed chlorophyll is empirically related to field

observations and thus exhibits similar trends and patterns as field
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observations. For further information, please see the response to charge

question 3c, number 8, bullet 3, below or the proposed rule TSD.

To improve on the proposed approach, continuous monitoring by satellite

would be necessary to derive more refined and reliable criteria. A potential

concern of the SAB is that all satellite missions have a finite duration and

may not be always available if the State chooses to use satellite data to

assess their coastal waters. EPA recognizes next generation satellites and

algorithms will be developed in the future, and criteria values will need to be

reviewed and adjusted with improving technologies. Future assessments

will use the climate data records from existing satellites such as MODIS.

MODIS reports suggest the sensor is healthy (NASA). Future NASA satellites

are planned to continue the climate data record , including the PACE (PreACE, aerosols, clouds, and ecosystem) satellite that is scheduled for launch

in 2019, as well as the European Space Agency (ESA) continuation of the

climate data record including the launch of Sentinel-3 in 2013, which

includes the Ocean and Land Colour Instrument (OLCI) based on MERIS.

Stakeholders may initiate robust validation of the satellite chlorophyll

measurements where coastal criteria are applied. Upon providing a robust

validation data set (not currently available within the 3 NM limit), derivation

from ChlRS-a to in-situ Chlorophyll-a would be possible.

Florida Coastal Waters

Approaches (Charge Question 3(c)):

“Does the approach EPA describes in Section 4.2 appropriately apply remote sensing data to ensure attainment and maintenance of balanced natural

populations of aquatic flora and fauna in Florida’s coastal waters? If not, please provide an alternate methodology utilizing available reliable data and

tools, and describe the corresponding advantages and disadvantages.”

8. The Panel notes the thorough approach to calibration, but has several

recommendations for consideration:

 According to the document, EPA used a 3 x 3 km pixel matrix and used only

in situ calibration data taken within 3 hours of the satellite overpass. This

should be sufficient, as tidal current velocities, particularly off the Florida

panhandle and over the wide West Florida shelf, are generally small (< 10

EPA appreciates the positive feedback on the validation process. More

information on satellite validation using in-situ chlorophyll measurements

that occurred within +/–3 hours of the satellite overpass can be found in the

proposed rule TSD.
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SAB Comment EPA Response

cm/s; He and Weisberg 2002). Largest values are about 20 cm/s in the

vicinity of the Big Bend and Florida Bay. Tidal ellipses here tend to be

perpendicular to the bathymetry except very close to the coast, where they

tend to parallel it (Koblinsky 1981; He and Weisberg 2002).

 The Panel recommends that satellite data within a larger, “coastal” context

be used for the calibration, i.e., including data from outside the 3-mile zone.

Because the calibration presented was not strong (r2 = 0.52), this inclusion

of additional data should improve the predictive power of the model. The

Panel also recommends that EPA cross-calibrate its imagery from multiple

existing (and future) sensors so that ChlRS-a values can be compared over

time.

EPA utilized the available field data that coincide with ChlRS-a data. EPA

followed the SAB’s recommendation to further illustrate the correlation

between ChlRS-a and field-based measures by considering data from

offshore. More information on this topic can be found within the proposed

rule TSD.

 Another issue on calibration concerns the relation between remotely

sensed chlorophyll and water column measurements. EPA calibrated the

satellite data to chlorophyll measured in the uppermost two meters of the

water column. The ratio between the chlorophyll concentrations in the

upper two meters and the full euphotic zone needs to be established for the

subtropical waters around Florida. In many cases, there is not a strong

relationship between total water column chlorophyll and near-surface

values, particularly in areas with upwelling and other circulation complexity.

A series of regressions were conducted by EPA to ensure that ChlRS-a and

monitoring sampled chlorophyll a demonstrate similar responses over time.

The statistically significant correlations observed between SeaWiFS, MODIS,

and MERIS ChlRS-a with monitoring sampled observation chlorophyll-a

indicated the default ocean color chlorophyll algorithm provides a similar

response as seen in the field observation data set. Therefore, the default

ocean color chlorophyll algorithm could be used universally in the identified

coastal segments. This concern is further addressed in the proposed rule

TSD. The MODIS and MERIS (no longer operational) satellites were adjusted

and normalized to SeaWiFS. VIIRS is now operational as of 2011, but was

not included in any analysis because data was not available at the time.

Only monitoring data from surface samples (< 6.6 ft [2 m]) were regressed

against the ChlRS-a because there was no consistent sampling methodology

with regard to depth among the different data sets. Furthermore, satellite

ocean color ChlRS-a more accurately represents a measure of the geometric

mean of chlorophyll within the first optical depth of the water column.

 The Panel recommends that obvious antecedent bloom data points be

removed from analyses as these are likely not representative of desired

“reference conditions” (p. 83, paragraph 1, regarding Karenia blooms).

EPA is including two options in the proposed rule TSD for numeric criteria

coastal waters; one option will derive values excluding the K. brevis blooms,

and the other will derive numeric values including K. brevis blooms. EPA has

considered the advantages and disadvantages associated both options, and
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analyses of cumulative distributions showed the criteria values for each

segment were minimally affected by inclusion or removal of observations

affected by K. brevis. EPA is proposing numeric nutrient criteria without the

data included, and will request public comment on whether this data should

be included in the data set used to derive numeric coastal criteria.

South Florida Inland Flowing Waters

Delineation and Data Sources (Charge Question 4(a)):

“Are the data sources identified in Section 2.4 and 5.4 appropriate for use in deriving numeric criteria in South Florida’s inland flowing waters (as discussed

in Chapters 2 and 5)? Is the SAB aware of additional available, reliable data that EPA should consider in delineating or deriving criteria for South Florida’s

inland flowing waters? Please identify the additional data sources.”

1. The Panel recommends that EPA subdivide South Florida inland flowing

waters into human-managed canals vs. natural flowing streams. EPA should

identify characteristics to separate these two classes of water bodies, with

one suggested characteristic being whether their flow regime is natural or

managed.

In developing revised nutrient water quality criteria for these waters, EPA is

focusing on translating the state of Florida’s existing narrative nutrient

criteria at 62.302.530(47)(a), which states: “In no case shall nutrient

concentrations of a body of water be altered so as to cause an imbalance in

the natural populations of aquatic flora and fauna.” The state of Florida’s

narrative, and EPA’s translation of it into numeric nutrient criteria, must be

protective of the state of Florida’s designated uses in class I, II, and III waters

codified at 62.302.400. The 2009 Clean Water Act 303(c)(4)(B)

Determination identified class I, II, and III waters as requiring revised water

quality standards for nutrients, and therefore to also propose numeric

nutrient water quality criteria protective of designated uses of Class III

waters. . Given these requirements, EPA believes distinguishing canals from

natural flowing waters in South Florida was contrary to EPA’s duty under the

Determination and the Clean Water Act. EPA recognizes the anthropogenic

origin and nature of the canals in the South Florida NWR. However, EPA

maintains that nutrient pollution is still an environmental water quality

problem in these waters and a threat to waters that are hydrologically

connected to them such as the Everglades Protection Area, tribal lands, and

downstream estuaries and coastal marine waters.

Since the SAB’s review, EPA has further subdivided the South Florida NWR

into five sub-regions based on information related to vegetation, soil type

and geomorphology. EPA also considered whether to subdivide south
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Florida inland flowing into managed canals and natural streams. In an

exploration of SAB’s recommendation, EPA found that most streams that

might be considered natural are located near the coast and are, at least

partially, tidal in nature and therefore outside the scope of the south Florida

inland analyses. Moreover, EPA found that some streams are a mixture of

natural and hydrologically modified segments, and that some natural

streams segments are downstream of managed canals. Ultimately, EPA

determined that there was insufficient data to separate natural streams

from managed canals and to develop separate criteria for natural streams

alone in south Florida.

2. The Panel recommends that EPA evaluate the appropriateness of

developing nutrient criteria for South Florida natural flowing lotic systems,

given their greater potential for valued ecological attributes relative to canal

systems.

EPA’s 2009 Clean Water Act 303(c)(4)(B) Determination identified class I, II,

and III waters as requiring revised water quality standards for nutrients. The

state of Florida has classified a large portion of the canals in South Florida, as

well as the natural flowing freshwaters, as Class III waters. Given the

Consent Decree requirements, EPA has a mandatory duty to propose

numeric nutrient water quality criteria to protect the state of Florida’s Class

III designated uses of these waters. To fully comply with the Consent Decree,

EPA considers placing greater emphasis on protecting the water quality of

natural flowing waters over canals in the South Florida NWR to be contrary

to Clean Water Act regulations and the state of Florida’s designated uses.

EPA is proposing DPV criteria for the South Florida NWR. EPA has also

developed a stressor-response approach for deriving IPVs for the South

Florida NWR as an alternative option for public comment.

3. Canals should be viewed as a source of nutrients to downstream, more

oligotrophic, systems rather than for any valued ecological attributes that

may be unique to them, and canal nutrient criteria would be in the form of

DPV. Depending on data availability, criteria could be developed for natural

flowing streams as in-stream protection values (IPV).

EPA agrees that downstream protection should be a factor for the canals in

the South Florida NWR. EPA also agrees that numeric nutrient water quality

criteria, in the form of IPVs and DPVs, are appropriate for natural flowing

freshwaters of South Florida. EPA is proposing DPV criteria for the South

Florida NWR. EPA has also developed a stressor-response approach for

deriving IPVs for the South Florida NWR as an alternative option.

4. The Panel is not convinced from the material provided that IPV nutrient

criteria are appropriate for these uniquely artificial and highly managed

See EPA answer to SAB comments #1 and #2 under charge question 4(a).
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ecosystems. The underlying problem is that the canals are classified as Class

III waters (with a designated use of recreation and balanced population of

fish and wildlife), although their primary purpose is flood control and

management of water supply.

5. EPA should look into datasets potentially available from the local

water/drainage districts (not water management districts), such as Lake

Worth; these local regulatory authorities can control water regulation and

were created for the purpose of reclaiming the lands within their boundaries

and to provide water control and water supply for settlement and

agriculture (see www.lwdd.net). In addition, agricultural interests that

border the canals (e.g., U.S. Sugar Corp.) may have useful data, although

these data may be proprietary.

The proposed inventory of inland flowing waters that catalogues and

distinguishes natural streams and canals should provide very useful

information, and could provide the basis for subdividing this category of

waters as recommended above.

EPA held technical outreach meetings in Florida to elicit input and data from

local stakeholders, among which will be located in South Florida.

Additionally, EPA engaged the South Florida Water Management District and

Florida International University to identify sources of data throughout south

Florida that may prove of use.

South Florida Inland Flowing Waters

Assessment Endpoints (Charge Question 4(b)):

“Are the assessment endpoints identified in Section 5.4 (balanced faunal communities, i.e., aquatic macroinvertebrates, and balanced phytoplankton

biomass and production) appropriate to translate Florida’s narrative nutrient criteria (described above) into numeric criteria for South Florida’s inland

flowing waters, given currently available data? Does the SAB suggest modification or addition to these assessment endpoints?”

6. If canal IPVs are to be developed, more information needs to be

presented on how balanced natural populations would be assessed for these

unique aquatic ecosystems.

EPA developed methods to characterize protection of Class III freshwaters in

south Florida and clarified in the proposed rule preamble what is meant by

biological balance and how it applies to the goals of the Clean Water Act.

EPA developed a stressor-response approach for deriving IPVs for the South

Florida NWR as an alternative approach to DPVs.

7. The Panel recommends further consideration and assessment of the

response variables to be used and the form of the nutrients (i.e., those with

short-term versus long-term bioavailability) that are most relevant.

EPA recognizes that phosphorus moves through the food web primarily as

organic phosphorus (after it has been incorporated into plant or algal

tissue), where it may be released as phosphate in urine or other waste (by

heterotrophic consumers) and reabsorbed by plants or algae; plants and

animals use nitrogen in mineral form such as ammonium ions (NH4+) or

nitrate ions (NO3-) for uptake although some bacteria and cyanobacteria
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(blue-green algae) that can convert nitrogen gas to the ammonium form

through biological nitrogen fixation. Nitrogen follows the same pattern of

food web incorporation as phosphorus, and is released in waste primarily as

ammonium compounds. These compounds are usually converted to nitrates

by nitrifying bacteria, making it available for uptake. As such, researchers

have found that inorganic forms of nitrogen and phosphorus can be well

correlated with response variables in some water bodies. In addition, the

mechanistic models that are being considered elsewhere explicitly model

and take into consideration the above processes.

8. EPA proposes a classification of inland water regions according to soil

order, land management systems or color of water (see below). Some

combination of these factors should be considered, taking into account

covariates.

EPA considered classifying inland waters based on information on hydrologic

units, soil composition, geology, land cover, historic plant distributions, ecoregion, and soil type. The Everglades has different soils (Histosols) and flow

than the western or eastern sub-regions. The Histosols are known to be

more organic and to contain higher concentrations of nitrogen and

phosphorus than other soils, especially from the Spodosols in the western

sub-region, as well as the Alfisols and Entisols. EPA believes that the five

sub-regions established in south Florida, which includes separating the

Everglades Protection Area from the area further to the west or east,

addresses the SAB’s concern related to considering humic soils in our

classification.

Currently, EPA does not appear (at least explicitly) to consider the potential

influence of humic soils in their classification of inland flowing water types,

with respect to their role in discoloration of waters; phytoplankton response

will be very different in waters that are naturally colored (i.e., influenced by

humics) vs. those that are not.

South Florida Inland Flowing Waters

Approaches (Charge Question 4(c)):

“EPA describes two approaches in Section 5.4 (reference conditions and stressor-response relationships) for deriving numeric criteria in South Florida inland

flowing waters. Compare and contrast the ability of each approach to ensure attainment and maintenance of balanced natural populations of aquatic flora

and fauna in different types of flowing water or geographical areas, given currently available data?”

9. If IPVs for naturally flowing lotic systems are developed, either of the S-R

or reference approaches could work, although it was not clear if the

EPA developed a stressor-response approach for deriving numeric nutrient

criteria for the South Florida NWR. EPA is proposing these criteria (i.e., IPVs)
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available data would show interpretable patterns. as an alternative and will request comment on this approach.

10. Citing insufficient information provided the panel does not recommend

using the LDI approach. Concern was also noted with the buffer distance

used.

EPA concluded to not use the LDI approach in South Florida due to the high

degree of physical configuration and modification of the flowing

freshwaters.

11. As with the approach based on reference conditions, the [stressorresponse] relationship between Chlorophyll-a and TN or TP is likely to be

modulated by the effects of hydrological, geological, and other covariates.

Failure to account for such factors may lead to criteria that are over- or

under-protective.

EPA considered this comment in the context of the classification of inland

waters based on potential modulating factors including soils, geology,

hydrologic unit, land cover and historic plant distributions. Since the SAB’s

review, EPA has further subdivided the South Florida NWR into five subregions based on information related to vegetation, soil type and

geomorphology. EPA believes that creating these five subregions allows the

EPA to consider the impact of hydrologic, geologic and other covariates in

developing numeric criteria including magnitude, duration, and frequency.

12. Flow conditions associated with chlorophyll measurements need to be

taken into account to elucidate whether those measurements are reflective

of near or farfield conditions.

In EPA’s stressor-response analysis performed in computing south Florida

alternative approach for inland IPVs, EPA performed an exploratory analysis

of the proportion of chlorophyll-a blooms occurring in the dry and wet

season. EPA found that both the wet and dry season had similar proportions

of observations exceeding the chlorophyll-a bloom threshold established in

south Florida. As a result, EPA proceeded with its south Florida inland

flowing water stressor-response analysis on an annual basis.

13. An assessment of the impact of estimation error on the accuracy of

frequency of exceedance calculations is needed.

EPA’s south Florida inland flowing water stressor-response analysis was an

alternative approach based on a multivariate logistic regression. In addition

to standard regression statistics for the model coefficients (i.e., standard

error), receiver operator characteristic (ROC) curves were used to evaluate

model performance. ROC curves are used to evaluate models focusing on

measures of sensitivity and specificity.

14. The Panel notes the following:

 A fundamental question that the EPA document leaves unanswered is how

such fitted regression models will be used to determine numeric criteria;

EPA is proposing alternative criteria in the South Florida NWR (i.e., IPVs) on

the basis of preventing frequent algal blooms. This approach is grounded in
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i.e., how they will determine the level of Chlorophyll-a that will be

considered protective of balanced phytoplankton and faunal communities.

This is a serious shortcoming that needs to be addressed.

the scientific literature with respect to lakes, which canals in south Florida

resemble during a portion of the year (i.e., limited or non-flowing dry

season). EPA used a multivariate logistic regression approach to relate the

frequency of exceeding an algal bloom threshold to TN and TP

concentrations. EPA will request comment on this alternative approach.

 As the EPA document notes, it has not been possible to develop stressorresponse relationships in which a biological endpoint other than chlorophyll

serves as the response. However, if there is a clear relationship between

Chlorophyll-a and TN, say, and a clear relationship between another

biological endpoint (e.g., a faunal community metric) and Chlorophyll-a,

then there would ordinarily be a clear relationship between that biological

endpoint and TN. The fact that it is difficult to identify this latter relationship

may reflect limitations of the statistical models considered so far. For

example, the effect of TN or TP on a biological endpoint may be modulated

by other factors. This effect could be obscured by omitting these factors

from the regression model.

See EPA response above.

 As with the approach based on reference conditions, the relationship

between Chlorophyll-a and TN or TP is likely to be modulated by the effects

of hydrological, geological, and other covariates. Failure to account for such

factors may lead to criteria that are over- or under-protective at some sites,

and it would again seem preferable to include such covariates in developing

numeric criteria. Furthermore, should TN and TP be considered

simultaneously (i.e., is a multiple or simple regression most appropriate)?

See EPA answer to SAB comment #11 under charge question 4(c).

 Some of the variability in the stressor-response relationship could be a

result of season. This should be investigated, and it may lead to the

formulation of different criteria for different seasons.

EPA examined the effect of season it the Agency’s multivariate logistic

regression, but found no evidence that season was a factor in affecting the

response. (See EPA answer to SAB comment #11 under charge question

4(c).)

 A substantial amount of effort will be put into identifying and quantifying

stressor-response relationships in these waters using correlative/regression

analysis. Considering the difficulty of working across the surface-subsurface

interfaces in deriving nutrient loading estimates, as well as effects of these

loads, the authors have done a good job of addressing these challenges. This

See EPA answer to SAB comment #12 under charge question 4(c).
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section could however benefit from closer process/response connections

(including applying modeling approaches) to receiving estuarine and coastal

waters.

 The results of a distribution approach (p. 108) are sensitive to the

distribution of sites along the disturbance gradient. If a larger proportion of

the samples are from more disturbed sites, then using the lower percentile

to set the criteria will result in a higher number than if a larger proportion of

the samples are from less disturbed sites. Some requirements for the

distribution of sites along the disturbance gradient should be specified.

EPA is proposing alternative criteria in the South Florida NWR (i.e., IPVs) on

the basis of preventing frequent algal blooms, not on the basis of a

reference approach suggest by EPA as a method to the SAB.

 If macroinvertebrate indices are to be used to relate impacts of nutrients

the relationship between nutrients and macroinvertebrates needs to be

more clearly established

EPA is proposing alternative criteria in the South Florida NWR (i.e., IPVs) on

the basis of preventing frequent algal blooms, not on the basis of a

macroinvertebrate index formerly suggest by EPA as a method to the SAB.

South Florida Marine Waters

Delineation and Data Sources (Charge Question 5(a)):

“Are the data sources identified in Section 2.4 and 5.5 appropriate for use in deriving numeric criteria in South Florida’s marine waters (as discussed in

Chapters 2 and 5)? Is the SAB aware of additional available, reliable data that EPA should consider in delineating or deriving criteria for South Florida’s

marine waters? Please identify the additional data sources.”

1. The Panel agrees that these waters should be considered separately for

purposes of nutrient criteria development.

EPA appreciates the positive feedback.

2. EPA might consider an alternative segmentation scheme that

incorporates alongshore and cross-shelf circulation patterns.

EPA considered two possible segmentation schemes for South Florida

estuarine and coastal waters: the originally-presented scheme developed by

Florida International University (FIU) scientists, and a second scheme

informed by the results of EPA’s cluster analysis without PCA (i.e. clustering

only on regulatory variables TN, TP, and Chlorophyll-a). The FIU scheme

includes variables that reflect the influences of large-scale circulation

patterns on water chemistry (salinity, temperature, turbidity); therefore this

issue is implicitly addressed.

South Florida Marine Waters

Approaches (Charge Question 5(b)):

“EPA describes two methods in Section 5.6 for using a reference condition approach for deriving numeric criteria in South Florida marine waters (leastdisturbed sites or bionomial test). Compare and contrast the ability of each approach to ensure attainment and maintenance of balanced natural
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populations of aquatic flora and fauna in South Florida marine waters, given currently available data?”

3. The Panel recommends a reconsideration of the rationale for doing both

a principal component and cluster analysis. EPA proposes to use a

combination of principal component analysis (PCA) and cluster analysis to

define coastal regions based on multivariate measurements with sites. As

the goal of cluster analysis is precisely to identify groups of similar sites, it is

unclear why PCA is also being proposed in this context.

EPA considered the SAB’s comments and found that both FIU’s approach,

which incorporated PCA, and EPA’s independent approach, which clustered

on the basis on only three water quality variables, yielded highly comparable

results. Thus, EPA is proposing criteria based on a segmentation approach

that reflects this weight-of-evidence.

4. Based on the history [...of South Florida Estuarine and Coastal Waters],

the Panel has the following recommendations:

 When setting reference conditions, EPA should consider historical

water management and structural changes and regional climatic variability

that have affected water delivery to South Florida estuaries and coastal

waters, recognizing that current conditions do not reflect historical

conditions.

EPA recognizes that substantial changes to hydrologic and water delivery

patterns in the South Florida NWR have taken place in the last century and a

half as a consequence of widespread anthropogenic activities, particularly

the development of drainage canals. However, when using the reference

condition approach, candidate criteria are derived from observations

collected from water bodies that represent conditions within a region that

support healthy biological conditions. That approach requires the ability to

define and identify water bodies that have healthy biological conditions and

relies on the availability of sufficient data from those reference water bodies

to characterize the distributions of nutrient variables. These conditions

being met, criteria are then computed as a function of the nutrient data

distributions.

 In particular, salinity should be considered a covariate because of its

role in maintaining the water quality necessary for seagrasses. We note,

however, that salinity is relevant (and in fact variable as a result of water

management) only in a very restricted part of this domain.

The cluster analysis developed by FIU focused on salinity, nutrients, and

other water chemistry measures of general ecological relevance, grouped

together into principal components that reflect the covariance relationships

among these variables. Although EPA’s own analysis focused only on TP, TN,

and chlorophyll-a, EPA’s cluster analysis results largely conform to those of

FIU. EPA’s proposed segmentation scheme therefore essentially constitutes

a modified version of FIU’s segments, in which FIU’s segment boundaries are

modified in a few places as informed by the results of our analysis. Both

segmentation schemes, thus implicitly addressed salinity as an influence on,

or reflection of water chemistry.
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 Seagrass coverage and the extent of epiphytic colonization should be

considered as endpoints, in addition to water column chlorophyll (see also

3.2.2).

EPA considered the use of seagrass coverage in South Florida waters. While

some studies have demonstrated increased epiphyte biomass with nutrient

pollution, others suggest a variety of causative factors, including potential

top-down control of epiphyte production by grazers. The use of epiphyte

community composition was also explored; however, current data relating

epiphyte dynamics to nutrient concentrations are limited both spatially and

in number. The development of an enrichment index based on the

taxonomic composition of algae could potentially be a worthwhile research

effort; however, it is not available at this time.

5. EPA proposes to use a reference condition approach using leastdisturbed sites or a binomial test applied to a distribution of raw data. Both

approaches have merit and the Panel encourages application of both to

provide a more robust evaluation of criteria.

EPA is not proposing criteria that incorporate a binomial expression.

6. The document should clarify which coastal and estuarine areas will be

under the jurisdiction of the forthcoming nutrient criteria, versus other

regulations (e.g., for federal and state protected waters).

EPA consulted the relevant geodetic and regulatory information and clearly

established the waters which would be affected by criteria developed for

south Florida.

Downstream Protection Values

Estuaries (Charge Question 6(a)):

“Are the methods EPA is considering for deriving downstream protection values (DPVs) for estuaries (excluding marine waters in South Florida) as described

in Section 6.1-6.4 appropriate to ensure attainment and maintenance of downstream water quality standards, given available data? Please describe

additional approaches and their advantages and disadvantages that EPA should consider when developing numeric criteria to protect these downstream

estuarine waters (excluding marine waters in South Florida), given available data?”

1. While agreeing with the goal, the Panel has concern with the overlap

between DPV and the Total Maximum Daily Load (TMDL) process.

While some similarities exist, the processes and goals are different. TMDLs

are applied to watersheds of impaired waters and are intended to eliminate

the impairment. DPVs, like all criteria, are intended to protect waters by

preventing impairments. Unless there is only one upstream source water,

developing DPVs requires distributing the maximum load that will not cause

impairment of downstream waters among several source waters according

to a science-based rationale.

2. If the DPV approach is pursued, we urge that selected apportionment

strategies not preclude cross-tributary nutrient trading or other approaches

EPA is proposing a pour point DPV, which would not necessarily drive

“apportionment” or allocation of nutrient loads. Furthermore, EPA’s
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to achieving the necessary load reductions. proposed downstream protection approach would not necessarily preclude

cross-tributary trading or other pollution management strategies that would

still maintain protection of all designated uses.

3. The Panel notes a few additional points to think about when considering

the wisdom of DPVs:

 There are other sources, such as direct (e.g., groundwater and

atmosphere) loadings to the estuary. How might those be addressed in the

determination of tributary DPVs?

Since EPA is not developing criteria that would apply to groundwater or

atmospheric deposition, EPA must consider these to be fixed. Thus, these

sources would be subtracted from the protective loading rate to calculate

the load that could enter the receiving water via streams and rivers.

 Referring to Figure 2, why should there not be DPVs for streams B2a

and B2b in order to protect stream B1?

This issue was addressed in the creation of the stream (IPV) criteria, which

do not change within watersheds. If the IPVs do not change along the

flowpath, then we expect that every streams’ criteria value protects the

downstream stream reach (i.e., when the water flows into the next reach, it

must already meet the criteria for that reach). This argument does not apply

to streams flowing into estuaries, however. Estuaries will have different

criteria for each nutrient, and protection of streams does not inherently

imply that the estuary will be protected.

4. EPA should justify the choice of the LSPC model and explain why it is the

most applicable model for this case.

The LSPC model is based on (and largely equivalent to) the widely applied

and well-accepted HSPF watershed model. A major strength of LSPC is that

it can utilize whichever local data sets are available, allowing EPA to address

some of the more complex hydrologic situations that arise in Florida (i.e.,

such as springs). LSPC is well-suited to the application to which EPA is

applying it. EPA has also considered results obtained from USGS’s SPARROW

watershed model, which provides a very different (i.e., empirical) approach

to assessing loadings from watersheds. EPA is not aware of another

mechanistic watershed model that would offer any advantage over LSPC.

5. The timeframe of the modeling should be linked to the response of

biological endpoints in the receiving waters; annual average values may

grossly under-predict the impact of large storm events.

EPA’s mechanistic models do reflect the dynamic nature of various

hydrologic events, including storms. EPA evaluated and considered varying

temporal scales in deriving the proposed numeric nutrient criteria.

6. In addition, the document needs to discuss the impact on criteria of P

cycling and transformation.

According to the analysis that EPA as conducted to date, we believe that P

cycling and transformation will occur according to natural laws and without
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regard for what the criteria are. Please refer to the response in #5, above.

Downstream Protection

South Florida Estuarine and Coastal Waters (Charge Question 6(b)):

“Are the methods that EPA is considering for deriving downstream protection values (DPVs) for marine waters in South Florida as described in Section 6.5

appropriate to ensure attainment and maintenance of downstream water quality standards, given available data? Please describe additional approaches

and their advantages and disadvantages that EPA should consider when developing numeric criteria to protect downstream marine waters in South Florida,

given available data”

1. Provide more information on how canals will be evaluated. A number of

primary canals empty directly into coastal waters, so it will be important to

incorporate all available data on N and P species for the terminal reach of

these canals and to provide a more detailed approach on how DPV criteria

will be developed.

EPA is proposing four methods for calculating DPVs. See the proposed rule

TSD and preamble for the different options proposed and the methodology

behind them. EPA’s mechanistic models reflect the conditions of the streams

or canals flowing into estuaries and links this to the estuary condition. EPA is

also proposing simpler approaches for calculating DPVs where data is not

presently available to apply water quality models. The dilution model

approach considers estuarine mixing to estimate DPVs that are protective of

the estuary criteria. The reference approach considers observed canal water

quality associated with the reference based criteria of the estuary. The

estuary NNC approach applies the estuary criteria to the canal to assure

protection under all conditions.

2. The time frame of modeling is important and should be linked to the

response of the endpoints in the receiving waters. Given the wide variation

in flow conditions for canals, the concentrations of nutrients in canal waters

are likely highly variable. Hence average nutrient concentrations in canal

waters when released to estuarine and coastal marine waters may not

adequately represent the concentrations needed to protect receiving

waters. If additional information is not available for nutrient concentrations

in the canals, discharge of canal waters to the receiving waterbodies needs

to take into consideration loading rates on a daily basis that will ensure the

receiving waterbodies meet their water quality standards.

EPA’s mechanistic models do reflect the dynamic nature of various

hydrologic events, including storms. EPA evaluated and considered varying

temporal scales in deriving the proposed numeric nutrient criteria. EPA is

also proposing simpler approaches for calculating DPVs where data is not

available to apply water quality models. Please refer to the response above

or the proposed rule TSD for more information.

3. In-stream/watershed P transformations should be considered in more

depth for streams, lakes and canals. Although less is known about P

EPA is only proposing DPVs at the pour points to estuaries. Since the pour

point is the end of the stream or canal where it empties into the estuary, no
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transformations within the canals of South Florida than for streams, the

physical and chemical processes that control P transport within a watershed

should be the same for canals. Additional consideration, however, must be

given to the special situations that result as a function of the wide-ranging

flow situations for the canal system.

Furthermore, it is important to understand the temporal parameters and

their range of variability. These factors will determine, in part, the

mechanisms that are most important under different sets of flow conditions.

transformations within the stream or canal need to be considered in

derivation of the DPV.

4. The continuum of fresh to saline waters must be considered in the

process of determining DPVs. For canal waters discharging to estuarine and

coastal marine waters, the issue of the continuum of fresh to saline water is

the same as discussed earlier in our response to charge question 6(a).

DPVs for both TN and TP were developed in addition to the alternative IPVs

for TN and TP. Under the alternative criteria proposed by EPA (i.e., IPVs for

canals), both the nitrogen and phosphorus DPVs and nitrogen and

phosphorus IPVs will apply, so that the most stringent value for nitrogen and

for phosphorus will determine target conditions. This will result in a set of

criteria that will protect the estuaries from the effects of excess nutrients.

EPA’s mechanistic models do reflect the continuum of fresh to saline waters.

EPA is also proposing simpler approaches for calculating DPVs where data is

not available to apply water quality models. Please refer to the response in

comment number 1 above or the proposed rule TSD.