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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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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 a s 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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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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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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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 freshwatersystems 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 organizatio ns 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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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. Se e 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 Estu aries

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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 appreciate s 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 stressor

response approach when developing criteria for Florida waters. EPA appreciate s the panel’s feedback and has evaluated the use of stressor

response 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 w ater 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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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 b elieves 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 Chl RS-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 incorporate d additional data beyo nd 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 utilize d the available field data that coincide with Chl RS- a data. EPA followed the SAB’s recommendation to further illustrate the correlation between Chl RS-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 Chl RS-a value within each coastal segment and set the lower limit for the Chl RS-a response. The proposed approach used nonparametric statistics and focused on the 90 th percentile, so the interferences by bottom reflectance and CDOM were minimized. To further protect against anomalies, EPA recommends that compliance with Chl RS-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 Chl RS-a will be use, incorporating bathymetry to will not

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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 Chl RS- 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 Chl RS- a and nutrient loads but a number of other factors also influence Chl RS- 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 Chl RS- 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 satellitesare 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 Chl RS-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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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 Chl RS-a values can be compared over time. EPA utilized the available field data that coincide w ith Chl RS- a data. EPA followed the SAB’s recommendation to further illustrate the correlation between Chl RS-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 Chl RS- a and monitoring sampled chlorophyll a demonstrate similar responses over time. The statistically significant correlations observed between SeaWiFS, MODIS, and MERIS Chl RS-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 Chl RS -a because there was no consistent sampling methodology with regard to depth among the different data sets. Furthermore, satellite ocean color Chl RS-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 Flowin g 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 dev eloping 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 materia l 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 al gae) 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 hydrologicunits, 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 [stressor

response] 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’sreview, 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 least

disturbed 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 an d 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 process es 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.