# External Peer Review of EPA’s

“Proposed Methods and Approaches for Developing Numeric Nutrient Criteria for Florida’s Inland Waters”

Peer Review Comments Draft Final

EPA Contract No. EP

- C

- 07

- 059 Work Assignment No. 1

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Submitted to: Jacques Oliv er Health and Ecological Criteria Division ( 4304T ) Office of Science and Technology U.S. Environmental Protection Agency 1200 Pennsylvania Avenue, NW Washington, DC 2046 0

Submitted by: Eastern Research Group, Inc. 110 Hartwell Avenue Lexington, MA 02 421

- 3136

August 11 , 2009 Printed on Recycled PaperQUALITY NARRATIVE STATEMENT

ERG selected reviewers according to selection criteria provided by EPA. EPA confirmed that the scientific credentials of the reviewers proposed by ERG fulfilled EPA’s selec tion criteria. Reviewers conducted the review according to a charge prepared by EPA and instructions prepared by ERG. ERG checked the reviewers’ written comments to ensure that each reviewer had provided a substantial response to each charge question (or that the reviewer had indicated that any question[s] not responded to was outside the reviewer’s area of expertise). Since this is an independent external review, ERG did not edit the reviewers’ comments in any way, but rather transmitted them unaltered to EPA.i 

## Table of Contents

Peer Reviewer Comments
1. Please comment on the use of the approaches and methodologies presented in the technical document, “Proposed Methods and Approaches for Developin g Numeric Nutrient Criteria for Florida’s Inland Waters,” for deriving numeric nutrient criteria, given the available data, protective of the Florida’s designated uses of Florida’s class III waters (i.e., “Recreation, Propagation and Maintenance of a Healthy, Well

- Balanced Population of Fish and Wildlife”).

................................ .. 3
2. Chapter 3. Please comment on the use of the SCI, LVI, and SDI as reliable indicators of the aquatic life designated use attainment and whether these metrics appear to be sensitive indicators to nutrient enrichment?

................................ ................................ ................................ ................................ ....... 11
3. Chapter 4. Please comment on the approach used, given the available data, to derive the proposed nitrate

- nitrite criteria for Florida’s streams (< 40 pcu).

................................ ................................ ..... 15
4. Chapter 5. Please comment on the regionalization of Florida’s streams in support of the nutrient benchmark approach.

................................ ................................ ................................ ........................ 18
5. Chapter 6. Please evaluate the stressor

- response approaches for numeric nutrient criteria development.

................................ ................................ ................................ ................................ ..... 20
6. Chapter 7. Please evaluat e the Nutrient Benchmark Distributional Approach.

................................ 24
7. Chapter 8. Please evaluate the reliability of the Nutrient Longitudinal Study to protect the aquatic life use downstream and whether th is approach can be applied to other estuaries or lakes in Florida?

................................ ................................ ................................ ................................ ........................... 27
8. Chapter 9. Please evaluate the methods for developing chlorophyll a numeric nutrient criteria for lakes.

................................ ................................ ................................ ................................ ................. 30
9. Chapter 10. Please evaluate the methods for developing chlorophyll a numeric nutrient criteria for lakes based on stressor

- response analyses.

................................ ................................ ....................... 34
10. Chapter 11. Please comment on the “all streams” statistical distribution approach for deriving numeric nutrient criteria

................................ ................................ ................................ .................... 40
11. Chapter 12. Please comment on extrapolating bac kground nutrient concentrations as an approach to deriving numeric nutrient criteria.

................................ ................................ ................................ ..... 41
12. Chapter 13. Please comment on the use of multiple regression and statistical distribution approach es to deriving numeric nutrient criteria.

................................ ................................ .............. 43
13. Chapter 14. Please comment on the downstream protection approaches.

................................ ......... 45
Additi onal Comments/References

................................ ................................ ................................ .............. 511 

## PEER REVIEWER COMMENTS

### 3

Specific Questions
1. Please comment on the use of the approaches and methodologies presented in the technical document, “Proposed Methods and Approaches for Deve loping Numeric Nutrient Criteria for Florida’s Inland Waters,” for deriving numeric nutrient criteria, given the available data, protective of the Florida’s designated uses of Florida’s class III waters (i.e., “Recreation, Propagation and Maintenance of a Healthy, Well
- Balanced Population of Fish and Wildlife”).

a. What are the strengths and weaknesses of approaches and methods employed given the available data? b. To w hat extent can each line of evidence be used independently to support the derivation of nume ric nutrient criteria for each of the parameters EPA has recommended? c. Given the data available, what additional technical considerations can you recommend in the derivation of numeric nutrient criterion for each parameter?



### Reviewer 1 The driving force for creation of the document I am currently reviewing comes from the

Clean Water Act. The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for s urface waters. The basis of the CWA was enacted in 1948 and was called the Federal Water Pollution Control Act, but the Act was significantly reorganized and expanded in 1972. "Clean Water Act" became the Act's common name with amendments in 1977. Reading this whole act quickly shows that the term fish is used approximately 68 time and recreation approximately 72 times, leading to the general goal of protecting waters so they are “Swimmable” and “Fishable” on into the future. This goal leads to an impossibl e management situation that the best swimming lakes are generally clear unproductive lakes (oligotrophic) and the best fishing lakes are generally green productive lakes (eutrophic). A strength of the document is that it attempts at all costs to set nutrie nt standards that are low, which would favor a swimming condition. However, a great weakness of the document is that fish are not considered in the document and if they were considered a low nutrient standard would not favor “Fishable.” Additionally, the F lorida Fish and Wildlife Conservation Commission had no part in the creation of this document, which I think is a great mistake and another weakness of the document. Their insights as to how nutrients relate to fish and wildlife should be part of this document. As the document and standards are set up now, most of the excellent fishing and wildlife observing lakes in Florida would be classified as impaired. The strengths in the document entitled “ , “Proposed Methods and Approaches for Developing Numeric Nut rient Criteria for Florida’s Inland Waters,” revolve around the general understanding that geology and the Ecoregion concept is the master variable determining water chemistry of aquatic systems. From my experience working on Florida aquatic systems, the f actor accounting for the largest amount of variance in nutrient concentrations of rivers, lakes and estuaries is the geology in which the system lies. This agrees with the basic Ecoregion concept that the USEPA already uses. This is a great strength of thi s document in Section 5 for streams and Section 14 for Estuaries because both Sections show the importance of geology and/or Ecoregion

.Unfortunately, this same concept is not used for Florida lake nutrient standards discussed in this document, another weakness. Within an individual Ecoregion the next factors accounting for variance in nutrient concentrations are all related to lake morphology and hydrology. These factors can account for significant variance in nutrient concentrations within an individual E coregion and for the most part, these factors are ignored in the current document adding another weakness. However, expanding the use of the Vollenwider Model concept described in Section 14.2.1 could greatly strengthen the scientific grounds for nutrient standards set in the document. This approach has been extremely successful in lakes (Bachmann and Canfield 1981) and shows great promise in Estuaries (Meeuwig et al. 1998; Meeuwig 1999; Meeuwig et al. 2000). Driving lake morphology and hydrology impacts on nutrient concentrations and lake trophic state is the year

- to

- year variation in water inputs from rainfall. I have tried to model impacts of rainfall to nutrient concentrations in lakes with little success (Hoyer et al 2005). The reason is that changes in lake water level can cause trophic state parameters to increase (25% of the time), decrease (~25% of the time) or have no impact (~50% of the time) depending on the dominant mechanisms working within individual lakes. The importance of this concept for th e current document is that many lakes have tremendous year

- to

- year variability and many of the approaches used in this document to define nutrient standards do not have enough long

- term data to define what true background variance is. Thus, setting standar ds on a lake after a 100

- year flood or draught could make it impossible for the lake to ever reach the standard again. Some form of long

- term variability needs to be part of any nutrient standard. The long

- term variability of lake water chemistry add diffi culty to the strength of the document, which is understanding the important role that color has on aquatic systems in Florida. However, lakes in Florida are extremely dynamic and can go from a color of 20 PCU to 150 PCU after one rain storm and maintain co lor over 40 PCC for months if not a year before they clear up. Thus, using a fixed 40 PTU as a cut of for clear and colored systems may not be the best approach for setting nutrient standards. One month a lake many meet a standard and the next be in violat ion. The approaches to setting standards in this document should not be independent of each other because all ecological processes are connected. Unfortunately, the report entitled “Proposed Methods and Approaches for Developing Numeric Nutrient Criteria f or Florida’s Inland Waters” shows that different groups were working independently of each other and not communicating. For example, the rivers and estuary groups followed an Ecoregion and water shed type approach and the lake groups did not. All of the di fferent Sections should follow the same general game plan. My recommendation for developing a nutrient standard for Florida is to first use all available data and develop the most comprehensive Ecoregions possible, following the lead of Griffith et al. 199 7. The upper 25% of the distribution of nutrient concentrations in lakes within an Ecoregion should be examined to see if they meet use and those that do not should be examined for restoration activities. Those that do should be monitored to make sure they are not changing. To make this determination, all long

- term water chemistry data available should be used to define normal background variance for nutrient concentrations in lakes that could then be used as a standard classifying any lake exceeding the de fined normal background variance as impaired or not meeting use.

### 5 Once the remaining lakes have be classified as meets use, monitoring lakes to see if they fall within normal back ground variance would work to maintain lakes in a swimmable and fishable condition. Finally, I would consult with the Florida Fish and Wildlife Conservation Commission to define how nutrients impact the fish and wildlife populations using aquatic systems and have them help define when nutrients in a system cause harm to the fishabl e waters. Canfield, Jr., D. E. and Bachmann, R.W. 1981. Prediction of total phosphorus concentrations, chlorophyll a, and Secchi depths in natural and artificial lakes. Can. J. Fish. Aquat. Sci. 38:414

- 423. Griffith, G. E., D. E. Canfield, Jr., C. A. Horsb urgh, and J. M. Omernick. 1997. Lake regions of Florida. Report to the Florida Department of Environmental Protection. U. S. Environmental Protection Agency, Corvallis OR. Hoyer, M. V., C. A. Horsburgh, D. E. Canfield, Jr., and R. W. Bachmann. 2005. Lake l evel and trophic state variables among a population of shallow Florida lakes and within individual lakes. Canadian Journal of Fisheries and Aquatic Sciences. 62: 1

- 10. Meeuwig, J. J., J. B. Rasmussen, and R. H. Peters. 1998. Turbid waters and clarifying mu ssels: their moderation of empirical chl:nutrient relations in estuaries in Prince Edward Island, Canada. Mar. Ecol. Prog. Ser. 171: 139

- 150. Meeuwig, J. J. 1999. Predicting coastal eutrophication from land

-use: an empirical approach to small non

- stratifie d estuaries. Mar. Ecol. Prog. Ser. 176: 231

- 241. Meeuwig, J. J., P. Kauppila, and H. Pitkanen. 2000. Predicting coastal eutrophication in the Baltic: a limnological approach. Can. J. Fish. Aquat. Sci. 57: 844

- 855.



### Reviewer 2 In m y document Question 1 is a "General Charge Question" with three general

considerations (i.e. strengths and weaknesses, validity of lines of evidence, additional technical considerations for deriving criteria) that I took into consideration throughout the document in reviewing the individual chapters. So, the general charges are addressed throughout the review, of course depending upon the contents of the individual chapters.

Reviewer 3 The State of Florida has developed multiple lines of evidence in support of numeric

nutrient criteria for inland waters. Those lines include effects

-based relationships between biological communities and nutrients, stressor

- response relationships between nutrients and periphyton indicators for streams and chlorophyll a for lakes and estuaries, de scriptive statistics, models linking downstream condition to upstream nutrient loads, and heuristic arguments based on historical comparisons, paleolimnology, and review of extant literature. Collectively, these lines of evidence are defensible and support numeric criteria. For some of the analyses, a few minor refinements are suggested to help make the results less ambiguous, and in some cases, more applicable.The biological indices, especially the Stream Condition Index (SCI) based on macroinv ertebrate community composition and structure, and the Lake Vegetation Index (LVI), were convincingly demonstrated to be robust measures of resource condition relative to a gradient of anthropogenic disturbance. The Stream Diatom Index was strongly influe nced by regional geology (however, component metrics were, apparently, sensitive to a nutrient gradient). Significant, though necessarily fractional, amounts of variation in SCI and LVI scores were explained by a nutrient gradient, particularly nitrogen. Unfortunately, the small sample size (N~75) used in the statistical analyses for both stream invertebrates and, to a lesser extent, lake vegetation, appeared to limit the ability to “read” the nutrient signal through the noise of confounding and collinear variables. The report was vague with respect to which SCI data were used in the analyses. For example, no mention is given as to whether the data were culled to remove sites influenced by spurious factors (e.g., sites known to be affected by toxic level s of pollution, highly degraded physical habitat, desiccation, combined sewer overflows, etc.) prior to analyses. If this was not done, it is highly recommended. The derivation of nitrate

- nitrite criteria for clear, spring streams employed historic comp arisons, stratification by water color, laboratory dose

- response experiments, analysis of hydrologic and demographic data, and change point analysis based on data collected over a nutrient gradient. As such, the methodology is particularly robust, and the criteria defensible, especially in terms of recreational and aesthetic uses. The regionalization with respect to nutrients was straightforward, methodologically sound, and in keeping with the results of others (i.e., collapsing multiple ecoregions into se veral nutrient regions

- sensu Robertson et al. 2006 1 ). The stressor

- response analyses presented in Chapter 6 were conducted on data retrospectively, but managed to avoid the tinge of data dredging by acknowledging collinearity among stressor variab les, and by noting that a measured stressor variable can serve as a proxy for unmeasured variables. The analyses showed statistically significant relationships between nutrients and biological metrics based on either macroinvertebrates or diatoms, but giv en the aforementioned caveats, were not considered sufficiently strong for derivation of criteria. Although the relationships were weak, and may not, in isolation, serve as a basis for criteria, change points in the biological metrics in relation to eithe r TP or TN (or DIN, NOx, etc.) would serve as an additional line of evidence for criteria. The results from the rapid periphyton assessment, however, appeared to provide the least ambiguous results, yet were used only to support the general theme that nu trient enrichment produces observable effects. Again, change point analysis on these data would augment the overall effort. The methods used to identify least

- impacted benchmark sites in Chapter 7 were rigorous and resulted in a population of sites th at yielded a reference range for nutrient concentrations in the various nutrient regions. The report correctly cited an important caveat for using a percentile approach, namely, that the approach fails to identify a threshold concentration over which biol ogical impairment is increasingly likely. The strength of the percentile approach hinges on the supposition of the absence of evidence

1 Environmental Management (2006) 37:209

- 229

### 7 is evidence of absence (i.e., no biological impairment observed at a few sites with high nutrient concentrations, ergo, the criteria should be protective). However, before this can be concluded, mitigating factors, specifically those that allow for good biological condition to be maintained in the presence of known or suspected stressors, must first be ruled out, or at lea st understood with an eye toward implementation. The reference range approach should be supplemented with an “all” sites approach (as in Chapter 11), wherein distributions of nutrient concentrations are examined by categorical level of SCI scores (e.g., p oor, fair, good, excellent ranges) for all sites within a region (or regions) where biological data exist. This would provide a contrast between degraded sites, sites meeting expectations, and benchmark sites that may help inferentially show the nutrient concentrations over which degradation is likely. The longitudinal study of the Steinhatchee and Waccasassa basins and estuaries loosely demonstrated that nutrient concentrations found in minimally disturbed watersheds are not associated with detrimental effects, particularly loss of seagrass beds. This study would have been much more compelling if an enriched system, especially one enriched with nitrogen, had been offered for comparison. Chapter 9 details a basis for chlorophyll a thresholds for Florida lakes based on empirical relationships between TP, TN and chlorophyll a (i.e., Trophic State Index), and augments that with several other lines of evidence, specifically, paleolimnology, BPJ, literature review, user perception, existing condit ion, and reference distribution. The report and appendices were vague with respect to which data were used (a subset of those referred to in Chapter 10?) and the strength and form (i.e., linear vs. non

- linear) of the relationships forming the TSI; however , having a direct, and empirically derived, stressor

- response model on which to base criteria is clearly a strength. The additional lines of evidence roughly converge on the proposed threshold of 20 ug/l chlorophyll a (i.e., meso

- eutrophic boundary) for c olored lakes, and the lower threshold of 9 ug/l (oligo

- mesotrophic boundary) for clear lakes in the panhandle region. The exercise in investigating the relationship between cyanobacteria and chlorophyll a was offered as evidence that the proposed chlorophyll threshold will protect beneficial uses; however, the exercise was equivocal. The real question is whether increasing nutrient concentrations over time alter the composition of the algae community in a given waterbody, thereby increasing the probability of a harmful bloom. The stressor

- response analyses for lakes provided in Chapter 10 presented two lines of effects

-based evidence, one based on an aquatic vegetation index (LVI), the other on chlorophyll a . The LVI was statistically associated with mean nutrient concentrations averaged over the preceding year, thus demonstrating a stressor

- response relationship. The strength of association (for both lake types), as the report acknowledges, was what one might have expected given that multiple factors inf luence lake vegetation, but was deemed insufficiently robust for derivation of nutrient criteria, except for TP in clear lakes. These data, however, should be used in change point analysis as an additional line of evidence supporting numeric criteria. Co rrecting for the extraneous environmental variables by using the residuals from a regression of the LVI on the ancillary variables in change point analysis might help. The statistical associations between chlorophyll a and nutrients were much stronger, ba sed on a large data set, and in keeping with numerous published results. These relationships were used to derive criteria.Compiling descriptive statistics on ambient water chemistry, as in Chapter 11, is a necessary step toward gaining a broa d understanding of the system at a population level. However, the reference approach, in the absence of biological data, provides the weakest line of evidence for criteria development. The all sites chemistry data should be, as previously mentioned, paire d with biological data (i.e., the SCI, SDI, or a sensitive component metric) and reexamined within ranges of the biological data. The effort toward extrapolating background nutrient concentrations (Chapter 12) was equivocal, perhaps because the work wa s done ad hoc with available data. Sorrano et al. (2008) demonstrated the application for lakes, but the applicability for streams is questionable, given that streams are open systems and inherently more variable than lakes. Furthermore, the approach, wi th respect to streams, would seem to offer little additional resolution beyond that given by the exhaustive benchmark approach (Chapter 7). The multiple regression models provided in Chapter 13 offer a more refined way to derive criteria than the conventio nal linear models appearing in Chapters 9 and 10, though the results from all three chapters generally comport each other, adding strength to the overall effort of defining criteria. The meat of Chapter 14 is section 14.1.14. The description of model de velopment preceding it is highly ancillary for the exercise of deriving nutrient criteria. A very general and emphatically brief summary of the TMDLs would suffice as a precursor, with details of the models appearing as appendices. To wit, simply stating and referencing that approved TMDLs have been developed for the respective estuaries identifying the target loads listed in Table 10 would suffice. Given that water quality models are abstractions, and have a good deal of inherent uncertainty, the derive d stream reach concentrations suggested as criteria in Table 10 should be compared to reference ranges (i.e., which percentile for both the benchmark sites and the all sites do they match). Also, some expression of uncertainty around the estimates should be provided. That said, linking protection of downstream uses with upstream concentrations is an important component of the criteria derivation process, and the results presented in Table 10 appear to generally comport with the other finding listed throughout the report, thereby adding strength to the overall effort.



### Reviewer 4 The document has remarkable breadth of coverage made possible in part because

Florida made the investment in building a massive data record. Considerable technical effort has been devoted to exploration of different approaches for development of numeric nutrient criteria. Not all approaches will be found to have equal merit for developing nutrient criteria in Florida, but the opportunity to compare and contrast those approaches is invaluable. After consideration of relative merits, EPA and Florida should be well

-positioned to move forward with criteria development.
Itwas disappointing, although understandable, that there was no synthesis component that might consider how the vari ous approaches fit together. It does not seem likely that all approaches will have equal merit in this case. Will one approach play a primary role and others be used as confirmation? At some point, it will be necessary to reconcile differences among the numbers produced by each method. This step may require

### 9 additional work on some methods; the level of effort, especially with regard to application of statistical tools was not uniform across the approaches. For example, more might be done to extract thresholds from the “wedge

- shaped” response relationships.
I would like to see more discussion about the interface between science and policy. Biological condition, for example, can be characterized largely by technical evaluations, but the threshold consist ent with use attainment is mainly a policy decision. That distinction is sometimes obscured behind discussions about the precision of possible thresholds.



### Reviewer 5 The document reviewed represents a compilation of methods and approaches from

several so urces, namely Florida’s Department of Environmental Protection (DEP), USEPA and their contractors, by which EPA proposes to assist the State of Florida in determining nutrient criteria for the protection of designated uses of inland waters as mandated by the Clean Water Act. The effort presented here represents a wide

- ranging assessment of techniques, from a number of perspectives, to determine comprehensive nutrient criteria for both N and P for inland waters. A series of relatively thorough, though ofte n high

- level, considerations of standard techniques is presented for establishing numerical water quality criteria for lakes, streams, rivers, springs and downstream waters. The approaches cover a range of biological response variables including invertebrates, periphyton, algae, Submersed Aquatic Vegetation (SAV), chlorophyll a. The controllable stressor variables of direct concern are nitrogen and phosphorus, although mention is made of the importance of other stressor variables, such as DO and color. EPA recognizes that a single nutrient criterion for all waters is unrealistic and will result in inadequate protection of inland waters. Therefore, EPA recommends the states adopt criteria for two stressor parameters, in this case TN and TP, and two resp onse variables, for example chlorophyll a and water clarity. The proposal does not explicitly include a second response parameter for consideration and focuses on chlorophyll a as a response parameter but does not treat water clarity at all. Though many secondary response variables are analyzed: invertebrates, lake vegetation, seagrass, fishery, lake trophic state, only chlorophyll a is proposed as a response parameter. Nor does the document consider stressor parameters other than TN and TP. Other can didates, such as low DO, organic matter load or sediment load, may be as or more appropriate stressors for some waters, however are not formally incorporated into recommendations. This is likely a function of the lack of availability of data and a desire to address (at least initially) the most common response parameters being used throughout the country. DEP and EPA clearly recognize the complex nature of the task at hand: proposed criteria must have a high probability of being effective and of eliciting the predicted results or the program will be undermined. Therefore, it is recommended that several elements be included in the proposed approaches, to wit:

 The approaches must be geographically based and be applicable statewide

 There must be provision f or differential application of criteria, depending on conditions and geography Downstream effects must be evaluated

 The approaches should be ecosystem

- oriented

 They should target specific response variables

 Approaches must be standardized and transportable

 The strategy must incorporate research and monitoring

 Tem poral variability should be taken into consideration

 Sampling protocol and schedules must be matched to the timescales of relevant processes Of necessity, many simplifying assumptions are made in the various analyses and recommendations throughout the document, some of which are innocuous and others should be further evaluated. Evaluations of these assumptions are elucidated in the individual chapter assessments. Some approaches presented are like ly not to be effective for all waters in Florida and some approaches are not sufficiently developed or expounded here to make a thorough consideration of them. Although the approaches should be geographically comprehensive, south Florida estuaries are not iceably absent from the discussion and analyses. The proposed models for downstream loading calculations are insufficient to assess whether criteria are protective in areas where downstream waters do not receive a coherent mass flow, such as in Florida Bay. Biological response is related to a number of variables that obscure the dose

- response relationships. A better understanding of the underlying interactions and processes will allow a refinement of the basic relationship. Understanding of the physics of the system is essential to understanding nutrient processing: depth, bathymetry, residence time, tidal prism are important factors determinant of rates and interactions. Also lacking is a clear recommendation for a gap analysis of information required be obtained for improvements in the establishment of criteria. The document lacks an outline of the kinds of data required to implement a comprehensive nutrient strategy. Such a plan would be effective if components include: a research and monitoring plan, or a reference to one, and an adaptive strategy for reviewing the effectiveness of the criteria, on a schedule, and revising the criteria as necessary. A general caveat about the hysteresis effect is also worthwhile at this point. While the aim is to maintain nutrient concentrations below a threshold in waters that are not impaired, for waters that are impaired, rolling back concentrations to the threshold concentration may not necessarily be restorative of impaired waters to a non

- impaired condition. Every increment above an empirically derived threshold produces an ecosystem that is in further imbalance, with biogeochemical alterations whose effects are not easy to detect, account or predict. Applying reference conditions or even dose

response exper iments does not account for changes leading to these hysteresis effects. The trajectory of the ecosystem backwards along a nutrient gradient is unlikely to be linear or to be the exact reverse of the trajectory forward along that gradient. Often, the dos e - response relationship is far different, and less favorable in the reverse direction. This fact, in context of the results of the statistical analyses, experiments and field observations included in this document argue for a protective threshold somewhat more conservative than the bare minimum required for prevention of a step increase in a relatively pristine system. In summary, there is a good foundation for establishing nutrient criteria presented here. Mass balance models and simple process

- oriented accounting for nutrient

### 11 transformations and flows would go a distance in supporting the nutrient dose

- response relationships and frequency distribution benchmarks. The proposal should succeed with incorporation of a plan for continued research and monitoring that will provide the information necessary to supply these models.

2. Chapter 3. Please comment on the use of the SCI, LVI, and SDI as reliable indicators of the aquatic life designated use attainment and whether these metrics appear to be sensitiv e indicators to nutrient enrichment?



### Reviewer 1 I understand the desire to tag a nutrient standard to some form of biological measure

because the Florida Statue F.A.C. 62

- 302.400 defines a designated use for its water of “Recreation, propagation and maint enance of a healthy, well balanced population of fish and wildlife.” With this in mind, I examined and tested the ability of an Index of Biological Integrity (IBI), using fish data, to account for variability in anthropogenic impacts (Schultz et al. 1999; Schultz et al. 2000). I found that the IBI could not account for the variability in anthropogenic impacts. The problem was that there are naturally occurring gradients in Florida that are related to individual metrics used to calculate an IBI that overshad ow anthropogenic impacts (trophic state, pH, lake surface area and others). Developing models relating metrics to these naturally occurring gradients then examining residuals and anthropogenic measures may be a good way of fine tuning IBIs but I have not y et attempted that analysis. For this vary reason I believe that the SCI, LVI and SDI are the wrong approach for setting nutrient standards for the State of Florida. My strength is not with invertebrates but I know individual species of aquatic plants and diatoms are found in lakes with different water chemistry along gradients of pH, alkalinity and nutrient concentrations (Hoyer et al 2004; Beal 1977). As mentioned in my general comments these water chemistry parameters correspond to different geological fa ctors across Florida. Thus any biological index that has metrics that vary with a naturally occurring gradient will be of little use in determining the extent of anthropogenic impacts. This seems to be pointed out with the SDI in the report showing the rel ation between pH and SDI in Section 3.7. As I mention, there may be a way to model the relations between SCI, LVI, SDI and naturally occurring gradients related to geology and then examine the relations between the residuals and anthropogenic measures.
Ano ther large shortcoming of the LVI is that there is no metric in it accounting for the total abundance of aquatic plants in a lake system. The presence or absence of individual plant species and/or plant community types have little impact on whole lake spec ies composition of other fauna. However, the lake’s total percent area covered (PAC) with aquatic vegetation and/or percent volume infested (PVI) with aquatic plants are directly related to the species composition of other fauna in lake systems. For exampl e, both fish and aquatic bird communities have individual species that increase as a percentage of the whole community when PAC and PVI increase and individual species that decrease when PAC and PVI decrease. Additionally, fish and bird communities have op portunistic species that maintain a constant percent of the community as aquatic plant abundance changes.Beal, E. O. 1977. A manual of marsh and aquatic plants of North Carolina with habitat data. Tech. Bul. No. 247. The North Carolina Agricultural Experiment Station. Hoyer, M. V., D. E. Canfield Jr., C. A. Horsburgh, and K. Brown. 1996. Florida freshwater plants a handbook of common aquatic plants in Florida lakes. SP 189. University of Florida/Institute of Food and Agricultural Sciences. Gainesville, Fl orida. Schulz, E. J., M. V. Hoyer and D. E. Canfield. 1999. An Index of biotic integrity: a test using limnological and fish data from 60 Florida lakes. Transactions of the American Fisheries Society 128: 564

- 577. Schultz E. J., M. V. Hoyer, and D. E. Canf ield Jr. 2001. Reply to comment: An index of Biotic Integrity: A test with limnological and fish data from sixty Florida lakes. Transactions of the American Fisheries Society 130:172

- 173.



### Reviewer 2 Chapter 3.

I commend South Carolina DEP on the developme nt of the SCI. Clearly they spent a lot of time and effort to produce a solid, scientifically defensible product. It is an excellent tool for assessing benthic health for general pollution impacts (organic, chemical stresses, and sedimentation problems). However, its use to detect nutrient pollution is likely to be only partially successful. It would work where a stream was chronically polluted by nutrients (downstream of a point source with no nutrient limits, a stream polluted by septic system leachate , a high

- fertilizer agricultural field perhaps); these situations would produce chronic algal blooms and consequent semi

- continuous issues with bottom hypoxia or food chain disruptions from excessive Cyanobacteria. However, in a situation where nutrient l oading is acute (i.e. rain event driven) like in a suburb for instance, blooms may be short lived. Benthic invertebrates are known (especially in the South) to colonize rapidly and be multivoltine, thus by sampling benthos rarely (such as every couple of years, or even twice a year) acute impacts will be missed and the SCI will be misleading in these circumstances. As to the LVI, invasive aquatic macrophytes will colonize and overgrow even pristine waters. While elevated nutrients will certainly exacerbat e such a situation, invasive nuisance species often do not require excessive nutrients to proliferate and the index will not reflect nutrient loading. Regarding the SDI, as noted in the material this diatom index has issues especially with the naturally

- ac idic pH values present in Florida (and other Southern) waters. Benthic diatom indices were developed by Ruth Patrick and others working in northern streams in Pennsylvania and such areas, where acid streams were un

- natural (caused by acid mine drainage, f

or instance) and devastating to many species that were not evolved under such conditions. Thus, the SDI at present remains more of a goal than a product useful for nutrient loading assessment in Florida waters.



### Reviewer 3 Biological indices have been wi dely and successfully employed. The SCI and the LVI

for Florida were clearly developed using well

- established and sound methodologies,

### 13 were convincingly demonstrated to be sensitive to environmental gradients and anthropogenic disturbance, and are therefor e good indicators of aquatic life use attainment. The periphyton based SDI was apparently still in a developmental stage for Florida waters, though the SDI has been demonstrated in other regions to be particularly sensitive to pollution gradients. Chapte r 3 does not explicitly address whether or not the indices are sensitive to nutrient gradients; chapter 6 does.



### Reviewer 4 The SCI and the LVI appear to be sensitive to human disturbance making them useful

reaching conclusions about use impairment. Relia bility was tested by having experts evaluate biological condition without foreknowledge of the SCI or LVI scores. There was very good correspondence between the expert assessments and the actual index scores. Each index (SCI and LVI) was developed to be responsive to human disturbance as defined by a human disturbance gradient (HDG). The HDG for the SCI included a water quality index that incorporated several water quality measurements, while the HDG for the LVI included ammonia concentration. Both indic es

– SCI and LVI

– respond to changes in nutrients, but they also respond to other facets of human disturbance. [Chapter 7 presents a more compelling demonstration of the relationship between disturbance and nutrients.] The “wedge

shaped” relationships that appear throughout the document are expected because of the multiple pathways by which human disturbance can affect biological communities. Wedge

- shaped relationships present a challenge in terms of defining thresholds for nutrient effects, but the challenge is worth confronting because the effect is real and important. The distinction between reference and “impaired” sites is not so clear that everyone will be convinced, the elegant statistical analyses notwithstanding. The underlying premise is that stressors produce a gradient of biological response (Biological Condition Gradient). When experts evaluated sites for biological condition (and without foreknowledge of SCI or LVI scores), they could agree about the qualitative evaluation of sites at the ends of the spectrum (reference vs. impaired), but did not agree about those in the middle of the spectrum. The results of the expert panel show clearly that reasonable people may disagree about the biological condition of sites in the middle of the stress or gradient. Nevertheless, the analysis is used to support the position that “not reference” equals impaired. This position seems to prejudge a policy decision regarding attainment, which is not necessarily synonymous with reference. Selecting the 2.5th percentile as the threshold for impairment would seem to be the quantification of a policy decision regarding use attainment. Yet, it suggests that 2.5% of all reference sites would be considered impaired. Give the very rigorous screening procedures used to select the benchmark nutrient reference sites, the threshold for use attainment is set quite high. A passage from the text (page 21) suggests that the willingness to tolerate misclassification of impacted sites may have been less than that for referen ce sites. Therefore, the risk is low (virtually non

- existent for the SCI) in applying the biological assessment tool and falsely identifying impacted sites as attaining an aquatic life use.In contrast to the optimism I feel about use of the SCI and LVI, there seems to be less to recommend the SDI (described as still under development in other parts of the report). The report concludes that it is “an unreliable tool for assessing adverse human effects on stream systems,” and I would not disagree. The sens itivity of diatom assemblages to pH is a strong confounding factor, but no one should be surprised that diatoms are sensitive indicators of pH. The extensive literature on acidification is replete with examples. Perhaps the broader question concerns the merits of including the entire algal community rather than restricting analysis to diatoms.



### Reviewer 5 This chapter describes two existing index approaches currently in use by DEP for

assessing condition of streams and lakes: the Stream Condition Index (S CI), and the Lake Vegetation Index (LVI). There is also a short discussion of the Stream Diatom Index (SDI) which is currently under development by DEP. It is not clear how the SDI would be used in relation to the SCI. All three techniques are tied into the EPA’s Biological Condition Gradient (BCG) approach of rating systems on a six

- tier scale of habitat degradation, a standard assessment methodology widely applied and validated throughout the country. The SCI was linked to the BCG via a calibration ex ercise and the two systems cross

- walked with a high degree of fidelity. The SCI is based on macroinvertebrates and generally applied by comparison to reference sites, since the pristine condition of most sites sampled has long

- since been altered by human impact. Through multiple lines of evidence, fundamental ecological concepts, expert opinion, reference conditions, SCI ratings were established which indicated impairment. The technique must account for, and remove, effects of natural variation and stres s on community response variables. The methodology for establishing the rating scale and determining the threshold for impairment appeared sound and well

- founded. Similar to the SCI, the Lake Vegetation Index incorporates four metrics that together give an indication of the health of the water body compared to a reference scale. A calibration of the LVI to BCG similar to that done with the SCI was performed with equally encouraging results. The LVI examines aquatic plant complexes as a measure of the h ealth status of the lake ecosystem. The index is an integrative approach that yields overall score of condition based on multiple factors. The application of the reference site approach is well

- justified and appears be based on a methodology that yields statistically valid results. The general interpretation of the highly variable results in the low range of the Human Disturbance Gradient (HDG) is reasonable. Sampling guidance in order to reduce Type 1 errors (false positives) is well constrained and re asonable. Analysis of variability at a site over time reflects the inherent temporal variability that may be expected in the natural world when applying this index. Both the SCI and LVI approaches deliver a robust, standard way of identifying impaired wat ers for which nutrient criteria should be targeted and that are linked to the BCG used by EPA throughout the country. The utility of the SDI, based on diatom community structure, is less clear at this point. While the technique has been used in Scandinav ia (Soininen and Kononen, 2004) and Western Europe (Prygiel, 1994) for many years, the application to Florida waters is as yet untested and will require further development. If improvements are made to the diatom index, it could provide a needed complement to the information provided by the SCI for streams.

### 15

3. Chapter 4. Please comment on the approach used, given the available data, to derive the proposed nitrate
- nitrite criteria for Florida’s streams (< 40 pcu).



### Reviewer 1 My major concern about the appr oach used to set nitrate

- nitrite standards for clear (<40 PCU) is that only concentration is used and the total load of nitrogen is not accounted for in different systems. This is important to me because I examined impacts of nutrients to the growth of aqu atic plants and periphyton in 17 central Florida streams (Canfield and Hoyer 1988) and five coastal streams (Hoyer et al. 2004) and in each case concentration was not related to total biomass of aquatic plants and/or periphyton. Both studies showed that physical factors (canopy cover, water clarity, mean depth, stream velocity, substrate type, and/or salinity) were more important to the growth of plants and/or periphyton in the rivers than nutrient concentrations. Additionally, each study showed that the percentage of nutrient incorporated in the total biomass of aquatic plants and/or periphyton was extremely small compared to the annual load suggesting that regardless of concentration plenty of nutrients are available throughout the year to support the growth of aquatic plants. Canfield, D. E., Jr., and M. V. Hoyer. 1988. Influence of nutrient enrichment and light availability on the abundance of aquatic macrophytes in Florida streams. Canadian Journal of Fisheries and Aquatic Sciences 45: 1467

- 1472. Hoyer, M. V., T. K. Frazer, S. K. Notestein and D. E. Canfield, Jr. 2004. Vegetative characteristics of three low

- lying Florida coastal rivers in relation to flow, light, salinity and nutrients. Hydrobiologia 528:31

- 43.



### Reviewer 2 Chapter 4. I really liked the approach used in the derivation of a nitrate benchmark for clear

water spring

- sourced systems in Florida. It was based on multiple lines of evidence. There were two types of bioassays performed, and since I have utilized and published results of bioassays on a number of occasions I was pleased by this. I also liked the fact that field data were included utilizing periphyton coverage and nutrient data, with regressions performed. In fact, strong statistical analysis was a hallmark in this criterion derivation. A couple of comments to improve the scientific validly of the approach follow. I noted that the great majority of the literature cited within this chapter consisted of Florida DEP reports and other reports (USGS)

– which are “grey literature”, and n ot peer - reviewed by the academic scientific community. That weakens the arguments a bit (although I agree that the proposed standard appears reasonable). The authors should get deeper into the peer

- reviewed literature on this (if there is literature avai lable on the subject). The second issue is that of ammonium. This is a form of inorganic nitrogen that is readily utilized by algae, yet no data are provided on its prevalence in the spring sites. In North Carolina the inorganic N in groundwater can be dominated either by nitrate or ammonium, depending upon sources (i.e. nitrate often dominates downflow from golf courses, but ammonia dominates where septic system leachate is a factor). To strengthen their arguments the authors need to provide data on am

monium in the springs

– if it is low then the proposed standard is valid, but if it is high adjustments may need to be made. In fact, ammonium is usedin Chapter 6 (see Fig. 6.1) so it should be taken into account here as well.



### Reviewer 3 Chapter 4 clearly articulates the beneficial uses of Florida’s clear, spring fed streams by providing the historic narrative and photographic comparisons. This approach is particularly apt for the issue of nutrient enrichment, where concentrations tend to rise slowly ove r time, attendant effects are subtle, and the changing condition becomes culturally normative (at least until conditions become egregious). The empirical evidence presented in Figure 4

- 4 corroborated the anecdotal historic accounts, and set the stage for the experimental work. The concentrations found to saturate algal growth in the laboratory experiments dovetailed nicely with the change point thresholds identified in the field surveys. The TMDLs described in section 4.7 pulled together multiple lines o f evidence: comparison of existing condition (i.e., nitrogen concentrations) with reference condition, longitudinal field surveys, and change point analysis to identify target concentrations. Again, the thresholds found in the TMDL work converged with the field surveys and laboratory studies. In total, Chapter 4 presents a highly defensible basis for nitrogen criteria applicable to clear streams.



### Reviewer 4 The proliferation of nuisance algae in Florida’s spring ecosystems over the last 50 years is distu

rbing (and the photographic documentation in the report is dramatic). The attendant ecological changes are significant, as are the concerns about impairment of recreational use. The scale of disturbance is astonishing, and there is little doubt that it i s of anthropogenic origin. The application of herbicides

– intended to suppress non

- native vegetation

– apparently created a disturbance that may have facilitated algal dominance. It is not clear how the disturbance may have complicate efforts to develop nutrient thresholds. The documentation of increasing nitrogen concentrations seems thorough. The connection to human population growth is logical, although the basis for the proposed lag time should be strengthened. It is asserted, but not documented, that “nitrate

nitrite has been linked to many of the observed detrimental impacts in spring systems.” Nevertheless, I would agree that lower nitrate concentrations are be desirable. An issue not discussed is the appropriateness of deriving criteria based o n studies of a nuisance species (

Lyngbya ) in a disturbed ecosystem. The laboratory studies identify nitrate concentrations below which Lyngbya biomass and growth rates are low. I searched in vain for an explanation of how this information would lead to c onclusions about the nitrate concentrations supportive of a healthy native plant community in the spring ecosystems. Even the field surveys contain no information about nitrate concentrations in springs that still have healthy native plant communities. Th e rest of the chapter makes good use of field data to identify thresholds based on periphyton abundance. The case for the proposed threshold of 0.35 mg/L needs to be stronger; visual inspection of the figures might lead readers to conclude that a lower number would be more representative.



### Reviewer 5 This chapter described the derivation of criteria for TN and TP for springs and clear streams in Florida. The DEP recognizes the unique importance of the clear stream

### 17 class of Florida aquatic ecosystems. Pol lution of groundwater and the reduction of groundwater supply through consumptive use have increasingly become threats to spring ecosystems, leading to replacement of native SAV by exotic species, algal overgrowth and the development of thick benthic algal mats. Secondary problems include organic matter accumulation, hypoxia, loss of water transparency and deleterious shifts in faunal composition, including to toxic species.
Itis proposed that the spring analysis and protocol for criteria development be expanding to all clear stream systems. This broadening of target systems may be applicable but there are differences between stream and a spring ecological systems which may present difficulty with transportability. These inequalities include differential source waters, biogeochemistry and ionic composition and higher temperatures that may affect biota differentially and promote uncertainty in predictions deriving from nutrient enrichment. Moreover, given the nature of sources and nutrient inputs in the two types of flowing waters, N inputs to stream sources may be more directly detectable and effectively controllable than those to springs drawing from subsurface inputs, arguing for a different set of analytical tools at least (and possibly nutrient crite ria) for the two types of systems. By one criterion, namely the presence of nuisance macroalgae, a nutrient criterion of xx is suggested. By a second criterion, “excessive” algal growth, another is suggested. On both lines of evidence, a TN criterion of 0.35 mg/L is proposed to represent a threshold with a significant margin of safety. Based on the data presented though, both criteria seem to suggest a threshold closer to 0.23 would more effectively provide that margin.
Notes p. 49: wouldn’t the conserv ative target concentration be 401 instead of 420 μgN/L? The inconsistent use of units (μg and mg) is distracting. Concentrations should all be expressed in one unit, preferably μg. p. 51: why 0.23 is unnecessarily protective is not made clear

- what is th e support for this statement? The authors make a point to state that the microcentrifuge experiment that produced the 0.23 result is likely the more accurate of the two experiments

- why disavow that statement now? Further if the range between 0.23 and 0. 44 mg/L “clearly demonstrate” an imbalance of aquatic flora, why is 0.23 “unnecessarily protective?” Figure 4

- 12: While there is clearly a step around 0.44 (consisting of only two points), there is equally clearly an increase beyond about 0.24 mg/L. Why disregard that? It appears that the lower threshold is being set at too high a concentration. There is a school of thought that the first evidence of alteration of the ecosystem in response to a stressor such as nutrients is already beyond the important threshold

- that the historic buffering and homeostatic properties of the system have been exceeded and the system is in motion, possibly toward a change in state. At the least, autocatalytic properties may begin to create feedbacks that amplify the negati ve effects of stressors (Odum, 2007).4. Chapter 5. Please comment on the regionalization of Florida’s streams in support of the

nutrient benchmark approach.



### Reviewer 1 This could be the strongest section of the document and I wish the approach was

broa dened to each section. I cannot overemphasize the importance of the variable geology in Florida and its strong impact on the water chemistry of aquatic systems. Griffith et al (1997) defined 47 Lake Regions in Florida based on water chemistry, hydrology an d physiography of over 1,000 Florida lakes. This may be a lot of regions and some of them may be able to be combined but collapsing them to only five nutrient regions dilutes some of the complicated geology present in Florida. I think combining all availab le data in Florida and refining Griffith et al. (1997) regions would be the best approach for setting nutrient regions for the state of Florida. Griffith, G. E., D. E. Canfield Jr., C. A. Horsburgh, and J. M. Omernick. 1997. Lake regions of Florida. EPA/R

- 97/127 U.S. Environmental Protection Agency, Corvalis, OR.



### Reviewer 2 Chapter 5

Clearly there is strong regionalization in terms of TP for Florida’s streams; it is well known that phosphate mining is a major industry and that P releases from the Gulf Coas t rivers impact algae blooms in western Florida Bay. The authors did a logical job of working through several techniques to obtain their final product. Kriging is well known as a grouping technique of choice in these situations. I have a few comments fo r consideration:

1. Much is made of the “nutrient reference streams/sites” but these are not really explained until later in the report (Chapter 7). At least some information on their criteria as presumably unimpacted systems should be up front in Chapter 5. 2. Itis not explained why the Everglades region is not addressed in this chapter.
3. The TN stream nutrient regions deserve their own map, like the one for TP on Figure 5

- 7.



### Reviewer 3 Robertson et al. (2006) demonstrated that collapsing ecoregions (and drawing ad hoc

boundaries) into aggregated nutrient regions was an effective way of setting regional expectations for ambient nutrient concentrations. The methods presented in Chapter 5 appear rigorous, and accomplished the objective of stratifying meaningful population units.



### Reviewer 4 Establishing a spatial framework is an important practical component of criteria

development. EPA provided a good starting point with the elaboration of the ecoregion approach. States are well served by the initial framework, but can use local knowledge to improve the scheme. Florida has taken a logical approach by adapting the ecoregion

### 19 boundaries to accommodate those geological considerations that affect phosphorus concentrations in surface waters. The number of regions seems manageable from a regulatory perspective and, although the scheme was developed to recognize geologic factors controlling phosphorus concentrations, it does not seem to be in conflict with nitrogen distributions. The result seems to be a sui table companion to the nutrient benchmark approach.



### Reviewer 5 Chapter 5 discusses a scheme for the regionalization of the state in order to develop a

spatial framework for better understanding of nutrient effects on inland waters and in recognition that differences in landscape or seascape settings can have an overarching effect on nutrient dose

- response relationships in the environment. The narrative describes the procedure undertaken for determining, verifying, refining and classifying regions for dete rmination of stream nutrient criteria for P and N. Regionalizations were established based first on the EPA ecoregions, then refined based on taxonomy of biological distributions, then finally by nutrient levels. It is not clearly explained how the ecore gion approach and the biological taxonomy approach were used in support of the nutrient approach, if at all. Biology may not reflect underlying nutrient regime or biogeochemistry.
There is much description, a disproportionate amount of space in fact, of the means by which a part of the western peninsula is split two subregions: Peace River and Bone Valley, based on TP concentration. The discussion of regionalization based on TN is barely mentioned, although TN is more heterogeneous and therefore more dif ficult to classify. Further, there is no discussion how the southern portion of Florida would be subdivided into, perhaps, Everglades, rocky glades, marl prairie, coastal plain and riverine environments, creating equally heterogeneous landscapes. As demo nstrated in the application of nutrient regionalization in later chapters, the step is a productive one and does assist in the evaluation and quantification of effects of nutrients on biological responses; further detail on state

- wide regionalization is re quired.
Notes P 61: The statement that bioregions were not sufficiently homogeneous with regard to nutrient concentration has no backup. What were the criteria for homogeneity and why? The alternatives based on a slew of variables are not defined well nor is a justification provided for their use. How will the disparate regionalizations between N and P driven be reconciled to each other and to the biogeography? Or will they? Does the biology reflect the nutrient regionalization(s)? TN or TP or whatever is limiting? This would have been an interesting analysis

- there is more to regionalization than classifying based on nutrient levels as surely the authors understand. How will the regionalization be connected to the criteria formation? This is not des cribed in this section although it may be referenced in other parts of the document. Itwould be useful to understand how the regionalization will be incorporated into the overall process of criteria development here as part of the chapter describing the classification framework itself.5. Chapter 6. Please evaluate the stressor
- response approaches for numeric nutrient criteria

development.

a. Please provide any additional approaches or methods that could use the available data to derive numeric nutrient crite ria. b. Can the stressor
- response approach, as described, dependably correlate in
- stream nutrient concentration with measurement of biological condition at the same place and time? What else may need to be considered? c. What issues need to be considered when s tressor
- response based criteria are applied across the regionalization scheme presented in Chapter 5 (or other an alternative scheme)?



### Reviewer 1 As mentioned above, and the conclusions of Section 6, other factors (pH, color, canopy

cover, stream velocity, water color and aquatic plant abundance) appear to be driving the biological responses of rivers more than nutrient concentrations. However, fish and aquatic bird’s abundances in a wide range of rivers are directly related to nutrient concentrations , so the basic productivity of rivers is still functioning similar to lakes. Therefore, I feel the best approach to evaluate biological stressor

- response is to make sure to separate streams into ecoregions based on geology, hydrology and physiography then deve lop the best models relating biological measures to physical factors of the stream and compare the residuals of these models to nutrient concentrations within ecoregions. Hoyer, M. V., and D. E. Canfield Jr. 1991. A phosphorus

- fish standing crop relationship for streams. Lake and Reservoir Management 7: 25

- 32. Hoyer, M. V., S. K. Notestein, T. K. Frazer, and D. E. Canfield, Jr. 2006. Bird density, biomass, and species richness on five Florida coastal rivers, with comparisons to Florida lakes. Hydrobiologia. 567: 5

- 18.



### Reviewer 2 Chapter 6

As I indicated earlier, using benthic taxa to assess nutrient impacts can at best provide partial guidance. However, I agree that there is a general trend of negative responses to increasing TN and ammonium. To strengthe n this point the authors need to add to Figure 6

- 1 the r2 and p values, so the reader can see the individual statistics associated with the relationships (and see if they are indeed statistically significant). I also have a question regarding the first p aragraph on page 73

– why would % very tolerant taxa show an adverse response to increasing N? To the point of alternative techniques, there are a couple of approaches that I have found useful. In addition to searching for nutrient criteria, it is useful to determine nuisance levels of periphyton biomass that can afflict streams. Dodds et al. (1998) analyzed data sets from several hundred streams for nutrients, benthic chlorophyll and planktonic chlorophyll using a frequency distribution approach and divi ding the sets into lower, middle and upper thirds, with the dividing line of the lower two thirds the border between oligotrophic and eutrophic streams, and the middle

-upper dividing line being the border between mesotrophic and eutrophic streams. Table 1 of that paper

### 21 provides the suggested boundaries for those parameters. A follow

-up paper (Dodds et al. 2002) utilized worldwide data sets and both parametric and non

-parametric statistics to analyze stream data and found significant relationships between N and P and mean and maximum chlorophyll a (benthic). They also provided breakpoints (Table 6 of that paper). While these papers utilized data from northern streams in and outside the US, Florida appears to have a significantly large data set to utilize these techniques (both as a whole and by individual ecoregion) as a complement to the already

-utilized approaches they have taken. By the way, those authors (as well as others such as Eugene Welch) consider benthic chlorophyll a concentrations of 100

- 150 mg/m2 to be nuisance levels of benthic algal biomass. Dodds, W.K., J.R. Jones and E.B. Welch. 1998. Suggested classification of stream trophic state: distributions of temperate stream types by chlorophyll, total nitrogen, and phosphorus. Water Research 32: 1455

- 1462. Dodds, W.K., V.H. Smith and K. Lohman. 2002. Nitrogen and phosphorus relationships to benthic algal biomass in temperate streams. Canadian Journal of Fisheries and Aquatic Sciences 59:865

- 874. Another approach that would certainly provide an additional basis for determining stream nutrient criteria would be nutrient addition bioassays conducted on stream water for various ecoregions. We have done so in North Carolina Coastal Plain streams that are heavily colored, and have utilized both pristine and impacted systems (Mallin et al. 2001; 2004). We utilized response variables including chlorophyll a (planktonic), bacteria counts, ATP, and biochemical oxygen demand (BOD5 and BOD20). Our results found breakpoints for nitrogen (either nitrate, ammon ium , or urea) between 200 and 500 ppb, above which there was significant phytoplankton growth and consequent significant BOD increases. We also found no significant algal response to phosphorus inputs, but significant bacteria and ATP responses to P loadi ng above 500 ppb (and significant BOD responses)

– see Mallin et al. (2001; 2002 and 2004). Thus, the response to N by phytoplankton chlorophyll a seen by the Florida DEP statistical analysis in the more colored streams is not all surprising to me. It is important to note that phytoplankton can utilize organic N as well as inorganic N; organic N (such as urea) is characteristic of waste from cattle feedlots and grazing areas, which are abundant in Florida. An additional point is that there are heterotrophi c responses to nutrient loading that are not usually measured or even considered. Our streamwater bioassays found significant stimulation of BOD via the indirect route of N stimulation of algal loom formation and subsequent decay, as the Florida DEP also notes as a problem in this document. However, the direct impact of nutrients (especially phosphorus) on bacterial growth and BOD increases needs consideration as well, as seen in the publications listed below. Mallin, M.A., L.B. Cahoon, D.C. Parsons and S .H. Ensign. 2001. Effect of nitrogen and phosphorus loading on plankton in Coastal Plain blackwater streams. Journal of Freshwater Ecology 16:455

- 466. Mallin, M.A., L.B. Cahoon, M.R. McIver and S.H. Ensign. 2002. Seeking science

based nutrient standards fo r coastal blackwater stream systems. Report No. 341. Water Resources Research Institute of the University of North Carolina, Raleigh,N.C. Mallin, M.A., M.R. McIver, S.H. Ensign and L.B. Cahoon. 2004. Photosynthetic and heterotrophic impacts of nutrient lo ading to blackwater streams. Ecological Applications 14:823

- 838. An additional paper that delves more into the heterotrophy aspect of eutrophication is below: Dodds, W.K. 2006. Eutrophication and trophic state in rivers and streams. Limnology and Oceanogra

phy 51:671

- 680. There was a question as to whether time and place issues essentially throw a wrench in the nutrient loading and biological response paradigm. One must remember that streams are not totally “canopied” unless they are in parks and reserves. In reality streams wend their way through forests (canopied), then open farm fields (full sunlight), and road crossings (full sunlight). Thus in a nutrient

- impacted stream there will be opportunities to form algal blooms even if much of it is in a forest . As to stream discharge, while elevated streamflow will certainly suppress bloom formation, in Florida the slope of the land is extremely gentle in most areas, and elevated flows will be seen only after rain events. Thus, there should be plenty of oppor tunities for algal blooms to form in nutrient

- enriched streams. In North Carolina we have documented very dense algal blooms in blackwater streams downstream from nutrient sources, including streams that spend time in forested areas (Mallin et al. 2004).



### Reviewer 3 a) Please provide any additional approaches or methods that could use the

available data to derive numeric nutrient criteria. The regressions involving the SCI and SDI (and/or their component metrics) appear confounded by multicollinearity. Fo r the purposes of examining effects

-based relationships, NOx and ammonia nitrogen should not be combined into a single variable, as the two are measuring different aspects of the pollution gradient. Ammonia nitrogen is a marker for organic enrichment and toxicity, whereas nitrate

- nitrite nitrogen is a good indicator of nutrient enrichment from properly treated municipal effluent and agricultural pollution. NOx should be included in the regressions in lieu of other expressions of cross

- correlated nitrogen given the work presented in Chapter 4. Change point analysis along a NOx gradient should be done using the residual variation in biological metrics following regression on conductivity, color and ammonia nitrogen. The wide confidence intervals resulting from bootstrapping during change point analysis should not be construed as a limitation. Rather, the median change points found for each metric should be considered in aggregate

– do they generally fall within the same ballpark? If so, that shows a stron g signal that can be used as a line of evidence supporting criteria.
Gradient AConditionGradient B, C, etc.

### 23 Quantile regression applied to wedge

- shaped data sets should be used to identify a subset of data that is responding to a gradient of interest. The two data sets can then be compared to help understand the secondary gradients, and to perform direct gradient analysis on the data that are relatively less influenced by the secondary gradient(s).

b) Can the stressor

- response approach, as described, dependably correlate in

stream nutrient concentration with measurement of biological condition at the same place and time? What else may need to be considered? The report is vague with respect to which data are used for the SCI regressions. The sample size of ~ 75 appears rather small. Were these data collected prospectively along a nutrient gradient, randomly selected, or the result of a data cull to remove spurious sites from existing data? As described, the results add another line of evidence to the whole body of work. c) What issues need to be considered when stressor

- response based criteria are applied across the regionalization scheme presented in Chapter 5 (or other an alternative scheme)? The two issues are sample size within strata, and collecting data along a defined gr adient within strata to properly derive criteria specific to a region. Clearly, nitrogen criteria derived for a nitrogen limited region cannot be applied to a region primarily phosphorus limited as the criteria would be over

-protective. However, across r egions, states, and in disparate parts of the country, identified nutrient thresholds generally fall in the same ballpark (~ 0.02

- 0.07 mg/l TP, and ~ 0.5

- 1.0 mg/l N), such that criteria derived for one region can be reasonably applied to another if the two are relatively homogeneous with respect to parent geology.



### Reviewer 4 There is a refreshingly candid recognition that conditions in natural streams make it

difficult to elucidate dose

- response relationships in as clean a manner as would be possible in l aboratory situations. Under controlled conditions, the relationships between nutrient concentrations and biological responses have been studied exhaustively and can be defined quantitatively. Certainly, the same processes are in play in the natural envir onment, but the responses to stressors are likely to be more variable because other factors are not controlled. The increased variability does not mean that the fundamental relationships between nutrients and biological responses are no longer operative, however. Nutrient supplies set an upper bound on algal growth, for example, but the observed amount of chlorophyll often will not reach the potential defined by the nutrient supply. Nutrients control growth, but not loss factors (e.g., grazing or scouring ). In addition, growth may be suppressed by toxics, like heavy metals. This scenario, in which nutrients set only the potential for growth, is fully consistent with the wedge

- shaped relationships that appear so often in the report. At high nutrient con centrations, algal response may be high or low depending on the role that other factors, such as flow, may play in regulating algal biomass. Similarly, the SCI may be high or low at low nutrient concentrations because biological condition can be suppresse d by other factors. At thesame time, however, when nutrients are high, the SCI is unlikely to be high. Deriving dose

- response relationships from field data is a worthy goal, despite the difficulties, because they would facilitate identification of thresh olds for nutrient impairment. Do suitable applications exist for dealing with the wedge

- shaped relationships? It would be disappointing if none exists, although it would not preclude drawing on these data for confirmation of thresholds derived by other methods.



### Reviewer 5 Relationships between nutrient concentrations and various biotic parameters in the

ecosystem were developed in order to assess if quantifiable dose

- response algorithms could be used in establishing nutrient criteria. The analysis of do se - response characteristics of nutrient enrichment on macroinvertebrates, periphyton abundance and chlorophyll a concentrations yielded ambiguous results. While all analyses showed the adverse impact of nutrients on ecosystem components, the high degree o f variability in the relationships rendered the establishment of well

- constrained quantitative relationships untenable.
Itis likely that the utility of applying analysis of macro

- invertebrates in relation to nutrients to determine dose

- response curves that can be used to establish quantitative criteria is of dubious value. While impairment of a stream will undoubtedly redound through the trophic chain, looking at higher trophic levels as a first cut and as a means to determine nutrient criteria is not likely to be effective beyond its utility as a screening tool. The instantaneous effect of nutrient enrichment is felt in the microbial and plankton communities, whose impairment then links to other ecosystem components such as invertebrates. THAT component will suffer directly through a potentially long trophic chain that sometimes must pass through the detrital stage, or via negative impacts on environmental conditions such as reduced DO and changes in transparency and prey composition.

6. Chapter 7. Ple ase evaluate the Nutrient Benchmark Distributional Approach.

a. What, if any, additional measures should be considered in the selection of benchmark sites to ensure the selection of minimally disturbed sites? b. Is there anything that can address or reduce the natural variability in the benchmark distribution to enhance its representativeness for each Florida Bioregion? c. In Florida many surface waters have naturally low dissolved oxygen levels. Are there any issues to consider when including waters that experien ce naturally low levels of DO as reference streams for nutrients? d. What issues should be considered if the distribution of a reference condition parameter (e.g., total N) substantially overlaps with the distribution of that parameter in all waters of a bior egion?



### Reviewer 1 Again, I like the idea of separating the rivers into groups using an Ecoregion concept.

However, I have always had a problem with setting up reference benchmarks within regions due to the large amount of within and among variance assoc iated with any biological and/or water chemistry measurements. As pointed out above, much of this

### 25 variance is due to physical factors (color, canopy cover, stream velocity, slope, mean depth etc..) that have nothing to do with anthropogenic impacts. The se lection process Listed in Chapter 7 could cause the elimination of lakes from the data base that are truly not impacted and it could also cause the selection of rivers that are unique and not really representative of the individual Ecoregion. For this sect ion, I would recommend an approach of modeling what factors account for the most variance in biological measures and nutrients concentrations within individual Ecoregions and the plot the residual against measurements of potential of anthropogenic impacts (LDI). Any relations or break points between the residuals and measures of potential anthropogenic impacts may help point to a nutrient standard.



### Reviewer 2 Chapter 7

Please define WBID up front in this chapter I am extremely impressed by the way DEP has gone about choosing reference sites for nutrient criteria. It was a multifaceted approach utilizing LDI, 303(d) list, the proposed N criteria, aerial photos, site visits, statistical analysis, and expert opinion. I can think of nothing that would improve upon their selection process. As to natural variability in a benchmark stream, one aspect that may not have been considered is tidal action in freshwater streams. In the Coastal Plain, streams even 20 miles inland can move with the tides, so sampling at a given tidal stage (say mid

- tide outgoing) can reduce any variability from that source. The question about naturally low DO values is interesting. The Coastal Plain in NC, SC and GA has numerous blackwater streams that have naturally low pH and low DO. This is due to their draining extensive swampy areas where the water is in contact with organic sediments and bacterial action, which draws down the DO; thus the water entering such streams already has low DO. Additionally, these streams receive copious i nputs of DOM from the watershed, which is essentially food for bacteria, which then impart a BOD on the water. In unimpacted waters there are healthy animal communities that are adapted/evolved to situations of pH of 3

- 4, and DO of 4.0 (LMB fishing can be quite good!). Thus, these streams should not be excluded from use as benchmarks; in fact, their inorganic nutrient levels are usually quite low (the majority of their nutrient load is in the refractory organic form).



### Reviewer 3 a) What, if any, additional measures should be considered in the selection of

benchmark sites to ensure the selection of minimally disturbed sites? The methods used to identify, screen, cull and eventually select benchmark sites were rigorous and sound. b) Is there anything that can address or reduce the natural variability in the benchmark distribution to enhance its representativeness for each Florida Bioregion? The real question is what steps can be taken to understand the variability inherent in natural systems. With respect t o nutrients, some of the benchmark sites have relativelyhigh nutrient concentrations co

- occurring with good biological condition. Yes, that is in keeping with physically intact systems having a higher assimilative capacity than degraded systems, or syste ms overly taxed. A careful examination of the sites where good biology and high nutrient levels intersect should be done with an eye toward identifying mitigating factors like canopy cover, local stream gradient (i.e., slope), substrate composition, the f orm of nutrient resulting in the high concentration (e.g., wetland

- derived nitrogen vs. nitrate from groundwater), etc. That information would then aid in interpreting data from all sites. c) In Florida many surface waters have naturally low dissolved oxygen levels. Are there any issues to consider when including waters that experience naturally low levels of DO as reference streams for nutrients? The daily range of DO is the key to understanding nutrient enrichment. For streams with naturally low DO (blackwater streams), the DO per se does not define the reference condition. In those cases, high DO concentrations during the day may signal enrichment. d) What issues should be considered if the distribution of a reference condition parameter (e. g., total N) substantially overlaps with the distribution of that parameter in all waters of a bioregion? I simply cannot emphasize strongly enough the need to examine the distributions of nutrient concentrations within categorical ranges of the SCI (o r some other biological measure/metric) for benchmark sites and for all sites by region.



### Reviewer 4 Considerable effort has been applied to the task of screening benchmark sites. The

steps seem reasonable in general. Exclusion of sites on the basis of a nitrate threshold seems like a clever basis for identifying far

- field effects transmitted via groundwater, although setting the threshold at 0.35 mg/L presumes adoption of the proposed criterion. The exclusion of sites with SCI <40 reflects the assumptio n, already mentioned above, that impaired equals “not reference.” Perhaps this is a trivial matter with regard to the number of sites excluded. I have reservations about equating “representativeness” with a minimization of variability in the benchmark se t. It seems to suggest that an “ideal” number exists for reference, rather than a range. Very strict criteria have been used to select those sites that are minimally disturbed. In addition, sites were excluded when nutrient concentrations were “outliers .” While it is true that these procedures reduce variability, it is not a foregone conclusion that they improve the representativeness of the remaining sites. Exclusion of nutrient outliers is troubling because it seems contrary to the following statement on page 85: One disadvantage of using the benchmark approach is that it does not identify the specific nutrient levels at which biological impairment occurs. For this reason, it cannot be concluded a priori that adverse effects on aquatic life actually occur at concentrations above these values. The rigorousness of the benchmark screening process leads me to believe that all

### 27 nutrient concentrations observed at the benchmark are fully protective of the use. Consequently, it causes me to wonder why the i mpairment should not be set to the concentration that represents an outlier with respect to the benchmark distribution. The final question on the Technical Charge is not a topic addressed explicitly in the chapter, but it is an interesting issue (if I und erstand it correctly). When there is substantial overlap between distributions of TN (for example) at reference sites and at all sites in the bioregion, there are two obvious interpretations

– most sites are close to reference conditions, or undisturbed h as given way largely to minimally disturbed. In either case, it undermines the statistical distribution approach to characterization of reference conditions based on a percentile of all sites. In the present situation, given the rigorousness of the proce ss to select nutrient benchmark sites, it would be logical to conclude that most sites in the region were in attainment.



### Reviewer 5 The crux of the document for establishment of nutrient criteria is embedded in this

chapter, where DEP advocates an explici t recommendation to utilize the benchmark approach in lieu of the dose

- response approach in the establishment of specific nutrient criteria for Florida’s inland waters. The dose

- response analysis, described in Chapter 6, was insufficiently robust to devel op a quantitative nutrient criterion for either N or P. Consequently, an analysis of the site distributional approach was undertaken. An elaborate screening protocol is described for winnowing available sites to benchmark pool. Though some assumptions c an be questioned, the overall impression is of a conservative approach, ensuring a valid list of candidate datasets with which to establish minimally impacted benchmark sites. The lowest SCI scores for the benchmark sites with respect to N and P concentrations show no dose

- response relationship between nutrients and SCI. Florida DEP considered using 75, 90, 95 and 99 percentiles of benchmarks, with adjustment for nutrient region, for use in setting numeric nutrient criteria for TN and TP, settling on the 90 th percentile. The strengths of this recommendation include: General applicability, standardization, speed. Weaknesses include: Lack of mechanistic understanding of processes underlying the patterns, Lack of predictability, lack of inclusion of far fi eld effects downstream as (described in analysis of Chapter 8). The proposed N and P criteria selected are supported by a significant amount of underlying analysis and are credible options as a first

- cut. Continued assessment of the effectiveness of thes e criteria through a variety of standardized performance measures is critical in determining their validity. These performance measures are not considered in this document and it is a recommendation that a rigorous protocol of evaluation be implemented.

7. Chapter 8. Please evaluate the reliability of the Nutrient Longitudinal Study to protect the aquatic life use downstream and whether this approach can be applied to other estuaries or lakes in Florida?



### Reviewer 1 This nutrient longitudinal study focus es on only nutrient concentrations and not nutrient

loads. Upstream concentrations have little to due with the whole load to Deadman Bay or Waccassassa Bay, which could potentially change chlorophyll and thus water clarityin the Bays potentially impacting the important grasses. Adding the data that has already been collected to discharge values and using the Vollenweider approach described in Section 14 would allow the prediction of the change in the nutrient concentration of the river needed to a signific ant change in the bays. As mentioned above, this approach has been extremely successful in lakes (Bachmann and Canfield 1981) and shows great promise in Estuaries (Meeuwig et al. 1998; Meeuwig 1999; Meeuwig et al. 2000). Canfield, Jr., D. E. and Bachmann, R.W. 1981. Prediction of total phosphorus concentrations, chlorophyll a , and Secchi depths in natural and artificial lakes. Can. J. Fish. Aquat. Sci. 38:414

- 423. Meeuwig, J. J., J. B. Rasmussen, and R. H. Peters. 1998. Turbid waters and clarifying mussels : their moderation of empirical chl:nutrient relations in estuaries in Prince Edward Island, Canada. Mar. Ecol. Prog. Ser. 171: 139

- 150. Meeuwig, J. J. 1999. Predicting coastal eutrophication from land

-use: an empirical approach to small non

- stratified estuaries. Mar. Ecol. Prog. Ser. 176: 231

- 241. Meeuwig, J. J., P. Kauppila, and H. Pitkanen. 2000. Predicting coastal eutrophication in the Baltic: a limnological approach. Can. J. Fish. Aquat. Sci. 57: 844

- 855.



### Reviewer 2 Chapter 8

Florida DEP conducted the longitudinal study in naturally phosphate

- rich river basins to assess whether nutrient concentrations representative of the upper portion of the benchmark site distribution were protective of the designated uses of the downstream (estuarine) waters. Samp lings were performed for a variety of standard physical, chemical, and biological parameters, and they were performed at the sites during the same day, which is an appropriate approach to reduce intraday variability. Whether it was winter or summer, the r esults showed no algal blooms, low to moderate nitrate concentrations, low TSS, low turbidity, normal Secchi depths, and with a couple of exceptions, generally good dissolved oxygen levels. As noted the benthic communities were in good shape, and periphyton coverage was no problem. TN was either lower than or average compared with moderate sized rivers elsewhere. Historical trend lines did not appear to show any concerns, except for an apparent increase in TN in the Waccasassa River over time

– which di d not translate into increased chlorophyll a . The estuarine chlorophyll a concentrations were not at levels that would be a problem to estuaries in general, and the seagrass beds, while the seagrass coverage appeared to be robust. I would concur with the conclusion that the estuaries are not being adversely affected by the (generally) naturally high TP concentrations in the headwaters. This should be an appropriate tool to help assess baseline concentrations and affects in other estuaries and lakes in Fl orida.



### Reviewer 3 Itis important to describe relatively intact systems as basis for comparison with those

more disturbed, and from that standpoint, this chapter has value. As a standalone, however, this chapter offers little insight. It would be really helpful to meld the results of Chapter 8 with those of Chapter 14, including doing a model of nitrogen loading for the Waccasassa and Steinhatchee estuaries for comparison (and validation) to the others

### 29 presented in Chapter 14. Similarly, a description o f the condition of seagrass beds in the estuaries listed in Table 10 in Chapter 14 should be compared to those for the Waccasassa and Steinhatchee for context.



### Reviewer 4 The longitudinal study seeks to demonstrate “proof of concept” by showing no adverse

effects in the estuary when tributary streams meet benchmark nutrient conditions. Although the longitudinal studies showed that the two rivers and two receiving estuaries are minimally disturbed, I would hesitate to conclude that they constitute proof of concept. Criteria for each water

-body type would likely be based on concentration thresholds, but the concentration in the stream alone does not translate directly into the concentration expected in the estuary (or lake). Mass transport and the hydrauli c properties of the estuary (or lake) also would be needed to make such a prediction.
Itdoes not seem practical on a statewide basis to derive stream criteria that are uniformly protective of uses in every estuary. Large differences among estuaries in hy draulic properties, for example, would preclude simple application of the same stream criteria everywhere (least common denominator?). Conversely, there is no reason to assume that all streams are in attainment just because they terminate in an estuary th at is in attainment. Criteria should be set separately for streams and estuaries (or lakes) to be protective of uses in each system. The TMDL process is well

- suited to the task of reconciling situations where the stream is in attainment, but the estuary d ownstream is not. There is no reason to try to preempt that process.



### Reviewer 5 Downstream reaches (streams and estuaries) are the ultimate recipients of watershed

nutrient inputs and are usually the most susceptible waterbodies to loadings, despite the often attenuated nature of the upstream loads of constituents. They are also most complicated due to geochemical interactions, the heterogeneous nature of physical forcings, differences in water residence times, nutrient turnover, nutrient mass balance ch aracteristics, differences in biota and biological processing. This chapter describes what purports to be a pilot study of the nature of upstream nutrient effects on downstream estuaries. The window on the subject is somewhat limited here as the two estu aries selected are in the same geographic area, the same bioregion, the same nutrient region, subjected to similar loadings, low levels of nutrient impact (meaning little elucidation of nutrient processing), generally similar processes and biology, and a l imited timeframe of analysis (two samplings in 2008 and 2009). In fact, the study is attempting to show that the presence of unspecified seagrass and existence of an unspecified fishery of indeterminate province proves that the upstream benchmarks are pro tective of downstream waters. The analysis is minimal in the extreme. The supporting evidence of an unimpacted fishery, its description or its history is non

- existent. There is no exposition of the type of seagrass in the downstream receiving waters, the SAV density, condition, its antecedent history, or documentation of any change over time. A fruitful dataset to mine for additional analysis along these lines would be that of the Tampa Bay seagrass restoration program (e.g. Greening and Janicki, 2006 ). Still, there is the fact that SAV found downstream of a benchmark concentration isencouraging. Such assessments might be considered more a screening tool

- if there is impairment in the downstream estuary, upstream protective action must be taken; i f there is no apparent impairment, further assessment may still be required to truly comprehend the effect of upstream impacts on downstream communities and ecosystems. The conclusion that the benchmark is protective appears accurate as far as it goes, but there are many factors, assumptions and questions that remain untested by this pilot study. The fact the chlorophyll a increased at every station in the downstream direction is noteworthy. The high concentrations of organic compounds observed and hypothesized as being derived from exports from surrounding marshes gives a sign that nutrient transformations in the watershed are a potential source and nutrient spiraling may generate unanticipated loads of transformed species (organic N such as humics, urea , ammonium) with varying bioavailability that can and will cascade through the ecosystem in unpredictable ways. Marine end member nutrient subsidies provide additional inputs to estuaries that also must be accounted when determining whether impairment d ownstream might result from inputs upstream. A nutrient that may be limiting in a freshwater spring may not be in the downstream receiving water body. General understanding of estuarine circulation and coastal water mass transport, if not outright circul ation modeling, will be required in many cases for true assessment of nutrient fate and transport and downstream effects. Furthermore, as with interpretation of any of these studies, the non - linear response of downstream systems to upstream inputs may res ult in rapid crossing of thresholds or tipping points earlier in the nutrient loading trajectory than expected. Caution must be applied in interpreting the results of such underspecified analyses in two of the most unimpacted streams in the state. Appl ication of this analysis to lakes bears the same caveats. Each distinctive water body (stream, lake, estuary, spring, river) should be assessed in its own context for response to nutrient criteria.

8. Chapter 9. Please evaluate the methods for developing chlorophyll a numeric nutrient criteria for lakes.

a. Please provide any additional considerations which might provide support for numeric nutrient criteria development.



### Reviewer 1 The trophic state scale as originally defined is a gradient without a real b reak point so I

have always had difficulty with one individual chlorophyll number as a standard. The standards that are being proposed are reasonable and I appreciate the groupings by color and specific conductance. As mentioned above, color can become a p roblem with this proposed chlorophyll standards because with one rainfall color can change from low to high with one rainfall shifting the chlorophyll standard from 10 to 20 μg/l which is a huge difference. Using specific conductance to get at differences based on geology is conceptually a good idea but there are many lakes in Florida near the coast that have high specific conductance because of saltwater interferences (e.g., Walton County Dune Lakes).

### 31 The proposed chlorophyll standards also do not take in to account the abundance of aquatic plants within individual lakes. Lake with abundant aquatic macrophytes will maintain low chlorophyll levels. However, if the macrophytes are controlled or die naturally that same lake will have much higher chlorophyll le vels. This needs to be accounted for in any type of chlorophyll standard. Getting back to the original purpose of setting standards, keeping waters fishable and swimmable for the future, almost all of Florida’s exceptional fishing lakes would have chlorop hyll concentrations exceeding 20μg/L making them impaired on paper. This is one reason why I mentioned in my general comments that Florida Fish and Wildlife Conservation Commission needs to be involved with setting nutrient standards. The approach I like the most that was reviewed in the document is the one taken by Alabama of maintaining the existing condition. Several studies (Knowlton et al 1984; Terrell et al. 2000) have calculated normal background variance of chlorophyll in lakes and they are all qui te similar. Taking the abundant long

- term data that is now available and defining normal background variance would be a good way to setting a chlorophyll standard. This would require constant monitoring of lakes but any lake that has an annual mean exceeding the normal background variance could be defined as not meeting use. The monitoring would be expensive with state biologists but volunteers in Florida LAKEWATCH have cost effectively been measuring chlorophylls for over 20 years so it could be accomplish ed on a large scale. Knowlton, M. F., M. V. Hoyer, and J. R. Jones. 1984. Sources of variability in phosphorus and chlorophyll and their effects on use of lake survey data. Water Resources Bulletin 20: 397

- 407. Terrell, J. B., D. L. Watson, M. V. Hoyer, M. S. Allen, and D. E. Canfield Jr. 2000. Tem poral water chemistry trends (1967

- 1997) for a population of Florida waterbodies. Lake and Reservoir Management 16: 177

- 194.



### Reviewer 2 Chapter 9

I appreciate the use of the variety of approaches DEP has taken in devising the proposed lake chlorophyll a thresholds. They have adapted the TSI to Florida’s rather unique situation of lakes to properly account for colored waters interference with Secchi depth measurements, and incorporated rather conservative N/P r atios to devise their TSIs. As to the use of paleolimnological studies

– I am not a fan of their use to set numeric criteria. While they can provide some excellent information on past histories of large systems such as Chesapeake Bay, and provide strong evidence for pollution episodes (metals in cores) and species changes, I do not feel their level of historic specificity is clear enough for setting these criteria. I do feel that expert opinion supports the 20 μg/L criterion, though. As to biological re sponses, there is something that DEP should consider both as a potential reason for chlorophyll a use as a response variable, and impacts of increasing chlorophyll a concentrations. This would be the impact of chlorophyll a on biochemical oxygen demand (B OD5 and longer

- term, perhaps BOD20). In a selection of Coastal Plain waters (urban lakes, urban streams, estuarine tidal creeks, and a largeriver) Mallin et al. (2006) found strong correlations between chlorophyll a concentrations and BOD levels. I assume that Florida DEP has a rather robust BOD data set and perhaps they could produce regression equations for BOD as a response variable to chlorophyll a (or, for that matter, examine the use of BOD as a response variable to N and P concentrations). BOD is more closely linked to hypoxia than is chlorophyll. Mallin, M.A., V.L. Johnson, S.H. Ensign and T.A. MacPherson. 2006. Factors contributing to hypoxia in rivers, lakes and streams. Limnology and Oceanography 51:690

- 701.



### Reviewer 3 Chapter 9 is essential ly a heuristic exercise, but a presentation of how the equations

listed on page 126 were derived (scatter plots, statistical output, etc.) would have been helpful. Presumably these are based on regressions using data from the 313 lakes referred to on the same page. Otherwise, the information present has value in that it shows convergence across regions and studies, thereby strengthening the target criterion of 20 ug/l chlorophyll a
. The section relating cyanobacteria abundance to chlorophyll a levels off ered little towards understanding effects of nutrient enrichment. It simply argues that maintaining existing conditions, will, in general, prevent HABs. A better approach would be, where data are available, to look at trends in cyanobacteria abundance ov er time for selected lakes where nutrient concentrations have increased. a) Please provide any additional considerations which might provide support for numeric nutrient criteria development. The results from Chapter 9 should be melded with those f rom Chapter 10. Specifically, for lakes where the LVI was scored, the TSI should be calculated, and the scores regressed against each other. That might show a significant change point in the LVI in relation to the TSI, thus bolstering both indices as eff ects

-based outcomes.



### Reviewer 4 Florida has already developed a proposal for chlorophyll criteria in lakes, and the

chapter summarizes multiple lines of evidence in support of those criteria. The development of lake criteria benefits from long experience is assessing lake water quality. Past assessments have focused largely on trophic state using a Trophic State Index (TSI). Carlson’s original concept for a TSI was modified by substituting nitrogen for Secchi depth and by averaging the three component i ndices. Although Carlson did not recommend averaging component indices, it is not without precedent. The use of a TSI for criteria development is practical, especially when there is a strong interest in supporting fishery yield (to the extent that fisher y productivity is related to trophic state). Six lines of evidence were examined in the chapter. The conclusion is drawn that they “converge to support the Florida IWR TAC’s original recommendation that 20 μg/L of chlorophyll a in colored lakes is protec tive of designated uses.” All approaches are not necessarily mutually compatible, however. a.) Florida is fortunate in dealing principally with natural lakes because paleolimnological studies can be used to good advantage. These studies suggest that at

### 33 least some Florida lakes have always been relatively productive. If some lakes were productive prior to human disturbance, it argues for caution in the application of a reference distribution approach, wherein low productivity is presumed to reflect minimally disturbed conditions. b.) It is not clear what role expert opinion (i.e., what other states have done) should play in view of the other options available, unless it is a matter of seeking reassurance in similar conclusions. c.) Biological response i s clearly a desirable approach, and several states have presented ideas. Minnesota has probably done the most in this regard. [Note that, the information attributed to Colorado is mistaken because no proposals have been made yet for nutrient criteria.] Criteria developed for fishery support may not be uniformly compatible with all uses in other states. d.) User perceptions would seem to be a good basis for defining thresholds for aesthetics in particular, but work in Texas suggests that “acclimation” of the observer may affect perceptions. 2 One of the difficulties in considering criteria simultaneously for fishery support (likely to be on the high side of chlorophyll) and user perception (likely to want clearer water) is the potential for objectives to be in conflict. What approach would Florida take to balance fishery and aesthetic considerations if these were found to be in conflict? e.) Maintenance of existing conditions can be a strong approach for setting thresholds in situations where there has b een a relatively long history of data collection and conditions have remained relatively stable. Generally, this would be more applicable to site

- specific criteria development for a single lake where it might be practical to assume that uses are being met currently. It is difficult to see how it would address use protection on the statewide level. f.) The reference approach is mentioned only briefly in the chapter. Supporting materials show that much effort was invested in this approach, which also prod uced recommendations for nutrients and transparency. However, as mentioned above, development of criteria with this approach would have to be reconciled with the paleolimnological information. The connection between chlorophyll and toxins produced by cyanobacteria is examined in some detail because of the proposed magnitude of the chlorophyll criterion. An annual average chlorophyll concentration of 20 ug/L creates a measurable risk that one or more instantaneous values might exceed the World Health Organization’s moderate risk threshold of 50 ug/L. Previous studies have shown a tendency for cyanobacteria to become the dominant phytoplankton at higher chlorophyll levels. Under the circumstances, it was prudent to address the issue in the criteria develo pment process. Evaluation of data from a large set of lakes dispelled this concern.



### Reviewer 5 This chapter discusses the history and background of the derivation of trophic state

indices for lakes that have been used in Florida and several lines of evid ence for the established chlorophyll a standard for lakes. Paleolimnological studies indicate that some lakes in Florida have had naturally high chlorophyll a levels even prior to human habitation, around the currently established standard threshold of 20 μg/L. This is consistent with paleologic evidence from the region arguing for establishment of a chlorophyll a threshold around that range. Certain colored lakes had even much greater concentrations several times higher which supports the application of site specific

2 http://www.twca.org/downloads/report/report_no_appendix.pdf ; see Conclusions.alternative criteria (SSAC) for lakes that warrant a deviation from a lower criterion. Biological responses of macroinvertebrates and fisheries have been investigated but so far have not proved useful as ecological attributes for specifying nutrient criteria. Based on these and several additional lines of evidence including user perceptions and threshold for maintaining existing conditions, DEP has settled on a chlorophyll a threshold of 9 μg/L for clear lakes and 20 μg/L for high conductivi ty lakes. These are reasonable thresholds given the lines of evidence presented. In the absence of sufficient data, DEP has proposed to use the 90 th percentile of reference conditions for nutrient criteria. This is also a reasonable alternative but the evidence for its use is not presented in this chapter.
Notes p. 124: Note misleading sentence structure: Florida lakes do not have cool

- water fisheries (true) but do have oxygenated hypolimnia (contrary to the implication).

9. Chapter 10. Please evaluat e the methods for developing chlorophyll a numeric nutrient criteria for lakes based on stressor
- response analyses.

a. Please provide any additional considerations which might provide support for numeric nutrient criteria development. b. Please evaluate the pro posed classification and sub
- classification approach for lakes.



### Reviewer 1 I mentioned above problems with the LVI and that naturally occurring gradient like pH

and nutrient concentrations that are impacted by geology are related to the LVI. Therefore, I am

glad to see the Section 10 suggests that nutrient relations with LVI are not robust enough to be used here to determine nutrient standards. If chlorophyll standards are set at 9 μg/L for clear waters and 20 μg/L for colored and highly conductivity clea

r lakes them the modeling conducted in Section 10 is done well and correctly. The corresponding nutrient standards would reflect the set chlorophyll standards. I am concerned and not sure we have the ability to easily classify lakes into the color and/or c onductivity groups that are being recommended. For sure, using color data Lake Okeechobee as any kind of a model for other lakes in the state is not appropriate because there are no other lakes in the state like Okeechobee. Using 40 PCU as the cut off for colored and clear lakes can be a difficult boundary to really define. For example, Grasshopper Lake in Lake County Florida would be classified as colored for 4 years and clear for 4 years between 2000 and 2008 (Figure 1). Florida LAKEWATCH has color data o n multiple lakes that show the same kind of difficulty. Additionally, 18 coastal dune lakes in Walton County Florida (Hoyer and Canfield 2008) show data where the lakes would be classified as low conductivity and/or high conductivity depending on the year data are collected (Figure 2). I feel much more work needs to be done with long

- term data to better define the lake groups based on color and conductivity.

### 35 Figure 1. Relationship between color and date in Grasshopper Lake, Lake County Florida between 200 0 and 2008 (Florida LAKEWATCH, unpublished data).Figure 2. Relationship between salinity and date in Alligator Lake, Walton County Florida between 2003 and 2008 (Florida LAKEWATCH, unpublished data). Hoyer M. V. and D. E. Canfield, Jr. 2008. Findings f rom workshops on citizen’s concerns regarding the future management of Walton County Coastal Dune lakes. Report to Chactawhatchee Basin Alliance and Coastal Dune lakes Advisory Board. Florida LAKEWATCH, Department of Fisheries and Aquatic Sciences, Univers ity of Florida/Institute of Food and Agricultural Sciences. Gainesville, FL.



### Reviewer 2 Chapter 10

Macrophyte analysis

– the lack of a strong correlation between nutrients and macrophyte coverage is not at all surprising to me. Even at log scale there i s a remarkable amount of scatter in the plots. As alluded to earlier in this review (Chapter 3) invasive macrophyte species do not need high nutrients to overtake a water body; just a lack of natural grazers and competitors. Additionally, as pointed out in this chapter, emergent or otherwise rooted macrophytes draw mainly upon soil nutrients to sustain the, which would not be reflected in the water column nutrient concentrations. One further note on this: on page 135, line 5; it states that lake vegetati on exhibited a significant adverse response to nutrients. Actually it was a positive response (though weak). Chlorophyll a analysis

– The DEP has analyzed a robust data set to draw its chlorophyll

- nutrient responses, and I agree that yearly averages are appropriate. Unlike

### 37 in northern states, blooms can occur is spring and fall in Florida lakes (they can do so as well even in the Carolinas). The response relationships are strong and little scatter is present on the regression graphs. I am also pleased with the way DEP has broken out the colored lakes by degree of color. It is evident that in highly colored systems there will be a dilution of the regression strength with less available light. That having been said, highly colored lakes can and do suppo rt algal blooms, especially the shallow lakes that characterize much of Florida. While applying the criteria for the moderately

colored lakes to the highly colored lakes may be considered by some a bit overprotective, I support this approach, having seen dense blooms in colored lakes in the Carolinas. I am pleased with the use of 20 ug/L of chlorophyll a for colored lakes and for the clear but high conductivity lakes. However, I feel that the 9 μg/L response criterion for the clear, low conductivity lake s is too high. These systems are really gems that need stricter protections. I have been in them and, while their biotic purposes may be protected by 9 μg/L, their aesthetic ones may not be. For a large

- scale example of what I am getting at we can look to Lake Tahoe, once one of the clearest lakes in the world but now inexorably becoming more eutrophic due to land development along the shoes and airborne N. I also wish to note that, on a worldwide scale, Wetzel (2001) Table 13

- 18, uses a mean of 1.7 μg/L with a range up to 4.5 μg/L for his definition of oligotrophic lakes. So I would favor a chlorophyll a response criteria of 5 μg/L for clear, low conductivity Florida lakes. Wetzel, R.G. 2001. Limnology: Lake and River Ecosystems , 3 rd Ed. San Diego, Ac ademic Press, 1006 p. The attempt to determine a relationship between chlorophyll a and the percent of cyanobacteria dominance is interesting. I surmise that it was not particularly successful in that cyanobacteria respond strongly to physical factors as well as nutrients

– by that I mean that cyanobacteria are adapted to the warm waters and high sunlight that characterizes so many Florida lakes. I would like to recommend DEP have a look at some work out of JoAnn Burkholder’s group at North Carolina Stat e University, in which they found that TP and chlorophyll a were both significant predictors of total cyanobacterial abundance (see Touchette et al. 2007). They also found the presence of cyanotoxins in drinking water reservoirs, and I wonder if DEP has a program to do so, and what nutrient factors these toxins may be related to. Touchette, B.W., J.M. Burkholder, E.H. Hannon, J.L. Alexander, C.A. Kinder, C. Brownie, J. James and C.H. Britton. 2007. Eutrophication and cyanobacterial blooms in run

- of

- river impoundments in North Carolina, USA. Lake and Reservoir Management 23:179

- 192.



### Reviewer 3 a) Please provide any additional considerations which might provide support for

numeric nutrient criteria development. As noted for the SCI and streams, the stresso r - response relationship between the LVI and nutrients appears to offer an additional line of evidence for identifying thresholds for setting criteria. Again, using the residuals of the LVI following regression on color and conductivity in change point analysis over a gradient of TN or TP should be tried.b) Please evaluate the proposed classification and sub

- classification approach for lakes. A separate slopes regression model would help here. Coding the three color/conductivity strata

– 1, 0, and 1, would allow one to directly compare differences between the strata in unit response of chlorophyll to nutrients, and help to evaluate the appropriateness of the chlorophyll a targets.



### Reviewer 4 The derivation of criteria by this stressor

- response anal ysis appears to aim at a tiered

approach for nutrients. If a lake is “biologically healthy” and chlorophyll does not exceed the appropriate threshold, some latitude is granted for phosphorus and nitrogen concentrations. This is a very practical way of ac knowledging uncertainty in the dose

response relationship. In the present case, however, it is not clear what action would be taken if chlorophyll is within bounds, but one or both nutrients exceed the upper threshold (lower prediction interval). There se ems to be a strong rationale in the report and in supporting documents for partitioning lakes into clear and colored categories. It is not apparent if all lakes can easily be segregated into those two groups, or if there is an unbroken continuum of lakes. Itmay be an important practical matter if two similar lakes having 39 and 41 pcu respectively might be assigned standards that differ by a factor of two. Less information is presented regarding the merits of conductance as an additional classification v ariable, although there is little doubt that higher nutrient concentrations in general would be associated with increasing solute concentrations. It might be interesting to learn more about the TAC’s reasoning regarding the 100 umho/cm dividing line, but I don’t have any particular reservations about accepting their conclusion. Using a rolling average for color seems like a very sound, if somewhat data intensive, approach. Florida presently has independent approaches for development of criteria based on c hlorophyll or lake vegetation. Are the two approaches drawing on the same set of lakes? Lakes in my area (and I believe it is true elsewhere) that have an abundance of macrophytes typically have very sparse phytoplankton populations even when nutrient co ncentrations in the water column would normally support more phytoplankton. Conversely, lakes with moderate to high levels of suspended algae rarely develop any substantial growth of macrophytes. If this observation applies to Florida lakes, it might hav e implications for the criteria development strategy. A plot of chlorophyll vs. LVI mi ght be helpful.



### Reviewer 5 The preferred means of determining a nutrient criterion for inland waterbodies is use of

a stressor

- response relationship. Florida DEP addre ssed the determination of nutrient criteria for lakes based on two response variables: lake vegetation and chlorophyll a. Both groups of primary producers are expected to respond to nutrient enrichment, but in different ways: macrophyte vegetation, generally benthic vegetation would largely be expected to decrease in response to enrichment, as a function of reduced light in the water column. This light attenuation is attributed to the increase in phytoplankton chlorophyll a that occurs with increased nutrient availability. As such, the macrophyte response is indirect

- nutrients are not affecting the plants themselves, in fact would tend

### 39 to promote increases in macrophyte growth, all else being equal. But given that most macrophyte species are generally unable to grow to the lake surface, they will be primarily impacted by the more direct response of phytoplankton growth to nutrient enrichment. As such, because it is at least the second link in this chain, any relation between nutrients and macrophytes wo uld be expected to be looser, with the degree of “play” dependent on many other factors. In fact, DEP investigated the relationship between macrophytes and nutrients and found exactly that to be the case

- using the lake vegetation index (LVI) a weak, th ough significant correlation with nutrient concentration was found. An adverse (i.e. inverse) response of vegetation to nutrients was apparent but insufficiently robust to be applicable as a basis for establishing nutrient criteria. A more effective relationship between nutrients and phytoplankton chlorophyll a was found, and produced a useful basis for establishing nutrient criteria as discussed in the previous chapter (Chapter 9). Authors recommend that the criteria be performance

-based. This is a reasonable and acceptable way to proceed

- provided that it works both ways. The recommendation of the chapter’s authors is that if nutrient criteria are exceeded but there is no exceedance in the designated response variable (chlorophyll a), then no nutri ent reductions are needed. This makes sense ecologically and from a management point of view. However and conversely, when data show that nutrients are within in compliance of established criteria, yet chlorophyll a criteria are exceeded, then one would expect that nutrient reductions would have to be undertaken. This reflects on a much larger issue that permeates this document: every one of the analyses and criteria presented are statistically

-based, usually based on a lot of long

- term monitoring data a nd a very few variables. This results in the emergence of general patterns that are accompanied by high variability. Fifty

- to

- sixty percent of explained variance is considered exceptional. The performance

-based approach proposed by DEP for lake chlorop hyll a begs the question of what is responsible for the large variability associated with all nutrient

based dose

- response relationships. The variability is a function of lake and stream physical and biological processing of nutrient inputs. The large variability of bathymetry, hydrology, physico

- chemistry, flushing, tidal signal, and biology makes one marvel that nutrient

- chlorophyll relationships are as robust as they are. Yet the refinement and true understanding of those relationships will only be ac hieved by an understanding of the processes operating within the ecosystem, their rates and the timescales of these processes with respect to the nutrient supply. This so

- called impedance matching (Ulanowicz and Hannon, 1987) is an ecosystem principle that reflects how well

- tuned a system is to its cross

-boundary flows, and that determines, in time and space, its ability to process these flows, both as inputs and export. The remainder of this sum is left within the system for a time as a stock or pool wit h which the system can push off in a variety of trajectories, depending again on internal processing. Therefore, while accepting and endorsing DEP’s call for performance

-based approach to establishment of criteria, this is a recommendation for investment in additional research into ecological relationships and evaluation of systems or classes of systems and their driving processes. Within a modicum of understanding of these mechanisms, managers will be able to make informed decisions about whether and ho w to shape the Site Specific alternatives for managing nutrients, beyond what the useful and necessary screening of blind statistical approaches provides.

### 10. Chapter 11. Please comment on the “all streams” statistical distribution approach for

deriving numer ic nutrient criteria



### Reviewer 1 Again using the Ecoregion concept to form the base for analyses is a good start that

needs to be used throughout the document. The second paragraph in Section 11 points out that “Multiple factors can strongly influence the expression of biological responses to nutrient across water bodies, such as water velocity, residence time, availability of other nutrients, presence of grazers, availability of light (due to tree canopy cover and/or water transparency) and availability of suitable habitat. I have mentioned above, that in my experience physical factors dominate most aspects of stream biology and overshadow impacts of nutrients. For this reason I have a hard time with this approach to setting standards. No matter what percentage of the data distribution you use for a standard, some streams that are meeting use and functioning fine will be considered impaired.



### Reviewer 2 Chapter 11

Florida DEP certainly has a robust “All Streams” data set with which to work. The outlier removal process could use a bit of tweaking, in my opinion. I liked that they did not use the removal of the upper adjacent value

– that seems rather confusing to me. What does concern me is using TN of 100 mg/L and TP of 15 mg/L as screening thresholds. L evels of nutrients found in raw human sewage include TN of 35 mg/L, ammonium of 15 mg/L and TP of 10 mg/L (Clark et al. 1977). Therefore, unless DEP is sampling raw sewage ditches it would be reasonable to remove outliers more in line with these concentrations that the ones DEP utilized! Clark, J.W., W. Viessman, Jr., and M.J. Hammer. 1977. Water Supply and Pollution Control, 3 rd edition. IEP

- A Dun

- Donnelly Publisher. I do have another issue with the statistical approach. DEP kicked out data when there were 4 or less observations within a year. Ho9wever, a lot of variability can occur with only 5 or 6 samples as well, both seasonal and event

- driven. I suggest drawing the line at 8 observations or less as year as a cutoff point for data sets. Natural l og transformation is proper for nutrients and chlorophyll

– my own laboratory regularly does this for our publications. Finally, the comparisons between the empirical and theoretical 25 th percentiles produced tight agreement in general. Thus, with the ex ception of the upper outliers and number of observations I am in support of this approach.



### Reviewer 3 To reiterate what I noted in the general comments, descriptive statistics are necessary

for a broad understanding of systems at the population level. How ever, the reference approach, in the absence of biological data, provides the weakest line of evidence for criteria development. The all sites chemistry data should, emphatically, be paired with biological data (i.e., the SCI, SDI, or a sensitive component metric) and reexamined within ranges of the biological data.



### Reviewer 4 The “all streams” approach has been touted by EPA ostensibly because it can be applied

### 41 to situations where dose

- response relationships are not available and reference conditions do not exist or are very scarce. However, because reference (or minimally disturbed) sites seem readily available in Florida, there is little motivation to use the all streams approach. It is not reassuring to know that “the 25 th percentile from the All Str eams data was less than the 75 th percentile ... from the Benchmark data set.” Some reference sites still will be classified as impaired.



### Reviewer 5 The All Streams approach to developing water quality criteria is an alternative

suggested by EPA for areas where data insufficiency precludes the development of specific numerical nutrient criteria for a region. For the Florida nutrient database, this is an interesting data exercise that presents an alternative benchmark for a nutrient region. The lower 25 percentile nutrient benchmarks for all streams, the TN and TP criteria proposed by EPA as the upper nutrient threshold for this analysis, represents a much lower concentration for both nutrients than the 90 th percentile reference benchmark as calculated in Ch apter 7. This is a spare chapter that presents data without significant analysis. The information presented here is lacking recommendation or interpretation. It would have been an improvement to present actual shapes of nutrient concentration frequency distributions graphically, and specifically with the two alternative approaches overlain for each nutrient for each nutrient region. The All Streams approach is presented as a fail

- safe option to criteria determination and, in the absence of more sophistic ated analyses or data sufficiency; it presents a reasonable, quite conservative stop

- gap provision. The next step that would have been anticipated was not taken here

- that is relating the nutrient thresholds as calculated using All Streams to various esti mates of stream condition as was done for the other alternatives, dose

- response and nutrient benchmark distributional approach. It was not explained why that was not undertaken, but obviously the All Streams statistical distribution approach is not being considered as an option for establishing numerical nutrient criteria for Florida (nor can its worthiness as an option be thoroughly assessed given the minimal analysis presented).

11. Chapter 12. Please comment on extrapolating background nutrient concentra tions as an approach to deriving numeric nutrient criteria.



### Reviewer 1 As the conclusion of Section 12 states, the data used in this section are too cloudy to be

of any significant use in determining nutrient standards.



### Reviewer 2 Chapter 12

I agree that candidate nutrient criteria cannot be reliably derived using the Dodds and Oakes (2004) method. A few comments on Chapter 12: 1) My Chapter 12 citations of tables and figures did not match the ones supplied. I assume Table 1 is actually Table 12

- 5, Figure 1 is Figure 12

- 3, Figure 2 is 12

- 2, andFigure 4 is 12

- 4. 2) Regarding the 9% increase between 1995 to 2004, I think we can safely assume it is due to increased landscape development (been to Gainesville lately? I couldn’t recognize the place when I dro ve through last winter....). 3) The directions of the correlations certainly are similar to what we see in the Coastal Plain of the Carolinas. TN and TP are negatively correlated with forest, TIN positively correlated with urban land and negative with wetlands, and so on. We also find fecal coliforms and TSS negatively correlated with wetlands, by the way.



### Reviewer 3 Itis a moot point. Having rigorously identified benchmark sites that are good

representations of regional background conditions obviates the need for extrapolating historic background conditions.



### Reviewer 4 Itseems unfair to say that the Dodds and Oakes method didn’t work (“candidate

nutrient criteria could not be reliably derived using the Dodds and Oakes (2004) methods as applied here w ith the available data”); it was not given an adequate test because, as stated in the report, the required data were not available. Instead, LDI scores were used in a simple regression model, from which only weak patterns were evident. The effort to deriv e background conditions based on the LDI relationship seemed perfunctory in view of the very promising results presented previously in the report. In Chapter 7 (Figure 7

- 2), nutrient export (kg/ha/y) was strongly related to LDI for the St Mark’s watershed , and background yields could have been estimated. Perhaps the results for one watershed are not replicated elsewhere, but at least the effort should have been made to explore the possibility.



### Reviewer 5 This chapter presents an interesting concept that describes modeling that enables the

back

- calculation of natural nutrient levels in unimpacted hydroscapes by extrapolating the relationship between some index of land use and water

-borne nutrient levels to the y - intercept where anthropogenic land use purp ortedly equaled zero. The authors chose the LDI (Landscape Development Intensity) index of human disturbance calculated from the area

- weighted value of land use type, because it is a standard calculation of DEP and exists for many sites in Florida. The results are predictably scattered

- there is no evidence of a clean relationship with low variance with such an exercise using an integrative parameter such as the LDI index. Nonetheless the results are intriguing and not altogether worthless. The study de sign basically assumes that inorganic N and TP are tracers for human activity, on the assumption that these constituents, particularly nitrate, nitrite and ammonium would become more part of the landscape with increasing human activity. Because organic N is produced and released in great quantities by natural forested lands and wetland communities, it is predicted to be poorly correlated with LDI. The results do show significant relationships between nutrients and LDI, and no significance between organic N and LDI.

### 43 The non

- linearity of N vs. LDI is to be expected and renders the hoped

- for linear trajectory to an intercept on the nutrient axis an unattainable goal. Nutrient releases and transformation in the landscape resulting from human impact are fraught with variability, thresholds, breakpoints, non

- linearities such that a simple linear back

projection is not realistic. The simple fact that human impact alters the system’s hydrology in unpredictable ways will create a non

- linear nutrient response. Ultimately though there are more effective ways of deriving benchmarks for nutrients in unimpacted waters that are presented in Chapters 6 and 7.

12. Chapter 13. Please comment on the use of multiple regression and statistical distribution approaches to deri ving numeric nutrient criteria.



### Reviewer 1 For reasons mentioned above, I am not comfortable with setting standards based on a

percentage of a distribution of data. There are too many lakes that are functioning well and meeting uses that will be considere d impaired. Similarly, without more work on long

- term color data in lakes, I am uncomfortable with the separation of lakes into colored and clear lakes based on a measured color of 40 PCU.



### Reviewer 2 Chapter 13

I am in agreement that large variability in chlorophyll a and nutrient concentrations renders a linear regression inefficient for this task, and that the non

-parametric model is likely to yield more relevant results. Editing remark

– page 175, middle, Figure 2 should read Figure 13

- 3 Ibelieve.
P age 182

– there are some issues with the Outliers and Invalid Data. Nitrate is kicked out if it is above 75 mg/L, yet TN is kicked out if it is above 20 mg/L

– a disconnect here. The highest nitrate I have seen in a stream is 25 mg/L (below a failing was tewater treatment plant) thus DEP needs to bring this expulsion criterion down to 20 or 25 mg/L. As to chlorophyll a , the highest level I have seen in a bloom is 400 μg/L, while DEP is using 1,000 μg/L as a criterion. I suggest cutting that way down to at least < 400 μg/L. As to Secchi depth, I am not aware of Florida lakes that are 50 m deep, so why use a Secchi of 50 m to kick out an outlier? How about 10 m? Another concern I have is determining annual averages using all available data for a given station in a year. What if it is only 3 data points? Many programs are skewed toward “growing season” sampling (admittedly Florida has a long growing season) but this would tend to skew the data for some lakes toward elevated chlorophyll in the means. I su ggest using a lower limit of 8 samples in a year to create a mean, with samples taken seasonally to collect lower

- impact periods as well.



### Reviewer 3 The multiple regression models provided in Chapter 13 offer a more refined way to

derive criteria than the conventional linear models appearing in Chapters 9 and 10, though the results from all three chapters generally comport each other. Moreimportantly, however, the results suggest that once static numeric criteria are derived for either nitrogen or phosph orus, those criteria should be interpreted as having uncertainty when applied to a specific waterbody, and therefore not applied with the traditional independent application reserved for toxicants. Figures 13

- 5 and 13

- 7 clearly show the range of potential criteria derived from a population of lakes. As with Chapter 11, the distributional analyses of data are important for understanding the system at a population level, but are not particularly helpful for deriving criteria. Again, melding in the LVI and examining the chemistry data within categorical levels of the LVI would help to lend context to the percentile ranges.



### Reviewer 4 I am not familiar with multiple logistic regression, but it seems like an innovative

analytical approach, and the graphs are informative. Placement of the diagonal line (now set to the “average ratio between ln (TN) and ln(TP)”) deserves more attention because it makes an important statement about the nutrient regime. The ratio used in the graph (0.588/0.013 = 45:1) is very h igh and indicative of a phosphorus

- limited situation. Placement of the diagonal line might be adjusted according to expectations for a particular region. For example, in supporting references for Chapter 9, an N:P ratio of 16:1 was assumed to have relevance for distinguishing between limitation by N or P. The output of the within

- lake model (Figure 13

- 2) shows the risk inherent in basing assessments solely on nutrient concentrations. Basing decisions on nitrogen and phosphorus relationships from the enti re data set would place criteria well below anything observed in the lake, even though most chlorophyll measurements in the lake are in attainment of the 5 ug/L threshold. The analysis seems to add weight to the notion that a tiered approach would be usef ul. Why are the distributional statistics for lakes determined on a statewide basis when there are identifiable geographic patterns for phosphorus and nitrogen in streams?



### Reviewer 5 Chapter 13 provides an intriguing analysis of the use of non

-parametric statistics and

Bayesian modeling techniques in establishing nutrient criteria for lakes. The analysis presents a proof

- of

- concept exercise that demonstrates how a set of TN and TP criteria mi ght be developed using multiple regression models. The results of the analysis supports an earlier recommendation in this review that within

- lake models of TN

- TP and chlorophyll a will yield the most robust results and the most likely statistical approximation of a mechanistically based cause and effect relationship.
Various aspects of the balance between site specificity, model robustness and the need for a large enough sample size to support three degrees of freedom leads to the expansion of the sample size across similarly classed lakes such that a large pool of lakes (93) can be fit to the model. It is curious that the entire pooled dataset in figure 13

- 4 shows individual lakes within the pool seem to trend to a lower slope than the slope of all pooled observations. This is not discussed in the text. Overall, the nonparametric multiple regression approach to setting nutrient criteria protective of a specific chlorophyll threshold for lakes seems to hold promise and should be further explored.

### 45 Itis of passing note that here as in other chapters, the distinctive ness of colored lakes is brought up and significant attention is devoted to incorporating terms in the model that will account for color. There are a number of colored lakes that show a negative relationship between color and chlorophyll a. While this mo st obviously may be related to light attenuation, there are other possibilities. Often the constituents of colored dissolved organic matter may be inhibitory to phytoplankton growth, and they may often act as binding or chelating agents for nutrients, red ucing bioavailability. Therefore, the complication of dose

- response mechanisms introduced by colored waters continues to plague efforts to quantify relationships with simple models.

13. Chapter 14. Please comment on the downstream protection approaches.

a. D oes the modeling approach provide a sound, scientific basis for determining numeric nutrient loadings from upstream waters to estuaries? b. Could these approaches be used to determine nutrient loadings for other waterbody types (i.e., lakes)? c. Given the availa ble information, do these approaches account for spatial variability, distance from downstream water, and estimated assimilation? d. Do you know of any alternative approaches to capturing the relationship between upstream and downstream water quality in a WQS
.


### Reviewer 1 The downstream protection approaches described in Section 14 are sound and

consistent with the conventional approach used for decades to manage eutrophication in lakes (Bachmann and Canfield 1981). While it has not been used extensively, Voll enwider type models have successfully estimated actual total phosphorus concentrations in estuaries and have tied nutrient concentrations to different land uses (Meewig et al 1998; Meewig 1999). Breaking the estuaries into watershed and measuring the actua l loads from different sources is the only way to really manage aquatic systems. Using some form of Vollenwider loading model will allow managers to pinpoint significant loads that may be causing unwanted eutrophication. One significant problem I have with Section 14 is that there is an assumption that nitrogen is the only important nutrient controlling trophic state in estuaries. In 2000 I sampled near shore coastal waters from three stations off of every Florida County that touched the ocean. These data s howed that total phosphorus accounted for significantly more variance in measured chlorophyll than total nitrogen, strongly suggesting that phosphorus in the primary limiting nutrient in near shore coastal waters of Florida (Hoyer et al. 2002). Tampa Bay i s an exception to this and nitrogen is more important there, but that is because Tampa Bay receives water from phosphorus rich soils. Therefore, the modeling efforts accomplished in Section 14 should be done using phosphorus instead of nitrogen. Canfield, Jr., D. E. and Bachmann, R.W. 1981. Prediction of total phosphorus concentrations, chlorophyll a , and Secchi depths in natural and artificial lakes. Can. J. Fish. Aquat. Sci. 38:414

- 423. Hoyer, M. V., T. K. Frazer, S. K. Notestein and D. E. Canfield, Jr. 2002. Nutrient,chlorophyll, and water clarity relationships in Florida’s nearshore coastal waters with comparisons to freshwater lakes. Canadian Journal of Fisheries and Aquatic Sciences 59: 1

- 8. Meeuwig, J. J., J. B. Rasmussen, and R. H. Peters. 1998. Tu rbid waters and clarifying mussels: their moderation of empirical chl:nutrient relations in estuaries in Prince Edward Island, Canada. Mar. Ecol. Prog. Ser. 171: 139

- 150. Meeuwig, J. J. 1999. Predicting coastal eutrophication from land

-use: an empirical ap proach to small non

- stratified estuaries. Mar. Ecol. Prog. Ser. 176: 231

- 241. Meeuwig, J. J., P. Kauppila, and H. Pitkanen. 2000. Predicting coastal eutrophication in the Baltic: a limnological approach. Can. J. Fish. Aquat. Sci. 57: 844

- 855.



### Reviewer 2 C hapter 14

14.1.5

– I am concerned about one of the statements on page 188. It states “in the absence of more specific information it may be appropriate to reduce the anthropogenic contribution of the TN load to estuaries by a constant fraction.” This is not appropriate. As is pointed out within this very chapter, Florida estuaries vary widely in their watershed/water ratios, their percent loading by individual sources, their total loads, their size, depth, flushing, and certainly their response variable s such as seagrass coverage and fisheries. So, the answer here is that if necessary specific information is not available

– DEP needs to get the funding to obtain that information. There is no “one size fits all” solution for ecological problems such as this.
14.1.18

- Another concern I have is that of the contribution of septic systems to the nutrient load in estuarine waters. While DEP certainly accounts for direct point source contributions of nutrients to estuaries in their models, it is known from research in the Carolinas that nutrients from septic systems directly enter estuarine waters as well (Cahoon et al. 2006). Especially on the west coast of Florida there are many septic systems with direct or near

- direct access to estuaries. In studies in Sarasota Bay and Charlotte Harbor it has been found that fecal microbes from septic systems enter the surface waters on the outgoing tide (Lipp et al. 1999; 2001); thus, presumably ammonium and TP will as well. This should be factored in for estuaries wh ere septic system use is prevalent. Cahoon, L.B., J.C. Hales, E.S. Carey, S. Loucaides, K.R. Rowland and J.E. Nearhoof. (2006). Shellfish closures in southwest Brunswick County, North Carolina: Septic tanks vs. storm

- water runoff as fecal coliform sources

. Journal of Coastal Research 22:319

- 327. Lipp, E.K., S.A. Farrah and J.B. Rose. (2001). Assessment and impact of fecal pollution and human enteric pathogens in a coastal community. Marine Pollution Bulletin 42:286

- 293. Lipp, E.K., J.B. Rose, R. Vincent, R.C. Kurz and C. Rodriquez

- Palacios. (1999). Diel variability of microbial indicators of fecal pollution in a tidally influenced canal: Charlotte Harbor, Florida. Southwest Florida Water Management District, Technical Report.

### 47 The tide is an important c onsideration in obtaining accurate measures of nutrient loading to downstream waters. The most accurate way of accomplishing this is by use of boat mounted acoustic Doppler current profiling (Reed et al. 2004). This process has been utilized to obtain th e most comprehensive modeling of nutrient loading, trends over time and patterns in the Neuse River Estuary to date (Burkholder et al. 2006). Additionally, in terms of spatial variability, the sampling scheme supporting that effort was able to conclusivel y show that collecting data only mid

- stream leads to incorrect loading and impact estimates. By that I mean that near

- shore sampling should be accomplished as well as mid

- stream, because due to wind, current and tidal patters some of the largest algal blo oms are found in shallower areas near

- shore. Reed, R.E., H.B. Glasgow, J.M. Burkholder and C. Brownie. 2004. Seasonal physical

chemical structure and acoustic Doppler current profiler flow patterns over multiple years in a shallow, stratified estuary, with implications for lateral variability. Estuarine, Coastal and Shelf Science 60:549

- 566. Burkholder, J.M., D.A. Dickey, C. Kinder, R.E. Reed, M.A. Mallin, G. Melia, M.R. McIver, L.B. Cahoon, C. Brownie, N. Deamer, J. Springer, H.B. Glasgow, D. Toms and J. Smith. 2006. Comprehensive trend analysis of nutrients and related variables in a large eutrophic estuary : A decadal study of anthropogenic and climatic influences. Limnology and Oceanography 51:463

- 487. Finally, I recommend that the modelers also have a look at the following paper: Ensign, S.H., J.N. Halls and M.A. Mallin. 2004. Application of digital bathymetry data in an analysis of flushing times of two North Carolina estuaries. Computers and Geosciences 30:501

- 511. This paper provides an approach that determines both flushing time of the estuary and assimilation of N within that estuary, and consequent export to sea.



### Reviewer 3 a) Does the modeling approach provide a sound, scientific basis for determining

numeric nutrient loadings from upstream waters to estuaries? The concentrations identified in Table 10 of Chapter 14 are simply an additional line of evidence that support identification of criteria. Models are abstractions and depend on the quality of inputs. The TMDLs presented appear to have been developed by adhering to good methods, and were well

- calibrated using empirical data. The approach would be more compelling if the examples for intact systems (as previously noted) were included for comparisons. b) Could these approaches be used to determine nutrient loadings for other waterbody types (i.e., lakes)? Yes, it would have been nice to see the Vollenweider example worked out for a few lakes. c) Given the available information, do these approaches account for spatialvariability, distan ce from downstream water, and estimated assimilation? I am not sufficiently familiar with the vagaries of the SPARROW model to comment on this point. d) Do you know of any alternative approaches to capturing the relationship between upstream and downstream water quality in a WQS. Short answer, no. The load

-based targets for a receiving body are the most straightforward, and defensible on an ad hoc basis. In other words, criteria derived to protect the use of a given class of waterbodies should stand unles s superseded by another need.



### Reviewer 4 The SPARROW model was designed for estimating nutrient loads, and it has typically

been applied to large regions (e.g., multi

- state). While there is no conceptual reason why the model could not be applied to lakes as well as estuaries, there may be a practical limitation to the lower bound on geographic scale. As stated in a recent USGS fact sheet 3 : In general, SPARROW models illustrate the broad spatial patterns of water quality well, but may be less accurate for a single stream because of limitations in the underlying data sets. I am not sufficiently familiar with SPARROW to know if it incorporates process (e.g., denitrification) that would be relevant to assimilative capacity. I think the larger issue concerns the extent to which this approach provides information useful to the development of nutrient criteria for streams. Some of the concerns are the same as those I cited for the Nutrient Longitudinal Study (Chapter 8). There is a fundamental question about linking attainment in estuaries with attainment in tributary streams. SPARROW provides nitrogen load estimates that are used to drive models (not presented) that predict concentrations in each estuary. It is not clear if the linkage includes contribution s of nitrogen generated by the marsh grasses within the estuary. Based on existing thresholds, conclusions are reached about total loads (and thus a flow

- weighted concentration) consistent with attainment in estuaries. In the context of the TMDL process, it looks like a reasonable approach.
Itremains a mystery how this information relates to the criteria that are appropriate for attainment in streams. Given the differences among estuaries in hydraulic conditions, for example, it is hard to imagine how generalizations can be made about the allowable load, much less the appropriate concentrations in tributary streams. Perhaps that was the motivation for the comment on page 211: Itis important to note that values derived from this approach are not applic able to protection of instream conditions or use attainment.
The section on lake modeling is so brief that it is hard to evaluate. Just like estuaries,

3 SPARROW fact sheet

– http://pubs.usgs.gov/fs/2009/3019/

### 49 there is a fundamental issue about the linkage between concentration

-based standards in lakes and in the tributary streams. Criteria are defined to protect uses in lakes; if they aren’t being met, a TMDL should be developed.



### Reviewer 5 Two potential methods are presented for assessing the “protectiveness” of watershed

nutrient criteria to downstream wate rs - estuaries and lakes respectively. The bulk of the chapter deals with a description of application of the Spatially Referenced Regression on Watershed Attributes (SPARROW) model, developed by USGS. This model is used to estimate TN loading from the watershed to the receiving estuary for 13 estuaries in the state. While the model shows promise as a tool for estimating N loads to many Florida estuaries, it is important to note that several Florida estuaries would be inappropriate as targets for SPARROW modeling. Specifically, several estuaries of the southern peninsula, such as Florida Bay, Whitewater Bay and Rookery Bay, are not amenable to analysis by the SPARROW watershed model. Large interaction of surface flows with groundwater flows, the lack of mass flow or well

- constrained point

- source input, and multiple ungauged inputs would render such modeling ineffective. There is a need also to evaluate the spatial heterogeneity of receiving waters, particularly in estuaries. The gradients that characterize estuarine systems demand that spatial analysis be performed, or at least considered, at the sub

-basin or sub

- estuary scale (Madden et al. 2008). Direct loadings from point sources in the upper estuaries render those areas different in the extreme from the lower estuary, or even mid

- estuary. Spatially complex receiving waters create complex hydrodynamic circulations, nutrient regimes and biological responses. Nutrient spiraling, airshed loading and other uncertainties will combine create complex dose

- response relationships. Adaptation of SPARROW analysis to the sub

- estuary scale is warranted. Temporal scales are also exceedingly important to estuarine processing of nutrients

- the timestep of the sampling protocol and of the analysis is critical and these need to be evaluated in the establishment of criteria. Seasonality, pulses, and low frequency oscillations, such as ENSO, will impart variability in physical and biological processing of nutrient inputs. The section describing application of the V ollenweider model to downstream lakes represents a start to the issue of protectiveness of upstream criteria inland receiving waters. There is minimal discussion of implementation presented. The model is valid for the application described

- calculation o f P loading and concentration in lakes as functions of discharge, residence time, lake volume and flow

- weighted nutrient concentration. Yet some aspects of watershed management are not adequately addressed. The total loading rate can be calculated, but the lake would be receiving loading from multiple sources, both point and non

-point. Any action taken would be dependent on the source(s) of the nutrient and a balancing of the source reductions necessary to achieve compliance. How that would be apportion ed or even determined among the sources is left for later exposition. The widening of the application from single lakes to regions of lake should be undertaken with caution. The uncertainties of the model when applied to a single lake will be amplified exponentially if broadened to groups of lakes, with the attendant issues of assigning and apportioning reduction becoming even more intractable. The protectiveness of the upstream nutrient criteria should be approached with more rigor with respect to lakes, with individual modeling efforts per lake and strict determination of the terms in the model, including sources, atmospheric deposition and processing.Furthermore, it is probable that the suggestion to address lake regions by averaging of terms across groups of lakes would generate additional uncertainty to the point where models would break down. An understanding of lake mean depth and morphoedaphic factors is necessary to completely assess the fate of P entering a lacustrine system. Biogeochemical fate and transformation of nutrients, in this case P, will be dependent on the nature of the soils and sediments, presence of groundwater seeps and nutrient inputs, presence of phosphatic rock, fluctuations in lake depth, and biological variables such as whether or not benthic vegetation is present, the presence and types of phytoplankton communities, predation and trophic interactions within the system, types of fauna present. P dynamics will also be dependent on status of other nutrients

- N dynamics an d cycling, N limitation of primary production, nitrification

- denitrification coupling (Jenkins and Kemp 1994), and C limitation of primary production. In short, simple models will work well as a primary screening tool as applied to individual lakes with well

- constrained datasets and boundary conditions but there is a large uncertainty associated with demanding too much predictive capability from them, especially when used to “batch process” the information for groups of lakes.

### 51 

## Additional Comments/Ref erences

Reviewer 1 Preface

Itis obvious that individual scientists have spent several years creating this document. This is truly a large, technical and complicated document, especially with all of the appendices, to review in a short two

- week time. I cou ld spend several months following lines of analyses and testing them with data I have available or finding other available data to test them. With that said, I will give my best general and specific comments on this document with the caveat that I could do a much better job with much more time. Additionally, in the future of such endeavors, giving reviewers much more time and even chances to question the original authors would lead to a much stronger final document.



### Reviewer 2 My Peer Review Charge has no "Specific Question 1". "Specific Charge Questions"

begin with 2. (Chapter 3). In my document Question 1 is a "General Charge Question" with three general considerations (i.e. strengths and weaknesses, validity of lines of evidence, additional technical considerations for deriving criteria) that I took into consideration throughout the document in reviewing the individual chapters. So, the general charges are addressed throughout the review, of course depending upon the contents of the individual chapter s. Overall, I am pleased that Florida DEP has spent a lot of time and resources attempting to obtain nutrient criteria. I am supportive of the majority of the techniques utilized within the document. There are a few approaches I took issue with as noted within. I have also supplied some alternatives (some which can be used in parallel) that DEP may wish to try (I have supplied references) to provide greater scientific validity to their efforts in this very important process.



### Reviewer 3

Reviewer 4

Re viewer 5 Conclusions and overall recommendations

This effort represents a good foundation for the development of nutrient criteria for inland waters in the State of Florida. However, overall, the document is a mixed result due to several methodologies i n the process of being developed; lack of statewide applicability and the most effective current methodology for streams the SCI as a good functional baseline from which to start. The Dose

- Response analyses proved unsatisfactory yet should, with additiona l research and information development, hold promise. Methods to determine whether the upstream criteria are protective of downstream waters are insufficiently evaluated in this document. The SPARROW

### 52 model should be applied cautiously and only to appropriate systems in assessing downstream effects, namely those with well

- defined channel flows, and well

- especially to receiving reaches and coastal waters. The Nutrient Distributional Approach represents a good backstop where data are insufficient to develo p specific numeric criteria. What the document mostly lacks is an overall orientation and strategy, a set of clear recommendations, and an implementation plan for bringing these various approaches to bear. A determination of the boundaries of analysis, of what protocol takes precedence, when each would be applied, where each is applicable, how data and results are to be synthesized to arrive at criteria is wanting. Recognizing that this is a work in progress, there is the expectation that a coherent strategy for combining the information in these individual chapters will be developed. It is expected that with additional input and review, and development of the document and well

- rounded approach, such a strategy for implementation will be forthcoming.
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