Five Peer Reviewers

• Roger Bachman, University of Florida
• James Peterson, University of Wisconsin-Madison
• Val Smith, University of Kansas
• Nina Caraco, Institute of Ecosystem Studies, NY
• Douglas Knauer, Wisconsin Department of Natural Resources

Public commentors

• North Carolina Department of Environmental & Natural Resources; Div. of Water Quality
• Association of Municipal Sewerage Agencies
• US Army Corps of Engineers
• Wisconsin Department of Natural Resources
• Minnesota Pollution Control Board
• Vermont Agency of Natural Resources

Charge to Peer Reviewers and a brief summary of their responses

• 1. To the development of nutrient criteria using an ecoregional and water body-type specific approach.

  Two reviewers felt ecoregions are too large; that variability of lakes even at the ecoregion level and the different lake responses to nutrients would make ecoregions ineffective. Site specific criteria or smaller subdivisions were preferred. The other reviewers felt the ecoregion approach will work, especially when the described further spatial and resource class refinement is exercised where needed. The final version of the manual emphasizes the importance of ecoregion refinement by further subdivision and physical classification.

• 2. To the selected indicator variables of Total Phosphorus, Total Nitrogen, Chlorophyll-a, and Secchi depth or similar measure of turbidity.

  All agreed with the choices although there was some discussion about the role of Secchi depth and algal vs inorganic turbidity vs macrophyte obstructions. A discussion about the proper use of Secchi depth measurements is in the manual.

• 3. To the rationale for nutrient criteria development.

  One reviewer strongly disagreed with the reference condition approach as not likely to represent an unbiased sample of the population of lakes in a region; with the use of percentiles of the distribution of indicators as not scientifically sound; and that historical information implied pre-settlement conditions. Another was concerned with the potential that selection of a quartile in heavily enriched agricultural areas may be inadequate, and that historical information may not extend back far enough to establish a sufficiently "natural" baseline for criteria development. The other reviewers endorsed the approach as described.

  Please see comments below regarding reference condition and quartiles. The final version of the manual identifies and relates the roles of science and of resource management in environmental protection decision making. Historical information is described as setting a perspective based on conditions in the past which may be either optimal or degraded, whereas reference condition is described as a measure of attainable present conditions.

  All reviewers offered additional specific comments on content, format, syntax, and other technical and professional elements of the original draft. The authors are indebted to them for their constructive responses and believe the present version of the manual is greatly improved by their contributions.

General Comments

• 1. The work has been long needed and is a good effort which should stimulate positive State responses to the problem. With EPA criteria, states can overcome political and economic inertia associated with addressing this problem.

  Authors concur.

• 2. A good attempt, but ecoregional reference conditions and criteria are too general. Criteria should be site-specific.

  EPA encourages the development of site-specific nutrient criteria where possible, but also acknowledges that this approach to developing nutrient criteria may not be very practical given the costs and efforts required to develop nutrient criteria for individual waterbodies within a region. Nutrient ecoregions delineate areas of broad scale similarities in geography, ecosystems, and related nutrient conditions which. RTAG's, including member States/Tribes, are encouraged to refine and further subdivide. These ecoregional reference conditions and criteria are believed to be a reasonable alternative approach to the inappropriate single, nation-wide criterion approach which fails to address regional variability; and the too refined individual water body approach. This regionalization and water body-type specificity has been endorsed by the EPA-SAB for biological criteria, and nutrient criteria share much the same ecological orientation.

• 3. Criteria are not necessary in all regions of the country. They should only be developed when degradation of the ecosystem by excess nutrients is demonstrated.

  Cultural eutrophication of the Nation's surface waters is a pervasive pollution problem - especially for lakes and reservoirs as demonstrated by 305(b) reports and any review of the literature. Further, ecosystem degradation may be deferred to areas located a considerable distance downstream if hydraulic residence time is low or measurements are made during adverse growing periods. To do so would separate eutrophication abatement from the source of the problem and adversely assign remediation to the downstream recipient of these excess nutrients. The regional reference condition approach helps address both of these concerns.

• 4. Nitrogen and phosphorus criteria are not necessary, only biological response criteria should be employed because other factors such as light, residence time, turbidity and sedimentation may be limiting.

  The program allows for classifications to accommodate uniquely colored waters or other special classes for nutrient criteria development. Algal response as manifested in chlorophyll concentration, Secchi depth, dominant species or other acceptable measures including macrophyte growth and biomass reflect a relatively direct reaction of the addition to excess nutrients especially N and P (Chapter 5). The literature abounds with demonstrations of primary production reactions to nitrogen and phosphorus additions to water systems, most notably studies by Sawyer (1947), Vollenweider (1968) and by Schindler (1978), and it seems incongruous to not address these causes.

• 5. Most lakes are not nitrogen limited, therefore, nitrogen criteria are not pertinent.

  EPA recognizes that for phosphorus limited systems, it might be economical to just manage the phosphorus. However, nitrogen is more mobile and can become part of a cumulative downstream effect, especially for estuarine waters. There are also nitrogen limited freshwater lakes in various regions of the country so it is prudent to address both of these nutrients in the EPA program.

• 6. The control of nutrients should be voluntary rather than mandatory.

  Voluntary management is an admirable approach to nutrient control and is supported by EPA. The USDA voluntary land use demonstration and education programs are an important part of nutrient management. The establishment of nutrient criteria provides a benchmark for assessing the effectiveness of such initiatives and the dual application, as part of the standards regulatory approach, is an incentive for more successful voluntary activities. The one approach does not preclude the other, and management plans to meet nutrient standards, TMDLs or permits can effectively incorporate cooperative initiatives.

• 7. The use of percentile values of a distribution of concentrations for a reference condition is arbitrary and lacks a scientific rationale for criteria development.

  The median, mean, and mode are measures of central tendency commonly used in science to represent the distribution of a population of observations. However, science alone cannot address all aspects of environmental management decision making and in this instance the prudent resource management decision is to select a more conservative value than the central tendency - the upper or lower quartile for a distribution of reference lakes or a sample of all lakes in a class respectively. The upper quartile of the reference lakes, while leaving a margin of protection for environmental quality, is more realistic than presuming that half of the reference set itself does not meet reference condition requirements. The opposite applies when using a sample of all lakes in a class where it is known that many of the constituent lakes are not of reference quality. Further, data analyses performed to date in Minnesota indicate that the lower 25^th percentile from a sample representative of the entire population of lakes in an ecoregion roughly approximates the upper 25^th percentile of the reference data. It is important to also note that in the final version of this manual it is more clearly indicated that the quartile based reference condition is only one component of the criterion.

  The EPA is charged with making such science based decisions and does so routinely to protect public health and the environment by applying best scientific principles together with prudent judgment. Choosing the upper or lower quartile of a selected distribution ,as described above, is a prudent risk management decision informed by scientific information.

• 8. "Downstream impacts" is unclear and implies both immediate downstream effects and impacts to perhaps distant coastal areas. It should be consistent and relate only to areas immediately downstream from the lake or reservoir.

  The intent of the manual is to promote concern by all parties for downstream effects within a few miles or to the next downstream receiving water system e.g., the next lake or reservoir. Collectively, this approach should have a cumulative positive benefit to the nations estuarine and coastal marine waters which are the ultimate recipients of continental discharges. (p.viii, 1-15, 7-7). In addition, the Clean Water Act directs EPA and States and Tribes to develop criteria and standards that are protective of downstream uses (Section 131.10(b) of the CWA).

• 9. Distinctions must be made between natural lakes and man-made reservoirs in criteria development.

  The manual establishes that natural lakes and man-made lakes or flowages are similar and can often be treated the same. However, reservoirs built for power generation, flood control, navigation or irrigation are a separate class of water body and should be treated as such. (p3-1). Material has been included in the April 2000 edition of the manual specifically addressing this concern. (p.3-4ff,7-18,19).

• 10. Case histories are presented without any reference to a EPA opinion of these examples. Do they represent what EPA is willing to approve or is the information just food for thought?

  The case histories are included to illustrate the array of plausible approaches to nutrient measurement and control at this time. They are only intended to promote further discussion and investigation at this early stage of the program.

• 11. If designated uses are being met, the criteria may be immaterial.

  The ecoregional criteria are intended to reflect in part the most natural conditions obtainable, or reference conditions (p.8-1 ff), and therefore should be protective of most designated uses (as well as most beneficial uses under the Clean Water Act). More stringent State criteria to protect uses more sensitive than the reference condition and derived criteria are entirely acceptable and the EPA antidegradation policy further substantiates this approach. There is sufficient flexibility in the program to address particular designated uses relative to the best attainable natural enrichment condition reflected in an ecoregional nutrient criterion. The ecoregional criteria help protect against establishing designated uses based on degraded conditions. The key is that nutrient criteria are set at a level to protect the most sensitive designated uses in a given region/watershed. Since EPA is not in a position to evaluate the specific needs of each species and each use, the reference condition approach is used as a surrogate to maintaining and restoring high quality water uses.

• 12. The Regional technical Assistance Groups (RTAG's) appear to be operating as surrogates for EPA in evaluating state WQ standards.

  The RTAG's are intended to be technical assistance and advisory groups comprised of federal specialists and involving their counterparts in states and tribes (p.1-7,1-9). The RTAG's provide information and assistance to EPA in the development of ecoregional nutrient criteria (Section 304(a) of the Clean Water Act), and advise the States and Tribes as they prepare nutrient criteria. However, EPA not the RTAG will approve or disapprove any nutrient criteria adopted by States or Tribes.

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