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OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
June 25,2015
EPA-SAB-15-010
The Honorable Gina McCarthy
Administrator
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, N.W.
Washington, D.C. 20460
Subject: Early Advice on an Ensemble Modeling Approach for Developing Lake Erie
Phosphorus Objectives
Dear Administrator McCarthy:
The U.S. Environmental Protection Agency's Region 5 requested a consultation with the Science
Advisory Board (SAB) regarding the development of preliminary phosphorus objectives, loading targets
and allocations for Lake Erie. An SAB consultation provides expert advice on a technical question at an
early stage in a science activity. The SAB augmented the Ecological Processes and Effects Committee
with subject matter experts to form the Lake Erie Phosphorus Objectives Review Panel to provide
advice, through the Chartered SAB, on the agency's initial efforts to develop the preliminary phosphorus
objectives.
The binational phosphorus objectives are being updated to achieve the nutrient objectives for Lake Erie,
pursuant to Annex 4 of the 2012 Great Lakes Water Quality Agreement (GLWQA). The SAB reviewed
the methodology presented in EPA's Draft Technical Approach for Lake Erie Phosphorus Load-
Response Modeling (2014) to provide early advice on the agency's approach. The document describes
the framework that the EPA will use to model indicators of eutrophication, the ensemble of models
relevant to Lake Erie, and the available data to develop, calibrate and validate the models.
The SAB was asked to comment on the eutrophication response indicators, the models chosen to
evaluate the eutrophication response in Lake Erie, the ensemble modeling approach and the efficacy of
setting phosphorus loads and concentration targets. The charge questions are attached. The SAB Lake
Erie Phosphorus Objectives Review Panel met in Chicago on December 10, 2014, to receive briefings
from EPA Region 5 staff, presentations by invited technical experts from Canada, and comments from
the public. The draft EPA Technical Approach describes the agency's initial efforts to develop the
preliminary phosphorus objectives and in some parts does not provide sufficient information for robust
responses to the charge questions. The SAB provides responses to the charge questions and
recommendations below and notes where the agency needs to provide additional information.
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C. 20460

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Eutrophication Response Indicators
The SAB was asked whether the proposed eutrophication response indicators provide a scientific
foundation for the Lake Erie Ecosystem Objectives. The EPA identified four eutrophication indicators
and selected models that will provide an ensemble of results to compare the indicators and phosphorus
levels in Lake Erie. The four indicators are:
1.	phytoplankton as represented by chlorophyll-a,
2.	cyanobacteria blooms in the western basin of Lake Erie,
3.	hypoxia in the central basin of the lake, and
4.	phosphorus content stored in Cladophora.
The SAB found that the first three indicators are reasonable choices, have a foundation in the available
science concerning Lake Erie nutrient dynamics, and can be estimated from the models. In contrast, the
SAB found that there may not be a sufficient history of reliable data collection to develop models based
on the, fourth indicator, phosphorus content of Cladophora.
The traditional indicators of eutrophication (focusing on phosphorus concentrations, total phytoplankton
biomass and chlorophyll-a) should be supplemented by monitoring changes in the composition of the
biological communities in the ecosystem, focusing on the relative abundance of phytoplankton, changes
in the oxidation state of sediments, and changes in the form and isotopic composition of nitrogen and
phosphorus. The agency should also be mindful that factors such as nutritional status and physical
environment can add uncertainty to approaches that use chlorophyll-a to predict planktonic biomass.
There is evidence that the total phosphorus loading in Lake Erie has not changed markedly during the
past couple of decades, but the response of the lake's biology has changed in ways that are undesirable
(e.g., toxic blooms and hypoxia), poorly understood, and difficult to predict. Specifically, the biological
communities in the lake have changed and thus altered the patterns, rates, and amounts of phosphorus
cycling internally in the ecosystem, including its regeneration from sediments. The agency should
consider this rapid recycling of phosphorus between the bacterial and phytoplankton communities and
release from sediments. The regional climate is changing. Sediment and nutrient loading, the
temperature of the lake waters, degree of stratification, and length of the ice-free season have increased.
Also, there appears to be an increase in the fraction of total phosphorus that is dissolved and therefore
more bioavailable. Thus, the traditional dose-response assumptions of models, based solely on total
phosphorus, may be insufficient to develop the phosphorus objectives. The SAB notes that there is
limited detail in the draft technical approach addressing spatial and temporal scales and recommends
that the agency increase the discussion of spatial-temporal variations (i.e., spatial distribution, spatial
resolution, sampling timelines, and seasonal variation) and rationale used to develop the preliminary
phosphorus objectives.
Selection of Models and the Ensemble Modeling Approach
The SAB was asked whether the models chosen to evaluate the eutrophication response in Lake Erie are
appropriate and reflect the best available science. The SAB finds that ecosystem simulation models and
an ensemble modeling approach are appropriate and powerful tools to address the problem of
phosphorus pollution in Lake Erie and to make predictions for the future state of the Lake Erie
ecosystem. However, some of the models chosen for the ensemble assume that the productivity of Lake
Erie is limited solely by available phosphorus. The direct relation of phosphorus concentration in lake
waters to the productivity of phytoplankton is probably still robust but other factors in addition to
phosphorus (i.e., possible co-limitation by nitrogen) may need to be considered to minimize hypoxia and
algal blooms. Increased loading of nitrogen has shifted the available nitrogen in lake water, the nitrogen-
to-phosphorus ratio, and the nutrient uptake from the changing composition of the biota.

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Although the ensemble approach is reasonable, there are questions about how the models will be
combined. Providing more detail on this topic should be a priority for the EPA. Also, there are questions
about the efficacy of the specific models included in the ensemble, some of which do not include much
of the lake's biology. The SAB notes that recent published literature in ecology speaks of major
changes in the biology of ecosystems as representing a "regime shift." Regime shifts are associated with
changes in the species composition in ecosystems that alter the pathways and rates of biogeochemical
cycling and make a return to the prior state impossible. It is possible that Lake Erie has undergone such
a regime shift that will be better addressed in the process models, but not easily captured in the empirical
or statistical models.
The SAB notes that the current response indicators are relatively simple and easy to measure. The
agency will need to determine if they are sufficient to address the eutrophication problems of Lake Erie.
The draft Technical Approach did not provide sufficient detail to assess how the agency will evaluate
the similarities and differences among the models to develop preliminary phosphorus loadings to Lake
Erie. The SAB notes that there are methods to conduct uncertainty and sensitivity analyses individually
and across the models, yet at this stage, there was insufficient information available to the SAB to
provide specific recommendations about the efficacy of individual models. The SAB will need to
receive a fuller discussion on the precision and validation of various alternative models in subsequent
reports.
Developing Preliminary Phosphorus Loads and Concentration Targets
The SAB was asked whether the models included in the ensemble, used singly or in combination,
provided a scientifically grounded basis for the required update of phosphorus load targets for Lake Erie.
The SAB notes that monitoring the loading of nitrogen and phosphorus to Lake Erie is appropriate to
understand the lake's nutrient regime and implement management practices. However, the biology in the
lake responds to concentrations, not loadings. The agency needs to consider both loads and
concentrations. Concentrations of available phosphorus developed from modeled load estimates are
based on complex physical and biological processes as discussed in the other charge question responses.
Therefore, the agency will need to periodically assess the models and their projected target loadings to
assess the relevance between loads and available phosphorus concentration in meeting management
objectives.
According to the draft Technical Approach, the EPA and the GLWQA Annex 4 work group will "apply
an adaptive management approach in which the phosphorus concentrations and loading targets are
revisited periodically" to develop the phosphorus objectives. The SAB agrees that the modeling
approach must be flexible given the complexity, changing biology and shifts in the physical dynamics of
Lake Erie. The SAB encourages the EPA to expand the explanation of its plans to implement adaptive
management. For example, the 2011 Lakewide Action and Management Plan for Lake Erie includes a
plan to revisit nutrient management actions and targets on an annual basis and integrate revision into the
five-year Lake Erie LaMP management, work planning, and reporting cycle. The EPA should include
more detail on the monitoring, data, and analyses needed to implement an adaptive management strategy
for the phosphorus objectives.
The SAB appreciates the opportunity to provide the EPA with early consensus advice on the modeling
approach for developing phosphorus targets for Lake Erie and looks forward to the agency's response.
The SAB notes that the Draft Technical Approach for Lake Erie Phosphorus Load-Response Modeling
(2014) presents the agency's initial plan to develop the preliminary phosphorus objectives and that the

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plan likely will evolve. More detailed comments from individual panel members on these major
recommendations and additional suggestions are available on the SAB website.
The SAB anticipates a subsequent review of the preliminary phosphorus targets to provide advice on (1)
whether the process used to develop the targets was appropriate to meet the nutrient Lake Ecosystem
Objectives as defined in the GLWQA and (2) whether the recommended targets are derived from the
best available information on the phosphorus sources and trophic status of Lake Erie.
Sincerely,
/S/
/S/
Dr. Peter S. Thorne
Chair
Dr. William H. Schlesinger
Chair
SAB Lake Erie Phosphorus Objectives Review
Panel
Science Advisory Board
Enclosures
(1)	Roster of Lake Erie Phosphorus Objectives Review Panel Members
(2)	Roster of SAB Members
(3)	Charge to the SAB for the Consultation of Lake Erie Phosphorus Objectives

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NOTICE
This report has been written as part of the activities of the EPA Science Advisory Board (SAB), a public
advisory group providing extramural scientific information and advice to the Administrator and other
officials of the Environmental Protection Agency. The SAB is structured to provide balanced, expert
assessment of scientific matters related to problems facing the agency. This report has not been reviewed
for approval by the agency and, hence, the contents of this report do not represent the views and policies
of the Environmental Protection Agency, nor of other agencies in the Executive Branch of the federal
government, nor does mention of trade names of commercial products constitute a recommendation for
use. Reports of the SAB are posted on the EPA website at http://www.epa.gov/sab.
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U.S. Environmental Protection Agency
Science Advisory Board
Lake Erie Phosphorus Objectives Review Panel
CHAIR
Dr. William Schlesinger, President Emeritus, Cary Institute of Ecosystem Studies, Millbrook, NY
MEMBERS
Dr. Merryl Alber, Professor, Department of Marine Sciences, University of Georgia, Athens, GA
Dr. James Ammerman, Adjunct Professor, School of Marine and Atmospheric Sciences, Stony Brook
University, Stony Brook, NY
Dr. Steven Bartell, Principal, Vice President and Technical Director, Cardno ENTRIX, Greenback, TN
Dr. Hunter Carrick, Professor, Biology, Central Michigan University, Mount Pleasant, MI
Dr. Celia Chen, Research Professor, Department of Biological Sciences, Dartmouth College, Hanover,
NH
Dr. John P. Connolly, Senior Technical Advisor and Principal Engineer, Anchor QEA, LLC, Montvale,
NJ
Dr. Richard Di Giulio, Professor, Nicholas School of the Environment, Duke University, Durham, NC
Dr. Robert Diaz, Professor, Department of Biological Sciences, Virginia Institute of Marine Science,
College of William and Mary, Gloucester Pt., VA
Mr. Doug Endicott, P.E., Great Lakes Environmental Center, Traverse City, MI
Mr. James J. Fitzpatrick, Project Principal Engineer, HDR Engineering, Mahwah, NJ
Dr. Robert T. Heath, Professor Emeritus, Department of Biological Sciences, Kent State University,
Kent, OH
Dr. Lucinda Johnson, Center Director, Center for Water and the Environment, Natural Resources
Research Institute, University of Minnesota Duluth, Duluth, MN
Dr. J. Val Klump, Professor and Associate Dean of Research, School of Freshwater Sciences, Great
Lakes WATER Institute, Univ. of Wisconsin-Milwaukee, Milwaukee, WI
Dr. Thomas W. La Point, Professor, Department of Biological Sciences, University of North Texas,
Denton, TX
Dr. Douglas McLaughlin, Principal Research Scientist, Northern Regional Center, National Council
for Air and Stream Improvement, Kalamazoo, MI
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Dr. Kenneth Reckhow, Independent Consultant and Professor Emeritus, Nicholas School of the
Environment, Duke University, Durham, NC
Dr. Ramesh Reddy, Graduate Research Professor & Chair, Soil and Water Science Department,
University of Florida, Gainesville, FL
Dr. Emma Rosi-Marshall, Associate Scientist, Cary Institute of Ecosystem Studies, Millbrook, NY
Dr. Eric P. Smith, Professor, Department of Statistics, Virginia Polytechnic Institute and State
University, Blacksburg, VA
Dr. William Stubblefield, Senior Research Professor, Department of Molecular and Environmental
Toxicology, Oregon State University, Corvallis, OR
Dr. Maurice Valett, Professor of Systems Ecology, Division of Biological Sciences, University of
Montana, Missoula, MT
SCIENCE ADVISORY BOARD STAFF
Mr. Thomas Carpenter, Designated Federal Officer, U.S. Environmental Protection Agency, Science
Advisory Board (1400R), 1200 Pennsylvania Avenue, NW, Washington, DC
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U.S. Environmental Protection Agency
Science Advisory Board
CHAIR
Dr. Peter S. Thorne, Professor and Head, Department of Occupational & Environmental Health,
University of Iowa, Iowa City, IA
MEMBERS
Dr. George Alexeeff, Director, Office of Environmental Health Hazard Assessment, California
Environmental Protection Agency, Oakland, CA
Dr. Joseph Arvai, Max McGraw Professor of Sustainable Enterprise, Director, Erb Institute, School of
Natural Resources & Environment, University of Michigan, Ann Arbor, MI
Dr. Sylvie M. Brouder, Professor and Wickersham Chair of Excellence in Agricultural Research,
Department of Agronomy, Purdue University, West Lafayette, IN
Dr. Thomas Burbacher, Professor, Department of Environmental and Occupational Health Sciences,
School of Public Health, University of Washington, Seattle, WA
Dr. Ingrid Burke, Director and Wyoming Excellence Chair, Haub School and Ruckelshaus Institute of
Environment and Natural Resources, University of Wyoming, Laramie, WY
Dr. George Daston, Victor Mills Society Research Fellow, Global Product Stewardship, The Procter &
Gamble Company, Mason, OH
Dr. Costel Denson, Managing Member, Costech Technologies, LLC, Hockessin, DE
Dr. Michael Dourson, President, Toxicology Excellence for Risk Assessment, Cincinnati, OH
Dr. Joel Ducoste, Professor, Department of Civil, Construction, and Environmental Engineering,
College of Engineering, North Carolina State University, Raleigh, NC
Dr. David A. Dzombak, Hamerschlag University Professor and Department Head, Department of Civil
and Environmental Engineering, College of Engineering, Carnegie Mellon University, Pittsburgh, PA
Dr. Elaine M. Faustman, Professor and Director, Environmental and Occupational Health Sciences,
University of Washington, Seattle, WA
Dr. R. William Field, Professor, Department of Occupational and Environmental Health, and
Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA
Dr. H. Christopher Frey, Distinguished University Professor, Department of Civil, Construction and
Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, NC
Dr. Steven Hamburg, Chief Scientist, Environmental Defense Fund, Boston, MA
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Dr. Cynthia M. Harris, Director and Professor, Institute of Public Health, Florida A&M University,
Tallahassee, FL
Dr. Robert J. Johnston, Director of the George Perkins Marsh Institute and Professor, Economics,
Clark University, Worcester, MA
Dr. Kimberly L. Jones, Professor and Chair, Department of Civil and Environmental Engineering,
Howard University, Washington, DC
Dr. Catherine Karr, Associate Professor - Pediatrics and Environmental and Occupational Health
Sciences and Director - NW Pediatric Environmental Health Specialty Unit, University of Washington,
Seattle, WA
Dr. Madhu Khanna, ACES Distinguished Professor in Environmental Economics, Department of
Agricultural and Consumer Economics, University of Illinois at Urbana-Champaign, Urbana, IL
Dr. Nancy K. Kim, Independent Consultant, Independent Consultant, Albany, NY
Dr. Francine Laden, Mark and Catherine Winkler Associate Professor of Environmental
Epidemiology, Harvard School of Public Health, and Channing Division of Network Medicine, Brigham
and Women's Hospital and Harvard Medical School, Boston, MA
Dr. Lois Lehman-McKeeman, Distinguished Research Fellow, Discovery Toxicology, Bristol-Myers
Squibb, Princeton, NJ
Dr. Cecil Lue-Hing, President, Cecil Lue-Hing & Assoc. Inc., Burr Ridge, IL
Dr. Elizabeth Matsui, Associate Professor, Pediatrics, School of Medicine, Johns Hopkins University,
Baltimore, MD
Dr. Denise Mauzerall, Professor, Woodrow Wilson School of Public and International Affairs, and
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ
Dr. Kristina D. Mena, Associate Professor, Epidemiology, Human Genetics, and Environmental
Sciences, School of Public Health, University of Texas Health Science Center at Houston, El Paso, TX
Dr. Surabi Menon, Director of Research, Climate Works Foundation, San Francisco, CA
Dr. James R. Mihelcic, Professor, Civil and Environmental Engineering, University of South Florida,
Tampa, FL
Dr. H. Keith Moo-Young, Chancellor, Office of Chancellor, Washington State University, Tri-Cities,
Richland, WA
Dr. Eileen Murphy, Director of Research Development, Office of Research and Economic
Development, Rutgers University, Piscataway, NJ
Dr. James Opaluch, Professor and Chair, Department of Environmental and Natural Resource
Economics, College of the Environment and Life Sciences, University of Rhode Island, Kingston, RI
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Dr. Martin Philbert, Dean and Professor, Environmental Health Sciences, School of Public Health,
University of Michigan, Ann Arbor, MI
Mr. Richard L. Poirot, Air Quality Planning Chief, Air Quality and Climate Division, Vermont
Department of Environmental Conservation, Montpelier, VT
Dr. Stephen Polasky, Fesler-Lampert Professor of Ecological/Environmental Economics, Department
of Applied Economics, University of Minnesota, St. Paul, MN
Dr. David B. Richardson, Associate Professor, Department of Epidemiology, School of Public Health,
University of North Carolina, Chapel Hill, NC
Dr. Amanda D. Rodewald, Director of Conservation Science, Cornell Lab of Ornithology and
Associate Professor, Department of Natural Resources, Cornell University, Ithaca, NY
Dr. William Schlesinger, President Emeritus, Cary Institute of Ecosystem Studies, Millbrook, NY
Dr. Gina Solomon, Deputy Secretary for Science and Health, Office of the Secretary, California
Environmental Protection Agency, Sacramento, CA
Dr. Daniel O. Stram, Professor, Department of Preventive Medicine, Division of Biostatistics,
University of Southern California, Los Angeles, CA
Dr. Paige Tolbert, Professor and Chair, Department of Environmental Health, Rollins School of Public
Health, Emory University, Atlanta, GA
Dr. Jeanne VanBriesen, Professor, Department of Civil and Environmental Engineering, Carnegie
Mellon University, Pittsburgh, PA
Dr. John Vena, Professor and Founding Chair, Department of Public Health Sciences, Medical
University of South Carolina, Charleston, SC
Dr. Elke Weber, Jerome A. Chazen Professor of International Business, Columbia Business School,
New York, NY
Dr. Charles Werth, Professor and Bettie Margaret Smith Chair in Environmental Health Engineering,
Department of Civil, Architectural and Environmental Engineering, Cockrell School of Engineering,
University of Texas at Austin, Austin, TX
Dr. Peter J. Wilcoxen, Associate Professor, Economics and Public Administration, The Maxwell
School, Syracuse University, Syracuse, NY
Dr. Dawn J. Wright, Chief Scientist, Environmental Systems Research Institute (Esri), Redlands, CA
SCIENCE ADVISORY BOARD STAFF
Mr. Thomas Carpenter, Designated Federal Officer, U.S. Environmental Protection Agency, Science
Advisory Board (1400R), 1200 Pennsylvania Avenue, NW, Washington, DC
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Charge to the Science Advisory Board for the Consultation of
Lake Erie Phosphorus Objectives
Prepared by the EPA Region 5 Water Division
November 4, 2014
Background
The U.S. Environmental Protection Agency (EPA) Region 5 is co-leading a binational
workgroup to develop and implement the Nutrients Annex ("Annex 4") of the 2012 Great Lakes
Water Quality Agreement (GLWQA) in accordance with Article 3(b) of the GLWQA. Under
Annex 4, the U.S. and Canada (herein referred to as "the Parties") are charged with establishing
binational Substance Objectives for phosphorus concentrations, loading targets and allocations
for the nearshore and offshore waters of Lake Erie by February 2016. While the Annex applies
to all Great Lakes, only Lake Erie has time-bounded commitments, reflecting the Parties'
commitment and understanding of the need for prompt action to combat the algae issue there.
Lake Ecosystem Objectives
Pursuant to Article 3(l)(b)(i), the Parties adopted the following Lake Ecosystem Objectives
related to nutrients for Lake Erie:
1.	minimize the extent of hypoxic zones associated with excessive phosphorus loading,
2.	maintain the levels of algal biomass below the level constituting a nuisance condition;
3.	maintain algal species consistent with healthy aquatic ecosystems in the nearshore;
4.	maintain cyanobacteria biomass at levels that do not produce concentrations of toxins that
pose a threat to human or ecosystem health; and
5.	maintain mesotrophic conditions in the open waters of the western and central basins of Lake
Erie, and oligotrophic conditions in the eastern basin of Lake Erie.
The Annex 4 workgroup has adopted the following general approach for establishing
new/revised Substance Objectives and loading targets for Lake Erie:
1)	establish eutrophication response indicators and metrics related to the nutrient Lake
Ecosystem Objectives (LEOs);
2)	use multiple models to compute appropriate load-response relationships and attribute
these to the eutrophi cation response indicators of concern;
3)	synthesize and interpret the results of the ensemble of models to derive phosphorus
concentrations and loading targets needed to meet the nutrient LEOs, taking into account the
bioavailability of various forms of phosphorous, related productivity, seasonality, fisheries
productivity requirements, climate change, invasive species and other factors, such as
downstream impacts, as necessary;
4)	apply an adaptive management approach in which the phosphorus concentrations and
loading targets are revisited periodically.
Due to the complexity of the issue and the need to rely on existing information in the short term,
we anticipate refinements in response to peer review and stakeholder feedback. Ongoing
monitoring and evaluation will be critical as we track the changes in phosphorus concentrations
and loads, in addition to other drivers like hydrology and climate, and the ecological response.
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Additional Resources: The EPA identified several reports as supplementary material on the
efforts taken in the Lake Erie basin to better understand the background and context of this work.
These three reports provide additional background information on the efforts to understand and
manage excess nutrients in Lake Erie and the preliminary work on approaches to develop
phosphorus objectives:
•	Lake Erie Binational Nutrient Management Strategy: Protecting Lake Erie by Managing
Phosphorus. Prepared by the Lake Erie LaMP Work Group, 2011.
•	Status of Nutrients in Lake Erie Basin. Prepared by the Lake Erie LaMP Work Group,
2009.
•	An Approach for Determination of Phosphorus Objectives and Target Loads for Lake
Erie. Discussion paper prepared by LimnoTech for Environment Canada, May 2013.
Charge to SAB:
The EPA requests the Science Advisory Board (SAB) provide early advice on the approach
(Phase I consultation) and subsequent review (Phase II Peer Review) of preliminary binational
phosphorus objectives, loading targets and allocations for the nearshore and offshore waters to
achieve the Lake Ecosystem Objectives related to nutrients for Lake Erie, pursuant to the Annex
4 of the 2012 GLWQA.
The objective of the SAB consultation is to obtain early advice on the modeling approach being
applied to inform the updated phosphorus targets for Lake Erie. The purpose of the subsequent
review of the preliminary phosphorus targets will be to obtain advice on (1) whether the process
used to develop the targets was appropriate to meet the nutrient Lake Ecosystem Objectives as
defined in the GLWQA and (2) whether the recommended targets reflect the best available
information on the phosphorus sources and trophic status of Lake Erie. EPA and Environment
Canada are particularly interested in advice pertaining to future applicability of this work as we
develop a phosphorus reduction strategy for Lake Erie and begin evaluating phosphorus targets
for other Great Lakes.
Document for Review: The SAB will review the methodology presented in EPA's Draft
Technical Approach for Lake Erie Phosphorus Load-Response Modeling. The document
describes the framework approach the EPA will use to model eutrophication response indicators,
the ensemble of models relevant to Lake Erie, and the available data to develop, calibrate, and
validate the models.
Phase 1 Consultation Questions:
1. Please comment on whether the eutrophi cation response indicators proposed sufficiently
address and provide the scientific foundation for the Lake Ecosystem Objectives for Lake
Erie. During your evaluation of the eutrophi cation response indicators, identify other
metrics appropriate for measuring eutrophi cation response in Lake Erie and other Great
Lakes that should be considered, and whether there is a method (model) available to
measure this response.

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2.	Please comment on each of the models chosen to evaluate the eutrophication response in
Lake Erie? Are the models appropriate for representing the eutrophi cation response
indicators? Do the models reflect the best available scientific knowledge?
3.	Please comment on the appropriateness of the ensemble modeling approach to examine
the suite of eutrophi cation response indicators. Are the models included in the ensemble,
when used either singly or combined, sufficient to provide a scientifically grounded basis
for the required update of phosphorus load targets for Lake Erie?
4.	An anticipated outcome of the modeling exercise is to better understand and quantify what
types of conditions would be expected in the lake based upon different levels of
phosphorus loading, and to use that information to inform selection of phosphorus loading
targets needed to meet the nutrient Lake Ecosystem Objectives. The phosphorus loading
targets could be converted to concentration targets, particularly for river mouths/nearshore
zones. Please comment on efficacy and value of establishing target values for both
phosphorus loads and concentrations in order to meet to the Lake Ecosystem Objectives.
How can we ensure the phosphorus concentration and loading targets are internally
consistent with respect to the eutrophi cation response indicators of concern?
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