in the Northern Gulf of Mexicoin the Northern Gulf of Mexico

An Integrated AssessmentAn Integrated Assessment

May 2000National Science and Technology CouncilCommittee on Environment and Natural Resources

The National Science and Technology Council

President Clinton established the National Science and Technology Council (NSTC) byExecutive Order on November 13, 1993. This cabinet-level council is the principal means forthe President to coordinate science, space, and technology policies across the federal gov-ernment. The NSTC acts as a “virtual” agency for science and technology to coordinate thediverse parts of the federal research and development enterprise. Membership consists of theVice President, the Assistant to the President for Science and Technology, cabinet secre-taries, agency heads with significant science and technology responsibilities, and other WhiteHouse officials.

An important objective of the NSTC is the establishment of clear national goals for federalscience and technology investments in areas ranging from information technologies, environ-ment and natural resources, and health research, to improving transportation systems andstrengthening fundamental research. The council prepares research and development strate-gies that are coordinated across federal agencies to form an investment strategy that isaimed at accomplishing multiple national goals.

To obtain additional information regarding the NSTC, contact the NSTC ExecutiveSecretariat at (202) 456-6100.

The Committee on Environment and Natural Resources

The Committee on Environment and Natural Resources (CENR) is one of five committeesunder the NSTC. It is charged with improving coordination among federal agencies involved inenvironmental and natural resources research and development, establishing a strong linkbetween science and policy, and developing a federal environment and natural resourcesresearch and development strategy that responds to national and international issues.

To obtain additional information regarding the CENR, contact the CENR ExecutiveSecretariat at (202) 482-5916.

In tegra ted Assessmento f Hypoxia in the

Northern Gulf o f Mexico

MAY 2000

National Science and Technology CouncilCommittee on Environment and Natural Resources

D. James Baker, Co-ChairNational Oceanic and Atmospheric Administration

Rosina Bierbaum, Co-ChairWhite House Office of Science and Technology Policy

Ghassem AsrarNational Aeronautics and Space Administration

James DeckerU.S. Department of Energy

Roland DroitschU.S. Department of Labor

Albert EisenbergU.S. Department of Transportation

Delores EtterU.S. Department of Defense

Terrance FlanneryCentral Intelligence Agency

George FramptonCouncil on Environmental Quality

Timothy GerrityDepartment of Veterans Affairs

Charles GroatU.S. Department of the Interior

Len HirschSmithsonian Institution

Kathryn JacksonTennessee Valley Authority

Eileen KennedyU.S. Department of Agriculture

Margaret LeinenNational Science Foundation

Paul LeonardU.S. Department of Housing and Urban Development

Norine NoonanU.S. Environmental Protection Agency

Kenneth OldenU.S. Department of Health and Human Services

David SandalowU.S. Department of State

Wesley WarrenOffice of Management and Budget

Craig WingoFederal Emergency Management Agency

Samuel WilliamsonOffice of the Federal Coordinator for Meteorology

Committee on Environment and Natural Resources

CENR Task Force on Harmful Algal Blooms and Hypoxia

Hypoxia Working Group

Don Scavia, ChairNational Oceanic and Atmospheric Administration

Mark AndersonOffice of Science and Technology Policy

Kay AustinU.S. Environmental Protection Agency

Mary BelefskiU.S. Environmental Protection Agency

Dale BucksU.S. Department of Agriculture

Herb BuxtonU.S. Geological Survey

David CorrellSmithsonian Institution

Mike DowgialloNational Oceanic and Atmospheric Administration

John FieldNational Oceanic and Atmospheric Administration

Penelope FirthNational Science Foundation

James GiattinaU.S. Environmental Protection Agency

Louis GoodmalUnited States Navy

Don GoolsbyU.S. Geological Survey

Tom PullenU.S. Army Corps of Engineers

Donald PryorNational Oceanic and Atmospheric Administration

Joseph Schubauer-BeriganU.S. Environmental Protection Agency

Tim StricklandU.S. Department of Agriculture

Fred SwaderU.S. Department of Agriculture

Larinda Tervelt-NortonU.S. Environmental Protection Agency

Ken TurgeonMinerals Management Service

Nancy Foster, ChairNational Oceanic andAtmospheric Administration

Mary ClutterNational Science Foundation

Michael DavisUnited States Army

Allen DearryU.S. Department of Health and Human Services

Harold GuardUnited States Navy

George HoskinU.S. Food and DrugAdministration

Glenda HumistonU.S. Department of Agriculture

Eric LindstromNational Aeronautics and Space Administration

Daniel SakuraCouncil on EnvironmentalQuality

Mark SchaeferU.S. Department of the Interior

Lois SchifferU.S. Department of Justice

Frances SharplesOffice of Science andTechnology Policy

Harold ZenickU.S. Environmental Protection Agency

i i � HYPOXIA IN THE NORTHERN GULF OF MEXICO

HYPOXIA IN THE NORTHERN GULF OF MEXICO � i i i

Acknowledgments

Hundreds of scientists, from a wide array of different fields, contributed over the years to the extensiveknowledge base on which this assessment depends. An intensive collaborative effort over the past two years hasassembled and reviewed available information. Special thanks are due to all who participated, particularly the manypeer reviewers and the Editorial Board, whose efforts have sharpened thinking and clarified presentation.

Hypoxia Assessment Reports

As a foundation for the assessment, six interrelated reports that examine various aspects of the hypoxia issuewere developed by six teams with experts from within and outside of government. The research teams wereestablished not to conduct new research, but rather to analyze existing data and to apply existing models of thewatershed-Gulf system. This integrated assessment draws heavily from the results in these six reports.

Each of the reports underwent extensive peer review by independent experts guided by an editorial board.Editorial Board members were Dr. Donald Boesch from the University of Maryland, Dr. Jerry Hatfield from theU.S. Department of Agriculture, Dr. George Hallberg from the Cadmus Group, Dr. Fred Bryan from LouisianaState University, Dr. Sandra Batie from Michigan State University, and Dr. Rodney Foil from Mississippi StateUniversity.

Topic 1. Characterization of Hypoxia. Describes the seasonal, interannual, and long-term variation of hypoxia in thenorthern Gulf of Mexico, and its relationship to nutrient loading. It also documents the relative roles of natural andhuman-induced factors in determining the size and duration of the hypoxic zone.

Nancy N. Rabalais, Louisiana Universities Marine Consortium—LeadR. Eugene Turner, Louisiana State UniversityDubravko Justic, Louisiana State UniversityQuay Dortch, Louisiana Universities Marine ConsortiumWilliam J. Wiseman, Jr., Louisiana State University

Topic 2. Ecological and Economic Consequences of Hypoxia. Presents an evaluation of the ecological and economicconsequences of nutrient loading, including impacts on Gulf of Mexico fisheries and the regional and nationaleconomies.

Robert J. Diaz, Virginia Institute of Marine Science—Ecological co-leadAndrew Solow, Woods Hole Oceanographic Institution—Economics co-lead,

with the assistance of many others

Topic 3. Flux and Sources of Nutrients in the Mississippi–Atchafalaya River Basin. Identifies the sources of nutrients withinthe Mississippi–Atchafalaya system and within the Gulf of Mexico, estimating both their location and the relativeimportance of specific human activities in contributing to these loads.

Donald A. Goolsby, U.S. Geological Survey—LeadWilliam A. Battaglin, U.S. Geological SurveyGregory B. Lawrence, U.S. Geological SurveyRichard S. Artz, National Oceanic and Atmospheric AdministrationBrent T. Aulenbach, U.S. Geological SurveyRichard P. Hooper, U.S. Geological SurveyDennis R. Keeney, Leopold Center for Sustainable AgricultureGary J. Stensland, Illinois State Water Survey

Topic 4. Effects of Reducing Nutrient Loads to Surface Waters within the Mississippi River Basin and Gulf of Mexico. Estimatesthe effects of nutrient source reductions in the Mississippi–Atchafalaya Basin on water quality in these waters andon primary productivity and hypoxia in the Gulf.

Patrick L. Brezonik, University of Minnesota—Upper watershed co-leadVictor J. Bierman, Jr., Limno-Tech, Inc.—Gulf of Mexico co-leadRichard Alexander, U.S. Geological SurveyJames Anderson, University of MinnesotaJohn Barko, Waterways Experiment Station, U.S. Army Corps of EngineersMark Dortch, Waterways Experiment Station, U.S. Army Corps of Engineers

iv � HYPOXIA IN THE NORTHERN GULF OF MEXICO

Lorin Hatch, University of MinnesotaGary L. Hitchcock, University of MiamiDennis Keeney, Iowa State UniversityDavid Mulla, University of MinnesotaVal Smith, University of KansasClive Walker, Blackland Research CenterTerry Whitledge, University of AlaskaWilliam J. Wiseman, Jr., Louisiana State University

Topic 5. Reducing Nutrient Loads, Especially Nitrate–Nitrogen, to Surface Water, Ground Water, and the Gulf of Mexico.Identifies and evaluates methods to reduce nutrient loads to surface water, ground water, and the Gulf of Mexico.

William J. Mitsch, The Ohio State University—LeadJohn W. Day, Jr., Louisiana State UniversityJ. Wendall Gilliam, North Carolina State UniversityPeter M. Groffman, Institute of Ecosystem StudiesDonald L. Hey, The Wetlands InitiativeGyles W. Randall, University of MinnesotaNaiming Wang, The Ohio State University

Topic 6. Evaluation of Economic Costs and Benefits of Methods for Reducing Nutrient Loads to the Gulf of Mexico. Evaluatesthe social and economic costs and benefits of the methods identified in Topic 5 for reducing nutrient loads, andassesses various incentive programs and any anticipated fiscal benefits generated for those attempting to reducesources.

Otto C. Doering, Purdue University—LeadFrancisco Diaz-Hermelo, Purdue UniversityCrystal Howard, Purdue UniversityRalph Heimlich, Economic Research Service, U.S. Department of AgricultureFred Hitzhusen, The Ohio State UniversityRichard Kazmierczak, Louisiana State UniversityJohn Lee, Purdue UniversityLarry Libby, The Ohio State UniversityWalter Milon, University of FloridaTony Prato, University of MissouriMarc Ribaudo, Economic Research Service, U.S. Department of Agriculture

CCoonntteennttssExecut ive Summary … 2

1 . The Problem … 6

2. Causes o f Gulf o f Mexico Hypoxia … 10Coastal Eutrophication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Nutrient Over-Enrichment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Sources, Loads, and Trends of River Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

3. Consequences o f Hypoxia and Nut r ient Over-Enr ichment … 24Consequences in the Gulf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Consequences in the Mississippi–Atchafalaya River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

4. Ef fects o f Changing Nut r ient Loads … 28Effects if Average Loads Are Unchanged . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29Effects if Average Loads Increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Effects if Average Loads Are Reduced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

5. Approaches for Reduc ing Nut r ient Loads … 36Reducing Nitrogen Loads to Rivers and Streams in the Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Restoring and Enhancing Denitrification and Nitrogen-Retention Processes . . . . . . . . . . . . . . . . . . . . . . . . .41Cost-Effective Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

6. Adapt ive Management : Act ion , Moni tor ing , and Research … 46Monitoring and Research in a Modeling Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Monitoring Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Appendix … 55Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Conversion Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57