in the Northern Gulf of Mexico in the Northern Gulf of Mexico

An Integrated Assessment An Integrated Assessment

May 2000

National Science and Technology Council

Committee on Environment and Natural Resources
The National Science and Technology Council

President Clinton established the National Science and Technology Council (NSTC) by

Executive Order on November 13, 1993. This cabinet-level council is the principal means for

the President to coordinate science, space, and technology policies across the federal government. The NSTC acts as a “virtual” agency for science and technology to coordinate the

diverse parts of the federal research and development enterprise. Membership consists of the

Vice President, the Assistant to the President for Science and Technology, cabinet secretaries, agency heads with significant science and technology responsibilities, and other White

House officials.

An important objective of the NSTC is the establishment of clear national goals for federal

science and technology investments in areas ranging from information technologies, environment and natural resources, and health research, to improving transportation systems and

strengthening fundamental research. The council prepares research and development strategies that are coordinated across federal agencies to form an investment strategy that is

aimed at accomplishing multiple national goals.

To obtain additional information regarding the NSTC, contact the NSTC Executive

Secretariat at (202) 456-6100.

The Committee on Environment and Natural Resources

The Committee on Environment and Natural Resources (CENR) is one of five committees

under the NSTC. It is charged with improving coordination among federal agencies involved in

environmental and natural resources research and development, establishing a strong link

between science and policy, and developing a federal environment and natural resources

research and development strategy that responds to national and international issues.

To obtain additional information regarding the CENR, contact the CENR Executive

Secretariat at (202) 482-5916.
Integrated Assessment

of Hypoxia in the 

Northern Gulf of Mexico

MAY 2000

National Science and Technology Council

Committee on Environment and Natural Resources
D. James Baker, Co-Chair

National Oceanic and 

Atmospheric Administration 

Rosina Bierbaum, Co-Chair

White House Office of Science 

and Technology Policy

Ghassem Asrar

National Aeronautics and 

Space Administration

James Decker

U.S. Department of Energy

Roland Droitsch

U.S. Department of Labor

Albert Eisenberg

U.S. Department of Transportation

Delores Etter

U.S. Department of Defense

Terrance Flannery

Central Intelligence Agency

George Frampton

Council on Environmental Quality

Timothy Gerrity

Department of Veterans Affairs

Charles Groat

U.S. Department of the Interior

Len Hirsch

Smithsonian Institution

Kathryn Jackson

Tennessee Valley Authority

Eileen Kennedy

U.S. Department of Agriculture

Margaret Leinen

National Science Foundation

Paul Leonard

U.S. Department of Housing 

and Urban Development

Norine Noonan

U.S. Environmental Protection Agency

Kenneth Olden

U.S. Department of Health 

and Human Services

David Sandalow

U.S. Department of State

Wesley Warren

Office of Management and Budget

Craig Wingo

Federal Emergency Management Agency

Samuel Williamson

Office 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, Chair

National Oceanic and 

Atmospheric Administration

Mark Anderson

Office of Science and Technology Policy

Kay Austin

U.S. Environmental Protection Agency

Mary Belefski

U.S. Environmental Protection Agency

Dale Bucks

U.S. Department of Agriculture

Herb Buxton

U.S. Geological Survey

David Correll

Smithsonian Institution

Mike Dowgiallo

National Oceanic and 

Atmospheric Administration

John Field

National Oceanic and 

Atmospheric Administration

Penelope Firth

National Science Foundation

James Giattina

U.S. Environmental Protection Agency

Louis Goodmal

United States Navy

Don Goolsby

U.S. Geological Survey

Tom Pullen

U.S. Army Corps of Engineers

Donald Pryor

National Oceanic and 

Atmospheric Administration

Joseph Schubauer-Berigan

U.S. Environmental Protection Agency

Tim Strickland

U.S. Department of Agriculture

Fred Swader

U.S. Department of Agriculture

Larinda Tervelt-Norton

U.S. Environmental Protection Agency

Ken Turgeon

Minerals Management Service

Nancy Foster, Chair

National Oceanic and

Atmospheric Administration

Mary Clutter

National Science Foundation

Michael Davis

United States Army

Allen Dearry

U.S. Department of Health 

and Human Services

Harold Guard

United States Navy

George Hoskin

U.S. Food and Drug

Administration

Glenda Humiston

U.S. Department of Agriculture

Eric Lindstrom

National Aeronautics 

and Space Administration

Daniel Sakura

Council on Environmental

Quality

Mark Schaefer

U.S. Department of the Interior

Lois Schiffer

U.S. Department of Justice

Frances Sharples

Office of Science and

Technology Policy

Harold Zenick

U.S. Environmental 

Protection Agency

ii ■ HYPOXIA IN THE NORTHERN GULF OF MEXICO
HYPOXIA IN THE NORTHERN GULF OF MEXICO ■ iii

Acknowledgments

Hundreds of scientists, from a wide array of different fields, contributed over the years to the extensive

knowledge base on which this assessment depends. An intensive collaborative effort over the past two years has

assembled and reviewed available information. Special thanks are due to all who participated, particularly the many

peer 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 issue

were developed by six teams with experts from within and outside of government. The research teams were

established not to conduct new research, but rather to analyze existing data and to apply existing models of the

watershed-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 the

U.S. Department of Agriculture, Dr. George Hallberg from the Cadmus Group, Dr. Fred Bryan from Louisiana

State University, Dr. Sandra Batie from Michigan State University, and Dr. Rodney Foil from Mississippi State

University.

Topic 1. Characterization of Hypoxia. Describes the seasonal, interannual, and long-term variation of hypoxia in the

northern Gulf of Mexico, and its relationship to nutrient loading. It also documents the relative roles of natural and

human-induced factors in determining the size and duration of the hypoxic zone. 

Nancy N. Rabalais, Louisiana Universities Marine Consortium—Lead

R. Eugene Turner, Louisiana State University

Dubravko Justi ́c, Louisiana State University

Quay Dortch, Louisiana Universities Marine Consortium

William J. Wiseman, Jr., Louisiana State University

Topic 2. Ecological and Economic Consequences of Hypoxia. Presents an evaluation of the ecological and economic

consequences of nutrient loading, including impacts on Gulf of Mexico fisheries and the regional and national

economies. 

Robert J. Diaz, Virginia Institute of Marine Science—Ecological co-lead

Andrew 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 within

the Mississippi–Atchafalaya system and within the Gulf of Mexico, estimating both their location and the relative

importance of specific human activities in contributing to these loads.

Donald A. Goolsby, U.S. Geological Survey—Lead

William A. Battaglin, U.S. Geological Survey

Gregory B. Lawrence, U.S. Geological Survey

Richard S. Artz, National Oceanic and Atmospheric Administration

Brent T. Aulenbach, U.S. Geological Survey

Richard P. Hooper, U.S. Geological Survey

Dennis R. Keeney, Leopold Center for Sustainable Agriculture

Gary 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. Estimates

the effects of nutrient source reductions in the Mississippi–Atchafalaya Basin on water quality in these waters and

on primary productivity and hypoxia in the Gulf.

Patrick L. Brezonik, University of Minnesota—Upper watershed co-lead

Victor J. Bierman, Jr., Limno-Tech, Inc.—Gulf of Mexico co-lead

Richard Alexander, U.S. Geological Survey

James Anderson, University of Minnesota

John Barko, Waterways Experiment Station, U.S. Army Corps of Engineers

Mark Dortch, Waterways Experiment Station, U.S. Army Corps of Engineers
iv ■ HYPOXIA IN THE NORTHERN GULF OF MEXICO

Lorin Hatch, University of Minnesota

Gary L. Hitchcock, University of Miami

Dennis Keeney, Iowa State University

David Mulla, University of Minnesota

Val Smith, University of Kansas

Clive Walker, Blackland Research Center

Terry Whitledge, University of Alaska

William 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—Lead

John W. Day, Jr., Louisiana State University

J. Wendall Gilliam, North Carolina State University

Peter M. Groffman, Institute of Ecosystem Studies

Donald L. Hey, The Wetlands Initiative

Gyles W. Randall, University of Minnesota

Naiming Wang, The Ohio State University

Topic 6. Evaluation of Economic Costs and Benefits of Methods for Reducing Nutrient Loads to the Gulf of Mexico. Evaluates

the social and economic costs and benefits of the methods identified in Topic 5 for reducing nutrient loads, and

assesses various incentive programs and any anticipated fiscal benefits generated for those attempting to reduce

sources. 

Otto C. Doering, Purdue University—Lead

Francisco Diaz-Hermelo, Purdue University

Crystal Howard, Purdue University

Ralph Heimlich, Economic Research Service, U.S. Department of Agriculture

Fred Hitzhusen, The Ohio State University

Richard Kazmierczak, Louisiana State University

John Lee, Purdue University

Larry Libby, The Ohio State University

Walter Milon, University of Florida

Tony Prato, University of Missouri

Marc Ribaudo, Economic Research Service, U.S. Department of Agriculture
Contents

Executive Summary ... 2

1. The Problem ... 6

2. Causes of Gulf of Mexico Hypoxia ... 10

Coastal Eutrophication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Nutrient Over-Enrichment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Sources, Loads, and Trends of River Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

3. Consequences of Hypoxia and Nutrient Over-Enrichment ... 24

Consequences in the Gulf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Consequences in the Mississippi–Atchafalaya River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

4. Effects of Changing Nutrient Loads ... 28

Effects if Average Loads Are Unchanged . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

Effects if Average Loads Increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Effects if Average Loads Are Reduced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

5. Approaches for Reducing Nutrient Loads ... 36

Reducing Nitrogen Loads to Rivers and Streams in the Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Restoring and Enhancing Denitrification and Nitrogen-Retention Processes . . . . . . . . . . . . . . . . . . . . . . . . .41

Cost-Effective Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

6. Adaptive Management: Action, Monitoring, and Research ... 46

Monitoring and Research in a Modeling Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

Monitoring Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Appendix ... 55

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

Conversion Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57