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National Centers for Coastal Ocean Science
Gulf of Mexico Hypoxia Assessment
HYPOXIA IN THE GULF OF MEXICO
Progress towards the completion of an Integrated Assessment

Introduction

Scientific investigations in the Gulf of Mexico have documented a large area of the Louisiana continental shelf with seasonally-depleted oxygen levels (< 2mg/l). Most aquatic species cannot survive at such low oxygen levels. The oxygen depletion, referred to as hypoxia, begins in late spring, reaches a maximum in midsummer, and disappears in the fall. After the Mississippi River flood of 1993, the spatial extent of this zone more than doubled in size, to over 18,000 km2, and has remained about that size each year through midsummer 1997. The hypoxic zone forms in the middle of the most important commercial and recreational fisheries in the coterminous United States and could threaten the economy of this region of the Gulf.

Nutrient over-enrichment from anthropogenic sources is one of the major stresses impacting coastal ecosystems. Generally, excess nutrients lead to increased algal production and increased availability of organic carbon within an ecosystem, a process known as eutrophication. There are multiple sources of excessive nutrients in watersheds, both point and non-point, and the transport and delivery of these nutrients is a complex process which is controlled by a range of factors. These include not only the chemistry, but also the ecology, hydrology, and geomorphology of the various portions of a watershed and that of the receiving system. Both the near-coastal hydrodynamics that generate water column stratification and the nutrients that fuel primary productivity contribute to the formation of hypoxic zones. Human activities on land can add excess nutrients to coastal areas or compromise the ability of ecosystems to remove nutrients either from the landscape or from the waterways themselves.

The Assessment Process

As part of a process of considering options for response to hypoxia, the EPA formed the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force during the Fall of 1997. The Task Force asked the White House Office of Science and Technology Policy to conduct a scientific assessment of the causes and consequences of Gulf hypoxia through its Committee on Environment and Natural Resources (CENR). A plan to develop the assessment was completed in March of 1998 and presented to a Task Force convened by the EPA which includes federal, state and tribal government representatives. More recently, the charge to submit an assessment of hypoxia in the Gulf of Mexico was written into law at the end of the 105th Congress (Section 604a of P.L. 105-383).

In addition to this assessment, P.L. 105-383 calls for the development of a plan of action to reduce, mitigate, and control hypoxia in the northern Gulf of Mexico. The Action Plan will be developed by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force. The integrated assessment is intended to provide scientific information as a basis of the Action Plan but it is not intended to make recommendations for action nor is it the only source of information that will be considered in developing the Action Plan.

While the National Oceanic and Atmospheric Administration (NOAA) has been asked to lead the CENR assessment, oversight is spread amongst several federal agencies and the assessment itself is being conducted by teams that include academic, federal, and state scientists from within and outside the Mississippi River watershed The assessment of the causes and consequences of Gulf hypoxia is intended to provide scientific information that can be used to evaluate management strategies, and to identify gaps in our understanding of this problem. While the focus of the assessment is on hypoxia in the Gulf of Mexico, the effects of changes in nutrient concentrations and loads and nutrient ratios on water quality conditions within the Mississippi-Atchafalaya riverine systems is also addressed.

Under the leadership of CENR, a Hypoxia Work Group was formed to conduct the hypoxia science assessment. The Work Group is composed of representatives from the Department of Agriculture, the Department of Commerce, the Department of Defense through both the Army Corps of Engineers and the Office of Naval Research, the Department of Health and Human Services through the National Institute of Environmental Health Services, the Department of Interior through the Minerals Management Service and the U.S. Geological Survey, the Environmental Protection Agency, the National Science Foundation, and the Smithsonian Institution.

The goals of the hypoxia science assessment are to document the state of knowledge of the extent, characteristics, causes, and effects (both ecological and economic) of hypoxia in the northern Gulf of Mexico. The assessment will compile existing information on nutrient sources, identify alternatives for reducing nutrient inputs, and examine the costs and benefits associated with reducing the nutrient loads to surface waters.

Hypoxia Assessment Reports

As a foundation for the assessment, six interrelated reports which examine various aspects of the hypoxia issue were developed by six teams with experts from within and outside of government. The research teams were not established to conduct new research, but rather to analyze existing data and applied existing models of the watershed-gulf system. However, they were encouraged to specifically identify additional research or data needed to fill knowledge gaps.

Each of the reports underwent extensive peer review by independent experts. To facilitate a comprehensive review process of the reports, an editorial board was selected by the Work Group based on nominations from the Task Force and other organizations. Editorial Board members were Dr. Donald Boesch from the University of Maryland, Dr. Jerry Hatfield from the US 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. The Editorial Board worked with the Hypoxia Work Group to select reviewers for the six reports, and served as brokers between the lead authors and the reviewers to ensure that significant comments were addressed.

These six now completed reports are to provide the foundation for the final integrated assessment that will be used by the Task Force to evaluate alternative solutions and management strategies. To download and view the reports using Adobe Acrobat, please click on the titles.

TOPIC 1. Characterization of hypoxia. (Updated report (as of July 20, 2000) available for downloading in pdf, Topic 1 (12.5 Mb) This report describes the seasonal, interannual, and long-term variation of hypoxia in the northern Gulf of Mexico, and its relationship to nutrient loadings. It also documents the relative roles of natural and human-induced factors in determining the size and duration of the hypoxic zone. Lead: Nancy Rabalais, Louisiana Universities Marine Consortium.

TOPIC 2. Ecological and economic consequences of hypoxia. (Updated report (as of July 20, 2000) available for downloading in pdf, Topic 2, 378 kb) This report presents an evaluation of the ecological and economic consequences of nutrient loading, including impacts on Gulf of Mexico fisheries and the regional and national economy. Ecological co-lead: Robert Diaz, Virginia Institute of Marine Science. Economics co-lead: Andrew Solow, Woods Hole Oceanographic Institution, Center for Marine Policy.

TOPIC 3. Flux and sources of nutrients in the Mississippi-Atchafalaya River Basin. (Updated report (as of July 20, 2000) available for downloading in pdf, Topic 3, 4 Mb) This report identifies the sources of nutrients within the Mississippi/Atchafalaya system and within the Gulf of Mexico with two distinct components. The first is to identify where, within the basin, the most significant nutrient additions to the surface water system occur. The second, more difficult component, is to estimate the relative importance of specific human activities in contributing to these loads. Lead: Donald Goolsby, U.S. Geological Survey. For more on the USGS role in the hypoxia issue, including additional on-line information and reports on nitrogen sources and transport in the Mississippi River Basin, please go to the USGS Hypoxia in the Gulf of Mexico Web page.

TOPIC 4. Effects of reducing nutrient loads to surface waters within the Mississippi River basin and Gulf of Mexico. (Updated report (as of July 20, 2000) available for downloading in pdf, Topic 4, 4 Mb) This report 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 of Mexico. Modeling analyses was conducted to aid in identifying magnitudes of load reductions needed to effect a significant change in the extent and severity of the hypoxia. Upper watershed co-lead: Patrick Brezonik, University of Minnesota. Gulf of Mexico co-lead: Victor Bierman, Limno-Tech.

TOPIC 5. Reducing nutrient loads, especially nitrate-nitrogen, to surface water, groundwater, and the Gulf of Mexico. (Updated report (as of July 20, 2000) available for downloading in pdf, Topic 5, 5.7 Mb) The focus of this report was to identify and evaluate methods to reduce nutrient loads to surface water, ground water, and the Gulf of Mexico. The analysis was not restricted to reduction of sources alone, but included means to reduce loads by allowing the system to better accommodate those sources through, for example, modified hydraulic transport and internal cycling routes. Lead: William Mitsch, Ohio State University.

TOPIC 6. Evaluation of economic costs and benefits of methods for reducing nutrient loads to the Gulf of Mexico. (Updated report (as of July 20, 2000) available for downloading in pdf, Topic 6, 3.4 Mb) In addition to evaluating the social and economic costs and benefits of the methods identified in topic 5 for reducing nutrient loads, this analysis included an assessment of various incentive programs and any anticipated fiscal benefits generated for those attempting to reduce sources. Lead: Otto Doering, Purdue University.

The Topic Report files are large and may take some time to download. Printed copies of the reports can be requested from:

NOAA National Centers for Coastal Ocean Science
Coastal Ocean Program
1315 East West Highway, Room 9700
Silver Spring, MD 20910
telephone: 301-713-3338
fax: 301-713-4044
e-mail: coastalocean@cop.noaa.gov

Public Comments

As published in the Federal Register on May 4, 1999, the public has been invited to comment on these report for the purposes of providing input to the Integrated Assessment and, subsequently, the Action Plan.

The public comment period on the six hypoxia reports formally closed on August 2, 1999. Following are the comments received:

Several commenters referred to the following two recent reports on hypoxia in the Gulf of Mexico:

"Gulf of Mexico Hypoxia: Land and Sea Interactions"
Council for Agricultural Science and Technology, Ames, Iowa
ph: 515-292-4512
www.cast-science.org

"The Role of the Mississippi River in Gulf of Mexico Hypoxia"
Ann Carey et al., Environmental Institute, University of Alabama
Sponsored by The Fertilizer Institute, Washington, DC
ph: 202-675-8250
www.tfi.org

Integrated Assessment

The Integrated Assessment examines the distribution, dynamics and causes of hypoxia in the northern Gulf of Mexico; its ecological and economic consequences; the sources and loads of nutrients transported by the Mississippi River to the Gulf of Mexico; effects of reducing nutrient loads; and the social and economic benefits of such methods. The Integrated Assessment is based on the six peer-reviewed hypoxia assessment reports and the public comment received on them. (The Draft integrated assessment is available for download in pdf 260 kb. Figures are available as separate file, pdf, 560 kb.)

This assessment is intended to be useful to non-specialists as well as specialists. It has been written as a concise summary of the state of knowledge using a minimum of specialized scientific terminology.

In addition to this assessment, P.L. 105-383 calls for the development of an plan of action to reduce, mitigate and control hypoxia in the northern Gulf of Mexico. The Action Plan will be developed by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force. This Integrated Assessment is intended to provide scientific information as a basis for the Action Plan but it is not intended to make recommendations for action nor is it the only source of information which the Task Force will consider in developing the Action Plan.

As published in the Federal Register on October 21, 1999, the public has been invited to comment on this draft of the Integrated Assessment. (The Federal Register notice is available for download in pdf, 32 Kb.) Comments will be considered in developing the final version of the Integrated Assessment.

Science Meeting

A Gulf Hypoxia Science Meeting was held on December 3, 1999 (Download the meeting minutes in pdf, 81 kb). Scientists with the full range of perspectives covered by the hypoxia assessment reports and the public comment on them were invited. The objectives were to identify the areas of convergence (where there is general agreement among the scientific community) and identify the essence of disagreements, why the disagreements may be there and what it would take to resolve them. Integrated Assessment will take into account the results of the meeting.

Public Comments on the Draft Integrated Assessment

As published in the Federal Register on October 21, 1999, the public has been invited to comment on this draft of the Integrated Assessment. (The Federal Register notice is available for download in pdf, 32 Kb.) The public comment period on the draft Integrated Assessment formally closed on December 20, 1999. Following are the comments received:

In response to user feedback, some of the large files previously on this page have been replaced with smaller and easier to download versions of the same documents. The documents that have been replaced are highlighted with a red bullet (). The first two documents, previously in color, were replaced with black and white documents. The color pages, which may take longer to download, are listed separately.

Responses to Public Comment

Public comments were carefully reviewed. Responses were written to address issues raised by the public comments, and to explain how comments were incorporated into final Integrated Assessment. This response document also includes new data that helps clarify issues raised in the public comments.

Most attention is directed to comments received on the IA but comments on the six reports which have not been otherwise resolved are also addressed. These responses are directed to issues raised by the public comments; suggestions about specific wording changes have been addressed separately in drafting and revising the IA.

In addition to responses in this document and in the draft and final versions of the IA, public comments were addressed in a public meeting of the MR/GM Task Force and a science meeting in December of 1999 which focused on causal issues raised in the public comments. Finally, a number of comments included suggestions that would more appropriately be considered in the context of developing the Action Plan. The Working Group encourages the MR/GM Task Force to give them full consideration.

Responses in this document are organized by the following categories:

  1. Assessment and Action Plan Process
  2. Contributing Factors
  3. Nitrogen Concentration and Flux: Trends and Sources
  4. Gulf Hypoxic Zone History
  5. International and National Hypoxic Zone Comparisons
  6. Nutrient Control Practices
  7. Adaptive Management, Monitoring and Research
  8. Modeling of Management Options and Impact

Download the response document (pdf, 140 kb). Note: Figure 7.3 on page 30 is not included in the response document. Click here to download (pdf, 212 kb).

Final Integrated Assessment

The Final Integrated Assessment of Hypoxia in the Northern Gulf of Mexico was released in May 2000.

Download the Final Integrated Assessment (pdf, 12.6 Mb).

To download the report in sections, use these links:

Update as of November 1, 2000

The Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, at an October 11 meeting, reached agreement on an Action Plan, based on the Integrated Assessment, to reduce the extent of hypoxia in the Gulf of Mexico. Following is a report of the Task Force meeting from the American Association for the Advancement of Science's ScienceNOW.

12 October 2000 7:00 PM

Agreement to Shrink Dead Zone

BATON ROUGE, LOUISIANA--Negotiations have been raging for months over how to shrink the "dead zone" in the Gulf of Mexico (Science, 23 June, p. 2111). On 11 October, federal and state officials finally agreed on an ambitious $1-billion-per-year plan to revive as much as 30 percent of the dead zone by 2015. The plan could also help head off a crash of Gulf fisheries, officials say.

Dead zones are becoming more common worldwide in areas where coastal waters are swamped with nutrients, particularly nitrogen, from sewage or fertilizer. The excess nitrogen allows algae populations to explode. Dead algae in turn feed bacteria, which gobble up most of the oxygen in the water. Shellfish suffocate, and fish must swim for more healthful waters. The Gulf of Mexico's dead zone swells each summer to about 18,000 square kilometers--roughly the size of New Jersey. Researchers blame the 1.6 million metric tons of nitrogen, much of it from farm fields, that washes down the mighty Mississippi River each year.

The new plan aims to reduce that total. Under the plan, more money would go to programs that reduce excess nutrients in streams and rivers feeding into the Mississippi, which drains 40 percent of the continental United States. These programs would cut fertilizer use on farms, establish wetlands and buffer strips near streams to soak up excess nitrogen, and reduce discharges from sewage treatment plants. The plan also calls for funding scientific efforts to track the flow of nitrogen.

Efforts to reduce farm runoff provoked most of the controversy. Environmentalists wanted to specify nitrogen reduction goals. Farmers and agriculture officials balked, fearing that they might be forced to use less fertilizer and thereby possibly cut crop yields. In the end, officials agreed on a flexible plan to try to reduce nitrogen in the Mississippi by 30 percent, which researchers say will increase oxygen enough to partly restore the dead zone.

The consensus plan is "real progress," says Len Bahr, an environmental adviser to Louisiana Governor Mike Foster. Getting the farmers and environmentalists to agree was a major achievement, says Susan Heathcote of the Iowa Environmental Council: "Without consensus, it wasn't going to go anywhere."

--DAN FERBER

Reprinted with permission from Ferber, D. (2000). Agreement to Shrink Dead Zone. ScienceNOW: www.sciencenow.sciencemag.org/cgi/content/full/2000/1012/1. Copyright 2000 American Academy for the Advancement of Science. Readers may view, browse, and/or download material for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or in part, without prior written permission from the publisher.

In addition, the Science Museum of Minnesota now offers an opportunity for multimedia exploration of hypoxia in the Gulf of Mexico and related issues.

Email specific questions about the project to: hypoxiawg@cop.noaa.gov.
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