Hypoxia in the Northern Gulf of Mexico: A National Water Quality Blight Gets Another Look

In 2001 the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force, made up of senior representatives from federal, state, and tribal agencies released an Action Plan for mitigating, reducing, and controlling hypoxia in the northern Gulf of Mexico. The plan described immediate, voluntary actions for state and federal partners. It also required a periodic reassessment of the underlying scientific understanding of hypoxia and a revised plan every five years to meet the goal to reduce its size to a five-year running average of 5,000 sq km; about a third of its current size. In June 2005 the Task Force approved plan for a two-year process to reassess the science and revise the 2001 Action Plan.

The conclusion of the science that supported the 2001 Action Plan was that increased nitrogen from the Mississippi Basin was the principle cause of the growth in the size of the annual zone. The first step in the reassessment was a peer review of an EPA White Paper that questioned the relative roles of nitrogen (N) and phosphorous (P) as limiting nutrients for algal production in the Gulf. Although the paper was judged by the peer reviewers to be flawed, it did raise important questions for consideration by the Task Force during the reassessment. All reviewers noted the importance of a dual nutrient approach, especially additional consideration of processes affecting the bioavailability of N and P. The following issues were identified as important areas for consideration in the reassessment process:

• Addition of bioavailable P from particle bound P in marine waters
• Release of bioavailable P from sediments (especially under eutrophic conditions)
• Recycling of phosphorus from phytoplankton
• Nitrification and denitrification
• Contributions of P from deeper Gulf waters
• Mechanisms related to near-shore Gulf waters stratification,
• Gulf hydrodynamics in relation to Mississippi River Basin discharges
• Additional bioassay in near-shore northern Gulf waters
• Further historical evaluation of N and P loadings and flows related to hypoxic response
• The spatial and temporal dynamics of phytoplankton production

A summary of peer review comments and EPA's response can be found at: http://www.epa.gov/msbasin/taskforce/review_summ.htm.

The backbone of the reassessment process is a series of scientific symposia, an expert review of all available information by EPA's Science Advisory Board (SAB), and a review of ongoing action items by the Task Force. Interested stakeholders may comment on SAB panel members, submit information for consideration by the SAB panel, and comment on draft reports through the SAB website at http://www.epa.gov/sab.

The EPA and USGS are also engaged in updating modeling data on nutrient loads throughout the Mississippi River watershed using USGS's SPARROW model. The intent of this study is to identify those watersheds that are the key contributors of nutrients and sediments to the Gulf of Mexico and would provide the most benefit to the basin for targeted nutrient reduction strategies. The model will be calibrated to take into consideration the variability in land use/land cover, basin slope, soil types, and point-source loadings present throughout the study area. The SPARROW model will then be used to estimate phosphorus, nitrogen, and sediment loadings from all of the watersheds (at approximately the 14 digit HUC scale) in the study area.

The Task Force is appealing to the scientific community for expert participation and contributions to the reassessment. One symposium has already been held in September 2005, which focused on nutrient management in the Upper Mississippi River Sub-basin. Scientific experts in multiple disciplines are encouraged to participate or attend the three upcoming symposia -- Gulf Science (April 25-27 in Baton Rouge), Lower Mississippi River (wetlands emphasis, early June in Memphis), and Sources, Fate, and Transport Synthesis (this Fall). Information on registration, dates, location and paper solicitation will be announced on the hypoxia website at http://www.epa.gov/msbasin/taskforce/reassess2005.htm.

Proceedings from these symposia will be available for public review and for the SAB panel. The panel will then synthesize the current scientific understanding of hypoxia in the northern Gulf of Mexico and provide recommendations to the Task Force on appropriate revisions to the Action Plan of 2001.

For more information on hypoxia, the Task Force, and the reassessment go to the website at www.epa.gov/msbasin or send an email with questions to gulf-hypoxia@epa.gov.

Gulf of Mexico Hypoxia Symposium

Co-sponsored by: The U.S. National Oceanic and Atmospheric Administration 
and the U.S. Environmental Protection Agency

25-27 April 2006 Baton Rouge, Louisiana

Purpose: to evaluate the current scientific understanding of factors influencing hypoxia in the Gulf of Mexico and to assess the appropriateness of models used to guide management activities for reducing hypoxia in the region.

Additional information on the symposium may be found at http://www.cop.noaa.gov/stressors/pollution/features/fs-2005-11-25-hyp.html