98-869 - Marine Dead Zones: Understanding the Problem
13-Aug-2007; Eugene Buck; 16 p.
Update: Previous Releases:
Sep. 20, 2006
November 23, 1998
Abstract: An adequate level of dissolved oxygen is necessary to support most forms of aquatic life. While very low levels of dissolved oxygen (hypoxia) can be natural, especially in deep ocean basins and fjords, hypoxia in coastal waters is mostly the result of human activities that have modified landscapes or increased nutrients entering these waters. Hypoxic areas are more widespread during the summer, when algal blooms stimulated by spring runoff decompose to diminish oxygen. Such hypoxic areas may drive out or kill animal life, and usually dissipate by winter. In many places where hypoxia has occurred previously, it is now more severe and longer lasting; in others where hypoxia did not exist historically, it now does, and these areas are becoming more prevalent.
The largest hypoxic area affecting the United States is in the northern Gulf of Mexico near the mouth of the Mississippi River, but there are others as well. Most U.S. coastal estuaries and many developed nearshore areas suffer from varying degrees of hypoxia, causing various environmental damages. Research has been conducted to better identify the human activities that affect the intensity and duration of, as well as the area affected by, hypoxic events, and to begin formulating control strategies.
Near the end of the 105th Congress, the Harmful Algal Bloom and Hypoxia Research and Control Act of 1998 was signed into law as Title VI of P.L. 105-383. Provisions of this act authorize appropriations through NOAA for research, monitoring, education, and management activities to prevent, reduce, and control hypoxia. Under this legislation, an integrated Gulf of Mexico hypoxia assessment was completed in the late 1990s. In 2004, Title I of P.L. 108-456, the Harmful Algal Bloom and Hypoxia Amendments Act of 2004, expanded this authority and reauthorized appropriations through FY2008. Legislation has been introduced in the 110th Congress to reauthorize and amend the Harmful Algal Bloom and Hypoxia Research and Control Act.
As knowledge and understanding have increased concerning the possible impacts of hypoxia, congressional interest in monitoring and addressing the problem has grown. The issue of hypoxia is seen as a search for (1) increased scientific knowledge and understanding of the phenomenon, as well as (2) cost-effective actions that might diminish the size of hypoxic areas by changing practices that promote their growth and development. This report presents an overview of the causes of hypoxia, the U.S. areas of most concern, federal legislation, and relevant federal research programs. This report will be updated as circumstances warrant.