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Hypoxia
Hypoxia refers to a condition that exists in a body of water when dissolved oxygen falls below healthy levels necessary to support animal life. A hypoxic zone has been identified in the northern Gulf of Mexico, along the Louisiana-Texas coast, in recent decades. It develops every summer, with dissolved oxygen concentration in bottom water reaching less than 2 parts per million. Measurements of the hypoxic zone since 1985 indicate a trend to annual increase in size. The maximum measured extent of the hypoxic zone in the Gulf was reached in 2002, at about 22,000 square km – larger than the area of the state of Massachusetts. The phenomenon affects an area of important commercial and recreational fisheries, although it affects not only fisheries, but the whole ecosystem. This annual hypoxic zone has been referred to as "the dead zone”, although this is not accurate since hypoxia in the Gulf of Mexico is a bottom-water phenomenon and does not affect the entire water table, so the entire zone is not "dead". Nevertheless, it has affected the shrimping industry, which has shifted fishing efforts away from the hypoxic zone. Hypoxia in the Gulf of Mexico is caused primarily by excess nitrogen delivered into Gulf waters from the Mississippi river. The excess of nitrogen leads to excessive production of algae, which in turn can kill marine organisms by reducing the concentration of dissolved oxygen in bottom waters, due to decomposition of the large amounts of organic material. The increased nitrogen input into the northern Gulf of Mexico in recent decades seems to be a result of deforestation and artificial agricultural drainage, river chanelization for flood control and navigation, and increase in nitrogen fertilizer input from agricultural practices. More than one million tons of nitrogen reaches the Gulf via the Mississippi River system each year. The primary approaches to reduce hypoxia in the Gulf of Mexico would include reduction of nitrogen loads to catchments feeding into the Gulf, and restoration and enhancement of nitrogen retention within river basins. Some management practices necessary to achieve this include but are not limited to: Application of nitrogen fertilizers at the recommended rates and not higher; implementation of alternative cropping systems; improvement of manure management; increase of the area of wetlands and vegetated riparian buffers to enhance denitrification and increase nitrogen retention. The hypoxic zone in the northern Gulf of Mexico has raised concerns in the affected region, with research and policy recommendations to address and alleviate hypoxia in the area. In the Unites States, a federal interagency group, Mississippi River/Gulf of Mexico Watershed Nutrient Task Force has been working on a draft action plan for reducing, mitigating and controlling hypoxia in the region. Several agencies have programs looking into the problem and trying to identify and implement solutions, including NOAA’s Coastal Ocean Program at the Center for Sponsored Coastal Ocean Research (CSCOR), the United States Geological Survey (USGS), the United States Environmental Protection Agency, and the Louisiana Universities Marine Consortium. References: Committee on Environmental and Natural Resources (CENR). 2000. Integrated assessment of hypoxia in the Northern Gulf of Mexico . National Science and Technology Council Committee on Environment and Natural Resources, Washington, DC, USA. Center for Sponsored Coastal Ocean Research (CSCOR). 2003. Gulf of Mexico Ecosystems and Hypoxia Assessment. US Environmental Protection Agency (USEPA). 2005. Mississippi River Basin Challenges: Hypoxia. US Geological Survey (USGS). 2005. - The Gulf of Mexico Hypoxic Zone. Additional Information: Hypoxia in the Gulf of Mexico: A Growing Problem US Environmental Protection Agency - Task Force on Gulf Hypoxia Hypoxia in the Gulf of Mexico and Related USGS Activities Hypoxia in the Northern Gulf of Mexico Size of Dead Zone Over Time Keywords: Hypoxia, Dead zone, Nutrient |
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Harte
Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi.
To give proper credit to the original authors, please cite information taken from GulfBase by the original source as displayed. 
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M. Nipper, J.A. Sánchez Chávez,
and J.W. Tunnell, Jr., Editors. 2010.
GulfBase: Resource Database for Gulf of Mexico Research.
World Wide
Web electronic publication. http://www.gulfbase.org, 09 February 2010. |
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