Restoring Life to the Dead Zone: Addressing Gulf Hypoxia, a National Problem
USGS Fact Sheet 016-00
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The hypoxic zone is an area of approximately 6,000-7,000 square miles of water with oxygen levels below 2 parts per million. Trawlers are unable to catch any shrimp or bottom-dwelling fish at this low level of oxygen, and dead organisms have been found there.
The zone occurs between the inner and mid-continental shelf of the northern Gulf of Mexico, from the Mississippi River birdfoot delta westward, to the upper Texas coast.
There has been awareness of the problem since the 1970's, but scientists are unsure whether or not this is a recent problem that has been worsened by nutrient application.
The zone is caused by increased nutrients from the Mississippi River, especially nitrogen and phosphorus from fertilizers, animal wastes, and domestic sewage; seasonal river discharges worsen the nutrient enrichment. Average nitrate-nitrogen concentration in the river's mainstem has doubled since 1950, with commercial fertilizers being the largest source. Nutrients encourage algal blooms, alter the food chain, and eventually deplete the area of oxygen.
Attacking the Problem
About 25% of the nitrogen load in the Mississippi River originates in the Lower Mississippi River Valley, downstream of the Mississippi-Ohio River confluence. While most work related to the hypoxia issue involves either nitrogen reduction in the upper reaches of the Mississippi Basin or in understanding the relation of nutrient loading and the hypoxia zone offshore, the USGS National Wetlands Research Center has chosen to take another approachusing inland and coastal wetlands to attack the hypoxia problem.
With NAWQA researchers, Center scientists will
Information from the research is particularly needed by the U.S. Fish and Wildlife Service, National Oceanic and Atmospheric Administration's National Marine Fisheries Service, National Park Service, U.S. Environmental Protection Agency, U.S. Department of Agriculture's Natural Resources Conservation Service, and the States of Arkansas, Texas, Louisiana, and Mississippi.
With additional funding, the Center can
For more information, contact:
U.S. Geological Survey