Thursday, August 5, 2010

Annual Gulf of Mexico "Dead Zone" Report Holds Few Surprises

The Gulf of Mexico's "dead zone" this year is among the largest on record, according to the results of the 25th annual dead-zone survey conducted by the Louisiana Universities Marine Consortium.  The dead or hypoxic zone, an area with levels of dissolved oxygen low enough to severely limit marine life, is 7,722 square miles in size this year; an area slightly smaller than the area of New Jersey.  This year's area is slightly lower than the record of 8,000 square miles measured in 2001.  You can read a complete New York Times article on this study here, and view the Louisiana Universities Marine Consortium media release on its findings here
According to the USGS, "the hypoxic zone in the northern Gulf of Mexico refers to an area along the Louisiana-Texas coast in which water near the bottom of the Gulf contains less than 2 parts per million of dissolved oxygen, causing a condition referred to as hypoxia. Hypoxia can cause fish to leave the area and can cause stress or death to bottom dwelling organisms that can’t move out of the hypoxic zone. Hypoxia is believed to be caused primarily by excess nutrients delivered from the Mississippi River in combination with seasonal stratification of Gulf waters. Excess nutrients promote algal and attendant zooplankton growth. The associated organic matter sinks to the bottom where it decomposes, consuming available oxygen. Stratification of fresh and saline waters prevents oxygen replenishment by mixing of oxygen-rich surface water with oxygen-depleted bottom water."

Most of the nutrients referred to by the USGS in the above quote originate from agricultural runoff in the Mississippi River Basin (see: Nutrient Control Actions for Improving Water Quality in the Mississippi River Basin and Northern Gulf of Mexico

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