Gulf dead zone declines with drought
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WASHINGTON, August 2, 2012 -Scientists supported by the National Oceanic and Atmospheric Administration (NOAA) found the size of this year's Gulf of Mexico oxygen-free ‘dead zone' to be the fourth smallest since mapping of the annual hypoxic, or oxygen-free area began in 1985.
Measuring approximately 2,889 square miles, the 2012 area is slightly larger than Delaware.
Hypoxia is fueled in part by runoff from agricultural and other human activities in the Mississippi River watershed, which stimulates an overgrowth of algae that sinks, decomposes and consumes most of the life-giving oxygen supply in bottom waters, according to NOAA.
The survey also found a patchy distribution of hypoxia across the Gulf, differing from any previously recorded. This is in stark contrast to last year, when flood conditions, carrying large amounts of nutrients, resulted in a dead zone measuring 6,770 square miles, an area of the state of New Jersey.
“The smaller area was expected because of drought conditions and the fact that nutrient output into the Gulf this spring approached near the 80-year record low,” said Nancy Rabalais, Ph.D., executive director of the Louisiana Universities Marine Consortium who led the survey cruise.
“What wasn't expected was how the scattered distribution of hypoxia areas differed from any others documented in the past,” Rabalais said. “Confirmed, however, is the strong relationship between the size of the hypoxic zone and the amount of fresh water and nutrients carried to the Gulf by the Mississippi River.”
The smallest recorded dead zone to date measured 15 square miles in another drought year: 1988. The average size of the dead zone over the past five years has been 5,684 square miles, which NOAA says is more than twice the 1,900 square mile goal set by the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force.
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