Dead zone in gulf could be largest on record

NEW ORLEANS - Researchers predict a "dead zone" of oxygen-depleted waters off the Louisiana and Texas coasts could grow this summer to 10,084 square miles — making it the largest such expanse on record.

If the preliminary forecast holds, the researchers say, the size of the so-called "dead zone" would be 17-21 percent larger than at anytime since the mapping began in 1985 — and about as large as the state of Massachusetts. Another forecast is planned next month.

The report Monday from scientists at Louisiana State University and the Louisiana Universities Marine Consortium is based on May nitrate loads on the Mississippi River at Baton Rouge.

Excess nutrients can spur the growth of algae, and when the algae die, their decay consumes oxygen faster than it can be brought down from the surface. As a result, fish, shrimp and crabs can suffocate, threatening the region's commercial fishing industry.

"Tropical storms and hurricanes have the potential of disrupting the physical structure of the water column and aerating the bottom layer," the forecasters noted. "If no strong storms appear, then this year’s dead zone is predicted to be 17-21 percent larger than previously measured, and to stretch into Texas continental shelf waters."

R. Eugene Turner, who led the recent modeling effort, said in a statement that "the intensive farming of more land, including crops used for biofuels, has definitely contributed to this high nitrogen loading rate."

Researchers say the largest dead zone measured was 8,894 square miles in 2002. It was about 7,900 square miles last year.

"The prediction of a large hypoxic zone this summer is because the nitrate loading this May, a critical month influencing the size, was exceptionally high," said Turner. "The size of the hypoxic zone last year was only slightly below the largest zone measured. The nitrate concentration in May 2008 is 79 percent of that in May 2007, but the river discharge was 75 percent higher. This means that nitrogen loading to the Gulf of Mexico in May this year will be 37 percent higher than last year and the highest since measurements began in 1970."

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