Gulf of Mexico Dead Zone Is Smaller Than Expected (Update2)

By Brian K. Sullivan

The so-called dead zone in the Gulf of Mexico, where oxygen levels drop too low to support most life near the ocean’s bottom, is smaller this year than expected, the National Oceanic and Atmospheric Administration <> said today.

The zone encompasses about 3,000 square miles (7,770 square kilometers), less than half the size scientists had forecast last month, when they estimated it would be as large as 8,500 square miles, or about the size of the state of New Jersey, NOAA said in a release.

While smaller than anticipated, the dead zone “was severe where it did occur, extending closer to the water surface than in most years,” the release said.

The dead area occurs when the Mississippi and other rivers wash nutrients, mostly from agricultural runoff, into the Gulf, spurring the growth of algae that decomposes and consumes most of the oxygen in the water. The phenomenon threatens commercial and recreational fishing in the Gulf which generates about $2.8 billion annually, NOAA said.

Wind and waves west of the Atchafalaya River <> delta in Louisiana may have mixed oxygen into the water, reducing the size of the dead area, said Nancy Rabalais, a NOAA-supported scientist from the Louisiana Universities Marine Consortium <> in Chauvin, Louisiana.

Shrimp and Crabs

The dead zone is defined as water with 2 milligrams or less of oxygen per liter, Rabalais said on a conference call today.

“That’s the level where a shrimp trawler won’t catch anything,” Rabalais said. “If an animal can swim away they will, and if they can’t they will die.”

During the survey, Rabalais said she saw shrimp and crabs that usually live on the bottom of the Gulf swimming at the surface looking for oxygen.

The dead zone has averaged 6,000 square miles over the past five years, including 2009, and the goal is to reduce the average size to 2,000 square miles or less by 2015, the statement said. Last year, the zone was the second-largest on record, at about 8,000 square miles, according to NOAA. The largest recorded was about 8,500 square miles in 2002.

Increased bio-fuel production in the U.S. Midwest has also added to the amount of nitrates flowing into the Gulf, from the fertilizer required to grow corn for the process, said Donald Boesch, president of the University of Maryland Center for Environmental Science <> in Cambridge, Maryland, on the conference call today.