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Drought results in fourth smallest Gulf of Mexico "dead zone" since 1985

By Jean Caspers-Simmet
simmet@agrinews.com

Date Modified: 10/03/2012 10:11 AM

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DES MOINES —National Oceanic and Atmosphere Administration-supported scientists have 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 area began in 1985.

Alan Lewitus, with NOAA's Center for Sponsored Coastal Ocean Research, reported the findings at the recent Hypoxia Task Force meeting in Des Moines.

Measuring approximately 2,889 square miles, the 2012 area is slightly larger than Delaware, Lewitus said. The last time the dead zone was this small was in 2000 when it measured 1,696 square miles, an area slightly smaller than Delaware.

The survey also found a patchy distribution of hypoxia across the Gulf differing from any previously recorded, Lewitus said.

"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 size of New jersey," he said.

Lewitus said that the smaller area was expected because of drought conditions and the fact that nutrient output into the Gulf this spring was near the 80-year record low.

"What wasn't expected was how the scattered distribution of hypoxia areas differed from any other documented in the past," Lewitus said. "Confirmed, however, is the strong relationship between the size of the hypoxic zone and the amount of fresh water and nutrients carried into the Gulf by the Mississippi River."

Research cannot rely on any one year of data because of the extreme variability and weather events, Lewitus said.

"But we can see that nutrient reduction is appropriate management to reduce hypoxia," Lewitus said.

The smallest recorded dead zone to date measured 15 square miles in 1988, another severe drought year. The average size of the dead zone over the past five years has been 5,684 square miles more than twice the 1,900 square mile goal set by the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force.

Hypoxia is fueled by nutrient 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.

Prior to the LUMCON cruise, two surveys in June, one led by a NOAA-supported Texas A&M team and another by NOAA's Southeast Fisheries monitoring and assessment program's summer survey found, very little hypoxia in the Gulf.

The hypoxic zone off the coast of Louisiana and Texas forms each summer and threatens Gulf fisheries.