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Oct 12, 2010 10:05 PM by Alison Haynes

250 square-mile dead zone in La. sound

NEW ORLEANS (AP) - Researchers mapped a 250-square mile area of low oxygen this summer in Chandeleur Sound and say the dead zone possibly formed after state officials opened a river diversion to keep oil from a damaged BP well from fouling marshes.
The report by the Lake Pontchartrain Basin Foundation, which monitors water quality, said the dead zone formed sometime between May and July in the weeks after a Mississippi River diversion at Caernarvon was opened to wash oil threatening the Louisiana coast out to sea. River water contains a lot of nutrients, which can lead to a dead zone.
Still, John Lopez, a coastal scientist with the foundation, said Tuesday it was far from clear what caused the dead zone this year.
"We're just starting to see this thing," Lopez said. "It could be something that develops every summer."
He said the low oxygen might have suffocated immobile shellfish and invertebrates in Chandeleur Sound.
The group said a dead zone was observed in 2008 too after the Army Corps of Engineers opened a spillway on the Mississippi River to ease high river levels. The nutrient-rich water is thought to have caused the dead zone then.
In August, a red tide was reported in Chandeleur Sound which might have been caused by high nutrient levels, the report said.
Eugene Turner, a coastal scientist and dead zone expert at Louisiana State University, said the diversion probably caused the low oxygen levels.
"When you add freshwater and nutrients to an estuary you are going to have consequences," Turner said.
Martin T. O'Connell, a University of New Orleans fish biologist who studies Chandeleur Sound, said more research is needed to study the dead zone.
"My gut feeling is that it happens on a regular basis," O'Connell said. "It's something we have to keep an eye on."
Every summer, a separate dead zone forms in the Gulf of Mexico. The dead zone in deeper waters is caused by bacteria feeding on algae blooms from the flow of farming runoff and other nutrients from the Mississippi River. This year's area measured at least
7,722 square miles.

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