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Feds find no dead zones caused by BP's oil spill
Study suggests dispersants were used properly
By MATTHEW TRESAUGUE
HOUSTON CHRONICLE
Sept. 7, 2010, 8:32PM
Bacteria feeding on oil leaked from BP's ill-fated well have not sapped oxygen levels in the Gulf of Mexico, a new federal study concluded Tuesday.
Researchers found a 20 percent drop in oxygen levels within 60 miles of the well head into August, but the levels weren't low enough to create "dead zones" that are harmful to marine life.
The findings suggest BP and federal officials properly used chemical dispersants at the mile-deep well head, not just at the surface, to break oil into tiny droplets that are easier for naturally occurring bacteria to digest, said Steve Murawski, the National Oceanic and Atmospheric Administration's chief scientist for the spill response.
"Did we hit the sweet spot here? To some extent, that's true," Murawski said.
Scientists have warned that if the chemicals are too successful and allow a surge in bacteria, the microbes can use up all the oxygen in the water and kill the fish and other organisms. Dispersants also can hide the oil below the surface.
A recent study by the Woods Hole Oceanographic Institution concluded there was little "appreciable" surge in bacteria growth and oil consumption around a subsea plume that stretched more than 20 miles from the BP well.
A handful of studies have been conducted on the impacts of the spill on the Gulf of Mexico ecosystem, but there is little agreement on the extent of the damage.
"I certainly hope they are correct because it would be one less issue of concern, but I am not yet convinced we can sound the all clear on this one," said Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies in Corpus Christi.
Since BP began using the chemicals, federal scientists have been looking for signs of unusually low oxygen levels and had not found them.
For the latest report, the multiagency team based its findings on measurements taken from 419 locations in the Gulf over three months.
Oxygen levels didn't drop too low partly because of the mixing of oxygen-rich waters with depleted areas in the Gulf, Murawski said, adding that they needed to drop 75 percent for the water to be considered a dead zone.
The Gulf already has a dead zone that forms off the Texas and Louisiana coasts each summer.
The oxygen-starved area is caused by the Mississippi River's discharge of nutrients – primarily commercial fertilizers – from Midwestern states. Sometimes fish can swim away from dead zones, but many bottom-dwellers simply die.