Microbes munch oil, haven't robbed Gulf of oxygen

WASHINGTON - Federal scientists are reporting the best possible scenario for BP's leaked oil: Microbes are munching the underwater oil, but not robbing the Gulf of Mexico of much needed oxygen or creating so-called "dead zones."

Oxygen levels in some places where the BP oil spilled are down by 20 percent, but that's not nearly low enough to create the dead zones where fish can't live, according to a 95-page report released Tuesday.

Trying to disperse the oil underwater is like walking a tightrope. In an unusual move, BP released 771,000 gallons of chemical dispersant at the leaking well head, about a mile deep, instead of just on the water surface to break up the oil into tiny droplets.

That makes it easier for the oil-eating microbes to do their job, but in doing so they deplete the water of oxygen at places. Scientists were hoping that the oil was degrading but not at a rate that would cause lack of oxygen problems.

"Has it hit the sweet spot? Yes. Was it by design? Partly," said Steve Murawski (murr-OW-ski), the National Oceanic and Atmospheric Administration senior scientist who headed the federal team. Oxygen levels would have had to drop another 70 percent to be classified as dead zones, he said.

The Gulf of Mexico already has a yearly major problem with a natural dead zone - the size of Massachusetts this year - because of farm runoff coming down the Mississippi River.

Federal officials had been tracking oxygen levels and use of chemical dispersants since the oil spill. Had the oxygen plummeted near dangerous levels, the dispersant use would have been stopped, said Greg Wilson, science adviser at the Environmental Protection Agency's emergency management office.

Dispersant use is the source of fierce debate. While it makes it easier for bacteria to degrade the oil, it also tends to hide oil below the surface, and there are concerns about toxicity

One reason that oxygen levels didn't drop too low is because of natural mixing in the Gulf, which kept bringing oxygen from other areas into the lower oxygen levels, Murawski said.

But there were indications that the bacteria was eating the oil underwater - at depths of about 3,300 feet - because oxygen levels sagged, lending more weight to claims last month by the government that much of the oil had degraded, dissolved or evaporated, Murawski said.

From April to July, about 172 million gallons of oil flowed into the Gulf of Mexico from the damaged well. Last month, two non-governmental academic teams of researchers found invisible underwater plumes of oil remained deep underwater in the Gulf

The new work is based on data collected from May through August at 419 locations by nine government and private research ships in the Gulf.

Larry McKinney, director of a Gulf of Mexico research center at Texas A&M University in Corpus Christi, said the new federal data showed that it was a "nearly perfect" outcome.

"They hit it on the head, which is good," said McKinney, who was not involved in the report.

But he noted that earlier pronouncements by the federal government - like last month's about most of the oil being gone - were viewed suspiciously by outside scientists as overly optimistic and because supporting data wasn't made public. He said the federal government has "created this cloud of suspicion that maybe they didn't need to if they were just more open."

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Online:

NOAA report: http://tinyurl.com/39cbbs4

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