Last Modified: Sunday, February 20, 2011 at 9:06 p.m.
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"Methane, the volatile gas that triggered the explosion of the BP Deepwater Horizon oil rig last April, made up at least a third of the total volume of material discharged into the Gulf of Mexico during the three-month disaster.
While the crude oil received all the attention, methane was largely overlooked as a component of the spill, despite its potential to also cause environmental damage.
As scientists try to figure out how much methane was released, the fate of the gas has become somewhat controversial. A report in Nature Geoscience recently tried to estimate the amount of methane released -- 260,000 to 500,000 tons. The research sets a higher figure compared to previous studies, and calls into question earlier assertions that bacteria consumed all the gas released.
By the highest estimates, the burst rig pumped more than 6 million barrels of oil -- about 800,000 tons -- into the Gulf of Mexico between late last April and mid-July, according to the Nature Geoscience report. There are 42 gallons in a barrel.
During the same period, as much as 500,000 tons of gas -- with an energy equivalent of more than 3 million barrels of oil -- may have also escaped into the Gulf of Mexico, based on the well's reservoir capacity.
Methane and other gases released during the spill are a concern because they can disrupt the balance of life in the Gulf, and persist for years in the cold, deep sea environment. In addition to feeding the growth of bacteria, the substance -- which dissolves in water -- can be toxic to sea life.
"When discussing the spill, it has been the tendency of both the government and BP to completely ignore the gas that was released. I think they are responsible legally and ethically," said Ian MacDonald, a biological oceanographer at Florida State University, who co-authored the new study. The lead author was Samantha Joye, a professor with the University of Georgia's department of Marine Science.
Last summer, during the disaster, researchers found methane in highly concentrated plumes near the well head, in waters ranging from about a half-mile to three-quarters of a mile deep. Some of the methane observed was also in an ice-like form, called methane hydrate, caused by extreme pressure.
The plumes coincided with oxygen depletion, but the depletion was not severe. Joye's report suggests microbes were limited in their ability to eat the methane by low oxygen and scarcity of other nutrients.
"The amount of methane was more methane than the amount of oxygen available to break it down," MacDonald said.
Another team of scientists visited the area near the wellhead in late August through early September and reached a different conclusion. The team, led by John Kessler of Texas A&M University, found normal methane concentrations.
In June, while the gusher was still active, methane concentrations were 10,000 to 100,000 times more than the natural background concentration, Kessler said. His team concluded that bacteria ate it all by August. He pointed to low oxygen levels in the water, the residual presence of bacteria that eat methane, and residual traces of oil.
"We see no other logical conclusion, other than methane itself was completely consumed by the bacteria living in these waters," Kessler said.
MacDonald said the methane may have become diluted and harder to find, but was not likely to be entirely consumed so rapidly. His team also estimated that a much larger amount of methane was released. Kessler's high estimate of the methane released -- 200,000 tons -- was lower than Joye's lowest possible estimate.
"The important thing that we're doing is we're establishing a number for the amount of gas that was released," MacDonald said. "We are the first people to sit down and make those calculations."