Researchers have discovered that in the five months following the devastating April 2010 Macondo well blowout, naturally occurring bacteria that exist in the Gulf of Mexico (GOM) consumed and removed at least 200,000 tons of oil and natural gas that spewed into the deepwater from the ruptured wellhead.

Teams from the University of Rochester in New York and Texas A&M University analyzed data to determine not only how much oil and gas was eaten by the naturally occurring bacteria, but also how the characteristics of the bacteria’s consumption had changed over the five-month period.

“A significant amount of the oil and gas that was released was retained within the ocean water more than one-half mile below the sea surface,” said the University of Rochester’s John Kessler, who co-authored a paper published in Environmental Science and Technology. “It appears that the hydrocarbon-eating bacteria did a good job of removing the majority of the material that was retained in these layers.”

Kessler worked with graduate research assistant Mengran Du at Texas A&M to analyze more than 1,300 profiles of oxygen dissolved in the GOM water spanning a period of four months and covering nearly 30,000 square miles. The research was supported by the National Science Foundation with additional contributions from the National Oceanic and Atmospheric Administration, the Sloan Foundation, BP plc/the Gulf of Mexico Research Initiative and the Chinese Scholarship Council.

The researchers calculated how many tons of oil and gas had been consumed and at what rate by first measuring how much oxygen had been removed from the ocean.

“When bacteria consume oil and gas, they use up oxygen and release carbon dioxide, just as humans do when we breathe,” Du said. “When bacteria die and decompose, that uses up still more oxygen. Both these processes remove oxygen from the water.” Du added that it is this lower oxygen level that the researchers could measure and use as an indicator of how much oil and gas had been removed by microorganisms and at what rate.

According to Kessler, the research provides the first measurements of how the rate at which the bacteria ate the oil and gas changed as the GOM disaster progressed, which is considered a key to understanding the spill and predicting the behavior of future spills.

“Interestingly, the oil and gas consumption rate was correlated with the addition of dispersants at the wellhead,” said Kessler. “While there is still much to learn about the appropriateness of using dispersants in a natural ecosystem, our results suggest it made the released hydrocarbons more available to the native Gulf of Mexico microorganisms.”

Measurements taken at the spill site indicate that the bacteria’s consumption of oil and gas had ended by September 2010.

“It is unclear if this indicates that this great feast was over by this time or if the microorganisms were simply taking a break before they start on dessert and coffee,” said Kessler. “Our results suggest that some (about 40%) of the released hydrocarbons that once populated these layers still remained in the Gulf post September 2010, so food was available for the feast to continue at some later time. But the location of those substances and whether they were biochemically transformed is unknown.”

Previous research of the GOM spill had shown that oil and gas were trapped in underwater layers, or plumes, and that the bacteria had begun consuming the oil and gas. By using a more extensive data set, the researchers were able to measure how many tons of hydrocarbons released from the spill had been removed in the deepwater. The team’s research suggested that most of what once composed these large underwater plumes of oil and gas was eaten by the bacteria.

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