Naturally-occurred bacteria in the U.S. Gulf of Mexico consumed and removed in the five months following the Macondo oil spill at least 200,000 tons of oil and natural gas that was dispersed into the deepwater Gulf from Macondo, according to researchers at the University of Rochester and Texas A&M University.
The study results, published this week in Environmental Science and Technology, include the first measurements of how the rate at which the bacteria ate the oil and gas changed as Macondo progressed - information that is fundamental to understanding both this spill and predicting the behavior of future spills.
"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 John Kessler, a co-author of the study and associate professor of the University of Rochester's Department of Earth and Environmental Sciences, in a statement.
"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 said.
Kessler and graduate research assistant Mengran Du at Texas A&M analyzed over 1,300 profiles of oxygen dissolved in the Gulf of Mexico water spanning a period of four months and covering nearly 30,000 square miles.
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," said Du. "When bacteria die and decompose, that uses up still more oxygen. Both these processes remove oxygen from the water."
Previous studies of the Macondo spill show that oil and gas were trapped in underwater layers, or plumes, and that the bacteria had started consuming the oil and gas. By using a more extensive data set, the researchers were able to measure just how many tons of hydrocarbons released from the spill had been removed deep Gulf waters.
The research findings suggest that the majority of what once composed these large underwater plumes of oil and gas were eaten by the bacteria.
The oil and gas consumption rate was correlated with the addition of dispersants at the wellhead, Kessler said.
"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."
The researcher's measurements showed that the consumption of oil and gas by bacteria had stopped in 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 [started] on dessert and coffee," said Kessler.
Approximately 40 percent of the released hydrocarbons that once populated these layers still remained in the Gulf after September 2010, so food was available for the feast to continue to at some later time.
"But the location of those substances and whether they were biochemically transformed is unknown," Kessler said.
Kessler told Rigzone that many different types of bacteria contributed to consuming the oil, as different bacteria consume different compounds.
Following the Macondo incident, researchers began examining what had happened to most of the oil spilled from the well. One study found a type of oil-eating bacteria – a newly discovered species related to the Oceanospirillales – adapted to the cold water and was twice as plentiful inside the oil plume as outside, PBS reported in August 2010.
This type of bacteria made up 90 percent of all bacteria in the oil plume, PBS reported.
The National Science Foundation supported the research, with additional contributions from the National Oceanic and Atmospheric Administration, the Sloan Foundation, BP and the Gulf of Mexico Research Initiative, and the Chinese Scholarship Council.
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