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Environment: Deepwater Horizon blowout may have released 250,000 tons of natural gas into the atmosphere

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The massive Deepwater Horizon oll spill spreads a sheen across a huge section of the Gulf of Mexico in May 2010. Photo courtesy NASA.

Findings show value of long-term post-spill monitoring

Staff Report

FRISCO — Methane-munching microbes in the Gulf of Mexico may have been overwhelmed by the sheer volume of gas released during the 84-day Deepwater Horizon oil disaster in 2010.

“Most of the gas injected into the Gulf was methane, a potent greenhouse gas that contributes to global climate change, so we were naturally concerned that this potent greenhouse gas could escape into the atmosphere,” said University of Georgia researcher Samantha Joye.” Many assumed that methane-oxidizing microbes would simply consume the methane efficiently, but our data suggests that this isn’t what happened.”

Joye has been deeply involved in monitoring the environmental impacts of the spill. In 2012, she was part of a team of scientists who recommended a new response model for deep-water spills. She was also part of a group of scientists who questioned the extensive use of chemical dispersants to try and treat the spill.

By most estimates, the broken well deep on the Gulf seafloor spewed about five million gallons of oil and up to 500,000 tons of natural gas into Gulf of Mexico. Early reports suggested that microbes would be able to break down the oil, but after a couple of months of going gangbusters, microbial activity slowed — probably because there weren’t enough other basic nutrients in the ecosystem to sustain the amount of bacteria needed to process the methane, according to Joye, who published findings on the research in the journal Nature Geoscience .

Joye and colleagues from other universities and government organizations measured methane concentrations and the activity of methane-consuming bacteria for ten months, starting before the blowout with collection of an invaluable set of pre-discharge samples taken in March 2010.

The abundance of methane in the water allowed the bacteria that feed on the gas to flourish in the first two months immediately following the blowout, but their activity levels dropped abruptly despite the fact that methane was still being released from the wellhead.

“For these bacteria to work efficiently, they need unlimited access to nutrients like inorganic nitrogen and trace metals, but they also need elevated methane levels to persist long enough to support high rates of consumption,” Joye said. “The bacteria in the Gulf were probably able to consume about half of the methane released, but we hypothesize that an absence of essential nutrients and the dispersal of gas throughout the water column prevented complete consumption of the discharged methane.”

Joye insists that while her group’s conclusions differ from those presented in previous studies, there is no serious conflict between their analyses.

“The issue here was short-term sampling versus long-term time series sampling,” she said. “I hope our paper clearly relays the message that long-term sampling is the only way to capture the evolution of a natural system as it responds to large perturbations like oil well blowouts or any other abrupt methane release.”

Ultimately, scientists need to better understand the behavior of these microbes so that they may better gauge the environmental impacts of future accidents and methane releases due to climate change, she said.

“It’s only a matter of time before we face another serious incident like Deepwater Horizon,” Joye said. “The key is understanding the things that regulate how fast bacteria can consume methane, and that will give us insight into the ultimate fate of this potent greenhouse gas in our oceans.”

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