ecosystems ,

Will oil spill expand Gulf’s dead zone?

MICHIGAN STATE (US)—The worst oil spill in U.S. history could worsen and expand the oxygen-starved “dead zone” in the Gulf of Mexico, known for its inhospitability to marine life, suggests Michigan State University professor Nathaniel Ostrom.

It could already be feeding microbes that thrive around natural undersea oil seeps, he says, tiny critters that break down the oil but also consume precious oxygen.

“At the moment, we are seeing some indication that the oil spill is enhancing hypoxia,” or oxygen depletion, Ostrom says. “It’s a good hint that we’re on the right track, and it’s just another insult to the ecosystem—people have been worried about the size of the hypoxic zone for many years.”

The dead zone, which can grow to the size of a small U.S. state, is believed to stem from urban runoff and nitrogen-based fertilizers from farmland swept into the Gulf by the Mississippi River.

Higher springtime flows carry a heavier surge each year, nourishing algae blooms that soon die and sink. Those decay and are eaten by bacteria that consume more oxygen, driving out marine life and killing that which can’t move, such as coral.

With the spill overlapping a section of the dead zone, the impact on that region is unknown.

As it happened, Ostrom was researching nitrogen cycling in the Gulf in late May. When the British Petroleum Deepwater Horizon offshore drilling rig blew out and sank April 20, Ostrom and collaborator Zhanfei Liu from the University of Texas at Austin quickly landed federal support to expand their inquiry. They’ll be analyzing water samples in the coming months, hoping to determine if the oil in the water will promote oxygen starvation, and if so, how.

Oil-hungry microbes can be expected to consume more oxygen from the water as they feast on hydrocarbons, Ostrom says. But the oil slick and chemical dispersants also could reduce the flow of oxygen from the atmosphere to the ocean, and possibly reduce the sunlight available to nourish oxygen-producing marine plant life.

Ostrom points to the oil-eating microbes as likely the biggest, if unrecognized, players in the drama. “We’re fortunate to have them,” he says. “They’re doing the cleanup—not BP.”

The project was supported by the National Science Foundation and Michigan State University.

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