Saturday, 29 January 2011

Gulf oil spill's environmental impact: How long to recover?

What scientists know about how oil spills affect the environment is drawn from a range of past events, no two of which have been alike. Because the blowout occurred 5,000 feet below below the water surface, the Gulf oil spill is unchartered territory.

A thick oil slick spread off the Louisiana coast, as seen in this photo taken May 4. The spill has the potential to affect Louisiana's fragile Gulf Coast marshes for decades, say scientists.
Eric Gay/AP
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By Mark Guarino and Peter N. Spotts, Staff Writers / May 10, 2010
Grand Isle, La.; and Boston
For four days, Myron Fischer has taken time to stroll the beach here on Elmer’s Island – a small, fragile barrier island and newly minted state wildlife refuge on Louisiana’s Gulf Coast.
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Occasionally, he wades into the water to get a closer look at seabirds bobbing and drifting on the sea surface. He returns to the sand, shells cracking under his boots, and says that these patrols are “not something we do on a normal basis.”
But these have not been normal times for Mr. Fischer, director of the state’s new marine biology lab on Grand Isle.
The April 20 undersea oil blowout that destroyed the Deepwater Horizon oil rig and killed 11 oil workers some 40 miles offshore has spewed more than 3.5 million gallons of oil into the Gulf so far. And efforts to slow or halt the 200,000 gallon-a-day flow have failed to this point.
On Saturday, tar balls as big as golf balls began washing ashore on Alabama's Dauphin Island, a barrier island that helps protect the entrance to Mobile Bay and some 16 miles of coastline to the west.
The blowout has been “a new challenge for everyone, for all academia, the science community, the universities,” Fischer says.
What scientists know about how oil spills can affect the environment – and for how long – is drawn from a range of past events, no two of which have been alike. It means that “the leading scientists can build a model for what they think is going to happen, but we may wake up the next morning and not know exactly what to expect,” says Fischer.
Comparisons with the Exxon Valdez spill, for example, can be misleading because of significant differences in the type of oil, the ecosystems affected, and the way natural processes break down oil.
Moreover, the uncertainty is greater in the current spill. For the most part, researchers have studied the aftermath of surface spills. The Deepwater Horizon blowout occurred at 5,000 feet, dispensing crude oil from seafloor to surface.
Many of the long-term effects may remain hidden as natural processes and chemical dispersants break up the oil into small globules dense enough to sink to the bottom. There, it has the potential to affect bottom dwellers for decades.
“This is uncharted territory in terms of assessing the effects of a spill from a deep well like this,” says Judy McDowell, a scientist at the Woods Hole Oceanographic Institution in Massachusetts.
Dr. McDowell was a coauthor of a 
2003 National Academy of Sciences report that remains a seminal work for understanding the behavior of petroleum and petroleum products spilled in marine and coastal environments, many marine scientists say.
For Louisiana in particular, a key area of concern is coastal marshes. They are the breeding ground as well as home base for a wide range of marine life vital to the region’s fishing industries. Moreover, the wetlands provide a first barrier against storm surges from hurricanes.
But southern Louisiana’s wetlands already are stressed – vanishing as the Mississippi Delta sinks beneath the ocean at a rate that, by some estimates, averages 50 acres a day. In addition, the fisheries off the coast are exposed to an annual “dead zone” each spring as nutrient-rich water from the continental heartland moves down the Mississippi and into the Gulf, triggering algae blooms. When the algae die and decompose, the process uses up much of the dissolved oxygen in the water. Fish flee, but bottom dwellers – crabs and other shellfish – generally can’t move fast enough to do so.
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