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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.

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Still, she says, it took about a decade before researchers began to see the kinds of organisms in the harbor one would have seen prior to the spill, such as fiddler crabs. Dr. Reddy has continued to take samples from the marsh, and some 40 years later, oil remains trapped in the sediment three to eight inches below the surface. And it has changed little chemically since its arrival.

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“If you stick a shovel into the ground and lift it, you will smell diesel fuel,” he says. “And when you analyze it, it doesn’t look like it’s been significantly changed chemically. And the fiddler crabs, mussels, and marsh grasses are not as healthy” as they are at pristine sites.

Yet above ground, he adds, the marsh looks to have recovered to the point where it could grace a tourist’s postcard.

Another nearby site affected by a spill in 1974 and still under study has not fared as well. In many places, the marsh grass still hasn't returned. And when a research team looked at aerial photos of the site taken before the spill, the researchers found evidence of post-spill erosion in areas that received the most oil. The oil worked its way into the soil, killing off marsh grasses that would have stemmed the erosion.

Reddy cautions that the impact of oil spills depends a great deal on location and dose. Differences in air and ocean temperatures can play a significant role in the pace at which biological processes can begin to blunt the effects of oil.

Research efforts such as this represent a cautionary tale of another sort, according to Joanna Burger, a Rutgers University ecologist. Beware of the small numbers, as in: Only 20 percent of the wetlands have been affected.

“The problem is it’s always the 20 percent of the marsh that’s on the edge, in the intertidal zone,” she says. “That’s the most productive zone in terms of invertebrates and small fishes. And it’s where the herons and egrets feed. You might have destroyed only 20 percent of the marsh, but you might have destroyed 90 percent of the animal production.”

The point is not lost on Louisiana’s Fischer: “As we lose the coastal edge, we are losing the productivity of the area. Throughout history we have had various types of small tragedies such as freezes and pollutants, but we’ve never experienced a large case of oil intrusion into the estuarine areas. What would happen? I don’t have the answer.”

Related:

Transocean Deepwater Horizon oil rig explosion shows new risks

Ecological risk grow as Deepwater Horizon oil rig sinks in Gulf

Spread of Gulf oil spill puts fragile Louisiana Coast on alert

IN PICTURES: Louisiana oil spill and Destructive oil spills

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