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Oil spill hastened damage to Louisiana marshes

The 2010 BP oil spill accelerated the loss of Louisiana's delicate marshlands, which were already rapidly disappearing before the largest oil spill in U.S. history, a new study reports.

As the oil washed into the marshlands, it coated and smothered thick grasses at their edge. When the grass died, deep roots that held the soil together also died, leaving the shore banks of the marshlands to crumble, said Brian Silliman, the University of Florida researcher who led the new study.

"We already knew that erosion leads to permanent marsh loss, and now we know that oil can exacerbate it," Silliman said.

In Louisiana's Barataria Bay, oiled marshes eroded at about twice the rate of nonoiled marshes, receding nearly 30 feet per year, Silliman's team found.

"Doubling the rate of erosion is a huge number," said Zoe Hughes, a marsh researcher at Boston University who was not involved in the research. "It's very significant in areas where you have erosion anyway."

About 45 linear miles of Louisiana marshes were moderately to heavily oiled during the spill.

The researchers found that the accelerated erosion lasted about 18 months. By then, grasses had regrown on exposed mudflats in the formerly oiled marshes, securing the edges from further sped-up erosion.

But the marshlands lost during the spill are gone for good. "When you get edge erosion, it's gone," Hughes said. "It's not coming back."

Situated at the foot of the Mississippi River, Louisiana's salt marshes are a "lifeblood" for the state, Silliman said. Shrimp, oysters, clams and fish hatch in the marshes, making these areas vital to the state's fishing industry.

The marshes also act as a two-way buffer: They protect the mainland from storms and attendant storm surges while simultaneously soaking up fertilizers and other runoff from farms that can cause damaging algae blooms in the Gulf of Mexico.

The study was published Monday in the Proceedings of the National Academy of Sciences. It was funded by a $200,000 grant from a $500 million research fund BP set up after the spill.