The 2010 Gulf oil spill has contributed to historic erosion rates for Louisiana's costal marshes. (Photo by Deepwater Horizon Response via Flickr.)

The Louisiana bayou is still struggling to recover from the 2010 oil spill that caused its coastal wetlands to erode at historic rates.

Louisiana's delicate marshes were rapidly disappearing before BP's Deepwater Horizon dumped five million barrels of oil into the Gulf of Mexico. But now, two years after the largest oil spill in U.S. history, the erosion of the bayou has accelerated at an alarming pace.

"These salt marshes, in many ways, are the lifeblood of the coastal communities there in Louisiana," said Ben Silliman, a marine biologist at the University Florida who studies them.

Known as America's hardest working wetlands, the bayou is home to valuable fisheries that support local economies. It also acts as a sponge to absorb important nutrients that protect the open waters from potential harmful algal blooms.

And in the case of storms, the marshes can protect the shoreline from incoming waves by acting as a bit of a natural seawall. They help control flooding by absorbing water as the sea level rises during storms.

Silliman said the marshes were eroding even before the 2010 oil spill. Levees along the Mississippi River have starved them of the sediment and fresh water they need to survive for decades. But oil from the BP disaster overwhelmed the bayou’s steep outer edge.

"It looked like a thick, black belt along the shoreline," Silliman said. 

Though marsh grasses are typically resilient to oil — studies shows that they often grow back within one to two years — but there was simply too much of it in 2010.

Smothered in oil, the marsh grasses started to die and decay. The oil killed their roots, which collect the sediments the wetlands so desperately need.

The effects of the oil spill were startling. Silliman said the annual erosion rate on the bayou's outer edge doubled for more than 18 months, from five to 10 feet per year.

To make matters worse, the wetlands are sinking at the same time the sea level is rising.

"It's a bit of a double-whammy for these marshes to try to keep up with the stresses in the system," Silliman said.

The U.S. Army Corps of Engineers has announced a plan to remove mud from the Mississippi River and relocate it to wetlands along the Gulf of Mexico. Historically, the corps has used dredges to move the river mud out of the shipping channel by getting it to flow out to the Gulf. But that practice is seen by engineers and scientists as a waste of valuable mud that Louisiana needs to restore its shrinking coast, according to the Associated Press.

With the hope of reclaiming vital marshes, Silliman said he was excited about the project's potential.

"It will be a massive, massive effort," he said. "It's encouraging that we're all at the table discussing it."

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