Deepwater Horizon Spill Caused Shore Erosion in the Gulf of Mexico

Deepwater Horizon Spill Caused Shore Erosion in the Gulf of Mexico
November 3, 2016

Environmental disaster stories often play out like Shakespearean tragedies. They hit their climax in act two—Romeo talks to Juliet on the balcony, Macbeth kills King Duncan, Iago causes the fight that pits Othello against his wife and lieutenant—and what follows is a slow spiral of destruction.

The BP oil spill in the Gulf of Mexico follows the same pattern. The explosion of the Deepwater Horizon oil platform, which killed 11 people in April 2010 represented a fiery climax while the gush of oil spreading through the Gulf and onto the shore—the slow spiral.

Deepwater Horizon PlatformThe new movie "Deepwater Horizon" tells the story of the climax, translating the events that are harrowing enough in print onto the screen, while a new study from Duke University’s Nicholas School of the Environment helped create a richer picture of what happened in the aftermath.

Apart from harming the wildlife in the Gulf of Mexico and destroying property, the 100 million gallons of spilled oil also had an effect on the land, specifically causing it to erode away into the sea.

Brian Silliman, an associate professor of marine conservation biology at Nicholas, surveyed more than 270 miles of coastline from Lousisiana to Alabama and found that in the worst-hit shores of the Gulf Coast, the beach eroded roughly 1.5 meters per year faster than normal.

Shoreline erosion happens all over the world, anywhere the right combination of sea level change, waves and currents can pick up sand from a beach and move it somewhere else. It happens on the Outer Banks frequently, which is why many communities opt to nourish their beaches by replacing lost sediment.

Marsh GrassFor decades, engineers have been working on methods to stop this type of erosion with sea walls, rocky revetments and other structures, but the best results have come from swamp grasses. The roots of the swamp grasses cling to shoreline soil, slowing down the erosion process. States all along the Atlantic Coast are planting grasses to slow beach erosion.

Those grasses grow naturally along the Gulf Coast and as the oil from the Deepwater Horizon spill spread, it washed up on shore and coated these grasses, suffocating them. When the grasses died, the roots lost their hold on the soil, allowing it to erode.

Silliman charted how quickly the coastline eroded compared to the percentage of the grass killed by oil at different locations along the Gulf Coast. He found that erosion did not dramatically increase until 90 percent of the grass stems in the area were covered in oil. 

This study, published in the journal Nature Scientific Reports, marks the first time that scientists have established a threshold of how much oil a marsh can withstand. Areas that received less than 90 percent oil cover did not show accelerated erosion, and Silliman says it is possible that these areas could recover, replacing much of their former grass.

But for the locations above the 90 percent mark, two years of rapid erosion left mud where the marsh grass used to be. That said, after a few years, beyond where the oil actually coated the grass, erosion rates went back to normal.

In the years since the oil spill, more and more information has come to light about its effects. Some, like fisheries, can be restocked and regrown; while others, like an expanse of shoreline, cannot. But as we learn more, the image of the tragedy becomes ever clearer.

—Daniel Lane

Daniel covers science, medicine, engineering and the environment in North Carolina.

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