NASA/U.S. Geological Survey (USGS) annual maps of the Louisiana marshlands reveal what the agencies say is widespread shoreline loss where the coastline was most heavily coated with oil during the 2010 BP Deepwater Horizon oil spill in the Gulf of Mexico.

Following the spill, the length of shoreline that receded more than 13 feet per year quadrupled compared to the year before the spill. The land losses occurred mainly in areas where the shoreline had been impacted by oil—which is known to weaken or kill vegetation, leading to loss of the roots that help hold soil together.

2010 photo of a shoreline in Louisiana impacted by the BP Deepwater Horizon oil spill. Image credit: Bruce A. Davis/Homeland Security2010 photo of a shoreline in Louisiana impacted by the BP Deepwater Horizon oil spill. Image credit: Bruce A. Davis/Homeland SecurityA research team led by USGS geophysicist Amina Rangoonwala used airborne remote sensing imagery to analyze shoreline loss across nearly the entire upper Barataria Bay, located on the western side of the Mississippi River Delta, beginning a year before the spill and extending for 2.5 years after it.

To determine whether the erosion was likely to be caused by the oil, the researchers also compared shoreline loss linked to the deposited oil with shoreline erosion caused by high waves from Hurricane Isaac in 2012.

They found that although erosion occurred at isolated sections of the shoreline before the spill, the pre-spill shoreline (as analyzed from 2009 to 2010) was largely stable. In the first year after the spill (2010 to 2011), the erosion pattern changed dramatically, from isolated to widespread.

Erosion occurred mainly along shorelines with documented heavy-to-moderate oil coating. In the second year after the spill, the higher loss rates extended to areas that had less oil coating.

“Our study uniquely shows that the patterns of shoreline recession seen in this region can be directly related to distinctly different causes: broadly dispersed erosion due to oiling from the Deepwater Horizon spill and enhanced, but spatially limited, erosion due to intense storm impacts,” says Rangoonwala.

The impacts of the spill documented by the team included both the loss of wetlands due to shoreline erosion and island fragmentation—in which small islands are broken into even smaller islands, creating more shoreline.

According to the researchers, land lost from fragmentation is unlikely to be reestablished, particularly in this part of the Mississippi River delta, where levees prevent an influx of new sediments from the river. This will alter natural coastal defenses against flooding.

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