Oil spill caused more loss of land, study says
Six years after the Deepwater Horizon oil spill devastated the shore of the Gulf of Mexico, scientists are still taking stock of the damage it caused. And increasingly, they’re reporting that widespread shoreline erosion and loss of wetlands — which can hurt important salt marsh ecosystems and leave coastal areas, and the city of New Orleans, more vulnerable to sea-level rise — was a major side effect of the disaster.
A study, published last week in the journal Geophysical Research Letters, reports extensive shoreline recession in the Mississippi River Delta as a result of the oil spill — and it finds that the spill’s impact was even more widespread than the erosion caused by Hurricane Isaac two years later.
Elijah Ramsey III, a research oceanographer with the U.S. Geological Survey, authored the paper along with Amina Rangoonwala of the USGS and Cathleen Jones of NASA’s Jet Propulsion Laboratory.
Ramsey said erosion is occurring even without the oil spill for different reasons throughout the delta.
For decades, shoreline loss in the region has been linked to such factors as sea level rise, damming of the Mississippi River upstream (preventing it from delivering as much sediment to the delta as it once did), and oil and gas extraction. But the researchers wanted to see how these baseline erosion patterns may have changed following the Deepwater Horizon spill in 2010 and the impact of Hurricane Isaac in 2012.
The researchers focused on the upper Barataria Bay, off the coast of Louisiana on the western edge of the Mississippi River Delta, which is characterized by marshland and numerous small islands. To document the recent changes it’s undergone, the researchers relied on aerial radar data collected by NASA between 2009 and 2012.
Before the oil spill, the researchers observed that there was, indeed, some erosion occurring in isolated areas along the shoreline, which is made up of sensitive coastal wetlands composed of grasses, shallow waters and small islands. But these patterns dramatically changed in 2010. Following the spill, the researchers observed widespread erosion throughout the entire study area, in many cases leading to the fragmentation and even neardestruction of islands in the area.
Most of the affected areas retreated 4 to 8 meters, although in the most severe cases, the researchers saw shorelines receding by 12 meters or more.
In areas that experienced the heaviest oiling, shoreline recession was most severe and often began to occur almost immediately, while some less severely impacted areas exhibited a slightly delayed response.
Over the next two years, shoreline losses tended to remain highest in areas that had experienced the most severe oiling and the highest amounts of shoreline recession, even while the losses declined in places that had been hit less severely. This makes sense, given what scientists know about the way oil affects vegetation in coastal areas.
“What happens is the oiling weakens the roots of the vegetation” along the shore, said Rangoonwala, a geophysicist with the U.S. Geological Survey and the paper’s lead author. Naturally, this effect will be more severe the more oil is present, Rangoonwala said. These roots are what hold the soil in place to begin with, so after they’re lost, the marshland tends to fall apart more easily.