Six years after a disastrous blowout at British Petroleum’s Deepwater Horizon well in the Gulf of Mexico spewed crude oil into the environment for four months, researchers have found it is accelerating the erosion of vulnerable marsh and wetlands along the U.S. Gulf coast, leaving “coastal areas, and the city of New Orleans more vulnerable to sea level rise,” the Washington Post reports.

“Shoreline loss in the region has been linked [previously] 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,” the Post notes.

But now, new research has found that erosion was most severe “in areas that experienced the heaviest oiling” in the BP disaster, “and often began to occur almost immediately.” By contrast, “less severely impacted areas exhibited a slightly delayed response.”

“Shoreline losses tended to remain highest in areas that had experienced the most severe oiling,” the paper adds, “while losses declined in places that had been hit less severely.”

The mechanism for the faster erosion is crude oil’s toxicity to the grasses and other plants that anchor the sediment of wetlands. “What happens is the oiling weakens the roots of the vegetation,” said U.S. Geological Survey geophysicist Amina Rangoonwala, the paper’s lead author. “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,” the Post explains.

“Marsh degradation is irreversible in many cases,” adds reporter Chelsea Harvey, and “while disasters like hurricanes may cause more severe damage to the shoreline in localized areas, the impact of an oil spill may be more widespread.”