Deepwater Horizon was spilling oil on a long-lost beach

Long after the Deepwater Horizon oil spill, the marshy shores of the Gulf of Mexico were still feeling the effects of the disaster. The marsh grass retained the plant-derived oil, and the soil continued to rot faster than before the meltdown, causing beaches to recover faster than otherwise, a new study shows.

After the explosion in April 2010, the Deepwater Horizon rig pumped nearly 800 million liters of oil into the sea (SN: 2/12/20). The disaster killed dozens of people and countless sea life. But the oil and its fruits are destructive to the ecosystem of the gulf, both underwater and on the shore;SN: 4/3/15).

But the oil also caused structural damage to beaches by killing marsh plants crucial to holding the soil in place, researchers reported on January 25. Environmental pollution. This coast may be more vulnerable to tropical storms that are increasing in intensity due to climate change.

“If the plants are damaged in any way, shape or form, you lose a lot of land,” says Giovanna McClenachan, an ecologist at Nicholls State University in Thibodaux, La.

McClenachan was working on her Ph.D. There was a disaster at the state university in Baton Rouge, Louisiana. She and her supervisor, marine ecologist Eugene Turner, quickly set up research plots on the southern Louisiana coast. Three times a year, for the next eight years, they carried out tests on the strength of the soil with a spear vane, a common tool used by farmers to test the strength of the soil and analyze the amount of oil it contained.

They also examined satellite images from 1998 to 2021 to analyze what the marsh vegetation looked like before, during and after the spill over a much longer period of 23 years.

Field testing revealed that, immediately after the Deepwater Horizon disaster, oil concentrations of some of the volatile components of oil, aromatics, in the marsh soil jumped from an average of 23.9 nanograms per gram of sediment before the spill to 17,152 nanograms per gram of sediment in 2011. By 2018, the average level at He had dropped 247 nanograms per gram of feces — but they were still more than 10 times higher than before.

Only half of the strength is turned down after they are turned. Before the summit, the average force of the top 30 centimeters of the soil was 26.9 kilopascals, which is a measure of pressure in physics. The soil strength was lowered to 11.5 kilopascals in 2011. While her strength then began to recover at a rate of 5 percent per year, she still has not fully recovered since 2018, the last year of the field study, when she climbed to 16.4 kilograms.

This is in part due to the strong storms that have occurred over the years since they turned. McClenachan says the initial oil spill killed much of the vegetation on what was then the shore of the marsh. When they departed, he only retained the roots of the marsh grass and washed them. But the oil remained in the water and pushed further into the swamp, where it killed many plants.

“The soil hasn’t recovered strength because the oil is still in the swamp, and that makes these erosion events really strong in storms that didn’t happen before the oil spill,” McClenachan says.

Analysis of satellite images showed that the loss rate of the marsh doubled after the spill. Beaches in the study area are already receding at an average of 0.8 meters per year before subsidence due to a combination of natural movement of the marsh plain and human-caused factors such as rising sea levels. But that loss has increased by an average of 1.7 meters per year since then, but 12 months after Hurricane Isaac hit Louisiana in 2012, the tide has receded by about 2.5 meters.

Some research has questioned whether it is oil spills that affect beach erosion rather than storms over the past decade. But Hurricane Katrina, which hit the Louisiana coast in 2005, years before the oil spill, did not cause nearly as much damage to the coast as the weaker storms after the oil spill, McClenachan’s satellite analysis shows. It is not an either/or question; rather, the effect of the ongoing oil spill has made the beaches more vulnerable to damage.

The new study is unique in that it also sheds light on the stability of the soil itself, says Scott Zengel, an environmental scientist with Planning Research Inc., a private research consultancy in Tallahassee, Fla., that often analyzes the impacts of the Deepwater Horizon disaster.

“It confirms the idea that there really was an erosion effect,” adding that the length of the study complements previous research showing that oil has played a role in changes to the marsh.

These changes can be mitigated to some extent. Zengel’s work shows that techniques like planting marsh grass can help reduce the rate of beach erosion. For soil boosting retention, he says “it really shows in the plants one of the main factors”.