Marshes could recover from oil contamination

Richard Bogren, Breitenbeck, Gary A.  |  1/4/2011 1:08:23 AM

News Release Distributed 08/17/10

With the capping of the Deepwater Horizon and the ending of new oil washing into Louisiana’s coastal wetlands and marshes, observers are reporting plants sprouting in areas that had been denuded by the oil spill. And that shouldn’t be a surprise, according to Gary Breitenbeck, a plant scientist with the LSU AgCenter.

When oil contacts the above-ground portions of marsh plants, it generally kills the plants within only a few days, he said. But the affected area often recovers in one to two months.

“The dense root systems and rhizomes of many marsh plants will send up new shoots that form healthy plants,” Breitenbeck said. “It’s akin to burning a field or meadow.”

Some people claim that Louisiana’s coastal marshes always recover from an oil spill. Breitenbeck cautions, however, that unless you absolutely know where the marsh was before the oil arrived, you can be deceived into believing all the marsh has recovered when the outer edges, in fact, may have died and been eroded away.

“With enough light-weight oil, the the oil can permeate fine marsh sediments, damaging roots and rhizomes,” he said. “The roots then decay, and the oil absorbed in the sediments and dead plant materials washes out into the Gulf. What doesn’t recover turns into open water.”

Hydrocarbons kill plants by attacking cell membranes so they leak from “a chemical kind of burn,” Breitenbeck said. Lighter hydrocarbons are more phototoxic and kill more quickly.

“It’s like comparing the effects of putting gasoline on plants versus motor oil,” he said. “The gasoline will kill the plant rapidly, but the motor oil will kill the plant slowly, if at all. In general, the longer the carbon chains in the petroleum product, the less toxic it is. Grass will grow on asphalt – a mixture of some of the longest-chained hydrocarbons.”

The microorganisms that degrade hydrocarbons can consume the oil or convert it into other substances. In the presence of an oil spill, these organisms will proliferate.

Some of these organisms have been identified in laboratory tests where hydrocarbons were used as their only “food.”

“Marine hydrocarbon-degrading organisms exist naturally, consuming small oil spills around underwater wells,” Breitenbeck said. “Create the right environment, and populations will explode. There are many natural strains of microorganisms that have adapted to attacking hydrocarbons in Louisiana marshes.”

In open water these organisms are mostly bacteria. In marshes, both bacteria and fungi can play a role.

“We don’t know what’s going to happen in the long term,” Breitenbeck said. “It depends on weather. We don’t know if a hurricane will be good or if it will be bad. A lot of oil is lurking off the coast of Louisiana and other states – Mississippi, Alabama and Florida.”

Oil has been on beaches, but relatively small amounts have found their way into the marsh, he said. The results will depend on both the amount of oil that enters the marshes and the character of the oil itself.

“It is imperative that we minimize the impact of this spill on coastal land loss,” Breitenbeck said. “Once the vegetation is killed and the underlying sediments are allowed to erode, that area of marsh is lost – probably forever.”

Rick Bogren

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