BioEd Online

As oil still flowing from a ruptured pipeline into the Gulf of Mexico starts to lap at the Louisiana shore, ecologists and coastal residents are preparing for an environmental catastrophe that could unfold over the coming months.

The pipeline from the Deepwater Horizon oil rig that exploded 80 kilometres offshore on 20 April and sank two days later has been spewing out a plume of crude oil at a rate of at least 5,000 barrels of oil (800,000 litres) each day. Some estimates put that rate much higher: based on analyses of satellite data, the nonprofit organization SkyTruth, based in Shepherdstown, West Virginia, said at the weekend that as much as 26,000 barrels (4.1 million litres) a day could be escaping from the wellhead. Efforts to plug the leak with remotely operated vehicles have been unsuccessful, and a relief well that BP plans to drill to stop the flow could take three months to complete.

Late last week, high winds pushed the 5,000-square-kilometre oil slick northward toward the fragile marshlands of the Louisiana coast. One finger of the slick, composed of thick globules of oil, is hovering within 10 kilometres of the coast. Models had suggested that it could reach the southern coast of Louisiana, near Venice, by Tuesday or Wednesday, but today winds shifted, steering the slick away from the coastline.

Though the main body of oil is yet to hit land, oily sheen from the western edge of the slick has been lapping at the marshlands of the Mississippi Delta since 30 April. "If you put your hands in [the water], they come out black and greasy," says Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium. "You can see oily substances around the stems of the salt marsh plants."

Fierce winds over the weekend made it difficult for crews to collect samples from the main body of oil, whose chemical makeup will largely determine the extent of environmental impact and the difficulty of cleanup, says Ed Overton, a chemist at Louisiana State University. "If this is the heavy oil [as] we suspect, it's just like road tar," he says. "It doesn't go away. It's not very biodegradable, and it's not easy to wash off with dispersants, soaps or beach cleaners."

Marshland menace

The spill could be devastating to breeding bird colonies, and to the tens of thousands of migratory birds that will be arriving over the next several weeks. The marshland is also a critical nursery habitat for larvae and young fish, blue crabs, shrimps and oysters, the base of the food chain for marine fisheries in the northern Gulf of Mexico.

As for the marshland grasses themselves, if the bulk of the oil has been weathered and degraded and the grasses are only lightly oiled, it is likely that only the leaves and the stems would die off this year, says Irving Mendelssohn, a wetland ecologist at Louisiana State University. Structures below ground would remain intact and could regenerate within a year.

But if tarry, sticky oil repeatedly washes ashore, coating the plants to the point that they cannot photosynthesize, the smothering effect would kill the plants above and below ground. If the grasses die off, "you can get ponds forming and coalescing into large lakes, and really the complete loss of wetland areas," says Mendelssohn. And the cleanup process itself can be devastating to marshlands, he adds.

Wider impacts

With the economy of the Gulf states dependent on clean coastal water, seafood and tourism, estimates of the cost of the spill have already been put at $14 billion. It is also shifting politics on President Obama's hopes of ending a moratorium on new offshore drilling; late last week, Obama put those plans on temporary hold.

Officials have the additional concern that the oil slick could get picked up by a warm ocean current called the Loop Current, which shuttles warm water northward from the Yucatán Peninsula up the Gulf of Mexico before veering up the eastern tip of Florida. If the oil slick became entrained in the Loop Current, oil could get dispersed to the shorelines of Mississippi, Alabama, the Florida Keys and the east coast of Florida.

"If it stays where it is now…the effect is local," says Yonggang Liu, an oceanographer at the University of South Florida in St. Petersburg. But if the slick gets pulled into the Loop Current, the effects on coastal environments could be "disastrous". The Loop Current is heading northward and is currently within 70 kilometres of the oil slick. "That is very dangerous," says Liu.

Weaker winds are expected over the next few days, which could slow the spread of oil. For now, workers onshore are preparing for the unknown, laying hundreds of thousands of feet of oil-containment boom to corral the incoming oil and setting up rehabilitation facilities for oiled birds. "We're in slow motion here," says Overton. "We feel like we're tumbling over the cliff. But we haven't hit the bottom yet so we don't know how hard that bottom is."