Handle with care. That's the advice of coastal ecologists and geologists to those who are planning the clean-up of the Gulf ecosystems threatened by the Deepwater Horizon oil spill.
Louisiana's ecologically important but fast-eroding marshes, which serve as nurseries for commercially important shrimp and fish, are the main worry. In such a sensitive habitat, removing the oil can do more harm than good. When the tanker Amoco Cadiz ran aground off France's Brittany coast in 1978, clean-up teams attempted to save the Ile Grande salt marsh by removing oiled sediments. This was held responsible for the subsequent accelerated erosion of the marsh and the delay in vegetation recovery.
That mistake won't be repeated. But "there are few options for dealing with the oil that have no adverse consequences", warns Denise Reed, a specialist in coastal restoration at the University of New Orleans. Just treading on a marsh can push oil deep into the sediment, and the alternative, vacuuming oil off the marsh from boats, is not always possible.
Even benign-sounding proposals like spraying nutrients to boost oil-munching bacteria can be damaging. When Eugene Turner of Louisiana State University in Baton Rouge added phosphorus to plots in a Louisiana salt marsh, it reduced the growth of roots of the dominant grass, Spartina alterniflora, undermining the integrity of the marsh (Estuaries and Coasts, vol 31, p 326).
Plans to build sand berms on islands along the Louisiana coast are another concern. Louisiana's governor, Bobby Jindal, believes the berms can keep oil from reaching the marshes, but not everyone is convinced. The $350-million project "was conceived without any serious consultation with the scientific community", says John Day, of Louisiana State University. "It almost certainly won't work."
Plans to build 206 kilometres of berms on the islands were met with concern by federal agencies. The islands are key nesting grounds for shore birds, including terns and brown pelicans, and agencies urged for limited construction during nesting season. But on 27 May, the US Army Corps of Engineers issued an emergency permit to build 72 kilometres of berms. Construction could start this week, during nesting season. Even this shrunken plan worries coastal geologists. Sand is scarce in Louisiana, and that used for the berms "is going to get oiled, and they are going to have to throw it away", says Joseph Kelley of the University of Maine in Orono.
Greg Stone of Louisiana State University supports building up the islands, but worries about dredging sand too close to them. Waves increase in energy over dredged areas, he says, which accelerates erosion. Careful studies are needed before work starts, he says, "to make sure we are not running into a very dark alley".
The berms will be about 90 metres wide at the base and will rise 2 metres. Birds that feed at the water's edge will have a tough time, as they won't be able to reach their normal feeding grounds, says Kim Withers of Texas A&M University in College Station. But the oil could have even worse effects, she adds. "It's almost a lose-lose situation."
The grim situation caused by the Deepwater spill makes for uneasy alliances and strained silences. One normally vocal advocacy group didn't want to say anything, and another person, speaking off the record, noted "an air of repression".
This article was originally published on New Scientist.
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