Gulf oil spill's environmental impact: How long to recover?
What scientists know about how oil spills affect the environment is drawn from a range of past events, no two of which have been alike. Because the blowout occurred 5,000 feet below below the water surface, the Gulf oil spill is unchartered territory.
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Dr. McDowell was a coauthor of a 2003 National Academy of Sciences report that remains a seminal work for understanding the behavior of petroleum and petroleum products spilled in marine and coastal environments, many marine scientists say.
For Louisiana in particular, a key area of concern is coastal marshes. They are the breeding ground as well as home base for a wide range of marine life vital to the region’s fishing industries. Moreover, the wetlands provide a first barrier against storm surges from hurricanes.
But southern Louisiana’s wetlands already are stressed – vanishing as the Mississippi Delta sinks beneath the ocean at a rate that, by some estimates, averages 50 acres a day. In addition, the fisheries off the coast are exposed to an annual “dead zone” each spring as nutrient-rich water from the continental heartland moves down the Mississippi and into the Gulf, triggering algae blooms. When the algae die and decompose, the process uses up much of the dissolved oxygen in the water. Fish flee, but bottom dwellers – crabs and other shellfish – generally can’t move fast enough to do so.
If the blowout “turns into something that takes months to shut off ... that is our biggest concern,” says James Cowan Jr., a fisheries ecologist at Louisiana State University in Baton Rouge. With the ecosystem already distressed, “We are concerned it may be at a tipping point.”
In trying to assess the potential effect of oil on the Gulf Coast wetlands, a 1969 spill in Massachusetts’ Buzzards Bay might offer close – if still imperfect – parallels, say Dr. McDowell and Woods Hole colleague Christopher Reddy.
It opens a window on the biological processes that over time help ease the effects of the spill. But it also highlights the long-term effects that can remain after much of the surface evidence has vanished.
The spill involved the barge Florida, which ran aground, dumping 175,000 gallons of diesel fuel. The first organisms to recolonize the area were “opportunistic species” such as carbon-loving worms and microbes, McDowell says. As they ate up their carbon-rich food source – in effect cleansing the harbor of much of the hydrocarbons – they died off, making way for species that normally inhabited the harbor and its marshland to return.