Gulf spill: Where did the oil go – and what did it do?
One year after the Deepwater Horizon blow-out began the worst oil spill in US history, scientists continue to investigate the effects of the oil and its residues.
A year after the worst off-shore oil spill in US history began, scientists continue to sample the sea floor and comb beaches and marshes in an attempt to track the fate of oil that spewed for nearly three months from the Deepwater Horizon blow-out.Skip to next paragraph
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But the emphasis has long since shifted from debates over a simple "Where's Waldo" kind of accounting, to measuring how the oil degrades with time in various environments, and the effects the remnant chemicals can have on the habitats they encounter.
The effort should give restoration teams a better sense of where they need to focus their work. It should also provide benchmarks to more effectively gauge the resilience of land and ocean organisms after their assault by oil and the dispersants used to break up slicks.
IN PICTURES: Gulf oil spill one year later
The BP spill "gave nature a stress test," says marine scientist Christopher Reddy of the blow-out's environmental aftermath. In trying to assess how nature is responding, it's vital to know how the chemical agents responsible for the stress change over time, he says.
Accounting for the oil
Shortly after BP capped the blow-out on July 14, and oil stopped flowing, federal officials released a checkbook-like accounting of the oil's fate. But it proved controversial.
The uncertainties in some of the categories were large. The report had not undergone a rigorous peer review. Indeed, the numbers were never meant to represent a rigorous, definitive accounting, according to a white paper prepared by the staff of the National Commission on the BP Deepwater Horizon Spill and Offshore Drilling.
Instead, the results intended to give the National Incident Command an general idea of how to allocate clean-up resources.
In fact, the balance sheet showed that only about 25 percent of the oil could safely be categorized as "gone" – either from skimming, burning, or being loaded onto tankers.
Chemical dispersants, evaporation and natural degradation had taken their own toll on nearly half of the oil released, according to the document, but scientists pointed out that while such processes can reduce the volume of hydrocarbons in the ocean, it also can leave what's left in a form that takes far longer to break down.
Finally, 26 percent of the oil released fell into the balance sheet's "residual" category – oil washed ashore or trapped in sand or sea-floor sediments, for instance.