Monica Hernandez / Eyewitness News

NEW ORLEANS -- One year after the beginning of the worst environmental disaster in U.S. history, scientists say thechemical signature of oil, the so-called 'oil plumes'beneath the surfaceof the Gulf, have disappeared. But they say oil from the BP spill still lingers.

'We're getting tar balls on the beaches, so that has to come from somewhere,'said Dr. VernonAsper, professor of Marine Sciences at University of Southern Mississippi.

And it's not just tar balls. Since the spill, hundreds of dead dolphins and sea turtles have washed ashore.

'Here are two animals that breathe air. They've got to come to the surface, they've got to interact with whatever they find at the surface,' said Asper.'So what is going on there? Is it an oil spill effect or not? We need to know.'

It's one of the answers Asper is hoping to find as he continues researching the spill.

He was one of the first to detect oil below the surface, fromthe research vessel 'Pelican' just a few weeks after the Deepwater Horizon explosion. One year later, Asper has more questions than answers.

'The question is, what is still going on in the environment?' asked Asper. 'Where is this oil and what effect is it having?'

At this point, scientists don't know how damaging the effects of the spill will be. Asper predicts we'll know 90 percent of the effects one year from now,and believes it willtake a decade to fully understand them.

Meanwhile, the head of the Environmental Protection Agency toured the Gulf Coast Wednesday. Lisa Jackson said much of her information is reassuring.

'Mother Nature deals with oil and gas seeps in theGulf of Mexicoall the time,' said Jackson.'And so, what we had hoped happen would, which is the majority of it stayed out of the marshes, out of the wetlands, out at sea.'

The EPAsaid it will continue to monitor the spill's impact. The agency also said it would continue to learn about ways to rebuild the Gulf and restore wetlands.

Still, as signs of the spill continue to surface, so do concerns about what it mean's for the Gulf's future.

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