MOBILE, Ala. — Now that BP’s damaged Gulf well appears under control, scientists are struggling to answer two questions: How much oil ended up in the Gulf, and what will be the long-term effects?
Federal estimates of the flow rate from the Deepwater Horizon well covered a wide range. But there was one number consistently used by BP and the Coast Guard as they calculated dispersant use. In letters between BP’s Doug Suttles and federal officials, that number was 53,000 barrels per day, or 2,226,000 gallons.
That means that over the course of the 87 days that the well was uncontrolled in the Gulf, about 192 million gallons of oil were released.
Subtract from that the 45 million gallons BP said it collected with its cap, skimmed off the Gulf’s surface or burned, and that leaves about 147 million gallons of oil.
Some of that oil has already washed up on beaches and marshes, but the lion’s share remains unaccounted for.
Officials with BP PLC, the well’s majority owner, declined to comment on how much oil had flowed into the Gulf and referred the Press-Register to federal officials. BP and federal officials have been scaling back spill response, saying that less and less oil is being found on the Gulf’s surface.
Rob Kiene, a scientist with the Dauphin Island Sea Lab, said the big question is whether there is more oil hidden below the waves.
“Has the oil mixed down into the water column? Is it spreading around? Will it be coming up?” he asked. “All of those questions are being investigated.”
Retired Coast Guard Adm. Thad Allen said last week that the government was in the process of “putting together what we call an oil budget” that would provide a rough estimate of what happened to the oil.
Allen, who is leading the government response to the spill, said scientists “will continue to basically slowly fill out what I would call an MRI of the Gulf, where you take slices and look at the presence of hydrocarbons moving forward.
“But we’re in kind of a new area here,” he added, “where we’ve never had this amount of oil in the water before.”
Ed Overton, a Louisiana State University chemist who has been analyzing oil samples for the federal government and the Press-Register, said the Gulf had done a remarkable job of breaking down the oil. Many of the samples he has been looking at show the oil has almost entirely degraded, he said.
“I think the worst is past us,” Overton said. “We’re going to continue seeing oil coming ashore, and there will be impacts, but the bacteria in the Gulf are doing a better job of handling the oil than anybody expected.”
Dispersants, he said, “helped put the oil in a form where that bacteria could work on it.”
Asked then if underwater dispersant use had been effective, Overton said it appeared that it had, at least by breaking up oil and keeping it from beaches and marshes.
But he added that the jury was still out on all of the biological implications of dispersant use.
Harriet Perry, who studies crabs at the University of Southern Mississippi, reported a month ago finding crab larvae with globs of oil beneath their shells, one of the first examples of oil moving into the food chain. Perry said she believed the dispersant had broken the oil down into small enough particles that it was able to work its way beneath the larval crabs’ shells.
Perry said her concern is that the larvae are important food items for many fish and other creatures in the Gulf.
Monty Graham, also of the Sea Lab, predicted scientists would be able to detect the oil’s fingerprint in nature for a long time. Full ecological impacts will become apparent over years, not just months, he said.
“We are talking about a lot of oil that was released. It is still out there, even if it has been degraded,” Graham said. He pointed to studies from Exxon Valdez showing that spill’s impacts linger today, more than 20 years after the spill.
Graham said questions remain regarding plumes of oil detected underwater since the BP spill began. Those plumes, he said, may have been linked to low oxygen readings measured off the Alabama coast throughout the spill. His more recent research cruises have documented better oxygen levels, he said, though they remain lower than would normally be expected.
The Sea Lab’s Kiene said that the time of year also may have helped lessen any damage.
“We have the warm temperatures helping promote the volatile fractions of the
oil to go into the atmosphere at a higher rate. We had high temps for the microbes that eat the oil. We had high sunlight so the ultraviolet radiation could degrade the oil,” Kiene said.
“Of course,” he cautioned, “you could also argue that we had all the larvae present in the Gulf. We will have losses there, for all kinds of larvae.”
Kiene said that he feels the Gulf will emerge “in pretty good shape.”
“I was really depressed with how much was out there,” he said, “and how it kept coming and coming. Overall, though, we didn’t have a whole lot of oil come ashore.”
