Ten-year legacy of the Exxon Valdez Oil Spill
Ten years ago this month, the tanker Exxon Valdez met Bligh Reef, polluting Prince William Sound with 10.8 million gallons of crude oil from the North Slope. Ten years later, scientists still debate the effects of the accident on the waters and wildlife of Prince William Sound.
Bob Day and Steve Murphy are ornithologists who work for ABR, Inc., Environmental Research and Services. They've studied seabirds in Prince William Sound since the time of the spill to determine how oiled areas affect the birds. They found seabird numbers declined immediately after the spill, but they also discovered that most species came back to areas that were once tainted with crude oil. "We were surprised how quickly most species recovered," Day said. "By 1991, most of the species showed no evidence of avoiding the spill area." Using bird counts taken before the spill, they found that numbers of birds in the sound in 1991 were at levels that would be expected had there been no oil spill, Murphy said. Though the researchers initially were funded by Exxon, they insist that their study was rigorous and objective, and they believe that, from a seabird's point of view, the sound has mostly recovered from the disaster 10 years ago.
Terry Bowyer was one of many University of Alaska scientists who worked on oil spill studies. A wildlife biologist with the Institute of Arctic Biology, Bowyer studied the spill's effects on river otters, a species vulnerable to oil spills because it dens on land, feeds in the ocean, and spends lots of time on oiled beaches. The work of Bowyer and others led the river otter to be one of the two species declared recovered by the Exxon Valdez Oil Spill Trustee Council.
The other animal is the bald eagle, also a predator near the top of the food chain. "Top carnivores should be the last to recover," Bowyer said. "It's hard to believe that other species haven't recovered."
Bowyer said lots of oil remains buried in the shore sediments of Prince William Sound, but he thinks river otters aren't now exposed to levels high enough to cause them damage. "The ecosystem turned out to be very resilient to what I think was a heinous crime," he said. "But you have to be cautious about saying the sound is fully recovered."
Oil from the Exxon Valdez may be causing hidden problems, said Evelyn Brown, a research associate at the Institute of Marine Science who was the lead scientist of a Pacific herring study in Prince William Sound. Oil that clung to particles of sand or silt very likely stuck to zooplankton and was eaten by fish, causing reproductive and immune-system problems that are hard to track. Pink salmon in the spill path, for example, suffered reduced growth from ingesting oiled particles, Brown said. Brown thinks researchers didn't do a complete job of tracking the path of oil in areas near shorelines, where many fish species rear their young. "We have no idea how much of that oil wound up in the fish and everything that eats them, and what the community and ecosystem impacts are today," she said.
Joan Braddock, a microbiologist at the Institute of Arctic Biology, was one of several researchers who tried to track the 10.8 millions of spilled oil. In a paper published in Environmental Science and Technology, Braddock and others estimated that in 1992, about 20 percent of the spilled oil had evaporated, about 14 percent was recovered, about 13 percent was still out there in sediments of beaches, less than one percent remained in the water, and an incredible 50 percent underwent biodegradation, a process in which microorganisms fed on the crude oil and converted it to carbon dioxide and water vapor, the same gases we exhale.
"My personal opinion is that the system has recovered remarkably," Braddock said. "But how many events like this can a system stand?"
