SCIENCE -- April 20, 2011 at 9:33 AM ET
One Year Later, Where Has All the Oil Gone?
The Gulf of Mexico has always been an oily place. Early sea captains wrote in their log books of slicks of oil. Mayan Indians used natural tars to seal their water jugs and waterproof their canoes. As many as 50 million gallons of oil seep naturally into the Gulf from the sea floor.
And because of this chronic exposure, the Gulf is primed with a rich, microbial population, ready to consume oil and associated gases, like methane. Gulf oil is naturally occurring, and pervasive.
But an estimated 250 million gallons released at once, experts say, is a tremendous amount for the environment to absorb.
One year ago, on April 20, 2010, BP's deepwater Macondo well ruptured and blew out, releasing a massive geyser of oil that gushed wildly for 86 days, until the well was finally sealed in September.
With the one-year anniversary of that date, people are revisiting the Gulf and oil spill experts, assessing the fallout from last year's spill. What's in the water now? Where did the oil go? And what has it done to the ecosystem?
The answers are unsatisfying and unanimous: no one knows.
It's getting harder to find the oil in water samples in the Gulf, which means direct effects are less visible, said David Valentine, a microbial geochemist at the University of California, Santa Barbara, who has studied the Gulf oil spill at length.
"There's undoubtedly some levels of residual material out there, but the levels have dropped dramatically. Even the bacteria that grew after the spill have a finite lifetime and then they themselves are consumed."
For its part, the government's leading scientific agency that studies the environmental impacts, the National Oceanic and Atmospheric Adminstration (NOAA), says it knows there is residual oil in and along the Gulf, but it does not appear to be in substantial quantities.
"We know there is oil still out there -- on beaches, as tarballs or tarmats, and on the seafloor in isolated patches," NOAA Administrator Jane Lubchenco told the NewsHour in a statement. "However, thanks to an aggressive response and significant help from Mother Nature, most of the oil is gone."
Still, there are plenty of questions, and concerns about how indirect effects, like declines in growth and reproduction caused by stress from oil exposure, can take a tremendous toll, said Thomas Shirley, an oil spill expert at Texas A&M University.
"I'm talking about the ghosts of all the animals that might have existed if there hadn't been the stress," he said. "I'm not really a bunny hugger - I'm pretty practical about it. I put oil in my car, recognize the need for it, but I try to be a practical scientist...and I think we haven't quantified the effects yet."
History tells us that oil spill effects don't always show up immediately. It wasn't until four years after the Exxon Valdez ran aground on March 24, 1989, spilling an estimated 11 million gallons of oil, that the Herring fisheries collapsed. Herring deposit their eggs in shallow water on rockweed and seagrass, areas which were likely contaminated with sticky oil and tar. Immediately after the spill, many older Herring stuck around. But over time, the industry noticed flagging reproduction and a plunge in the numbers of younger generation herring.
Herring exist at the base of the food chain -- as food for salmon, marine mammals, eagles and other seabirds. And the Gulf, Shirley said, consists of similar kinds of forage species. "If the spill has damaged any of these forage species, it would have cascading effects throughout the food web," he said. "And they might not be visible in the first year. That's what we learned in Exxon Valdez: to look for things that occur later."
In the Gulf, the focus has moved from the water to the sediments and the beach, Valentine said. Sediment is the material that falls to the sea floor, and little is known about how much this oil sediment exists. Pockets of tar found in or around the sandbars are still evident. Oil itself is composed of thousands of different compounds, and tar is made up of the oil's heaviest components, "the sticky ooze that's left over after nature has its way with oil."
According to Valentine, the outstanding question remains: Where did all the oil go?
"Dispersant doesn't destroy it; it just changes its form a little bit," he said. "One of the important questions is taking the balance of where that oil went and really nailing down what happened to it all."
Lubchenco says the Obama administration understands there are still a number of questions about the longer-term impact of the spill and that it, too, wants to find answers.
"We remain concerned about the long-term health of the Gulf and are committed to holding the responsible parties accountable for restoring the damage caused by this spill," she said.
But to get those answers, more research funding is needed, Shirley says.
"When people ask, what is the damage? I would say, we don't really know yet. When they ask, is the Gulf recovering well? I would say we don't know if we don't know the damage."