baltimoresun.com
Post-spill gulf environment appears to have escaped catastrophe, for now
Much of the BP oil spill's effect on the ecosystem won't be known for years, and peril remains, experts warn. Still, the Gulf of Mexico has recovered more quickly than many expected last summer.
By Bettina Boxall, Los Angeles Times
April 20, 2011
Reporting from Grand Isle, La.
Hundreds of brown pelicans are doing what they always do on Cat Island in the spring: wheeling above the mangroves, nesting and jostling for space on this noisy rookery a few miles off the Louisiana coast.
A year after the Deepwater Horizon oil rig exploded, killing 11 workers and unleashing the largest offshore oil spill in U.S. history, life on Cat seems pretty much back to normal, as it does in most of the Gulf of Mexico environment.
But when Todd Baker takes a close look, he sees that not all is right. Before the spill, "this was a lush green island; you couldn't see the ground," recalled Baker, a biologist with the Louisiana Department of Wildlife and Fisheries. The black mangrove bushes on which pelicans build nests are thin and scraggly, damaged by the oil that sloshed over the two-acre island. A strip of the plants disappeared, wiped out by a loose, wave-driven boom set by spill cleanup crews. It plowed through the dense stand like a bulldozer, destroying nesting perches.
Nests built on the newly exposed sand could be washed away in storms. If the mangroves don't recover, more of the island will erode, imperiling the rookery.
The northern gulf's brown pelican population didn't escape the spill unscathed. But precisely how it was affected, Baker said, "we don't know yet."
The monster spill's toll on the gulf environment is turning out to be more subtle — and at this point, elusive — than was feared when BP's blown-out well spit light crude into mile-deep waters for three long months.
Beaches that were coated last summer with a rusty-colored goo, the product of oil and toxic chemical dispersants, are clean. As of Tuesday, all federal waters had been reopened to fishing. Only a small fraction of ocean and sediment samples taken by the federal government found oil compounds at levels harmful to aquatic life.
PORTRAITS FROM THE GULF
One year later, five people whose lives were changed by the oil spill share their stories.
"It's been difficult to confirm everybody's worst fears," said Ian MacDonald, an oceanography professor at Florida State University. "My statement all along has been that we probably are not going to see … an acute toxic impact. Instead what we should be concerned about is a marginal reduction in the productivity and biodiversity of the components of the gulf ecosystem…. But that's not something that you know right away."
A small army of government and academic scientists is examining the gulf ecosystem from top to bottom to figure out what the release of 4.1 million barrels of oil and 1.8 million gallons of chemical dispersant did to the environment. They may not have answers for years.
A combination of factors helped the gulf escape ecological catastrophe. The oil was a light crude. Weather, currents and the application of dispersants deep in the ocean kept much of it offshore. The warm-water gulf ecosystem, adapted to abundant natural oil seeps, proved efficient at producing hydrocarbon-consuming microbes that munched their way through the oil and methane.
"Quicker than anyone thought," oil and gas levels in most of the spill area have returned to normal levels, said David Kennedy, an assistant administrator of the National Oceanic and Atmospheric Administration with 30 years of spill experience.
That does not mean, he emphasized, that there is no problem. "The story is not told yet; there's so much still to look at."
Much of the looking is being done as part of the Natural Resource Damage Assessment, a legal process involving federal and state agencies as well as BP and the other companies involved in the Deepwater Horizon drilling operation. Those corporations will pay for the work and will be liable for the costs of environmental restoration.
On Louisiana's Barataria Bay, a federal biologist is using a telephoto lens to photograph the dorsal fins of bottlenose dolphins as they gently breach the olive-brown waters. The fins have unique nicks and notches, which the scientists will use to identify individuals for a population survey. Later in the project, they will obtain tissue samples using a dart fired from a .22-caliber rifle and compare the results with similar data collected last May, before the spill hit the bay.
Shore populations such as the Barataria dolphins tend to stay in their territory, so they were exposed to the oil when slicks spread to the coast. "They're not going to say, 'I don't like it anymore,' and just leave," said Lori Schwacke, a NOAA scientist who is leading the dolphin surveys.
In the years since the 1989 Exxon Valdez oil spill off Alaska, an orca group in Prince William Sound has experienced a steep decline for reasons not fully understood. "It is awfully suggestive that those animals suffered some sub-lethal impacts," said Eric Zolman, a NOAA scientist working with Schwacke. "That's the concern here."
Since the start of the gulf spill, about 300 dolphins, most of them dead, have washed ashore between Texas and Florida. Twelve had visible signs of oil on them. Federal officials have not revealed necropsy results, nor causes of death. They say they are evaluating information with extra caution because the findings could become evidence in the legal case against BP.
"We may be dealing with multiple factors," said Blair Mase, an NOAA marine mammal stranding coordinator.
The jump in dolphin deaths began before the Deepwater Horizon explosion, and was probably linked to a cold snap that lowered the water temperature. But another peak in deaths occurred during the spill, and a third in recent months, when an unusually large number of infant and fetal dolphins washed up on the Mississippi-Alabama shoreline.
Monty Graham, a scientist at the Dauphin Island Sea Lab in Alabama, is studying the way the spill was processed by microbes. It's possible, he says, that the huge dump of hydrocarbons could have altered the base of the northern gulf's food web in a way that depleted food reserves for pregnant dolphins, leaving them and their young more vulnerable to this winter's stresses.
"I completely believe that this could have been a trophic cascade to the mothers, causing them to not be able to have enough tolerance for the cold conditions when they came," Graham said.
There has also been a surge in sea turtle deaths this spring, most of them involving the endangered Kemp's ridley. NOAA says no oil was found internally or externally during necropsies performed on 26 turtles recovered last month on the Mississippi coast. Some injuries suggested they had been hit by boats, and the agency is investigating whether others drowned after becoming entangled in fishing gear or were poisoned by undetected algal blooms.
The oil has not completely disappeared. As of early April, 66 miles of gulf shoreline, most of it in Louisiana, were still tainted by heavy or moderate amounts of oil or tar balls. Biologists continue to recover oiled birds. And University of Georgia geochemist Samantha Joye has reported that on a December research voyage she came across large patches of the gulf floor covered with oil residue and empty of the typical bottom-dwelling sea life.
Biologists also believe many birds and sea mammals that died during the spill sank to the bottom, never to be counted.
Nonetheless, the gulf is in better shape than many expected last summer, when images of the oil-belching BP well dominated the news.
"We're fortunate the gulf is a big place," said Christopher D'Elia, dean of the School of the Coast and Environment at Louisiana State University. "I thought it was going to be worse than it actually was. That was a happy surprise."
In Mississippi and Alabama marshes, recent sampling of young fish and larvae yielded numbers that "look like anything we would expect in a normal year," said George Crozier, executive director of the Dauphin Island Sea Lab.
The population of red snapper, an important commercial catch, even appears to be up, probably a result of last year's fishing closures and previous catch limits the federal government imposed to rebuild the fishery.
Still, the BP spill was another blow to an environment suffering from chronic degradation. The rate of wetland loss in Louisiana is staggering. Runoff and Mississippi River water carry an excess of nutrients into the gulf, promoting algal and plankton growth that create low-oxygen "dead zones." Fishing stocks are depleted. Thousands of offshore oil and gas wells dot the horizon.
"It may take awhile to really appreciate what this body blow did to that longer-term health," Kennedy said. "We know there's injury."
0 comments:
Post a Comment