In the year since the wellhead beneath the Deepwater Horizon rig began spewing rust-colored crude into the northern Gulf of Mexico, scientists have been working frantically to figure out what environmental harm really came of the largest oil spill in American history.

What has emerged in studies so far is not a final tally of damage, but a new window on the complexities of the gulf, and the vulnerabilities and capacities of biological systems in the face of environmental insults.
There is no doubt that gulf water, wildlife and wetlands sustained injury when, beginning on April 20 last year, some 4.9 million barrels of oil and 1.84 million gallons of dispersants poured into the waters off Louisiana. But the ecosystem was not passive in the face of this assault.
The gulf, which experiences a natural seepage of millions of gallons of oil a year, had the innate capacity to digest some of crude and the methane gas mixed with it. Almost as soon as the well was capped, the deep became cleaner to the eye. By the same token, dozens of miles of marsh still remain blackened by heavy oil, government crews are still grooming away tar balls that wash up ceaselessly on beaches and traces of the dispersants are still found floating in the currents.
Biologists are nervously monitoring as yet unexplained dolphin strandings this year, trying to come up with a realistic count of birds and mammals killed during the spill and working to understand what happens when the gulf floor is covered with the remains of oil-eating bacteria. “It is really kind of hard to get a grasp of the big picture, and it is not for a lack of trying,” said Christopher Reddy, a senior scientist at the Woods Hole Oceanographic Institution who studies long-term consequences of oil spills.
“Hundreds of scientists are working day and night trying to carve out a piece of that giant puzzle, but it is an entire region and it is complicated.”
How the regional ecosystem has responded, its strengths and weaknesses, will keep scientists busy analyzing data for years and help them in understanding the effects of environmental disasters.
After an oil spill, the government is responsible for toting up the ecological damages in something called a Natural Resource Damage Assessment. The document, which requires battalions of researchers, makes the case for damages that the companies responsible for the spill should pay to restore the ecosystem to its pre-spill health. The companies hire their own teams of assessors, who might paint a very different picture. The two sides settle or go to court.
At of the end of January, the government said its scientists alone had taken 35,000 images, walked more than 4,000 miles of shoreline and culled more than 40,000 samples of water, sediment and tissue.
The scientists are also testing how to estimate what they can’t count precisely, like animal deaths. One group of evaluators is scattering bird carcasses offshore and measuring how many sink and how many wash ashore. Those numbers will be used to calculate how many birds may have died in addition to the ones that were found and counted.
(Source: The New York Times)