Oil spills leave their corrosive legacy
No one can be sure of the ecological recovery from the BP oil spill off the Gulf of Mexico
On the rocky beaches of Alaska, scientists plunged shovels and picks into the ground and dug 6,775 holes, repeatedly striking oil — still pungent and dangerous a dozen years after the Exxon Valdez infamously spilled its cargo.
Shorelines hit by oil in the past offer clues to what people living along the Gulf Coast can expect now that the great oil calamity of 2010 may be nearing an end.
Every oil spill is different, but the thread that unites these disparate scenes is a growing scientific awareness of the persistent damage that spills can do — and of just how long oil can linger in the environment, hidden in out-of-the-way spots.
At the same time, scientists who have worked to survey and counteract the damage from spills say the picture in the gulf is far from hopeless.
Disasters like the Valdez in 1989, the Ixtoc 1 in Mexico in 1979, the Amoco Cadiz in France in 1978 and two Cape Cod spills, including the Bouchard 65 barge in 1974 have allowed scientists to paint a more complex portrait of what happens after a spill.
It is hard for scientists to offer predictions about the present spill, for two reasons. The ecology of the Gulf of Mexico is specially adapted to break down oil, more so than any other body of water in the world.
And because this spill is emerging a mile under the surface and many of the toxic components of the oil are dissolving into deep water and spreading far and wide, scientists simply do not know what the effects in the deep ocean are likely to be.
Increasing the stress
Perhaps the greatest single hazard from the Deepwater Horizon disaster in the gulf is the long-term erosion of delicate coastal wetlands it could cause.
Louisiana’s coastline contains some of the most productive marshes in the world, delivering an abundance of shrimp and oysters and providing critical habitat and breeding ground for birds and fish.
The Louisiana marshes are eroding at an extraordinary rate — a football field’s worth sinks into the Gulf of Mexico every 38 minutes, according to the Louisiana Office of Coastal Management — and the worry now is that the oil spill will accelerate that erosion.
George Hampson, now retired, was on the scientific team at the Woods Hole Oceanographic Institution that studied a series of spills in the area. He recalled that after the 1974 spill the beach grasses, called spartina, which had grown like luxuriant matting along the shore, died.
Spartina, a common beach grass that fills the marshes along the North Atlantic and in the Gulf of Mexico, is a crucial factor in keeping marshlands from eroding into the sea. Its roots act as a vast net keeping soil in place.
Over the course of the next several winters, six feet of shore eroded, including a sand berm that stood above the rest of the beach. And as the view from the pebbled road indicates, the vegetation still struggles for a foothold today.
Oil spills produce a powerful impulse to clean up the oil and restore as much of the environment as possible. But that impulse can itself be a source of destruction.
In Alaska, after the Exxon Valdez spill, Exxon power-washed oiled beaches with high-pressure, hot-water sprayers. It made for dramatic television images, with the company seemingly working hard against the spill. But scientists ultimately determined that it was a disaster for the tidal ecology, with clams and other organisms showing greatly delayed recovery on the laundered beaches, compared with oiled beaches that were not cleaned.
The lesson, scientists say, is not that people should never try to clean up an oil spill. It is possible to do too little as well as too much. But the calculation of how much to do is tricky, demanding deep scientific understanding of an area’s ecology. Applying supposed common sense has repeatedly led to mistakes.
Already in Louisiana, battles have erupted between the Army Corps of Engineers and local residents, led by Governor Bobby Jindal, over proposals to build sand and rock barriers to block the oil from coming into the marshes. The corps has been cautious on approval permits and recently rejected a plan to build a rock barrier outside Barataria Bay, arguing that such structures would change water-flow patterns to the possible detriment of the marsh ecology.
Research
The other day, a Mexican fishing boat threaded its way deep into a coastal mangrove swamp on the Bay of Campeche. It carried two scientists, an American, Wes Tunnell, and a Mexican, Julio Sanchez.
They were looking for remnants of an oil spill that happened 30 years earlier, when the Ixtoc 1 well in the bay exploded and gushed oil for 10 months. It has stood for decades as the worst accidental release of oil in any ocean. (It may or may not have been surpassed by the BP spill; estimates vary.)
To the untrained eye, the Mangroves in Mexico appeared healthy, billowing up from the shoreline in shades of green.
But Tunnell pointed out subtle signs of damage. There were clearings in the foliage, instead of an unbroken tangle of roots and mangrove trees. The branches of the outer layer of red mangroves seemed stunted.
The Ixtoc blowout of 1979-80 is the closest analogy to the BP spill, even though it happened in much shallower water. Ixtoc soiled hundreds of miles of beaches, all the way to Texas.
Because oil constantly seeps into the gulf from natural fissures, the water is teeming with microbes adapted to break oil down and use it as food. The breakdown happens faster there than in colder bodies of water, and the warm water helps some species recover faster, too.
No one can be sure that the recovery from the BP spill will be a replay of Ixtoc. But the greatest reason for optimism is nature’s demonstrated capacity to handle the assaults on it.
“Thirty years ago, that 140 million gallons of oil went somewhere,” Tunnell said. “The gulf recovered and became very productive again. My concern is: Is it as resilient today as it was 30 years ago?”
