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In Gulf Oil Spill, Fragile Marshes Face New Threat  

2010-05-02 04:29:35|  分类: 历史与文化 |  标签: |举报 |字号 订阅

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In Gulf Oil Spill, Fragile Marshes Face New Threat - 雪山飞狐 - JOKUL VOLANT TOD

Ann Heisenfelt/European Pressphoto Agency

Thousands of feet of containment boom line the Louisiana coast, an effort to protect the shore from the encroaching oil spill.


Published: May 1, 2010

COCODRIE, La. — With oil gushing into the Gulf of Mexico unabated and officials giving no indication that the flow can be contained soon, towns along the Gulf Coast braced Saturday for what is increasingly understood to be an imminent environmental disaster.

The spill, emanating from a pipe 50 miles offshore and 5,000 feet underwater, was creeping into Louisiana’s fragile coastal wetlands as bad weather and rough waters hampered cleanup efforts. The White House announced that President Obama would visit the region on Sunday morning.

The imperiled marshes that buffer New Orleans and the rest of the state from the worst storm surges are facing a sea of sweet crude oil, orange as rust. The most recent estimate by the National Oceanic and Atmospheric Administration says the wreckage of the Deepwater Horizon rig, which exploded on April 20 and sank days later, is gushing as much as 210,000 gallons of crude into the gulf each day. Concern is mounting that the flow may soon grow to several times that amount.

The wetlands in the Mississippi River delta have been shrinking at a rate of about one football field an hour for decades, deprived of sediment replenishment by levees in the river, divided by channels cut by oil companies and poisoned by farm runoff from upriver. Hurricanes Katrina and Rita took large, vicious bites.

The questions that haunt this region are how much more can the wetlands take and does their degradation spell doom for an increasingly defenseless southern Louisiana?

Many variables will dictate just how devastating this slick will ultimately be to the ecosystem, including whether it takes days or months to seal the leaking oil well and whether winds keep blowing the oil ashore. But what is terrifying everyone from bird watchers to the state officials charged with rebuilding the natural protections of this coast is that it now seems possible that a massive influx of oil could overwhelm and kill off the grasses that knit the ecosystem together.

Healthy wetlands would have some natural ability to cope with an oil slick, said Denise Reed, interim director of the Pontchartrain Institute for Environmental Sciences at the University of New Orleans. “The trouble with our marshes is they’re already stressed, they’re already hanging by a fingernail,” she said.

It is possible, she said, that the wetlands’ “tolerance for oil has been compromised.” If so, she said, that could be “the straw that broke the camel’s back.”

To an untrained eye, the vast expanses of grass leading into Terrebonne Bay, about 70 miles southwest of New Orleans, look vigorous. Locals use boats as cars here, trawling though the marsh for shrimp or casting for plentiful redfish. Out on the water, the air smells like salt — not oil — and seabirds abound and a dolphin makes a swift appearance.

But it is what is not visible that is scary, said Alexander Kolker, a professor of coastal and wetland science at the Louisiana Universities Marine Consortium. Piloting a craft through the inland waterways, he points out that islands that recently dotted the bay and are still found on local navigation maps are gone. Also gone are the freshwater alligators that give the nearby town Cocodrie its name — French settlers thought they were crocodiles.

All evidence, he says, that this land is quickly settling into the salt ocean.

The survival of Louisiana’s coastal wetlands is not only an environmental issue here. Since successive hurricanes have barreled up from the gulf unimpeded, causing mass devastation and loss of life, just about every resident of southern Louisiana has begun to view wetlands protection as a cause of existential importance. If the wetlands had been more robust when Hurricane Katrina’s waters pushed up from the ocean, the damage might not have been as severe.

But they were not. Levees holding back the Mississippi River have prevented natural land replenishment from floods. Navigation channels and pipeline canals have brought saltwater into fragile freshwater marshes, slowly killing them, and the sloshing of waves in boats’ wakes has eroded natural banks.

The state has lost an area the size of Delaware since 1932 and is still losing about 24 square miles a year. Not all the damage is caused by humans: the hurricanes of 2005 turned about 217 square miles of marsh into water, according to a study by the United States Geological Survey.

Garret Graves, director of the Governor’s Office of Coastal Activities, said that since Hurricane Katrina, extraordinary efforts at restoration had been made and to some extent had slowed the decline. But, he said, a severe oil dousing would change that.

“The vegetation is what holds these islands together,” he said. “When you kill that, you just have mud, and that just gets washed away.”

A federal judge has affirmed the necessity of robust wetlands for the city of New Orleans, finding last fall that the degradation of wetlands and natural levee banks by the federal government’s negligent maintenance of a navigation channel had created a path for Hurricane Katrina’s storm surge right up to the city.

Oil is likely to take similar open pathways into the marsh. For this reason, the state’s approach to fighting the oil slick is the same as its approach to creating a heartier and more storm-surge-resistant marshland: it is diverting the Mississippi River and its healthy load of sediment to counter a potential influx of oil and strengthen vegetation.

Normally, these grasses have great resiliency. They are similar to a lawn, said Irving A. Mendelssohn, a professor at Louisiana State University who has done studies on the effect of oil on the local ecology. If they are damaged only above the ground, they will grow back swiftly. But if the roots die, the plant dies and the ground underneath it sinks into the sea within a year.

A coating with a sheen of oil would do little harm, Dr. Mendelssohn said. But, he said, “if you have oil coming in consistently, the cumulative effect could be severe. If the plants keep getting reoiled, you get a smothering effect. The vegetation could no longer do photosynthesis, and then it can’t sustain itself.”

If the volume of oil does not increase drastically, it is likely to ooze down the saltwater channels, hemmed in by grasses. But then there is the potential nightmare of a tropical storm, even a low-level one, with a surge of several feet that sends oil far into the freshwater marshes, which are more fragile and almost impossible to clean.

That is where the health of the marsh can make a critical and possibly fatal difference. On the way to Terrebonne Bay, which was not yet affected by oil on Friday, Dr. Kolker pointed out signs that the marshes were weak: cypress trees, for example, dying by the side of Route 10. Farther out, local fishermen tell of pelicans whose nests were so crowded onto what remains of sinking barrier islands that they looked like Manhattan co-ops.

“The area can only sustain so many environmental insults,” he said.

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