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How oil-damaged marsh grasses recover could affect gulf's rebound

By David A. Fahrenthold
Washington Post Staff Writer
Monday, July 26, 2010; A05

ON TAMBOUR BAY, LA. -- In the next act of the drama of the Gulf of Mexico oil spill, two of the most important heroes don't look like heroes. They are just thin green stalks, sticking out of grass too wet to stand on.

They are cordgrass and wiregrass, common species that wave in the winds in south Louisiana's coastal marshes. Except, in some places, they aren't waving anymore: Where oil has sloshed into the marshes, their stalks are matted and gooey and on their way to death.

What happens next -- whether these two grasses rebound or vanish -- will be a very important piece of the gulf's larger environmental story. Now that the well has been capped, the next question is whether marsh and marine ecosystems can shrug off the oil's damage, or whether it will leave them with lasting wounds.

"Many of us are much more worried about the marsh than we are about fish and shrimp and all that," said Denise Reed, a wetlands expert at the University of New Orleans. "If those plants die, they don't come back. And the marsh is gone."

Louisiana's coastal marshes are vital to ecosystems that extend far into deep, open water: They shelter "juvenile" shrimp, crabs and fish until these creatures are large enough to venture into open water. For these places, marsh grasses are as vital as water. Their roots hold the land together, giving support to loose, wet sediment that would otherwise erode.

"They are the marsh, basically," said Andy Nyman of Louisiana State University. "Once they die . . . it just floats away." Humans, too, depend on the grasses, since the marshes are a natural barrier against storm surges headed toward New Orleans.

Already, there are about 200 square miles of oiled coastline in Louisiana alone, said Robert Barham, secretary of the state's Department of Wildlife and Fisheries. He said most of that is marshland, which means around 5 percent of the state's 3,900 square miles of marsh is oily.

That number may not seem overwhelming, but Louisiana is already losing 24 square miles of wetlands to erosion every year. Scientists say the state cannot afford to lose another large chunk all at once.

The question now is: How much will die?

Humans will play some role in determining the answer. On a recent boat ride through the marshes south of Cocodrie, La., some workers could be seen trying the delicate approach to marsh cleaning, using a long stick with a plastic mop on the end to dab oil out of grass.

Some could be seen trying another approach. One crew was throwing white absorbent "boom" down onto a heavily oiled patch, then stomping it down to sop up the oil. There were also reports of damage from the boom itself, driven in by the most recent storm.

Scientists say that it is hard to get all the oil out of an oiled patch, and that trying too aggressively could just mash oil deeper into the plants' roots.

"It's like going to a doctor, you know: 'Do no harm' as the first rule,' " said Eugene Turner, another scientist at LSU. He said that even an attempt to wipe off clumps of grass with paper-towel-like sheets could backfire, since it just spreads the oil around.

"You make sure it gets on all the leaf," he said, instead of just a part.

So, then, the grasses are largely on their own.

If a blade is hit by oil, it could die by smothering: The crude could coat the blade and cut off the exchange of oxygen and carbon dioxide that plants depend on for photosynthesis. It could die by poisoning: If oil hasn't been "weathered" by the sun and bacteria, the grass could take toxins in through its roots.

Or the oil could cause harm in less obvious ways. It could sink into the sediments around the plant's roots and upset the chemical balances the plant depends on. The oil could also kill the tiny crabs and worms whose burrowing allows needed oxygen to reach those roots.

Thankfully, this is not wimpy grass.

Scientists say many oiled plants will simply shed dead stalks and put up new ones. If those are killed by another slug of oil, it will put up others.

It's already happening. One recent day, Alexander Kolker of the Louisiana Universities Marine Consortium went out onto the state's Barataria Bay to look at heavily oiled patches of grass. In among the black, he said, there were little spots of green.

New shoots, already pushing up through the oil.

"It killed the stems but it didn't kill the roots," Kolker said. "It's exciting that we're seeing, you know, grasses come back, and it suggests that this ecosystem has some degree of resilience."

But this can't last forever. If oil stays on the plant, or if new oil hits the same stretch of marsh, the reserves of nutrients and energy stored in the grasses' roots will be exhausted.

"It can tolerate one or even two oilings," Nyman said. "But over and over again? That's another question."

The real proof of the grasses' success, scientists say, won't come until next spring. If oiled plants such as these survive, boaters in the marsh will see another waving expanse of green shoots.

If the grasses do not make it, scientists say that the marsh will be gone, and that boaters will see . . . nothing but open water.

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