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BIRDFOOT DELTA, Louisiana (Reuters) - Marsh grasses are the tough guys of the plant world. Left alone, they dominate coastal marshes from Texas to Newfoundland. Burn their stems and leaves, and they come back bushier than ever.
They help slow down hurricanes and filter pollution. As impenetrable to humans as a green wall, they shelter birds, fish and endangered mammals, and act as nurseries for commercial species like shrimp and crabs.
But let oil get into their roots and underground reproductive systems, and they can wither and die. If the grasses go, they could take parts of Louisiana's fragile wetlands with them, which means thousands of acres (hectares) of productive and protective marsh could turn into open water.
BP's Deepwater Horizon spill in the Gulf of Mexico has the potential for this kind of damage, and enough oil has coated some patches of marsh grasses to make them appear black when viewed from above.
Fortunately, their green shoots tell another story. Irv Mendelssohn, a wetland ecology expert who has been watching oil's impact on plants for three decades, offers a cautiously optimistic prognosis for their recovery from this latest environmental insult.
"There was a lot of fear before any data was gathered that this could be really damaging to coastal wetlands," Mendelssohn said after a one-day tour of marshes off Louisiana's southern edge. "As it turned out, we actually didn't see much oil. In fact, we didn't see any oil on the water's surface in the bays."
That doesn't mean there isn't any or that there won't be in the near future as material from the broken well continues to spread out. Wetlands aren't the only things in its path.
Environmental advocates worry about what oil treated with dispersant chemicals will do to birds, fish and other wildlife that come in contact with it -- and there are pea-sized rust-colored blobs of this material floating around the Birdfoot Delta, near where pelicans and gulls perch and feed.
Doug Inkley, senior scientist at the National Wildlife Federation, said it is simply too soon to tell what the BP spill's impact will be on the Gulf ecosystem, which ranges from deep-diving sperm whales to endangered Kemp's Ridley sea turtles to centuries-old coral reefs to the tiny phytoplankton at the bottom of the Gulf food web.
"Nobody really knows what's happening so far underwater, and it's a complex system," Inkley said. "You don't know which part of it you can knock out and not have a huge effect."
But to Mendelssohn, a professor at Louisiana State University's School of the Coast and Environment, the early evidence suggests that "marsh-oiling" may be a lot less extensive than initially feared.
To conduct their survey of selected sites, Mendelssohn and two colleagues earlier this month launched an outboard-powered Boston Whaler from the marina at Venice, moving out into the eastern part of the delta.
The trio -- Mendelssohn, David White of Loyola University in New Orleans and Qianxin Lin of Louisiana State University -- set out at mid-morning for four hours among the reeds.
They knew just where to look, because federal SCAT teams (short for Shoreline Cleanup and Assessment Technique teams) have been ranging around the Gulf since shortly after the blowout, noting where oil has shown up. The SCAT surveys indicated oil on eastern sections of the Birdfoot Delta.
The tools the group used were simple: their eyes, their expertise and a camera. Mendelssohn and White dressed for the heat, in shorts, water shoes and caps; Lin looked ready to return to his Baton Rouge office, wearing long pants and a short-sleeved shirt. They had all driven hours to get to the delta on a simmering July day.
At each of four sites, Mendelssohn said, they were able to maneuver the shallow-draft boat right up next to the stands of grass, some of the reeds shoulder-high, others elephant-high.
They took no measurements and did not set foot in the marsh, recording what they saw in photographs, identifying what needs further study and observation.
Mendelssohn and his colleagues are among the throngs of environmentalists and other scientists who have descended on the Gulf Coast since the spill, with many concentrating on the commercial species at risk. Almost everything on the deluxe seafood combination plate -- clams, crabs, crawfish, shrimp, flounder, striped bass and sea trout -- lives some part of its life in a marsh.
While much of the public attention has focused on the people who harvest what the marsh helps provide, the marshes themselves are under threat. And that's the focus of Mendelssohn's inquiry.
A welcome sight for the three-man team was green shoots popping out on the oil-blackened stems of reeds in the Birdfoot Delta, a watery area southeast of Venice at the very toe of Louisiana's boot. Although not confirmed by direct testing, the shoots are a strong indication that the roots are healthy.
"What that told us immediately, which we did not know up to this point, is that even though the (reeds) had been oiled ... it was not killing the plant...
"This makes me believe that the long-term impact, at least at this point in time, on these reeds communities will be relatively small -- again, just on the vegetation. There will be new shoots being formed, and as long as they're not being oiled again, the vegetation should show a minimal impact."
Another positive sign, he said, was that the oil had not penetrated deep into the coastal marshes, perhaps six to nine feet. At the edge, they're black with weathered crude; inside the thicket, the plants are green.
With a scientist's habitual reserve, though, Mendelssohn ticked off caveats to this assessment: He and his colleagues didn't see every marsh, there may be areas of wetland contamination that are not yet charted, more oil could arrive in these places, and any hurricanes this year have the potential to drive oil deep into marshes and swamps.
(There's a difference between marshes, which are mostly leafy grasses and reeds, and swamps, which are mostly woody plants and trees like cypress. Both are wetlands.)
When asked to rank the overall potential havoc that could be caused to Gulf coastal wetlands compared to other oil spills he has responded to in Canada, Texas, California and elsewhere in Louisiana, Mendelssohn said: "From what I've seen so far, this looks fairly minor."
This is good news to officials in Louisiana who raised alarms early on about what would happen if leaking BP oil from the Gulf of Mexico got into the marshes.
"The day we have all been fearing is upon us today," Louisiana Governor Bobby Jindal told reporters on May 19 as a blanket of black oil washed into his state's wetlands just shy of a month after the April 20 blowout at the Deepwater Horizon rig. "This wasn't tar balls. This wasn't sheen. This is heavy oil in our wetlands. It's already here but we know more is coming."
You can see where oil from the BP spill has gone and is expected to go at www.geoplatform.gov/gulfresponse; the projected path of the oil is shown on a near real-time basis, with forecasts going two days forward. It shows the results of SCAT teams' inspections of the shoreline, with ratings ranging from bright red for "heavy oiling" to blue for "no oil observed."
The majority of the Birdfoot Delta -- so named because that's what it looks like from the air -- is rimmed in blue on the site, meaning an oil-free area, though there are some red X's indicating beached oil.
What Mendelssohn calls his "recon" marsh mission was an important part of the picture because of the potentially lethal effect of oil contamination, which can kill wetland reeds and grasses in two ways, singly or in combination.
So once oil gets into a wetland, how do you get it out?
There are at least four ways to do it, but not all would work if there is a large-scale oiling of Louisiana's coast, according to Mendelssohn's colleague Lin.
One technique is to spray high-volume, low-pressure streams of water on oil-covered marsh plants, just as you'd rinse off a greasy plate. But Louisiana's thick stands of marsh grass are so dense that water sprays might not penetrate them, Lin said.
Wiping off the oil with absorbent pads is another option, but this is so labor-intensive it is more appropriate for use on small-scale areas of oil contamination. Because people have to get into the marsh to do it, it poses another difficulty: the presence of human workers can cause marsh damage on its own if they have to get into the center of a patch of reeds.
Lin suggested bioremediation -- the use of fertilizers like nitrogen and phosphorus to encourage microbes in the soil to break down the oil -- as a possibility. He said this method would have to be used with extreme care, however, since the same chemicals are already flowing down the Mississippi River in the form of farm run-off, causing an annual summer "dead zone" in the Gulf of Mexico, where extremely low levels of oxygen make it hard for any wildlife to survive.
That leaves in-situ burning, a century-old technique long used by Louisiana wetlands managers and landowners. Setting fire to a marsh may seem destructive, but as long as there's a layer of water even one a few inches (cm) thick, it can be an effective way to get oil out of a contaminated wetland.
The layer of water insulates the plants' roots and underground stems called rhizomes from the heat of the fire, Lin said.
"For this oil spill, mostly you will have adequate water over the marsh surface," he said in an interview at his office in Baton Rouge. "Instantly, or in a very short time, it can remove all of that oil, up to 90 percent of that floating oil from the water's surface, and also remove all of that oil coating the plant material."
In-situ burning was used to clean up oil that spilled into wetlands for 40 days after Hurricane Katrina, Lin said. "We monitored plant recovery in terms of structure and function of a marsh, and we found no difference between burned and adjacent marsh -- which means that marsh recovery is very quick in a year or so, no difference at all."
It's critical that the oil be dealt with because it can be fatal to the grasses. First, if the oil itself is toxic -- as some of the BP oil may be -- it can poison the plants by direct contact, breaching their cell walls and interfering with basic metabolism, including respiration and the ability to take in nutrients.
Second, oil can kill indirectly if it coats the plants' leaves enough to clog small openings called stomates. Stomates take in carbon dioxide, which plants need to turn sunlight into fuel for growth in the process of photosynthesis.
The worst-case scenario would be if the spilled oil gets deep into the soil to coat rhizomes, which produce new shoots each spring. If the roots and rhizomes die, the plants' days are probably numbered.
One other factor, illustrated in a YouTube video featuring Mendelssohn here is what happens if the rhizomes collapse. Rhizomes are air-filled tubes; when they die, they deflate, and the soil around them deflates along with them.
These marsh areas sit just above sea level, so if they sink, the Gulf of Mexico can flow right over them and wetlands can be lost through a phenomenon known as subsidence and compaction -- the sinking and squashing of the coastal soil that lowers the land below the water.
The loss of wetlands is no idle threat in Louisiana; it occurs daily, with 35 square miles (90 sq km) or more lost to open water each year, over an acre an hour for the last half-century or more. This has been caused in part by building of levees on the Mississippi River that prevent sediment from being deposited in the marshes.
The Birdfoot Delta has some of the highest subsidence rates in coastal Louisiana -- over a half-inch (12 mm) annually -- and Louisiana has some of the highest subsidence rates in the United States. With 40 percent of U.S. wetlands in Louisiana, that puts a nationally critical buffer zone in danger.
While his initial assessment is optimistic, Mendelssohn sounded a wary note, based on the sheer volume of oil coming from the BP site.
"We know there's a lot that's been spilled, an estimate of 40,000 to 60,000 barrels a day," he said at his desk in Baton Rouge. "And we don't know exactly where all that is. So if because of a hurricane or storms or high water, some of this oil that maybe has not degraded too much gets pushed into wetlands ... there could be some serious effects, and the plants may be either stressed or killed by that.
"But we don't know yet. That's a big uncertainty."