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Scientists are learning how Hurricane Katrina affected the marshes of southeastern Louisiana. The area's geography is unlike anyplace else on Earth. Much of what looks like terra firma on a map is actually marshland floating like a pancake on a plateful of syrup. Those marshes form a buffer against storms and flooding, so their condition now will affect how the region is rebuilt. In this NPR-National Geographic Radio Expedition, NPR's Christopher Joyce made a trip into liquid, Louisiana.
CHRISTOPHER JOYCE reporting:
Scientists believe Hurricane Katrina created a giant storm surge. It gathered in the Gulf of Mexico and barreled westward up a wide swampy delta toward New Orleans. It may have been more than 20 feet high by the time it hit the city's eastern suburbs. Storm scientist Jimmy Johnston rolls out a map at the Lafayette offices of the US Geological Survey where he works. He pinpoints levees that run northeast and southeast of the city. He says they formed a triangular channel that focused the surge.
Mr. JIMMY JOHNSTON (US Geological Survey): Because of that, it didn't spread like a sheet. It just came in and started shirring because it's kind of a funnel. That storm funneled up into that area here.
JOYCE: Inside that funnel is a lot of marshland. Marshes soften the blow from storms, but ship channels and development have replaced much of these wetlands. And now Katrina has dealt the marshes a natural blow. To see what the damage is, you need to get into a plane and take along a guide, like Professor Harry Roberts.
(Soundbite of plane engine)
JOYCE: Roberts runs the Coastal Studies Institute at Louisiana State University. He says the levees along the Mississippi keep the river from flooding, and that's good for people but bad for marshes. Flooding lays down sediments like a layer cake, and that's where marshes take root.
Professor HARRY ROBERTS (Coastal Studies Institute, Louisiana State University): The sediment is a buffer to damage, so as long as you're bringing sediment in and building the surface and creating a shallow-water environment with a lot of sediment in it that attenuates the storm waves and the storm surge, the damage is minimal to the natural environment.
JOYCE: As we fly east over New Orleans, the city landscape gives way to a carpet of dark green grasses. We're heading toward the Bird Foot Delta, named for its shape on the map. Below where the hurricane passed through, the carpet is no longer uniform. Wind and waves have cut channels through.
Prof. ROBERTS: Now we're seeing the St. Bernard marshlands that were just literally devastated by Hurricane Katrina. And you're seeing some of the outflow features from the water that was built up on the storm surge that came through this area and then flows back across the marshes.
JOYCE: Farther east where the levees end, there's more sediment. The salt grasses here are well anchored and appear intact. But a fishing town on the delta has been smashed.
Prof. ROBERTS: That is just amazing. There are ships--look at these two menhaden ships on the highway. Those are big ships. Oh, man. That's incredible.
JOYCE: We head farther east toward the Chandeleur Islands, a crescent of land about 60 miles east of New Orleans. When we get there, though, there's not much left.
Prof. ROBERTS: No beach, no sand, just patches of marshland. Where there used to be that beautiful island arc, you see now a linear set of marsh patches, and that's all there is to it. All the sand's gone.
JOYCE: Roberts says it will take years for the islands to recover, if ever. What did survive was held together by island marshes, sort of like a green glue. That glue forms a perimeter to the south of New Orleans as well. Much of it in the Jean Lafitte National Park. It's a hot wet place with cut grass and alligators. We get there by airboat, a flat-bottomed skiff with a big fan that literally blows the boat over the water. Scientist from the US Geological Survey and the National Park Service are making their first foray into the park after the hurricane. There are patches of dry land, a few trees--wax myrtle, bald cypress and water oak. Many of these are now flattened. As the airboat crew searches for a navigable channel, David Muth of the Park Service describes the place as liquid lane.
Mr. DAVID MUTH (National Park Service): What we're looking at is a floating or semifloating freshwater marsh. It's called a Louisiana float on(ph) and--a floating mat of organic material held together by roots of living plants on the top.
JOYCE: Sedges, ferns, bulls tongue--all of it floats on a foot or two of water with another eight feet of muck underneath. When hurricanes flood the area, the mat simply rises. But high winds can tear up that mat, and too much salt water can kill the plants outright. That's what worries Chris Swarzenski, an ecologist with the Geological Survey.
Mr. CHRIS SWARZENKSI (US Geological Survey): There's a lot of open water where there used to be marsh, and it's sort of like a puzzle shape with little areas where there's ponds now maybe 20, 30 feet across. Before, this was all kind of a solid marsh.
(Sound of siphoning)
JOYCE: Swarzenski siphons water samples out of the muck. He's relieved to see that the salt level is about normal. So sea water did not get into this part of the marsh. In fact, except for birds and things that swim, nothing much can get in here. The airboat skipper has to drive over the marsh in places. It's a distinctly strange experience to look over the side of a boat onto land. Eventually, the marshes open up into a lake. We float up to what's left of a centuries-old Indian midden, a refuse heap of clam shells. It's in danger of eroding away as the marshes retreat. Tom Doyle is an ecologist with the Geological Survey.
Mr. TOM DOYLE (US Geological Survey): It's important that we figure out how to slow this process down because at one point or another, this organic marsh will continue to erode at rates that in a matter of years, we can predict most of it will be gone.
JOYCE: The team says what they've seen today looks bad in places but not fatal. But they wonder whether a bigger, healthier wetland around New Orleans would have slowed the storm. Did ship channels, like the Mississippi River Gulf outlet, pierce the spongy perimeter and deliver a storm surge like a knife into the city's back? The Park Services' David Muth thinks so. He thinks the marshes need to be restored to protect the city, but he also realizes that the Mississippi River must also be contained to bring commerce into the heartland.
Mr. MUTH: Can you maintain the Port of New Orleans and oceanic shipping and still divert enough of the Mississippi River water and sediment and fresh water to rebuild wetlands? And the answer is absolutely yes. It's just a question of engineering and money. The cheap way is the way we're doing it now, and you ask yourself the question: Is that the smartest thing we could've done?
JOYCE: Muth speaks from the heart. His own home in New Orleans was submerged in several feet of water. He doesn't know where he's going to live, but if it's in New Orleans, he hopes the marshes will still be there.
Mr. MUTH: You can rebuild Louisiana's marshes over the next 50 years. It's just a matter of making the decision and doing it. And if this doesn't spur us to do it, we'll never do it.
JOYCE: For Radio Expeditions, I'm Christopher Joyce, NPR News.
INSKEEP: Radio Expeditions is a co-production of NPR and the National Geographic Society. Photos of the marshes and the scientists on the survey team are at npr.org.
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