STEVE INSKEEP, host:
Hurricanes Katrina and Rita will long be remembered for the destruction they caused. But a controversial new research paper in Science magazine says these storms also helped to build new coastal wetlands. The report concludes that big storms, rather than rivers, are the main source of new material for marshlands that help protect the coast.
NPR's Richard Harris reports.
RICHARD HARRIS: Marshlands along the Gulf Coast are constantly being eroded away by the sea, as well as by human activities. The wetlands would disappear altogether if they weren't replenished with fresh sand, silt and clay. Some comes directly from the rivers that flow into the Gulf, but Eugene Turner at Louisiana State University wanted to find out how much of that material is delivered by storms. So after Hurricanes Katrina and Rita, he surveyed hundreds of spots along the coast, from Texas to Mississippi, to see how much new sediment the storms had brought in. The answer was a lot.
Mr. EUGENE TURNER (Louisiana State University): The dominant source of sediments onto the wetlands appears to come from hurricane events and not from the Mississippi River. Before flood-protection levees it might have flowed over its banks, and that was not the dominant source.
HARRIS: That's a touchy thing to say in southern Louisiana. For decades, conservationists have been hoping to rebuild the wetlands by getting sediment out of the Mississippi River. Massive projects are proposed for this purpose. Turner isn't saying those would be a complete waste, but he argues that rebuilding strategies should be based on a better understanding of where the sediment actually comes from.
Mr. TURNER: The main issue here, though, for the scientists, is to try to be clear about the cause and effect relationships, because if you can't do that, you'll end up having a misplaced cure, maybe, and one that hurts. And of course, there's a lot of money in here. These are billions of dollars.
HARRIS: But advocates of getting river sediment out into the marshlands aren't about to back down on the basis of this study. Virginia Burkett at the U.S. Geological Survey says Turner and his colleagues did a good job of showing that storms can push around a huge amount of sediment.
Ms. VIRGINIA BURKETT (U.S. Geological Survey): But what they neglect to point out is that while sediment was being deposited in some marshes, over 200 square miles of coastal marsh and barrier islands were lost or converted to open water during Katrina and Rita.
HARRIS: In fact, some of the places that got the most new sediment were directly next to barrier islands that were largely washed away by the storms, she says. So there's still a need for more sediment, and ultimately that all comes down the rivers.
Ms. BURKETT: If hurricanes are a fact of life and, you know, they can rework sediments - but the premise that we do not need to allow the Mississippi River to deposit sediments naturally on the shelf is very short-sighted, in my opinion.
HARRIS: Right now, much of that sediment is held in the Mississippi River channel by the network of levees. And when it reaches the Gulf, a good deal of it gets spewed into deep waters. So the river is not delivering as much as it used to to the coastline. Besides, Denise Reed at the University of New Orleans says coastal management these days isn't simply a matter of understanding the natural processes that maintain the wetlands. Scientists are trying to figure out how to repair decades of damage caused by activities such as channel cutting for oil and gas exploration.
Professor DENISE REED (University of New Orleans): If we really want to rebuild the coast, then we have to do more than just get sediment on the top of existing marshes. We actually have to build land in open water.
HARRIS: And a good source of sediment for that purpose is still the rivers, she says.
Prof. REED: So even if hurricanes can help keep some marshes more healthy in some areas, they're not going to affect the whole coast, fortunately. We don't want hurricane storm surges to affect the whole coast on a regular basis. But we can manage river waters to do that for us.
HARRIS: Now, study author Eugene Turner doesn't dismiss river sediment projects entirely, but he says there should be more focus on other measures like refilling the channels that have been cut into the marshes and paying more attention to the plants that are already re-growing and filling in the marshlands that had been disrupted by the hurricanes.
Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.
