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Still a Mystery

Alex KolkerEveryone agrees that Louisiana is sinking. A complicated web of factors contribute to the land’s subsidence: sea-level rise related to global warming, ground compaction related to extraction of oil and the draining of swamps for urban development, dredging of oil-and-gas production canals in the wetlands, and saltwater intrusion killing freshwater marsh grass.

An important element in the loss of wetlands in Louisiana lies at Old River Control, 200 miles northwest of New Orleans. Here is the nexus of the U.S. Army Corps of Engineers’ mighty dam effort to stop the Mississippi River from flooding and from being captured by the Atchafalaya River.

But the single most important factor in wetlands loss, says Törnqvist, “is undoubtedly the fact that we have levees all along the main rivers—the Mississippi and the Atchafalaya—that prevent the wetlands from being nourished with fresh annual layers of sediment, as was the case in the natural state.”

Located 315 miles above the Gulf of Mexico, Old River Control is a structure engineered to keep the majority of the Mississippi River’s flow heading south toward Baton Rouge and New Orleans, preventing it from changing its course and joining the Atchafalaya River.

The Mississippi River previously freely jumped its banks every millennium or so. The river meandered within an arc about 200 miles wide depositing sand and silt for building the land of coastal Louisiana.

Old River Control came online in 1963 and along with the extensive levee system downriver that was constructed in the 1930s as part of the New Deal program has successfully curbed the Mississippi River in south Louisiana from doing what it did for eons—deposit sediment to build land.

The sediment of the river doesn’t build up the delta anymore. The sediment is funneled offshore and falls off into the deep waters of the Gulf of Mexico.

Alex Kolker, a research professor in the Department of Earth and Environmental Sciences, studies marine sediments. He’s charting the depths of Barataria Bay, a body of water near Grand Isle. By crisscrossing the bay in a boat equipped with sonar, he’s gathering data about how fast the delta is sinking. He’s surveying the ever-changing depth of water, trying to put a proverbial measuring stick at the bottom of the bay.

“We know the bay is subsiding, but how fast is still a mystery that I’m busy working on,” says Kolker.

That the wetlands are quickly disappearing, Kolker can tell simply by looking at global-positioning-system maps of the area. Some places where the maps indicate marshland or solid ground, the research boat smoothly glides through water. “The land is no longer there—and the maps can’t be that old,” he says.

Kolker arrived at Tulane in January 2007 with an interest in how climate change and human impacts affect coastal areas. He has done work in Long Island Sound, N.Y., studying wetlands loss. And using data from sites in the Atlantic Ocean—near New York City; Charleston, S.C.; Halifax, Nova Scotia; Stockholm, Sweden; and Cascais, Portugal—he has researched variability in sea-level rise in relation to high- and low-pressure weather systems, wind-driven processes and dynamic sea-level change—the change by storms that is often most damaging to people, property and ecosystems.

The scale of the Louisiana wetlands and coastal ecosystem is much bigger than the Long Island wetlands, which are a blip on the map in comparison, says Kolker.

Barataria Bay is “beautiful and magical,” he says. Grand Isle, the barrier islands, the marshes, lakes, bayous, estuaries, rivers and the Gulf make it a “unique area.”

“Professionally, this is ground zero,” says Kolker. “This is the place to be doing what people in my field do.”

School of Science and Engineering, 201 Lindy Boggs Center, New Orleans, LA 70118 504-865-5764 sse@tulane.edu