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Hurricane Katrina's Ecological Legacy: Lost Swamps, Crops, Islands

Craig Guillot
for National Geographic News
August 23, 2006
 
A year after Hurricane Katrina hammered the
U.S. Gulf Coast and spurred massive flooding in New Orleans, the
ecological impacts are still being felt throughout the region.

In particular, human-driven coastal erosion and saltwater intrusion—issues that have long been damaging the region's natural storm buffers—were made worse by the powerful hurricane.

The flooding in New Orleans that began on August 30, 2005, "was really an unnatural disaster," said John Day, a distinguished professor emeritus at the Louisiana State University (LSU) School of the Coast and Environment in Baton Rouge.

"We spent the last century doing almost everything we could to destroy our coast in all sorts of ways—putting levees on the Mississippi River, slicing thousands of kilometers of canals, massive oil and gas production."

For example, Day says, the canals that connect the city to the coast allow storm surges to travel inland, bringing salt water that damages the land.

One such canal, known as the Mississippi River Gulf Outlet, was built in the mid-1960s to be a 76-mile (122-kilometer) shortcut between the Gulf of Mexico and New Orleans.

Hailed as an engineering marvel at the time, the canal is rarely used today.

Before the record hurricane season of 2005, salt water brought inland by the canal was fingered as the culprit in the death of thousands of acres of cypress swamp, a natural buffer against storms.

And when Katrina hit, levee failures on the canal allowed water to pour into St. Bernard Parish and New Orleans East (read "New Orleans Flooded in Wake of Hurricane Katrina" [August 2005]).

"Had those cypress swamps been in place, the levees probably wouldn't have failed," Day said.

Toxic Stew

The continuing effects of saltwater intrusion driven by Katrina and Hurricane Rita—which hit the Gulf Coast about a month later—can be still seen in the wilting trees and plants far from the coast.

Steven D. Linscombe is southwest regional director of the Louisiana State University Agricultural Center in Baton Rouge.

He says that inland saltwater intrusion driven by Rita caused the state's rice crop to decrease by 20 percent this year.

Some fields could take up to two years to recover.

"Our rice acreage was down in southwest Louisiana by about 80,000 to 90,000 acres [32,400 to 36,400 hectares] because of the storm surge," Linscombe said.

"Much wasn't planted because of soil contamination or contaminated waterways that would be used to flood [rice fields]."

Lake Pontchartrain is one of the few examples of quick ecological recovery following the record storm season.

In the weeks after Katrina, polluted floodwaters dubbed the toxic stew were pumped directly from the streets of New Orleans into the lake (read "New Orleans Floodwater Fouled With Bacteria, Chemicals" [September 2005]).

Carlton Dufrechou, an environmental engineer and executive director of the Lake Pontchartrain Basin Foundation, estimated that about 10 billion gallons (38 billion liters) of contaminated water were dumped in Pontchartrain.

"The good thing was that it was less than 10 percent of the lake's volume," Dufrechou said. "We started to see the bacteria counts drop almost immediately after the pumping stopped in October."

"Lost" Islands

Barrier islands that extend from Texas to Florida have historically served as the Gulf Coast's major natural protection from hurricanes.

The long thin islands just off shore buffer the mainland from strong winds and ocean waves.

But battering from intense tempests over the years has taken its toll on these islands.

Hurricane winds cut Petit Bois Island from Dauphine Island 150 years ago, and in 1969 Hurricane Camille sliced Ship Island in half.

What's more, canals and levees along the Mississippi River prevent fresh sediment deposits from building the islands back up.

Louisiana's Chandeleur Islands—which have shrunk considerably in the past decade—were almost wiped off the map due to Katrina (read "Many Islands 'Gone,' Wetlands Gutted After Katrina, Experts Say" [September 2005]).

Rick Clark, chief of science and resources management for the Gulf Islands National Seashore, says that Katrina's towering storm surge completely washed over most of the barrier islands along the Mississippi coast, scattering hefty amounts of debris.

"A substantial amount of our recovery effort was just getting that inorganic debris off [Ship Island]," Clark said.

"Some of it is still scattered; heavy equipment and all-terrain vehicles that might have ended up in a pond or an area that is just too sensitive for us to go in right now."

For the future, scientists say, there are many viable solutions for restoring and protecting the coast against further storm damage.

LSU's Day says that thick layers of sediments deposited over the coast can help create wetland sustainability, but it will become more difficult to maintain in coming years because of more frequent and more intense hurricanes.

"This is really a wake-up call. It says to us that we cannot live on this coast the way we have been living," Day said.

"In the next 50 years the idea of having several hundred thousand people living below sea level will just become an impossibility."

Mark Schexnayder, hurricane programs coordinator for the LSU Agricultural Center, says that raising public and political awareness of the threats to Louisiana's ecology is the most critical path of action.

"We're trying to build people's awareness of the [canals], the port, and how it all relates to the rest of the country for goods and oil and gas," Schexnayder said.

He adds that pipelines could be one of the easiest ways to divert sediments carried by the Mississippi River to areas outside the levees, where they can be used to reestablish wetlands.

"Katrina was bad, but it wasn't the worst it could get," he said. "Just wait till we don't have any wetlands to buffer us."

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