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FROM VOLUME 12, NUMBER 5, MAY 1999

Disappearing Louisiana

Item #d99may56

In a story carried on Feb. 21, 1999, by the Christian Science Monitor Service, Colin Woodard called attention to the fact that the swamps and marshes of southern Louisiana are disappearing at the rate of 40 acres a day, which is 25 to 35 mi2 a year, which amounts to an area larger than the state of Rhode Island since 1930. The main reason that this land is sinking beneath the water is because southern Louisiana is largely an alluvial plain deposited there by the Mississippi River. As time goes by, those deposited sediments are compacted and sink or erode away. The control of the Mississippi has eliminated the input of fresh water and new sediments that in ages gone by would have renewed the surface and fertilized its vegetation. In addition, the oil and gas industry has cut canals, channelling the sediment-bearing flows away from the marshes, allowing seawater intrusion, and permitting oil and gas extraction that further contributes to subsidence. Finally, the sea-level rise of the past century has contributed to the problem and could grow worse with sea level rising 1 to 3 feet during the next century because of global warming. These events have wide impacts because shrimp and other commercially important seafoods depend on the marshes for habitat and nourishment during critical phases of their lives. Even though the state continues to issue new permits for canal dredging, state and federal authorities are funding and constructing new levee structures to divert some of the Mississippi’s flow to rejuvenate the marshes with sediments and fresh water. In addition, a number of projects are being proposed to realign the movement of water and sediment across southern Louisiana.