Louisiana coastal plan rivals Everglades restoration

The U.S. Army Corps of Engineers (Corps) has completed a blueprint for the $10–14 billion restoration of Louisiana’s vanishing coastal wetlands, an area that has lost 1900 square miles of wetlands since 1930. The project rivals the Everglades restoration in scope and in cost, and is, some say, just as controversial (Environ. Sci. Technol. 2002, 36, 374A).

The Corps’ Louisiana plan outlines a series of ambitious activities to divert Mississippi River flow, restore barrier islands, and create new marshes, some of which have already been tried as pilot projects. But new research results are casting doubt on the mechanisms that have been assumed to cause the record rates of land loss, and some scientists question parts of the plan.

The blueprint, known as the Louisiana Coastal Area study, is slated to appear in the Federal Register. The study, which focuses on 4600 square miles of coast between Texas and Mississippi, will be open for comments from the public before it is submitted to Congress next spring for authorization and funding, says Gerry Duszynski, deputy assistant secretary of the Louisiana Department of Natural Resources. The Corps developed the study with assistance from local, state, and federal agencies as well as nearly 100 scientists.

The goal is to slow down or stop coastal wetland loss, which so far totals 1900 square miles, Duszynski says. Left unchecked, subsidence and erosion will consume another 1000 square miles, nearly the area of Rhode Island, by 2050.

“Land loss has long been a natural process on the Mississippi River delta, but human activities have greatly accelerated it,” says Harry Roberts, a geologist at Louisiana State University. The force of gravity pulling on delta mud up to 500 feet thick causes dewatering and compaction of sediment, leading to subsidence and eventual flooding with seawater if land is not replenished with fresh river sediment. When the river moves away from one delta and begins building a new one, ocean waves and currents erode the edge of the old delta, while the delta interior deteriorates because of subsidence, he says.

In the past, land loss processes were counteracted by natural land building on the delta. Now, damming of major tributaries of the Mississippi has cut the river’s land-building sediment load by more than half, and a 1600-mile system of levees and control structures prevents the river from flooding and replenishing wetlands with sediment, Roberts says. The plan addresses these losses with proposals to divert river water and mud to build and restore wetlands, a technique that has been proven to work in Breton Sound, east of the Mississippi River.

But many geologists say the plan doesn’t consider all of the sources of wetland loss. “In order to fix problems, we must know the different processes driving land loss and where they are operating,” Roberts says.

“The restoration plan also needs to take into consideration subsidence induced by oil and gas extraction,” adds Bob Morton, a research geologist at the U.S. Geological Survey. He has found that large areas of wetland loss in south-central Louisiana correspond in time and space to oil and gas production. From 1930, wetland loss increased to a maximum of 40 square miles per year and has since declined to a loss of 24 square miles per year. This trend correlates with the rate of oil and gas production, which peaked in the 1960s and 1970s and has since dropped off, he says.

Large withdrawals of water, oil, and gas lead to rapid declines in pressure below the surface that cause compaction of overlying rock layers, Morton explains. The compaction reactivates faults, with blocks of land sliding down along the face of the fault. Morton says the plan overlooks this effect and instead appears to be based on the assumption that wetlands loss has been caused mainly by lack of sediment and channelization of the river. “It’s as if all the engineers ignored subsidence until now,” Morton says. If this effect is ignored, the Corps will waste money on replenishing sediment in an area that is rapidly subsiding, he adds.

Sherwood Gagliano, president of Coastal Environments, Inc., a Baton Rouge consulting firm, agrees that through the restoration program, areas with fault-related subsidence must be identified to avoid carrying out projects at such sites. However, although Gagliano says that fault-related subsidence is responsible for as much as 50% of the total land loss in coastal Louisiana, he insists that slumping river sediments in the Gulf of Mexico and earthquakes as far away as Alaska are triggering the faults.

“Environmental groups are concerned that the plan may not have provisions to halt oil and gas activities, such as dredging for canals and pipelines, that are responsible for 40% of wetland loss,” says Maurice Coman, chairperson of the Delta chapter of the Sierra Club. He notes that industry’s role in destroying wetlands is very controversial and that the state wants to stay in good graces with industry.

“If Morton is correct, it is good news for the restoration effort, because with oil and gas production in decline, subsidence rates may also decline,” adds Bob Dean, a coastal engineer at the University of Florida who chairs a National Research Council panel charged with reviewing the Corps’ blueprint. The NRC panel plans to submit its comments to Congress this spring, in time for members to review it with comments from the public.

The blueprint doesn’t provide exact details of all the restoration methods, because the science behind them has not been worked out, Duszynski says. For example, using pulsed diversions of river water to build land without harming oyster beds hasn’t been attempted. If Congress approves funding, which could happen as early as 2004, the Corps plans to launch a research program on the many interacting factors that cause land loss, Duszynski says. —JANET PELLEY