LSU Study: Mississippi River diversions led to wetland loss, not growth

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Two Mississippi River diversions created to reduce salinity levels in Breton Sound and the Barataria Basin, and a crevasse that cut through the river’s east bank levee in Plaquemines Parish, actually caused the loss of more wetlands than they helped build, according to a new study led by LSU researchers.

But experts caution that the study does not necessarily portend similar results for the two massive diversions planned along the lower Mississippi in the next few years — diversions designed with the specific goal of land-building.

Those new, much larger diversions — called the Mid-Barataria and Mid-Breton Sediment Diversion Projects — are slated to cost $2.2 billion and are a major focus of Louisiana's effort to rebuild the state's rapidly eroding marshes.

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The LSU study found that the likely reasons the Caernarvon and Davis Pond freshwater diversions and the Fort St. Philip crevasse resulted in wetland losses was that the nutrient-rich freshwater they transported weakened the ability of wetland grasses to hold together organic soils during hurricanes and other storms, drowned wetlands by high water levels, and caused physical scouring of some wetlands.

LSU oceanography and coastal sciences professor Eugene Turner, lead author of the peer-reviewed study published in Restoration Ecology, said the study demonstrates a need to include “on-the-ground results” of such diversions in the computer modeling being used to determine if the Mid-Barataria and Mid-Breton projects will be successful. Those diversions, unlike the ones in the study, are designed to build land rather than decrease salinity, and the volume of water and sediment they would introduce into the marshes is far greater.

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