Mississippi River Freshwater Diversions in Southern Louisiana: Effects on Wetland Vegetation, Soils, and Elevation

A Position Paper by the Technical Panel from the
Workshop on Response of Louisiana Marsh Soils and Vegetation to Diversions

December 5, 2012

Coastal Louisiana lost 4,877 km2 of land area between 1932 and 2010 (Couvillion et al. 2011). Freshwater Diversions are a technique to address one cause of wetland loss: failure to maintain elevations sufficient to support emergent vegetation forming the wetland habitat. This report examines the effects of Freshwater Diversions from an ecological perspective, and focuses on wetland plant community productivity and composition, wetland elevation, and wetland soil strength. Each section assesses available information, information gaps, and identifies data needed to ensure successful marsh stabilization and restoration.

Diversions of river water into adjacent coastal wetlands are a part of all plans to mitigate for the extensive loss of Louisiana’s coastal wetlands. Diversions can be broadly characterized as Sediment Diversions, designed for significant land-building in areas that currently are open water, and Freshwater Diversions, designed to flow into existing, but degrading marsh systems to reverse or slow the rates of degradation. This paper explores the effects on marsh properties of diversions in the lower Mississippi River designed for freshwater delivery (i.e. Freshwater Diversions). Evaluation of the effects of Sediment Diversions is not emphasized in this investigation.

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Teal, J.M., R. Best, J. Caffrey, C.S. Hopkinson, K.L. McKee, J.T. Morris, S. Newman and B. Orem. 2012. Mississippi River Freshwater Diversions in Southern Louisiana: Effects on Wetland Vegetation, Soils, and Elevation. Edited by A.J. Lewitus, M. Croom, T. Davison, D.M. Kidwell, B.A. Kleiss, J.W. Pahl, and C.M. Swarzenski. Final Report to the State of Louisiana and the U.S. Army Corps of Engineers through the Louisiana Coastal Area Science & Technology Program; coordinated by the National Oceanic and Atmospheric Administration. 49 pages.