USE OF FRESHWATER DIVERSIONS TO SUSTAIN WETLANDS OF THE MISSISSIPPI RIVER DELTA PLAIN IN COASTAL LOUISIANA

Freshwater diversions, controlled inflows of Mississippi River water into adjacent wetlands, are an integral component of efforts to restore and sustain the deteriorating MRDP (Mississippi River Delta Plain) landscape. Restoration efforts may be considered successful if wetland soils are formed and sustained that can keep pace with long-term sea level trends, and are resilient to erosive forces such as storm surge.

Successful restoration depends in part on the characteristics of the inflowing water. Flows associated with freshwater diversions generally are too slow to carry substantial amounts of mineral sediments to recipient marshes. Factors affecting the sustainability of recipient marshes are limited to a lowering of surface-water salinity, which creates habitat space for diverse low-salinity plant communities that thrive in highly organic soils. An additional factor affecting the sustainability of target marshes is the chemical composition of river water and how its constituents interact with the highly organic soils of low-salinity reaches of the MRDP. The restoration outcome also depends on the marsh type.

Studies of two distinct wetland areas which deteriorated even as they received long-term subsidies of river water are discussed. Data suggest that rather than enhancing sustainability, the influx of river water may have contributed to the deterioration and also reduced marsh resiliency to storm surges.