Effects of Hydrologic Alterations on the Vegetation and Soils of Marshes in Southern Louisiana.
Date of Award
Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
Irving A. Mendelssohn
Hydrology is the primary forcing function in wetlands. Therefore, alterations to hydrology, which can result from either natural or anthropogenic causes, can have dramatic effects on wetland structure and function. Structural marsh management, one type of anthropogenic alteration, employs levees and water control structures to reduce or reverse wetland loss and enhance the productivity of natural renewable resources. Its use is becoming increasingly popular in southern Louisiana as a solution to the problem of marsh deterioration despite the fact that very line comprehensive data is available on the effectiveness of this practice. Associated with the use of structural marsh management is the potential problem posed by hurricanes which can deposit large volumes of saline water inside management areas which are then retained by the encompassing levees. The purpose of this dissertation was two-fold: first, to determine if structural marsh management improved primary productivity by reducing salinities and providing water level control; and second, to determine what factors governed the ability of an impounded freshwater marsh to recover from storm-induced exposure to high salinity waters. In order to address the first goal, three pairs of managed and unmanaged marshes were monitored for one growing season during a drawdown year. Marsh pairs were located in the Fina LaTerre Mitigation Bank site, at Rockefeller Refuge, and at Avoca Island, Louisiana. Comparison of the three marsh pairs illustrated that while structural marsh management can effectively accomplish the goals ascribed to it, its use is not uniformly effective in improving soil and water level conditions and increasing primary productivity. It appears that the effectiveness of structural marsh management depends on location, design, marsh type, and sophistication of the plan used. The second goal was accomplished by conducting a greenhouse experiment using mesocosms containing sods of intact freshwater marsh soil and vegetation. The mesocosms were exposed to a simulated saltwater intrusion event followed by establishment of a variety of recovery-phase salinity and water level conditions. Higher salinities during recovery exerted a strong influence on the rate and degree of vegetation recovery resulting in less regrowth and diminished species richness. This effect was exacerbated by flooding.
Flynn, Kathryn Marie, "Effects of Hydrologic Alterations on the Vegetation and Soils of Marshes in Southern Louisiana." (1992). LSU Historical Dissertations and Theses. 5301.