Various navigational modifications to the Lower Savannah River have severely impacted the distribution of tidal freshwater wetlands in the river's deltaic floodplain. Construction of a tide gate (a one-way flap valve across one of the river's main distributaries) in the mid-70's resulted in the conversion of 8,000 acres of tidal freshwater wetlands to a tidal brackish/saline system. These 8,000 acres represented 25% of the total acreage of tidal freshwater wetlands along the coast of South Carolina and Georgia. Subsequent to intense studies conducted in the mid 80's documenting the loss of these wetlands and striped bass fishery brooding areas, the tide gate was taken out of operation. This action permitted flushing of the marshes by natural tidal actions to resume, leading to substantial conversion of brackish to freshwater marsh in much of the Savannah National Wildlife Refuge by 1993-1994.
Recently , the river's main channel has been deepened and upstream migration of the salinity wedge has negated much of the positive benefits of removal of tide gate operation. Currently, there are pending plans to deepen the river even further, placing the fate of the remaining freshwater wetlands in further jeopardy. I have initiated a new research project to reassess the composition of the Savannah National Wildlife Refuge marshes at previously sampled sites following our previous protocols to clarify the amount of marsh conversion that has occurred since the tide gate was made inoperable. Development of a current vegetation map from satellite imagery and comparison to 1986-1987 imagery will provide a spatial assessment of marsh change during that time.
My students and I will refine our previously developed vegetation succession model to include better algorithms for competitive interactions along the various gradients of hydroperiods and salinities. Our previous model predictions of potential marsh conversion with tide gate removal will be compared with hydrologic scenarios with and without the current and proposed deepening projects to assess impacts and recommend mitigative strategies. This project has just begun and will be conducted jointly with Cynthia Loftin of the Maine Cooperative Fish and Wildlife Research Unit. I will be principal investigator of the plant/hydrology studies and succession model development and refinement. Dr. Loftin will conduct the vegetation change detection analyses. The studies are currently funded by the Fish and Wildlife Service with additional support to be provided by the Army Corps of Engineers.