GROUNDWATER FLOW AND SALT MARSH MIGRATION: THE FOREST/MARSH BOUNDARY

Salt marshes migrate landward in response to sea level rise, but the rate of this migration is not constant and can be influenced by pulse disturbances. Long term observations at Sapelo Island, Georgia, show that salt marsh migration has occurred during droughts but the mechanism for this migration is unclear. Drought is thought to influence salt marsh migration by reducing fresh groundwater discharge from the upland, and the strength of this effect depends on the width of the adjacent upland. Rising sea level also encroaches on the upland, which could cause a movement of the freshwater lens inland. A two-dimensional numerical model was built to simulate groundwater flow and solute transport based on the Marsh Landing marsh at Sapelo Island. The model is designed to estimate salinity changes in response to climatic factors, such as drought and sea level rise. Following further calibration, the model will be used to track salinity and movement of the freshwater lens through the forest/marsh boundary over a 20 year period that corresponds with plant community observations at the site. Observing the changes in salinity at this location will provide important patterns that could influence vegetation and migration of the salt marsh.