THE EFFECTS OF A MIGRATING SHELL RIDGE ON THE SALT MARSH AT FORT PULASKI (SAVANNAH, GEORGIA)

There is an oyster shell ridge along the north channel of the Savannah River that has been migrating westward alongshore and southward onshore since the 1970s. As the ridge encroaches upon the salt marsh of the island it is negatively impacting Spartina alterniflora along the riverbank and causing large sections of devegetated peat to erode into the river. The purpose of this study was to monitor the salt marsh behind the ridge to detect changes in the density and height of S. alterniflora along 8 pairs of transects extending 21 m into the marsh perpendicular to the shell ridge and to explore potentials impacts of the ridge on marsh sedimentation. The density of live S. alterniflora reached maximum density in the month of October and was reduced in the second year of this study (83.6 / m² in 2005 and 69.9 / m² in 2006). There are obvious seasonal growth cycles with mean densities of 57.6 / m² in February 2006 cm and 62.9 / m² in June 2006. Maximum heights of S. alterniflora (mean of tallest blades in each quadrat) were observed in October 2005 (96.0 cm) and, similar to S. alterniflora density, were reduced the following October (68.3 cm). Shortest heights were observed in February 2006 (33.5 cm) and intermediate heights in June (63.0 cm). Grain size analysis of surficial salt marsh sediments collected along the length of the shell ridge is underway. Sediment properties of control sites will be compared with those behind young and old portions of the shell ridge to determine whether the ridge is impacting sediment delivery to the salt marsh.