Sediment Accumulation in Salt Marshes Across the Southeastern United States

The southeast coast of the United States is home to an invaluable landscape of salt marshes. Marshes are positioned as transition zones between salty and brackish coastal waters and the terrestrial environments of the coastal plain. They are of broad ecological significance, serving as primary production zones, marine life nurseries and natural filters, absorbing and regulating nutrient exchange between terrestrial and marine environments. They are also of great economic importance, functioning as flood controls and erosion prevention/reduction systems for the coast. Marshes grow, shrink and migrate in response to sediment accretion and erosion. The factors influencing sedimentation include influx of sediment from rivers and streams, sediment supply from storm events, in situ sediment production, oceanic influx, and sea-level rise. Rates of sedimentation are expected to vary across a single marsh, between individual marshes, and from one system of marshes to another. This study examines three southeastern U.S. salt marsh systems – Outer Banks of North Carolina, Georgetown area of South Carolina and Savannah area of Georgia, to evaluate how sedimentation in these three systems responds to fluvial and tidal influences. The estuarine systems where these marshes are located vary significantly in river input and tidal range, allowing for examination of relationships with these and other factors, e.g., development and erosion. Sediment accumulation rates were measured using 210Pb and 137Cs geochronology. There was great variability from marsh to marsh, and system to system. In individual marshes, shoreline cores generally had the highest accumulation rates, but this varied significantly depending on marsh morphology and the proximity of tidal creeks. Winyah Bay yielded the highest average accumulation rates, while accumulation rates in Ossabaw Sound were often more similar to those at Pea Island, NC, than to those in Winyah Bay.