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. In this study three southeastern U.S. salt marsh systems are examined – one in the Outer Banks of North Carolina, another in the Georgetown area of South Carolina and a final site in the Savannah area of Georgia, to evaluate how sedimentation in these three systems responds to fluvial and tidal influences and potentially other factors. 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. In each system, real-time kinematic (RTK) elevation measurements, vegetal transition boundaries, and Russian core sediment samples are collected. Aerial photograph and GIS analysis is used to estimate erosion and other changes. Sediment accumulation rates at multiple sites within and across the different systems are measured, and the rate variability is evaluated. This study helps to provide a better understanding of the sediment dynamics in these systems and is needed to enable management for the preservation and responsible use of these vital marshes.