Short-term Changes in Marsh Edge Morphology: Constraining Mechanisms of Erosion and Expansion

Marsh edge morphology can change rapidly through erosional and depositional processes. Along seemingly similar stretches of marsh shoreline, erosion processes and rates can vary dramatically. In the Delaware Estuary, annual rates of edge erosion vary from a few centimeters to several meters across relatively short stretches of shoreline. Differences in erosion processes observed here include areas with and without vegetation growth seaward of the eroding marsh scarp. To better understand the factors that influence changes in marsh edge morphology, we examined wave energy, marsh scarp profile, and vegetation structure in relation to lateral erosion along two stretches of the Delaware Estuary for two years. Rates of erosion ranged from 0.01 to 4 m/yr. Variation in erosion rates occurred both along the shoreline and with depth of the shoreface, mostly associated with wave energy and wave height, respectively. In addition to direct removal of marsh peat, high energy waves shear aboveground shoots, resulting in soil anoxia within several meters of the marsh edge. Vegetation persisted seaward of eroding marshes where wave activity was dampened by a shallower bathymetric profile. The fate of these areas is under investigation. Further examination of these preliminary data will enhance our understanding of the relative importance of physical and biological processes influencing changes in marsh edge morphology.