Role of Submerged Aquatic Vegetation Characteristics and Presence on Marsh-Estuarine Sediment Fluxes: Barnegat Bay, New Jersey

Exchanges of sediment between marshes and estuaries affect the extent to which wetlands laterally retreat and vertically accrete, impacting coastal geomorphology. Yet, predicting sediment fluxes for marshes on regional scales (1 to 10's of kilometers) requires an understanding of the many processes that influence particle dynamics in these systems. For example, the presence of submerged aquatic vegetation (SAV) can attenuate waves and currents, and may reduce marsh-estuarine sediment fluxes in coastal systems. Yet, the effect of spatial and temporal variations in SAV presence and characteristics on marsh-estuarine sediment fluxes is largely unquantified on regional scales and seasonal timescales.

This study uses a process-based numerical model to analyze how variability in SAV presence, as well as characteristics such as shoot density and height, affects sediment fluxes to and from marshes in a back-barrier estuary, Barnegat Bay, New Jersey. The model is the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model, a three-dimensional numerical model that has recently been adapted to account for wave-induced marsh-edge erosion and vegetation-hydrodynamic interactions. The model also accounts for tidal, wind, and density-driven circulation, as well as sediment transport in submerged and intertidal portions of the estuary.

Preliminary model results for March-June 2012 demonstrate that reducing the density of SAV in estuaries increases marsh-edge erosion due to reduced wave attenuation in the estuary. The vegetation also reduced wave- and current-induced bed shear stresses in the estuary. Together, the enhanced sediment availability and bed shear stresses near marshes enhanced suspended sediment concentrations, as well as deposition on the marsh surface. Ongoing work includes quantifying how marsh-estuarine sediment fluxes vary depending on distance from an SAV patch, vegetation characteristics, and other metrics. Additionally, we will use the model to analyze how seasonal changes in plant characteristics and patchiness in vegetation affect sediment fluxes to and from marshes.