Role of Marsh-Edge Erosion and Submerged Aquatic Vegetation on Estuarine Sediment Fluxes and Light Attenuation

Exchanges of sediment between marshes and estuaries affect wetland stability and light attenuation, impacting coastal geomorphology and habitat. Predicting sediment fluxes for marshes and estuaries, as well as their impact on light attenuation, requires an understanding of the many processes that influence dynamics in these systems. For example, submerged aquatic vegetation (SAV) can attenuate waves and currents, and may thus reduce marsh-estuarine sediment fluxes in coastal systems. Yet, the effect of spatial and temporal variations in SAV on marsh-estuarine sediment fluxes, as well as the impact of marsh-edge erosion on estuarine turbidity and light attenuation, has remained largely unquantified.

This study uses a process-based numerical model to analyze how variability in marsh-edge erosion, SAV, and hydrodynamic conditions affect sediment fluxes between marshes and estuaries, as well as turbidity and light attenuation. We specifically used 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. It also accounts for tides, winds, waves, light attenuation, and sediment transport in submerged and intertidal portions of the grid. The model was applied to Barnegat Bay, New Jersey, and idealized marsh-estuarine shorelines.

Preliminary model results from the Barnegat Bay study site demonstrate that reducing the SAV plant density increases marsh-edge erosion due to reduced wave attenuation in the estuary. Reducing vegetation density also increases wave- and current-induced bed shear stresses in the estuary. Together, the increased sediment availability and bed shear stresses near marshes increase suspended sediment concentrations, as well as light attenuation and deposition on the marsh surface. Future work includes using models of idealized marsh-estuarine shorelines to quantify how sensitive these results are to varying wave conditions, marsh erodibility, SAV characteristics, and sediment properties. We will also consider the extent to which feedbacks between marsh-edge erosion, estuarine turbidity, light attenuation, and SAV loss occur.