Estuarine Processes Model Development

Lateral erosion of marshes is partially dependent on the thrust of wind-waves on the vertical marsh face. Several studies have quantified this dependence: the wave characteristics, water depth, and marsh elevation are the controlling variables for the magnitude of the thrust. The COAWST model simulates these parameters, and is a valuable tool for calculating the variation of thrust under different environmental conditions. We have integrated a model routine that calculates time-varying thrust within COAWST, and exports it as a model state variable which can be visualized within our oceanographic portal.

Estuaries with elevated nitrogen loading are prone to eutrophication, whereby increased primary production by phytoplankton and macroalgae can create hypoxia and low light conditions and alter an otherwise healthy ecosystem. We are modifying biogeochemical routines in ROMS (within COAWST) to represent estuarine processes such as light attenuation, algal respiration, seagrass kinetics, and diel oxygen dynamics. The models can then be used to simulate reductions in nitrogen loading, shifts in seagrass distribution, and feedbacks between physical processes and ecosystem function.

Coastal protection and biophysical feedbacks require modeling of the interaction between aquatic vegetation (emergent marsh and submerged seagrass) and hydrodynamics (currents and waves). Properly accounting for three-dimensional modification of the flow field requires specifying the vertical variation of plant distribution, and then extracting momentum and dissipating turbulence in the water column. This exerts a drag on the fluid flow, attenuates waves, and reduces shear stress within vegetated canopies, allowing for positive feedbacks between vegetation, sediment deposition, and water clarity.