Coupled hydrodynamic-vegetation growth model to predict Submerged Aquatic Vegetation (SAV) distribution in an estuary.

Abstract:

The presence of submerged aquatic vegetation (SAV) is a significant factor towards determining waterfowl habitat quality in estuarine and coastal ecosystems. Eastern Neck Wildlife Refuge is located in Chesapeake Bay’s eastern shore and provides habitat for approximately 100,000 migratory birds each year. However, SAV coverage has fluctuated annually with complete absence in some years. SAV loss is typically attributed to eutrophication and reduced light availability through epiphytic growth and suspended sediment. In return, the presence of SAV provides an important positive feedback loop on local water quality by modifying the local currents and attenuating waves, sequestering nutrients, and oxygenating the water column.

In this work we use the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system with a SAV growth model to better understand the driving mechanisms for the distribution of SAV biomass (growth/dieback) in Chesapeake Bay. Increased temperature, and high precipitation/sediment suspension events/storms within the model are hypothesized to cause increased SAV mortality while low suspended sediment and average water temperatures cause increased the SAV growth. Therefore, model simulations are run for various hydrodynamic and water quality conditions and comprise: 1) a high SAV stress year (2010/2011) with above average water temperatures and high nutrient loading events and 2) a low SAV stress year (2018) with average hydrodynamic and water quality conditions, favoring SAV growth. Resulting modeled SAV distributions are compared with the Virginia Institute of Marine Science (VIMS) SAV maps for those corresponding years. Ongoing modeling development includes the evaluation of SAV growth parameters (temperature, nutrients, runoff, etc.) on a multi-year scale to improve SAV distribution predictions.