Modeling the Florida Bay Ecosystem Using a Coupled Physical-Biogeochemical-Seagrass Model

Seagrass meadows, among the major sources of primary production in shallow waters worldwide, are significant contributors to the nutrients cycles in the ocean and an important component of many estuarine coastal ecosystems. Florida Bay (FB), a 2100 km^-2 estuary, is part of the largest semi-contiguous seagrass meadow in the world. This seagrass-dominated ecosystem receives freshwater flow and associated nutrient inputs directly from the Everglades, which are being modified significantly due to Comprehensive Everglades Restoration Plan (CERP). In the past 30 years, two widespread seagrass die-off events occurred during 1987-1991 and 2015-2016 in Florida Bay. These events raised questions regarding the impacts and benefits of watershed freshwater inputs that can buffer the frequent hypersaline conditions but also introduce nutrients and sediment to the bay. In order to investigate the ecosystem dynamics and understand the impacts of changing watershed freshwater inputs and climate change, a coupled physical-biogeochemical-seagrass model based on the COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) model has been developed and tested in both 1-D and 3-D configurations. Laboratory and field measurements of vital rates, salinity, nutrient concentrations, and seagrass biomass from this area and literature were used to calibrate the model parameters and gauge model skills. The results of a 3-D simulation show a good agreement with available data including the spatial pattern and seasonal cycle of the seagrass. Numerical experiments further suggest 1) increased nutrient inputs would increase phytoplankton blooms in the bay, 2) seagrass is important in modulating nutrient cycling and storing organic carbon, 3) epiphytes compete with phytoplankton for nutrients and light, and 4) epiphytes and phytoplankton modulate seagrass growth via light limitation.