Water Budget and Hydrodynamic Modeling of the A.R.M. Loxahatchee Refuge

The Arthur R. Marshall Loxahatchee National Wildlife Refuge is the only remnant of the northern Everglades in Palm Beach County, Florida (USFWS, 2000). It includes 143,238 acres (58,000 ha) and is located seven miles west of the city of Boynton Beach. The U.S. Fish and Wildlife Service (USFWS) has indicated that changes in water quantity, timing and quality are introducing negative impacts to the Loxahatchee Refuge's ecosystem. According to the USFWS (2000) changes in hydroperiod and water depths' pattern affect wading birds feeding pattern, apple snail reproductive output, and alligator nesting, and also alter the distribution of aquatic vegetation and tree islands. In addition, high nutrient runoff causes proliferation of cattails, and other undesirable species that negatively affect the ecosystem's balance. It is a priority for the Loxahatchee Refuge to ensure an appropriate water regulation schedule that will produce maximum benefits for flood control, water supply, fish and wildlife; and also to better understand and minimize the impacts of the excessive nutrients' loading. This study presents the development of water budget and hydrodynamic models that are being used to provide a quantitative framework for management decisions related to inflow and outflow quantities, timing, and quality. The water budget model was developed as a double-box model that predicts canal and marsh stages. This model was calibrated for the 5-year period of record between January 1995 and December 1999, and validated with data for the 5-year period of record between January 2000 and December 2004. Statistical analyses demonstrate the applicability of this model to predict temporal variation of water levels in both the marsh and the Refuge rim canal. A two-dimensional hydrodynamic model was set up for the Refuge using the unstructured finite volume model FVCOM. This model is being used to predict spatial and temporal distribution of water inside the Refuge, and the results show very good agreement between observed and predicted stages at specific locations. Efforts are underway to model the transport of conservative tracer and the dynamics of total phosphorus in the Refuge.