Eutrophication Model of Florida Bay

Topical Area: Water Quality

Carl F. Cerco, Mark Dortch, Barry Bunch, US Army Engineer Waterways Experiment Station

Vicksburg, MS

The CE-QUAL-ICM eutrophication model is being applied to Florida Bay. Objective of the project is to develop a calibrated water quality and sea grass model. When completed, the model will be used to examine management scenarios of freshwater flow diversions. Duration of the project is two years, commencing in January 1998.

CE-QUAL-ICM is an existing eutrophication model which has seen widespread application to water bodies such as Chesapeake Bay, Delaware Inland Bays, New York Bight, and the San Juan Estuary system. The model incorporates 24 state variables in the water column including salinity, temperature, solids, dissolved oxygen, phytoplankton, zooplankton, and various forms of carbon, nitrogen, phosphorus and silica. The model incorporates a sediment diagenesis submodel and a submerged aquatic vegetation submodel.

In view of the limited duration of the project, maximum utility will be made of the existing version of CE-QUAL-ICM. Never-the-less, revisions to the formulation and parameterizations will be completed. Among the revisions are addition of nitrite and total inorganic carbon to the suite of state variables. Wind-driven sediment resuspension will be added to aid in simulation of turbidity. The seagrass model will be parameterized to represent two species dominant in Florida bay, Thallassia and Halodule. Additional parameters appropriate to Florida Bay will be determined through application of the model to a two-year period. Once revisions and model calibration are complete, the ability of the model to represent long-term change will be examined through a simulation of the period 1986-1996.

Application of CE-QUAL-ICM requires transport information from a hydrodynamic model. For this application transport is derived from the existing RMA10-WES hydrodynamic model of Florida Bay. A water quality grid of roughly 1,000 elements will be overlaid in the RMA10 grid which contains roughly 13,000 elements. RMA10 will be applied to the years 1995-1996. For the ten-year water quality simulations, hydrodynamic simulations of typical wet, dry, and average flow conditions will be linked together to approximate ten years of hydrodynamics.

At present, effort is focused on assimilation of the data base, model revisions, and linkage to RMA10. Plans for the first year also call for development of loads and initial model application. In the second year, model calibration will be finalized, the long-term run will be completed, and flow-diversion scenarios will be examined.