A SEDIMENT RESUSPENSION AND WATER-QUALITY MODEL OF LAKE-OKEECHOBEE

The influence of sediment resuspension on the water quality of shallow labs is well documented. However, a search of the literature reveals no deterministic mass-balance eutrophication models that explicitly in clude resuspension. We modified the Lake Okeechobee water quality mode l - which uses the Water Analysis Simulation Package (WASP) to simulat e algal dynamics and phosphorus, nitrogen, and oxygen cycles - to incl ude inorganic suspended solids and algorithms that: (1) define changes in depth with changes in volume; (2) compute sediment resuspension ba sed on bottom sheer stress; (3) compute partition coefficients for amm onia and ortho-phosphorus to solids; and (4) relate light attenuation to solids concentrations. The model calibration and validation were su ccessful with the exception of dissolved inorganic nitrogen species wh ich did not correspond well to observed data in the validation phase. This could be attributed to an inaccurate formulation of algal nitroge n preference and/or the absence of nitrogen fixation in the model. The model correctly predicted that the lake is light-limited from resuspe nded solids, and algae are primarily nitrogen limited. The model simul ation suggested that biological fluxes greatly exceed external loads o f dissolved nutrients; and sediment-water interactions of organic nitr ogen and phosphorus far exceed external loads. A sensitivity analysis demonstrated that parameters affecting resuspension, settling sediment nutrient and solids concentrations, mineralization, algal productivit y, and algal stoichiometry are factors requiring further study to impr ove our understanding of the Lake Okeechobee ecosystem.