Numerical Modeling of Concentrations of Phytoplankton and Nutrients In A Mississippi Delta Lake By Considering The Sediment Associated Processes

Water quality in inland waterbodies is significantly affected by suspended sediment and bed sediment. Suspended sediment affects solar radiation penetrate into the water column and reduces the growth rate of phytoplankton. Dissolved nutrients can either be released or accumulated on suspended sediment particles due to desorption and adsorption kinetics. Nutrients adsorbed on bed sediment can also be released to the water column due to diffusion. In addition, nutrients attached on the sediment may exchange between the water column and bed layer as sediment resuspension or deposition occurs. Mathematical formulas were derived to quantitatively estimate sediment-associated nutrient fluxes and subsequently tested using field measurements and laboratory data. These formulas were included in the water quality model, CCHE-WQ, developed by the National Center for Computational Hydroscience and Engineering, University of Mississippi, to simulate phytoplankton kinetics, nutrient cycles, and dissolved oxygen balance by considering sediment associated processes. The CCHE-WQ model was applied to simulate concentrations of phytoplankton and nutrients in Beasley Lake, a shallow Mississippi Delta lake with special emphasis on sediment-related processes. The simulated results were compared with field observations collected by the United States Department of Agriculture- Agricultural Research Service, National Sedimentation Laboratory. Evaluations of model comparisons with measured data showed high correlations for temperature, concentration of suspended sediment, and inorganic phosphorus and lower correlation with the concentration of chlorophyll. This study shows that there are strong interactions between sediment-associated processes and water quality constituents in the Mississippi Delta lakes.