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Title: Numerical Simulation of Sediment-Associated Water Quality Processes for a Mississippi Delta Lake

item CHAO, XIAOBO - University Of Mississippi
item JIA, YAFEI - University Of Mississippi
item Shields Jr, Fletcher
item WANG, SAM S. Y. - University Of Mississippi
item COOPER, CHARLES - Retired ARS Employee

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2009
Publication Date: 10/1/2009
Citation: Chao, X., Jia, Y., Shields Jr, F.D., Wang, S., Cooper, C.M. 2009. Numerical Simulation of Sediment-Associated Water Quality Processes for a Mississippi Delta Lake. Ecohydrology. 2(3): 350-359. DOI: 10.1002/eco.72 [online].

Interpretive Summary: Runoff from cultivated fields often triggers water quality degradation in lakes. Since lake water quality reflects a host of natural and human influences, however, it is hard to link improved soil conservation to ecological improvements. A computer model was developed to simulate the water quality and algal population density of a natural lake surrounded by farm land in the Mississippi Delta region. The model was validated using field data and included equations to simulate effects of suspended and bed sediments on lake nutrient levels and light penetration, which control algal production. A series of model runs then showed how the lake ecosystem would respond to increasing or decreasing the amount of sediment reaching the lake in agricultural runoff. Lake ecology was found to be governed by suspended sediment concentration. These findings allow researchers to quantify the benefits of expenditures for management practices and conversation measures.

Technical Abstract: Three major sediment-associated processes were presented to describe the effects of sediment on lake water quality processes: the effect of suspended sediment on the light intensity for the growth of phytoplankton (PHYTO), the adsorption–desorption of nutrients by sediment, and the release of nutrients from bed sediment. A formula was generated from field measurements to calculate the light attenuation coefficient by considering the effects of concentrations of chlorophyll and suspended sediment (SS). The concentrations of adsorbed and dissolved nutrients because of adsorption–desorption were calculated using two formulas that were derived based on the Langmuir Equation. The release rates of nutrients from the bed sediment were calculated by considering the effects of the concentration gradient across the water-sediment interface, pH, temperature and dissolved oxygen (DO). Model algorithms describing the adsorption and desorption of nutrients from sediment particles as well as the release of nutrients from bed sediment were tested using laboratory data. These sediment-associated water quality processes were included in a three-dimensional (3D) water quality model, CCHE3D WQ, to simulate the concentrations of PHYTO and nutrients in a shallow Mississippi Delta lake with special emphasis on sediment-related processes. The simulated concentration of PHYTO (as chlorophyll) and nutrients were generally in good agreement with field observations. This study shows that there are strong interactions between sediment-associated processes and water quality constituents.