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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #202972

Title: Numerical simulation of sediment related processes in water quality model

item Shields Jr, Fletcher
item Cooper, Charles

Submitted to: International Hydro-Science & Engineering International Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/10/2006
Publication Date: 9/13/2006
Citation: Chao, X., Jai, Y., Shields Jr, F.D., Cooper, C.M. 2006. Numerical simulation of sediment related processes in water quality model. Proceedings of the 7th International Conference on Hydro-Science & Engineering,Philadelphia, PA, September, 2006. ISBN 0977447405.

Interpretive Summary: Lakes in agricultural watersheds sometimes experience water quality problems due to soil eroded from surrounding fields that enters the lake with runoff, and predicting water quality responses to conservation efforts is difficult due to poorly-understood processes that relate plant nutrients like phosphorus to sediment on the lake bottom and suspended in the water. An existing computer model of water movement in lakes was modified to better represent the effects of such sediments on phosphorus concentrations. The modified model was adjusted using data from a lake in the Mississippi Delta and showed that lake ecology was strongly linked to sediment movement into the lake. These findings are a first step in quantifying the benefits of conservation practices applied to cultivated lands near natural lakes.

Technical Abstract: Sediment is a major nonpoint-source pollutant, and the exchange of materials between water and sediment is an important component of the lake eutrophication process. Suspended sediment increases water surface reflectivity and light attenuation in the water column. Nutrients can be absorbed to sediment particles and desorb from sediment to the water. In addition, nutrients can also be released from bed sediment. In this study, a water quality model, CCHE3D_WQ, was applied to simulate the concentrations of phytoplankton and nutrients in a shallow, natural lake with special emphasis on sediment-related processes. A formula was generated from field measurements to calculate the light attenuation coefficient using the concentrations of chlorophyll and suspended sediment. The concentrations of adsorbed and dissolved nutrients due to adsorption-desorption were calculated using two formulas derived based on the Langmuir Equation. The release rates of nutrients from the lake bed were calculated by considering the effects of the concentration gradient across the water-sediment interface, pH, temperature, dissolved oxygen concentration, and flow conditions. Model algorithms describing the adsorption and desorption of nutrients from sediment particles as well as their release from bed sediment were tested using laboratory experimental data. Model simulation results show that there are strong interactions between sediment-related processes and nutrient concentrations.