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United States Department of Agriculture

Agricultural Research Service

Research Project: UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS

Location: Water Quality and Ecology Research

Title: Three-Dimensional Numerical Simulation of Water Quality and Sediment-Associated Processes with Application to a Mississippi Delta Lake

Authors
item Chao, Xiaobo -
item Jia, Yafei -
item Shields Jr, Fletcher
item Wang, Sam S. Y. -
item Cooper, Charles -

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2010
Publication Date: May 15, 2010
Citation: Chao, X., Jia, Y., Shields Jr, F.D., Wang, S., Cooper, C.M. 2010. Three-Dimensional Numerical Simulation of Water Quality and Sediment-Associated Processes with Application to a Mississippi Delta Lake. Journal of Environmental Management. 91 (2010) 1456-1466. doi:10.1016/j.jenvman.2010.02.009.

Interpretive Summary: Runoff from cultivated fields often triggers water quality degradation in receiving waterbodies that is harmful to aquatic ecosystems. Since 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. These findings allow researchers to quantify the benefits of expenditures for management practices and conversation measures.

Technical Abstract: A three-dimensional water quality model was developed for simulating temporal and spatial variations of phytoplankton, nutrients, and dissolved oxygen in freshwater bodies. Effects of suspended and bed sediment on the water quality processes were simulated. A formula was generated from field measurements to calculate the light attenuation coefficient by considering the effects of suspended sediment and chlorophyll. The processes of adsorption-desorption of nutrients by sediment were described using the Langmuir Equation. The release rates of nutrients from the bed were calculated based on the concentration gradient across the water-sediment interface and other variables including pH, temperature and dissolved oxygen concentration. The model was calibrated and validated by applying it to simulate the concentrations of chlorophyll and nutrients in a natural oxbow lake in Mississippi Delta. The simulated time series of phytoplankton (as chlorophyll) and nutrient concentrations were generally in agreement with field observations. Sensitivity analyses were conducted to demonstrate the impacts of varying suspended sediment concentration on lake chlorophyll levels.

Last Modified: 9/23/2014
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