Numerical Modeling of Flow Circulation and Chlorophyll Concentration in an Oxbow Lake in the Mississippi Delta

Author(s): Chao, X.; Jia, Y.; Locke, M.; Lizotte, R.

The Mississippi Delta is one of the most intensively farmed agricultural areas of the United States. The quality of surface water resources in this area are particularly vulnerable due to excessive sediment, nutrients, and pesticides transported from upland watershed.

Beasley Lake watershed (BLW) located in Sunflower County of the Mississippi Delta, was selected as one of the Conservation Effect Assessment Project (CEAP) benchmark watersheds to assess environmental benefits derived from implementing USDA conservation programs. The loads of flow, sediment and water quality from the upland watershed were measured by the USDA-ARS National Sedimentation Laboratory (NSL). The weekly or biweekly samples of suspended sediment, nutrients, chlorophyll, bacteria, and other selected water quality variables in the lake were also collected and analyzed. Field measurements show that the concentrations of nutrients and sediment of the lake are greatly affected by the loads of upland watershed.

A water quality model, CCHE_WQ has been developed by National Center for Computational Hydroscience and Engineering, and applied for predicting the distributions of nutrient, phytoplankton, dissolved oxygen, etc., in natural lakes. In Beasley Lake, wind shear is the major driving force for flow hydrodynamics. The flow circulations were simulated using CCHE hydrodynamic model, and the CCHE_WQ model was applied to simulate the concentration of chlorophyll in the lake. The simulated results were generally in good agreement with field measurements. The sensitivity scenarios show that the lake primary productivity is mainly limited by suspended sediment concentration, while it is less sensitive to concentrations of nitrogen and phosphorus.br />
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