EVALUATING THE IMPACTS OF CROP ROTATIONS ON GROUNDWATER RECHARGE AND WATER TABLE DEPTHS THROUGH A WATERSHED MODELING APPROACH

The Mississippi River Valley Alluvial Aquifer (MRVA), which underlies the Big Sunflower River Watershed (BSRW), is the most heavily used aquifer in Mississippi. Because the MRVA is primarily used for irrigating crops such as corn, cotton, soybean, and rice, the water levels have been declining rapidly over the past few decades. Each crop rotation practice demands certain irrigation amounts and applications, which in turn can affect the hydrogeology of the aquifer. The objective of this study is to assess the impacts of crop rotation practices on groundwater recharge rates and water table depths in the BSRW using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was hydrologically calibrated for monthly streamflow using observed streamflow data from 3 USGS gage stations (Merigold, Sunflower, and Leland). Because this study focuses on groundwater processes, the model was also calibrated for water table depths at several ground water wells throughout the BSRW. The observed water table depths used to calibrate the model were provided by the Yazoo Management District (YMD). The model was evaluated based on the coefficient of determination, Nash-Sutcliffe Efficiency, and root mean square error statistics. The crop rotation scenarios that will be employed in this study are corn after soybean, soybean after rice, and continuous soybean. This study will provide some insight into which crop rotation practices cause the most fluctuations on groundwater recharge and water table depths.