Stream restoration in the Mississippi Alluvial Valley: Streamflow augmentation to improve water quality in the Sunflower River, Mississippi, USA

Water quality in the Big Sunflower River has been significantly degraded as a result of alteration of the natural hydrology of the region. Discharge in the river is linked to rainfall and runoff during the winter and spring, runoff from agricultural irrigation during the summer, and groundwater discharge during the late summer and fall. Recently the withdrawal of groundwater for use in irrigation has reduced aquifer levels to the point that fall discharge in the river is intermittent and dominated by wastewater inputs.  The result is a substantial reduction in water quality. To offset this deterioration, a restoration effort has been initiated to increase the volume of water moving through the upper reaches of the Big Sunflower River. Supplementation is accomplished by pumping water from the Mississippi River Alluvial Aquifer and transporting it into the Big Sunflower River Basin during periods of low discharge. Water pumped from the Mississippi River Alluvial Aquifer water has significantly lower specific conductance than the Big Sunflower River as reduced iron compounds are spontaneously oxidized upon exposure to the atmosphere. Dissolved oxygen concentrations were lower during the low flow conditions of the fall even with the addition of water from outside of the basin, and generally improved as water temperatures decreased during the winter. The addition of water to the Big Sunflower River system to supplement the groundwater discharge has been moderately effective at improving water quality during critical periods. It is yet to be determined if this focused restoration effort will have unanticipated or undesirable impacts on other components of the ecosystem.