Abstract
The Mississippi Delta, a portion of the Mississippi Alluvial Plain (MAP) located in northwest Mississippi (USA), is an area dense with industrial-level agriculture sustained by groundwater-dependent irrigation supplied by the Mississippi River Valley alluvial aquifer. Observed declines in groundwater-level elevations and streamflow, contemporaneous with increases in irrigation, have raised concerns about future groundwater availability and the effects of groundwater withdrawals on streamflow. To quantify the impacts of groundwater withdrawals on streamflow and increase understanding of groundwater and surface-water interaction in the MAP, hydrograph-separation techniques were used to estimate baseflow and identify statistical streamflow trends. The analysis was conducted using the US Geological Survey Groundwater Toolbox open-source software and daily hydrologic data provided by a spatially distributed network of paired groundwater wells and streamgage sites. This study found that statistically significant reductions in stream baseflow occurred in areas with substantial groundwater-level declines. The use of hydrograph-separation and trend analyses to quantify the impacts of groundwater withdrawals and the use of streamflow as a proxy for changes in groundwater availability may be applicable in other altered environments. Characterizing and defining hydrologic relations between groundwater and surface water will help scientists and water-resource managers refine a regional groundwater-flow model that includes the Mississippi Delta, which will be used to aid water-resource managers in future decisions concerning the alluvial aquifer.
Highlights
Sustainable agriculture in the United States depends on appropriate management of groundwater resources
This study focused on the Mississippi Delta (Fig. 1a), an area of dense agricultural activity in northwest Mississippi, with known water-level declines in the alluvial aquifer (Boswell et al 1968; Pennington and Stiles 1994; Ackerman 1996; Renken 1998)
Hydrograph separation results for the Big Sunflower River near Anguilla, MS (USGS station No 07288700, Fig. 8a, graph E; Table 2), the most downstream site on the Big Sunflower River, varied but there was a slight increase in US Geological Survey (USGS) station No Period of record
Summary
Sustainable agriculture in the United States depends on appropriate management of groundwater resources. Water use in the United States in 2000 (the most recent year for which comprehensive groundwater withdrawal data have been published) was estimated at 1,544.4 billion liters per day (BL/ day) [408 billion gallons per day (Bgal/day)] and freshgroundwater withdrawals comprising about 315.3 BL/day (83.3 Bgal/day), or approximately 20% of daily water use (Hutson et al 2004). An estimated 34.1 BL/day of groundwater was withdrawn from the Mississippi River Valley alluvial aquifer (alluvial aquifer) alone in the year 2000 (Clark et al 2011). The alluvial aquifer, Hydrogeol J (2019) 27:2167–2179 located in the south-central United States, is the upper most aquifer underlying the Mississippi Alluvial Plain (MAP) and is the third largest provider of groundwater in the United States (Maupin and Barber 2005). According to local groundwater modeling studies (Telis 1991; Barlow and Clark 2011; Clark et al 2011), the current rate of freshwater withdrawals is unsustainable
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