Location: Watershed Physical Processes Research
Project Number: 6060-13000-029-036-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 15, 2023
End Date: Sep 30, 2026
Objective:
Groundwater recharge can be an important determinant of agroecosystem sustainability, but well constrained estimates are limited. ARS National Sedimentation Laboratory (NSL) has ongoing data collection activities associated with Conservation Effects Assessment Project (CEAP) and Long-Term Agroecosystem Research (LTAR) programs that can be leveraged to obtain estimates of groundwater recharge at the sites. A Postdoctoral Associate with the Cooperator will (1) develop, implement, and refine groundwater recharge measurement protocols; (2) operate hydrogeophysical instrumentation, install and maintain in situ field instruments, and collect physical field samples of soil and water; and (3) develop new hydrogeophysical models and use variably saturated flow models calibrated/validated with the new data to quantify fluxes in the vadose zone and determine how agricultural management may affect groundwater recharge.
Approach:
One or more established methods will be applied to quantify groundwater recharge, including analysis of heat transport, geochemical tracers, Darcian flux based on soil water content and potential measurements, or water table fluctuations. The use of stable isotopes of water for estimating groundwater recharge will also be investigated using an isotope analyzer newly acquired by WPPRU. Hydrogeophysical methods will be applied to help characterize lithologic heterogeneity and to provide fine resolution (temporally and spatially) measurements, which then will be correlated with measurements of soil water movement and volumetric moisture content. Research will focus on existing NSL sites associated with the Conservation Effects Assessment Project (CEAP) and LTAR programs, including Goodwin Creek Experimental Watershed (GCEW) in Panola County and the Lower Mississippi River Basin (LMRB) LTAR sites in the Delta region of Mississippi. At GCEW, a transect of five wells will be installed (expected by December 2023) covering a hillside pasture adjoining a flat row-crop field adjacent to the creek, which will be monitored for groundwater level and temperature. Current data collection at LMRB includes precipitation, evapotranspiration (ET), and runoff at corn, soybean, or sweet potato fields. At both sites, additional data collection will include sensors at five depths to monitor soil moisture content, temperature, and electrical conductivity, and at three depths sensors will measure soil matric potential. In situ sensors and associated instrumentation will be provided by NSL and data collection support will be provided by WPPRU. Newly developed hydrogeophysical models and variably saturated flow models will be calibrated/validated with the new data. These models will be applied to quantify fluxes in the vadose zone and determine how agricultural management may affect groundwater recharge. Research will focus on groundwater recharge under natural conditions, but also may include assessment of managed aquifer recharge technologies such as riverbank filtration, injection wells, and vadose-zone recharge wells.
