Groundwater/surface-water interactions and sources of nitrogen and uranium in an irrigated area of Nebraska, USA

The effects of irrigation canals and the North Platte River on groundwater in western Nebraska, USA, were evaluated using chemical and isotopic data. The data indicated that groundwater in the associated alluvium generally is <20 years old with estimated recharge rates from about 10 to >100 cm year^-1. Most groundwater is derived from surface water, as shown by H₂O and U isotope analyses. Seasonal losses of canal water to the aquifer cause changes in groundwater quality. In the deepest parts of the alluvium, some water quality may reflect precipitation recharge, older river water, or cross-formational flow. The distribution and isotopic composition of NO₃ ^- are consistent with increased fertilizer use over time. Relatively high U concentrations in groundwater may be attributed to dissolution of volcanic ash or other minerals in underlying bedrocks. The relatively high concentration of U in surface water at times is attributed to seepage from U-rich groundwater and flow of U-rich surface water from a tributary.

The effects of irrigation canals and the North Platte River on groundwater in western Nebraska, USA, were evaluated using chemical and isotopic data. The data indicated that groundwater in the associated alluvium generally is <20 years old with estimated recharge rates from about 10 to >100 cm year^-1. Most groundwater is derived from surface water, as shown by H₂O and U isotope analyses. Seasonal losses of canal water to the aquifer cause changes in groundwater quality. In the deepest parts of the alluvium, some water quality may reflect precipitation recharge, older river water, or cross-formational flow. The distribution and isotopic composition of NO₃ ^- are consistent with increased fertilizer use over time. Relatively high U concentrations in groundwater may be attributed to dissolution of volcanic ash or other minerals in underlying bedrock. The relatively high concentration of U in surface water at times is attributed to seepage from U-rich groundwater and flow of U-rich surface water from a tributary.