Stable isotopic composition of precipitation in the semi-arid north-central portion of the US Great Plains

Abstract

Where data are available, hydrologic studies may use stable oxygen and hydrogen isotopes to investigate, groundwater/surface water interaction, groundwater recharge and advective/diffusive transport, to estimate groundwater ages or to unravel paleohydrology. Such studies require that the isotopic composition of precipitation be known, as precipitation is a major input to groundwater and surface water systems. Oxygen-18 ( δ 18O) and deuterium ( δ 2H) data for precipitation are lacking for the semi-arid portion of the north-central Great Plains of the US, and thus there is need to establish additional meteoric water lines as isotope input functions across the region, as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation. This study examines the δ 18O and δ 2H composition of precipitation for a representative site near North Platte, Nebraska in the semi-arid north-central Great Plains during the years 1989 through 1994. Oxygen-18 values range from −30.5 to +1.7‰. Deuterium values range from −228 to +11‰. Yearly arithmetic mean values for the North Platte station are −9.8 and −71‰, respectively. Weighted yearly means for δ 18O and δ 2H over the 6-year period were −9.6 and −69‰, respectively. North Platte values show a strong isotopic enrichment between winter and summer precipitation, and a strong δ 18O– T correlation r 2=0.845 for mean monthly values of 0.54‰ per degree Celsius. The local meteoric water line for the site is δ 2H=7.66 δ 18O+4.96.