Hydrological and isotopic characterization of river water, groundwater, and groundwater recharge in the Heihe River basin, northwestern China

摘要

We used hydrochemistry and environmental isotope data (υ18O, υD, tritium, and 14C) to investigate the characteristics ofnriver water, groundwater, and groundwater recharge in China’s Heihe River basin. The river water and groundwater could bencharacterized as Ca2C–Mg2C–HCO3nu0001–SO4n2u0001 and NaC–Mg2C–SO4n2u0001–Clu0001 types, respectively. Hydrogeochemical modellingnusing PHREEQC software revealed that the main hydrogeochemical processes are dissolution (except for gypsum andnanhydrite) along groundwater flow paths from the upper to middle Heihe reaches. Towards the lower reaches, dolomitenand calcite tend to precipitate. The isotopic data for most of the river water and groundwater lie on the global meteoricnwater line (GMWL) or between the GMWL and the meteoric water line in northwestern China, indicating weak evaporation.nNo direct relationship existed between recharge and discharge of groundwater in the middle and lower reaches based on thenisotope ratios, d-excess, and 14C values. On the basis of tritium in precipitation and by adopting an exponential piston-flownmodel, we evaluated the mean residence time of shallow groundwater with high tritium activities, which was around 50 yearsn(a). Furthermore, based on the several popular models, it is calculated that the deep groundwaters in piedmont alluvial fannzone of the middle reaches and in southern part of the lower reaches are modern water, whereas the deep groundwaters innthe edge of the middle reaches and around Juyan Lake in the lower reaches of Heihe river basin are old water.