Major-ion chemistry, δ13C and 87Sr/86Sr as indicators of hydrochemical evolution and sources of salinity in groundwater in the Yuncheng Basin, ChinaChimie des ions majeurs, du δ13C et du 87Sr/86Sr en tant qu’indicateurs de d’évolution hydrochimique et de l’origine de la salinité des eaux souterraines du bassin du Yuncheng, ChineIones químicos mayoritarios, δ13C y 87Sr/86Sr como indicadores de evolución hidroquímica y de fuentes de salinidad en el agua subterránea en la Cuenca Yuncheng, China用主要离子组分、δ13C和 87Sr/86Sr示踪中国运城盆地地下水化学演化及盐分来源Química de iões maiores, δ13C e 87Sr/86Sr como indicadores da evolução hidroquímica e da origem da salinidade na água subterrânea da Bacia de Yuncheng, China

Processes controlling hydrogeochemistry in the Yuncheng Basin, China, were characterised using major-ion chemistry, 87Sr/86Sr ratios and δ13C values. Evapotranspiration during recharge increased solute concentrations by factors of ∼5–50 in deep palaeowaters, while higher degrees of evapotranspiration have occurred in shallow, modern groundwater. Aquifer sediments (loess) contain approximately 15 weight% calcite; trends in groundwater HCO3 concentrations and δ13C values (ranging from −16.4 to −8.2‰) indicate that carbonate weathering is a significant source of DIC. Groundwater 87Sr/86Sr ratios (0.7110–0.7162, median of 0.7116) are similar to those in both loess carbonate (0.7109–0.7116) and local rainfall (0.7112), and are significantly lower than Sr in aquifer silicates (0.7184–0.7251). Despite evidence for substantial carbonate dissolution, groundwater is generally Ca-poor (< 10% of total cations) and Na-rich, due to cation exchange. Saturation with respect to carbonate minerals occurs during or soon after recharge (all calcite and dolomite saturation indices are positive). Subsequent carbonate dissolution in the deep aquifer must occur as a second-stage process, in response to Ca loss (by ion exchange) and/or via incongruent dissolution of dolomite and impure calcite. The latter is consistent with positive correlations between δ13C values and Mg/Ca and Sr/Ca ratios (r2 = 0.32 and 0.34).