Characteristics of Chemistry and Stable Isotopes in Groundwater of the Chaobai River Catchment, Beijing

Environmental isotopes and chemical compositions are useful tools for the study of groundwater flow systems. Groundwater of the Chaobai River catchment, Beijing was sampled for chemical and stable isotopes analyses in 2005. Geochemical signatures evolve progressively from CaMg-HCO3 to NaK-HCO3, and then to Na-HCO3 compositions as groundwater flows from the mountain to discharge areas. Groundwater can be divided into two groups on the basis of stable isotope compositions: ancient groundwater and modern groundwater. Modern groundwater (-9.9%0 to -6.6%0 for δ18O) plots along a line with a slope of 4.0 on a δ2H versus δ18O diagram, reflecting evaporation during the process of recharge, whereas ancient groundwater samples (30 to 12 Ka.) are different in isotopic composition (-11.0%0 and -68.2%0 for δ18O and δ2H, respectively), reflecting the cold and arid climate in the last glacial period. The results have important implications for groundwater management in Beijing City.