Hydrological processes and water quality in arid regions of Central Asia: insights from stable isotopes and hydrochemistry of precipitation, river water, and groundwater

As a globally important arid region, Central Asia has attracted considerable attention owing to the water crisis. However, a systematic review of large-scale hydrological processes in this region is lacking, leading to a limited understanding regarding this topic. Thus, by collecting published hydrogen and oxygen isotopic data for precipitation, river water, and groundwater in Central Asia, a comprehensive stable isotopic and hydrochemical database was created for the first time to clarify the isotopic signatures of water from different sources and the evolution processes of river water and groundwater. The local meteoric water line was derived from the stable isotopic precipitation values and defined as & delta;D = 7.52 & delta;O-18 + 6.29 (R-2 = 0.9515; n = 185); thereafter, the hydrological processes were tracked by comparing the isotopic characteristics of the water samples. A close relationship between river water and precipitation was revealed. In addition, the ionic ratios indicate that chemical weathering controls the chemical composition of river water upstream, and evaporation is the main factor controlling the chemical composition of river water downstream. Owing to their high total hardness values, most river water and groundwater are suitable for irrigation, but not for drinking. In the future, long-term field observations of isotopic and ionic compositions from river water, groundwater, and glacier meltwater should be intensified because the baseline of these data is still insufficient. The results of this study provide a significant opportunity to explore the hydrological processes and the evolution of water resources in Central Asia due to global climate change.