Environmental effect and spatiotemporal pattern of stable isotopes in precipitation on the transition zone between the Tibetan Plateau and arid region
In the transition zone between the Tibetan Plateau and the arid region of northwestern China, the spatiotemporal patterns and environmental controls of stable isotopes in precipitation remain unclear. A network of 19 sampling stations was established across the Qilian Mountains to observe stable isotopes in precipitation, and 1310 precipitation event-scale samples were collected. The local meteoric water line (LMWL) was obtained and expressed as δD = 7.99δ18O + 14.57 (R2 = 0.96). The spatiotemporal patterns of the stable isotopes were mainly dominated by the co-influence of the water vapor sources and the local environment. The westerly circulation, monsoon circulation, and Arctic circulation accounted for 79%, 13%, and 8% of all precipitation events in the study region, respectively. The rainout process also caused oxygen isotope depletion for continuous precipitation events. When the temperature increased by 1 °C, δ18O increased by 0.47‰, but this increase varied with the temperature range. The effect of precipitation amount was apparent in summer and was caused by sub-cloud evaporation. In addition, δ18O decreased by 0.13‰ for every 100 m increase in altitude in the Qilian Mountains. Future research should focus on quantifying the co-influence of sub-cloud evaporation, local moisture recycling, and water vapor sources on stable isotopes in precipitation.