Abstract: The Qilian Mountains in western China are an important ecological security barrier and are the primary water sources for the inland river basins in the region. In this paper,we collected precipitation samples and meteorological data in eastern Qilian Mountains from July 2013 to July 2014 to analyze the temporal variations of the δ¹⁷O in precipitation and to discuss the influence of temperature,precipitation amount and vapor pressure on the δ¹⁷O content. Based on this,the moisture sources of the study area were studied.The results show that the isotopic composition exhibited an obvious seasonal variation which indicated the higher δ¹⁷O values in summer and autumn,and the lower values in winter and spring,¹⁷O has significant temperature effect without precipitation effect, ¹⁷O has a positive correlation with water vapor pressure in dry season.The local meteoric water line (LMWL) was established as δ′¹⁷O = 0.509δ′¹⁸O -0.157 8 (R ²=0.97,P ＜0.01),and its slope was lower than the slope of the global meteoric water line (GMWL),which indicated that the precipitation was mainly controlled by continental air masses.The ¹⁷Oexcess values were low in summer and high in winter and at least 38% of the precipitation events underwent strong subcloud evaporation.Based on the comprehensive analysis of the local meteoric water line and ¹⁷Oexcess,we found that the precipitation in study area is mainly controlled by local moisture recycling and continental air mass.The precipitation in the eastern Qilian Mountains was mainly controlled by westerly and southeastern monsoon carrying water vapor,while the effect of southeastern monsoon is mainly concentrated in the summer.This study improves knowledge of the isotope evolution of precipitation in the Qilian Mountains,and lays the foundation for further research on isotope hydrology in the cold and arid regions.

Key words: precipitation, δ17O, moisture transports, Qilian Mountains