祁连山东部大气降水δ17O变化特征及水汽输送

Variation characteristics of δ17O in precipitation and moisture transports in eastern Qilian Mountains

祁连山作为我国西部重要生态安全屏障,是河西走廊内陆河流域核心水源区。通过测定2013年7月~2014年7月收集的降水样品中δ17O与δ18O值,分析了祁连山东部乌鞘岭大气降水中δ17O的特征,在此基础上对水汽来源进行了研究。结果表明:降水稳定同位素17O存在夏高冬低的变化特征;17O存在显著的温度效应而不存在降水量效应,17O与水汽压在干季呈现正相关关系。研究区大气降水的氧同位素降水线方程为:δ′17O=0.509δ′18O-0.16,低于氧同位素全球降水线斜率;过量δ17O表现出夏低冬高的特点;综合分析氧同位素大气降水方程线和过量δ17O变化,发现该区域大气降水主要受局地水循环和大陆气团控制。祁连山东部地区主要受到西风和东南季风携带水汽影响,东南季风携带水汽对于祁连山东部的影响主要集中于夏季。研究可提高对祁连山区降水同位素演化的认知,为寒旱区同位素水文学的进一步研究奠定基础。

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(R2=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.