黄河流域大气降水氢、氧稳定同位素时空特征及其环境意义

摘要

Variation of δ18 O in precipitation is a physical process of evaporation and condensation and closely related to various factors, such as latitude, altitude, distance from coast, seasonal variation and precipitation amount, and have characteristics of regular change. According to isotope data in precipitation and meteorological data obtained from upper, middle and lower reaches of the Yellow River Basin, spatial and temporal variation characteristics of isotope in precipitation was analyzed. The relationship between stable isotopes in precipitation and temperature, as well as precipitation amount, reveal the changing regularity of stable isotopes in precipitation over the Yellow River Basin. The results indicate that the seasonal variations of stable isotopes in precipitation have different features in the upper, middle and lower reaches of the Yellow River Basin, with enrichment of stable isotopes in summer and depletion in winter for the upper reaches, and opposite features present in the middle and lower reaches. The spatial distribution shows that stable isotopes in precipitation tends to decrease from upper reaches to lower reaches generally, with significant fluctuation and the extremum area. Different reaches of the Yellow River have different isotope process, and the altitude effect and circulation of internal continent affect stable isotopes in precipitation significantly in the upper reaches, 'while stable isotopes in the middle and lower reaches are influenced by monsoon system and local factors. Analysis of local meteoric water line and correlation of d-excess in precipitation with vapor pressure suggests that rainfall events undergo secondary evaporation accompanied by isotope fractionation during rain drops descent from the cloud base to the ground.%大气降水δ18O值的变化是一个蒸发和凝结的物理过程,与纬度、海拔、距海岸的距离、季节和降水量等因素有关,具有规律变化的特征.根据黄河流域上中下游地区取得的降水同位素数据和降水气象资料,分析了该区域降水中δ18O的时空变化特征.研究了流域上中下游降水中稳定同位素与温度和降水量的关系,揭示了流域降水中稳定同位素的变化规律.结果表明,流域上游和中下游降水中稳定同位素具有不同的季节变化特征,上游地区表现为夏季富集、冬季贫化,中游和下游则与之相反；在空间变化上,流域降水稳定同位素自上而下整体趋于逐渐贫化,波动明显,存在显著的极值区；黄河流域上、中下游具有不同的同位素过程,上游地区受海拔效应和内陆循环影响显著,而中下游则主要受季风系统和局地因素的影响.局地大气水线以及d与大气水汽压关系的分析表明,流域降水在从云层底部降落到地面的过程中,具有明显的二次蒸发现象,并伴随着同位素的分馏.