长江水δ~(18)O和δD时空变化特征及其影响因素分析

稳定同位素示踪技术已成为研究河流的水文过程及其变化的重要手段,尤其在河网交错密集和水力关系复杂的长江流域。通过分析枯水期和丰水期长江水及大气降水中δ~(18)O和δD组成的变化,揭示其时空变化特征及其影响因素。结果发现长江流域大气降水δ~(18)O组成表征出明显的空间分布差异特征,长江河源区降水δ~(18)O值最低,随着海拔高度降低降水中δ~(18)O值自长江上游向下游地区逐渐减小,这与流域的水汽来源及海拔高度密切有关;枯水期长江水δ~(18)O和δD值明显要高于丰水期,原因在于丰水期河水受到较弱的蒸发富集作用和大量降水补给影响;无论在丰水期还是枯水期长江水自上游到下游其同位素值呈逐渐增大的趋势,这主要受不同河段支流和湖泊等水体补给的影响。三峡大坝的蓄水和放水过程对河水同位素组成产生一定的影响,丰水期对相应河段河水同位素组成的影响不大,但在枯水期则影响较为明显,这将对充分认识长江流域大气降水-河水-湖水间水力联系与探讨其水资源合理利用提供科学依据。

STUDY ON SPATIAL AND TEMPORAL VARIATIONS OF δ18O AND δD IN YANGTZE RIVER WATER AND ITS FACTORS

Stable isotope methods are important tools for investigating the riverine hydrological processes and its variations,especially in the Yangtze Basin with densely staggered riverine network and complex hydraulic linkages.This study investigated the δ18O and δD in Yangtze River water and precipitation to reveal the spatiotemporal variations of isotopic compositions and their factors during the wet and dry seasons.The results showed that the δ18O in precipitation experienced an evident spatial variation in the Yangtze River Basin.Low δ18O values were found in the Yangtze sources and become decreased from the upper reaches to lower reaches of Yangtze River,which was closely associated with its moisture source and altitude.The δ18O and δD of river water in the dry season showed greater than those in wet season attributing to weaker evaporation enrichment and greater precipitation recharge in the wet season.Despite of the wet and dry seasons,the stable isotopic contents exhibited an increase trend from the upstream to downstream mainly attributing to the recharge of tributary and lake along the Yangtze River.In addition,this study also revealed that the effect of impoundment and drain by Three Gorges Reservoir on the river isotopic compositions was greater in the dry season than those in the wet season.These findings will provide the scientific evidences on recognizing the precipitation-river-lake hydraulic linkages and investigating the rational utilization and management of water resources in the Yangtze River Basin.