怒江源区那曲流域夏季降水与河水稳定同位素特征分析

Variation Characteristics of Stable Isotopes in Summer Precipitation and River Water in Naqu River Basin,Tibetan Plateau

怒江源区是亚洲地区重要的水源涵养区和生态屏障建设区,识别其水循环演变机理及水源构成具有重要的意义。而同位素技术是解决上述问题的有效手段之一。因此,利用2017年7月与8月那曲流域采集的降水、河水和湖水样品δD和δ18O的测试结果,分析了研究区夏季降水、河水和湖水稳定同位素时空分布特征。结果表明,7月份降水与河水中δ18O的平均值均大于8月份,造成这种差异的主要原因在于受季风影响8月份降水增多。夏季降水中δ18O和过量氘的纬度和高程效应不显著,降水量是其主要影响因素。夏季河水中δ18O的纬度和高程效应均不显著。河水中过量氘与纬度和高程存在较好的相关性,且湖水对于过量氘的分布具有重要的调节作用。由于沿途诸多支流汇入干流,从错那湖开始到下游,干流河水中同位素呈递减趋势。

The source area of Nujiang River is an important water conservation area and an ecological barrier construction area in Asia. It is of great significance to identify the mechanism of water circulation evolution and the composition of water source. Stable isotopes have proven utility since they reflect the integration of processes at smaller scales. Based on the data of water,precipitation and lake water isotopes during July and August,2017,the characteristics of precipitation and water isotopes in Naqu River Basin are analyzed. During the Tibetan Plateau summer monsoon period,average δ18 O in precipitation and river water in July are more than those in August,which result from isotope fractionation due to the evaporation of raindrop and river water. The latitudinal and elevation effects of δ18 O in precipitation are not significant,and precipitation is the main factor for δ^18 O. The δ^18 O in the river water increases with latitude. The d-excess in river water decreases with increase in latitude in the north of Cuona Lake,but the opposite phenomenon appears in the south of Cuona Lake. It can be seen that lake water has an important regulating effect on the distribution of d-excess. The d-excess in river water is positively correlated with elevation. Because of many tributaries along the river,the isotopes in the river water decrease from upstream（ Cuona Lake） to downstream.