Hydrochemical Characteristics In The Upper Reaches Of The Yarlung Zangbo River In Summer

The Qinghai-Tibet Plateau and its surrounding areas are known as the"Asian Water Tower",which is the birthplace of many important rivers such as the Yarlung Zangbo River and the Yangtze River,and is also the main gathering place of glaciers,snow,permafrost and so on.Its ecological climate and evolution is one of the most important concerns of scientists all over the world.In the context of global warming,the Qinghai-Tibet Plateau is experiencing the process of glacier retreat,permafrost melting and water circulation,and the chemical weathering rate,material chemical cycle and ecological climate of the plateau surface have been significantly affected.As an important part of the global water cycle,the water chemistry characteristics of rivers not only reflect the effects of chemical erosion,but also reflect the influence of watershed climate change,soil characteristics,human activities and other factors,and to a certain extent reflect the water circulation of river basins,the migration and transformation of biological materials,so it is necessary to study the water chemistry characteristics of rivers in the Qinghai-Tibet Plateau.As a typical highland river on the Qinghai-Tibet Plateau,the physical and chemical circulation and water environment of the Yarlung Zangbo River have also been affected.At present,the research on the Yarlung Zangbo River basin is concentrated in the middle and lower reaches of the region,which is greatly influenced by human activities,which causes uncertainty for the accurate evaluation of the geochemical characteristics of highland rivers,and there are few systematic studies on the water chemistry characteristics of the upper reaches of the Yarlung Zangbo River basin.Based on this,this paper takes the upper reaches of the Yarlung Zangbo River as the research object,through field sampling and laboratory testing and other methods,the stable isotope composition of water body constant ions,rare earth elements and water body hydrogen and oxygen isotope is analyzed to explore the water chemistry characteristics of the upper reaches of the Yarlung Zangbo River basin in the summer,and obtains the following understanding:(1)The upper reaches of the Yarlung Zangbo River are less affected by human activities,the water quality is in good condition,and the DTP concentration varies from 0.000 to 0.101mg/l,with an average of 0.021 mg/l,the DTN concentration range is 0.004 to 0.427 mg/l,with an average of 0.155 mg/l,which meets the standard of surface water Class I.The water body in the upstream basin is generally weakly alkaline,Ca²⁺concentration varies from 9.60 to 75.45mg/l,with an average of 26.71 mg/l,and HCO₃^-concentration ranges from 16.78 to 134.20mg/l,with an average of 94.05 mg/l,Ca²⁺and HCO₃^-as the dominant ions,the water chemistry type is Ca²⁺-HCO₃^-type,and its water chemical ion control mechanism is"rock weathering type",which is mainly affected by the mineral weathering of carbonate rock,but also has a certain degree of silicate weathering;The analysis of graph,ion proportion and correlation shows that the mineral weathering of carbonate rock is the main source of ions in water bodies in basins,and the mineral weathering of silicate rock is also an important source of ions.(2)The content of dissolved rare earths in the upper reaches of the Yarlung Zangbo River is low,and the total content of dissolved rare earth elements varies from 6.63 to 95.83 ng/l,with an average value of 20.48 ng/l,well below the world river average(735 ng/l),The content of each dissolved rare earth element is sequenced as La>Ce>Nd>Sm>Dy>Pr>Er>Yb>Ho>Tb>Lu>Tm;Through the standardization of dissolved rare earth elements shale in water bodies,the parameter(La/Yb)_SNrange is 0.33 to 4.08,the mean is 0.79,and the parameter Ce/Ce^*is changed from 0.10 to 0.85,with an average value of 0.39,it is found that the water bodies in the upstream basin are characterized by negative anomalies of Ce,but the pattern of differentiation of the dissolved rare earth elements in the upstream basin is different,the tributaries and the water bodies in the mainstream river sections are shown to be rich in heavy rare earth elements,while the water bodies in the melting water section of the mainstream glaciers are shown as light rare earth element enrichment.(3)The range of change of hydrogen and oxygen stable isotope?¹⁸O in the upper reaches of the Yarlung Zangbo River ranged from-20.41‰to-14.06‰,with an average value of-17.65‰,and The range of?D is varied from-149.24‰to-99.83‰,with an average value of-132.16‰,and a stable isotope relationship of hydrogen and oxygen in the upstream basin was established?D=7.088?¹⁸O-6.201,and it is found that atmospheric precipitation is an important source of water bodies in the upper basin.There are some differences between the hydrogen and oxygen stable isotope characteristics of mainstream and tributary water bodies,and there is an elevation and latitude effect between the Chaiqu tributary and the main flow water body,and there is no obvious isotope fractionation effect on the tributary of Laiwuzangbu;The excess parameters of radon in the upper basin water body fluctuate greatly,and the range of change is 4.05‰to 16.04‰,with an average value of 9.01‰,which is mainly influenced by the altitude and latitude effect,evaporation and water-rock interaction.