The Study Of Hydrochemical Characteristics And Its Influencing Factors Of Naqu River In The Source Region Of The Nujiang River

River is the main channel of material and energy exchange between land and ocean,and the link between the two carbon pools.Precipitation,rock weathering and human activities may be the source of river solute,and the study of chemical composition of river solute can reveal the process of rock weathering and carbon sink capacity.The Tibetan Plateau is called the“Water Tower of Asia”.The outflow River originated from the Tibetan Plateau is an important channel for the transport of substances from the Tibetan Plateau to the ocean.It is of great significance to analyze the chemical composition of river solutes in the Tibetan Plateau for the study of carbon sink effect in the Tibetan Plateau.Naqu River is the source region of the Nujiang River.The Naqu River basin is a typical river source region on the Tibetan Plateau,which is less disturbed by human activities,and can truly reflect the hydrochemical characteristics of the plateau rivers.In this paper,Naqu River basin located in the source rerion of the Nujiang River is taken as the typical study area.The wet season is selected for field observation,sampling and laboratory detection.By means of statistical analysis,hydrochemical diagram and forward modeling,the chemical characteristics of Naqu River,rock weathering process,rock weathering rate and carbon sink effect of the basin were analyzed.The difference between Naqu River basin and other basins in hydrochemical characteristics and chemical weathering were analyzed.This study is helpful to understand the role of the rivers in the Tibetan Plateau in the global carbon cycle and global climate change,and also to provide reference for the scientific development of the Nujiang River.The main contents and achievements are as follows:?1?Analyzing the physiochemical properties and the control mechanism of hydrochemistry of rivers.The pH value of the river water in Naqu river basin is slightly alkaline,and the average TDS value of the river water is 235.87 mg/L.The main hydrochemical type of river water is Ca-HCO₃,the main control mechanism of hydrochemistry of rivers is rock weathering,and H₂CO₃ is the main reaction medium to participate in the basin rock chemical weathering.?2?Analyzing the contribution rate of different end-members to solute in river water.Basing on the forward modeling,the contribution of different end-members to the solute of Naqu river water in case 3 is as follows:carbonate rock?61.93%?>silicate rock?22.04%?>evaporite rock?15.30%?.The contribution of atmospheric precipitation is very small.?3?Analyzing the chemical weathering rates of different lithologies in the middle and upper reaches of Naqu River.In 2019,the silicate weathering rate in the middle and upper reaches of Naqu River is 6.82 t/km²/a.The carbonate weathering rate is 16.84 t/km²/a,11.32t/km²/a,14.08 t/km²/a for case 1,case 2 and case 3,respectively.The evaporite weathering rate is 2.20 t/km²/a,9.63 t/km²/a,5.92 t/km²/a for case 1,case 2 and case 3,respectively.The rock weathering rate is 25.87 t/km²/a,27.78 t/km²/a,26.82 t/km²/a for case 1,case 2 and case3,respectively.?4?Studying the carbon sink capacity in the middle and upper reaches of Naqu River basin.The mean value of consume rate of CO₂ by silicate weathering in the middle and upper reaches of Naqu River basin is 285.71×10³ mol/km²/a.The mean value of consume rate of CO₂ by carbonate weathering in the middle and upper reaches of Naqu River basin is102.24×10³ mol/km²/a,186.37×10³ mol/km²/a,144.30×10³ mol/km²/a for case 1,case 2 and case 3,respectively.The consume rate of CO₂ by silicate weathering in the middle and upper reaches of Naqu River basin is higher than the middle and lower reaches of the Nujiang River,Tuotuo River,Tongtian River,the middle and upper reaches of Lancang River,the upper reaches of the Yellow River and the middle and upper reaches of the Yarlung Zangbo River.