Study On The Hydrochemistry And Response Of Chemical Weathering To Climate Change In Alpine Basin

Rivers are an important part of the global carbon sequestration system.The amount of CO₂absorbed by the global river ecosystem can reach 0.7Gt C every year,which is equivalent to the amount of CO₂released by the marine ecosystem.It can provide reference for the accurate research and management of CO₂consumption and carbon emissions in the future.For the Yarlung Tsangpo River Basin,the largest alpine basin in China,rock weathering is the most important source of ions in river water and the most important way of river carbon sequestration process,and the chemical composition of river water is the indicator of the chemical weathering situation in the basin.The hydrochemical characteristics of alpine basin can provide the basis for clarifying the chemical weathering process and CO₂consumption of Alpine basin,which is of great significance to alpine basin The ecological protection of the source area is of great significance.In this study,river water samples were collected from the upper reaches of the Yarlung Tsangpo River Basin above Lazi County,Maquan River and the main tributary of the Yarlung Tsangpo River Basin,such as Doxung Tsangpo,in March,June and September.Based on the experimental results of three sampling,the following contents were studied:(1)The temporal and spatial distribution characteristics of hydrochemistry in the upper reaches of Yarlung Tsangpo River and the contribution of chemical weathering to river ions and the rate of chemical weathering were studied.The results show that the contribution of precipitation to river ions is low,and ions mainly come from chemical weathering,and the main water type is HCO₃^--SO₄^2--Ca₂⁺.The contribution of carbonate weathering to river ions in the mainstream of Yarlung Tsangpo River is higher than that in other tributaries.(2)According to the results of hydrochemical composition analysis,the CO₂consumed by weathering of carbonate and silicate rocks were calculated.The consumption of CO₂was mainly caused by the weathering of silicate and carbonate rocks.The consumption rate of CO₂in summer is higher than that in winter,and the consumption rate of CO₂was positively correlated with temperature;the increase rate of weathering rate of carbonate rocks was higher than that of silicate rocks from March to September.(3)According to Rcp2.6,Rcp4.5 and Rcp8.5 climate models,the changes of chemical weathering rate and CO₂consumption rate in 2045 were predicted.It was found that the annual average temperature in the upper reaches of the Yarlung Tsangpo River has increased significantly since 1976,and the warming rate is about4?/a,which is nearly five times of the world average.The main mechanism of the change of chemical weathering and CO₂consumption rate caused by climate change is that the warming accelerates the melting of glaciers in the alpine basin,and the increase of runoff intensifies the rock erosion,carbonate weathering is more sensitive to climate change than silicate weathering.It was predicted that the chemical weathering rate and CO₂consumption rate of the source of Yarlung Tsangpo River will increase slowly with the warming of the region in the future.