Hydrogeochemical Characteristics And Weathering Indicators In Lhasa River Basin

The hydrogeochemical and isotopic characteristics of rivers can reflect the sources of solute components,spatial and temporal distribution,trace back to the main weathering processes in the basin and the estimation of atmospheric CO₂ consumption.In this paper,taking the Lhasa River basin as the research object,the effects of the factors such as atmospheric precipitation,human activity and the weathering of rock on the water chemistry of the river basin are studied by analyzing the chemical characteristics of the river,the characteristics of the hydrogen and oxygen isotope and the characteristics of the uranium isotope.And the rock weathering rate and the carbon dioxide consumption of the river basin are estimated.The following research results are obtained:?1?The range of pH in the river water of Lhasa River is 6.4⁹.1,and the order of the average concentrations of major anions and cations is Ca²⁺>Na⁺>Mg²⁺>K⁺>NH₄⁺,HCO₃^->SO₄^2->Cl^->NO₃^-,The type of hydrochemistry in the basin is mainly HCO₃-Ca type;The average TDS of the river is 160.63 mg·L^-1,which is 1.6 times higher than the global river average(100 mg·L^-1),indicating that the basin has been subjected to strong chemical erosion.?2?The hydrogen and oxygen isotope studies show that the source of water supply in the middle and lower reaches of the river is simple,precipitation is the main source of recharge,and the recharge of groundwater is less;Through the study of uranium and uranium isotopes,it is shown that the weathering of carbonate rock is dominant,and the weathering of silicate rock is not the main source of uranium.?3?By means of Gibbs diagram,anion-cation triangle diagram,stoichiometric analysis and end-element eigenvalue analysis,it is shown that the main controlling type is controlled by rock weathering,and rock weathering is influenced by a mixture of three elements?carbonate rock,silicate rock and evaporate rock?.The influence of carbonate rock is dominant.?4?The calculated results of mass conservation show that the average contribution of carbonate weathering,atmospheric input,silicate weathering,artificial input and evaporation rock to the cation of river water is 76.68%,8.12%,5.79%,5.47%and 3.93%,respectively.The further quantitative results show that carbonate rocks dominate weathering.S7 sampling site,due to human activities,is also affected by the weathering of exogenous acid and sulfuric acid.?5?The results of forward deduction show that the weathering rates of carbonate rock and silicate rock are 19.1 t·km^-2·a^-1 and 2.56 t·km^-2·a^-1,respectively.Carbonate rock is more effective than silicate rock in restraining global warming.The CO₂ consumption of carbonate rock and silicate rock is 7.33×10⁹ mo1·a^-1 and 0.80×10⁹ mo1·a^-1,respectively.The CO₂ consumption of carbonate weathering is 9.16 times higher than that of silicate rock.The total chemical weathering rate is 21.68 t·km^-2·a^-1,which is slightly lower than the global average(24 t·km^-2·a^-1),and the CO₂ consumption is relatively low.But it is also an important part of regulating atmospheric CO₂ and constituting the global carbon balance.