外源酸输入对岩溶碳汇过程响应特征与核算方法优化OA

Fully exploiting and enhancing the potential of karst carbon sinks is one of the important pathways for achieving China's carbon peak and carbon neutrality goals.However,the input of exogenous acids and the weathering of silicate rocks significantly compromise the accuracy of assessing karst carbon sink fluxes.To reveal the patterns of dynamic influence of exogenous acid input and silicate weathering on karst carbon sinks,it is imperative to establish a revised method for carbon sink accounting.Accordingly,this study focuses on the Diaojiang River Basin in Guangxi,a typical karst area affected by both mining activities and complex geological conditions.The basin,located in northern Guangxi,experiences a subtropical monsoon climate characterized by distinct wet and dry seasons.Its lithology is complex,mainly including limestone,dolomite,and clastic interlayers.The upstream area of the basin suffers from severe sulfate pollution due to gypsum dissolution and historical mining activities,while the mid-to downstream areas are dominated by carbonate rocks and are continuously affected by human activities. This study employs a carbon isotope end-member mixing model with the stoichiometric relationships of carbonate and silicate weathering to quantify the proportions of three main sources of HCO3-in the river:silicate weathering,carbonate dissolution by carbonic acid,and carbonate dissolution by sulfuric acid.Based on this,the traditional hydrochemical-discharge method is systematically revised. The main results include the following five aspects:(1)At the Chehe section,the cations are predominant Ca2+,while anions are mainly SO42-and HCO3-;at the Jiusi and Baiwang sections,cations also are dominated by Ca2+,but anions are primarily HCO3-.The hydrochemical types of the basin show clear spatial differentiation:The upstream Chehe section is classified as SO4·HCO3-Ca type,while the mid-to downstream Jiusi and Baiwang sections are both of the HCO3-Ca type,reflecting the combined effects of geological background and human activities.(2)The ratios of Na+/(Na++Ca2+)at all sections of the Diaojiang River Basin range from 0.02 to 0.20,and the ratios of Cl-/(Cl-+HCO3-)range from 0.01 to 0.07,both below 0.5,indicating that the river water chemistry is significantly influenced by rock weathering.The relationships of Ca2+/Na+versus Mg2+/Na+and Ca2+/Na+versus HCO3-/Na+reflect that both silicate and carbonate rocks contribute to weathering processes at all three sections.The equivalent ratios of[Ca2++Mg2+]/[HCO3-+SO42-]at all sections are close to 1,confirming the involvement of sulfuric acid in the weathering process of carbonate rocks.(3)Analysis of the molar ratio relationships between 2SO42-/HCO3-and 2(Ca2++Mg2+)/HCO3-further supports the occurrence of upstream gypsum dissolution and the role of sulfuric acid in carbonate weathering.(4)The average contribution ratios of silicate weathering at the Chehe,Jiusi,and Baiwang sections are 2.9％,1.6％,and 1.4％,respectively;the average contribution ratios of sulfuric acid weathering are 33.4％,26.4％,and 21.3％,respectively.(5)Using the revised method,the annual carbon sink amounts at the Chehe,Jiusi,and Baiwang sections are calculated to be 2.26×105 kg C,1.96×106 kg C,and 3.00×107 kg C,respectively,which are significantly different from the unrevised results. In summary,the input of exogenous acids and the weathering of silicate rocks significantly alter the hydrochemical composition and carbon sink capacity of karst rivers.The revised carbon sink accounting method proposed in this study is able to effectively enhance the accuracy of watershed-scale karst carbon sink assessments under complex geological backgrounds and anthropogenic impacts,providing a reliable scientific basis for related research and policy development.