外源水和外源酸对万华岩地下河系统岩溶碳汇效应的影响

流域的岩石化学风化过程是全球碳循环中的重要环节。近年来流域水化学碳汇通量估算已越来越多地关注到外源水(硅酸盐风化)及外源酸对全球碳循环的影响。文章选取万华岩地下河流域为研究区,流域硅酸盐岩和碳酸盐岩分布面积占比为64%和36%,于2017年对洞口进行为期一年的取样监测,并分别于4月和9月对万华岩地下河系统内13个水点的离子组成进行监测,利用水化学平衡法和Galy模型,对流域岩石化学风化速率和CO2消耗通量进行了计算,对万华岩地下河系统的岩石风化和碳循环过程进行了分析。结果表明,万华岩地下河系统岩石风化消耗CO2的速率为31.02 t·(km2·a)-1;以碳酸岩风化为主,其风化速率为硅酸盐溶蚀的20倍;流域内碳酸盐岩风化对CO2消耗量占到整个流域的92.16%;不同岩石风化类型对碳通量的贡献率以碳酸溶解碳酸盐岩最大,为87.06%;流域上游的外源水对岩溶碳汇具有巨大的促进作用,外源水汇入后碳酸盐岩碳汇速率可以达到无外源水汇入流域的2倍;硫酸溶解碳酸盐岩次之,为9.24%;碳酸风化硅酸盐岩最小,为3.7%,在计算流域碳汇量的时候应将硫酸参与岩石风化的影响去除。

Effect of exogenous water and acid on karst carbon sink in the Wanhuayan underground river system

The petrochemical weathering process in the basin is an important part of the global carbon cycle.In recent years,increasing attention has focused on the effects of exogenous water(silicate weathering)and exogenous acid on the global carbon cycle in the estimation of hydrochemical carbon sink fluxes in the watershed.In this study,the Wanhuayan underground river system is selected as the study area,where the proportions of silicate rock distribution area and carbonate rock distribution area are 64%and 36%,respectively.In 2017,a one-year sampling monitoring was carried out at the entrance of the cave,and the ion composition of 13 water points in the Wanhuayan underground river system was monitored in April and September,respectively.The chemical weathering rate and CO2 consumption flux of the basin rocks were calculated by using the hydrochemical equilibrium method and Galy model.The process of rock weathering and carbon cycle in the system was analyzed.The results show that the rate of CO2 consumption by rock weathering in the Wanhuayan underground river system is 31.02 t·(km2·a)-1,with dominant carbonate weathering which is 20 times that of silicate rock dissolution.Moreover,carbonate weathering accounts for 92.16%of CO2 consumption in the whole basin.The contribution rate of different rock weathering types to carbon flux is 87.06%,of which carbonate dissolved carbonate rocks is the largest.The external water in the upper reaches of the basin has a great role in promoting the karst carbon sink.After the external water imported,the carbon sink rate of carbonate rock can be twice that of the non-external water sink in the basin.Sulphuric acid dissolved carbonate rocks took the second place,accounting for 9.24%;carbonate weathered silicate rock is the smallest,which is3.7%.The influence of sulphuricacidon rock weathering should be removed when calculating carbon sink in river basins.