Differences and influencing factors related to underground water carbon uptake by karsts in the Houzhai Basin, southwestern China

Abstract. Carbon sink in karstic areas is very important at a global scale. Consequently, accurate determination of the carbon sink of karst ecosystems has become a core issue in research. We used flow and carbon ion concentration data from three stations with different environmental background conditions in the Houzhai Basin, southwestern China, to analyse the differences in carbon uptake between stations and to determine their impact factors. The results show that carbon sink discharge was mainly controlled by the flow at each site. Preliminary analysis indicated that the rapid increase in flow only had a partial dilution effect on the ion concentrations due to the high speed and stability of chemical carbonate weathering. The Land-Use and Cover-Change (LUCC) type had important effects on the bicarbonate ion concentrations; under stable run-off conditions, the influence of flow variation on the ion concentration was lower than the effects of chemical carbonate weathering on bicarbonate ion concentrations under different environmental conditions (a comparison of Laoheitan and Liugu stations showed a difference of 150 %). However, if run-off increased significantly, the impact of run-off variation on bicarbonate ions was greater than the effects of chemical carbonate weathering caused under different environmental conditions. This work provides a reference for the calculation of the karst geological carbon sink.