Inorganic carbon flux and its source in the karst catchment of Maocun, Guilin, China

摘要

New findings have shown that the contribution of carbonate weathering to the atmospheric CO2 sink is far greater than previous estimates, through the combined action of carbonate dissolution, the global water cycle, and photosynthetic uptake of dissolved inorganic carbon (DIC). However, in order for calculations to be accurate, any carbon source effect should be deducted from the overall carbon sink. In this study, we carried out high temporal resolution monitoring of flow and hydrochemistry within the Xiaolongbei (XLB) silicate catchment and Beidiping (BDP) carbonate catchment for 1 year. We found the dissolved inorganic carbon concentrations to be higher in BDP than in XLB, and the annual inorganic carbon fluxes in BDP are roughly 23.8 times higher than those in XLB. Similarly, the rate of carbonate rock dissolution is much higher than the rate of silicate rock dissolution. We find carbonate rock dissolution to respond rapidly to rainfall events, and it is sensitive to rainfall changes on hourly, diurnal, and seasonal scales. The high rate of carbonate rock dissolution gives rise to the high concentrations of DIC, Ca, Mg, and to the high inorganic carbon flux in this basin. Differences between the theoretical and calculated contributions of atmospheric and soil CO2 to the DIC are possibly due to CO2 outgassing.