Distribution and magnitude of geologic carbon sinks: a water balance study of the Chaotian River basin, Guilin, China

Increasing CO₂ emissions have greatly affected Earth’s natural ecosystems. Existing studies suggest that missing carbon sinks always occur and increase progressively during the climate change driven by the carbon cycle. Some scholars propose that the carbonate weathering carbon sink can account for most of the missing carbon on a short time scale. However, undersaturated allogenic water can add to carbon sinks when flowing into karst basins. This study, conducted in the Chaotian River basin, showed that (1) HCO₃ ⁻ concentration in a karst area is 4–13 times that of non-karst areas, and the HCO₃ ⁻ concentration increased slowly when allogenic water flowed through a karst area until HCO₃ ⁻ reached saturation. (2) In plant or algae-rich areas, HCO₃ ⁻ has a clear diurnal variation. (3) The Chaotian River basin carbon sinks are 8,724.0 and 6,720.6 tC/a by the partition method and direct calculation method, respectively. The difference may be caused by aquatic photosynthesis, which is a process that should be considered more in carbon sink studies. (4) Addition of allogenic water to carbonate basin can increase carbon sink totals.