The impact of damming on geochemical behavior of dissolved inorganic carbon in a karst river

To determine the impact of damming on the geochemical behavior of dissolved inorganic carbon (DIC) in the Wujiang River basin, field measurements and samples were collected semimonthly for a year. The surface waters of the reservoirs contained concentrations of chlorophyll a up to 5.6 times higher than the upstream river. Compared with the entering waters, the contributions of HCO3 (-) and dissolved CO2 to DIC decreased, and the contribution of CO3 (2-) to DIC and the carbon isotopic composition of DIC (delta C-13(DIC)) increased in the surface waters of the reservoirs, while in the waters released, the DIC species showed reverse geochemical behaviors. The delta C-13(DIC) ranged from -10.2 aEuro degrees to 2.5 aEuro degrees, indicating that significant contributions were from carbonate weathering, photosynthesis, and respiration. After the damming of a river, the bioactivity of phytoplankton was enhanced, and this affected the geochemistry of DIC compared to an unimpacted river and delta C-13(DIC) can be used to discern these changes. High-frequency monitoring of river-reservoir systems is necessary to evaluate the efflux of CO2 and provide a better understanding of the carbon sinks and sources in the impounded river.