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

Abstract

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 (δ 13CDIC) increased in the surface waters of the reservoirs, while in the waters released, the DIC species showed reverse geochemical behaviors. The δ 13CDIC ranged from −10.2 ‰ to 2.5 ‰, 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 δ 13CDIC 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.