Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Pages 204-
Time series observations are useful to better constrain the chemical fluxes, chemical weathering rates and the processes controlling the fate of chemical species in rivers based on isotopic analysis. The link between the hydrological conditions and chemical weathering, dissolved carbon dynamics is hypothesized to play a important role in moderating CO2 concentrations for the riverine carbonate system. In this study, we analyzed hydrochemistry and carbon isotopic compositions of dissolved inorganic carbon (DIC) based on high-frequency sampling in the Wujiang River draining the carbonate area in southwestern China. The concentrations of major elements show significant temporal variations in the Wujiang River. Concentrations of major dissolved solute do not strictly follow the dilution process with increasing discharge, and biogeochemical processes lead to variability in the concentration-discharge relationships. There is a generally negative correlation between 13CDIC values and discharge. The values of 13CDIC in Wujiang River changing with hydrological variability could not be interpreted in terms of simple dilution. The water stored in the matrix porosity and soil water with high contents of biological CO2 would flow into the river induced by high discharge, leading to decrease of 13CDIC in the Wujiang River. The concentrations of dissolved carbon and the carbon isotopic compositions decreased with discharge increasing, suggesting that hydrological conditions and biogeochemical processes influenced on dissolved carbon dynamics in the riverine system. The concentration of DICbio (DIC from biological sources) derived from a mixing model increases with increasing discharge, indicating that DICbio influx is the main driver of the chemostatic behaviors of riverine DIC in this typical karst river. The study highlights the sensitivity of chemical weathering and carbon dynamics to hydrological conditions in the riverine system.
