Variabilities of dissolved inorganic carbon along chain-shaped karst river-reservoir continuum: The control of cascade damming

Study Region: The natural river, reservoir profiles, and inflow/outflow waters of ten cascade reservoirs along the Xijiang River in the subtropical karst region of southern China were studied. Study Focus: The dissolved inorganic carbon (DIC) concentrations and physicochemical processes were analyzed during August 2020 (summer, rainy season) and January 2021 (winter, dry season) using isotope tracer techniques and DIC dynamic analysis to evaluate the cascade damming effects. New Hydrological Insights for the Region: DIC increased in inflow due to organic matter (OM) decomposition, influenced by carbonate weathering and thermal stratification. In stratified reservoirs, surface DIC decreases from aquatic photosynthesis, while bottom layer accumulated DIC as “storage” in summer dominated by OM decomposition and release in winter. Bottom discharge creates an anti-seasonal outflow phenomenon, enhancing downstream DIC and result in a stacking effect while distance disrupts it. Non-stratified reservoirs function as “conduits” preserving river-like DIC levels. These findings contribute to a comprehensive river carbon cycle model of the Xijiang River, underscore the role of cascade damming in riverine carbon cycling and highlight implications for hydrological management and carbon sink quantification.