Hydrology-driven chemical weathering and CO2 consumption in a mixed-lithology karst river system

Study region The study region is the Maocun subterranean river catchment, a typical mixed‑lithology karst system in Guilin, Southwest China. The goal is to characterize chemical weathering in karst regions that may shape river chemistry and play a crucial role in the global carbon cycle. Study focus The complex hydrogeochemical processes involved in solute transport and dissolution-reprecipitation often obscure the original weathering signals, hampering accurate estimation of chemical weathering intensity, CO 2 consumption rate, and their impact on the hydrochemistry. To address these, we quantify solute sources, evaluate secondary calcite precipitation impacts, and how seasonal hydrology modulates weathering rates and carbon sink dynamics. New hydrological insights for the region Our results, together with a Bayesian mixing model integrated with radiogenic Sr isotopes ( 87 Sr/ 86 Sr) and the cation-normalized ionic ratios reveal carbonate weathering dominates cationic load (~62%) across the catchment, while silicate weathering contributes 65% of cations only in the silicate-dominated headwater. Secondary calcite reprecipitation increased downstream, along with distinct spatial variations in hydrochemistry and isotopes. Interestingly, the highest carbonate (CWR) and silicate (SWR) weathering rates both occur during floods, confirming discharge co-regulates weathering intensity and CO 2 consumption. Our findings demonstrate that rock chemical weathering is a major source of riverine solutes of this region, clarify the regulatory role of seasonal hydrology in chemical weathering, and emphasize the necessity of correcting for secondary carbonate precipitation to improve the accuracy of carbon sink estimation, especially in carbonate-oversaturated river systems.