Shifting controls on DIC export in the Doce River Basin during baseflow conditions: from rock weathering to anthropogenic forcing

Tropical rivers play a disproportionately important role in global carbon fluxes, yet they remain underrepresented in biogeochemical datasets. This study investigated the fluvial fluxes of Dissolved Inorganic Carbon (DIC) and dominant hydrochemical processes in 499 small tropical rivers and streams across the Doce River Basin (DRB), Brazil, a region affected by the 2015 Fundão Dam collapse, the world’s largest mining tailings dam failure and Brazil’s most severe environmental disaster. Water samples were collected during dry-season baseflow conditions in 2010. Surface-water chemistry reflects the combined influence of silicate weathering and anthropogenic inputs, with a mean DIC fluvial flux of 5.44 kg C km −2 day −1 . Rock weathering is the dominant basin-scale control on DIC concentrations, as indicated by a factor explaining 40.6% of the total hydrochemical variance (Ca2 + , Mg2 + , Na + , HCO 3 − ), consistent with the basin’s predominantly silicate lithology and localized contributions from carbonate-bearing units upstream. Anthropogenic inputs act as a secondary but systematic control, particularly in the midstream sector, where pasture land use is associated with higher DIC concentrations (r = +0.448, p < 0.001), while mining and urban effluents locally enrich alkalinity and major ions. Micro-basins dominated by natural land cover show lower mean DIC concentrations (5.24 mg C L −1 ) than anthropogenically influenced sub-basins (11.13 mg C L −1 ), a 2.1-fold difference. As these results derive from a single dry-season campaign, they should not be extrapolated to an annual DIC budget. Overall, this study provides a hydrogeochemical characterization of tributary systems in the DRB, supporting future monitoring and environmental assessment efforts.