Spatial and temporal patterns of pCO₂ in the subtropical Dong River basin were mainly affected by C inputs and in-stream metabolism, both of which varied due to differential catchment settings, land cover, and hydrological conditions. CO₂ fluxes in the wet season were 2-fold larger than in the dry season due to high pCO₂ and turbulence caused by high flow velocity. The absence of high CO₂ fluxes in small rivers could be associated with the depletion effect caused by abundant precipitation.