Determination of dissolved inorganic carbon export and the controlling factors in small mountainous Rivers, Taiwan

Riverine dissolved inorganic carbon (DIC), mainly sourced from rock weathering and soil respiration, constitutes the majority of the riverine total dissolved carbon transported to the ocean. Taiwanese rivers exhibit extremely high erosion and are hypothesized to export disproportionately high DIC. Yet, the magnitude, composition, and drivers of DIC export in subtropical mountainous rivers remain poorly understood. This study analyzed DIC compositions, concentrations, and yields across 43 rivers in Taiwan. Considering physio-geographic factors, the main influences and spatial patterns of DIC distribution were identified. The results revealed an average DIC concentration of ∼ 17.28 mg-C L−1, with HCO3– accounting for over 90 % of DIC. The average DIC yield of 27.65 ton-C km−2 yr−1 is tenfold greater than the global average (2.58 ton-C km−2 yr−1). Stepwise regression showed that proportion of agricultural land was positively correlated, and proportion of sandstone, shale, and argillite (SSA) was negatively correlated with DIC concentration and yield, respectively. Concentration–discharge (C–Q, C = aQb) analysis indicated that the intercept (a) was positively associated with agricultural land use and negatively with SSA coverage. The slope (b) increased with catchment slope, emphasizing the role of landscape controls. These findings underscore that SSA (via rock weathering) and agricultural land (via soil respiration) substantially elevates DIC sources, while the warm, wet climate and high catchment slope (via physical erosion) promote carbonate dissolution. This study provides a piece of the missing puzzle in elucidating the significance of DIC export from subtropical mountainous rivers within the global riverine carbon budget.