Climate Warming and Soil Drying Lead to a Reduction of Riverine Dissolved Organic Carbon in China

Dissolved organic carbon (DOC) is a dynamic component of riverine carbon pools that plays a vital role in determining regional carbon balance. However, owing to limitations in observational data and methodologies, the spatiotemporal dynamics of riverine DOC at a regional scale and their underlying driving factors remain poorly understood. In this study, we compiled riverine DOC concentration measurements for China, using which we analyzed the spatial and temporal patterns of DOC concentrations from 1982 to 2020, and examined the potential driving factors, including climate, vegetation, soil, and hydrology. The results revealed that the average annual DOC concentration in Chinese rivers for the assessed period was 4.06 mg L⁻¹, with the highest concentrations found in Northeast China (i.e., the Songliao River). We also found that there had been a significant reduction in annual DOC concentrations in Chinese rivers from 1982 to 2020, associated with significant declines in DOC in spring and summer. Further analyses revealed that these reductions in DOC concentrations could mainly be attributed to the synergistic effect of climate warming and soil drying. In addition, the total flux of DOC from major rivers in China and the average DOC yield were estimated at 8.15 Tg yr⁻¹ and 1.16 g m² yr⁻¹, respectively. Our findings in this study provide foundational data support for the accurate assessment of regional carbon budgets and offer theoretical insights for developing a regional land-ocean-aquatic continuum (LOAC) carbon cycling model for China.