Spatiotemporal dynamics, source and flux of dissolved black carbon in the monsoon-influenced Yangtze River system

The Yangtze River is the most important source of dissolved black carbon (DBC) for the East China Sea. However, knowledge regarding the source, fluxes, and fluvial transport of DBC in the Yangtze River is lacking, due mainly to the seasonal influences of the East Asian monsoon. To fill this knowledge gap, we measured DBC in water samples collected in the whole river under different hydrological conditions. In 2023, the DBC flux in the Yangtze River was significantly lower before the rainy season (3.29 Gg C per month) than after the rainy season (5.38 Gg C per month). By comparing the concentrations and condensation degree before and after the rainy season, it was found that the significant increase in DBC flux mainly originated from the contribution of midstream soil carbon pools, which characterized by highly condensate DBC. Finally, we estimated the total annual DBC flux of the Yangtze River to be 53.22 Gg C in 2023. This study quantified the significant contribution of the soil carbon pool to the Yangtze River DBC pool (74.39 %). Greater attention should be paid to the impact of soil erosion and hydrology conditions variations on the DBC within terrestrial-aquatic continuums.