Sources and fluxes of the riverine particulate organic carbon of Chinese rivers

Rivers play an important role in the global carbon cycle, exporting terrestrial carbon to the ocean and acting as biogeochemical reactors which can exchange carbon dioxide(CO2) with the atmosphere. Physical erosion in river catchments can mobilize particulate organic carbon(POC) from the terrestrial biosphere(biospheric POC) and organic carbon derived from sedimentary rocks(petrogenic POC). Erosion and transport of biospheric and petrogenic POC have different impacts on the atmospheric CO2 budget across a range of timescales. Although Chinese rivers export large amount of sediment and organic carbon into the marine system, there remain few comprehensive attempts to synthesize the national pattern of the sources and fluxes of riverine POC. Here, we synthesize the content, carbon isotopic ratios and flux of POC in main Chinese rivers, along with the fluxes of sediment. Our analysis reveals that the POC content and carbon isotopic ratios vary across the different rivers with wide difference in the hydro-climate background. The POC of the main Chinese rivers could be explained as a mixture of petrogenic carbon and C3 vegetation with minor input of C4 plants. The POC sources and fluxes of these rivers are controlled by the physical erosion, climate, geology, geomorphology, and human activities. We recalculate the particulate organic caron flux and find that the biospheric and petrogenic POC in 31 rivers (including 12 rivers of Taiwan and draining 47% of Chinese territory) are 4.29±0.81MtC/a and 2.04±0.22MtC/a, accounting for 2.7+1.3/-0.9% and 4.7+6.6/-2.8% of global POC fluxes into the ocean, respectively. In the last decades, the Chinese rivers had been suffering suspended sediment flux reduce, which changes the POC oxidation and burial in the reservoir. Further assessing these processes and fluxes are important for understanding the role of Chinese rivers on the global carbon erosion, export, oxidation, and burial.