An assessment of the riverine carbon flux of the Xijiang River during the past 50 years

Most Chinese rivers have experienced great changes in discharge and sediment during the past 50 years. This study attempts to examine the long-term dynamics of riverine carbon flux in the Xijiang River by applying the relationships between riverine carbon concentrations and discharge or sediment to the historical discharge and sediment records. Results show that POC (particulate organic carbon) flux in the Xijiang has experienced a decreasing trend, caused by reduced sediment supply. However, DOC (dissolved organic carbon) shows an increasing trend. Human activities including reservoir/dam construction and domestic/agricultural effluents may intensify the upward trend of DOC. DIC (dissolved inorganic carbon) shows a declining trend with a very small slope. Variation of DIC accords well with discharge/precipitation. For total carbon flux, a more or less constant, or very small decreasing trend is displayed.