Sources and fluxes of particulate organic carbon (OC) in the GangaBrahmaputra river system were estimated from 13 C/ 12 C ratios of bedrocks, soils, bank and suspended river sediments from a Himalayan watershed (Narayani, Nepal), and the Bangladesh floodplain. In the watershed of the Narayani, OC δ 13 C values for bank and suspended sediments have similar values and narrow .