Distribution of C, N and P in the sediments of the Ganges-Brahmaputra-Meghna river system in the Bengal basin

The Bengal basin is one of the geologically youngest and tectonically activ e drainage regimes of the world which includes the total Lower Ganges-Brahm aputra-Meghna (GBM) river system, one of the highest sediment dispersal sys tems in the world. The sediment load in this system comprises exclusively f ine sand, silt and clay. River bed sediments, and suspended matter from sta tions situated uniformly all over the basin, have been analyzed in order to understand the spatial distribution and biogeochemical processing of the C , N and P in the system. Among the Ganges, Brahmaputra and Meghna subbasins , variations in total phosphorus (TP) and nitrogen (TN) contents in the bul k and <63 mu m fraction of the bed sediments are statistically insignifican t, but total carbon (TC) content varies significantly among the three subba sins. There is a gradual increase in the concentration of TC from the Megln a towards the Ganges subbasin, attributable to the nature of the floodplain and bank materials which supply major sediment load to the river channels. The TP concentration is 2 to 5 times more in the suspended matter than tha t in any particle size fraction of the sediments. Although excellent correl ation between C-org and TN suggests their coorigin, the influence of inorga nic nitrogen is evident in very low C/N ratios. The C/N ratio varies from 2 to 11, suggesting complete degradation of the organic matter and/or enrich ment of inorganic nitrogen in the sediments. The plant available phosphorus (PAP) varies from 1.78% to 6.98% of TP, and indicates a significant anthro pogenic contribution. The C-org, TN and C/N ratio in the bed sediments of t he Lower GEM system are in the range comparable with other river basins of the subcontinent. (C) 1999 Elsevier Science Ltd. All rights reserved.