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1D - Soil and Sediment Contamination (TU9/10) Flux of particulate Cu, Pb, Zn, Mn, Ni, and Cr by the suspended load of the Brahmaputra river from the highland catchments of the Tibetan Plateau to the Bangladesh floodplains. mahanta, chandan1, Subramanian, V2, Goswami, R.K.1, 1 Department of Civil Engineering, Indian Institute of Technology-Guwahati, Guwahati -781039, Assam, India2 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi -110067, Delhi, India ABSTRACT- Heavy metal flux from the fragile Tibetan highlands through the sediment load of the Brahmaputra river (with one of the highest erosion in the world) to the Bangladesh plains remains unexplored. The entire midstream part of the river (the conduit between Tibet and Bangladesh) covering a stretch of 700 km. was sampled systematically to study the distribution and fractionation of trace metals like Cu, Pb, Zn, Mn, Ni, and Cr. Almost 90% sediment is carried as suspended load during monsoon as medium and fine sands (500 mg/l to 1800 mg/l). The suspended load ranged in size up to 400 micron with 70% to 80% of the load coarser than 40 micron. The average trace metal concentrations in the samples were of the order Mn > Zn > Ni > Cr > Cu > Pb with the suspended load showing increased enrichment relative to the bed load. Pre-monsoon and post-monsoon suspended sediment samples were marked with increased concentration of trace metals than the samples collected during monsoon. Control of particle size over concentration of metals were evidenced in the size fraction between 63 micron and 2 micron. Speciation studies revealed that all metals were strongly associated with the non-lithogenous fraction. In the suspended load, organic fraction dominated the flux of Cu more than any other metal. Exchangeable fraction was relatively enriched in concentration of Pb in the suspended load, though the residual phase carried the highest concentration. Environmental implications assessed with respect to Geo-accumulation and Microtox indices indicated that Cu was enriched to some degree of concern. Demographic and socio-economic parameters indicated that the anthropogenic factors contributing heavy metals to the Brahmaputra basin are likely to continue, resulting in pollution potential and further degradation of the watershed, subsequently contributing significantly to the modification of the inputs of these heavy metals to the downstream. Considering the enormous sediment load of the river (600 - 700 million tonnes/yr. transported to the Bangladesh part of the basin from India), the impact on the coastal ecosystems of both India and Bangladesh could be critical. Key words: Brahmaputra, Sediment, Heavy metals, Flux |
