Particle bound nutrients and heavy metals in the Bengal Basin

Abstract

The Bengal basin is one of the most important alluvial basins of the world because newlineof its size and location, density of population, catastrophic deposition of sediments, newlineincreased flooding and lower elevation above mean sea level. The sediment flux newlinethrough the basin is one of the highest on global scale. A significant portion of this newlinesediment load find its sink in the basin itself because of its lower elevation and newlinefrequent flooding. The textural, mineralogical and chemical nature of the sediments newlinethus have an important bearing on the environmental quality of the basin as well as newlinefor the Bay of Bengal. newlineRiver bed sediments, suspended sediments, shallow cores and river water newlinewere collected from the G-B-M system and its tributaries and distributaries in the newlineBengal basin during Dec-Jan 1991-92, Aug-Sept 1992, April-May 1993 and March- newlineApril 1994, from 34 stations distributed uniformly all over the basin. The sampling newlinestations are situated at pre-selected location representative of the river course, and newlinedepending on land traffic, avoiding the sit~s of instant tributary effect and other newlineapparent sources of pollution. newlineThe sediment load of the Ganges-Brahmaputra-Meghna river system consists newlineexclusively of fine sand, silt and clay at their lower reaches within the Bengal basin. newlineThe sediments have deposited under uniformly fluctuating, unidirectional energy newlinecondition as revealed from their statistical parameters. The sediments have a close newlinesimilarity in grain-size with the sediments of the surrounding floodplain. The mineral newlineassemblage is dominated by quartz and feldspars. Illite and kaolinite are the major newlineclay minerals and occur in almost equal proportions in the bed sediments. The heavy newlinemineral assemblage is dominated by unstable minerals which are mostly derived newlinefrom high-rank metamorphic rock. The characteristic smaller grain size viz., havin newlinelarge surface to mass ratios, and the mineralogy of sediments suggest that they are newlinesusceptible to large chemical adsorptive reactions, and thus could serve