Biogeochemical cycling of pollutants by watersediment interaction in a freshwater system a case study with the Brahmaputra river

Abstract

BIOGEOCHEMICAL CYCLING OF POLLUTANTS BY WATER-SEDIMENT INTERACTION IN A FRESHWATER SYSTEM Pollutants discharged into any aquatic system are mostly adsorbed on the suspended particles, which finally accumulate in the bed sediments. The distribution of these pollutants between the solid phase of the sediment and the water inside the pores provides important information about type and nature of water-sediment interactions that are considered important in studying biogeochemical cycling of the pollutants. The pollutant transport processes in a river system are very often controlled by sediment-water interactions. Collection and analysis of pore water present in the sediment has therefore become an important aspect of environmental monitoring programmes for identification of contaminants and in sediment quality assessment. The present work is an attempt to characterize bed sediments and their pore water with respect to the Brahmaputra river system. A number of physical and chemical parameters were measured for bed sediment and pore water at three different depths at thirteen locations. The parameters include pH, conductivity, alkalinity, sulphate, chloride, nitrate and ammonium content in pore water and water content, particle density, bulk density, porosity, sand, clay, slit, organic matter, sulphate, total phosphorus and bicarbonate in the dried sediment. Results have been reported from thirteen locations of the river. Nine heavy metals, viz, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were also determined along with Na, K, Ca, and Mg in both pore water and sediment. Sedimentation of particles in a river system results in the overlying water being trapped and entrained in the sediment. The sediments thus serve as a valuable sink for a large number of pollutants. The study of sediment-water interactions help in computing the fluxes of heavy metals and the nutrients through the river systems and for understanding the mobility and bioavailability of these elements entering the aquatic system through pollutant discharges....