GEOCHEMICAL FRACTIONATION OF HEAVY-METALS IN CHILKA LAKE (EAST-COAST OF INDIA) - A TROPICAL COASTAL LAGOON

Chilka lake, the largest coastal lagoon of Asia is one of the most dyn amic ecosystems along the Indian coast. Historically the lagoon has un dergone a considerable reduction in surface area due, in part, to inpu t from natural processes but mostly due to human activities. The purpo se of this investigation is to document the heavy metals' affinity for specific geochemical phases in the recently deposited sediments in th e lagoon. Thirty-three samples were collected and analyzed for differe nt geochemical phases of Fe, Mn, Cu, Cr, Ni, Pb, and Zn utilizing a se quential extraction scheme. In the nonlithogenous fraction, the exchan geable fraction was not geochemically significant, having <2% of the t otal metal concentration for all the elements. However, the carbonate fraction contained the following percentages of the total concentratio n: < 1% Fe, 13% Mn, 6% Cu, 4% Cr, 8% Ni, 13% Pb, and 12% Zn, suggestin g the detrital origin of the sediments. Reducible and organic matter-b ound fractions were the significant phases in the nonlithogenous fract ion, containing 9% Fe, 16% Mn, 15% Cu, 16% Cr, 16% Ni, 14% Pb, and 14% Zn in the former and 4% Fe, 3% Mn, 17% Cu, 3% Cr, 14% Ni, 15% Pb, and 14% Zn in the latter. The phenomenon has been attributed to the scave nging affinity of Fe-Mn oxides and affinity for sorption into organic matter of the lagoon sediments. The lithogenous, residual fraction gen erally considered as a guide for natural background values was determi ned to contain 87% Fe, 67% Mn, 61% Cu, 77% Cr, 61.3% Ni, 56% Pb, and 6 0% Zn of the total concentrations.