Environmental geochemistry of the Mahanadi River Basin

Abstract

The Mahanadi river is one of the major rivers in India, newlineflowing east and draining into the Bay newlineEncompassing 5 2 a basin area of 1.42x10 km, newlineof Bengal. newlinethe basin is newlinecharacterised by a tropical climate with average annual newlinerainfall of 155 cm. The basin geology is characterised by newlinePrecambrians of Eastern Ghats consisting of rock types as newlinekhondalites, charnockites, leptynites, granites, gneisses newlineetc., the limestones, sandstones and shales of the Gondwanas newlineand the coastal tracts constituted by the Recent deltaic newlinealluvium of the river with littoral deposits. A part of the newlinerichest mineral belt of the sub-continent consisting of iron newlineore, limestone, dolomite, bauxite, lead and copper deposits newlineoccur in the basin. Except for studies on water chemistry in newlinethe estuarine region of the river, not much work has been newlinereported from the Mahanadi river basin. Hence the present newlinestudy is aimed at determining erosion and deposition rates newlinein the basin, grain size distribution and mineral newlinecomposition in different size fractions of suspended and bed newlinesediments, heavy metal distribution in size fractions and newlinechemical fractions of the sediments. newlineWater, suspended, bed and core sediments were collected newlinein different seasons during 1986 and 1989 from selected newlinelocations of Mahanadi and its tributaries. Standard newlineprocedures were adopted for analysis of samples. Data on newlinedaily, monthly and annual water discharge for 10 years newline(1977/78 - 1986/87) and for 5 years of sediment discharge newline(1980/81 - 1983/84 and 1985/86) at the gaging stations were newlineobtained from the Central Water Commission, India. newlineHCO; , C ++ Mg++ d a , an dissolved silica, mostly newlineconstitute the water composition. Most of the ions are newlinereleased from carbonate rock weathering with 60% HCO; coming newlinefrom carbonate lithology. The high bicarbonate content newlineshows the intense chemical weathering taking place in the newlinebasin. Chemical erosion rate for indiVidual elements is newlinehigher in Mahanadi compared to other peninsular rivers in newlineIndia.