Trace element geochemistry of modern deltaic sediments of the Cauvery River, east coast of India

Abstract

In the river channel sediments, concentrations of trace elements (Cu, Co, Ni, Zn, Pb, Ga, V and Cr) increase downstream, but near the mouth Cu, Co, Zn, Pb and Ga values decrease considerably. This is attributed partly to desorption of these elements from fresh water clay minerals and control of Fe and Mn oxides over trace elements in the estuarine region. Among elements only Ga content shows a gradational decrease from fresh to saline environment, its content shows a 2-3 fold increase in river channel sediments than in marginal environments. Ni distribution does not show any variation in the deltaic sediments except in swamps. Not much variation is found in Cu, Co, Zn and Ga distributions in mangrove, swamps and tidal channel sediments, Pb content in mangrove and swamps is more or less same. Similarly in the marine sediments, trace metals distributions do not show any systematic trend either along or across the coast. Cu, Co, Zn, Pb, Ga and Cr are enriched in river channel sediments attributing the importance of terrigenous supply of traces to the deposition site. V and Ni are concentrated in estuary and swamps respectively. Lowest average concentrations of elements are observed in the following environments: Ga and Cr in marine, V and Zn in swamps, Cu in mangrove, Pb in tidal channels, Ni in river channel and Co both in tidal channels and swamps. Apart from terrigenous supply, oxides of Fe and Mn, organic matter, P and clay minerals play a significant role in the concentration of these metals in the delta.