Trace metal distribution in a shallow estuary

Abstract

The concentrations of the trace metals Fe, Cu, Cd, Zn, and Mn in estuarine waters were observed in the Muthupet estuary during the post-monsoon and the pre-monsoon period, in the bed sediments during the pre-monsoon period. Mn behaved conservatively while Fe, Cd, and Zn showed mid-estuary maxima during the pre-monsoon period. Fe was supplemented by the river discharge during the post-monsoon. The concentration of Fe reduced towards the river mouth; a sudden drop occurred at the turbidity maximum zone. The variations of Cu, Cd, and Zn with salinity and suspended particulate matter (SPM) were similar with their concentrations increasing with salinity and the SPM. Fe decreased with salinity and SPM during the post-monsoon, while peak concentration of Fe occurred at high salinity and SPM reaches. The peak concentrations of Fe, Cd, and Zn in the bed sediments occurred at the mid-estuary. Thus, the study proved that the Muthupet estuary acts as a sink for Fe. The phenomenon controlling the trace metals in the estuarine waters is distinct on a seasonal scale and also on the type of metals; river discharge controlled the concentration of Fe in water during the post-monsoon and resuspension of bed sediments during the pre-monsoon; Cu, Cd, and Zn are supplemented by the resuspension of the bed sediments.