Distribution and seasonal variation of trace metals in surface sediments of the Mandovi estuary, west coast of India

The concentration and distribution of selected trace metals in surface sediments of the Mandovi estuary were studied to determine the extent of anthropogenic inputs from mining activities and to estimate the effects of the monsoon on geochemical processes in this tropical estuarine system. Analysis of bulk sediments from the Mandovi estuary shows that the concentrations of iron, manganese, cobalt, copper, zinc and lead vary from 2.2 to 49.7%; < Detection Limit (DL)-1.61%; 2.5-45.3 mu g g(-1); 11.5-77.5 mu g g(-1); 19.9-83.5 mu g g(-1); and 4.5-46.5 mu g g(-1), respectively. An important observation is that, in general, lowest metal concentrations are found during the monsoon, compared to the pre- and post-monsoon. Comparison of the metal levels in the sediments from different areas of the estuary indicates that there is a detectable anthropogenic input to the Mandovi estuary. The enrichment of Fe and Mn reflects the intensity of anthropogenic inputs related to iron ore processing in the upstream region of the estuary, however, the highest enrichment levels were not found near the mouth region. I-geo, values calculated for Fe (2.5) and Mn (3.4) showed higher values in the pre-monsoon period in the upstream region of the estuary than in the post-monsoon and monsoon seasons. Cu and Zn enrichment in the river mouth region, associated with high organic carbon contents, is indicative of the influence of organic wastes from municipal sewage entering the estuary. The intermetallic relationship revealed the identical behaviour of metals during its transport in the estuarine environment. (c) 2005 Elsevier Ltd. All rights reserved.