Spatio-temporal distribution of major and trace metals in estuarine sediments of Dhamra, Bay of Bengal, India--its environmental significance.

The research depicts the spatial and temporal variation of major and trace metals in marine sediments at various monitoring stations of Dhamra estuary, Bay of Bengal, Odisha. The concentration and distribution of selected metals in surface sediments of the estuary were studied in order to assess the spatial extent of anthropogenic inputs viz., mining activities and to estimate the effects of seasonal variations on geochemical processes in this particular tropical estuarine system. Surface sediments reflect the presence of trace and major metals in parts per million, and the concentrations vary in the range of Cu (0.083 to 127.2), Ni (17.35 to 122.8), Co (1.2 to 31.58), Pb (0.8 to 95.86), Zn (12.1 to 415), Cd (0 to 11) and Cr (35.21 to 5,890), Fe (7,490 and 169,100), Mn (20 to 69,188), Ca (10 to 10,520), Mg (990 to 28,750), Na (300 to 51,700), and K (1,100 to 30,010). The comparison of spatial distribution of metal contents using GIS in marine sediments indicates that there is a substantial anthropogenic input in the Dhamra estuary. The enrichment of Cr is ascribed to the sedimentation of Brahmani River, passing through the mining region and discharging Cr pollutant to the sea. Similarly, the sources of Cd are attributable to corrosion-resistant paints used by a large number of trawlers. Contamination factor has been calculated for various metals to assess the degree of pollution. As per Hakanson's classification, Cr indicates very high contamination with considerable contamination of Cd, whereas moderate contamination of Pb, Zn, and Mn are observed in marine sediments. Pollution load index also indicate that there is deterioration of site quality in premonsoon season, which almost attains the baseline level in post monsoon and perfection in monsoon season (Tomlinson et al. (Helgolander Wissenschaftliche Meeresuntersuchungen, 33, 566-572, 1980)). The geoaccumulation index shows that the metal concentrations in sediments can be considered as background levels except Cr and Cd. The geoaccumulation index shows that Cr is moderately contaminated and it is higher in offshore region in post monsoon and monsoon than premonsoon season. All the calculated indices show that Cr and Cd levels are more than the desired limits in the marine sediments. Multivariate statistical analysis evaluates the plausible sources of contaminants, attributing to mining, industrial, and urban wastes by way of Brahmani River discharging to the estuarine region.