Heavy metal pollution and potential ecological risk assessment for surficial sediments of Deepor Beel, India

The present study has been conducted for three objectives for the assessment of sediment pollution loadings and their ecological risk. Firstly, the hierarchical clustering of the raw sediment dataset was carried out, which categorized the sampling locations into three statistically significant clusters, depending on their similarities in behaviours. Clusters 1, 2, and 3 corresponded to high, moderate, and low pollution sites, respectively. The principal component analysis was then carried out on the dataset for three different seasons; pre-monsoon, monsoon and post-monsoon respectively, which showed significant temporal changes in the pollution sources. Various indices such as contamination factor, pollution load index, enrichment factor, and the geo-accumulation index showed that the wetland is most affected in the post-monsoon season as compared to other seasons. At the same time, monsoon remains the best. This was attributed to the significant increase in the wetland's water depth during the monsoon, coupled with the rise in precipitation capacity during the post-monsoon. Secondly, the potential ecological risk due to the contaminants displayed that the post-monsoon period has the greatest number of sites under the moderate risk category. In contrast, all the sites during the monsoon attributed to low risk. Also, Cd was found to be the primary contributor to ecological risk. Finally, chemical speciation analyses of all the heavy metals were conducted to determine their available forms in the sediment column. Cr, Mn, and Mg were observed to have a profoundly negative impact on aquatic ecology (available in F1 fraction in higher percentages). While Fe was predominant in reducible (F3) form, Cd was found to have equal contributions in reducible and oxidizable (F3 and F4, respectively) forms. Cu and Pb displayed typical complex characteristics of all the fractions in almost equal proportions. The results of the study indicated that although the anthropogenic interventions to the wetland have not been significant till yet, as far as the sediment contamination is concerned, it would be too late if swift and appropriate measures are not taken for restricting future probable contaminations.