Sediment heavy metal speciation of Hirakud Reservoir—a Ramsar site in Mahanadi River in India

Abstract

Heavy metal speciation is an important tool for the assessment of sediment quality. This work was conducted to investigate the geochemical occurrence, distribution, and spatial variability of sediment heavy metals in the Hirakud Reservoir (a Ramsar site) of the Mahanadi River in India. Estimation based on a single-extraction (speciation) method revealed the dominance of Fe–Mn-bound (39.33%) fractions suggesting the potential mobility of heavy metals. Co-dominance of residual (35.03%) and organic matter–sulfide (23.02%) fractions indicate lattice-bound associations of elements under natural conditions and suggest anthropogenic organic input contribution respectively. The heavy metals distribution was spatially affected (p < 0.05). While, Ag, Cd, Hg, and Mo displayed extremely severe enrichment (EF > 50) and very strong geo-accumulation conditions (I_geo > 5); Cd and Hg displayed very high ecological risk (ERF > 320). However, the contamination factor for all heavy metals except Cd and Hg showcased low contamination (CF < 1). The principal component and cluster analysis revealed that the source of Mn, Mo, Hg, and Ag was mainly from anthropogenic or biogenic origin. The Fe and Al however displayed signs of being derived from multiple sources. However, the risk assessment code (RAC) results suggest that As exhibited a medium to very high risk (11 < RAC < 30) of bio-availability. Thus, the results of this study can be used for the formulation of strategies for the reduction of anthropogenic loads, planning for sediment quality management, and regular monitoring to curb the rising pollution issues of the reservoir.