Metal distribution in sediments of a drinking water reservoir: influence of reservoir morphometry and hydrodynamics

Metal(loid)s in the reservoir sediment tend to be released into the water column when encountering disturbances and thus pose threats to the aquatic system. In this study, sediment and pore water samples collected from eight cross sections in the Biliu River Reservoir (Dalian, China) were analyzed to determine the spatial distributions of six metal(loid)s and their associations with reservoir morphometry and hydrodynamics. The results show that total metal concentrations of the sediments are higher at the sites with greater water depths and are influenced by the reservoir morphometry. Mn is of great concern with respect to its increasing total concentration from the upstream sites to the dam sites. According to the improved BCR sequential extraction procedure, the acid-soluble fraction of Mn increases along the thalweg to the dam, implying the soluble Mn²⁺ in the upstream hypolimnion, and sediment is possible to be transported longitudinally by water currents. For Fe, Mn, Pb, Cu, and Zn, the reducible fraction accounts for more than 15% of the total metal concentration, which suggests that Fe–Mn (hydr)oxides could be important in scavenging these metals. High Mn concentrations in pore waters close to the dam, with an average value of more than 40 mg/L, give rise to significant Mn diffusive flux up to 296.1 mg/m²/day.