Geochemical associations and grain-size partitioning of heavy metals in lacustrine sediments

Abstract

A sequential extraction scheme is utilized to determine the geochemical fractionation of Fe, Mn, Cr, Cu and Zn in different grain size classes for sediment samples collected from within and around Little Traverse Bay, Lake Michigan. The partitioning of Fe, Cr and Cu in both sediment and presently-eroding coastal bluff samples are similar. Also, the concentrations of these metals in fine-grained particles are not proportional to the increased surface area of these grains compared with larger grain sizes. Both of these results indicate that these metals have undergone little authigenic change since entering the lacustrine environment. However, sediment Zn concentrations are significantly higher than in coastal bluff samples, and also have a different geochemical fractionation. This result is attributed to the precipitation of Zn in authigenic phases. In general, Mn shows relatively little mobility in the bay's oxidizing environment, except in areas where Mn nodules are forming.