Inorganic Chemistry of Particulate Matter from the Nearshore Zone of Lake Michigan

Particulate matter from a nearshore region of southeastern Lake Michigan serves as a sink for trace metals and a conveyor of trace metals to the sediments. Fe, K, Mg, and Mn are always more concentrated in the hypolimnion than in the epilimnion, and Ca, Cr, Cu, Na, Sr, Zn, and total P are generally more concentrated in the hypolimnion than in the epilimnion. Enrichment of these metals in the hypolimnion particulates is attributed to sediment resuspension. Comparison of trace metal concentrations in the particulates with those in phytoplankton and zooplankton indicates that the plankton are not a significant contributor to the trace metal particulate chemistry of this nearshore region. Significant fractions (33% to nearly 100%) of total Cr, Cu, Fe, Mn, and Zn concentrations in the water column are associated with particulates.During the warmer months, calcium carbonate precipitates. Particulate chemistry changes little with the CaCO₃ formation, with the exception of an increased amount of calcium. Variations in the concentrations of trace metals are controlled either by both dolomite and hydrated manganese oxides or by an unknown phase believed to be organic in nature.