Sorption of 65Zn and 109Cd by seston in southern Lake Michigan

The recent sediment in Lake Michigan contains 2 to 3 times more zinc and cadmium than the precultural sediment, indicating an increase in the input rates in recent times. Rain water collected over Lake Michigan contains concentrations of zinc and cadmium at least 2 orders of magnitude higher than does the lake water, indicating the potential for increasing concentrations in the lake water. Plankton community bioassay experiments with zinc and cadmium show that increasing the ambient concentrations by factors of 5 or 10 results in adverse effects on algal primary productivity and zooplankton abundance. These observations suggest the potential for adverse environmental impacts of zinc and cadmium on the Lake Michigan ecosystem. The potential for increasing zinc and cadmium concentrations in the lake water is dependent primarily on the capacity of seston to sorb and transport zinc and cadmium to the bottom by sedimentation, and subsequent release from the sediment. We investigated the sorption of zinc and cadmium by seston collected at offshore stations in southern Lake Michigan. We conducted time-series experiments during different phases of the plankton successional cycle to evaluate the sorption kinetics under conditions of varying particle abundance and physiological condition of the plankton