The effect of a large resuspension event in Southern Lake Michigan on the short-term cycling of organic contaminants

In January and March, 1998, a series of intense, northerly wind-driven storms suspended sediment over the entire coastline of the southern basin of Lake Michigan. The effect of large scale resuspension on organic contaminant cycling was investigated using a two-pronged sample collection strategy that included analysis of settling sediment trap material and discrete air and water samples collected before and after a major resuspension event. It was found that major resuspension events result in a large flux of contaminants. For example, 6.2 ng/cm(2) SigmaPCB (sum of 89 congener peaks) and 175 ng/cm(2) SigmaPAHs (sum of 31 compounds) fell through the water column in the southern basin between November and May but almost half of that occurred in the month of March after a series of intense storms induced a large-scale resuspension event in that month. Assuming the concentration of contaminants in settling sediments is similar throughout the basin, the March event brought similar to400 kg of SigmaPCBs and similar to13,000 kg SigmaPAHs into the water column. Furthermore, the data indicate that concentrations of dissolved phase SigmaPCB and SigmaPAHs declined significantly (alpha = 0.05) after the event and after resuspended sediment had settled from the surface waters. As a result of the depressed dissolved concentrations at the surface, the potential for gas-phase input to the lake increases on the southwestern coastal region near Chicago, IL and Gary, IN. The potential input of gas-phase contaminants was 8 kg for SigmaPCBs and 2,200 kg for SigmaPAHs over the 40-day lifetime of the near-shore event.