Airborne trace metal contamination of wetland sediments at Indiana Dunes National Lakeshore

For more than 100 yr, the wetland sediments at the Indiana Dunes National L akeshore (IDNL) and adjacent Indiana Dunes State Park have received atmosph eric input of trace metals from industrial sources located upwind and to th e west. This study documents the trace metal pollution of these sediments, both areally and with depth, and identifies trends in metal distribution an d mobility. Twenty-five wetland sediment cores were taken across IDNL, at v arying distances from the principal industrial sources, and from environmen ts with different disturbance histories land thus different hydroperiods). Strong-acid extractable concentrations of Cd, Cr, Cu, Mn, Ni, Pb, Se, and Z n were determined at intervals for each of the cores. Total metal extractio ns and a Pb-210 chronology also was determined for one of the cores. Metal concentrations in near-surface sediments are comparable to those found in o ther soils and sediments in the region, and show surficial enrichment over background levels; including Zn concentrations as high as 1700 ppm, Pb as h igh as 280 ppm, and Mn as high as 2700 ppm. Surficial sediment concentratio ns of Pb, Zn, Cr, and Cu are elevated at sites in close proximity to anthro pogenic sources, while the other metals do not exhibit a trend in concentra tion with distance from sources. Lead, Cr, and Cu appear to be relatively i mmobile after deposition, while Cd, Ni, and Se appear to have some mobility . The duration and/or frequency of flooding appear to be important in deter mining the mobility of Zn and Mn. The findings of this research provide imp ortant insight into the effects of cumulated human impacts on wetland syste ms, and can serve as an aid in the planning of wetland restoration projects , several of which are currently underway at IDNL.