RETENTION OF METALS IN A FLOODPLAIN ENVIRONMENT, OTTAWA RIVER, NW OHIO

Trace metals within floodplain and terrace sediments collected along the Ottawa River of the Wildwood Metro Park in Toledo, Ohio were investigated to determine the relative contribution of typical metal binding constituents in controlling metal distribution. Sediment cores were collected along a transect moving away from the river to determine the impact of distance from the river channel. All samples were sequentially extracted to determine the distribution of metals between the exchangeable, carbonate, oxide, and organic phase. The amount of organic matter (OM), sand, silt and clay were also determined. The exchangeable phase contains the most easily leached and bio-available metals and was the dominant phase for Sr and Cd. The carbonate phase represents acid soluble metals and contained the most significant amounts of Ba, Sr and As. Metals co precipitated, occluded, or adsorbed to hydrous oxides represent the reducible, or oxide phase. The oxide phase was found to be primarily responsible for the retention of Co, Fe, Mn, Ni, Pb, Se, and Zn. The fourth, and most strongly bound metals, is the organic phase. The metals which were found primarily in this last extraction were Al, As, Cu, Mo, Ni and Se. Ba, Cd, and Sr were found in multiple phases, with Cd being associated with oxide/exchangeable and Sr in exchangeable/carbonate phase. Metal behavior showed both positive and negative correlations to %OM, %clay and %silt, and distance from river. Al, Fe, and Mo all displayed negative correlations to both %OM and clay content and exhibited no pattern with increasing distance from the river channel. Ba, Cd, Cr, Mn, Se, and Sr all displayed strong positive correlations and increased with increasing distance from river. As, Co, Cu, Ni, Pb, and Zn all show a weak correlation to %OM and %clay and exhibited no change with distance from river. With the exception of Al, Fe, Mo, and Pb, metal concentrations were higher in the floodplain samples relative to the terrace samples.