GEOMORPHIC VARIATION IN TRACE METAL CONCENTRATIONS IN A FLUVIAL ENVIRONMENT, OTTAWA RIVER, TOLEDO, OHIO

Surface sediment samples were collected from a 1000 m meander reach of the Ottawa River, Ohio and analyzed for trace metals (Zn, Pb, Sr, Mn, Cu, Cr, Co, Ba, Ti, Cd, and Hg) by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) to determine the local variability in their concentrations between geomorphic features. Eight metals (Zn, Pb, Sr, Mn, Cu, Cr, Co, and Ba) show significantly different concentrations between five fluvial geomorphic features namely, flood plains, point bars, lateral bars, pools, and riffles. Among the features, flood plains and lateral bars are places where flows are decelerated due to surface roughness and vegetation cover, promoting the deposition of fine-grained sediments and organic matter. Thus, flood plains and lateral bars consistently exhibit the highest metal concentrations. The lowest metal concentrations in point bars are attributed to relatively coarse-grained sediment and low organic matter content. The difference in mean metal concentration between flood plains and point bars ranges from 5 times for Co to 12.5 times for Pb. It was found that Zn, Sr, Mn, Cu, Cr, Co, and Ba are influenced by similar transport and interaction processes, and possibly have common sources, while Pb shows a weak to non-significant association with other metals indicating either a different mode of transport or separate anthropogenic sources. The concentrations of all metals in 89% of the samples are below the Threshold Effect Level (TEL) and the Probable Effect Level (PEL), and thus sediment contamination issues are to be minor concern in this section of the river. The finding that flood plains serve as sediment-associated metals sink can have important implications for monitoring and regulation, impact assessment, and remediation of contaminated sediments in metal contaminated section of the Ottawa River or for other rivers having similar geomorphical, hydrological, and sedmentological characters.