Heavy metal storage in near channel sediments of the Lahn River, Germany

Heavy metal pollution in urban, industrial, and mined watersheds of Europe is well documented, but less is known about metal contamination in agrarian watersheds or those with no history of mining. Along a 75-km reach of the Lahn River, central Germany, near-channel flood-plain sediments (<5 m from the active channel) have mean concentrations of Cd, Cu, Pb, and Zn that exceed background values. Vertically, metal concentrations are highest at 15 or 20 cm below the flood plain. Although mean metal concentrations in the watershed are below mean values found in more industrial watersheds of western Europe, individual near-channel sites along the Lahn River have metal concentrations approaching those found in more urbanized drainage basins. Several sites along the Lahn are “excessively contaminated” with Cd and “moderately/strongly” contaminated with Cu, Pb, and Zn. Metal concentrations are generally higher and more variable downstream from metal-producing locations and in the vicinity of industrial facilities. Topographic and geomorphic factors appear to have minimal influence on near-channel metal concentrations. The elevated concentrations of metals in geomorphically sensitive channel banks and near-channel sediments raise the possibility of future metal pollution in the Lahn River watershed even as metal emissions to the environment decline.