Heavy metal trends in floodplain sediments and valley fill, River Lahn, Germany

Sampling along the River Lahn, a major tributary to the River Rhine that fl ows through an agrarian region of west-central Germany, reveals that heavy metal pollution occurs outside major industrial regions and mined landscape s. Along a 60-km reach of the river between Marburg and Wetzlar, mean conce ntrations of Cu, Pb and Zn at depths of 5 and 15 cm in four floodplain tran sects were greater than background levels. Concentrations declined sharply between 15 and 25 cm. Laterally, concentrations peaked at the bank top and in the near-channel zone of the floodplain. Beyond the near-channel zone (g enerally up to 100 m from the channel) concentrations were much less and fa irly uniform to the valley wall. The clustering of metals close to the chan nel suggests that they are a fluvial rather than an eolian deposit. During floods of a moderate magnitude, sediments and attached metals are deposited soon after the river overtops its banks. Although the overall store of met als in the valley is less than that along the Rhine, near-channel metal con centrations are similar to those along rivers draining major industrial and mined areas. (C) 2000 Elsevier Science B.V. All rights reserved.