Trace metal concentrations along tributary streams of historically mined areas, Lower Lahn and Dill River basins, central Germany

Abstract

Watersheds with a history of mining frequently have high concentrations of trace metals stored in downstream floodplain sediments. To assess the contribution of tributary streams to the elevated trace metal concentrations previously documented along the lower Dill and lower Lahn Rivers of central Germany, I examined the concentrations of Cu, Pb, and Zn in fourteen cores collected from near-channel sediments along 9 tributary streams. Five tributaries empty into the lower Dill River and 4 drain into the lower Lahn River. The tributary streams drain areas that were mined for Fe, Cu, and Pb for more than a century, with the last mine closing in 1983. Cores were also collected from near-channel sediments at 7 sites along the lower Lahn River to more broadly assess the storage of trace metals along the river. Large quantities of Cu, Pb, and Zn from mining activity are not stored in near-channel positions along the length of the sampled tributaries. Mean and median concentrations of Cu, Pb, and Zn along the tributaries are less than the mean and median concentrations along the lower Dill and Lahn Rivers; concentrations along the tributaries differ little from background trace metal levels and are less than contamination standards contained in the German Federal Soil Protection Act. The mean concentrations of Cu, Pb, and Zn along the lower Lahn River are greater than background concentrations and mean concentrations exceed contamination standards from the German Federal Soil Protection Act. Tributary streams are not a source for the elevated trace metal concentrations found along the lower Dill and Lahn Rivers and mined areas will likely not serve as a source of future heavy metal pollution. The results of this study indicate that the mining process did not release large quantities of metals to the fluvial system.