Recent changes in heavy metal contamination at near-channel positions of the Lahn River, central Germany

Short-term monitoring of heavy metal concentrations along rivers affords the opportunity to examine the persistence of contaminants in the fluvial environment. This paper examines changes in the concentrations of Cu, Pb, and Zn at near-channel positions along a 75-km reach of the Lahn River, an agrarian watershed in central Germany, between 2000 and 2007. Thirty-three sites sampled in 2000 were re-sampled in 2007 in order to document changes in trace metal contamination. The concentrations of Cu and Pb decreased between 2000 and 2007, whereas the concentration of Zn was statistically unchanged. The Pb concentration decreased at 82% of the sample sites over the study period, whereas Cu concentrations decreased at 70% of the sites. Site-to-site variation in the concentrations of Pb with distance downstream from potential source areas declined between 2000 and 2007. The downstream variation in Cu also decreased over the study period, albeit to a lesser degree. The decrease in Pb, and to a lesser extent Cu, concentrations adjacent to the Lahn River appears to reflect the recent reductions in the release of trace elements to the environment. Zinc concentrations were unchanged, suggesting that it is derived from different sources than are Cu and Pb or is cycling through the watershed differently than Cu and Pb. Lower concentrations of Cu and Pb in channel bank sediments translate to a reduced risk of future downstream heavy metal pollution in the study area.