Human impact on fluvial sediments: how to distinguish regional and local sources of heavy metals contamination

Regional contamination of southern Moravia (SE part of the Czech Republic) by heavy metals and magnetic particles during the 20th century was quantified in fluvial sediments of the Morava River. The influence of local sources to the regional contamination of the river sediments and impact of sampling sites heterogeneity were studied in profiles with different sedimentology (facies) and lithology. For this purpose, hundreds of samples were obtained from regulated channel banks and naturally inundated floodplains and proxy elementary analyses have been carried out by X-ray fluorescence spectroscopy (ED XRF), further calibrated by ICP MS. Magnetic susceptibility as a proxy of industrial contamination was determined and the age model has been obtained by 210Pb dating method. After establishing the lithological background from floodplain profiles, assessment of heavy metal contamination was done by using enrichment factors (EFs) of heavy metals (Pb, Zn, Cu, Cr) and magnetic susceptibility. Floodplain sedimentary profiles were found to be realiable for assessment of contamination and reconstruction of large scale, i. e. a really averaged regional contamination, while regulated channel banks are suitable for obtaining of more or less qualitative information of influence of local point sources in the area because sediments from regulated river banks qualitatively reflect the actual local contamination of the river system. It allowed us to distinguish the influence of local sources of contamination by comparing with more spatially averaged contamination signal from more distal floodplain profiles. The study area is rather weakly contaminated (EF similar to 1-2), while individual sediment strata from regulated channel banks contains several times larger concentrations of heavy metals.