Chemical and physical partitioning in contaminated stream sediments in the River Ystwyth, Mid-Wales.

This study investigates contemporary fluvial contamination of stream sediments by Pb, Zn and Cu from a mine near Aberystwyth, Wales. Of particular interest is the association between metal cations and particulate substrates and which is investigated using a selective extraction procedure. Emphasis is also placed on the difference between adsorptive phases depending on particle size. As particle size decreases the labile phase becomes dominant, with the easily and moderately reducible fraction being the major scavenging agent of soluble cations. Zinc and copper are largely held as residual rock or ore particles and are therefore expected to have a longer residence time in sediments. Recent floodplain development is difficult to interpret due to reworking of upstream metal-rich alluvium. However evidence is presented to suggest that once silt and clay size particles enter the main channel they are largely removed from the system.