GEOMORPHOLOGY OF HEAVY-METALS IN THE SEDIMENTS OF QUEEN-CREEK, ARIZONA, USA

Data from Queen Creek, a dryland stream in southcentral Arizona, show that the distributions of heavy metals (especially Cu, Pb, Zn, and V) in sediments are strongly related to the spatial aspects of fluvial processes. Cu/Zn and Cu/V ratios permit discrimination between materials polluted by eroded mine tailings and those containing only erosion products from the surrounding metalliferous terrain. In stratigraphic sections, metal ratios discriminate between pre-industrial alluvium and post-industrial flood deposits. On valley floors, channels and active alluvium have the highest metal concentrations, while other process environments have decreasing amounts associated with decreasing frequencies of inundation. Materials from the mine tailings become progressively diluted with increasing distance from the source. Metals appear to be chemically stable once they are precipitated and adsorbed in the alkaline dryland conditions. Spatial variability of metal concentrations are more important than variability associated with particle size in explaining the fate of contaminants in the fluvial sediment system.