Distribution of Pb, Zn, Cu, Ni, and As in Riparian Soils, Streams and Upland Areas in An Urbanized Alabama Watershed.

Sediment and water transport and redistribution along urban streams are major riparian soil processes that affect soil and water chemistry of watersheds. Urbanized watersheds typically generate runoff with high pollutant loads that end up in the drainage ways. This study was carried out to evaluate the importance of riparian soils with respect to water and soil quality protection using a watershed case study in North Alabama. Five sampling sites (grouped into upstream, midstream and downstream locations) along the Aldridge Creek in North Alabama were identified for collecting riparian soil samples and stream water samples for Pb, Zn, Cu, Ni, and As analysis. The results indicated that the trace metal concentrations of riparian soils were greater than those of sediments. Trace metal concentration in the riparian soils varied from 20-34 µg/g soil for Pb, 50-85 µg/g soil for Zn, 6-17 µg/g soil for Cu, 11- 18 µg/g soil for Ni and 5-21 µg/g soil for As. The metals concentrations in the riparian soils were 7-55% higher than that of the upper slopes indicating that the riparian zone is a potential source or sink of the metals along the flow pathways between the upper slope soils and the stream.  Although the concentrations of Zn (6-13 µg1^-1), Cu (17-19 µg1^-1) and Ni (19-21µg1^-1) in the stream water were not elevated, As (27-39µg1^-1) and Pb (16-19µg1^-1) concentrations exceeded USEPA maximum contaminant level guidelines. Whereas there were significant differences in the distribution of trace metals in soils between the Upslope and Riparian soil locations at the Upstream, Midstream, and Downstream Sites, there was no significant difference in the stream water trace metals concentration between the sites in the watershed.