Poster: Heavy metals & phytoremediation

Abs # 58: Seasonal and spatial phytoaccumulation patterns of Cu and Zn in an arid watershed with AMD

Presenter:	Silk, Wendy K, wksilk@ucdavis.edu
Authors	Bambic, Dustin G (A)   Silk, Wendy K (A)   Alpers, Charles N (B)   Green, Peter G (A)
Affiliations:	(A): U.C. Davis (B): U. S. Geological Survey

Surface water, soil, and plants were sampled for a year in the semi-arid Hinckley Run watershed affected by acid mine drainage (AMD). We found a pronounced seasonal variation in [Cu] and [Zn] in stream water. The effect of the acidic, metalliferous stream on soil metal bioavailability was large but very local. That is, the metal extractable with dilute salt solution was 50 - 100 fold greater in soil found within a meter of the stream. However, the total metal content of the soil (as determined by extraction with 2 M HCl) was unaffected by the stream. Three plant species dominate the watershed: California brome (Bromus carinatus), a native grass; slender vetch (Vicia tetrasperm), a native legume; and a rye grass (Lolium multiflorum), an introduced grass. We found large differences in [Cu] among the species. Lolium shoots acquired more than 300 ppm Cu, while shoots of brome and vetch contained a maximum of 15-20 ppm Cu. This is not surprising in light of the large variation among species described in the literature. More surprising is the dramatic seasonal decrease in shoot Cu content. In both grass species, at all locations sampled, the [Cu] of the shoot tissue fell from toxic to deficient levels between February and March. In contrast, the leguminous vetch maintained rather constant shoot [Cu] throughout the growing season. The tissue metal content of the dominant plant species showed little dependence on distance from the stream bed. Overall the results cast doubt on the utility of the concept of “phytoavailability” of metals in soil, due to great variation among plant species and the seasonal trend in tissue metal content. The results demonstrate the importance of considering temporal variation in analyzing metal transport in arid environments.