Effects of metals and arsenic on riparian communities in southwest Montana.

: Concentrations of metals and arsenic in floodplain soils of Silver Bow Creek and the upper Clark Fork River in southwest Montana were related to phytotoxic responses by individual plants in laboratory experiments, vegetative community structure and composition in the field and wildlife habitat. Samples collected from barren or very sparsely vegetated mixed mine tailings and alluvium deposits (slickens) in the floodplains along Silver Bow Creek and the Clark Fork River had concentrations of As, Cd, Cu, Pb and Zn that were significantly elevated relative to reference sites. Laboratory phytotoxicity tests demonstrated severe and rapid effects of the elevated concentrations of metals and As on hybrid poplar and standard test species (alfalfa, lettuce and wheat): growth inhibition of hybrid poplars was nearly 100% and of standard test species ≥75%. Vegetation community measurements revealed that slickens have replaced riparian forest, shrub, hay fields and pasture land; in doing so, the slickens have reduced both the compositional and structural heterogeneity of the riparian habitat. This reduction in habitat complexity has reduced the capacity of the area to provide a diversity of suitable wildlife habitat.