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 relate d to phytotoxic responses by individual plants in laboratory experimen ts, vegetative community structure and composition in the field and wi ldlife habitat. Samples collected from barren or very sparsely vegetat ed mixed mine tailings and alluvium deposits (slickens) in the floodpl ains along Silver Bow Creek and the Clark Fork River had concentration s of As, Cd, Cu, Pb and Zn that were significantly elevated relative t o reference sites. Laboratory phytotoxicity tests demonstrated severe and rapid effects of the elevated concentrations of metals and As on h ybrid poplar and standard test species (alfalfa, lettuce and wheat): g rowth inhibition of hybrid poplars was nearly 100% and of standard tes t species greater than or equal to 75%. Vegetation community measureme nts revealed that slickens have replaced riparian forest, shrub, hay f ields and pasture land; in doing so, the slickens have reduced both th e compositional and structural heterogeneity of the riparian habitat. This reduction in habitat complexity has reduced the capacity of the a rea to provide a diversity of suitable wildlife habitat.