Mining legacies in the Snake River watershed: The interaction of biogeochemistry, stream ecology, and human use

Because of its extensive scale and diverse water quality, ecological, and societal consequences, acid-rock drainage (ARD) is one of the greatest environmental challenges facing the Western United States. In order to evaluate the diverse range of impacts that result from ARD contamination of natural waters, this research addressed the issue from three different perspectives.; In the first section of this dissertation, constraints imposed by ARD-contaminated waters on the burgeoning Western recreation economy are highlighted to illustrate modern societal consequences of this environmental legacy. Further, if potential climate scenarios and estimates of future mountain population growth are both eventually realized, limitations imposed by ARD-impacted water are theorized to be even more severe.; The next section considers the spatial and temporal dynamics of water chemistry within the Snake River watershed, a Colorado drainage impacted by ARD of both natural and anthropogenic origin. Snowmelt driven metal dilution was determined to be the dominant driver of seasonal variation in stream metal chemistry, and low flow periods (i.e. base-flow and drought conditions) yielded peak metal concentrations. Loss of reactive metals (e.g. Al and Fe) was characterized at multiple confluences, while less reactive metals (e.g. Zn) were transported throughout the watershed - driving the determination of ecosystem risk within downstream reaches of the Snake River.; In the third section, an in-situ, caged rainbow trout study revealed significant fish toxicity and fish stress within Snake River study sites. Trout mortality was positively correlated with concentrations of metals calculated to be approaching or exceeding toxicity thresholds (Zn, Mn, Cu, Cd). Significant metal accumulation on the gills of fish stocked at ARD impacted study sites supported an association between elevated metals and fish mortality. Observations of feeding behavior and significant differences in fish relative weights between study site and feeding treatment indicated feeding and metals-related fish stress. As such, ARD-related decreases in benthic macroinvertebrate abundance likely influence long-term survival of fish stocked in stream reaches with moderate aqueous metals levels.; Taken together, this study provides evidence for the many levels at which ARD is important for the future of communities in the mountain West.