Date of Award
Master of Science (MS)
Diane M. McKnight
Acid rock drainage (ARD) and acid mine drainage (AMD) are widespread problems affecting streams in the Rocky Mountain west and other areas with historic mining activity. Streams affected by ARD have low pH and elevated metal concentrations that can negatively impact aquatic biota by eliminating sensitive species and reducing the complexity of the food web. While the impacts of acid drainage on aquatic ecosystems are somewhat well documented, there has been much less investigation into how ARD affects nearby terrestrial organisms and ecosystems. A previous study in the Snake River watershed in Summit County, Colorado, showed that nestling Tree Swallows (Tachycineta bicolor) living in nest boxes had elevated metal concentrations in their tissues at sites where aquatic invertebrates also had elevated metal concentrations. It has not yet been determined whether ARD affects the behavior, survival, reproduction, or population dynamics of avian species living adjacent to ARD streams.
The objective of this study was to determine whether birds are less likely to breed near ARD- and AMD-impacted streams in the Snake River. Ingesting elevated metals, particularly toxic metals such as lead (Pb) and cadmium (Cd), may lower fecundity or survival of breeding birds, resulting in lower occupancy. To address this objective, I collected water and benthic macroinvertebrate samples from sites at both acidic and relatively pristine streams in the watershed. Samples were analyzed for concentrations of trace metals and rare earth elements (REEs), which are an emerging concern in the study area. I also conducted avian point counts at those same sites and used occupancy models to relate water quality variables to the presence of various avian species in the study area. When variables were included in the best model (as determined by Akaike Information Criterion), and those models also predicted occupancy better than models without covariates, I determined that those variables were important predictors of occupancy for a given species.
Results showed that previously reported trends of increasing dissolved metal concentrations in the study area have continued, likely due to warming summer temperatures. Dissolved metal concentrations were not good predictors of metal concentrations in benthic macroinvertebrates, due to different species from different functional feeding groups dominating acidic versus neutral streams. REE concentrations, which have rarely been studied in aquatic invertebrates, were mostly correlated with lead (Pb) concentrations in invertebrates. Concentrations of some REEs in invertebrates were as high or higher than those for cadmium (Cd) or Pb.
Avian point counts indicated that most bird species detected in the Snake River watershed were present at most sites. Occupancy models showed that the occupancy of a few habitat-specialist species (Lincoln’s sparrow, Wilson’s warbler, and white-crowned sparrow) was well predicted by the availability of shrub or forest habitat. For other species, neither habitat type nor water quality were important predictors of occupancy. There was some evidence to support further investigation of the transfer of Pb from benthic invertebrates to breeding white-crowned sparrows based on the inclusion of invertebrate Pb concentrations in the best models for this species. Overall, this study does not support the proposition that there is a need to monitor terrestrial organisms during efforts to remediate AMD streams.
Watson, Kelly Elsbeth, "Impacts of Acid Mine Drainage on Breeding Birds and Benthic Invertebrates in the Snake River Watershed, Summit County, Colorado" (2018). Environmental Studies Graduate Theses & Dissertations. 61.