Date of Award
Open Access Master's Thesis
Master of Science in Environmental Engineering (MS)
Administrative Home Department
Department of Civil and Environmental Engineering
Cory P. McDonald
Committee Member 1
Noel R. Urban
Committee Member 2
W. Charles Kerfoot
Torch Lake, located in Michigan’s Upper Peninsula, was a site of copper ore processing from the 1860s through the 1960s. During this time, various mining by-products were deposited into the lake and along its shoreline, including mine tailings and associated heavy metals contaminants (e.g., copper). It was anticipated that natural sediment deposition would cover and attenuate toxic sediments over time, but a comprehensive assessment of the benthos has not been performed since a baseline survey conducted in 1999 and 2000. This study was conducted in 2018 to evaluate the current benthic community status as well as sediment composition and metal concentrations, in order to evaluate natural recovery and spatial drivers of community density.
In comparison with the baseline, an overall increase in macroinvertebrate densities was observed and recovery rates are spatially variable. Macroinvertebrate densities were depth-dependent and exhibited a northeast gradient across the nearshore of the lake. Greatest densities occurred along the eastern shoreline and near the main tributary, while the lowest densities may be influenced by proximity to historical mining activity along the western shoreline. The northern basins, near the main tributary input, were significantly greater in macroinvertebrate density from nearshore sites in the lake’s main basin. Habitat quality in the northern basins sites was highly heterogeneous and drivers of macroinvertebrate density in this region include currents and increased sediment deposition zones.
The relative effects of mine tailings and metal toxicity on macroinvertebrate density are modulated by spatially dependent physical and chemical properties in the nearshore, as well as the depth dependence of sediment composition between the offshore and nearshore. Considering habitat variability in future sampling efforts would facilitate a more complete assessment of environmental drivers of benthic conditions and recovery. In addition, an appropriate reference site is needed to more effectively gauge the degree of benthic degradation and to provide future restoration targets for the AOC and potential BUI removal.
Leach, Anya Clare, "ASSESSING BENTHIC RECOVERY IN THE TORCH LAKE AOC", Open Access Master's Thesis, Michigan Technological University, 2019.