Paleo-Ecotoxicology of Yellowknife (Northwest Territories, Canada) Lakes Impacted by Historic Gold Mining Activities

This thesis explores the ecological impacts of legacy arsenic contamination on Cladocera (Branchiopoda, Crustacea) from historic gold mining in Yellowknife lakes (Northwest Territories, Canada) using a paleo-ecotoxicological approach. I examined Cladocera subfossils preserved in the modern and pre-1850 lake sediments of 23 lakes in the region, and the Daphnia resting egg bank of Pocket Lake, a highly contaminated lake in which striking ecological changes were previously recorded. Cladocera assemblage changes since pre-1850 were dependent on local, lake-specific limnological conditions. Littoral/benthic taxa dominated the cladoceran assemblage of the most contaminated lakes, while pelagic Bosmina were dominant in lakes with low arsenic. No viable Daphnia resting eggs were found in Pocket Lake, indicating that future resurrection ecology studies from Daphnia populations are not feasible. My research provides new information on the ecotoxicological effects of arsenic contamination in lake ecosystems, and the potential of using Cladocera as paleo-ecotoxicological indicators.