Legacy impacts of historical gold mines on the cladocera assemblages of two Nova Scotian lakes

Abstract

Historical gold mines in Nova Scotia released toxic tailings into nearby environments from the 1860s to ~1945. Tailings high in contaminants, such as arsenic and mercury, were disposed of, untreated, into nearby surface waters, which can negatively impact ecosystems and biota. There are now ~360 inactive gold mines from 64 mining districts throughout Nova Scotia and little is known regarding the long-term ecological harm historical mining has caused. I used a paleolimnological approach for two Nova Scotia lakes located downstream of historical gold mines, to investigate contaminant levels within sediment cores before, during and after the mining periods. I then examined Cladocera assemblages to determine the bioindicator responses to environmental changes associated with mining, as well as post-mining stressors such as urbanization and climate change. Changes in contaminant concentrations and zooplankton assemblages were more pronounced at deep and oligotrophic Lake Thomas, as opposed to shallow and dystrophic Gegogan Lake. Cladoceran assemblages showed statistically significant (P < 0.05) differences between the pre-mining, mining, and post-mining periods at both study lakes. Sedimentary mercury levels peaked at ~6 and 65 times Canadian Council of Ministers of the Environment (CCME) guidelines, and ~165 and 58 times for arsenic, at Gegogan Lake and Lake Thomas, respectively. While geochemical recovery is underway, my findings can inform decisions regarding development of areas near historical mines and management of aquatic ecosystems impacted by mining contaminants