Impacts of legacy contaminants from historic gold mining on lakes in Dartmouth, Nova Scotia

Abstract

Historic gold mining activities in Nova Scotia (Canada) occurred prior to modern waste management practices and contaminants were released into the environment. One notable example is the Montague Gold Mine which operated from 1863–1940. Although environmental monitoring data are sparse, nearby freshwaters likely received contaminants from past mining activities through inputs from surface waters and the atmosphere. To investigate the long-term effects of historic gold mining practices on lake ecosystems, I examined zooplankton remains and sediment geochemistry archived in dated sediment cores from impacted (Lake Charles) and reference (Loon Lake) lakes. Sedimentary concentrations of arsenic (As) were used to infer past mining activities. Sedimentary chlorophyll-a concentrations were used as a proxy of trends in lake primary production. Cladoceran assemblages of both lakes were significantly different (p < 0.05) during the time period of mining, compared to pre- and post-mining periods. Geochemical and zooplankton changes were most extreme in Lake Charles, which recorded levels of As contamination that exceeded sediment guidelines by, on average, 300 times since gold mining began. Despite the Montague Gold Mine closing 80 years ago, modern bioindicator and geochemical measures differ from the pre-mining periods, suggesting that past mining activities and likely also recent anthropogenic stressors, have impacted lake ecosystems.