Biogeochemical evidence of eutrophication and metal contamination of Frame Lake, City of Yellowknife, Northwest Territories, Canada

The sediments of Frame Lake, Yellowknife, NWT were examined to evaluate human impact due to urbanization and mining and provide background information for potential remediation efforts. Physical and geochemical analyses were carried out on cores from two sites targeting the lake’s deep basins. Pb-210 analysis was used to establish chronological control and determine recent sedimentation rates. Frame Lake contains sediments spanning the whole of the Holocene from the time of deglaciation to the present. With the development of the city and increasing human population over the last ~80 years Frame Lake has become increasingly eutrophic. The source of nutrient loading is generalized and probably not exceptionally high; however, due to its limited depth, extensive winter ice cover and low turnover rates, the lake appears to be sensitive to the resulting biological oxygen demand. Frame Lake sediments were found to contain elevated concentrations of metals attributable to gasoline combustion (Pb), mining and ore processing (e.g. As, Cu) and other sources (Zn). While most of these elements peak below the sediment surface and contamination has decreased in recent years, concentrations remain above levels recommended for the protection of aquatic life. It is apparent that contaminants previously deposited within the catchment are still supplying the lake and in the case of As, that post-depositional translocation within the sediments is taking place.