John Wiley & Sons, Ltd.

Reconstructing the ecological impacts of eight decades of mining, metallurgical and municipal activities on a small boreal lake in northern Canada

As a result of long‐term metal mining and metallurgical activities, the sediment of Ross Lake (Flin Flin, MB, Canada) is highly contaminated with metals and other elements. Although it is likely that effluents were discharged into Ross Lake as early as the late 1920 s, lake biophysical data were not collected until 1973, more than four decades after the onset of mining and municipal activities. The early influence of these activities on the ecology of Ross Lake is unknown, as are the effects of improvements to metallurgical effluent quality and discontinuation of municipal wastewater discharge into the lake's north basin. To address this knowledge gap, analyses typical of paleolimnological investigations were applied to cores of sediment collected in 2009 from the south basin of Ross Lake. Stratigraphic analyses of physicochemical sediment characteristics (e.g., the concentrations metals and other elements, organic carbon organic nitrogen, δ13C and δ15N values) and subfossil remains (diatoms, Chironomidae, Chaoborus, and Cladocera) were used to infer historical biological and chemical changes in Ross Lake. With the onset of mining activities, concentrations of various elements (e.g., arsenic, chromium, copper, zinc, and selenium) increased dramatically in the sediment profile, eventually declining with improved tailings management. Nevertheless, concentrations of metals in recent sediments remain elevated compared to pre‐industrial sediments. Constrained cluster analyses demonstrated distinct pre‐ and post‐industrial communities for both the diatoms and chironomids. The biodiversity of the post‐industrial diatom assemblages were much reduced compared to the pre‐industrial assemblages. The post‐industrial chironomid assemblage was dominated by Chironomus and to a lesser extent by Procladius, suggesting that Ross Lake became a degraded environment. Abundances of Cladocera and Chaoborus were severely reduced in the post‐industrial era, likely due to metals toxicity. Overall, improvements to the management of both metallurgical and municipal effluent are reflected in the physicochemical sediment record; nevertheless, the ecology of Ross Lake remains impaired and shows minimal signs of returning to a pre‐industrial state. Recommendations are made regarding possible future investigations at this site and the need for a framework to help assess causation using paleolimnological and other site data. This article is protected by copyright. All rights reserved

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