Microbial community development in Base Mine Lake, the first end-pit-lake in the Alberta oil sands region

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One challenge facing the oilsands industry in Canada is reclaiming mining-impacted environments. A particular problem is the liquid tailings waste produced during bitumen extraction, which contains various chemical constituents of concern such as naphthenic acids. The long-term land reclamationplans of several oilsands mining operations include the construction of End-Pit Lakes (EPLs). These are below-grade bodies of water in surface mining pits that will eventually become integrated into local watersheds. They should ideally function in long-term containment and reclamation of tailings. At the end of 2012 Syncrude commissioned Base Mine Lake (BML) as the first full-scale pilot EPL in the oilsands region. BML contains a 50-m-deep layer of tailings overlain with a 10-m freshwater cap. The biology, chemistry, and physical properties of the lake have been intensively monitored since 2013. BML behaves in many ways similarly to a natural, seasonally stratified subarctic lake. There is an active microbial community but still a very limited colonization by higher organisms. Active management of suspended solids in the water has caused the lake has become clearer over time, leading to an increase in algal growth. The primary goals of our research project are: 1) To monitor the development of microbial communites in the lake over time. To date we have noted a gradual increase in the species diversity of higher (eukaryotic) organisms, suggesting that the lake is becoming more natural over time. 2) To understand the roles of key microbes in bioremediation of organic pollutants. Understanding these microbes and their bioremediation potentials may inform management strategies to maximize their activities. 3) To understand the increasing role of algae in the carbon cycle of the lake. The lake may be transitioning from a primarily heterotrophic system based on degradation of hydrocarbons to a primarily phototrophic system based on algal growth. This may change parameters such as oxygen status and bioremediation potential.