Lakes of the Bécancour River basin (southern Quebec, Canada) are in a precarious state since many decades as they are suffering from high sediment loads and advanced eutrophication. This situation affects the socio-economic and touristic potential of the neighbouring municipalities and is inconvenient for their residents as it impacts water supply, resort activities and recreational uses (e.g., swimming, fishing, boating).
Past asbestos mining activities that happened during more than a century in the Thetford Mines region and the mine tailings left on the ground by this industry have often been pointed out to partly explain the bad condition of the Bécancour River basin. Other activities, such as the waste water discharges, have also been blamed. The human context in which the lakes have evolved is however complex and information is lacking on the changes that the water bodies underwent through time. Therefore, it is hard to identify with certainty the factors that are responsible for the problems nowadays observed in the Bécancour River basin. The research project aims to measure the real impact of the mining activities and human development on the high sediment loads and accelerated eutrophication problems observed in the lakes from the river network by closely studying their limnological and sedimentological evolution using a paleolimnological approach based on the analysis of sediment cores.
In particular, the study aims to reconstruct the evolutionary history of pond Stater, and Lakes Bécancour, à la Truite, William and Joseph, which all correspond to current or historical extensions of the Bécancour River. The specific objectives of the research project are to 1) Define the pre-anthropogenic characteristics of the lakes and their natural variability in order to establish a reference framework; 2) Reconstruct the evolution of their trophic state, and the variations in their sediment accumulation rates and their general condition in relation to the history of the mining activities and human development of the territory in order to identify with certainty the causes of the high sediment loads and accelerated eutrophication problems; 3) Evaluate their deterioration level in order to determine if their bearing capacity has been exceeded. In order to achieve these objectives, the lake sediments are analyzed using different physical, geochemical and biological proxies coupled with radiometric dating.
The new knowledge generated by the research project will result in recommendations that will help the decision-making of the local authorities and organizations in their efforts for the preservation and restoration of the lakes from the Bécancour River basin. The new insights gained into the limnological and sedimentological history of these water bodies will allow a complete revision of the elements that have to be prioritize and done in order to improve their general condition. In a broader context, the research project will also result in an important paleolimnological reference dataset that will contribute to a better understanding of the impacts of the asbestos mining activities and their residues on the aquatic ecosystems, and of the mechanisms of cultural eutrophication in a complex context of human activities.
