Reconstitution paléolimnologique de l'évolution de l'état trophique de deux lacs de la région minière de Fermont (Québec subarctique, Canada)
|Abstract:||The recurring emergence of important cyanobacterial blooms at the water surface of lakes Sans Nom and Carheil (Fermont, subarctic Quebec) over the last few years raised concerns about their health as this phenomenon usually indicates an advanced eutrophication process. Some actions have been initiated in order to promote their recovery. However, little information was available concerning the evolution of their limnological condition up to now, which was limiting our understanding of the problem that was affecting them. This research project aimed to fulfill this lack of knowledge using a paleolimnological approach. The results indicate that lakes Sans Nom and Carheil had been relatively stable for thousands of years until approximately the onset of the industrial era (~ 1850 AD) when some changes progressively took place in their condition. The modifications in the diatom assemblages (microscopic algae; class Bacillariophyceae) preserved in the sediments linked to this period likely reflect regional climatic change. The declining health of the lakes is however only evident since the mid-1970s which corresponds with the establishment of the town of Fermont and the beginning of waste water inputs from the catchment. The increase in the relative abundance of diatom taxa typical of enriched environments (e.g., Aulacoseira subarctica) and the almost complete disappearance of species indicative of good ecological conditions (e.g., Discostella stelligera) coincide with other changes in geochemical proxies (e.g., carbon/nitrogen ratios) and demonstrate the increase in the water primary production. The deterioration level of the lakes remains however moderate, suggesting good prospects for recovery. The conclusions presented in this study may be used by the local authorities to guide their decision regarding the management of the water quality of lakes Sans Nom and Carheil.|
|Document Type:||Mémoire de maîtrise|
|Open Access Date:||9 July 2018|
|Collection:||Thèses et mémoires|
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