La prolifération de cyanobactéries en réservoir tempéré nordique (le Lac Saint-Charles, Québec, Canada): variabilité et facteurs de contrôle
|Advisor:||Laurion, Isabelle; Vincent, Warwick F.|
|Abstract:||The occurrence of harmful blooms of cyanobacteria in freshwater ecosystems is subject to growing public as well as scientific concern. An improved understanding of the factors controlling the proliferation of bloom-forming taxa is an essential requirement for the adequate prediction and management of this water quality problem. The overall objective of this thesis was to understand the cyanobacterial community dynamics of a north-temperate reservoir. The Lake St. Charles reservoir is a major source of drinking water for Quebec City, Canada, and cyanobacterial blooms have appeared episodically in the lake since autumn 2006. Physical, chemical and biological variables were measured over 5 consecutive summers (2007-2011). This confirmed the mesotrophic status of the lake, and underscored the large interannual variation in limnological conditions that provided intermittently favorable conditions for cyanobacterial growth and dominance. There were pronounced variations in cyanobacterial community biomass and structure among the 5 years, including in the dominant species (Microcystis aeruginosa, Anabaena flos-aquae and Aphanocapsa/ Aphanothece sp.). In addition, large differences in community biomass and composition were observed spatially, with significantly higher cyanobacterial concentrations in the north relative to south. These results indicated that there were contrasting environmental controls (phosphorus, temperature, stability of the stratification) acting on the different taxa of cyanobacteria. This large spatial and temporal variability also reflects the dynamic nature of high through-flow reservoirs such as Lake St. Charles. In situ sediment mapping implied that benthic resting cells, if present, were mostly below detection at all sites. This low potential to inoculate the water column from sediments contrasts with many lakes affected by cyanobacteria blooms and indicates the potential for a rapid response to nutrient loading control in the Lake St. Charles watershed. This research has highlighted the markedly dynamic nature of freshwater reservoirs, their potential sensitivity to eutrophication despite a short hydraulic residence time, and the need for continuous monitoring in order to detect the appearance of bloom-forming cyanobacteria.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||19 April 2018|
|Collection:||Thèses et mémoires|
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