Étude sur les mésocosmes au Petit-Lac-Saint-François et à la Baie Missisquoi : influence des nutriments azotés sur les cyanobactéries

Blue-green algae, or cyanobacteria, can dominate plankton communities to form blooms, which can be toxic. However, the factors that trigger the production of toxins by cyanobacteria are not fully understood. The objective of this study was to assess and compare the impact of various forms of nitrogen on the production of cyanotoxins. To achieve this, mesocosms were installed in two lakes in the Southeast region of Quebec province in 2017 and 2018 at the end of the summer, when blooms were more present. Five experiments were conducted for this research: 2 at Petit-Lac-St-François (PLSF) and 3 at Missisquoi Bay. Each test included control mesocosms with no added nutrients and mesocosms injected with one of the following forms of nitrogen: nitrate, nitrite, ammonium or urea. Samples were taken at the beginning of the experiment (time zero) and 48 hours after the addition of nutrients. Samples were analyzed for: toxin concentrations, taxonomic counts, specific nutrient concentrations and, for the 2017 tests, toxic gene copy numbers.