Seasonal changes in composition of the cyanobacterial community and the occurrence of hepatotoxic blooms in the eastern townships, Québec, Canada

Abstract

Four eutrophic lakes in the eastern townships (Québec, Canada) were sampled on a biweekly basis between May and October 2001 to examine seasonal changes, and to study the role of taxonomic and environmental factors in cyanobacterial toxin production. Microcystin-LR (MC-LR) equivalent content was determined using a protein phosphatase inhibition assay on extracts of lyophilized plankton. Three of the lakes showed a similar pattern of maximum water column toxicity in late summer, while in the fourth, toxicity was highest in spring and then declined over the year. Variations in water toxicity level could be attributed to the abundance of two potentially toxigenic genera, Microcystis and Anabaena. A multiple regression model explained 75% of the variation in microcystin (MC) concentration, based on water column total nitrogen concentration (TN) and the biomass of these two genera. Microcystis and Anabaena genera appeared to be similarly toxic in all lakes. Increased water column stability, higher light extinction coefficient and a lack of dissolved nutrients were all associated with increased total biomass of toxigenic cyanobacterial genera. © The Author 2005. Published by Oxford University Press. All rights reserved.