Data for "Extreme midsummer rainfall event drives early onset cyanobacterial bloom"

The prevalence and increasing global distribution of cyanobacteria-dominated harmful algal blooms is strongly associated with changing climatic patterns and local biogeochemical and hydrological processes. Changes to precipitation frequency and intensity, as predicted by current climate models, are likely to alter bloom development and composition due to nutrient fluxes and water column mixing. However, few studies have directly documented the effects of precipitation events on cyanobacterial composition, biomass, and toxin production. In this study, we describe an early-initiated cyanobacterial bloom in Conestogo Lake, a eutrophic flood control reservoir located in southwestern Ontario, following heavy rainfall and subsequent flooding within the catchment. A surge in bioavailable phosphorus resulted in biomass increases of <i>Aphanizomenon flos-aquae</i> throughout the reservoir approximately 2 weeks post-flooding. Anabaenopeptin-A and three microcystin congeners (microcystin-LR, -YR, and -RR) were detected at varying levels across sites during the bloom period, which lasted between 3 - 5 weeks. In addition, each of the three sampled sites varied in physical and chemical properties throughout the sampling campaign suggesting different eco-zones within the reservoir that may be influenced by flow. Together, these findings indicate that water column mixing and phosphorus concentrations were the key drivers for the early cyanobacterial bloom in Conestogo Lake and further highlight the complex relationship and variability within reservoir systems. Therefore, effective management goals and mitigation strategies for bloom-related water quality impairment must be both responsive and adaptive to the complexity of drivers affecting blooms.