Characterization of Cyanobacterial Communities in Lakes Requires Consideration of Diurnal and Spatial Variation

Distribution of cyanobacteria is impacted by several factors, including water column mixing and buoyancy regulation responses to light availability that create oscillatory diurnal migration patterns within the water column. These dynamic fluctuations are not typically reflected in monitoring protocols, which frequently focus on surface depths and either ignore sampling time or recommend large midday timeframes (e.g., 10AM-3PM), thereby precluding accurate characterization of cyanobacterial communities. While diurnal vertical migration of cyanobacteria has been reported in marine and eutrophic freshwater systems, reports in oligotrophic freshwater lakes are scant and characterization have focused on individual 24-hour periods neglecting to consider day-to-day variability. To evaluate the impact of diurnal migrations and water column stratification on cyanobacterial abundance, communities were characterized using a multi-time point sampling series across a 48-hour period in a shallow well-mixed lake interconnected to a thermally stratified lake in the Turkey Lakes Watershed (Ontario, Canada). Amplicon sequencing of the V4 region in the 16S rRNA gene was performed to characterize microbial community composition.