Research Feature
The impact of diurnal fluctuations on accurate characterization of risk

Key messages

  • Cyanobacteria experience diurnal fluctuations in water column position which may be more sporadic than anticipated

  • Cyanobacterial communities can vary significantly between interconnected lakes requiring tailored sampling protocols to reflect this diversity

  • Significant changes in cyanobacterial community structure and abundance can be observed between different sampling years signifying higher risk and the crucial need for monitoring

Water Treatment Costs Reduced by
per cent

Summary

Cyanobacteria increasingly threaten recreational water use and drinking water resources globally. They require dynamic monitoring to account for variability in their distribution arising from diel cycles associated with oscillatory vertical migration. While this has been discussed in marine and eutrophic freshwater contexts, reports of diurnal vertical migration of cyanobacteria in oligotrophic freshwater lakes are scant. Typical monitoring protocols do not reflect these dynamics and frequently focus only on surface water sampling approaches, and either ignore sampling time or recommend large midday timeframes (e.g., 10AM-3PM), thereby preventing accurate characterization of cyanobacterial community dynamics. To evaluate the impact of diurnal migrations and water column stratification on cyanobacterial abundance and composition, communities were characterized in a shallow well-mixed lake interconnected to a thermally stratified lake in the Turkey Lakes Watershed (Ontario, Canada) using amplicon sequencing of the
16S rRNA gene across a multi-time point sampling series in 2018 and 2022. This work showed that cyanobacteria are present in oligotrophic lakes and their community structure varies: (i) diurnally, (ii) across the depth of the water column, (iii) interannually within the same lake, and (iv) between different lakes that are closely interconnected within the same watershed. It underscored the need for integrating multi-timepoint, multi-depth discrete sampling guidance into lake and reservoir monitoring programs to describe cyanobacteria community dynamics and signal change to inform risk management associated with the potential for cyanotoxin production. Ignoring variability in cyanobacterial community dynamics and reducing sample numbers can lead to a false sense of security and missed opportunities to identify and mitigate changes in trophic status and associated risks such as toxin or taste and odour production, especially in sensitive, oligotrophic systems.


Publications

Sporadic diurnal fluctuations of cyanobacterial populations in oligotrophic temperate systems can prevent accurate characterization of change and risk in aquatic systems. https://www.sciencedirect.com/science/article/pii/S004313542400099X
Photo: Working onsite with partner X.

Contributors

University of Waterloo:
Ellen Cameron
Anjali Krishna
Monica Emelko
Kirsten Müller
Support in sample collection/site access  to Turkey Lakes Watershed provided by Environment and Climate Change Canada (2018 sampling season) and Natural Resources Canada (2022 sampling season).