Abstract：
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 (such as that reported herein) 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 odor production, especially in sensitive, oligotrophic systems.
摘要：
蓝藻日益威胁着全球的娱乐用水和饮用水资源。它们需要动态监测，以说明与振荡垂直迁移相关的diel周期引起的分布变化。虽然这已经在海洋和富营养化淡水环境中进行了讨论，关于贫营养淡水湖中蓝藻昼夜垂直迁移的报道很少。典型的监测方案不能反映这些动态，经常只关注地表水采样方法。并忽略采样时间或建议较大的中午时间范围(例如，10AM-3PM),从而阻止了蓝藻群落动态的准确表征。为了评估昼夜迁移和水柱分层对蓝藻丰度和组成的影响，社区的特征是在一个浅层混合的湖泊中，该湖泊与土耳其湖泊流域的热分层湖泊相互连接（安大略省，加拿大）在2018年和2022年的多时间点采样系列中使用16SrRNA基因的扩增子测序。这项工作表明，蓝藻存在于贫营养湖泊中，其群落结构（i）在昼夜变化，(ii)跨越水柱的深度，（iii）在同一湖泊内每年一次，以及（iv）在同一流域内紧密相连的不同湖泊之间。它强调了整合多时间点的必要性，对湖泊和水库监测计划进行多深度离散采样指导，以描述蓝藻群落动态和信号变化，从而为与蓝藻毒素产生潜力相关的风险管理提供信息。忽略蓝藻群落动态的可变性（如本文报告的）和减少样本数量可能会导致错误的安全感和错失机会来识别和减轻营养状态的变化以及相关风险，如毒素或味道和气味的产生，特别是在敏感，贫营养系统。
