The risk of human exposure to cyanotoxins is partially influenced by the location of toxin-producing cyanobacteria in waterbodies. Cyanotoxin production can occur throughout the water column, with deep water production representing a potential public health concern, specifically for drinking water supplies. Deep cyanobacteria layers are often unreported, and it remains to be seen if lower incident rates reflect an uncommon phenomenon or a monitoring bias. Here, we examine Sunfish Lake, Ontario, Canada as a case study lake with a known deep cyanobacteria layer. Cyanotoxin and other bioactive metabolite screening revealed that the deep cyanobacteria layer was toxigenic [0.03 μg L^–1 microcystins (max) and 2.5 μg L^–1 anabaenopeptins (max)]. The deep layer was predominantly composed of Planktothrix isothrix (exhibiting a lower cyanotoxin cell quota), with Planktothrix rubescens (exhibiting a higher cyanotoxin cell quota) found at background levels. The co-occurrence of multiple toxigenic Planktothrix species underscores the importance of routine surveillance for prompt identification leading to early intervention. For instance, microcystin concentrations in Sunfish Lake are currently below national drinking water thresholds, but shifting environmental conditions (e.g., in response to climate change or nutrient modification) could fashion an environment favoring P. rubescens, creating a scenario of greater cyanotoxin production. Future work should monitor the entire water column to help build predictive capacities for identifying waterbodies at elevated risk of developing deep cyanobacteria layers to safeguard drinking water supplies.

中文翻译：

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深蓝藻层：蓝藻风险管理中被忽视的一个方面


人类接触蓝藻毒素的风险部分受到水体中产生毒素的蓝藻位置的影响。蓝藻毒素的产生可能发生在整个水体中，深水的产生代表了潜在的公共卫生问题，特别是对于饮用水供应。深层蓝藻层通常未被报道，较低的事故率是否反映了不常见的现象或监测偏差还有待观察。在这里，我们将加拿大安大略省的翻车鱼湖作为案例研究湖泊，该湖具有已知的深层蓝细菌层。蓝藻毒素和其他生物活性代谢物筛查显示，深层蓝藻层具有产毒性[0.03 μg L ^–1微囊藻毒素（最大值）和 2.5 μg L ^–1鱼腥肽（最大值）]。深层主要由异丝菌浮丝菌（表现出较低的蓝藻毒素细胞配额）组成，背景水平发现冬红浮丝菌（表现出较高的蓝藻毒素细胞配额）。多种产毒浮游丝菌物种的共存强调了常规监测的重要性，以迅速识别并进行早期干预。例如，翻车鱼湖中的微囊藻毒素浓度目前低于国家饮用水阈值，但环境条件的变化（例如，响应气候变化或营养物质改变）可能会形成有利于冬凌草的环境，从而产生更多的蓝藻毒素。未来的工作应该监测整个水体，以帮助建立预测能力，识别深层蓝藻层形成风险较高的水体，以保障饮用水供应。