Cyanobacterial blooms have been increasing in frequency and intensity but are often considered an issue restricted to temperate and tropical lakes. Here we report on one of the first occurrences of recurring cyanobacterial (Planktothrix spp.) blooms in a sub-Arctic lake from Yellowknife (Northwest Territories, Canada) and provide a long-term environmental context for the recent blooms using local meteorological data and multi-proxy paleolimnological analyses. Multiple co-occurring regional (gold mining emissions and climatic change) and local (land clearance and urbanization) stressors have impacted Jackfish Lake during the 20^th and early-21^st centuries, which have led to biological responses across multiple trophic levels. The unprecedented post-2013 cyanobacterial blooms were likely a cumulative response to nutrient enrichment and complex climate-mediated changes to lake thermal properties. A regional analysis of eight lakes around Yellowknife revealed that reduced ice cover duration and longer growing seasons have led to an increase in whole-lake primary production, whilst urban lakes were also fertilized by nutrients from local land-use changes in their catchments. Our findings suggest that anthropogenically nutrient-enriched sub-Arctic lakes, akin to their lower-latitude counterparts, may be vulnerable to cyanobacterial blooms in a warming world.

蓝藻水华的频率和强度一直在增加，但通常被认为是仅限于温带和热带湖泊的问题。在这里，我们报告了来自耶洛奈夫（加拿大西北地区）的亚北极湖中首次发生的循环蓝藻（浮游菌属）水华，并使用当地气象数据和多-代理古湖泊学分析。20时多同时出现的区域（采金排放和气候变化）和地方（土地清理和城市化）应激已经影响杰克菲什湖^届和早期21^日几个世纪以来，这导致了跨多个营养级别的生物反应。2013 年后史无前例的蓝藻水华可能是对养分富集和复杂气候介导的湖泊热特性变化的累积反应。对耶洛奈夫周围八个湖泊的区域分析表明，冰盖持续时间减少和生长季节延长导致全湖初级生产增加，而城市湖泊也因集水区当地土地利用变化而产生的养分施肥。我们的研究结果表明，人为营养丰富的亚北极湖泊，类似于它们的低纬度湖泊，在变暖的世界中可能容易受到蓝藻大量繁殖的影响。