Monitoring and risk communications of Cyanobacteria Harmful Algal Blooms (CHAB) in Nova Scotia (NS), Canada

Introduction: In Nova Scotia (NS), Canada, cyanobacterial harmful algal blooms (CHABs) are increasingly emerging during summer and fall, driven by complex ecological interactions within freshwater ecosystems. These blooms represent a dual threat to public health and aquatic ecosystems, contaminating drinking water supplies, disrupting recreational activities, and undermining biodiversity. Over a five-year period, systematic sampling across 17 lakes in NS identified four dominant and potentially toxic cyanobacteria species: Dolichospermum flos-aquae, D. planctonicum, Microcystis aeruginosa, and Aphanizomenon sp. These species are associated with the production of highly hazardous cyanotoxins, including anatoxin-a and microcystins, with congeners including MC-LR and MC-LY frequently detected. The proliferation of those raises urgent concerns for human health risks and ecological impacts such as fish kills, loss of biodiversity, and disrupted food webs. Methodology: This study integrates five years of field observations, laboratory analyses (physical-chemical parameters and cyanotoxins), environmental parameters to identify key drivers of bloom formation. The mathematical modelling to investigate the CHAB dynamics is also used. Results & Discussions: Results reveal that rising temperatures, nutrient enrichment (particularly from agricultural runoff), and prolonged thermal stratification are the primary triggers for CHABs in the region. Spatial analyses indicate shallow, nutrient-rich lakes are most vulnerable to persistent and intense blooms, while deeper, oligotrophic systems exhibit lower but increasing bloom frequencies. Model simulations demonstrate future temperature increases and extreme weather events are likely to exacerbate CHABs, intensifying toxin production and bloom duration. Conclusion: The findings underscore the critical need for proactive monitoring and adaptive management strategies to mitigate the impacts of CHABs in NS. Real-time sensor networks and satellite remote sensing are essential tools for early bloom detection and public health protection. Future research should prioritize integrated approaches, combining field studies, laboratory experiments, and predictive modeling, to address the growing threat of CHABs in the context of a changing climate.