Data-driven insights into Microcystis dominance: Multi-lake analysis for water management

Understanding the drivers of harmful cyanobacterial blooms is critical for safeguarding freshwater quality, particularly in reservoirs that serve as drinking water sources. This study presents a comparative, cross-continental analysis of five lakes and reservoirs located in distinct climatic and ecological regions (i.e., Myponga, Wivenhoe, Tingalpa - Australia; Suwa - Japan; and Kinneret - Israel), focusing on Microcystis spp. and co-occurring cyanobacteria. By applying Self-Organizing Maps, Regression Trees, and Principal Component Analysis, we identified key physicochemical and ecological factors influencing Microcystis dominance across these systems. Total phosphorus (TP) emerged as the most consistent predictor of Microcystis dominance, while nitrogen forms and processes such as internal phosphorus loading also played important roles in some sites. Although TP reflects phosphorus present in the water column, internal loading can drive short-term TP increases, highlighting the need to consider both external inputs and sediment release when interpreting bloom drivers. Temperature and water column stratification effects varied across sites, i.e., strong in some systems (e.g., Myponga, Tingalpa) but weak or inconsistent in others (e.g., Suwa, Wivenhoe, Kinneret). Genus-level dynamics indicated that Microcystis, Dolichospermum, and Aphanizomenon often dominated in isolation, leading to low community richness and higher biomass. In contrast, genera like Pseudanabaena, Planktolyngbya, and Raphidiopsis co-occurred more frequently under stratified conditions, forming more diverse but less biomass-dense blooms. Our findings offer valuable guidance for water resource managers by identifying both universal and lake-specific drivers of Microcystis dominance. While the strong influence of phosphorus reinforces the importance of nutrient reduction strategies, the role of interacting factors, such as nitrogen forms, thermal dynamics, and inter-genus competition, demonstrates the necessity of site-specific management approaches. This harmonized, multi-lake assessment provides a rare ecological framework that can inform predictive modelling and effective management strategies.