Context Phytoplankton communities in tropical reservoirs are shaped by eutrophication and regional climate, which act as ecological filters. Aims To compare the environmental drivers of phytoplankton blooms in reservoirs across the monsoon–savanna and semiarid regions of north-eastern Brazil. Methods We analysed phytoplankton communities and environmental variables from 28 reservoirs by using canonical correspondence analysis (CCA) and generalised additive models (GAMs) to identify the influence of environmental variables. Key results A clear regional dichotomy emerged. Semiarid reservoirs showed low diversity and intense blooms dominated by Cyanobacteria. By contrast, monsoon–savanna reservoirs sustained more diverse, mixed blooms, where Bacillariophyceae and Cryptophyta were prominent. Key drivers included ammonia, total dissolved solids (TDS), turbidity and salinity. Conclusion The impact of eutrophication on bloom formation is modulated by regional climate. Semiarid systems are highly prone to Cyanobacterial dominance because of a synergy between nutrient enrichment and the selective pressure of high salinity. Implications Our findings highlighted the need for region-specific water management that addresses both nutrient loads and the hydrological impacts of climate, particularly in vulnerable semiarid ecosystems.
Tavares et al. (Wed,) studied this question.