Seasonal dynamics and diversity of cyanobacteria in a eutrophied Urban River in Brazil

Surface water bodies are vulnerable to cyanobacteria overgrowth, primarily owing to nutrient enrichment, rising temperatures, and recurrent droughts. Regular cyanobacteria monitoring in water systems is crucial to prevent and manage health risks associated with toxin exposure. Surface water samples were collected from the Jundiai River in Sao Paulo State, Brazil for 3 years (2018–2022) to study the seasonal changes and species diversity of cyanobacteria. The study also aimed to understand the relationship between cyanobacteria abundance, climate, water quality, and hydrological parameters. Data analyses revealed a pattern of significantly elevated cyanobacterial cell counts during the dry season (DS), accompanied by an increase in the cyanobacterial species. The identified species poses a threat to water safety owing to the potential production of toxins, as well as causing unpleasant taste and odor. The DS is marked by higher nutrient concentrations and lower water flow. Phosphorus levels remain high, allowing cyanobacteria to grow without being limited by nutrients. In future scenarios, the primary concern for the Jundiai River is not temperature rise but droughts that create a stable environment for cyanobacteria proliferation. This research provides valuable data for river water users and contributes to a broader understanding of the global cyanobacterial dispersion.