Environmental factors influencing CyanoHABS in climate change scenario: spatio-temporal analysis in Brazilian semi-arid reservoirs

Several environmental factors have been shown to promote cyanobacteria in semi-arid regions, including high temperature, long photoperiods, alkaline pH, and nutrient pollution. Furthermore, global warming trends are particularly intensified in these regions, with droughts becoming longer and more severe due to higher evaporation and lower precipitation volume. The goal of this study was through canonical correspondence analysis that incorporated environmental parameters (biotic and abiotic components) to prognosticate blooms of cyanobacteria and cyanotoxins in 20 drinking water reservoirs (2,489 samples) in the semi-arid region of Ceará, Brazil. Across four years, 114 different phytoplankton taxa were identified; however these reservoirs were dominated by cyanobacteria (24 taxa), interestingly, specific cyanobacterial taxa were influenced by different biotic and abiotic factors. For example, nitrogen-to-phosphorus (N:P) and evaporation were positively related to saxitoxin-producing taxa, especially Raphidiopsis raciborskii, while temperature, electrical conductivity, total phosphorus, and transparency were positively associated with microcystin-producing taxa, such as Microcystis aeruginosa. Climate forecasts predict higher evaporation and temperatures in the semi-arid Ceará region, which will likely magnify droughts and water scarcity as well as promote toxic cyanobacterial blooms in reservoirs in the future. Therefore, understanding the factors associated with algal blooms dominated by specific taxa is paramount for water resource management.