Online first articles

Humid highland forest enclaves form critical water sources and wet refugia within the surrounding semi-arid landscapes of northeastern Brazil. However, maintaining water quality in these systems is increasingly challenging because of anthropogenic pressure and climate change. Reynolds phytoplankton functional groups (RFGs), which cluster species based on shared ecological traits and sensitivities, are valuable bioindicators of environmental change. In this study, we examined temporal variations in RFGs in three reservoirs located in humid upland enclaves subjected to varying levels of environmental variability. Physical and chemical variables, along with phytoplankton composition, were monitored monthly over one year. Results showed significant differences in the composition of RFGs among the reservoirs. Water transparency and pH were identified as the primary environmental drivers shaping community structure. The strongest associations were found with flagellated unicellular and colonial cyanobacteria (Lo), filamentous cyanobacteria (S1), and elongated diatoms (MP). These findings highlight light availability and pH as key factors influencing the dynamics of phytoplankton in tropical reservoir ecosystems. The conservation of reservoirs in highland enclaves requires greater attention considering the increasing effects of global warming and anthropogenic pressure. Measures are needed to avoid water over-enrichment, cyanobacterial blooms, and reduced water availability.