Cyanobacteria and Cyanotoxins in Azorean Lakes: Spatial and Temporal Analysis of Long-Term Monitoring Data (2003–2018) ^†

Eutrophication became the main environmental problem of Azorean lakes at the end of the 20th century, resulting mainly from the intensification of anthropogenic activities in the catchments. This problem raised great public concern, leading to the implementation of monitoring programs to assess the status of the Azores inland waters. During the monitoring programs, many cyanobacterial species were present in high abundance, and several blooms and cyanotoxins have been recorded over the years. In this work, monitoring data from twenty-three lakes, from 2003 to 2018, were analyzed to understand the distribution and dynamics of the presence of cyanobacteria and cyanotoxins, as well as the importance of local and global environmental factors. Although we found some interannual variability, the results confirm a high abundance of cyanobacteria in many lakes, frequently of toxic species. Besides a high correlation between the lake trophic state and the abundance of cyanobacteria, some changes in the communities, namely regarding the dominant species, suggest the influence of global factors as drivers of these changes. This study contributes to improving cyanotoxin monitoring programs and mitigation actions to control harmful cyanobacterial blooms (HCBs).