Assessment of the risk of cyanobacterial bloom occurrence in urban ponds: probabilistic approach

Blooms of toxic cyanobacteria became a common feature of eutrophic temperate lakes and ponds owing to human induced eutrophication. Occurrence of cyanobacterial blooms in an urban context may pose serious health concerns. This necessitates the development of tools for assessment of the risk of noxious bloom occurrence. A five year study of 42 Brussels ponds showed that cyanobacteria have threshold rather than linear relationships with environmental variables controlling them. Hence, linear relationships have limited predictive capacity for cyanobacterial blooms. A probabilistic approach to prediction of bloom occurrence using environmental thresholds as conditions in conditional probability calculation proved to be more useful. It permitted to quantify the risk of cyanobacterial bloom occurrence and thus to single out the conditions and thence the ponds the most prone to cyanobacterial bloom development. This approach can be applied for the assessment of the risk of cyanobacterial bloom occurrence in urban ponds and thus can facilitate monitoring planning and setting restoration priorities.