A Summer of Cyanobacterial Blooms in Belgian Waterbodies: Microcystin Quantification and Molecular Characterizations

In the context of increasing occurrences of toxic cyanobacterial blooms worldwide, their monitoring in Belgium is currently performed by regional environmental agencies (in two of three regions) using different protocols and is restricted to some selected recreational ponds and lakes. Therefore, a global assessment based on the comparison of existing datasets is not possible. For this study, 79 water samples from a monitoring of five lakes in Wallonia and occasional blooms in Flanders and Brussels, including a canal, were analyzed. A Liquid Chromatography with tandem mass spectrometry (LC-MS/MS) method allowed to detect and quantify eight microcystin congeners. The mcyE gene was detected using PCR, while dominant cyanobacterial species were identified using 16S RNA amplification and direct sequencing. The cyanobacterial diversity for two water samples was characterized with amplicon sequencing. Microcystins were detected above limit of quantification (LOQ) in 68 water samples, and the World Health Organization (WHO) recommended guideline value for microcystins in recreational water (24 mu g L-1) was surpassed in 18 samples. The microcystin concentrations ranged from 0.11 mu g L-1 to 2798.81 mu g L-1 total microcystin. For 45 samples, the dominance of the genera Microcystis sp., Dolichospermum sp., Aphanizomenon sp., Cyanobium/Synechococcus sp., Planktothrix sp., Romeria sp., Cyanodictyon sp., and Phormidium sp. was shown. Moreover, the mcyE gene was detected in 75.71% of all the water samples.

Automated summary

Belgium currently monitors toxic cyanobacterial blooms through regional environmental agencies, but protocols and locations are inconsistent. This study analyzed water samples from five lakes in Wallonia, as well as occasional blooms in Flanders and Brussels. Microcystin concentrations were detected using LC-MS/MS, while the presence of the mcyE gene and dominant cyanobacterial species were determined through PCR and DNA sequencing. The results showed that most samples exceeded the recommended guidelines for microcystin concentrations, and a diverse range of cyanobacterial species were identified. The mcyE gene was present in the majority of samples.