Rapid Monitoring of Cyanobacteria in Lakes—A Case Study in the Wel River Catchment, Poland

The purpose of the study was to ascertain the effect of cyanobacterial abundance and its taxonomic structure on the results of measurements made by a fluorometric device designed to detect in situ chlorophyll a and phycocyanin. A multiparameter water quality probe was tested at 10 lakes located in the Wel River catchment. We found a strong correlation between the chlorophyll a concentration determined by laboratory procedure (CHL-a) and that obtained as a result of the probe measurements (YSI CHL-a) (R = 0.78) as well as between the YSI CHL-a and the total phytoplankton biomass (R = 0.73), whereas YSI CHL-a was not a good predictor of cyanobacterial biomass (R = 0.24). The phycocyanin recorded by the probe was proportional to the total biomass of cyanobacteria (R = 0.86); however, this cyanobacterial taxonomic structure influenced the fluorometric signal. Nevertheless, our study showed significant differentiation of phycocyanin measurement distribution at different levels of cyanobacterial abundance (<2 mg L⁻¹, between 2 and 10 mg L⁻¹, and >10 mg L⁻¹), which indicates that the PC-YSI measurements are valuable in the detection of increased risk of exceeding health alert thresholds recommended by the WHO.