Abstract
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.