Factors Affecting the Interpretation of Online Phycocyanin Fluorescence to Manage Cyanobacteria in Drinking Water Sources

Abstract

Recently, in situ YSI EXO2 phycocyanin fluorescence probes have been widely deployed as a means to determine cyanobacterial abundance in drinking water sources, yet few studies have evaluated the effects of natural organic matter (NOM) and the ambient water temperature on the probe readings. In this study, Suwannee River NOM was added to laboratory cultivated cyanobacterial species to test the performance of the phycocyanin probe. The impact of temperature on phycocyanin fluorescence was evaluated by monitoring the laboratory cultivated cyanobacterial species and extracted phycocyanin pigment. Additionally, in situ phycocyanin fluorescence of the field samples from the water intake of a drinking water treatment plant (DWTP) in 2018 were compared with grab sample laboratory taxonomic analyses. We found: (1) the presence of Suwannee River NOM leads to the decrease in cell-bound cyanobacterial phycocyanin readings; (2) increasing ambient water temperature reduces dissolved and cell-bound cyanobacterial phycocyanin readings; (3) field study phycocyanin probe readings significantly correlated with the total cyanobacterial biovolume (R = 0.73, p < 0.1), and the relationship depends on the biovolume of dominant cyanobacterial species; (4) phycocyanin probe readings have a strong positive correlation with the natural light intensities; and (5) probe users should be fully aware of the sources of interferences when interpreting the results and apply the other physical-chemical parameters data simultaneously generated by the fluorometry to improve the probe’s measurements.

Evidence-based framework to use in situ phycocyanin readings for cyanobacterial risk assessment within drinking water treatment plants

“…† Previous reports of this diversity showed similar species dominance patterns. Specifically, in the source water of DWTP A, Microcystis aeruginosa, Dolichospermum spiroides are the most biovolume dominant species; 14,20,39 in the source water of DWTP B, Woronichinia naegeliana, Microcystis aeruginosa are the biovolume dominant species; 35,40,41 and in DWTP C, Dolichospermum sp., Microcystis aeruginosa are the biovolume dominant species. 15,42 The speciation of the CB as the water progresses through the treatment processes, provides information on the selective CB removal.…”

“…The dominant species differ whether you consider cell counts and biovolumes, due to the large difference between the cell sizes of the species present (up to 600-fold). 39,43 The composition of species in different treatment processes in DWTPs B and C are provided in supplementary (Fig. S4 Environmental Science: Water Research & Technology Paper removed over 2.6 log by clarification.…”

“…The interpretation of data generated by the PC probes with simultaneously measured other physio-chemical parameters in source water improves their interpretation. 39,46 Significant correlations between the physio-chemical parameters and PC readings in the raw water of the DWTPs have been reported, but no study has described the relationships between these physio-chemical parameters inside the DWTPs. A multivariate approach through PCA biplot was performed to describe how the physio-chemical parameters changed inside the DWTPs.…”

“…Secondly, in situ probes in the field can be affected by environmental conditions such as the presence of Chl-a, water turbidity, and water temperature. 39,52,53 Besides, the variability of CB species in field samples may account for the great dispersion of the biovolume when transferred to PC readings. Even from the same study, different tested strains of Microcystis aeruginosa resulted 3.5 times different equivalent RFU values.…”