Detection and Monitoring of Cyanobacteria and Green Algae in River Water Using Derivative Spectrophotometry

Monitoring of microalgae in source water has become more important than ever, especially due to worsening eutrophication as well as global warming and an increase in potentially toxic cyanobacterial bloom formation. This research investigated using longer cuvette pathlengths (50-and 100-mm) and Savitzky-Golay (S-G) first derivative of absorbance for detection and monitoring of Microcystis aeruginosa (cyanobacteria) and Chlorella vulgaris (green algae) in river water to provide realistic conditions in determining the method performance. Further, differences between the absorbance spectra of cyanobacteria and green algae were analyzed to identify key peaks from different photopigments for monitoring purposes. For both microalgae, correlations between cell concentrations, absorbance, and derivative of absorbance measurements were investigated. In addition, method detection limits (MDLs) were established, and calibration curves were made to carry out sensitivity analyses. A strong linear relationship (R 2 > 0.9) was observed between concentration and absorbance for all peaks of interest (such as 682 nm for photopigment Chl-a and 632 nm for phycocyanin). Finally, the performance and MDLs were compared for both microalgae in river water with deionized water. Results obtained using 100 mm pathlength and S-G derivative were found to be the most sensitive and had the lowest MDLs of 12,798 cells/mL and 8,546 cells/mL for M. aeruginosa for phycocyanin and Chl-a peaks in river water; whilst C. vulgaris had the lowest MDL of 13,695 cells/mL for Chl-a peak in river water. These results indicate that using longer cuvette pathlengths and employing derivative spectrophotometry, the method described can be potentially used for early detection and monitoring of cyanobacteria and green algae in real environmental samples