Performance evaluation of in situ fluorometers for real-time cyanobacterial monitoring

Detecting the presence of cyanobacteria is an integral part of maintaining high water quality standards. In situ fluorometers are tools which may allow for the detection of cyanobacteria in real-time but there are few studies that review fluorometer performance. A systematic study that evaluated the performance of a range of fluorometers using key cyanobacterial species of interest and two known sources of interference (green algae and added turbidity) was undertaken. Specifically, six fluorometers and four cyanobacterial species were investigated. A good correlation (R² ≥ 0.92 and p-value of <0.001) was obtained for mono cell culture suspensions, with robust performance exhibited for all fluorometers. Limits of detection for the fluorometers and multiplier factors which enable direct comparison of fluorometers were developed. The addition of green algae caused fluorometer performance to decrease by either overestimating or underestimating the concentration of cyanobacteria in a cellular suspension. Some fluorometers were more susceptible to these interference sources; the magnitude of the fluorometer measurement inaccuracy was dependent on cyanobacteria concentration and interference source. This study indicates that while there are inherent problems with fluorometers, the extent of the impact from interference sources can be characterised and potentially corrected to enable successful cyanobacteria detection in the field.