Detection of phycobilin pigments and their seasonal change in Lake Kasumigaura using a sensitive in situ fluorometric sensor

A two-channel fluorometric sensor system for the detection of the water bloom phytoplankton Microcystis aeruginosa has been developed. Excitation wavelengths of 620 nm and 440 nm were used; the former for detecting the cyanobacteria themselves, and the latter for subtracting the interference due to eukaryotic algae present in the sample. The fluorescence of the cyanobacteria and eukaryotic algae was measured at 645 nm and 680 nm, respectively. Applied to real samples from Lake Kasumigaura, Japan, after ultrasonication, this fluorometric method is capable of the rapid determination of phycocyanin. We used this sensor system for monitoring surface water in Lake Kasumigaura in 9 months in laboratory experiments. Moreover, an automatic device based on this system was used for the continuous in situ monitoring of phycocyanin in lakewater. As expected, higher levels of phycocyanin due to cyanobacteria were observed, compared to chlorophyll a due to eukaryotic algae in summer.