Cyanobacterial blooming represents an extreme risk for the environment, for ecocystems and mammals. Its early detection is thus of key importance in water management. Standard methods of phytoplankton monitoring come with numerous limitations, therefore upgrades are needed that will give results in real time. One method that enables immediate detection and quantification of cyanobacteria and other phytoplankton, is the measurement of fluorescence of photosynthesis pigments. When biomass is known, measurements of phycocyanin (PC) and chlorophyll (CHL) fluorescence can also detect the stress, or changes to the physiological state, of cyanobacteria.
Our sensors were first used on axenic laboratory algae and cyanobacteria cultures, and then samples from the Koseze Pond, the Hotinja vas Pond and Lake Bled. It was discovered that the relationship between the PC- and CHL fluorescence, and standard methods of phytoplankton quantification (determining the biovolume and CHL extraction), is linear. The correlation coefficients between standard methods and PC- and CHL fluorescence were very high. Measurements of CHL fluorescence at the Koseze Pond showed high correlations with the phytoplankton biovolume throughout the entire two-year measurement period, even though the species composition was significantly altered. In stage two, we analized the cellular changes, induced by electrochemical treatment (with boron doped diamond electrodes), which were characterized by transitionally increased PC- and, less obviously, CHL fluorescence. The CHL signal reaches its peak value 6 hours after the induced damage, and the PC signal after 10 hours. Furthermore, the change in the ratio between PC- and CHL fluorescence is observed. On the basis of the results of our measurements, we believe that the CHL- and PC sensor combination is an optimal solution for determining the presence of the bacterioplankton. The system enables quantitative and qualitative detection of phytoplankton in a body of water, and thus coordinated application of measures, developed to reduce the detrimental effects of cyanobacteria in the case of excessive reproduction.