Delayed fluorescence excitation spectroscopy: A rapid method for qualitative and quantitative assessment of natural population of phytoplankton

Natural phytoplankton samples were analyzed by a spectrometer which is designed to measure delayed fluorescence (DF) excitation spectra in the range from 400 to 728 nm. It was possible to detect taxonomical changes in the algal assemblage of Lake Kinneret, Israel using DF spectra as analytical signature. The ratio of spectrally integrated excitation delayed fluorescence to chlorophyll a concentration (DF/chlorophyll) in samples collected from Lake Kinneret, Israel, fluctuated throughout the investigation period, which covered the annual bloom of the dinoflagellate Peridinium gatunense. The DF/chl ratio increased with the initiation of Peridinium population build up, reached the highest value when the algal bloom reached its peak and declined with the decrease of algal density. DF intensity was positively correlated with the primary productivity at the depth of maximal productivity, indicating that DF intensity may be used as a rapid probe of this variable.