In situ profiles of phytoplankton : algal composition and biomass determined fluorometrically

Abstract

A new methodology enabling rapid evaluation of the phytoplankton community structure and distribution with high spatial and temporal resolution in situ is introduced. This is based on the concept that four 'spectral groups' of phytoplankton (green, blue, brown, mixed) are each characterised by specific photosynthetic pigment compositions and, consequently, by specific excitation spectra of chlorophyll-fluorescence. We have developed a submersible fluorometer which measures the emission intensity for excitation in five characteristic wavelength ranges employing pulsed light-emitting diodes (LED’s). These five spectral excitation ranges can be used to differentiate the four spectral groups of microalgae in situ within a few seconds. In examples of depth profiles of phytoplankton populations in a eutrophic lake we also show a significant correlation of deconvoluted fluorescence profiles to corresponding biovolume