Item

Abstract

The 'spectral groups' of algae (green, blue, brown, mixed) are each characterized by a specific composition of photosynthetic pigments, particularly relevant are: Chl a, phycocyanobilin, phycoerythrobilin, fucoxanthin, peridinin and, consequently, by a specific excitation spectrum of the Chl fluorescence. This was used in earlier approaches to determine the amount of chlorophyll and the algal group composition of phytoplankton. Yellow substances (coloured dissolved organic matter) may interfere with the measurement because of overlap in the excitation spectra with phytoplankton. In a new approach, built into a submersible instrument, we correct for the influence of yellow substances on the chlorophyll fluorescence. The newly-developed probe is a submersible fluorometer which measures the emission intensity at six characteristic wavelength ranges employing pulsed light-emitting diodes. The submersible probe transfers all data on-line to a computer or stores them in the probe (fluorescence data plus the simultaneously measured water pressure for depth determination). The six-point excitation spectra are deconvoluted on the basis of norm spectra which have been obtained by analysis of several species of each spectral group. The usage of an ultra violet (UV)-ecxitation source (370 nm LED) enables the differentiation between algal fluorescence and fluorescence of yellow substances