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Abstract

Members of the same division of algae have a similar pigment composition. This results in typical fluorescence excitation spectra with emission wavelength between 680 nm and 720 nm. It is, therefore, possible to assign algal classes to distinct spectral groups of algae. In order to measure a meaningful fluorescence excitation spectrum five light-emitting diodes were chosen and built into a new instrument. Their emission wavelengths fit the absorption wavelength of the pigments phycocyanin, phycoerythrin, fucoxanthin, peridinin and chlorophylls, respectively. Spectra of different algae from four spectral groups (blue-green algae)(cyanobacteria), green algae, browns and cryptophyta (Cryptomonas) were recorded. An average fluorescence spectrum per Chlorophyll a concentration in a sample of water for each spectral group of algae resulted. This allows the calculation of the chlorophyll a concentration and the distribution of four different spectral groups of algae from an excitation spectrum. Results of in-vivo and in-situ measurements are shown. The application of a submersible probe is discussed.