ABSTRACT: An underwater spectroradiometer was used to analyse the spectral distribution of light in 41 lakes containing all of the main pigmentary groups of planktonic phototrophic microorganisms: eukaryotic phytoplankton, cyanobacteria, Chromatiaceae and the different pigmented groups of Chlorobiaceae. Results were processed to allow to the identification of phototrophic microorganisms through the calculation of light attenuation spectra at certain depth intervals from incident light spectra. These attenuation spectra allowed the detection of photosynthetic pigments present in the analysed depth intervals from their in vivo spectral characteristics. The pigmentary groups of microorganisms could then be differentiated by their respective compositions in photosynthetic pigments. Although this method is limited by both optical characteristics of the lakes (narrow available light spectral ranges) and composition of the microbial communities (pigments overlapping or too-low-density populations), this kind of in situ, in vivo spectroradiometric attenuation spectra can provide a fast qualitative alternative to other pigment analyses; it is especially useful for obtaining a first estimate of the community composition and vertical structure of the water column that can be relevant to the improvement of the design of more specific and detailed sampling procedures or in situ experiments.

KEY WORDS: Spectroradiometry · Phototrophic bacteria · Phytoplankton · Microbial ecology · Photosynthetic pigments · In vivo absorption spectra · Light quality · Light spectrum

Published in AME Vol. 20, No. 3 (1999) on December 30
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1999