Spectroradiometric identification of phototrophic microorganisms in planktonic aquatic environments

An underwater spectroradiometer was used to analyse the spectral distributi on of Light in 41 lakes containing all of the main pigmentary groups of pla nktonic phototrophic microorganisms: eukaryotic phytoplankton, cyanobacteri a, Chromatiaceae and the different pigmented groups of Chlorobiaceae. Resul ts were processed to allow to the identification of phototrophic microorgan isms through the calculation of Light attenuation spectra at certain depth intervals from incident light spectra. These attenuation spectra allowed th e detection of photosynthetic pigments present in the analysed depth interv als from their in vivo spectral characteristics. The pigmentary groups of m icroorganisms could then be differentiated by their respective compositions in photosynthetic pigments. Although this method is Limited by both optica l 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 atte nuation spectra can provide a fast qualitative alternative to other pigment analyses; it is especially useful for obtaining a first estimate of the co mmunity composition and vertical structure of the water column that can be relevant to the improvement of the design of more specific and detailed sam pling procedures or in situ experiments.