Using DCMU-fluorescence method for the identification of dominant phytoplankton groups

For the identification of ecologically significant dominant groups of phytoplanktonic algae a polychromatic DCMU-induced fluorescence method is recommended. A special fluorometer equipped with a system of replaceable filters is used to differentiate three regions of the spectrum (410 ± 20, 510 ± 20 and 540 ± 10 nm) that can excite the basic light-harvesting pigments. Total and differential (for every algal taxon studied) chlorophyll a calculated from the fluorescence signals is in good agreement with biomass estimates from direct cell counts for several different trophic types of aquatic systems. This is made possible by the vizualization of the ratios of fluorescence signal values in their own coordinates: first, to decide whether it is necessary to correct linear equations in order to eliminate negative solutions; second, to determine the possibility of nulling the negative solution if a point is situated close to a side of the triangle; and third, to reduce the number of linear algebraic equations to two if the points are situated along one of the triangle sides or to one if the points are gathered at the apex. The polychromatic DCMU-induced fluorescence method can be used for monitoring natural phytoplankton populations to detect changes in their taxonomic structure.