Flow cytometric discrimination of various phycobilin-containing phytoplankton groups in a hypertrophic reservoir

Knowledge of phytoplankton structure is important information in water quality control. Lake restoration and sanitation measures in particular must be evaluated on the organismic level to valuate biological effects and assess the risk of potentially toxic Cyanobacteria blooms. We used and comparatively tested three independent methods for phytoplankton analysis in a hypertrophic reservoir under restoration.

Nine unialgal cultures and outdoor samples were examined by high-performance liquid chromatography pigment analysis, microscopical cell counting, and flow cytometric (FCM) light scatter and fluorescence analysis to measure the percentage contribution of the major algal groups to chlorophyll a and biovolume. The FCM instrument settings and identification criteria were developed using a single excitation wavelength at 514 nm to differentiate nine algal species representing the major groups of algae. Fluorescence was detected at 585, 620, 650, and 680 nm.

The results show that FCM is the only method for determining changes in the phytoplankton composition on both a chlorophyll a and biovolume basis.

Each of the three methods has specific advantages and disadvantages, and should be chosen depending on the experimental problem. FCM sorting allows the combination of all three and offers further new perspectives.