Intercalibrations of freshwater phytoplankton analyses

Phytoplankton is one of the biological quality elements of the Water Framework Directive of European Union for ecological classification of surface waters included. The reliability and comparability of phytoplankton data is, therefore, essential in assessment of the classification. The recently published standard for phytoplankton analysis based on the Utermohl technique supports stringent demands for comparability of data. We tested the comparability of phytoplankton analyses (Utermohl method) between professional and non-professional analysts. The coefficient of variation was highly variable, 10%-42% for professionals and 8%-57% for non-professionals. Elimination of the error caused by subsampling and the increase in the minimum number of enumerated units decreased the CV especially within professionals. CV was smaller (4%-19%) when samples were counted by one person. In order to minimize the variability caused by differences between subsamples, new methods for comparison testing both for technical enumeration and for species identification should be developed.