Phytoplankton assemblages as a criterion in the ecological classification of lakes in Finland

Implementation of the Water Framework Directive requires the formulation of lake types and classification of the lakes within each type using biological quality elements. In this study phytoplankton was used to test the lake typology of 32 non-impacted lakes belonging to eight of the ten lake types described in the preliminary Finnish typology. Phytoplankton did not accurately define these types, as only five lake groups were clustered in the DCA ordination analysis. The ecological status was preliminarily established for 23 impacted lakes using total phytoplankton biomass and the number of taxa. Impacted oligo-humic lakes were tentatively classified to a lower ecological status than in the general water quality classification carried out in the 1990s. Even more variation was observed when assessing the ecological status of humic impacted lakes. The number of taxa, on the other hand, appeared to overestimate the ecological status of the lakes, obviously due to the preliminary boundary classes used in this study.