PLANKTONIC ALGAE AS INDICATORS OF LAKE TYPES, WITH SPECIAL REFERENCE TO THE DESMIDIACEAE

The biological classification of lakes is briefly reviewed and the value and limitations of phytoplankton quotients for the assessment of trophic status are discussed. Comparisons are made between quotient determinations and the characterization of lakes in terms of their dominant phytoplankton species. The sensitivity of algal plankton to changes in water chemistry is examined in the light of experiments with mineral fertilizers and observations of natural or seminatural eutrophication. Special attention is paid to the use of desmids as indicators of trophic status. Studies of the British freshwater plankton have shown that many taxa of this supposedly oligotrophic algal group are most frequently associated with eutrophic waters.