Surface Sediment Diatom Assemblages and Lake Acidity

The diatom composition of surface sediments from 125 lakes was studied in relation to lake water acidity. According to the results of canonical correspondence analysis (CCA), the structure of the diatom assemblages correlates closely with the pH and the pH-related factors of lake water. Hustedt’s classification of diatoms seems to reflect pH fairly well. Acidobiontic diatom taxa, for example, clearly indicate acidic conditions. On the basis of weighted averaging, however, some diatom species classified to acidophilous can tolerate low pH to an equal degree. Contrariwise, euplanktonic diatoms, most of which are either alkaliphilous or circumneutral, appear sensitive to acidification since they are usually rare or totally absent in lakes of low pH. Comparing different pH-indicator methods based on diatom assemblages, pH was predicted more precisely by canonical correspondence analysis and by weighted averaging based on the optimum and tolerance of species than by multiple regression or diatom indices α and B.