Diatoms as quantitative indicators of pH and water temperature in subarctic Fennoscandian lakes

Weighted averaging (WA) regression and calibration based optima anti tolerances of lakewater pH and temperature are presented for diatoms in ecologically sensitive, subarctic Fennoscandian lakes. The study sites are mostly small, simple, oligotrophic, low-conductivity lakes with a pH range from 5.0 to 7.7 and a temperature range (after data screening) from 9.3 to 15.0 degrees C. Experiments with inverse and classical deshrinking, with or without tolerance downweighting, were used to identify the best calibration functions. The model estimates were adjusted by jackknifing procedures. WA by inverse deshrinking and with tolerance downweighting performed best for pH prediction, whereas simple WA was marginally superior for predicting water temperature. The established pH model is accurate to within +/- 0.39 pH units, and the temperature model to within +/- 0.88 degrees Celcius. Fifteen diatom taxa were identified as potential indicator species for pH and three for temperature.