A diatom-total phosphorus transfer function for freshwater lakes in southeastern Finland, including cross-validation with independent test lakes

A diatom total phosphorus (TP) training set and weighted averaging (WA) calibration model for lakes in eastern and southeastern Finland are presented. The data set comprises 78 lakes, with autumnal TP-range of 3–125 ug l–1, pH-range of 5.9–7.7, and lake area of 0.13–283 km2. The correlation between the observed and WA-reconstructed (jackknifed) log TP values in the training set is 0.86 (R2 = 0.73), and root mean squared error of prediction (RMSEp) 0.193 ug TP l–1. The transfer function was cross-validated using an independent test set of 30 lakes. The correlation between the observed and predicted log TP values for the 30 lakes is 0.89 (R2 = 0.79), and RMSEp 0.161 ug TP l–1. These performance statistics (R2, RMSEp), based on the independent cross-validation with the test set of lakes, are within the range of values based on jackknifing estimates, suggesting that diatoms provide reliable estimates of lakewater TP concentration in Finnish lakes.