Evaluation of the Phosphorus–Chlorophyll Relationship for Lakes Off the Precambrian Shield in Western Canada

Abstract

Summer chlorophyll (Chl), spring and summer total phosphorus (TP), and total nitrogen (TN) data were collected from 25 lakes off the Precambrian Shield in Alberta. Contrary to the results reported in previous studies in western Canada, the spring TP–summer Chl relationship (n = 29, r2 = 0.67) and TN:TP ratios were similar to those reported for other north-temperate lakes. However, there was less variation in the summer TP–summer Chl relationship (n = 34, r2 = 0.81) than in the spring TP–summer Chl relationship. This is a result of the variability in the summer TP:spring TP ratio which ranged from 0.5 to 2.9 in these lakes. In the shallow productive freshwater lakes TP concentrations increased dramatically between spring and summer (the average summer TP:spring TP ratio was 1.7), whereas in the thermally stratified freshwater lakes (most of which were partially meromictic) summer TP concentrations were much lower than spring TP concentrations (the mean ratio was 0.7). There was less chlorophyll per unit TP in saline lakes (i.e. lakes with more than 500 mg/L total dissolved solids) than in freshwater lakes.Key words: phosphorus, chlorophyll, western lakes, saline lakes, meromictic lakes