Relationship Between Nutrients, Dominant Ions, and Phytoplankton Standing Crop in Prairie Saline Lakes

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Abstract
We collected data from 20 saline lakes (total dissolved solids from 1000 to 91000 mg .cntdot. L-1) in southeastern Alberta [Canada] to compare relationships between phosphorus, nitrogen, and phytoplankton standing crop with those in freshwater lakes. In 18 lakes, Na+, Mg2+, SO42-, and HCO3--CO32- were the dominant ions. In these lakes there was a significant positive correlation between Ca2+ and chlorophyll a (Chl a), and there were significant negative correlations between Chl a and conductivity, pH, Na+, Mg2+, SO42-, HCO3-, and CO32-. When all 20 lakes were considered there were no significant relationships between Chl a and phosphorus or nitrogen. Empirical relationships for freshwater lakes, based on spring or summer total phosphorus (TP) or total nitrogen (TN), overestimated Chl a in all the study lakes. However, in saline lakes with similar ionic composition and TN to TP ratios greater than 12 (by weight), there was a significant positive relatioship between TP and Chl a. For the saline lakes with TN to TP ratios greater than 12, the deviations between the Chl a levels predicted from models developed for freshwater lakes and the observed levels were positively correlated with conductivity, total dissolved solids, and Na+ (r2 = 0.78-0.82, P < 0.001). We developed the first empirical model that describes nutrient-Chl a relationships for inland saline lakes. The deviation of measured phytoplankton biomass from that predicted by models developed for freshwater lakes can be explained by conductivity or dominant ion concentration.