Microbial nutrient limitation in prairie saline lakes with high sulfate concentration

Most of the lakes on the Canadian prairies are saline (~3 g liter- ’ salt). Sulfate ions are relatively more abundant in these lakes than anywhere else in the world. Studies indicate that some of these lakes do not conform to empirical models which link chlorophyll a to spring total phosphorus concentration. A suite of tests, including nutrient enrichment bioassays, sestonic and protein to carbohydrate ratios, alkaline phos-phatase activity, and 32P-turnover times were used to test microbial nutrient limitation in three prairie saline lakes. Although the concentration of soluble reactive P (SRP) was high (9-3 1 pg liter- I) in two of the lakes, little was available for microbial growth. Bacteria were responsible for 84 and 53 % of the 32P uptake in these two lakes. Production of high levels of alkaline phosphatase by the phytoplankton in one lake appears to keep their intracellular stores of P replete and PN: PP ratios in the P-sufficient range. Striking differences were noted when our data frcm saline lakes were compared to data from freshwater lakes. Our saline lakes were P-deficient at SRP concentrations ~3 1 pg liter-‘, while freshwater lakes were P-deficient at SRP concentrations < 1 pg liter-l High concentrations of dissolved organic C, pH, and ionic composition in saline lakes appear to play a.-ole in the availability of P. According to Hammer (1990), mo St of the lakes on th