MICROBIAL NUTRIENT LIMITATION IN PRAIRIE SALINE LAKES WITH HIGH SULFATE CONCENTRATION

Most of the lakes on the Canadian prairies are saline (> 3 g liter(-1) 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 e nrichment bioassays, sestonic and protein to carbohydrate ratios, alka line phosphatase activity, and P-32-turnover times were used to test m icrobial nutrient limitation in three prairie saline lakes. Although t he concentration of soluble reactive P (SRP) was high (9-31 mu g liter (-1)) in two of the lakes, little was available for microbial growth. Bacteria were responsible for 84 and 53% of the P-32 uptake in these t wo lakes. Production of high levels of alkaline phosphatase by the phy toplankton in one lake appears to keep their intracellular stores of P replete and PN:PP ratios in the P-sufficient range. Striking differen ces were noted when our data from saline lakes were compared to data f rom freshwater lakes. Our saline lakes were P-deficient at SRP concent rations <31 mu g liter(-1), while freshwater lakes were P-deficient at SRP concentrations <1 mu g liter(-1). High concentrations of dissolve d organic C, pH, and ionic composition in saline lakes appear to play a role in the availability of P.