LIGHT, NUTRIENTS, AND WATER TEMPERATURE AS DETERMINANTS OF PHYTOPLANKTON PRODUCTION IN 2 SALINE, PRAIRIE LAKES WITH HIGH SULFATE CONCENTRATIONS

Our data support empirical models indicating that algal productivity is low relative to total phosphorus (TP) levels in prairie lakes with high sulphate concentrations. Mean chlorophyll accounted for 91.1 % of the variance in euphotic zone primary production (SIGMAA) in Humboldt Lake (total dissolved solids (TDS) = 3.3 g.L-1; Z(max) = 6 m), while TP, total dissolved phosphorus, and water temperature accounted for 82.7% of SIGMAA variance in Redberry Lake (TDS = 20.9 g.L-1; Z(max) = 17 m). The relative importance of these variables to SIGMAA resulted from biological, chemical, and physical differences of these lakes. Light usually penetrated to the bottom of Redberry Lake due to a mean euphotic zone (Z(eu)) chlorophyll of 1.7 mg-m-3, while Humboldt Lake's mean Z(eu) was 3.4 m with a mean chlorophyll concentration of 62.6 mg.m-3. Chlorophyll was the dominant factor correlated with light penetration in Humboldt Lake (r2 = 0.65) but not in Redberry Lake. Photosynthetic capacity was correlated (r2 = 0.72) with water temperature only in Redberry Lake. The mean SIGMAA was 57.1 and 230.2 mg C.m-2.h-1 for Redberry and Humboldt lakes, respectively.