ALGAL PRODUCTIVITY, ALGAL BIOMASS, AND ZOOPLANKTON BIOMASS IN A PHOSPHORUS-RICH, SALINE LAKE - DEVIATIONS FROM REGRESSION-MODEL PREDICTIONS

Emerging evidence suggests that saline prairie lakes have relatively l ow chlorophyll concentrations, algal biomass, and primary production b ut high zooplankton biomass when compared with freshwater lakes with s imilar total phosphorus and total nitrogen concentrations. We investig ated the accuracy of various regression models in predicting algal pro duction, algal biomass, and zooplankton biomass in Redberry Lake, a sa line (20 g . L(-1)), phosphorus-rich (average total phosphorus concent ration 48 mu g . L(-1)), moderately deep (maximum depth ca. 17 m) lake . Annual primary production rates were 7.6-8.8 times lower than rates predicted from total phosphorus models developed for freshwater lakes whereas mean summer algal biomass was 4.6-9.1 times lower than model p redictions. Zooplankton biomass was 1.1-1.8 times higher than model pr edictions based on total phosphorus concentration, 2.0-2.8 times highe r than predictions based on algal biomass, and 5.8-7.9 times higher th an predictions based on chlorophyll concentration. Algal carbon turnov er times (algal biomass divided by algal productivity) were short, sug gesting rapid phytoplankton growth rates. Zooplankton grazing may have depressed phytoplankton accumulation rates and ultimately total prima ry production. Intense grazing may, in part, be a consequence of the h igh salinity of Redberry Lake, which limited planktivore abundance and reduced zooplankton diversity, resulting in dominance by large-bodied herbivores (Diaptomus sicilis, Daphnia pulicaria).