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 low chlorophyll concentrations, algal biomass, and primary production but high zooplankton biomass when compared with freshwater lakes with similar total phosphorus and total nitrogen concentrations. We investigated the accuracy of various regression models in predicting algal production, algal biomass, and zooplankton biomass in Redberry Lake, a saline (20 g . L(-1)), phosphorus-rich (average total phosphorus concentration 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 predictions. Zooplankton biomass was 1.1-1.8 times higher than model predictions based on total phosphorus concentration, 2.0-2.8 times higher than predictions based on algal biomass, and 5.8-7.9 times higher than predictions based on chlorophyll concentration. Algal carbon turnover times (algal biomass divided by algal productivity) were short, suggesting rapid phytoplankton growth rates. Zooplankton grazing may have depressed phytoplankton accumulation rates and ultimately total primary production. Intense grazing may, in part, be a consequence of the high salinity of Redberry Lake, which limited planktivore abundance and reduced zooplankton diversity, resulting in dominance by large-bodied herbivores (Diaptomus sicilis, Daphnia pulicaria).