The influence of environmental factors on seasonal changes in bacterial cell volume in two prairie saline lakes

Bacterial biovolumes of hypertrophic Humboldt Lake (total dissolved solids = 3.3 g liter^-1; 6 m deep) and oligotrophic Redberry Lake (total dissolved solids = 20.9 g liter^-1; 17 m deep), Saskatchewan, were measured concurrently with a variety of environmental variables to identify the major factors correlated with volume changes. There was no difference (P > 0.05) in mean bacterial volume between Redberry Lake (0.084 ± 0.034 m³ SD) and Humboldt Lake (0.083 ± 0.021 m³ SD). Statistical analyses suggested there were marked differences in the factors associated with the pronounced seasonality of bacterial cell volumes in these two lakes. Variance in bacterial volume in the epilimnion of Redberry Lake was best explained by a multivariate regression model which included ciliate abundance and chlorophyll concentration (r ² = 0.96). The model accounting for changes in hypolimnetic bacterial volume included ciliate numbers and primary production (r ² = 0.94), of the measured variables. Bacterial volume in Humboldt Lake was most highly correlated with primary production (r ² = 0.59). Bacterial production (estimated as the rate of thymidine incorporation into DNA) and growth (thymidine incorporation rate normalized to cell numbers) were not correlated to cell volume, with the exception of cocci volume in Humboldt Lake. Offprint requests to: R.D. Robarts.