The coupling of bacterial and phytoplankton production in Redberry Lake, Saskatchewan - an Oligotrophic, Prairie, Saline Lake with high DOC concentration

Abstract

Bacterial and phytoplankton production were concurrently measured for 2 years in Redberry Lake, an oligotrophic, saline prairie lake, together with a range of environmental variables. Correlative relationships were used to evaluate the hypothesis that phytoplankton DOC was an important substrate for bacterioplankton. The mean DOC concentration was 35.8 mg 1-1 while the mean concentration of total dissolved lipid was 125.9 μg 1-1. Chlorophyll concentrations were usually <1 μg 1-1 but were as great as 12.7 μg 1-1 just above the sediments at 16m. Maximum volumetric rates of primary production (A(max)) ranged from 3.2 to 31.6 mgC m-3 hr-1 at 2 m while areal, euphotic zone (̄X = 15.2 m) production varied from 246 to 976 mgC m-2 d-1. The mean number of bacteria was 7.98 X 106 cells ml-1. Published regression equations to predict bacterial numbers from mean chlorophyll concentration underestimated the mean number of bacteria in Redberry Lake. Volumetric rates of bacterial production were low at all depths, ranging from 0.01 to 0.2 mgC m-3 hr-1, giving an average daily rate of 26.1 mgC m-2 d-1. Gross bacterial production was calculated to be able to consume an average of 17.7%, or a maximum of 35.7%, of daily primary production. Bacterial production was correlated with primary production and water temperature at most depths while daily water column bacterial and phytoplankton production were correlated over the 2 years. Based on the data from the current study and previous studies on microbial limiting factors in this lake, we concluded that the correlations between bacterial and phytoplankton production were due to both the dependence of bacteria on phytoplankton for a supply of labile DOC and the co-limitation of both populations by inorganic nutrients (N and P).