Seasonal Patterns of Bacterial Abundance in an Arctic Lake

Abstract

Total bacterial numbers were determined at different times of the year in an arctic lake (0.1 to 3.1 x 106 cells ml-1), its inlet and outlet streams (0.4 to 2.9 x 106 cells ml-') and in the nearby Kuparuk River (0.3 to 2.7 x 106 cells ml-'). Bacterial counts were made with epifluorescence microscopy and acridine orange staining. The highest numbers of bacteria in Toolik Lake were found in the summer. The distribution with depth was irregular and maximum cell numbers in the water column were found at various depths. Small cells with a volume s0.1 jm3 made up the majority of the population in the streams. The peak spring-time bacterial counts observed in the streams and the lake presumably reflected the input of terrestrial bacteria and nutrients in run-off water. Within the lake, the spring peak of bacteria numbers occurred at the same depths that streamwater occurred (as traced with a fluorescent dye). Within a stream, no consistent correlations were found between discharge and bacterial numbers. A comparison of cell numbers between the Kuparuk River and the Toolik Inlet stream revealed a good correlation indicating common controlling factors such as the timing of surface run-off entering the streams. In general, the numbers found are similar to those in temperate lakes and streams.