Bacteriology of fresh water: I. Distribution of bacteria in English lakes

Abstract

1. The vertical distribution of bacteria has been determined in Windermere (north and south basins), Thirlmere, and Esthwaite Water; these lakes are oligotrophic bodies of water in the English Lake District. Studies on the horizontal distribution of bacteria have been confined to the north basin of Windermere.2. Bacterial counts at the mouth of the main river flowing into Windermere were about 200 times as great as counts in samples of water from the lake at a distance of 200 m. offshore from the point of entry of the river. In general there was a gradual decrease in numbers of bacteria with increasing distance from this 200 m. point but such decreases were relatively insignificant.3. During the winter period of circulation of water in the lakes numbers of bacteria were approximately the same at all depths on any one occasion. When the water in the lakes was stratified, however, the numbers of bacteria decreased with increasing depth in the epilimnion, but below the thermocline the numbers were approximately the same at all depths, except in the layer of water immediately above the mud where the bacterial population was somewhat greater.4. Progressive depletion of dissolved oxygen with depth in the hypolimnion during the summer months did not stimulate the growth of anaerobic bacteria, nor was the degree of depletion related to numbers of bacteria.5. Periodic fluctuations in numbers of bacteria which took place at all depths were found to be directly correlated with the amount of rain which had fallen in the drainage area during the week before the samples were taken. The correlation is most significant during the winter months, possibly on account of the high rainfall during those months. During the summer the relation was most marked in the upper layers of Windermere north basin, but in the lower layers to which rain had no access there was no correlation. In the south basin of Windermere, where the bacterial population has become more stable, numbers were not affected by the relatively small summer rainfall. There are indications that short early summer fluctuations in numbers of bacteria unrelated to rainfall may be related to maxima in algal growth.6. Changes in the temperature and concentration of inorganic substances in the lake waters have not shown any relation to fluctuations in the bacterial population, nor has any noticeable bacteriostatic effect of sunlight been apparent.