Aerobic heterotrophic and spore-forming bacteria in the water of Lake Hańcza

This paper presents the results of studies into the spatial distribution of aerobic heterotrophic and spore-forming bacteria in the water of Lake Hańcza - the deepest lake of Poland (108.5) - and its inflows and outflow. Experiments were carried out in the years 1997-2000. Water for analysis was sampled in 1-month intervals from April to October at 9 sites located on the lake (pelagic zone, inshore waters), another 4 located on inflows (rivers: Czarna Hańcza and Stara Hańcza, inflow "spod Prze omki", and Lake Boczniel), and one selected on the outflow of the Czarna Hańcza River. Statistically significant differences were demonstrated between the mean numbers of bacterial groups examined depending on the site, depth and period of water sample collection. In the water of Lake Hańcza, their counts were a few/dozen or so times lower than in water of watercourses inflowing to it. In the entire experimental period, the highest numbers of the bacteria examined were observed in the inflow of the Czarna Hańcza River. In the pelagic zone, their maximum numbers were usually reported in water at a depth of 1 m and at the bottom, i.e. 60-80 m. In experimental seasons, the highest mean counts of these bacteria occurred in the spring-summer months (June, August), whereas the lowest ones occurred in early spring (April). In particular experimental years, their lowest numbers were recorded in 1999, the highest - in 1997, 2000 years. The considerable fluctuations observed in the counts of heterotrophic bacteria may be linked with periodical changes in the concentration of mineral and organic matter in the lake. Recognition of the spatial (horizontal and vertical) distribution of heterotrophic bacteria in the water of Lake Hańcza suggests that, by actively participating in the processes of matter decomposition and energy circulation, these bacteria can effectively contribute to a reduction in the load of contaminations discharged into the lake with inflows and, consequently, become a quality indicator of water of this and other aquifers with various typology.