Vertical Distribution of Bacteria in Forest Lakes of Karelia

Abstract

Abstract—The total abundance of bacteria, the number of saprophytic, oligotrophic, and sulfate-reducing microorganisms, the shapes of bacterial cells, the primary and bacterial production, the destruction of organic matter, and the rate of sulfate reduction were studied in small Karelian lakes during the stagnation period. It has been shown that the uneven vertical distribution of light, temperature, oxygen, and hydrogen sulfide creates ecological niches for the development of many various groups of microorganisms. In most lakes, the minimum abundance of microorganisms was found in the surface water layer, while its maximum was in the near-bottom layers. The trophic status of a water body has a great influence on the formation and function of microbial communities. Autochthonic organic matter in the closed forest lakes under study (the local term is “lamba”) was formed due to phytoplankton photosynthesis, but bacterial production exceeded primary production in the hypolimnion of eutrophic lakes. The content of hydrogen sulfide, the abundance of sulfate-reducing bacteria, and the rate of sulfate reduction were maximal in the bottom sediments of eutrophic lambas.