Recent Studies on the Role of Microorganisms in the Cycling of Substances in Lakes1

This paper presents a review of current trends in research in the Soviet Union on the ecology of aquatic bacteria. The paper shows an increasing emphasis on in situ measurements of the rate or extent of conversion of carbon, nitrogen, sulfur, and iron from one form to another and on the bacteria responsible for these conversions. Theoretical considerations and results of several studies are summarized. These include measurement of bacterial biomass production and nitrogen fixation with isotopes, factors affecting decomposition of water humus in bog lakes, annual succession of iron bacteria in relation to the cycling of iron, nitrogen exchange between bottom sediment and benthic waters, the concept and calculation of nitrogen balance in a lake, and the bacteria responsible for the oxidation of sulfur. An attempt is made to incorporate this information into flow diagrams showing the dynamics of the cycling of the four elements discussed.