Consumption of organic matter by planktonic organisms in a mesotrophic ecosystem: radioactivity (on membrane filters) of plankton and detritus labeled by carbon (¹⁴C)

   To understand the mechanisms of formation of water quality in an aquatic ecosystem, the processes of formation of funds of dissolved organic matter (DOM) and detritus are essential. When the algae die off, the bulk of their contents enter the aquatic environment within one week. Detritus settles at a rate of about one meter per day. In deep water bodies, the destruction of detritus occurs to a significant extent in the water column; in shallow water bodies, it occurs mainly at the bottom. DOM is consumed by bacteria and algae. This article presents the results of an experimental study of the quantitative aspects of DOM transformation and metabolism using natural water samples immediately after they were taken from a mesotrophic freshwater ecosystem. The total heterotrophic activity of various fractions of plankton in natural water was determined. The specific heterotrophic activity (per a unit of biomass) was also determined. It was found that the specific heterotrophic activity of bacteria (per a unit of biomass) in all cases is higher than the activity of phytoplankton. The new results provide a detailed understanding of chemical-biotic interactions in aquatic ecosystems, which is important for the analysis of water self-purification processes.

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