ABSTRACT
The greatest fraction of nutrients dissolved in water are organic substances which are decomposed, transformed and mineralized by heterotrophic microorganisms. For this reason, investigations concerning energy transfer in an aquatic ecosystem, or practical examinations of the pollution load of surface waters, cannot be set up when based exclusively on more or less good counts of microorganisms of the production or destruction group. Above all, it is important for heterotrophic bacteria that productivity parameters for these numerical estimations are also provided. PARSON and STRICKLAND were successful in measuring the uptake of organic material in waters with uptake-kinetic methods; HOBBIE and WRIGHT developed a method for measuring the uptake of marked test-substrates in certain concentration ranges. As a result, for these substrates it was possible to measure the turnover in natural populations. Consequently, after frequent improvement of the technique in determining the decomposition rates of individual organic substrates, a way was found not only to determine static descriptions of an aquatic biotope, but also to make possible a dynamic description of nutrient transfers. The kinetic parameters computed from these measurements are: the maximum uptake velocity (Vmax), the turnover velocity (Tt) and the transport constant (Kt) (Michaelis Constant). The maximum uptake velocity of a substrate can be regarded as the "heterotrophic capacity" of the biotope for this substrate. One restriction is, however, that only quickly assimilatable substrates can be used, as for example hexoses, organic acids, amino acids, etc. Since this technique was tested practically only in oligotrophic waters, this study undertakes to investigate its applicability in polluted biotopes and to answer the question whether a decomposition gradient is reflected in the kinetic data. A small eutrophic lake in the eastern section of the Holstein Lake District (350 ha, 9.5 m mean water depth) was chosen as the test biotope. Emptying into the lake was the runoff of a biological water treatment plant with 12,000 population equivalents and without notable business and industry. In a rectangular investigation area at first with 30 sampling stations positioned close to the outlet of the water treatment plant into the lake, kinetic tests were carried out in 48 hour intervals and then compared with bacteriological, chemical and meteorological sample results taken at the same time. Two typical result-blocks are illustrated (Fig. 1-4, 5-8). The first shows four successive test days with periodically strong wind and light to fairly strong but short periods of precipitation. The second block illustrates conditions during a following period of fair weather with only very light wind intensities. The corresponding conditions of the stratification of the drainage water in the investigation area are illustrated by the distribution of coliform organisms. In two other tables the kinetic parameters and individual, dominant data are contrasted numerically...
