Hidrológiai Közlöny 1967 (47. évfolyam)
7. szám - A „Szervesanyag meghatározási problémák édesvizekben” című 1966. szeptember 25–28. között Tihanyben rendezett Szimpózium előadásai - Allen, Harold L.: Heterotróf baktériumok acetáthasznosítása egy tóben
296 Hidrológiai Közlöny 1967. 7. sz. Allén, H. L.: Heterotróf baktériumok activity C 1 4-labeled acetate to unfiltered lake water samples (25 ml) and following the kinetic removal of added acetate over a unit of time. It is fairly well established that uptake detected when adding 0—100 [Ág acetate l4 represents uptake primarily due to planktic bacteria. Uptake at higher substrate concentrations (0.5—5.0 mg acetate l1) follows simple diffusion kinetics, and is attributed to the planktic algae (Wright and Hobbié, 1965a, 1965b, 1966). Samples are then incubated at near insitu temperatures (16.3°C) on a shaking table in totál darkness (incubation period was 0.25 hours). After incubation, the samples were fixed with Lugol's acetic acid solution, filtered onto Göttingen membrane filters (pore size less than 0.45/i), airdried, desiccated, and counted in a proportional counter of known counting efficiency. Data from assayed filters were graphically and mathematically treated, according to modified equations for Michaelis-Menten enzyme kinetics, to obtain uptake parameters of maximum uptake velocity, substrate approximation and turnover time. Blank samples were prepared by immediate fixation with Lugol's solution after C 1 4-acetate was added. A blank sample was prepared for each incubated sample, and the assayed activity from the blank sample was substracted from each respective incubated sample. Recent experimentation has presented evidence that limited "pool-leakage" occurs by fixation with Lugol's solution. Immediate filtration, rather than fixation, results in activity values approximatelv 10% higher for acetate (Wright and Hobbié, 1966). Figure 1A indicates sampling stations used with corresponding depths sampled. Figure 1B, IC, and 1D represent the kinetic parameters associated with the heterotrophic removal of acetate by aquatic bacterial microrganisms. The kinetic parameters consist of the following: 1B) Vt, the theoretical maximum velocity of uptake, as fig acetate l" 1 hr _ 1 removed, IC) Kt + S n, the approximation of the natural substrate concentration, as fig acetate 1 _ 1, and 1D) Tt, the turnover time for the substrate to be completely removed from solution by the natural populations present in the sample in hours. The kinetic parameter, Kt+S n, is actuallv the sum of Kt, a constant similar to the Michaelis constant here defined as an affinity constant for the substrate, and S„, the in situ substrate concentration. Kt is considered to be quantitatively quite small in comparison to S n. The horizontal rangé of maximum rate of uptake was found to be 6.9—17.4 fig acetate l1 hr1, while the vertieal rangé was 9.2—10.5 ug acetate l" 1 hr 1 (Figure 1B and Table 1). The uptake rates essentially decrease from the west side of the pond towards the outflow. It has been suggested that bacteria increase their biomass as a direct re.spon.se to additional quantities of substrate, rather than increase their rate of uptake (Wright and Hobbié, 1966). Alsó, it has been shown that the rate of uptake, following MichaelisMenten enzyme kinetics, and identifiable as bacterial uptake operating at low substrate concentrations, is directly proportional to the bacterial biomass present (Wright and Hobbié, 1966). Thus, it is reasoned that totál counts of viable bacteria in Lake Lötsjön would follow the decrease towards the outflow and that dissolved organic materials more readily available to the bacteria in the western portion of the pond. The concentrations of dissolved organic carbon follow changes in Vt, the maximum rate of uptake (Table 1). Correlation of other chemical and physical properties with maximum rates of uptake is weak. The horizontal rangé of acetate approximations was found to be 5—150 /tg l1, while the verticai rangé detected was 6—7 fig ] ' (Figure IC and Table 1). The high K t+S n value found at Station 5, of 150 fig l1, is suggested to be the result of: 1) the excretion or liberation of dissolved organic matter by planktic algae, or other microorganisms, 2) degradation products resulting from microbial detemposition or free-enzymatic action, 3) extraneous material from outside the pond, or 4) dissolved organic matter which is possibly excreted into the water by submerged or emergent aquantic vegetation. Large portions of the western tip of the pond (littoral zone) are entirely covered by Scirpus, Phragmitis, Nuphar, Nymphaea, Carex, Potamogeton, Typha, and Utricularia. The aquatic vegetation present may function as a source of organic substrates for littoral and open water regions. Turnover times for acetate (Figure 1D and Table 1) represent the number of hours required Figure 1. Sampling stations and depths (A); Vt, kinetic parameters of theoretical maximum velocity of uptake, as fig acetate 7 _ 1 hr~' (B); Kt + S n, approximations of in situ substrate concentrations, as fig acetate 1 1 (C); Tt, natural turnover times for acetate in hours, as utilized by planktic bacteria in Lake Lötsjön, August 14, 1965. Selected morphometric parameters of Lake Lötsjön are given as maximum length of 453 m, maximum width of 165 m. maximum depth of 2.8m, and mean depth of 1.7 m. OUTFLOW
