Hidrológiai Közlöny 1967 (47. évfolyam)

7. szám - A „Szervesanyag meghatározási problémák édesvizekben” című 1966. szeptember 25–28. között Tihanyben rendezett Szimpózium előadásai - Wetzel, Róbert G.: Oldott organikus vegyületek két indiánai tóban

300 Hidrológiai Közlöny 1967. 7. sz. Wetzel, R. G.: Oldott organikus vegyületek K

t+S, JUL. AUG. SEP. OCT. NOV. DEC. Figure 2. Seasonal distribution of acetate: natural substrate concentrations (Kt + S

n)XlO~

3 mg l~', bacterial uptake velocity (V) X10'

1 mg l~' hrand substrate regeneration (Tt) in hours. Crooked Lake, Whitley-Noble Counties, Indlana, 1904. Points represent sampling periods and depths. it is apparent that uptake and effective utilization of these organic compounds are attributable to the bacterial populations. Caution must be exerted in referring to the Kt + S

nvalues as natural concentrations of the organic substrate. The estimations of the theoretical velocity (F) of substrate removal and utilization as measured are tliose of a composite heterogeneous plankton population. of which each component has its separate transport constant (Kt) and V. One population may have a high K

t for the specific substrate being assayed and is not assimilating this particular substrate efficiently while another population witliin the sample is very efficient and exhibits a low K

t value. When the uptake kinetics of these populations are assayed together, the high V of the ineffective population may mask the uptake of the efficient population when measured at higher substrate concentrations (Wright and Hobbié, 1965; J. Hobbié, personal communication). The substrate levels employed in the Crooked and Little Crooked lake analyses were low, usually beginning at 10 fig l~

l, and exhibited consistently active uptake kinetics at the lower levels. Thus, while this source of error was not apparent, its possibility is not precluded. Hence the expressions here of "natural substrate concentrations" must be viewed with these factors in mind. Natural substrate concentrations of glucose {Kt + Sn) decreased progressively in Crooked Lake from an autumnal maximum to low winter levels in the six-month period of investigation (Fig. 1). Thermal stratification terminated in the last week of November followed by weak periods of intermittent circulation. Ice cover did not occur until mid-January, 1965. Maximum observed glucose concentrations were found in the upper metalimnion in early September following a period of high algal production and accumulation in the metalimnion. The heterotrophic growth capacity (V) for glucose by bacterial populations, as inflicated by uptake velocities, decreased markedlv in the epilimnion, correlating directlv with the decreasing water temperatures and reduced substrate concentrations (Fig. 1). Turnover rates {Tt) of glucose in the epilimnion were relatively constant until the time of circulation in laté November. In the deeper waters during stratification the high rates of substrate regeneration decreased significantly in October and then increased again after overturn and colder temperatures. Regeneration times were much greater than those few data available for comparison, e. g. Lake Erken (Wright and Hobbié. 1966), Lake Lötsjön (Allén, in press) in southern Sweden. The seasonal distribution of acetate concentrations and its utilization in Crooked Lake were very different from those of glucose (Fig. 2). In spite of large variations in epilimnetic algal production rates, after Julv the distribution of acetate (Kt + Sn) was more uniform than glucose. Concentrations decreased steadily towards the winter period to less than 10 fi g/l in December. Utilization rates (V) of acetate were relatively constant at various strata until fali circulation in late November when lowest rates occurred. Turnover times of acetate were considerably lower than those of glucose and decreased significantly towards the winter period. These results indicate a probable distinct shift in the bacterial populations before and after stratification. Although the data for concentrations and the theoratical maximum velocities for substrate removal of galactose and fructose are too few for graphic treatment, seasonal trends are alsó apparent for these earbohvdrates (Table 1). Concentrations of galactose and fructose were much lower than glucose and acetate, and increased from midsummer to winter. Uptake velocities (V) of galactose and fructose were low, similar, and decreased very slightly towards \\-inter. Times required for turnover and substrate regeneration of galactose and fructose were very high and increased towards the colder period similar to that of glucose. The results indicate low levels of these isomers of glucose and a marked reduction in the ability for their utilization by in situ bacterial populations. The concentrations of glucose, galactose, fructose, and acetate in the adjoining Little Crooked Lake were roughlv two times those found in Crooked Lake (Table 2). Rates of heterotrophic utilization were generally higher in the trophogenic zone than in that of Crooked Lake. More im-