Figure 3 : Decrease in Organic Carbon concentration during the dark incubation of a lake water
sample from Lago di Mergozzo.
expect, the OC concentration decreases logarithmically ; thus the significance of the
decrease has been evaluated by using the logarithmic regression model. In both lakes the
decrease of OC concentration turned out to be statistically highly significant, with r =
0.978 for Lago Maggiore and r - 0.985 for Lago di Mergozzo.
In order to compare these findings with the results from other methods which express
heterotrophic activity in terms of uptake velocity, a rough evaluation of the mean velocity
of OC consumption was made. For the two experiments presented here the OC consumption rate turns out to be 11.6µgC/1 .h for Lago Maggiore and 50.2 µgC/ 1.h for Lago di
Mergozzo. These two values are close to the minimum and maximum rates found in some
twenty OC consumption measurements performed from 1981 to 1983. In three cases
during this period, working with samples taken in January and February, no significant
OC decrease occurred.
It should be noted that the variations in OC concentrations thus measured result not only
from heterotrophic breakdown but also from activities such as heterotrophic growth,
grazing, autolysis, etc...Nevertheless, since a decrease in OC concentration is generally
observed, the catabolic heterotrophic processes turn out to be the prevalent ones.
A further example of what can be obtained by microanalytical methods is presented in
Figure 4.
Figure 4 : Variations in Dissolved Organic Carbon concentration during the light-dark cycle in a lake water
sample from Lago di Mergozzo (dark periods are shaded).
106
sample from Lago di Mergozzo.
expect, the OC concentration decreases logarithmically ; thus the significance of the
decrease has been evaluated by using the logarithmic regression model. In both lakes the
decrease of OC concentration turned out to be statistically highly significant, with r =
0.978 for Lago Maggiore and r - 0.985 for Lago di Mergozzo.
In order to compare these findings with the results from other methods which express
heterotrophic activity in terms of uptake velocity, a rough evaluation of the mean velocity
of OC consumption was made. For the two experiments presented here the OC consumption rate turns out to be 11.6µgC/1 .h for Lago Maggiore and 50.2 µgC/ 1.h for Lago di
Mergozzo. These two values are close to the minimum and maximum rates found in some
twenty OC consumption measurements performed from 1981 to 1983. In three cases
during this period, working with samples taken in January and February, no significant
OC decrease occurred.
It should be noted that the variations in OC concentrations thus measured result not only
from heterotrophic breakdown but also from activities such as heterotrophic growth,
grazing, autolysis, etc...Nevertheless, since a decrease in OC concentration is generally
observed, the catabolic heterotrophic processes turn out to be the prevalent ones.
A further example of what can be obtained by microanalytical methods is presented in
Figure 4.
Figure 4 : Variations in Dissolved Organic Carbon concentration during the light-dark cycle in a lake water
sample from Lago di Mergozzo (dark periods are shaded).
106