A LIMNOLOGICAIv STUDY OP THE FINGER LAKES. 
5«-i 
has been placed in the third class because it belongs to the group of major lakes in 
other features. 
The minimum amount of oxygen in these lakes was found at the bottom, and it 
varied from 5.57 cc. per liter of water in Keuka Lake to 8.45 cc. in Seneca Lake, or 
from 63.8 to 91.7 per cent of saturation. It will be noted that all of the members of 
this class are the larger and deeper lakes of the group— that is, those that have been 
designated as the major lakes. The volume of the hypolimnion of each is relatively 
large in comparison with the epilimnion, very large indeed in the deepest ones, and this 
large body of cool water is able to hold in solution a proportionally large quantity of 
oxygen, so large that the respiration of the organisms inhabiting it and the decomposi- 
tion of the organic material which 
sinks into it from the upper water do 
not make extensive inroads upon the 
supply of free oxygen. The mem- 
bers of the first and second classes 
constitute the group of minor lakes. 
They are relatively small and shal- 
low bodies of water, in which the vol- 
ume of the epilimnion is large in pro- 
portion to that of the hypolimnion. 
How large a proportion of the 
oxygen supply of the hypolimnion is 
lost during the summer depends 
upon the amount consumed in respi- 
ration and decomposition and upon 
the volume of this stratum. If the 
volume of the epilimnion is relatively 
large in proportion to that of the hy- 
polimnion and it is well populated 
with plankton organisms, so that it 
contributes a large amount of de- 
composable material to the latter, the dissolved oxygen is rapidly consumed, so that 
very little may be left in this stratum by midsummer. On the other hand, when the 
hypolimnion is relatively very large and the upper water contributes only a compara- 
tively small amount of decomposable material, the total volume of oxygen suffers only 
a very small decrease. 
In the thermocline . — The quantity of dissolved oxygen in the thermocline is dependent 
in the main upon the amount in the hypolimnion. If it is practically exhausted from 
the lower water, there is generally a rapid decrease of oxygen as we pass downward 
through the thermocline. In Conesus Lake, for example, the amount decreased from 
6.0 cc. per liter of water at 8 meters to o.i i cc. at 10 meters. In Otisco Lake it declined 
from 5.77 cc. at 9 meters to 0.34 cc. at 12 meters. (See table xviii, p. 602.) But lakes 
Fig. 10. — Dissolved gases, Otisco Lake, Aug. i6, 1910. Forexplanation, 
see fig. 9, p. 580. 
