58 o 
BULLETIN OF THE BUREAU OF FISHERIES. 
— 
r 
\c 
4 - 
1 
1 
1 
1 
1 
, 
1 
1 
1 
1 
1 
1 
i 
■ 
\ 
\ 
/ 
V 
\ 
< 
\ 
i 
"T 
s 
1 
i 
\ 
ie iS 3o 
Conesus and Otisco Lakes are good representatives of this class. In the former all 
of the water below a depth of lo meters either possessed no free oxygen at all or con- 
tained only traces of it. The same was true of a few meters of the bottom water of 
Otisco Lake. (See table xvui, p. 602, fig. 9 and 10.) The oxygen disappears from the 
bottom water first because decomposable material is more abundant at that depth. This 
material is derived from plankton organisms and from shallow water and shore vege- 
tation. The specific gravity of the plankton organisms is so low that they sink 
through the cool, lower water 
very slowly and they thus pass 
through the earlier stages of 
decomposition at least before 
they reach the bottom. In this 
way they draw upon the oxy- 
gen supply at all depths in the 
hypolimnion so that, if such 
decomposing organisms are 
sufficiently numerous and the 
volume of this stratum is not 
too great, practically all of the 
dissolved oxygen may disappear 
from this region. 
If the decomposable ma- 
terial derived from the epilim- 
nion is not so abundant, or if 
the volume of the hypolimnion 
is relatively great, with a cor- 
respondingly large amount of 
oxygen, there is not a total 
exhaustion of this gas in any of 
this stratum, but only a marked 
decrease, such as was noted in 
Canadice and Hemlock Lakes. 
(See table xvm, p. 602, and 
fig. II and 12.) Here the water 
below 18 meters contained less 
than 50 per cent of the quantity of oxygen required for saturation ; the bottom water 
in the latter lake had as little as 8.4 per cent. 
If a still smaller quantity of decomposable material is derived from the upper 
water, or if the volume of the hypolimnion is still larger, the decrease of oxygen is 
correspondingly smaller, as in Canandaigua, Cayuga, Keuka, Owasco, Seneca, and 
Skaneateles Lakes, which belong to the third class. (Table xviii, p. 602, and fig. 13-18.) 
Perhaps Keuka Lake should be placed in the second class, since its bottom water con- 
tained less than two-thirds of the amount of oxygen required for saturation; but it 
Fig. 9. — Conesus Lake, Aug. 25, 1910. The curves for dissolved gases are desig- 
nated as follows: C=carbon dioxide; that portion to the left of the zero line 
indicates the alkalinity and that to the right the free carbon dioxide; 
Cb=fixed carbon dioxide; 0 =oxy gen; and T=teinperature. The vertical 
spaces represent the depth in meters and the horizontal spaces show the 
temperature in degrees centigrade and the cubic centimeters of gas per liter 
of water at normal temperature and pressure. The depths at which obser- 
vations were made are indicated by small circles and these points have 
been connected directly without any attempt to round off the curves. 
