70 
BUULETIN OF THE BUREAU OF FISHERIES. 
they reach the bottom. This would use up more of the oxygen of the upper hypo- 
limnion and there would be less decomposition and loss of oxygen at the bottom. 
This is shown in all of the very deep lakes of this section by the very small, if any, 
decrease in oxygen at the bottom, while in the lakes less than 95 m. deep (except 
Bear Lake) there is a marked decrease in the oxygen at the bottom. In some of the 
lakes not over 20 m. deep (Martha, Silver, Williams, Sammamish) there is a fairly 
large amount of oxygen at the bottom. Martha and Williams had few algae, but 
Sammamish and Silver had a fairly large amount of algae, which would die and 
decay later in the season. The oxygen at the bottom of some of the very shallow 
lakes (Spanaway, Goodwin, Cottage, Newman) is probably accounted for by a 
partial circulation. It is very probable that these lakes might be entirely circulated 
and changed to Group I by a high wind. The single set of results that we have 
could not answer this, but Cottage and Spanaway especially possess a large crop 
of algae, and the oxygen would either disappear entirely later in the summer, or the 
supply would be replenished by more or less complete circulation. 
Division 2 of Group II contains the lakes that lose all of the oxygen at the 
bottom during late summer. The following seven lakes belong in this division: 
Luna, American, Silver (in east Washington), Cow, Wildwood, Chatcolet, and 
Paradise. They vary in depth from 8 to 26 m. In most respects they are very 
similar to division 1 of this group. The complete removal of the oxygen is caused 
by a larger amount of organic material that decays in the hypolimnion or by a 
smaller supply of oxygen to carry out this decay. Here there is a more marked 
increase of free carbon dioxide caused by the decay and corresponding with the 
decrease in oxygen. 
SATURATION OF WATER WITH OXYGEN. 
The amount of oxygen dissolved by a unit volume of water is dependent upon 
the partial pressue of the oxygen in the air. When the atmospheric pressure is 
decreased by altitude or otherwise, the partial pressue of oxygen is correspondingly 
decreased and the amount of oxygen that a unit volume of water will absorb is 
decreased in the same proportion. 
The saturation of distilled water with oxygen has been determined with dry air 
at a pressure of 760 mm. by Fox (1907) and tabulated by Birge and Juday (1914). 
These figures have been used in calculating the per cent of saturation of the lakes 
at or near sea level. Juday (1915) states that the amount of oxygen 1 liter of water 
will absorb from the atmosphere is decreased approximately 1 per cent for each 
82 m. (270 feet) of altitude. It can not be calculated exactly, as the barometer 
varies from day to day at each elevation and as the temperature and humidity also 
vary. The results calculated in this paper have been taken from the Smithsonian 
Meteorological Tables, 1907, Table 25. Since the variation of the barometric 
pressure at any altitude is by far the largest error in this calculation, no attempt 
has been made to correct for humidity and temperature. 
Most of the lakes in western Washington are so near the sea level that it is not 
necessary to apply a correction, but with some of the mountain lakes it becomes 
important, as shown by the calculation for these lakes. 
