576 
BULLETIN OF THE BUREAU OF FISHERIES. 
DISSOLVED GASES. 
methods of observation. 
During the month of August, 1910, observations were made on 10 of the Finger 
Lake for the purpose of ascertaining the amount of dissolved oxygen and carbon 
dioxide in their waters. The samples of water for these determinations were obtained 
either by means of a pump and hose or with a closing water bottle. With one excep- 
tion the former method was used at all depths in the shallower lakes — that is, those 
not exceeding 30 meters (100 feet) in depth — and in the upper water of the deep lakes. 
The water bottle was used on Otisco Lake and in the lower strata of the deep lakes. 
The Winkler method was used for the determination of the quantity of dissolved 
oxygen and the Seyler method for the carbon dioxide. These methods have been 
fully described in a previous publication,** and further consideration of them is not 
necessary here. A new table of oxygen saturations (table xxi, p. 609) is included 
as a substitute for the previous one. It is based upon the more recent determinations 
of Fox,* who gives the results for degrees centigrade from —2° to H-30°. The inter- 
vening tenths of degrees have been interpolated. 
overturning and circulation of the water. 
The Finger Lakes belong to the temperate type, in which the water is subject to an 
overturning and a complete vertical circulation in the autumn and also in the spring. 
These phenomena are such important factors in the general distribution of the dis- 
solved gases that they deserve a brief description here as a preliminary to the discussion 
of the gases. When the surface water begins to cool in late summer or early autumn, 
it becomes heavier than the water below it and tends to sink, thereby producing con- 
vection currents. Through the agency of these currents and the wind the water of the 
epilimnion is thoroughly mixed, and as the temperature of this stratum declines with 
the advance of the season more and more of the lower water becomes mixed with the 
upper; that is to say, there is a downward movement of the thermocline and the epilim- 
nion becomes thicker at the expense of the hypolimnion. This process continues until 
the temperature of the epilimnion approaches that of the hypolimnion, when the whole 
body of water may be set into rotation by a strong wind. This phenomenon is known 
as the autumnal overturning, and it is followed by a complete circulation of the water, 
which continues until the lake becomes covered with ice. Seneca and Cayuga Lakes 
do not freeze over completely very often — on an average only about once in 20 years — 
so that their waters are subject to disturbance by the wind during the entire winter. 
As long as the temperature of the water remains above 4° in the autumn both the 
iwind and the convection currents are concerned in the production of the circulation, 
« Birge, Edward A., and Juday, Chancey: The Inland Lakes of Wisconsin: The dissolved gases of the water and their bio- 
logical significance. Wisconsin Geological and Natural History Survey, Bulletin xxn, Scientific Series No. 7, 259 p. 1911. 
>> Fox, Charles J. J.; On the coefficients of absorption of the atmospheric gases in distilled water and sea water. Part I. 
Nitrogen and Oxygen. Conseil Permanent International pour L’Exploration de la Mer. Publications de circoustance. No. 41, 
1907, 23 p., I pi. 
