HEAT 



95 



out the lake, but also serve to distribute 

 oxygen and other dissolved materials uni- 

 formly from top to bottom in decided con- 

 trast to the conditions found during winter 

 and especially during summer stratification. 

 The usual geographic classification of 

 lakes of the world is based on these relation- 

 ships. It was originally suggested by Forel 



II. 



Order 3. Temperature of bottom water 

 similar to that of surface 

 water; circulation tends to be 

 continuous except when sur- 

 face is frozen 



Tempera'.e lakes: surface temperatures 



vary abc-ve and below 4° C. 



Order l. Temperature of bottom water 

 at 4° C. throughout the year; 



10 12 14 16 18 



Temperature in Degrees C. 



22 



Fig. 11. Summer temperature-depth curves for the major Finger Lakes in New York, shown 

 to the depth of 50 meters. ( Redrawn from Birge and Juday. ) 



(1901), and, after being modified by 

 Whipple (1927) and Welch (1935), is as 

 follows: 



I. Polar lakes: surface temperatures never 



above 4° C. 



Order 1. Bottom water 4° C. through- 

 out the year; one circulation 

 period possible in summer, 

 generally none 



Order 2. Temperature of bottom water 

 varies, but not far from 4° C; 

 one circulation period in 

 summer 



two circulation periods pos- 

 sible (one in spring and one 

 in autumn), but generally 

 none 



Order 2. Temperature of bottom water 

 varies, but not too far from 

 4" C; two circulation periods 

 (one in spring and one in 

 autumn ) 



Order 3. Temperature of bottom water 

 similar to that of surface 

 water; circulation more or less 

 continuous except when sur- 

 face is frozen 



