26 



THE LIFE OF DEVILS LAKE 



I 

 I 



20- 



Au&.i<i,m^ 



15- 



AuG. 25,111^ 



Figure 5. Graphs illustrating surface temperatures across Creel Bay on August 19 and 



25, 1914. 



JunriS.IIII 



"\"IXV .. 



Figure 



6. Temperature and oxygen curves for Main Lake. Ordinates represent depths 

 metres, abscissas, temperatures in degrees centigrade and cc. of 0:> pr. I. 



In fall, as the lake freezes, the water at the surface, next to 

 the ice, is cooled slightly faster than that at the bottom, and its ex- 

 pansion near the freezing point causes the cooler water to remain at 

 the surface for a time. Gradually, however, conduction equalizes 

 the temperature of the two regions, which thereafter remains con- 

 stant until spring, when, the warming of the surface layer, and its 

 consequent condensation, again produces thoro mixing of the entire 

 body of water, the surface and bottom temperatures thereafter re 

 maining nearly constant until summer conditions ensue. Temporary 

 and slight variations occur, dependent on the changing conditions 

 produced by melting ice and snow, alternate freezing and thawing 

 during the early spring and the varying temperature of the air. 



Some tyjiical temperature and oxygen curves for different sea- 

 Bons are shown in figures 6, 7 and plate 7. 



