THE LIFE OF DEVILS LAKE 



25 



the maximum difference in no case exceeding 1^' C, and usually 

 being less than that. Some additional readings have been made, 

 especially along shore in summer time to determine temperature ex- 

 tremes in various parts of the lake. 



Beside these readings a series of records were made with a 

 thermograph during the summers of 1914-15, to obtain a comparative 

 record cf temperatures in air, at the surface and near the bottom 

 for all hours of day and night, for a period of several weeks, one 

 of which is shown in figure 4. These show, as might be expected, 

 the greater changes occurring at the surface, as compared with 

 lower levels of the lake. 



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21.11 



Figure 4. Thermograph records on Creel Bay for air and surface on August 13-14 and 



25-26, 1914. 



In a shallow lake such as Devils Lake no thermocline develops 

 and there is usually but little temperature difference between top 

 and bottom. In hot summer days the surface temperature rises a 

 few degrees above the bottom, but there is no distinct break between 

 the two. Similarh' the shallow water near shore, especially on 

 quiet sunny days, reaches a higher temperature than the surface 

 water in mid lake. Vice versa the surface and shore water are 

 cooled at night more than the bottom, so that more or less mixing 

 of the water occurs daily. 



As the lake warms in the spring the shore water naturally 

 warms faster than the main body, a condition similar to that de- 

 veloping on warm summer days, while reverse conditions occur as 

 the lake cools in autumn. Figure 5 well illustrates these differences. 



