34 



Nature of Aquatic Environ meat 



Fig. 6. Diagram illustrating the distribution of temperature in Cayuga Lake 



throughout the year. 



The yearly cycle — The general relation between sur- 

 face and bottom temperatures for the year are graphi- 

 cally shown in the accompanying diagram, wherein the 

 two periods of thermal stratification, "direct" in summer 

 when the warmer waters are uppermost, and "inverse" 

 in winter when the colder waters are uppermost, are 

 separated by two periods of complete circulation, when 

 all the waters of the lake are mixed at 4 C. The range 

 of temperatures from top to bottom is much greater in 

 the summer "stagnation period"; nevertheless there 



