SURFACE 



ui 

 u 



X 



t- 



Q. 6 



BOTTOM 



44 



46 48 50 52 54 56 



TEMPERATURE, DEGREES FAHRENHEIT 



58 



FIG. 10. — Vertical temperature sections, degrees F., in Fork Lake during the spring of 

 1939, showing a period of temporary stratification, March 24. 



tlon throughout the suimner. It is probable that, in the spring, stratification is estab- 

 lished and broken up several times before the lake finally reaches the summer condition. 

 Examples of these early spring changes are graphed in fig. 10. No instances of complete 

 circulation were recorded during the summer. The first fall overturn, mentioned above as 

 occurring on September 15, followed a violent storm. Temporary stratification was again 

 fovind on September 25, while the weather was still warm. It is probable that during the 

 fall there was occasionally complete stirring as in the spring. 



An experiment on the effect of artificial stirring was made on August 14 by Dr. C. L, 

 Schloemer and the senior author. Temperatures and oxygen samples were taken at 1-foot 

 depth intervals, ir the center of the lake, and then the lake was stirred for an hour with 

 a 4-horsepower outboard motor anchored at one location 10 feet from shore. Tempei^tures 

 and oxygen determinations were made again immediately afterward. The results of the 

 stirring are shown in table 12. They suggest the practicability of artificial means for 

 stirring oxygen into the lower waters of small artificial lakes. 



TABLE 12~THE EFFECT ON STRATIFICATION OF STIRRING FORK 

 LAKE WITH AN OUTBOARD MOTOR, AUGUST 14, 1939. 



16 



