GASES IN WATERS OF WISCONSIN LAKES. 



1279 



SPRING AND SUMMER. 



When the ice has disappeared in the spring (fig. 5) , the water is once more 

 mixed throughout the entire depth, and uniform conditions are again estab- 

 lished. The reaction becomes almost or quite neutral. Oxygen is present to 

 about the point of saturation, although, in figure 5, some trace of the winter's 

 diminution of oxygen is still present at the bottom. Carbonates and nitrogen 

 are distributed about uniformly at all depths. As the spring advances and the 

 algae begin their spring growth, the reaction of the water becomes increasingly 







I 



2 



3 



A 



5 



6 



7 



8 



9 



10 



li 



12 



13 



14 



15 



16 



17 



18 



19 



20- 



c 



4 2 



T 

 2 4 



Cb N 



6 8 10 .12 14 16 18 20 22 24 26 28 30 3? 34 36 38 40 42 44! 



22 

 23- 



T C N 



Fig. 4. — Lake Mendota, March 29, 1906. 



Cb 



alkaline. (Fig. 6.) The temperature rises, and soon the surface gains so 

 rapidly in warmth that the wind is unable to distribute the surface water 

 throughout all depths; the circulation becomes increasingly restricted, and sum- 

 mer conditions begin to develop. The temperature curve (fig. 7) shows a 

 marked difference between surface and bottom temperatures, and indicates a 

 temporary thermocline at the depth of 10 meters or more. Corresponding to 

 this stratification of the water and consequent shutting off of the lower water 

 with direct contact with the air, the oxygen in the lower water begins to decline 



