58 



PROBLEMS OF LAKE BIOLOGY 



TABLE IX 



Seasonal Variations of Periphytic Bacteria, Surface Water, Littoral Stations 



OF Lake Alexander. 



Temperatures are means of readings at beginning and end of immersion. Dates are median dates. 



ered the accumulation of these substances 

 in the bottom deposit to be important in 

 determining the production of methane, and 

 Kusnetzow (1935) believed that the absence 

 of oxyo-en in "fish-suffocating" lakes under 

 winter conditions is due to the liberation 

 of hydrogen and methane from the bottom 

 deposits of such lakes. Rossolimo and 

 Kusnetzowa (1934) found methane-produc- 

 ing bacteria to be more abundant in the 

 bottom deposits in winter than in summer. 

 Perhaps these facts have some bearing upon 

 the large numbers of periphytic bacteria 



noted at the bottom of Lake Mendota in 

 winter. 



Summary of Seasonal Distribution. Sea- 

 sonal fluctuations of bacteria apparently 

 are different in different types of lakes. In 

 high mountain lakes the semi-annual turn- 

 over, distributing bottom bacteria through 

 the water, apparently determines the max- 

 ima, though the effect of spring thaws and 

 autumn rains may be a factor. Plate counts 

 are probably affected considerably by sur- 

 face drainage washing bacteria into the 

 lakes. In a highlj^ eutrophic lake the plank- 



