THE LIFE or DEVILS LAKE 



29 



The orjijaiiic material, represented b}' free and combined am- 

 monia, naturalh^ varies markedly, not only with season, l)ut also 

 with locality and depth (fig'. 8). 



PrtSTS 

 ptr 



Plilliofl- 



-rto, 



• no. 



P»<tr5 

 5 -, 



j/w'r£e.'n,.B'ii«'niT'ji-«'Xj«'fl>,o'Sfp'£XT.'iv«'D«' 



Figure 8. Seasonal occurrence of organic material in Main Lake, Jan. -Mar.", 1914, 



Apr.-Dec, 1913. 



Dissolved gases also show marked variations with time and place, 

 which, to a certain exient, when plotted, take the form of cj'clical 

 curves dependent on the seasons. 



Especially is this true of dissolved oxygen. The amount of this 

 present in the lake depends on temperature, which in part deter- 

 mines the absorptive capacity of the water for gases and the 

 photosynthetic activity of plants; on amount and velocity of the 

 wind, determining amount of aeration ; on the number and activity 

 of the organisms present, and on the extent of decomposition taking 

 place in the water. 



The apparatus used for collecting oxygen samples is that recom- 

 mended in "Standard Methods" of the American Public Health 

 Association. 



Exact determination of oxygen in the lower layers is a matter 

 of considerable difficulty, due to currents generated by the raising 

 and lowering of the apparatus. When an oxygen free stratum 



