GASES IN WATERS OF WISCONSIN LAKES. 



1291 



PRACTICAL IMPORTANCE OF THE SUBJECT. 



If this scientific interest were all that the story affords, however, I should 

 not have brought it to the attention of this congress, whose interest rightly lies 

 in the fisheries. But these changes, which go on in the water of the lake, affect 

 not only the life of lower organisms but also that of the higher ones, including 

 the fish. No facts of environment show more clearly than do these how life 

 determines its own conditions. On the presence of a large or a small quantity 

 of plankton in the upper waters may depend the conditions which make the 

 lower water habitable or uninhabitable. The relation between the volume of 

 the lower water and the quantity of decomposing matter discharged into it 



OCb 



T 



CbC 



CCb 

 2 2 





 6 8 



10 12 14 16 



T 



18 20 22' 



Cb 



T C 



Fig. 19. — Silver Lake, August 21, 1907. 



Fig. 20. — Hammills Lake, August 17, 1908. 



determines whether this lower water shall be filled with animal life and support 

 a relatively abundant population of lake trout and whitefish, or whether life of 

 all kinds shall cease abruptly at the thermocline, or whether a scanty plankton 

 shall indeed leave abundance of oxygen in the lower water but provide a supply 

 of food for a scanty higher life. Thus the armual history of the lake discloses 

 facts that are fundamentally important in determining the amount and kind of 

 hfe which the lake may support and that which may wisely be introduced into it; 

 and it becomes plain that a knowledge of them is indispensable to an intelligent 

 use of the waters of the lake by those concerned in increasing the supply of fish. 

 In other words, it seems clear that a knowledge of lacustrine physics and 

 chemistry is just as necessary to the best economic utilization of the waters of 



