Nitrogen 



49 



The relative productiveness in open-water life of 

 these situations is shown in the last column of the table. 



The difference between these four adjacent bodies of 

 water explains some of the peculiarities of the table. 

 The rivers hold more solids in suspension than do the 

 lakes, although these lakes are little more than basins 

 holding impounded river waters. Spoon River holds 

 the least amount of dissolved solids, and by far the 

 greatest amount of suspended solids. Since the latter 

 are not available for plant food, naturally this stream 

 is least productive of plancton. Illinois River drains a 

 vast and fertile region, and receives in its course the 

 sewage and other organic wastes of two large cities, 

 Chicago and Peoria, and of many smaller ones. Hence, 

 its high content of dissolved matter, the cities being 

 remote, so there has been time for extensive liquefac- 

 tion. Hence, also, its high content of ammonia, of 

 nitrites and of nitrates. 



The two lakes are very unlike ; Quiver Lake is a mere 

 strip of shoal water, fed by a clear stream that flows in 

 through low sandy hills. It receives water from the 

 Illinois River only during high floods. Thompson's 

 Lake is a much larger body of water, fed directly from 

 the Illinois River through an open channel. Naturally, 

 it is much like the river in its dissolved solids, and in its 

 total organic nitrogen. That it falls far below the 

 river in nitrates and rises high above it in plancton 

 production may perhaps be due to the extensive con- 



