204 



the sum total of the averages of the nitrogenous matters (free 

 ammonia, organic nitrogen, nitrites, and nitrates) and also the 

 average plankton production — sets forth in brief the relative 

 fertility and production of the four localities. 



There is more nitrogenous matter in the streams than in 

 the lakes, but also less plankton. Nutrition for the plankton 

 is present, but time for breeding, owing to the more recent or- 

 igin of stream waters, has not been afforded there, while in the 

 lakes, which have somewhat of a reservoir function, there is 

 time for growth of the plankton, and the store of food is de- 

 pleted as compared with that in the river. It is also evident 

 that there are unutilized stores of food in the rivers affording 

 a basis for further development of the plankton. 



The Illinois River exhibits the greatest fertility ( total 

 nitrogenous matters 3,617 ), owing largely to sewage and in- 

 dustrial wastes. These matters cause the high chlorine (21.6) 

 and the large amount of free ammonia (.86) and organic nitro- 

 gen (1.03), while the abundant solids in solution (304.1) and the 

 nitrites (.147) and nitrates (1.58) show how large a part has 

 reached the last stage of decomposition. The unutilized prod- 

 ucts of decomposition are without exception in the data here 

 discussed greater in the waters of the channel than in the trib- 

 utary or impounded reservoir waters. 



In Spoon River the solids in suspension are highest (274.3) 

 and those in solution least (167.1), a condition due to the re- 

 cent origin of its water and to the large amount of silt which 

 it carries. The organic origin of some of this silt is shown by 

 the large loss on ignition (41.9), the oxygen consumed (14.1), the 

 albuminoid ammonia (.604), and the total organic nitrogen 



