194 



the latter. The small amount in Quiver Lake is attributable 

 to its greater independence of the river, to the paucity of its 

 plankton, and to the sandy nature of its drainage basin and 

 consequent share of spring water in its water supply. It is 

 noticeable that the large amount of submerged vegetation in 

 this lake does not contribute any great amount of organic 

 nitrogen to the water at any season of the year. 



The nitrogen as albuminoid ammonia is included in the to- 

 tal organic nitrogen, and exhibits almost identical relative 

 amounts in the four localities, though actual quantities are 

 only half as great. It represents the nitrogenous materials 

 which have not undergone decomposition. 



The nitrogen as "free" ammonia represents the ammonia 

 contained in the water in free or saline condition. It is a prod- 

 uct of the decomposition of organic matter in the first stages 

 of oxidation, and its quantity is an indication of the amount 

 of such matter present in the water in a partially decomposed 

 state. It is abundant where sewage occurs, and together with 

 the chlorine affords evidence of the degree of contamination. 

 The occurrences of free ammonia in the four localities (.86, 

 .245, .165, and .422) are not in most instances in the same ra- 

 tios as those of the chlorine (21.6, 3.8, 4.8, and 16.3) or of the 

 plankton (1.91, .384, 1.62, and 6.68). The excess (two to five 

 times as much) of decaying organic matter in the river as com- 

 pared with the other situations is apparent, and is doubtless due 

 to the concentration of sewage in its channel and to the more 

 recent access of the sewage there as compared with that in the 

 reservoir backwaters, as, for example, in Thompson's Lake. 

 The early stages of decay are in consequence more active in 

 the river. The free ammonia is high in both the river (.86) and 

 Thompson's Lake (.422) but lower in Spoon River (.245), where 

 the organic material in suspension is considerable, as indicated 

 by the loss on ignition, the albuminoid ammonia, and the organic 

 nitrogen and oxygen consumed. The decay of this matter and 

 the accompanying release of free ammonia has not been attained 

 as yet in a part at least of the silt in Spoon River to the same 



