Biological Survey — Erie-Niagara Watershed 59 



be borne in mind that this discussion applies only to the lake con- 

 ditions as determined at points one-half mile or more from shore. 

 The pollution problem in shallow water close to shore is handled 

 elsewhere in the State report.^ 



When sewage and other organic wastes are added to a body of 

 water decomposition soon sets to work. By the normal processes 

 of ''oxidation" large quantities of oxygen may be removed from 

 the water and used in breaking down the complex organic com- 

 pounds into simpler form. It may readily be realized that where 

 this goes on to any considerable extent the normal amount of 

 oxygen dissolved in water may be depleted in a marked degree. 

 Hence oxygen depletion is often taken as an indication of pollution. 



Oxygen depletion as a criterion of pollution must, however, be 

 used with consideration of other factors. Replenishment of the 

 supply of dissolved oxygen from the atmosphere and from the 

 photosynthetic process of green organisms in sunlight may serve 

 to maintain a relatively high percentage of saturation even in the 

 presence of pollution. This condition of plenty of free oxygen will 

 be found wherever large growths of algae furnish oxygen in excess 

 of the demands of oxidation reactions. Because of the interaction 

 of various factors judgment must be used in weighing the value of 

 the analyses for the interpretation of pollution condition. 



The minimum degree of oxygen saturation found in the lake 

 during the period of the survey was about 50% and the greatest 

 95%. A certain amount of oxygen depletion is normal for such a 

 body of water, because of the animal forms which use oxygen in 

 their respiration and to a greater extent because of the decom- 

 position of the bodies of dead organisms whose natural environ- 

 ment is the lake. An average oxygen content in Lake Erie of 

 approximately only 25% below the saturation point is due to the 

 normal respiration of the lake and is not indicative of pollution. 



The relative abundance of certain nitrogenous compounds is 

 used as an index to the amount of organic pollution. All of the 

 analyses showed that the several kinds of nitrogen determined 

 were present in quantities — signifying no objectionable pollution. 



The amount of free ammonia present never reached more than 

 .038 parts per million of nitrogen and on the average it occurred 

 as only about .016 parts per million. These figures are compara- 

 tively low. 



The analyses for albuminoid ammonia showed a minimum figure 

 of .06 and a maximum of .12 with an average of .08 parts per 

 million for the entire eastern end of the lake. And these figures are 

 comparatively low. 



The nitrate analyses indicate the presence of moderate amounts 

 of nitrogen in its completely oxidized state. The largest quantity 

 was determined in July at .20 parts per million; the smallest 

 occurred in August as .08 parts. Nitrates averaged .14 parts per 

 million. 



See report of Dr. F, E. Wagner, et al. 



