from the United States Lake Survey, retardations of U0-50 per cent due to ice 

 blockades are not infrequent in March and April. When the river is free from 

 ice, reductions in excess of 25 per cent of the mean are to be expected very 

 rarely. During the periods when chemical samples were taken in the present 

 investigation, the discharge was not far from the mean. The population of 

 municipalities contributing sewage directly to the river in 1930 was 1,850,3^40. 

 Therefore, with mean discharge, there would be 9 contributing persons per 

 second-foot. This figure is well above that which was regarded as allowable 

 by the International Joint Commission, but is much lower than that of Maumee 

 River and River Raisin during the months of July, August, and September. For 

 these months less intense pollution is to be expected in Detroit River at the 

 mouth than in the two rivers just mentioned. 



In fact there is reason to believe that Detroit River at the mouth would 

 show little or no chemical evidence of pollution at times of normal flow. 

 Frost, et al. (192U, pages 17U-178) were unable to detect, with certainty, the 

 effect of sewa^;e from Cincinnati on the nitrogen content of Ohio River when the 

 discharge exceeded 50,000 second-feet. At the time the analyses were made the 

 contributing population of Cincinnati was roughly 500,000 so that the degree 

 of dilution with a discharge of 50,000 second-feet would be about the same as 

 in Detroit River, with a contributing population of nearly two million and a 

 discharge of 200,000 second-feet. It is questionable whether Detroit River 

 would show very definite chemical evidence of pollution at the mouth even at 

 times of minimum flow. Conditions affecting dilution in Detroit River will 

 be given further consideration in connection with the discussion of results. 



All except a few of the chemical samples were taken when the lake was 

 free of ice, and when the streams other than Detroit River were discharging 

 less than the mean annual amount of water. It seems probable that, at times 

 of maximum discharge, dilution in these streams would be so great that it 

 would be difficult or impossible to- detect sewage pollution by the usual 

 chemical analyses. For example, on January l6, 1930, the dischrage of 

 Maumee River was 72,600 second-feet, so that there would be only four con- 

 tributing persons per second-foot of discharge at Toledo, or less than one 

 half the number for Detroit River at times of rrean flow. 



Portage River Section 



Oxygen, carbon dioxide, and hydrogen-ion concentration 



Chemical samples were taken in this area only in 1929 and 1930. The 

 only point at which sanples were taken regularly was Station l59, located 

 l/k Ddlfe north of Port Clinton Light, vrfiich is at the mouth of the river. 

 The depth at this station is 3.5 meters. The data obtained on l5 dates in 

 the two seasons are shown in Table 2ii. Because of the meager depth and 

 action of waves, the temperature was usually almost the same at top and 

 bottom; the greatest observed difference was 0.9*. On several occasions, 

 both surface and bottom sanples were taken, but the differences were too 

 small to have any importance. 



