the amount available to the plankton algae, for much of it would be 

 used as soon as it was formed. 



Conclusions regarding pollution 



The data on oxygen and nitrogen show that River Raisin near 

 its mouth was polluted. Determinations of nitrogen at all stations in 

 the lake near the river indicate that the nitrogen content had been 

 increased as a result of the discharge of polluted river water. The 

 most distant of these stations was two miles from the nouth of the 

 river, but in all probability the lal;e Xv'ater was affected for a some- 

 what greater distance in all directions. Marked withdrawals of oxygen 

 definitely referable to pollution were found only at the ncuth of the 

 river and at points not more than one-half mile distant. It is probable 

 that low oxygen occurred at greater distances in the water in immediate 

 contact with pclluced bottom. At the depths investigated the harmful 

 effect of the polluted water app;irently was restricted to a very small 

 area near the mouth of the river. River Raisin was less heavily 

 polluted than Maumee River, but more so than Portage River, 



Detroit River Section 



Oxygen, carbon dioxide, and hydrogen-ion concentration 



Chemical data obtained at Station 13li in 1929 and 1930 are 

 shown in Table Ul. This station is located in the lake fully 13 miles 

 from the mouth of the river, but it is included in the Detroit River 

 Section because it appears to be influenced markedly by the river. The 

 depth is 10 meters. 



The data from this station may be passed over, for the most 

 part, without comment. In many respects conditions here were very much 

 like those found in the Island Section, However, it should be noted 

 that carbonates were consistently low. Only one sample gave a methyl 

 orange alkalinity in excess of 90 parts per million, whereas most of 

 the sa;nples in other sections of the lake were above 90. Without doubt 

 the low methyl orange alkalinity was due to the influence of 

 Detroit River, which was consistently low also. 



Station 126 is also located in the lake, but only 5 miles from 

 the mouth of the river. The water here is derived directly from 

 Detroit River, except, possibly, under unusual conditions. Samples 

 were taken here on several dates in 1928, 1929, and 1930, The data 

 are given in Table U2, 



121 



