(1) Comparison of the coiKits at Station 126 and in Lake St. Clair on 

 the same day does not point toward wholesale destruction of plankton in 

 the river. Similar differences might be expected between two nearby- 

 stations in the same body of water. (2) There is no chemical evidence 

 of the presence in the water of poisonous substances in such concentra- 

 tion that they would kill plankton organisms (page 225)."^ (3) At the 

 mouth of Maumee River, where the water was much more heavily polluted 

 than in Detroit River, plankton was extremely abundant (Table 56), 



All of the available evidence, then, leads to the conclusion 

 that Lake Erie near the mouth of Detroit River is poor in plankton 

 because Lake St. Clair is poor in plankton, and that pollution, if it 

 is a factor at all, is one of minor importance. 



Comparison of abundance of phytoplankton 

 in different sections of Western Lake Erie. 



In the foregoing accounts of phytoplankton in the different 

 sections of the lake, attention \-jas directed to relative abundance. It 

 was shown that the Maumee Bay Section contained phytoplankton in 

 greater abundance than the other sections of the lake. The abundance 

 in the River Raisin Section was greater than in the Island or Detroit 

 River Sections, but less than in the Maumee Bay Section. The Detroit 

 River Section was shown to be poorest of all. 



This relationship was particularly well shown by the data of 

 1930, In 1929 the program was somewhat irregular and few of the 

 two-week periods were represented by samples from all sections. Hence, 

 it is not possible to draw up a table showing relative abundance satis- 

 factorily. In 1930, however, samples were taken in all s ections in six 

 consecutive two-week periods. In Table 62 the data from these samples 

 are condensed in such a way that the abundance of total phytoplankton 

 can be compared conveniently. For purposes of this comparison, the mean 

 of Stations 2^2 and 25U is used to represent the Maumee Bay Section, 

 because Station 2^0, at the mouth of the river, probably is not represen- 

 tative of a large area. The Portage River Section is represented by 

 Section l59. River Raisin Section by Station 117, and Detroit River 

 Section by Station 126. For the Island Section, the number of stations 

 varies as indicated in Table 53, but in each case the mean of all 

 stations visited during the period is used. 



Reference to the lowermost row of figures in Table 62 shows 

 that there were large differences in the mean abundance in the various 

 sections. Listed in descending order with respect to abundance the 

 sections are: Maumee Bay, River Raisin, Portage River, Island, Detroit 



197 



