These data show some characteristics in common with those for Maumee 

 Bay. There is some indication of seasonal changes such as those found in 

 the Island Section, especially in the data for 1930, which are more complete 

 than those for 1929. Also, as in Maumee Bay, the abiindance in 1930 was 

 decidedly greater than in 1929; and blue-greens were dominant over greens 

 and diatoms, except for the first two dates in both years, and the last in 

 1929. Moreover the total counts at Station 117 were much higher than those 

 in the Island Section for almost all comparable dates (Tables $1 and 53). 

 These points in common between the Maumee Bay Section and the Pliver Raisin 

 Section suggest that the influence of factors involved in plankton produc- 

 tion is somewhat the same in both. 



In abundance of phytoplankton. Station 117 resembles Station 25ii more 

 closely than the stations nearer Maumee River. For a period of three months 

 in 1930, the mean count at Station 117 was 751 thousand units per liter, and 

 9lt3 thousand units at Station 25U. Station 117 resembles Station 25U in 

 depth (both about six meters), and in the concentration of nitrogen compounds 

 (Tables 39 and 33). There is little doubt that both of these stations were 

 naturally rich in plankton as a result of their proximity to shallow water 

 and that this has been augmented by the addition of nutritive salts from the 

 rivers. As ir Maumee Bay and Portage FtLver Sections, the dominance of blue- 

 greens probably is a response to the increased amount of nutritive salts 

 resulting from pollution. 



Detroit River Section 



Station 126 is located in the lake, five miles from the mouth of Detroit 

 River. The 'depth is seven meters. The phytoplankton counts for this station 

 on five daites in 1929 and six dates in 1930 are given in Table 60 . 



There is little evidence of seasonal change in abundance, except possibly 

 in the increase in the samples at the end of the season. The outstanding fea- 

 ture of the data is the small amount of plankton. On July 9, 1929 the count 

 of diatoms was unusually high. On page 125 it was pointed out that Station 

 126 was probably affected by water brought from the southwest on that date. 

 Water from that direction would contain an abundance of plankton. Strangely 

 enough, the count of Station 126 on July 9 was higher than the count at 

 Station 117 (Table $9) on the same day. On June 20, 1929, the diatom count 

 at Station 126 was higher than the average for la>.e June in the Island Sec- 

 tion (Table 51). With these two exceptions the counts at Station 1?6 were 

 consistently lower than those in the Island Section for corresponding times 

 of the season, and, of course, very much lower than the counts ''n the Maumee 

 Bay and River Raisin Sections. This poverty of plankton in water from 

 Detroit River is shown further by the data from Station 219, at the lower 

 end of Bois Blanc Island, near the Canadian side of the river. The total 

 counts in thousands of units for this station on five dates in 1930 were 

 as follows; 70, 38, 21, 57, and I08. The average of these counts agrees 

 closely with the average at Station 126 for the same five dates. 



192 





