Plankton-poor Detroit River influences the abundance of 

 plankton in Lake Erie for a long distance from its mouth. This is 

 shown by the data from Station 13U, located 13 miles from the mouth of 

 the river (Table 6l) . 



On four dates in the two years (May 2? and July 3, 1929; and 

 July 8 and September 30, 1930) Station 13U had somewhat higher total 

 counts than the Island Section for comparable periods of time 

 (Tables 5l and 53). On the remaining eight dates the counts were lower 

 than those in the island Section, and, in general, very much lower. 

 Comparison of the data in Table 6l with those in Table 59 shows that 

 Station 13U was very poor in plankton as compared with Station 117. 



Although Station 13U is almost equally distant from Stations 

 117 and 126, its plankton is much more like the latter than like the 

 former. This may be seen r eadily by a comparison of abundance as shown 

 in Tables 59, 60, and 6l. It is also well shown by the number of 

 genera of green algae found at these stations in 1930, At Station 13ii 

 there were 13 generaj at Station 126, 11 genera; and at Station 117, 

 22 genera. Station 25U (Maumee Bay Section) yielded 19 genera. In the 

 number of genera of diatoms, the stations were not far different, but 

 Stations 126 and 13ii had only half as many genera of blue-greens as 

 Station 117, Thus, the stations of the Detroit Jliver Section were 

 poor in number of genera of algae as well as in abundance of total 

 phytoplankton as compared with the stations near the southwest corner of 

 the lake. 



Having concluded from the data presented above that Detroit 

 River was poor in plankton in 1929 and 1930, it seems desirable to account 

 for its poverty. Rivers are generally poor in plankton because current is 

 unfavorable for the organisms, but in a stream such as Detroit River, 

 one would expect little decline in abundance during the journey from 

 the source to the inouth.T/ That is, if the water were rich in plankton 



7/ 



—Under certain conditions, that is, with rapid current, rough bottom, 



and a heavy load of sediment, plankton organisms may be destroyed by 

 attrition. For example, Mississippi River below Rock Island Rapids 

 carried less than hO per cent of the amount of plankton found above the 

 rapids (Galtsoff, 192U) , Conditions in Detroit River do not appear to 

 be favorable for mechanical destruction of the plankton. 



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