1929 (Tables 5? and ^8). 



Because of the frequent and marked changes in conditions 

 resulting from the current reversals at Station 2^0, it would be 

 necessary to make a much more detailed study to determine the average 

 abundance of phyto plankton with any degree of accuracy. 



A number of investigators have found that certain species of 

 algae are tolerant to a high degree of pollution, and that the 

 tolerant species have considerable value as an index of pollution. 

 Much of our present knowledge of these index organisms has been 

 summarized by Whipple (1927)* In the present investigation no 

 attempt has been made to apply the method to the study of pollution. 

 To do so would require a detailed study at each station in order to 

 determine the species composition of the plankton. There was not 

 sufficient time available for such a study. In generic conposition, 

 the plankton at Station 2^0 was quite similar to the plankton of the 

 Island Section, However, there were notable differences in the 

 relative abundance of the genera, and of the groups also. The most 

 abundant genera of diatoms at Station 250 in 1930 were Melosira, 

 Synedra, Tabellaria, and Stephanodiscus, The most abundant greens were 

 Scenedesmus, Ankistrodesmus, Actinastrura, Tetrastrum, and Dictyosphaerium, 

 The most abundant blue-greens were Aphanizoraenon, Microcystis, 

 Coelosphaerium, and Merismopedia, 



Station 252 . Conditions at Station 2^2 are less changeable 

 than at- Station 250, because of the distance from the mouth of Maumee 

 River. The current of the river is so weak, during times of small dis- 

 charge, that its effect must be largely lost before reaching Station 252, 

 This does not mean that the water at Station 252 is unaffected by water 

 from the river, because there must be a general movement avay from the 

 river. It merely means that the periodic reversals of current affect 

 the station little or not at all. The depth at Station 252 is 3*9 

 meters, but the general area is not much more than one half as deep. 

 Table 5? shows the phytoplankton data collected at this station in 1929 

 and 1930, 



While the periods of time were very short, it is possible to 

 see a trend from low counts in summer to high ones in early autumn, 

 followed, in some cases, by a decline at the close of the season. The 

 diatoms were more abundant than the greens or blue-greens on four of 

 the five dates in 1929. In 1930, the di'atoms were relatively rare as 



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