BIOLOGICAL SURVEY OF THE UPPER MISSISSIPPI RIVER 157 



Table 8. — Total number of phytoplankton organisms per liter of water— Continued 



[S=shore; C = channel] 



Phytoplankton 



Sta. 

 9-C, 

 Sept. 17 



Sta. 

 10, 

 Aug. 27 



Sta. 

 11-S, 

 Aug. 28 



Sta. 

 11-S, 

 Sept. 18 



Sta. 

 11-C, 

 Aug. 18 



Sta. 

 11-C, 

 Sept. 18 



Sta. 

 12, 

 Aug. 2S 



Sta. 

 12, 

 Sept. 18 



Sta. 

 14-S, 

 Aug. 31 



Sta. 

 14-S, 

 Sept. 19 



Sta. 

 14-C, 

 Aug. 31 



Sta. 

 14-C, 

 Sept. 19 



Melosira 



Synedra __ 



83, 500 

 4, 270 

 3,090 

 800 

 1,630 

 800 

 30 

 30 



90 

 90 



4, 790 

 3,000 



4, 100 

 1,600 

 270 



60 

 800 



550 



460 

 400 

 1,320 



28,840 

 920 

 3,710 



4,010 



14, 760 

 1,800 

 3, 600 

 900 

 990 

 900 

 270 

 180 

 900 



1,200 

 1,600 



890 

 1,600 

 45 



17,470 

 3,300 

 2,380 



3,380 

 4,800 

 1,660 



Stephanodiscus 



i,666 



890 

 530 



Pleurosigma 







Scenedesmus . 



1,645 



780 

 4,200 

 360 

 600 

 690 



1,600 







3,260 



4,400 





Chlorella (colony) 









Fragilaria.. 







60 





1,500 

 60 



30 

 30 

 1,000 



90 



720 

 180 

 6,600 





Pcdiastrum 



90 



9, eoo 









Navicula 



1,600 







4,000 

 90 







Pandorina 



800 

 800 

 800 

 1,600 











Selenestrum 























Small diatoms 



8,935 

 1, 645 

 1,600 





3,200 



1,600 



1,200 



90 



150 









9, 720 



Nitzschia 



1,800 



2,700 





1,100 

 16,000 



Chlorella (single) 



28, 800 

 2,400 

 800 

 1,070 





3,600 

 400 

 400 

 360 



3,200 

 1,630 

 30 

 60 





12, 000 





Amphora 









500 























1, 600 

 240 



Ceratium 



90 

 90 

 90 





1,710 

 1,800 



6, 340 





4,500 



270 



5,510 

 180 

 1,100 



Anabaena 





30 



Lyngbya 



















Eudorina 





1,080 









120 

 30 











Asterionella 



510 





1,520 



1,100 



240 



60 



270 



180 



270 



120 

 4,800 



Stauroneis 



900 





Closterium 



30 

 30 

 210 

 150 

 480 



360 



90 

















Actinastrum 









90 

 210 

 60 

 60 





270 

 2, 520 









Microcystis ._ 





2,340 





570 

 210 

 60 



120 



360 

 30 

 300 





1,800 

 90 

 180 

 900 

 ISO 



60 



Aphanocapsa 









Ccelosphserium 





90 



180 





90 



45 





Aphanizomenon 









Staura strum 







90 



270 



30 

 90 





90 

 30 







45 





Dictyosphserium 













— 





Clathrocystis. 



30 











150 



270 





360 























In this survey, Pleurosigma spencerii, although not known to be tolerant, is 

 consistently much more abundant in the polluted section of the river than in the 

 unpolluted sections and in the tributaries. It is possible, therefore, that the dis- 

 tribution of P. spencerii is correlated with the degree of pollution and that this 

 species is a tolerant form. 



To determine more definitely whether the character of the phytoplankton 

 changes with the degree of pollution in the river, I compared the nine most abundant 

 phytoplanktonic forms (see Table 8) found at each of three groups of stations, each 

 group representing a different degree of pollution. Group I comprises stations 1, 8, 

 10, and 12 and represents unpolluted waters; Group II includes stations 2, 11, and 

 14 and represents presumably slightly polluted waters; and Group III consists of 

 stations 3, 5, 6, 7, and 9 and represents grossly polluted waters. The comparative 

 data are shown in Table 9. In this table the genera are listed according to their 

 abundance in Group I, in a descending order. . In each of the last three columns 

 the numeral indicates the order of abundance. 



Table 9 shows that seven of the genera that are among the nine most abundant 

 in Group I are also included in the nine that are most abundant in Group III. Six 

 of these seven genera are also among the nine listed for Group II, while Groups I 

 and II have eight of the nine most abundant genera in common. It may be seen 

 that Pleurosigma spencerii and Lyngbya sp.? are listed under Group III but nowhere 

 else. If, in the present survey, these species are considered tolerant forms, they 

 corroborate the conclusion based on a study of the bottom fauna, "that somewhere 

 between station No. 7, at Hastings, * * * and station No. 9, at Red Wing, 

 * * * the Mississippi River is recovering from its grossly polluted condition" 



