Table 1 



Comparison of Phytoplankton Populations in the Main Channel of 

 tnd 1974, Unde 



in September^ 



the Illinois River in 1898 and 1974^ Under Stable Low-flow Conditions 



Major Taxonomic Divisions 



Chlorophyta (desmids, green algae) 

 Bacillariophyta (diatoms) 

 Chrysophyta (yellow-brown algae) 

 Cyanophyta (blue-green algae) 

 Euglenophyta (euglenoid algae) 

 Pyrrophyta (dinoflagellates) 

 Total 



^ata were obtained from Kofoid, 1904: 314-340, and Colbert et al. , 1975: 

 E29-E36. Although Kofoid* s samples were taken upstream from the study 

 area, he conducted four studies (Kofoid, 1903: 273-283) of the longitudinal 

 distribution of plankton in the river (one study included the lower 80 

 miles of the Illinois) and concluded that the plankton in the main channel 

 was remarkably uniform. Hence, Kofoid 's samples from the Havana area are 

 probably generally representative of the main channel in the fall of 1898. 

 Both Kofoid and Colbert et al. (1975) used no. 20 plankton nets. Kofoid 

 also collected plankton on filter paper, but these results are excluded 

 from the table because Colbert et al. did not use micro-filtration. 



The total number of species taken on Sept. 6, 13, 20, and 27, 1898 at 

 one sampling station in the Illinois River near Havana (mile 128.5). 



C The total number of species taken at six sampling stations (miles 23.1, 

 45.6, 57.6, 58.3, 77.0, and 81.0) in the lower Illinois River. The station 

 at mile 2.5 was excluded because the number of species was much lower than 

 at the other six stations. 



The total number of individuals taken in the four collections in September, 

 1898, was divided by four to obrain an average density. 



The total number of individuals taken at six locations (excluding the 

 atypical results from river mile 2.5) was divided by six to obtain an 

 average density. 



14 



