ORDINATION OF MACROINVERTEBRATE COMMUNITIES 



755 



6 7 8 9 



STATIONS 



10 11 12 13 14 



Fig. 2 Macroinvertebrate Shannon— Wiener diversity values (H /sta- 

 tion) for June (O), August (□), and September (A) 1976 collection 

 dates, Great Miami River system, Ohio. 



was found at this station. Stations 1 to 4 were the only stations to 

 show H' values above 3.0, the level supposedly indicative of 

 clean-water areas (Wilhm, 1970a; Wilhm and Dorris, 1968). 



Diversity values at station 5 (Tait power-plant discharge) were 

 lower than those of station 4 on all occasions. Macroinvertebrate 

 diversity was quite low below the Dayton sewage-treatment plant 

 (station 6) on all three dates. For two of the three sampling periods 

 H' was below 1.0 at this point (1 and 22 in September); this is 

 indicative of highly polluted conditions (Wilhm, 1970a; Wilhm and 

 Dorris, 1968). The H' values at station 7 showed marked increases 

 over those of station 6, whereas moderate diversity values (between 

 1.0 and 3.0) were observed from stations 8 through 14 for all three 

 collection dates. 



Inspection of the number of taxa present per station at the 

 different collection times (Fig. 3) shows some repetition of the 

 diversity data; however, it adds clarity to the general picture of 

 changes in river biota. Upstream stations (1 to 3) exhibited high 

 species richness (S); station 4 (Tait power-plant intake) also had a 

 relatively high number of species present for all three sampling 

 periods. A marked decrease in number of total taxa occurred at 

 station 5 (Tait power-plant discharge) in comparison with station 4; a 

 further decrease occurred below the Dayton sewage-treatment plant. 

 Although S showed some increase at those stations downstream from 

 the Dayton sewage-treatment plant on all three dates, these 



