762 



BECKETT 



TABLE 3 



SUMMARY OF GREAT MIAMI RIVER DISCHARGE FOR 



JUNE, AUGUST, AND SEPTEMBER MACROINVERTEBRATE 



COLLECTION PERIODS, DAYTON, OHIO 



Once again a gradient correlating with wastewater and power-plant 

 discharges seemed apparent (Fig. 5). 



The September sampling period featured the lowest mean flow of 

 the three sampling periods, had the lowest minimum daily flow of 

 the stream year (October 1975— September 1976), and had the 

 lowest mean discharge for the week before sample collection 

 (Table 3). It is apparent that pollutional stresses are heightened at 

 this time of the year. With the maximization of pollution influences, 

 the more stenoecious species, e.g., the chironomid Rheotany tarsus 

 sp., the mayflies Baetis sp., and the Tricorythodes sp., have been 

 eliminated, or their numbers significantly reduced, in polluted areas. 

 The downstream areas of the river are then dominated by a few 

 widespread euryecious species, e.g., the chironomids Einfeldia sp., 

 Nanocladius sp., and Cricotopus bicinctus, the planarian Dugesia 

 tigrina, and the gastropod Physa sp, (see Table 4). This results in a 

 general faunal homogeneity among dovmstream stations. 



Station 5, at the Tait power-plant discharge, showed an interest- 

 ing change in biotic affinities over the study period. In addition to 

 being influenced by the warm water of the discharge, the macro- 

 invertebrates below the discharge were subjected to some chlorina- 

 tion effects, as chlorine is used to reduce microbial buildup in the 

 plant's condenser tubes. In June, macroinvertebrates at station 5 

 showed marked similarity to the upstream station (3) (Fig. 4); 

 station 5 was also fairly similar to station 4 (Fig. 5). In August the 

 macroinvertebrate composition of station 5 seemed to be somewhat 

 intermediate between the aggregations of macroinvertebrates at 



