180 



WARD, CANTON, AND GRAY 



TC-3 TC-4 TC-5 

 SAMPLING STATIONS 



TC-6 



Fig. 3 Annual range of Shannon — Weaver index values ( I ) and the 

 mean number of macroinvertebrate taxa per collection date (• — •) 

 for sampling stations on Trout Creek. 



caddisflies Agapetus and Brachycentrus, the mayfly Rhithrogena, 

 and the elmid beetle Optioseruus. Caddisflies were the most abun- 

 dant order by density at all Trout Creek sampling stations (at TC-7 

 trichopterans and dipterans each comprised 33% of the mean 

 density) and also comprised the largest biomass (at TC-2 trichop- 

 terans and ephemeropterans each comprised 28% of the mean 

 biomass). Plecopterans comprised less than 10% of the macroinverte- 

 brate numbers but were much more important gravimetrically. The 

 reverse was true for coleopterans, which were primarily small riffle 

 beetles. The relative importance of the five insect orders was similar 

 at all stations and exhibited no longitudinal trend. Other orders of 

 insects and noninsects were generally rare, and differences in their 

 distribution patterns cannot be reliably relegated to anything except 

 the sampling inadequacies inherent in studies of rocky streams 

 (Hynes, 1970). Even at the generic and specific level, many of the 

 common organisms were widely distributed. 



DISCUSSION 



Streams of the eastern United States which receive acid mine 

 drainage are characterized by lowered diversity and density and 



