filamentous algae on the cobble substrate, while substrates at the Upper and 

 Lower Sites were colonized by diatoms. 



Summer numbers of macroinvertebrates per square foot averaged 213% higher 

 at the Lower Site and 220% higher at the Upper Site than spring numbers at 

 either station, while spring and summer abundance was equal at the Middle 

 Site. This, in conjunction with the suggested increased productivity of the 

 Middle Site, was probably related to the presence of a large beaver dam 

 located immediately upstream from the Middle Site. The dam may have afforded 

 protection from harsh winter ice conditions, thus maintaining high spring 

 numbers of macroinvertebrates, while providing some nutrient enrichment to 

 stimulate production. 



Macroinvertebrate numbers per sample by individual taxon are given in 

 Tables 19, 20 and 21 for the Upper, Middle and Lower Sites. Macroinvertebrate 

 numbers were dominated by Diptera and Ephemeroptera at all three stations. 

 While numbers of Ephemeroptera were relatively evenly distributed among the 

 species, numbers of Diptera were markedly dominated by the chironomid, 

 Cricotopus c.f. nostocicola . This dominance occurred only at the Upper and 

 Middle Sites. Cricotopus c.f. nostocicola is a midge larva which lives 

 symbiotically in colonies of the blue-green alga Nostoc and is characteristic 

 of rheophile habitats. 



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