An indication of a similar effect was seen at McManus Creek where 

 Alloperia nymphs were present in the upstream area in densities exceeding 

 those in the mined and downstream areas. An emergence of adult plecopterans 

 was occurring in the mined area during the site visit, however, and this 

 probably caused the reduced densities of nymphs. Thus, the low nymphal 

 densities of Alloperia in the mined and downstream areas may have resulted 

 from an earlier emergence time rather than a lack of suitable habitat. The 

 observed density differences between upstream and mined areas, at sites 

 which were only sampled once, must be viewed with caution because of the 

 possibility that emergence periods were altered due to an altered thermal 

 regime. A major period of emergence may have occurred in one area just prior 

 to the site visit, thus leaving the area with low densities relative to an 

 area with a later emergence period. At present there is not enough infor- 

 mation on the natural emergence patterns, and the effects of temperature and 

 dissolved oxygen on those patterns, to predict how the arctic macro i nver te- 

 brate species would respond to changes in these habitat parameters. 



Creation of Pond Habitat. The creation of pond habitats al lowed aquatic 

 macro i nver tebrates typically found in a lentic habitat to colonize these 

 areas (Table 27). In these cases the change was from terrestrial to aquatic 

 habitat so there was not a direct effect on river communities. Indirect 

 effects could be enrichment of downstream communities by phy top I ank ton and 

 nutrients being carried out of the pit. The Southern Interior deep pits 

 (West Fork Tolovana River, Tanana River-Downstream, Tanana R i ver-Upstream) 

 had a higher diversity of organisms than the pits in other regions, probably 

 reflecting a more stable habitat. The age of the pit did not seem to exert 

 much effect because the West Fork Tolovana River and upper Tanana River- 

 Upstream pit both had similar configuration and similar fauna and density 

 but the former was 10 years newer than the latter. The low productivity of 

 the Tanana River-Downstream pit was evident; the density of chironomids at 

 the Tanana R i ver-Upstream pits, about 50 km upstream, was 5 to 20 times 

 greater than those at the downstream pit at a similar time of year. 



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