and climbers, e.g., Baetidae. Tr i chopferans often increased in these areas 

 and the dipteran family Tipuliidae was often associated with the finer 

 sediments found in mined areas. At two sites on large rivers showing in- 

 creased braiding as well as altered substrate ( Sagavan i rk tok River and 

 Ivishak River) there was an increase in the density of virtual ly al I taxa in 

 the mined area as compared to the upstream area (Table 24). The riffles in 

 the mined area in these two cases were in sma I I shal low channels with exten- 

 sive riffle area while the riffles in the upstream area were in large chan- 

 nels, were less extensive, and composed of a more coarse material. The 

 riffles in the mined area had greater detrital accumulation, and the de- 

 creased depth and velocity associated with the braided areas may have 

 allowed greater periphyton production. Such a situation would increase the 

 quality of the habitat for most of the species unless a critical parameter, 

 such as velocity, had been lost or altered. The increased braiding at other 

 sites, such as Oregon Creek and Penny River, may have contributed in a 

 similar manner to the altered species composition. 



The increased braiding at many of the sites led to changes in the water 

 temperature and dissolved oxygen in the mined area. An examination of the 

 seasonal variation in the riffle macro i nvertebrates at Aufeis Creek revealed 

 a pattern of density changes which indicated a possible effect of the al- 

 tered temperature and dissolved oxygen regime on the apparent densities of 

 certain macro i nvertebrates (Figure 60). In the ephemeropt eran taxa, Baetinae 

 and C i nygmu I a , the densities in the upstream area increased from the July to 

 August trip while those in and below the mined area decreased. Simuliidae 

 densities decreased between the two trips in the upstream area with simu- 

 liids absent in and below the mined area in August. The temperature at the 

 area between the two mined areas was 2.8 C (July) and 1.2 C (August) higher 

 than that in the upstream area. The immature stages of the three taxa ap- 

 parently emerged earlier in the areas affected by gravel removal than in the 

 unaffected upstream area. The altered water quality parameters may have 

 altered the emergence times of these three taxa because temperature and 

 dissolved oxygen can affect developmental rates (Hynes 1972). 



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