Response to Substrate Alteration. The two types of substrate alter- 

 ations observed during the study (a shift to unstable substrate and change 

 from laminar to turbulent flow) significantly affected the total numerical 

 densities of aquatic macro i nver tebrates in the mined area as compared to 

 undisturbed areas (Table 26). At Washington Creek, Oregon Creek (June and 

 August), al I Penny River, Kuparuk River, and McManus Creek (May) site 

 visits, macro i nver tebr ate densities in mined areas were significantly less 

 than those in the upstream area. At al I five sites there was a shift from a 

 moderately compacted gravel substrate to a very loose, unconsolidated sand- 

 gravel substrate (Table 25). A similar habitat change at the Sagavan i rk tok 

 River and Ivishak River sites resulted in a significant increase in the 

 density of aquatic macro i nver tebr ates. In five of the eight cases in which 

 there were total density decreases, there were density reductions in the 

 ephemeropt eran genus Cinygmula while in seven of the eight cases, there were 

 reductions in the dipteran family Ch i ronomi dae. The density increases at the 

 Sagavan irk tok River and Ivishak River sites both contained density increases 

 in the ephemeropt eran subfamily Baetinae and dipteran family Ch i ronomi dae, 

 as we I I as some other taxa. 



At two sites there was a change from laminar flow to turbulent flow 

 caused by substrate alteration. At both Ugnuravik River and Shaviovik River 

 sites, there was a significant decrease in total macro i nver tebr ate density, 

 primarily because of a decrease in Simuliidae densities. At Ugnuravik River, 

 the laminar flow was in the upstream (control) area, while at Shaviovik 

 River, laminar flow occurred in the mined area. 



At three of the five sites where there were decreased densities in the 

 mined area (Washington Creek, Oregon Creek, McManus Creek) there were also 

 aufeis fields associated with the mined area (Table 25). All three sites 

 were visited early in the summer so that any aufeis effects would have been 

 measured at their greatest magnitude. Later visits at two of the sites 

 (Oregon Creek, McManus Creek) indicated that densities in the mined area 

 increased to levels similar to those in the upstream areas. At Oregon Creek, 

 the summer recovery from aufeis effects was not complete for population 

 densities of Nemoura and Cinygmula, which remained below the densities 



202 



