At 13 sites the gravel removal method led to significant hydraulic 

 changes that secondarily impeded the vegetative recovery rate (Table 30). 

 Permanently ponded water and aufeis development caused the most significant 

 impediment. Permanently ponded water occurred at those sites where the 

 mining plan called for excavated pits, but also at sites where depressions 

 were scraped below summer water levels. The latter occurred at sites that 

 were directly connected to an active channel (Jim River); at sites that were 

 not directly connected to an active channel (Penny River); and at sites that 

 were originally not connected, but where gravel extraction caused an active 

 channel to reroute through the deep depression (Dietrich River-Downstream). 



Aufeis impeded vegetative recovery at four sites (Washington Creek, 

 Oregon Creek, Middle Fork Koyukuk River-Downstream, and Jim River), all of 

 which were directly connected to active channels. Aufeis development is 

 believed to occur annually at all sites, and affects the entire disturbed 

 area at Washington Creek and Oregon Creek and most likely affects much of 

 the disturbed areas at Jim River and Middle Fork Koyukuk River-Downstream. 



Two additional factors were impediments to vegetative recovery under 

 certain conditions: soil condition and length of growing season. Vegetative 

 recovery was occurring to some degree under a wide variety of soil type, 

 texture, nutrient, and moisture levels. Differences in the degree of develop- 

 ment and the species composition reflected the wide range of xeric and mesic 

 soil conditions. Soil nutrients were not found to be limiting factors at any 

 site regardless of its age, original condition, or final condition. However, 

 vegetative invasion was restricted by very compacted surface layers at 

 several of the more recent sites. These areas most frequently were associ- 

 ated with access routes over gravel surfaces leading to and from the mined 

 sites. At Dietrich River-Downstream, heavy equipment compacted the flood- 

 plain gravels approximately 25 cm adjacent to the gravel removal area 

 (Figure 73). This site was visited 3 years after completion and vegetation 

 had not invaded this access road although the unflooded banks of the materi- 

 al site were supporting pioneer communities. 



Another soil condition which restricted vegetative development 13 years 

 after site work, occurred at Oregon Creek. Inorganic materials were scraped 



242 



