The three sites with increased habitat diversity due to recent flow 

 were 3 to 4 years old and, in two cases (Dietrich River-Downstream and 

 Middle Fork Koyukuk R i ver-Upstream) , flow had only entered the site within a 

 year or two of the site study (Figure 49). The habitat diversity in these 

 areas will probably decrease within a few years as meander cutoffs are 

 completed and braiding characteristics are established. 



Inundated pits were formed when gravel removal was conducted away 

 from the active channel and the depression, usually deeper than I m, filled 

 with water either by direct connection to the river or through intergravel 

 flow. These areas developed characteristics typical of pond habitats, i.e., 

 mud bottom, rooted aquatic vegetation around shorelines, high density plank- 

 ton communities, and macroi nvertebrates typically associated with a lentic 

 environment. Two types of pits were included in the study: shallow (< 2 m) 

 and deep (> 2 m) pits (Table 14). Shallow pits (Penny River, Ugnuravik 

 River, Prospect Creek) normal ly froze to the bottom in the winter wh I le 

 deep pits (Dietrich R I ver-Upstream, West Fork Tolovana River, Tanana River- 

 Downstream, Tanana R I ver-Upstream) contained water year-round. 



Two of the deep pits (West Fork Tolovana River, Tanana R i ver-Upstream) 

 showed dissolved oxygen and temperature stratification in the summer of 

 study while the other two (Dietrich R i ver-Upstream, Tanana River-Downstream) 

 did not (Figure 50). The time at which stratification would be most pro- 

 nounced was missed at Dietrich Ri ver-Upstream and Tanana River-Downstream 

 and it is possible that there was some stratification mid-SLimmer; however, 

 the Tanana R i ver-Upstream and West Fork Tolovana River were thermally strati- 

 fied from early June to mid-September. Al I pits except the Tanana River- 

 Downstream pit were connected to the associated rivers. The Tanana River- 

 Downstream pit was on a vegetated island and connection to the river was 

 inundated only during annual high water events. This pit had clear water 

 (bottom visible to deeper than 5 m) , very little mud or silt even In the 

 deepest area, and virtually no thermal stratification. Aquatic vegetation 

 was absent except along the shoreline, despite the extreme water clarity. 

 Four of the five deep pits had extensive shal low areas, with over 25 percent 

 of the area less than I m deep. Only at the Tanana River-Downstream was a 

 majority of the area deeper than 2 m (Table 14). 



162 



