diversity values than mountain streams. The site near Collins 

 had very little in common, f loristically , with the closest sites 

 upstream (Highway 221) and downstream (Interstate 15). 



The site at Kelly Ranch had a diatom flora that was very 

 similar to the one at Dent Bridge (Table 7) . The two sites 

 shared over 80% of their diatom floras. Both sites suffered from 

 moderate impairment and partial support of aquatic life uses as 



indicated by low diversity and dominance by a single species. 

 Kelly Ranch also had a very small number of species for a prairie 

 stream. The causes of impairment at both sites were probably 

 siltation and the homogeneity of microhabitats (lack of habitat 

 diversity) . 



Both the Kelly Ranch and Dent Bridge sites were dominated by 

 Cymhella sinuata {=Reimeria sinuata) . ■ This is a free-living 

 species (Round et al . 1990) with ecological requirements that are 

 very similar to those of Amphora pediculus (Lowe 1974) . Amphora 

 pediculus was the second most abundant diatom at Kelly Ranch. 

 Both species probably tolerate siltation because of their 

 motility and/or free-living lifestyles. They are not included in 

 the siltation index because they are seldom abundant in streams. 

 Also common at both sites was Navicula tripunctata, a motile 

 species that is included in the siltation index. 



The diatom flora changed considerably between Kelly Ranch 

 and the site near the mouth of the Teton River. These sites had 

 less than a third of their floras in common (Table 7) . Habitat 

 conditions were evidently much improved near the mouth over 

 conditions at Dent Bridge and Kelly Ranch. 



^ 



11 



