In general, diatom species richness, diversity, and equitability were excellent. Most sites 

 supported more than 40 species and diversity values in excess of 4.00. None of the sites had a 

 diversity or species richness value that indicates unusual stress. Only in lower McCormick 

 Creek and Josephine Creek (both sites) did the dominant species contribute more than 25% of 

 the cells to the diatom assemblage (Table 5), The cause of stress at these sites was probably a 

 combination of sedimentation and elevated concentrations of inorganic nutrients. 



High diatom diversity in these samples suggests the absence of extreme natural stressors, 

 such as steep gradients, fast currents, low light, low nutrients, and constant cold temperatures. 

 The abundance of non-motile, free-living taxa (Diatoma spp., Fragilaria spp., and Synedra spp.), 

 attached species {Achnanthidium spp., Cocconeis placentula, Planothidium spp.), and motile, 

 free-living taxa {Navicula spp. and Nitzschia spp.) suggests a wide variety of substrates, 

 gradients, and current velocities. The disturbance index at most sites was relatively low, which 

 suggests moderate gradients and slower current velocities than most mountain streams (Table 5). 



Besides the absence of natural stressors and the presence of complex microhabitats, high 

 diatom diversity in these streams also suggests moderate enrichment by organic and inorganic 

 nutrients and little competition for available nutrients. Pollution index values, which indicate the 

 amount of organic loading, are uniformly lov/ for mountain streams. Many are at or below the 

 threshold for minor impairment. Similarly, siltation index values tend to be higher in Ninemile 

 Creek tributaries than in most mountain streams. 



Five of the sites supported teratological (deformed or physically abnormal) diatom cells. 

 In large numbers, abnormal cells may indicate metals toxicity. However, the percentage of 

 abnormal cells was within acceptable limits at all sites. The largest percentage of abnormal cells 

 (0.63%) was recorded in Big Blue Creek (Table 5). 



The similarity index ("percent community similarity") measures the cumulative 

 percentage of cells of each taxon that are shared by two stream sites. The similarity index can be 

 used to gauge the degree of environmental change that occurs between sites on the same stream. 

 Similarity index values for Ninemile tributaries suggest that ecological changes between adjacent 



