these sites is added to the percentage of motile diatoms, sedimentation index values would 

 approach but still not exceed the threshold for minor impairment (Table 4). 



Both sites on Hughes Creek supported diatom assemblages with excellent species 

 richness, diversity, and equitability for a mountain stream. The relatively small percentage of 

 Achnanthidium minutissimum at both sites indicates a stream with moderate gradient and current 

 velocity and little physical disturbance. The absence of teratological (abnormal) cells indicates 

 that toxicity from heavy metals is not likely to be a problem here. 



As with the non-diatom algae, the two sites on Hughes Creek supported very similar 

 diatom assemblages. The percent community similarity between the two sites was 60.35, which 

 indicates very similar floras and ecological conditions. Adjacent sites on the same stream 

 without intervening tributaries or point source discharges typically share 60 percent or more of 

 their diatom assemblages (Bahls 1993). 



Modal Categories of Ecological Attributes (Table 5) 



Several ecological attributes assigned by Stevenson and Van Dam et al. (1994) were 

 selected from the diatom reports in the appendix and modal categories of these attributes were 

 extracted to characterize water quality tendencies in Hughes Creek (Table 5). Most of the 

 diatoms that inhabit Hughes Creek may be characterized as non-motile, alkaliphilous, and 

 autotrophic, while tolerating high levels of organic nitrogen and a moderate amount of organic 

 loading. They prefer meso-eutrophic to eutrophic, fresh waters, and exert a continuously high 

 demand for dissolved oxygen. These categories are defined by Van Dam et al. (1994). 



