Nevertheless, 8 genera of non-diatom algae were found in the 

 sample collected at Station 1 (Table 4) . The number of non- 

 diatom genera increased to 10 at Station 2, perhaps in response 

 to a small increase in nutrients and water temperature at this 

 site. Unimpaired mountain streams in Montana typically support 1 

 to 10 genera of common non-diatom algae (Bahls 1993) . 



DIATOMS 



All but 2 of the 7 major diatom species in East Rosebud 

 Creek- -including the dominant species--were sensitive to 

 pollution (Table 5) . The dominant species at both sites was 

 Achnanthes minutissima. This opportunistic pioneer species is a 

 good indicator of disturbance or stress, which may be caused by 

 physical factors (e.g., channel scour), biological factors (e.g., 

 invertebrate grazing), or chemical factors (e.g., heavy metal 

 toxicity) . 



Such stress may be natural or cultural (anthropogenic) in 

 origin. In the case of East Rosebud Creek, this stress is likely 

 derived from the naturally swift, cold, and nutrient-poor waters 

 entering the study reach. Hence, the moderate impairment 

 recorded at Station 1 and the minor impairment recorded at 

 Station 2 can most likely be attributed to natural causes. 



The number of diatom species observed and counted, as well 

 as diatom species diversity, increased significantly from Station 

 1 to Station 2 (Table 5) . This was probably in response to small 

 increases in nutrients and water temperature as the stream left 

 the mountains and entered the foothills. Warmer, lower gradient 

 foothill and prairie streams in Montana typically support a more 

 diverse diatom flora than their colder and steeper counterparts 

 in the mountains (Bahls 1993; Bahls et al . 1992). 



