Some of the minor stresses indicated at the mountain sites (Table 8) appear to be natural 

 in origin. For example, high values for the disturbance index and percent dominant species 

 indicate minor stress related to steep gradient, cold temperatures, and low nutrient concentrations 

 in the South Fork of Birch Creek and the North and South Forks of Dupuyer Creek (Table 8). 

 High values for the pollution index and low values for the percentage of abnormal ceils indicate 

 that organic enrichment and toxic metals did not have a significant effect on the benthic algae at 

 these stream sites. 



Cut Bank Creek and Old Maids Coulee. Diatom metrics indicated minor impairment 

 from organic loading at both sites on Old Maids Coulee (Table 7). In addition, the downstream 

 site indicated minor impairment from sedimentation. The 2 sites shared more than half of their 

 diatom floras, indicating that only a minor change in ecological conditions occurred between the 

 upstream site and the downstream site. 



Diatom metrics indicate only minor impairment in Cut Bank Creek due to low species 

 richness and a large percentage of dominant species (Table 7). The dominant species at the 

 upper and middle sites was Encyonema auerswaldii, a species that is somewhat tolerant of 

 organic enrichment and found in both mountain and flatland habitats (Krammer 1997a). This 

 species reflects the transitional nature of Cut Bank Creek in this reach. The dominant diatom 

 species at the downstream site and the second most abundant diatom species at the middle site 

 was Achnanthidium minutissimum, a phosphorus specialist. The increasing abundance of this 

 species and the increasing pollution index values indicate decreasing concentrations of available 

 nutrients between the upstream and downstream sites on Cut Bank Creek. The upper and 

 middle sites shared almost three-quarters of their diatom floras, indicating that these sites were 

 virtually identical in terms of diatom species composition and ecological conditions. The middle 

 and lower sites shared about half of their floras, indicating a minor change in species 

 composition and ecological conditions. 



Two Medicine Drainage — Mountain Sites. Diatom metrics at the upper site on 

 the South Fork Two Medicine River indicated minor impairment from nutrient loading (Table 8). 

 A^ The dominant diatom species here was Synedra ulna, an eutraphentic species that tolerates some 



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