appears to be chronic metals toxicity resulting in large 

 percentages of abnormal diatom valves (Table 6) . The largest of 

 these percentages (11.40%) is comparable to that found in the 

 Eagle River of Colorado, a federal superfund site (McFarland et 

 al . 1997). Large percentages of teratological diatom valves have 

 also been observed in Tenmile Creek near Helena (Bahls 1998) and 

 in Elkhorn Creek near Wise River (Bahls 2001) . Both sites have 

 elevated heavy metals associated with historic mining activities. 



The percentage of abnormal diatom valves in the upper 

 Blackfoot River decreases in a downstream direction (Figure 1, 

 Table 6) . This likely indicates dilution of heavy metals by 

 cleanwater tributaries and/or an increase in buffering capacity 

 as the river becomes more alkaline. The percentage of abnormal 

 valves at the Flesher Pass Road (BlckftR-01) indicates severe 

 impairment and nonsupport of aquatic life uses. The percentage 

 above the Landers Fork (BlckftR-02) indicates moderate impairment 

 and partial support of aquatic life uses, and the percentage 

 above Nevada Creek (BlckftR-03) indicates minor impairment but 

 full support of aquatic life uses. 



Other than unusually large percentages of teratological 

 diatoms at the two upstream sites, diatom metrics indicate good 

 to excellent biological integrity and full support of aquatic 

 life uses in the upper Blackfoot River. Diatom diversity, 

 species richness, and the pollution index all increased in a 

 downstream direction, indicating a decrease in organic loading 

 and heavy metals concentrations. Except for small increases in 

 the siltation index, the diatoms indicate that biological 

 integrity improved from upstream to downstream in the upper 

 Blackfoot. Adjacent sites in the upper Blackfoot River had about 

 40% of their diatom floras in common (Table 6) , indicating that 

 moderate environmental change (recovery) occurred between them. 



Poorman Creek. The upper two sites on Poorman Creek also 



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