Similarly, siltation index values tend to be higher in Blackfoot tributaries than in most mountain 

 streams. 



Most 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 

 (1.74%) was recorded in Richmond 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 Blackfoot tributaries suggest that ecological changes between 

 adjacent sites on the same stream varied from un-measurable (>60% between the middle and 

 lower Monture Creek sites) to extreme (<20% between the two sites on Rock Creek). 



The diatom order Rhopalodiales includes genera {Epithemia and Rhopalodia) that are 

 known to harbor nitrogen-fixing endosymbionts within their cells. These symbiotic nitrogen- 

 fixers are single-celled cyanobacteria (blue-green algae). Nitrogen is likely the limiting nutrient 

 in waters that support large numbers of diatoms in the order Rhopalodiales. Among tributaries to 

 the Blackfoot River, diatoms in the order Rhopalodiales accounted for more than 2% of the cells 

 at the following sites: West Fork Clearwater River (both sites). Deer Creek (both sites), Black 

 Bear Creek, Blanchard Creek, Jefferson Creek (upper site), and Seven-Up Pete Creek. 



The following paragraphs highlight the key findings for each stream and each site based 

 upon the major diatom species and core diatom metrics in Table 5. 



Monture Creek. Except for a few teratological cells and slightly elevated disturbance 

 index values, diatom metrics indicate that Monture Creek had excellent biological integrity, no 

 impairment, and provided full support to aquatic life uses. Similarity index values indicate little 

 environmental change between the upper and middle sites and virtually no change between the 

 middle and lower sites. 



10 



