inorganic nutrients, including nitrogen and phosphorus. As in Washington Creek, the two sites 



shared 43% of their diatom assemblages. 



Braziel Creek. Braziel Creek was subject to minor impairment from sedimentation. The 

 siltation index approached but did not exceed the tlireshold for moderate impairment. In other 

 respects, Braziel Creek had nomial metric values for a mountain stream. 



Seven-Up Pete Creek. Aside from a few abnormal diatom cells, Seven-Up Pete Creek 

 had excellent biological integrity for a mountain stream. However, this stream supported the 

 smallest number of diatom species (36) of all the sites in the sample set. 



Modal Categories (Table 6) 



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

 selected from the diatom reports in the appendix. Modal categories of these attributes were 

 extracted to characterize water quality tendencies in tributaries of the Blackfoot River (Table 6). 



The majority of diatoms at most sites in the Blackfoot River TMDL planning area were 

 non-motile, alkaliphilous, nitrogen autotrophs that prefer fresh waters, moderate BOD levels, 

 high oxygen levels, and elevated concentrations of inorganic nutrients. However, the modal 

 categories at some sites represent significant departures in water quality when compared to most 

 other sites in the sample set. These departures, which may reflect increases or decreases in water 

 quality, are discussed below. 



Although most of the sites were dominated by non-motile diatoms, Blanchard Creek, 

 Black Bear Creek, and the lower site on Washington Creek were dominated by highly motile 

 diatoms. Meanwhile, Frazier Creek, the lower sites on Buffalo Gulch and Douglas Creek, and 

 the upper site on Jefferson Creek were dominated by moderately motile diatoms. These sites are 

 most likely to have sedimentation problems. 



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