Cedar Creek. Diatom metrics suggest minor impairment from sedimentation and 

 organic loading in Cedar Creek. However, the sedimentation index — 38% motile cells — was 

 close to the threshold for moderate impairment, which is 40%. One teratological diatom cell was 

 counted at this site. The dominant species {Navicula cryptotenella, Nitzschia dissipata. Synedra 

 rumpens, Synedra ulna), which are all cosmopolitan "increasers", indicate a habitat disturbed by 

 human activities and somewhat elevated concentrations of inorganic nutrients. 



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 Ninemile Creek (Table 6). 



The majority of diatoms at most sites were non-motile, nitrogen autotrophs that prefer 

 alkaline 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. Several sites were 

 dominated by diatom species that have not been classified with respect to one or more water 

 quality categories. 



Diatom species that prefer circumneutral (as opposed to alkaline) pH values were most 

 abundant in Stony Creek and Big Blue Creek. These streams are likely to have lower pH values 

 than the other streams. 



The modal category for oxygen demand was "continuously high" in Big Blue Creek and 

 upper Stony Creek. This is the nominal category for mountain streams. Most diatoms were in 

 the "moderate" category in lower McCormick Creek and upper Josephine Creek. Most cells at 

 the remaining sites were represented by species that have not been classified with regard to 

 oxygen demand. 



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