# 



non-diatom genera, it had the lowest diatom species richness and diversity values, the lowest 

 siltation index and pollution index values, and the largest percent dominant species and percent 

 abnormal cells of all four sites (Table 4, Figures 1 and 2). There are no known sources of heavy 

 metals in the West Fork drainage (Tina Laidlaw, USEPA, personal communication). 



Modal Categories (Table 5) 



Several ecological attributes assigned by Stevenson (digital communication) and Van 

 Dam et al. (1994) were selected from the diatom reports in the appendix and modal categories of 

 these attributes were extracted to characterize water quality tendencies in the Yaak River and the 

 West Fork of the Yaak River (Table 5). 



Most diatoms at the upper two sites on the Yaak River are non-motile freshwater 

 autotrophs that prefer pH values >7, continuously high concentrations of dissolved oxygen, a 

 moderate amount of organic loading, and variable concentrations of inorganic nutrients. At 

 Sylvanite, the modal categories were the same except that most diatoms here preferred pH values 

 of about 7 (circumneutral). 



The modal category for pH was also circumneutral in the West Fork of the Yaak River. 

 The modal category for trophic state in the West Fork was oligo-mesotraphentic, which indicates 

 smaller concentrations of inorganic nutrients than in the main Yaak River. The modal categories 

 for nitrogen uptake, oxygen demand, and saprobity were "not classified" in the West Fork. This 

 is because the ecological affinities of the dominant species {Synedra nimpens) in the West Fork 

 are unknown for these three environmental attributes. 



