with narrow filaments. Ulothrix and Stigeoclonium appeared as 

 short, unbranched filaments attached to the Schizothrix colony. 



East Boulder River Station 4. This sample was also sparse 

 and the entire sample was used to make diatom slides. 



East Boulder River Station 5. A species of Phormidiuw 

 with wide filaments occurred here. Stigeoclonium appeared as 

 short, unbranched filaments. Two species of Closteriu/n were 

 present. 



NON- DIATOM ALGAE 



Diatoms and cyanobacteria were present in all samples from 

 the East Boulder River (Table 4) ; green algae were present at all 

 sites except Station 4. The combination of diatoms, green algae, 

 and cyanobacteria is the usual complement of algae in mountain 

 streams in Montana (Bahls et al . 1982). The pollution-sensitive 

 red alga Audouinella was abundant at Station 2, rare at Station 3 

 (1998), and absent elsewhere. 



The number of non-diatom algal genera ranged from 1 at 

 Station 4 above Elk Creek to 7 at Station 2 below Dry Fork Creek. 

 Mountain streams in western Montana normally support between 1 

 and 10 genera of non-diatom algae, with an average of 5 (Bahls 

 1993) . The number of non-diatom genera tends to increase with 

 increasing nutrient concentrations. This may help explain why 

 the site below Dry Fork Creek supported the most genera. 



Cyanobacteria accounted for most of the biomass at all sites 

 except Station 1, where diatoms were dominant. Phorwidium and 

 Oscillatoria were the most abundant cyanobacteria at all sites 

 except Station 3 . These are closely related genera containing 

 many species that exhibit a wide range of pollution tolerance 

 (VanLandingham 1982) . 



8 



