^ Phormidhim, which was frequent. The branched filamentous green alga Stigeoclonium and the 

 filamentous cyanophyte Amphithrix were occasional components of the algal flora at this site. 



Sullivan Creek below Quintonkon Creek. Diatoms were also abundant and ranked 

 second to Hydrurus at this site. The filamentous green algae Zygnema sp. and Ulothrix zonata 

 were abundant and frequent here and ranked third and fourth in biovolume, respectively. An 

 increase in dominance by filamentous green alage generally parallels an increase in nutrient 

 concentrations in streams (Wehr and Sheath 2003). The filamentous cyanophyte Hydrocoleum 

 ranked fifth in biomass at this site. 



Skyiand Creek above Bear Creek. Hydrurus foetidus and diatoms were co-dominants 

 at this site and ranked first and second, respectively, in terms of biomass. The filamentous green 

 alga Ulothrix zonata, which was abundant, was the only other non-diatom species present at this 

 site (Table 3). 



Diatoms (Table 4) 



The four major diatom species from Sullivan Creek and Skyiand Creek are included in 

 pollution tolerance classes 3 or 2 and are either sensitive to organic pollution or only somewhat 

 tolerant of organic pollution (Table 4). None of the major diatom species are most tolerant of 

 organic pollution (pollution tolerance class =1). 



Sullivan Creek above Connor Creek. A very high value for the percent dominant 

 species {Hannaea arcus) and low values for the number of species counted and the diversity 

 index indicate moderate to severe stress at this site (Table 4). Since Hannaea arcus is a cold 

 stenothermal diatom and an attached pioneer species that is sensitive to organic pollution, its 

 dominance here is probably related to steep gradients, fast currents, cold temperatures, and/or 

 low nutrient concentrations. Hannaea arcus is one of the most common diatom species in 

 glacier- and snowmelt-fed streams of the Swiss Alps (Hieber et al. 2001). A high value for the 

 pollution index and zero values for the siltafion index and percent abnormal cells indicate that 

 J^ organic enrichment, sedimentation, and toxic metals did not affect the association of benthic 



diatoms at this site and that the stresses recorded here are probably natural in origin. The only 



