Diatoms (Table 4) 



The 12 major diatom species from Logan Creek are included in pollution tolerance 

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

 pollution (Tabic 4). None of the major diatom species in Logan Creek are most tolerant of 

 organic pollution (pollution tolerance class = 1). 



Tally Lake Campground . The most abundant diatom species at this site were 

 Cocconeis placentula and Achnanthidium mimitissimum (Table 4). These are both attached 

 species that resist disturbance and both are sensitive to elevated levels of organic pollution. The 

 third most abundant diatom at this site (Encyonopsis krammeri) is seldom reported from North 

 America but also sensitive to organic pollution. Overall, diatom metrics indicated good diversity 

 and equitability, low organic nutrients, and acceptable sediment levels for a mountain stream. 



Only a slightly elevated percent abundance of the dominant species (C. placentula) 

 indicated minor natural stress at this site. This diatom is adapted to living attached to rocks, and 

 its dominance here is probably substrate related. Otherwise, diatom metrics indicated excellent 

 biological integrity and full support of aquatic life uses. The Tally Lake site shared about 40% 

 of its diatom flora with the next upstream site (above Star Meadows), which indicates a minor to 

 moderate change in ecological conditions between the two sites. 



Above Star Meadows and Above Cyclone Creek. These two sites had virtually 

 identical diatom floras (70% community similarity) and will be discussed together. A somewhat 

 elevated percentage of motile diatoms indicated minor impairment from sedimentation at both 

 sites (Table 4). Both sites also supported large numbers o{ Achnanthidium minutissimum, which 

 indicates minor physical, chemical, or biological disturbance. Such disturbance may be caused 

 by substrate scour, toxic metals, and/or invertebrate grazing. Since no abnormal diatom cells 

 were observed at this site, metals toxicity may be ruled out. Overall, diatom metrics indicated 

 good diversity and equitability, low organic nutrients, and the absence of toxic chemicals. Other 

 than minor sedimentation and disturbance, diatom metrics indicated excellent biological integrity 



