Diatoms (Table 4) 



The eight major diatom species from Jackson Creek, Jennies Fork, and Granite 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). 



Jackson Creek. A large number of motile diatoms in the sample from Jackson Creek 

 indicate moderate impairment from sedimentation and only partial support of aquatic life uses at 

 this site (Table 4). The pollution index here was below the threshold for minor impairment, 

 indicating somewhat elevated organic loading for a mountain stream. In addition, a larger than 

 normal number of teratological diatom cells may indicate chronic toxicity from elevated heavy 

 metals at this site. Sometimes rapidly growing populations of diatoms will produce abnormal 

 cells when silica is limiting. However, teratological cells were recorded for six different species 

 in Jackson Creek, including five minor species that did not have large populations and were not 

 evidently in a rapid growth phase. 



Except for Achnanthidium minutissimum, which is sensitive, the major diatom species in 

 Jackson Creek are somewhat tolerant of organic pollution. Two of these species — Navicula 

 cryptotenella and Nitzschia linearis — are motile and adapted to living on shifting substrates of 

 fine sediment. The remaining major species — Planothidium lanceolatum {=Achnanthes 

 lanceolatd) — is an adnate, non-motile species that is adapted to living on sand grains. 



Jennies Fork. Achnanthidium minutissimum was the dominant diatom species in Jennies 

 Fork (Table 4). Large numbers of this adnate pioneer species indicates a high level of physical, 

 chemical, or biological disturbance in the form of scour, metals toxicity, or invertebrate grazing, 

 respectively. The abundance of Hydrurus foetidus at this site (see discussion above under Non- 

 Diatom Algae) indicates that physical scour is the most likely cause of disturbance in Jennies 

 Fork. The large number of A. minutissimum indicates minor stress from natural scour. 



