diversity index indicate minor stress related to steep gradients, fast currents, cold temperatures, 

 and low nutrient concentrations. Acceptable values for the pollution index and low values for 

 the siltation index indicate that organic enrichment and sedimentation did not have a significant 

 effect on the benthic algae at these sites. The two sites on Beaver Creek shared 68% of their 

 diatom associations (Table 4), indicating that they were virtually identical and that there was no 

 significant floristic or ecological difference between them. 



Beaver Creek below Hilgard Creek. Aside from minor natural stresses recorded at 

 this site, three teratological cells of Cocconeis placentula were observed during the diatom 

 proportional count. Abnomial diatom cells sometimes indicate elevated concentrations of heavy 

 metals (McFarland et al. 1997). However, there are many other possible causes of abnormal 

 diatom cells, including natural factors such as rapid population growth and crowding, silica 

 depletion, low water temperatures, and low pH. The araphid and monoraphid diatoms, which 

 include Cocconeis placentula, seem to be especially prone to producing teratological cells. 

 Given these circumstances, the minor stress indicated by abnormal cells at the upper site on 

 Beaver Creek is probably natural in origin. 



Beaver Creek at Highway 287. Aside from minor stresses recorded here, six abnormal 

 cells of Achnanthidium minutissimum, Cocconeis placentula, Encyonema silesiacum, and 

 Hannaea arcus were observed during the diatom proportional count. Three of these four species 

 are either araphid or monoraphid diatoms and were major species in this sample, which indicates 

 that they comprised rapidly expanding populations that may have been prone to producing 

 abnormal cells. Given these circumstances, the minor stress indicated by abnormal cells at the 

 lower site on Beaver Creek is also probably natural in origin. 



Modal Categories (Table 5) 



Several ecological attributes assigned by Stevenson and Van Dam et al. (1994) were 

 selected from the diatom reports in the appendix and modal categories of these attributes were 

 Uk extracted to characterize water quality tendencies in Beaver Creek (Table 5). Most of the diatom 



