other major diatom species at this site — Achnanthidium minutissimum — is also an attached 

 pioneer species that is sensitive to organic loading. 



Sullivan Creek below Quintonkon Creek. Although the equitability and diversity of 

 diatom species improved at this site compared to the upstream site, diatom species richness 

 remained low and still indicated moderate stress from natural causes. However, a significant 

 decline in the pollution index occurred between the upstream site and this site (Table 4), which 

 indicated a significant increase in organic loading. Although organic loading increased, the 

 pollution index at this site remained above the threshold for minor impairment. However, the 

 dominant diatom species here {Fragilaria vaucheriae) is somewhat tolerant of organic loading 

 and the large percentage of this species indicated minor impairment here. 



A few teratological cells oi Fragilaria vaucheriae and Hannaea arcus were also counted 

 at this site. Abnormal 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 diatoms, \\hich include F. vaucheriae and H. 

 arcus, seem to be especially prone to producing teratological cells (McFarland et al. 1997). 

 Given that populations of F. vaucheriae and H. arcus were very large and probably expanding at 

 the time, and given the austere environmental conditions prevailing at this site, the minor stress 

 indicated by a few abnormal cells in Sullivan Creek is likely natural in origin and not related to 

 heavy metals. The two sites on Sullivan Creek shared 43% of their diatom associations, which 

 indicates somewhat similar floras and minor environmental change. 



Skyland Creek above Bear Creek. The dominant diatom at this site was Encyonema 

 silesiacum, which is somewhat tolerant of organic pollution. A large percentage of this species 

 indicated moderate impairment here (Table 4). The pollution index also indicated minor 

 impairment from organic loading. Diatom species richness, equitability, and diversity were also 

 low and indicated minor impairment. Two abnormal cells oi Hannaea arcus were observed 

 during the diatom proportional count, again probably the result of natural causes. 



