Dominance by diatoms and green algae in Bear Creek may indicate 

 somewhat elevated concentrations of nutrients from natural and/or 

 cultural origins. 



DIATOMS 



The diatom association of Bear Creek was dominated by 

 Hannaea arcus , which contributed just over half of the diatom 

 cells (Table 4) . Hannaea arcus is the unofficial State Diatom of 

 Montana (Bahls 1974) and the namesake of my consulting business. 

 Patrick and Reimer (1966) report it from cool, flowing waters. 

 In a review of 11 diatom ecology papers, Lowe (1974) found 

 Hannaea arcus to prefer cold, flowing, and somewhat alkaline 

 waters, and to be indifferent to light organic pollution. In 

 Montana, this species is most abundant in mountain streams on the 

 east side of the Continental Divide (unpublished data) . 



A recent query to the Internet Diatom List regarding the 

 ecology of this species yielded 15 replies. To summarize the 

 replies, Hannaea arcus seems to prefer circumneutral fresh 

 waters, and mountain streams and large cold lakes in northern 

 latitudes, including Himalayan streams and Lakes Superior and 

 Baikal. It has also been reported from high southern latitudes 

 (Antarctica and South Georgia Island) . One researcher reported 

 the taxon to be sensitive to pollution from sewage. 



The abundance of Hannaea arcus in Bear Creek probably 

 reflects the abundance of a preferred host alga (Hydrurus) and 

 suitable water quality. Some nutrient enrichment may also be 

 implied by the dominance of Hannaea arcus at this site. 



Although it contributed only about 5% of the cells, 

 Gomphoneis minuta likely contributed a much larger share of the 

 biovolume at this site because of its relatively large size. 

 Gomphoneis minuta is found predominantly in the lower reaches of 



