becomes a nuisance in larger Montana rivers and streams that 

 receive domestic wastewater, for example, the Clark Fork River. 

 It is a good indicator of nutrient enrichment. 



The abundance of green algae and diatoms relative to 

 cyanobacteria may also indicate moderate nutrient enrichment in 

 Mol Heron Creek. Generally, cyanobacteria (blue-green algae) 

 indicate lower nutrient levels in mountain streams in Montana 

 (Bahls at al . 1992) . They cannot compete with diatoms and green 

 algae under moderate to heavy nutrient loading. 



DIATOMS 



Three major diatom taxa were co-dominants in Mol Heron Creek 

 (Table 4) . One of these was Hannaea arcus, the unofficial State 

 Diatom of Montana (Bahls 1974) and the namesake of my consulting 

 business. Patrick and Reimer (1966) report Hannaea arcus 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 (Montana 

 Diatom Database, unpublished data) .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 second co-dominant diatom taxon in Mol Heron Creek was 

 another pollution sensitive species: Diatoma vulgare (Table 4). 



7 



