Most diatoms at most of the sites were highly motile nitrogen autotrophs that tolerate 

 moderate levels of organics and prefer brackish, eutrophic, and alkaline waters. The modal 

 category for some of the attributes and sites was "not classified", which means that the 

 ecological preferences of the diatoms that comprise the largest group have yet to be determined. 



Modal categories at some sites represent a significant improvement in water quality 

 compared to other sites. For example, most diatoms in upper Horse Creek, upper Redwater 

 River, and Sand Creek were ''moderately motile". At other sites, the modal category was "highly 

 motile". At most sites, the modal category for salinity was "brackish", but it was "brackish- 

 fresh" at the lowest site on Horse Creek, the next to last site on Redwater River (airport), and 

 both sites on Sand Creek. 



Modal categories suggest possible inferior water quality conditions at the lower site on 

 Horse Creek and the airport site on the Redwater River. Both sites supported a predominance of 

 obligate nitrogen heterotrophs, as opposed to autotrophs at other sites. The modal category for 

 oxygen demand was "moderate" at these sites, whereas the modal category was "fairly high" at 

 other sites (Table 5). 



References 



APHA. 1998. Standard Methods for the Exanunation of Water and Wastewater. 20* Edition. American Pubhc 

 Health Association, Washington, D.C. 



Bahls, L.L. 1979. Benthic diatom diversity as a measure of water quality. Proceedings of the Montana 

 Academy of Sciences 38:1-6. 



Bahls, L.L. 1993. Penphyton Bioassessment Methods for Montana Streams (revised). Montana Department of 

 Health and Environmental Sciences, Helena. 



Bahls, L.L. , Bob Bukantis, and Steve Tralles. 1992. Benchmark Biology of Montana Reference Streams. Montana 

 Department of Health and Environmental Sciences, Helena. 



Barbour, M.T., J. Gerritsen, B.D. Snyder, and J.B. Stnbling. 1999. Rapid Bioassessment Protocols for Use 

 In Streams and Wadeable Rivers: Penphyton, Benthic Macroinvertebrates and Fish. Second Edition. 

 EPA/84 l-B-99-002. U.S. Environmental Protection Agency, Office of Water, Washington, D.C. 



Beaver, Janet. 1981. Apparent Ecological Characteristics of Some Common Freshwater Diatoms. 

 Ontario Ministry of The Environment, Technical Support Section, Don Mills, Ontario. 



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