No diatom species in the family Epithemiaceae were counted 

 at the upper site and only a few at the lower site, indicating 

 that nitrogen was probably not limiting to algal growth at either 

 site. Diatoms in this family often harbor nitrogen-fixing 

 cyanobacteria within their cells and are most often found in 

 waters where nitrogen is the limiting nutrient. 



The relatively low similarity index (32.13) indicated that 

 the two sites had somewhat dissimilar diatom floras and that a 

 moderate amount of change had occured between the two sites. 

 Adjacent reaches on the same stream, without intervening 

 tributaries or pollution sources, can expect to have at least 60% 

 of their diatom floras in common (Bahls 1993) . 



LITERATURE CITED 



APHA. 1998. Standard Methods for the Examination of Water and 

 Wastewater. 20th Edition. American Public Health 

 Association, Washington, D.C. 



Bahls, L.L. 1979. Benthic diatom diversity as a measure of 

 water quality. Proc . Mont. Acad. Sci . 38:1-6. 



Bahls, L.L. 1993. Periphyton 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. Stribling. 



1999. Rapid Bioassessment Protocols for Use in Streams and 

 Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and 

 Fish. Second Edition. EPA/841-B-99-002 . U.S. EPA, Office 

 of Water, Washington, D.C. 



Dillard, G.E. 1999. Common Freshwater Algae of the United 

 States. J. Cramer, Berlin. 



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