While not motile, the two most abundant diatoms at Station 2-- 

 Fragilaria capucina and Melosira varians- -are unattached, 

 tychoplanktonic species that thrive under low- flow conditions. 

 In slowly- flowing streams, Melosira varians is known to develop 

 massive growths consisting of long brown streamers (Krammer & 

 Lange-Bertalot 1991a) . All other metrics indicate good to 

 excellent biological integrity at Station 2. 



The pollution index declined slightly between Station 1 and 

 Station 2 (Table 6) , indicating a small increase in organic 

 loading between these sites. Both sites had a small number of 

 teratological cells, perhaps indicating small concentrations of 

 toxic chemicals. And both sites had small percentages of diatoms 

 in the family Epithemiaceae, which may indicate that nitrogen 

 concentrations are not limiting to algal growth in Billman Creek. 



Station 1 and Station 2 had less than 40% of their diatom 

 assemblages in common (Table 6) . Stations on adjacent reaches of 

 the same stream, without intervening tributaries or pollution 

 sources, usually have at least 60% of their diatom associations 

 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. 



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