disturbance index, and an elevated percent dominant species- -due 

 all or in part to the abundance of Achnanthes minutissima-- 

 indicated minor impairment with full support at Loma. In spite 

 of, or perhaps because of the relatively great distance between 

 the two sites (about 40 miles) , the Loma site had less than a 

 quarter of its diatom flora in common with the Dent Bridge site 

 upstream (Table 8) . 



ACKNOWLEDGEMENTS 



Carol Endicott of the Montana Department of Environmental 

 Quality, Monitoring and Data Management Bureau, provided the 

 author with copies of field data and with other helpful 

 information about station locations and sources and causes of 

 impairment along McDonald Creek and the Teton River. 



LITERATURE CITED 



American Public Health Association. 1998. Standard Methods for 

 the Examination of Water and Wastewater. 20th Edition. 

 A.P.H.A., Washington, D.C. 



Bahls, L.L. 1998. Biotic Integrity of Upper Tenmile Creek Based 

 on Periphyton Community Structure and Composition. Lewis 

 and Clark County Water Quality Protection District, Helena, 

 Montana . 



Bahls, L.L. 1993. Periphyton Bioassessment Methods for Montana 

 Streams (Revised) . Montana Department of Health and 

 Environmental Sciences, Helena. 



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

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



Bahls, L., R. Bukantis, and S. Tralles. 1992. Benchmark Biology 

 of Montana Reference Streams. Montana Department of Health 

 and Environmental Sciences, Helena. 



Barbour, M.T., J. Gerritsen, B.C. Snyder, and J.B. Stribling. 



1999. Revision to Rapid Bioassessment Protocols for Use in 

 Streams and Rivers: Periphyton, Benthic Macroinvertebrates , 

 and Fish. EPA 841-D-97-002 (Revised 1999) . 



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