were also assessed using Protocol II (Table 12) in Bahls (1993) . 

 This method compares selected metrics at study sites to the 

 corresponding metrics at an upstream control site, in this case 

 Big Spring Creek above Casino Creek at Brewery Flats (site #2) . 

 This approach can be used at any time of the year. 



Metric scores and impairment ratings using Protocol II are 

 presented in Table 6. In Protocol II, the upstream control site 

 is assumed to be relatively unimpaired and automatically scores a 

 perfect 100 percent for all metrics. The bioassessment using 

 Protocol II (Table 6) indicates that the site below Casino Creek 

 had excellent biointegrity and no impairment, and the site below 

 Lewistown had good biointegrity and minor impairment from a lower 

 diversity value, an elevated siltation index, and a somewhat 

 lower than expected similarity index. 



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. 1999. Use Support in Big Spring Creek Based on 

 Periphyton Composition and Community Structure. Montana 

 Department of Environmental Quality, 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. 



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