Preserved periphyton samples were shipped to the Academy of 

 Natural Sciences in Philadelphia for processing and analysis. 

 Samples were cleaned of organic matter, diatom strewn mounts were 

 prepared, and diatom proportional counts (400 cells) were 

 conducted according to standard methods (APHA 1998) , using the 

 extensive taxonomic resources available to the Academy. "Soft" 

 (non-diatom) algae were not analyzed by the Academy. 



The diatom proportional counts were used to generate an 

 array of diatom association metrics (Table 2) . A metric is a 

 characceristic of the biota that changes in some predictable way 

 with increased human influence (Barbour et al . 1999) . 



Three additional metrics were calculated for this study that 

 were not considered in the earlier analysis of these samples 

 (Levine 1996) . These are a disturbance index (percent abundance 

 of Achnanthes minutissima) , the number of species counted, and 

 percent abundance of the dominant species . Percent abnormal 

 cells, a metric that may serve as an indicator of metals 

 toxicity, was not recorded by the Academy. 



Metric values from the upper Boulder River were compared to 

 numeric criteria for streams in the Rocky Mountain and Montana 

 Valley and Foothill Prairies Ecoregions (Table 3). These 

 criteria are based on metric values measured in least -impaired 

 reference streams (Bahls et al . 1992) and on metric values 

 measured in streams that are known to be impaired by various 

 sources and causes of pollution (Bahls 1993). 



The criteria in Table 3 distinguish among four levels of 

 impairment and three levels of aquatic life use support: no 

 impairment or only minor- impairment (full support) ,- moderate 

 impairment (partial support) ,- and severe impairment (nonsupport) . 

 These impairment levels correspond to excellent, good, fair, and 

 poor biological integrity, respectively. 



