Metric values from the Blackfoot River and tributaries were 

 compared to numeric biocriteria or threshold values developed for 

 streams in the Rocky Mountain Ecoregions of Montana (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. 



Quality Assurance. Several steps were taken to assure that 

 the study results are accurate and reproducible. 



Upon receipt of the samples, station and sample information 

 were recorded in a laboratory notebook and the samples were 

 assigned a unique number compatible with the Montana Diatom 

 Database, e.g., 2156-01. The first part of this number (2156) 

 designates the sampling site (Blackfoot River at Flesher Pass 

 Road) ; the second part of this number (01) designates the number 

 of periphyton samples that have been collected at this site for 

 which data have been entered into the Montana Diatom Database. 



Sample observations and analyses of soft (non-diatom) algae 

 were recorded in a lab notebook along with station and sample 

 information provided by MDEQ . A portion of the raw sample was 

 used to make duplicate diatom slides. After completing the 

 diatom proportional count, the slide used for the count will be 

 deposited in the Montana Diatom Collection at University of 

 Montana Herbarium in Missoula. The other slide will be retained 

 by Hannaea in Helena. 



6 



