The criteria in Table 2 distinguish among four levels of stress or impairment and three 

 levels of aquatic life use support: (1 ) no impairment or only minor impairment (full support); 

 (2) moderate impairment (partial support); and (3) severe impairment (nonsupport). These 

 impairment levels correspond to excellent, good, fair, and poor biological integrity, respectively. 

 In cold, high-gradient mountain streams, natural stressors will often mimic the effects of man- 

 caused impairment on some metric values. 



Quality Assurance 



Several steps were taken to assure that the study results are accurate and reproducible. 



Upon receipt of the samples, station and sample attribute data were recorded in the 

 Montana Diatom Database and the samples were assigned a unique number, e.g., 2596-01. The 

 first part of this number (2596) designates the sampling site (Old Maids Coulee at mouth) and 

 the second part (01) designates the number of periphyton samples that 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 information on the sample label. A portion of the raw sample was used to 

 make duplicate diatom slides. The slide used for the diatom proportional count will be 

 deposited in the Montana Diatom Collection at the University of Montana Herbarium in 

 Missoula. The duplicate slide will be retained by Hannaea in Helena. Diatom proportional 

 counts have been entered into the Montana Diatom Database. 



Results and Discussion 



Results are presented in Tables 4 through 12, which are located near the end of this report 

 following the references section. Copies of aquatic plant field sheets are included as Appendix 

 A. Appendix B contains a series of diatom reports, one for each sample. Each diatom report 

 contains an alphabetical list of diatom species in that sample and their percent abundances, and 

 values for 65 different diatom metrics and ecological attributes. 



