^ 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. 



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., 3007-01 . The first part 

 of this number (3007) designates the sampling site (Little Dry Creek at Cohagen) 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 (MONTU) 

 in Missoula. The duplicate slide will be retained in Helena at the offices of Hannaea. Diatom 

 proportional counts have been entered into the Montana Diatom Database. 



Results and Discussion 



Results are presented in Tables 3, 4, and 5, which are located near the end of this report 

 following the references section. Appendix A consists of a series of diatom reports, one for each 

 sample. Each diatom report contains an alphabetical list of diatom species and their percent 

 abundances, and values for 65 different diatom metrics and ecological attributes. 



