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. 



Replicate periphyton samples were collected from site 03. 

 Both samples from this site were analyzed by Hannaea and the 

 results were compared side-by-side (Tables 4 and 5) . Diatom 

 metrics generated from the replicate samples resulted in 

 identical bioassessment ratings for this site: minor impairment 

 and full support of aquatic life uses. 



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., 2250-01. The first part of this number (2250) 

 designates the sampling site (Big Spring Creek at County Farm 

 below Lewistown) ; the second part of this number (01) designates 

 the number of periphyton samples that have been collected at this 

 site to date 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 University of Montana Herbarium in Missoula. 



