Using appropriate tools, microalgae were scraped, brushed, 

 or sucked from natural substrates in proportion to the rank of 

 those substrates at the study site. Macroalgae were picked by 

 hand in proportion to their abundance at the site. All 

 collections of microalgae and macroalgae were pooled into a 

 common container and preserved with Lugol's solution. 



The sample was examined to estimate the relative abundance 

 and rank by biovolume of diatoms and genera of soft (non-diatom) 

 algae according to the method described in Bahls (1993) . Soft 

 algae were identified using Dillard (1999), Prescott (1978), 

 Smith (1950) , and Whitford and Schumacher (1984) . These books 

 also served as references on the ecology of the soft algae, along 

 with Palmer (1977) . 



After the identification of soft algae, the raw periphyton 

 sample was cleaned of organic matter using sulfuric acid, and two 

 permanent diatom slides were prepared using Naphrax, a high 

 refractive index mounting medium, following Standard Methods for 

 the Examination of Water and Wastewater (APHA 1998) . Four 

 hundred and eleven diatom cells (822 valves) were counted at 

 random and identified to species. The following were used as the 

 main taxonomic and autecological references for the diatoms : 

 Krammer and Lange-Bertalot 1986, 1988, 1991a, 1991b; Patrick and 

 Reimer 1966, 1975. Lowe (1974) was also used as an ecological 

 reference for the diatoms. 



The diatom proportional count was used to generate an array 

 of diatom association metrics (Table 1) . A metric is a 

 characteristic of the biota that changes in some predictable way 

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



Metric values from Bear Creek were compared to numeric 

 biocriteria developed for streams in the Rocky Mountain 

 Ecoregions of Montana (Table 2) . These criteria are based on 



