was located at an elevation of 6,000 feet, just above the 

 confluence of Little Rock Creek. The lower site (Station 2) was 

 located at an elevation of 5,300 feet about 5 miles downstream of 

 Station 1 at the county road crossing east of Clyde Park. 



Both Cottonwood Creek and Rock Creek are classified B-l in 

 the Montana Surface Water Quality Standards. 



METHODS 



Perinhyton samples were collected by Patrick Newby of the 

 MDEQ Monitoring and Data Management Bureau following standard 

 operating procedures of the MDEQ Planning, Prevention, and 

 Assistance Division. 



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 samples were 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 

 samples were cleaned of organic matter using sulfuric acid, and 

 permanent diatom slides were prepared using Naphrax, a high 

 refractive index mounting medium, following Standard Methods for 



