Project Area and Sampling Sites 



The project area is located within the Middle Rockies Ecoregion (USEPA 2000). The 

 Big Hole watershed occupies a high mountain basin in the southwestern comer of Montana. The 

 surface geology of the watershed is complex, consisting mostly of Belt Series and Boulder and 

 Idaho Batholith Rocks in the uplands and Tertiary basin fill in the Big Hole Valley (Renfro and 

 Feray 1972). Climax vegetation consists of alpine tundra at the highest elevations, Douglas-fir 

 and subalpine fir forest at intermediate elevations, and mixed grassland/sagebrush steppe in the 

 Big Hole Valley. The main land uses are recreation, logging, ranching, and mining. 



Periphyton samples were collected at 42 sites on 22 tributaries of the Big Hole River 

 (Table 1). All sites are in USGS HUC 10020004 and are classified either A-1 or B-1 in the 

 Montana Surface Water Quality Standards depending on whether they are above or below the 

 Butte Water Company intake at Divide, Montana. 



Methods 



Periphyton samples were collected 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 importance of those 

 substrates at each study site. Macroalgae were picked by hand in propoiition to their abundance 

 at the site. All collections of microalgae and macroalgae were pooled into a common container 

 and preserved with LugoTs (IKI) solution. 



The samples were examined to estimate the relative abundance of cells 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 Smith (1950), Prescott (1962, 1978), John et al. 

 (2002), and Wehr and Sheath (2003). These books also served as references on the ecology of 

 the soft algae, along with Palmer (1969, 1977). 



