Project Area and Sampling Sites 



The project area is located in Fergus County in central Montana. Chicago Gulch and 

 Collar Gulch are headwater tributaries of Box Elder Creek (HUC 10040204), which is a tributary 

 of the Musselshell River. Chicago Gulch and Collar Gulch head northeast of Lewistown in the 

 Judith Mountains, an 'island range" of the Rocky Mountains assigned to the Middle Rockies 

 Ecoregion (USEPA 2000). 



Periphyton samples were collected at two sites on Chicago Gulch, a tributary of 

 Chicago Gulch, and three sites on Collar Gulch (Table 1 ). Elevations at the sampling sites 

 range from about 5300 feet above mean sea level at the upper site on Collar Gulch to about 4600 

 feet at the lower site on Chicago Gulch. Vegetation in the study area is mainly mixed conifer 

 forest (USDA 1976). Land uses include mining, logging, and livestock grazing. 



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 proportion 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 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). 



