effects of different stressors and provide a measure of 

 their aggregate impact; and 



• Periphyton and other biological communities may be the only 

 practical means of evaluating impacts from non-point sources 

 of pollution where specific ambient criteria do not exist 

 (e.g., impacts that degrade habitat or increase nutrients). 



PROJECT AREA AND SAMPLING SITES 



The project area is located near Powderville in northern 

 Powder River County in southeastern Montana (Map 1) . Mizpah 

 Creek heads about 12 miles west of the town of Broadus and flows 

 northeasterly about 70 miles to the point where it meets the 

 Powder River near Mizpah, Montana. 



The project area is within the Northwestern Great Plains 

 Ecoregion (Woods et al . 1999). The surface geology of the 

 watershed consists of coal -bearing deposits of the Fort Union 

 Formation (Renfro and Feray 1972) . Upland vegetation is mixed 

 grassland with some open ponderosa pine forest in the headwaters 

 (USDA 1976) . The main land use is livestock grazing, with hay 

 production in the valley bottom. 



Periphyton samples were collected at 2 sites on Mizpah Creek 

 on August 28, 2000 (Table 1) . These 2 sites bracket a 20-mile 

 section of upper Mizpah Creek that extends from Highway 59 north 

 of Broadus to the Custer County line (Map 1) . Elevations at the 

 sampling sites range from about 3,200 feet above mean sea level 

 at the upper site to 2,900 feet at the lowest site. Mizpah Creek 

 is classified C-3 in the Montana Surface Water Quality Standards. 



METHODS 



