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 in Carter, Fallon, Custer and 

 Prairie Counties in southeastern Montana. 0' Fallon Creek heads 

 near Ekalaka in northern Carter County and flows northerly for 

 about 80 miles, joining the Yellowstone River below Terry at the 

 unincorporated community of Fallon. Sandstone Creek, the largest 

 tributary of 0' Fallon Creek, begins near Baker (pop. 2354) and 

 flows westerly for about 25 miles, entering 0' Fallon Creek near 

 Ismay (pop. 31) . South Sandstone Creek ("South Fork" on the USGS 

 hydrologic map) enters Sandstone Creek near Plevna (pop. 191) . 

 Pennel Creek, another major tributary, enters 0' Fallon Creek 

 about 8 miles below the mouth of Sandstone Creek. 



The watershed of 0' Fallon Creek is located within the 

 Northwestern Great Plains Ecoregion (Woods et al . 1999). The 

 surface geology of the watershed is composed of the Fort Union 

 Formation, a coal -bearing sedimentary deposit of Paleocene age 

 (Renfro and Feray 1972) . Upland vegetation is predominantly 

 mixed grassland (USDA 1976) . The main land uses are livestock 

 grazing and dryland farming. The area is largely rural with 

 scattered farms . 



Periphyton samples were collected at eleven sites: 5 on 

 0' Fallon Creek, 2 on Pennel Creek, 3 on Sandstone Creek, and 1 on 

 South Sandstone Creek (Maps 1-4, Table 1) . Elevations at the 

 sampling sites range from about 3,000 feet near the head of 



