d^ Project Area and Sampling Sites 



The project area is located in Garfield County in east central Montana. Big Dry Creek 

 heads at an elevation of 3,500 feet south of Sand Springs in the southwestern comer of Garfield 

 County. It flows north and then east to meet Little Dry Creek about 25 miles east of Jordan and 

 just north of Montana Highway 200 near the Van Norman community. The combined flows of 

 Little Dry and Big Dry Creeks then continue north into the Big Dry Arm of Fort Peck Reservoir 

 on the Missouri River. 



The project area is within the Northwestern Great Plains Ecoregion (Woods et al. 1999). 

 The surface geology of the area consists of sandstone and shales of the Hell Creek Formation in 

 the headwaters and near the mouth of Big Dry Creek, and rocks of the coal-bearing Fort Union 

 Formation in between (Renfro and Feray 1972). The climate is semiarid and continental, with 

 cold winters and hot, dry summers. Upland vegetation is predominantly mixed grassland steppe 

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



Periphyton smples were collected at six sites on Big Dry Creek (Table 1). Elevations at 

 the sampling sites range from 2,650 feet at The Trees to 2,350 feet near the mouth. 



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 Lugol's (IKI) solution. 



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