SUMMARY 



In June 2001, composite periphyton samples were collected 

 from natural substrates at five sites on 0' Fallon Creek and from 

 six sites on Pennel , Sandstone, and South Sandstone Creeks in 

 southeastern Montana. Samples were collected following standard 

 operating procedures of the Montana Department of Environmental 

 Quality, processed and analyzed using standard methods for 

 periphyton, and evaluated following modified USEPA rapid 

 bioassessment protocols for wadeable streams. 



The upper site on 0' Fallon Creek (Willard Crossing) was 

 severely impaired due to siltation and suffered moderate 

 impairment due to salinity and organic loading. Water quality 

 improved downstream, although moderate impairment was still 

 evident at the site below Willard Crossing (salinity and organic 

 loading) and at Highway 12 (low diatom diversity and siltation) . 



The upper site on Pennel Creek was moderately impaired due 

 to siltation and organic loading. Diatom metrics at the lower 

 site on Pennel Creek indicated recovery and only minor impairment 

 and full support of aquatic life uses. 



The single site near the mouth of South Sandstone Creek was 

 dominated by two brackish water species of Synedra, resulting in 

 very low diatom diversity and a large percent dominant species. 

 South Sandstone Creek was severely impaired by salinity and did 

 not support aquatic life uses for a prairie stream. 



Diatom metrics at all three sites on Sandstone Creek 

 indicated moderate impairment due to siltation. In addition, the 

 upper site had a very large percent dominant species value, 

 resulting in a low diatom diversity index that also indicated 

 moderate impairment. Water quality in Sandstone Creek improved 

 somewhat from upstream to downstream. 



