SUMMARY 



In June 1999, composite periphyton samples were collected 

 from natural substrates at 4 sites on Painted Robe Creek in 

 southcentral Montana. Samples were collected following MDEQ 

 standard operating procedures, processed and analyzed using 

 standard methods for periphyton, and evaluated following modified 

 USEPA rapid bioassessment protocols for wadeable streams. 



The benthic algal flora at the uppermost site at Lehfeldt 

 (PRl-3) indicated perennial flows and cool waters with somewhat 

 elevated salt concentrations. An abundance of motile species 

 here, led by Navicula gregaria, indicated moderate impairment by 

 silatation with partial support of aquatic life uses. 



The benthic algal flora at Paulson (PR2-1) resembled that 

 of a mountain stream and was very different from floras upstream 

 and downstream on Painted Robe Creek. Algae at the Paulson site 

 indicated fresher waters and much less sedimentation than at the 

 Lehfeldt site. The pollution index at Paulson was acceptable 

 even for a mountain stream. Diatom metrics here indicated full 

 support of aquatic life uses, however dominance by Rhoicosphenia 

 curvata resulted in a rating of minor impairment. R. curvata is 

 a common epiphyte on the filamentous green alga Cladophora, which 

 was the dominant taxon at the Paulson site. 



The two downstream stations on Painted Robe Creek were 

 dominated by Rhizoclonium and brackish water species of Synedra. 

 Although salinity levels were higher here than at the upstream 

 sites, they were still within acceptable levels for prairie 

 streams. Both sites also had pollution and siltation index 

 values that were within the normal range for prairie streams. 

 Both sites provided full support of aquatic life uses with minor 

 impairment . 



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