Summary 



In the summer of 2003. periphyton samples were collected from 10 sites on 5 streams in 

 the Madison Raver TMDL planning area in southwestern Montana for the purpose of assessing 

 whether these streams are water-quality Umited and in need of TMDLs. The samples were 

 collected following MDEQ standard operating procedures, processed and analyzed following 

 standard methods for periphyton, and evaluated following modified USEPA rapid bioassessment 

 protocols for wadeable streams. 



Diatom metrics indicate moderate impairment (from sedimentation) and less than full 

 support of aquatic life uses at only one site: Elk River at end of West Fork Madison River Road. 

 Although this site had an elevated sedimentation index, it was virtually identical, floristically, 

 with the upstream site on Elk River. 



All of the other sites registered only minor impairment and provided full support of 

 aquatic life uses. The prevailing cause of impairment at these sites was sedimentation, which 

 resulted m minor impairment at all sites except the upper site on Gazelle Creek and the upper site 

 on Blaine Spring Creek. Minor impairment from organic loading was noted in Antelope Creek 

 and in Blaine Spring Creek below the fish hatchery. 



All but one of the sites (Blaine Spring Creek near mouth) supported at least a few 

 abnormal diatom cells. Most sites are within the normal range for abnormal cell numbers. 

 Gazelle Creek supported the largest percentage of abnormal cells (1.08-1.44%) and these may 

 indicate chronic toxicity from heavy metals. 



Blaine Spring Creek at bypass supported a distinctive diatom flora that indicates lower 

 pH and lower water temperatures compared to the other sites in the sample set. Naturally austere 

 conditions here resulted in depressed diatom species richness and diversity values. This site had 

 little in common, tloristically, with the next site downstream (below fish hatchery). 



