Summary 



In September and October of 2003, periphyton samples were collected from 30 sites on 

 19 streams in the Blackfoot River TMDL planning area in west central Montana for the purpose 

 of assessing whether these streams are water-quality limited 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. '' 



Siltation index values for Black Bear Creek, lower Buffalo Gulch, lower Douglas 

 Creek, and lower Washington Creek suggest severe impairment from sedimentation and non- 

 support of aquatic life uses. Siltation index values for Blanchard Creek, Wales Creek, Frazier 

 Creek, upper Buffalo Gulch, and upper Washington Creek indicate moderate impairment from 

 sedimentation and partial support of aquatic life uses. The low pollution index for Black Bear 

 Creek indicates moderate impairment from excessive organic nutrients and only partial support 

 of aquatic life uses. Diatom metrics suggest minor impairment from both organic loading and 

 sedimentation at most of the remaining Blackfoot tributary sites. 



Larger than normal percentages of teratological diatom cells (>1%) suggest that elevated 

 concentrations of heavy metals may be present in Richmond Creek and at the upper site on the 

 West Fork of the Clearwater River. Twenty-two sites supported smaller percentages of abnormal 

 diatom cells (<1%) and 6 sites had none. 



Diatoms were present in all of the samples. Most of the 34 major diatom species are 

 either sensitive to organic pollution or only somewhat tolerant of organic pollution. Only one of 

 the major diatom species — Nitzschia palea — is most tolerant of organic pollution and this species 

 was most abundant in Black Bear Creek. 



In general, diatom species richness, diversity, and equitability were excellent. Most sites 

 had more than 40 species and diversity values greater than 4.00. One site (lower Murray Creek) 

 had 73 species and a diversity index of 4.99, which are exceptional values for a mountain stream. 

 High diatom diversity in these streams suggests moderate nutrient enrichment (little Competition 

 for available nutrients) and the absence of extreme natural stressors, such as steep gradients, fast 

 currents, low light, low nutrients, and/or constant cold temperatures. Only one site — upper 

 Douglas Creek — had a low diversity value that indicates unusual stress. This was also the only 

 site where the dominant species contributed more than half of the diatom cells. The cause of 

 stress in upper Douglas Creek was probably excess inorganic nutrients. 



Streams where nitrogen- fixing cyanobacteria were common include the West Fork of the 

 Clearwater River (both sites), Deer Creek (both sites), Blanchard Creek, Buffalo Gulch (upper 

 site), Washington and Jefferson Creeks (upper sites), and Seven-Up Pete Creek. Nitrogen-fixing 

 diatoms in the order Rhopalodiales accounted for more than 2% of the cells in the West Fork of 

 the Clearwater River (both sites). Deer Creek (both sites), Black Bear Creek, Blanchard Creek, 

 Jefferson Creek (upper site), and Seven-Up Pete Creek. Nitrogen is most likely the limiting 

 nutrient at these sites. 



