SUMMARY 



In June of 2001, 12 periphyton samples were collected from 

 the Blackfoot River above Nevada Creek and from four tributaries 

 of the upper Blackfoot River in western Montana for the purpose 

 of assessing whether these streams are water-quality limited and 

 in need of TMDLs . The samples were collected following DEQ 

 standard operating procedures, processed and analyzed using 

 standard methods for periphyton, and evaluated following modified 

 USEPA rapid bioassessment protocols for wadeable streams. 



Diatoms with deformities were found in periphyton samples 

 collected from all 12 sites on the upper Blackfoot River and 

 tributaries. In samples from two sites- -BlckftR-01 and SbrC-02-- 

 teratological diatoms accounted for more than 10% of the cells 

 that were counted, indicating severe impairment and nonsupport of 

 aquatic life uses. At five sites- -BlckftR-02 , SbrC-01, AraC-01, 

 PoorC-02, and PoorC-01- - the percentage of teratological cells 

 indicated moderate impairment and partial support of uses . The 

 most likely cause of this impairment is elevated concentrations 

 of heavy metals. The remaining 5 sites suffered only minor 

 impairment and fully supported their aquatic life uses. 



In addition to having large percentages of teratological 

 cells, the two sites on Sandbar Creek also supported very large 

 populations of individual diatom species. At SbrC-02, 

 Achnanthidium minutissimum accounted for 86% of the cells in the 

 diatom association. Streams receiving mining wastes in western 

 Montana often support very large numbers of Achnanthidium 

 minutissimum, an indicator of chemical disturbance and elevated 

 concentrations of heavy metals. The upstream site on Sandbar 

 Creek (SbrC-01) supported a large number of Diatoma mesodon, a 

 cold-water stenotherm that is common in streams receiving mine 

 adit discharge water and flows recharged by groundwater. 



