Summary 



In August 2003, periphyton samples were collected from Dog Creek and Eagle Creek in 

 the Bullwhacker-Dog TMDL planning area in north 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 using 

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

 protocols for wadeable streams. 



A very large number of motile and highly motile diatoms at the Dog Creek site indicated 

 severe impairment from sedimentation and non-support of aquatic life uses for a prairie 

 stream. Depressed diatom species diversity and a large number of pollution tolerant diatoms also 

 indicated elevated levels of organic matter and inorganic nutrients at this site, which resulted in 

 moderate impairment. 



The two upstream sites on Eagle Creek had excellent biological integrity for a prairie 

 stream, indicating no impairment and full support of aquatic life uses. Even when compared 

 with biocriteria for a mountain stream, diatom metrics at the upper site indicated only minor 

 impairment from organic loading and sedimentation and full support of aquatic life uses. The 

 two sites had similar algal floras, indicating that little or no change in environmental conditions 

 occurred between them. 



A major change in taxonomic composition and community structure took place between 

 Eagle Creek site 2 and Eagle Creek site 3, which shared only 14% of their diatom floras. The 

 latter site supported only one genus of non-diatom algae {Chard) and a significantly smaller 

 number of diatom species. The diatom species that were present at this site indicated moderate 

 impairment from sedimentation and minor impairment from organic loading. 



Diatom species indicated alkaline waters and eutrophic conditions at all four sites. 

 Diatom species indicated variable conditions among the four sites with respect to salinity, 

 nitrogen uptake, oxygen demand, saprobity, dewatering, and sedimentation. 



