Summary 



In the summer of 2003, periphyton samples were collected from 1 1 sites on 5 streams in 

 McCone County, 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. 



Diatom metrics indicate severe impairment from organic loading at the middle site on 

 Horse Creek, Nelson Creek, the upper (Fairgrounds) site on the Redwater River, and the upper 

 site on Sand Creek. Moderate stress from organic loading was indicated at the upper and lower 

 sites on Horse Creek and the Cemetery Road site on the Redwater River. All other sites showed 

 minor impairment from organic loading. Some of this organic loading may be internal and 

 natural in origin. 



'D' 



Severe impairment from sedimentation was noted at the lowest (Highway 13) site on the 

 Redwater River. Moderate sedimentation was indicated at the lower site on Horse Creek and the 

 fairgrounds and airport sites on the Redwater River. All other sites showed minor impairment 

 from sedimentation except the upper site on Horse Creek, where the sedimentation index was 

 normal for a prairie stream. 



Diatoms that indicate elevated concentrations of dissolved solids were common at all 

 sites. Salinity, along with elevated organic loading, was the most probable cause of depressed 

 diatom species richness and diversity. Diatom species indicate brackish waters at most sites, but 

 somewhat lower levels of salinity were indicated in Horse Creek near mouth, Redwater River at 

 the airport, and both sites on Sand Creek. 



Large percentages of nitrogen-fixing diatoms were recorded in the samples from Nelson 

 Creek and the upper site on Horse Creek. Nitrogen is most likely the limiting nutrient at these 

 sites. Cyanobacteria, many species of which can fix atmospheric nitrogen, were also common in 

 Nelson Creek and the upper reaches of Horse Creek, as well as in Sand Creek and the Redwater 

 River. Cyanobacteria were absent from Prairie Elk Creek and lower Sand Creek. 



Algae in the division Euglenophyta {Euglena and Phacus) are known to be especially 

 tolerant of organic pollution. These algae were found only in samples collected from the 

 Redwater River below the airport and at Highway 13. Conversely, Prairie Elk Creek was the 

 only site where a pollution sensitive species {Achnanthidium minutissimum) accounted for more 

 than 10 percent of the diatom cells. 



Two abnormal diatom cells were counted at the Fairgrounds site on the Redwater River. 

 This is within the normal range for an unimpaired prairie stream. No abnormal cells were 

 observed at the other 10 sites that were sampled for this project. 



