Summary 



On the Fourth of July, 2003, periphyton samples were collected from 2 sites on Hughes 

 Creek in the Bitterroot River TMDL planning area in southwestern Montana for the purpose of 

 assessing whether this stream is 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 at both sites on Hughes Creek indicated excellent biological 

 integrity, no impairment, and full support of aquatic life uses. However, values for the 

 pollution index at both sites approached the threshold for minor impairment and indicate 

 elevated organic loading. This organic loading may be natural in origin. 



A large amount of fine sand was noted in the sample from the lower site on Hughes 

 Creek. However, values for the sedimentation index were well below the threshold for minor 

 impairment in a mountain stream. Nevertheless, both sites did support large numbers of 

 Planothidium lanceolatum, a diatom that is adapted to living on grains of sand. 



The diatom and non-diatom algal floras of Hughes Creek indicate moderate gradients and 

 current velocities with little disturbance, and cold, alkaline, and highly oxygenated waters with 

 somewhat elevated levels of organic and inorganic nutrients. Nitrogen is probably the limiting 

 nutrient in this stream. The two sites supported very similar floras, which indicates very similar 

 ecological conditions. Diatom species richness, diversity, and equitability were excellent. No 

 abnormal diatom cells were observed, which indicates the probable absence of toxic chemicals. 



