McVey Creek. Diatom metrics indicate minor impairment from organic loading and 

 sedimentation at site 01. An abundance oi Staurosira construens and Pseiidostaurosira 

 brevistriata at site 02 indicates gentle gradients and ver)' little physical disturbance. Both sites 

 supported a few teratological diatom cells. The two sites shared less than 40% of their diatom 

 floras, which indicates a moderate change in environmental conditions. 



Swamp Creek. Diatom metrics suggest moderate impairment from organic loading and 

 severe impairment from sedimentation at site 01 on Swamp Creek. Cells of the motile genera 

 Navicula and Nitzschia accounted for three-quarters of the diatoms in the sample from site 01. 

 One of the major species was Nitzschia palea, a nitrogen heterotroph that is very tolerant of 

 organic pollution. Conditions were somewhat better at site 02, where diatom metrics indicate 

 only minor impairment from organic loading and sedimentation. However, one of the major 

 species at site 02 was Navicula minima, which is also very tolerant of organic enrichment. Both 

 sites had a few abnormal diatom cells and shared only about one-third of their assemblages. 



Warm Springs Creek. Site 01 on Wami Springs Creek supported a large number of 

 Navicula minima, an eutraphentic nitrogen heterotroph. This resulted in a depressed pollution 

 index that suggests minor impairment from organic loading. Elevated percentages of motile 

 diatoms suggest minor impairment from sedimentation at both sites. A larger percentage of 

 Achnanthidium minutissimum suggests steeper gradients and more physical disturbance at site 

 02. Both sites supported a few teratological cells and they shared slightly less than half of their 

 diatom assemblages. 



North Fork Big Hole River. The pollution index at both sites was close to the threshold 

 for minor impairment from organic loading. Sedimentation was also a minor problem at both 

 sites. Site 02 supported 50% more motile diatoms than site 01 and the siltation index at site 02 

 approached (but did not exceed) the threshold for moderate impairment. The dominant species 

 at site 02 was a highly motile species of Nitzschia {N archibaldii). The other major species here 

 indicate somewhat gentler gradients and slower current velocities than site 01 . Both sites had a 

 few abnormal cells and they shared slightly more than half of their diatom assemblages. 



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