Table 6. Percent abundance of major diatom species^ and values 

 of selected diatom association metrics for periphyton 

 samples collected from the Judith River near Lewistown, 

 Montana on August 9, 2000. 



« 



Species /Me trie 

 (Pollution Tolerance Class) ^ 



Percent Abundance/Metric Values^ 



Mountain Criteria Plains Criteria'' 

 Jl J3 Jl J3 



Achnanthes biasolettiana (3! 

 Achnanthes winutissima (3) 

 Cymhella laevis (3) 

 Cymbella rnicrocephala (2) 



Cells Counted 

 Total Species 

 Species Counted 

 Species Diversity- 

 Percent Dominant Species 

 Disturbance Index 

 Pollution Index 

 Siltation Index 

 Percent Abnormal Cells 

 Percent Epithemiaceae 

 Similarity Index 



^ A major diatom species is here considered to be one that 



accounts for 5% or more of the cells in one or more samples of 

 a sample set . 



^ Underlined values indicate good biological integrity, minor 



impairment, and full support of aquatic life uses; bold values 

 indicate fair biological integrity, moderate impairment, and 

 partial support of aquatic life uses; all other values 

 indicate excellent biological integrity, no impairment, 

 and full support of aquatic life uses when compared to diatom 

 criteria for mountain and plains streams in Tables 3 and 4 . 



^ 3 = sensitive to pollution; 2 = tolerant of pollution; 

 1 = most tolerant of pollution. 



* Only metric values that exceed diatom biocriteria for plains 

 streams are shown. 



