Table 6. Percent abundance of major diatom species'- and values 

 of selected diatom association metrics for periphyton 

 samples collected from Casino Creek near Lewistown, 

 Montana on August 8, 2000. 



Species /Me trie 

 (Pollution Tolerance Class) ^ 



Percent Abundance/Metric Values^ 



Mountain Criteria Plains Criteria^ 

 CI C2 CI C2 



(3) 



Achnanthes minutissima 

 Amphora pediculus (3) 

 Gowphonerna kobayasii (3) 

 Gomphonewa parvulum (1) 

 Navicula cryptotenella (2 

 Navicula minima (1) 

 Navicula tripunctata (3) 

 Nitzschia dissipata (3) 



Cells Counted 

 Total Species 

 Species Counted 

 Species Diversity 

 Percent Dominant Species 

 Disturbance Index 

 Pollution Index 

 Siltation Index 

 Percent Abnormal Cells 

 Percent Epithemiaceae 

 Similarity Index 



3 .41 



59 . 10 



3 .6; 



27 .91 32.04 



2.12 



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. 



