Modal Categories (Table 6) 



Several ecological attributes were selected from Table 7 and modal categories of these 

 attributes were extracted from the appendix to characterize water quality tendencies at the two 

 sites (Table 6). Modal categories for the selected attributes were nearly identical for the two 

 sites. The majority of diatoms at both sites were non-motile nitrogen autotrophs that exert a 

 continuously high demand for dissolved oxygen. Nitrogen autotrophs require inorganic nitrogen 

 (nitrates and ammonia) as nutrients. The majority of diatoms at both sites also indicate fresh, 

 alkaline waters with only a small amount of BOD loading. Most diatoms at Johnstone's indicate 

 eutrophic waters that are rich in inorganic nutrients. The modal category for trophic state near 

 the mouth was "variable". Diatoms in this category can prosper under a wide range of nutrient 

 regimes from oligotrophic to hypereutrophic. 



References 



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Bahls, L.L. 1993. Periphyton Bioassessment Methods for Montana Streams (revised). Montana Department of 

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