and Lange-Bertalot 1986) . In Montana, Navicula duerrenbergiana 



is most common in silty prairie streams, including the lower 

 reaches of the Redwater and Musselshell Rivers (unpublished 

 data) . In the Southern Fort Union Coal Region, this taxon has 

 been reported from the lower reaches of Armells, Mizpah, Pumpkin, 

 and Rosebud Creeks, where it prefers warm, brackish waters and 

 tolerates some suspended sediment and turbidity (Bahls et al . 

 1984) . 



Next in abundance in Big Dry Creek was Diploneis puella. 

 This diatom prefers brackish waters with muddy bottoms. Next in 

 abundance was Navicula recens . In Europe, N. recens is common in 

 brackish waters and in large rivers, such as the Rhein and the 

 Weser (Krammer and Lange-Bertalot 1986) . 



Also common in Big Dry Creek, and to a lesser extent in 

 Little Dry Creek, was Nitzschia palea. This diatom is very 

 tolerant of organic loading and of low levels of dissolved 

 oxygen. It is a good indicator of nitrogen enrichment. 



Little Dry Creek 



Diploneis puella- -the diatom that prefers brackish waters 

 with muddy bottoms- -was also a major diatom species in Little Dry 

 Creek (Table 5) . However, also abundant here were Achnanthes 

 minutissima and Cymbella af finis. Both of these diatoms prefer 

 cool, flowing waters and do not tolerate heavy organic loading or 

 low concentrations of dissolved oxygen. They are sensitive to 

 pollution and are the dominant diatoms in many mountain streams 

 of central and western Montana (unpublished data) . 



