pollution; Diatoma vulqare and Nitzschia dissipata will tele 

 weak organic pollution but thrive where oxidation is complete; and 

 Navicula cryptocephala var. veneta and Nitzschia palea are tolerant 

 of organic pollution. The characteristically aerophilous Navicula 

 mutica is an anomaly in the Yellowstone River. The total abundance 

 of Nitzschia species is generally regarded as a suitable indicator of 

 nitrogenous pollution. With one exception, to be discussed later, 

 these indicator taxa behaved as expected considering their pollution 

 tolerances and the nature and amount of enrichment. Relative abundance 

 values for all major taxa were reasonably close at the stations bracketing 

 the study section (stations I and IX). 



The most striking feature about the diversity measures in Table 

 III is the position held by the Yegen Drain collection (VII). Here, 

 taxa observed, taxa counted, Margalef, Shannon, maximum and minimum 

 diversities, evenness and equitability were all conspicuously and un- 

 expectedly maximum. On the other hand, stations in the CI arks Fork 

 River (II), below the Corette plant (V), and below Yegen Drain (VIII) 

 all had depressed diversity levels indicating they were subject to 

 some perturbation. As with relative abundances of the major species, 

 values for diversity measures at the most upstream and downstream 

 stations (I and IX) were fairly close (Table III). 



