RESULTS 



Algal Nutrients 



The results of algal nutrient analyses are presented in Table II. 

 The Yegen Drain (VII) was a major contributor of all species of nitro- 

 gen and phosphorus. The Clarks Fork River (II) introduced appreciably 

 higher levels of nitrate while phosphate was elevated below the Corette 

 plant (V). Overall, comparing nutrient concentrations at Laurel (I) 

 and Huntley (IX), nitrogen species were not appreciably concentrated by 

 discharges through Billings, but phosphate and total phosphorous were. 

 Non-Diatom Algae 



Diatoms dominated the flora at all stations except in and below 

 Yegen Drain where Oscillatoria and Stigeoclonium were the dominant algae, 

 respectively. Euglena and a filamentous bacterium resembling Sphaerotilus 

 were also evident at these two sites. Cladophora glomerata was abundant 

 at Laurel and below the Corette discharge. The remaining 11 genera of 

 non-diatom algae--all greens and blue-greens--were relatively uncommon. 

 Diatoms 



The structure of benthic diatom associations at the nine sites is 

 given in Table III. 



The seven major taxa are those that contributed 10 percent or more 

 relative abundance in one or more collections. Pollution tolerances 

 for these taxa were obtained from Cholnoky (3) and Lowe (7). Generally, 

 Achnanthes minutissima and Cymbella affinis are intolerant of organic 



