Summary and Conclusions 



Allochthonous material apparently plays a significant role in the 

 energetics of the Yellowstone River. A diverse array of aquatic micro- 

 organisms, representing several phyla of plants and animals, were ob- 

 served. No macrophytes were found in the samples and it is presumed 

 that algae are the only significant primary producers in the river. 



The algal flora is primarily Bacillariophycean-Chlorophycean 

 with the blue-greens (Myxophyceae) contributing relatively little in 

 terms of volume. The non-diatom algal flora was represented by four 

 divisions, five classes and 39 genera. 



There is little distinction between the non-diatom plankton and 

 periphyton floras of the river; most taxa, and all of the more fre- 

 quently occurring algae, are common to both communities. The bulk 

 of the net plankton consists of dead or dying benthic algae detached 

 from the periphyton. 



Diatoms clearly dominated the net plankton while Cladophora 

 qlomerata and diatoms fairly evenly co-dominated the phycoperiphyton. 

 Many of the subordinate non-diatom taxa exhibited interesting pre- 

 ferences for a particular river reach and/or season of the year. 



The major non-diatom alga of the Yellowstone River is Cladophora 

 glomerata , a cosmopolitan green alga that often becomes a nuisance 

 in response to nutrient enrichment. Elsewhere in Montana, luxuriant 

 growths of C. g lomerata are associated with productive fisheries. An 

 impoundment on the Yellowstone would enhance the production of 



■23- 



