Results 



General Observations . A large portion of many of the plankton 

 samples consisted of bits of detritus and recognizable pieces of 

 terrestrial plants, indicating that allochthonous organic matter may 

 contribute significantly to the energetics of the river. Non-diatom 

 algae appearing in the plankton, particularly in winter, usually 

 appeared in a senescent and piecemeal condition. This was especially 

 true of the filamentous Chlorophyta, which were apparently detached 

 from their holdfasts, torn to bits by the current and introduced into 

 the floating community as incidental plankton or tychoplankton. This 

 probably occurs when new growth exceeds the plant's ability to maintain 

 itself in the current and represents a built-in mechanism for keeping 

 the growth of large filamentous benthic algae under control. No aquatic 

 macrophytes, i.e., angiosperms or mosses, were found in the samples, how- 

 ever, they may be present in the river. A host of non-algal macroscopic 

 creatures was observed, including nematodes, oligochaetes, protozoans, 

 rotifers, ostracods, tardigrades, bacteria, fungi, water mites, the 

 nauplius stage of a copepod and very early instars of midges and mayflies. 



Non-diatom Flora . A checklist of algae taxa from the Yellowstone 

 River and tributaries appears in Appendix C. The Yellowstone River was 

 respresented by four divisions, five classes, and 39 genera of non-diatom 

 algae. It is appropriate to note here that identification of the red 

 alga Audouinella in Part 1(1) was incorrect. This has since been posi- 

 tively identified as senescent Stigeoclonium , which responds inconclusively 



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