Methods 



Instructions for sampling the periphyton and phytoplankton com- 

 munities were supplied to field personnel prior to commencement of 

 sampling. Representative samples were obtained in the following manner: 



Phytoplankton . Plankton samples were collected by suspending nets 

 of various mesh sizes in the current for a period of 5 minutes or until 

 a few cubic centimeters of drifting material were entrapped. Nine of 

 the 126 "plankton" samples were collected using invertebrate drift nets, 

 mesh size unknown. Twenty-seven more were obtained with a large oceano- 

 graphic plankton net, mesh size also unknown. For the remaining three- 

 quarters of the plankton samples a Wisconsin-type plankton net with a 

 mesh size of 80 microns was used. No effort was made to collect nanno- 

 plankton and for the purpose of this report "plankton" should be con- 

 sidered only as net plankton. 



Periphyton . Benthic algal growths were scraped with a carefully 

 cleaned pocket knife from whatever substrates they happened to colonize. 

 Substrates (mud, rocks, logs, etc.) were scraped in proportion to their 

 importance at a given station. Samples were also representative of the 

 amount of pool, riffle and run habitat present at or near each station. 

 No attempt was made to gather a quantitative sample, i.e., to determine 

 the number, weight or volume or organisms per unit of bottom area. 



The great majority of samples was collected at monthly intervals 

 between August 1974 and April 1975. All samples were preserved with 

 either formalin or Lugol's solution and shipped to Helena for analysis. 



