Field and Laboratory Procedures 



At each station, periphyton samples were obtained by scraping 

 natural substrates in proportion to the surface area of each type 

 that was exposed for colonization. (Rocks predominated at most 

 stations.) Substrates from both sluggish and rapidly flowing water 

 were sampled in order to minimize possible bias caused by current 

 effects. This procedure allows for collection of a composite sample 

 that is representative of the range of physical conditions prevailing 

 at each site at the time of collection. 



From each sample, a subsample was taken and scanned microscopically 

 to determine the presence and relative importance of non-diatom algae. 

 Then, in a manner prescribed by the Environmental Protection Agency (4), 

 each sample was acidified and oxidized, a permanent mount was prepared, 

 and a diatom species proportional count was performed. 



Nutrient analyses were performed at the Department of Health and 

 Environmental Sciences' water laboratory in Helena following methods 

 outlined by the American Health Association (1). 

 Diversity Measures 



Two diversity indexes were applied to the diatom species relative 

 abundance figures obtained from the proportional counts:. Margalef's 

 index (9), 



A - S - 1 



and Shannon's index (12), 



D = -k(Ni/N) log (N^/N) 

 i 



