BACKGROUND 



Plafkin et al . (1989) list several reasons why biological 

 surveys are superior to water quality analyses for determining 

 use support. The first of these reasons is that biological 

 communities measure our success at protecting the biological 

 integrity^ of waterbodies, which is a goal of the federal Clean 

 Water Act . 



The periphyton or phytobenthos community is a basic 

 biological component of all aquatic ecosystems. Collectively, 

 periphyton accounts for much of the primary production and 

 biological diversity in Montana streams. Stevenson and Bahls 

 (1999) list several advantages for using periphyton in biological 

 assessments of streams. 



Periphyton is a diverse assortment of simple photosynthetic 

 organisms, called algae, and other microorganisms that live 

 attached to or in close proximity of the stream bottom. Most 

 algae, such as the diatoms, are microscopic. Diatoms are 

 distinguished by having a cell wall composed of opaline glass- - 

 hydrated amorphous silica. Diatoms often carpet a stream bottom 

 with a slippery brown film. 



Some algae, such as the filamentous greens, are conspicuous 

 and their excessive growth may be aesthetically undesirable, 

 deplete dissolved oxygen, interfere with fishing and fish 

 spawning, clog irrigation intakes, create tastes and odors in 

 drinking water, and cause other problems. 



^ Biological integrity is defined as "the ability of an 

 aquatic ecosystem to support and maintain a balanced, integrated, 

 adaptive community of organisms having a species composition, 

 diversity, and functional organization comparable to that of the 

 natural habitats within a region" (Karr and Dudley 1981) . 



