INTRODUCTION 



Composite periphyton samples were collected at 2 sites on 

 McDonald Creek and 15 sites on the Teton River in 1998. Analyses 

 of the McDonald Creek samples and of 9 of the Teton River samples 

 were reported earlier (Bahls 1999) . This report addresses the 6 

 Teton River samples that were not included in the earlier report. 



This report evaluates the support of aquatic life uses, and 

 probable causes of impairment to those uses in the Teton River. 

 This evaluation is part of a larger assessment that was conducted 

 by staff of the Montana Department of Environmental Quality. 



Evaluation of use support in this report is based on the 

 species composition and community structure of periphyton 

 (benthic algae) communities at 6 sites that were sampled in July 

 and August of 1998. The periphyton or phytobenthos community is 

 a basic biological component of all aquatic ecosystems. 

 Periphyton accounts for much of the primary production and 

 biological diversity of Montana streams (Bahls et al . 1992). 



Plafkin et al . (1989) and Stevenson and Bahls (1999) list 

 several advantages of using periphyton in biological assessments 

 of streams: 



• Algae are universally present in large numbers in all 

 streams and unimpaired periphyton assemblages typically 

 support a large number (>30) of species; 



• Algae have rapid reproduction rates and short life cycles, 

 making them useful indicators of short-term impacts,- 



• As primary producers, algae are most directly affected by 

 physical and chemical factors, such as temperature, 

 nutrients, and toxins; 



• Sampling is quick, easy and inexpensive, and causes minimal 

 damage to resident biota and their habitat; 



• Standard methods and criteria exist for evaluating the 

 composition, structure, and biomass of algal associations; 



