INTRODUCTION 



This report evaluates the support of aquatic life uses, and 

 probable causes of impairment to those uses, in Painted Robe 

 Creek in southcentral Montana. This evaluation is part of a 

 larger assessment that was conducted by Warren Kellogg of the 

 Natural Resources Conservation Service, USDA. This assessment 

 was performed at the request of local producers who are concerned 

 about water quality, primarily salinity. Several bulls have died 

 recently, potentially due to alkali poisoning (Carol Endicott, 

 MDEQ, personal communication) . 



Evaluation of use support in this report is based on the 

 species composition and community structure of periphyton 

 (benthic algae) communities at 4 stream sites that were sampled 

 in June of 1999. 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; 



