INTRODUCTION 



This report evaluates the support of aquatic life uses, and 

 probable causes of impaiirment to those uses, in Careless Creek, 

 Lodgepole Creek, and the South Fork of Lodgepole Creek in the 

 Musselshell River basin of central Montana. This evaluation is 

 part of a larger assessment that was conducted by staff of the 

 Natural Resources Conservation Service, USDA, and the Montana 

 Department of Environmental Quality (MDEQ) . 



Evaluation of use support in this report is based on the 

 species composition and structure of periphyton (phytobenthos , 

 benthic algae) communities at 3 sites, one on each stream, that 

 were sampled in July and August of 1999. The periphyton 

 community is a basic biological' component of all aquatic 

 ecosystems. Periphyton accounts for much of the primary 

 production and biological diversity in 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; 



