INTRODUCTION 



This report evaluates the support of aquatic life uses, and 

 probable causes of impairment to those uses, in Box Elder Creek 

 in central Montana. This evaluation is part of a larger study 

 that is being conducted by the Riparian and Wetland Research 

 Program of The University of Montana in cooperation with the U.S. 

 EPA, MDEQ, BLM, and private landowners. Objectives of the study 

 are (l) to evaluate several indicators that are used to monitor 

 grazing levels in riparian areas, and (2) to determine if there 

 are relationships between these indicators and water quality, 

 riparian condition, and stream function. The goal is to be able 

 to predict water quality using grazing use level indicators in 

 riparian areas (RWRP Website) . 



Evaluation of use support in this report is based on the 

 species composition and community structure of periphyton 

 (benthic algae) communities at 8 stream sites that were sampled 

 in early August 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; 



