INTRODUCTION 



This report evaluates the biological integrity, support of 

 aquatic life uses, and probable causes of impairment to those 

 uses, in lower Squirrel Creek near Decker, Montana. 



This evaluation is part of a study being conducted by staff 

 of the Montana Department of Environmental Quality (MDEQ) to 

 determine the chemical and biological effects of groundwater 

 discharges to Squirrel Creek. The discharged groimdwater 

 originates from test wells that are being used to dewater 

 underlying coal beds for the purpose of determining the capacity 

 and economic feasibility of methane gas production. 



Evaluation of use support in this report is based on the 

 species composition and structure of periphyton (phytobenthos, 

 benthic algae) communities at 3 stream sites that were sampled on 

 May 4, 2000. 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, dissolved salts, and toxins; 



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

 damage to resident biota and their habitat; 



