INTRODUCTION 



This report evaluates the support of aquatic life uses, and 

 probable causes of impairment to those uses, in the Redwater 

 River, the East Redwater River, and Little Dry Creek in eastern 

 Montana. This evaluation is based on species composition and 

 community structure of periphyton (benthic algae) communities at 

 8 sites on the Redwater River and 1 site each on the East 

 Redwater River and Little Dry Creek that were sampled in May 

 1999. 



Plafkin et al . (1989) list several reasons why biological 

 surveys are superior to water quality analyses for determining 

 use support. The first of these reasons is that biological 

 communities measure our success' at protecting the biological 

 integrity^ of waterbodies, which is a goal of the federal Clean 

 Water Act . 



The periphyton or phytobenthos community is a basic 

 biological component of all aquatic ecosystems. Collectively, 

 periphyton accounts for much of the primary production and 

 biological diversity of Montana streams. 



Stevenson and Bahls (1999) list several advantages for 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; 



' Biological integrity is defined as "the ability of an 

 aquatic ecosystem to support and maintain a balanced, integrated, 

 adaptive community of organisms having a species composition, 

 diversity, and functional organization comparable to that of the 

 natural habitats within a region" (Karr and Dudley 1981) . 



