INTRODUCTION 



Benthic macroinvertebrate populations are known to be key indicators of stream 

 ecosystem health (Hynes 1960). Life spans for some of these creatures are as long as three years, 

 and their complex life cycles and limited mobility mean that there is ample time for the 

 community to respond to cumulative effects of environmental perturbations. The analysis of 

 macroinvertebrate communities can thus be related to a stream's biological health, or integrity, 

 defined by Karr and Dudley (1981) as "the capability of supporting and maintaining a balanced, 

 integrated, adaptive community of organisms having a species composition, diversity and 

 functional organization comparable to that of natural habitat of the region." 



The multimetric approach to bioassessment using benthic macroinvertebrates uses 

 attributes of the assemblage in an integrated way to reflect overall biotic condition. Community 

 attributes which can contribute meaningfully to bioassessment include assemblage structure, 

 sensitivity of community members to stress or pollution, and fimctional traits. Each metric 

 component contributes an independent measure of the biotic integrity of a stream site; combining 

 components into an overall score reduces variance and increases precision of the assessment 

 (Foreetal. 1995). 



This report presents multimetric bioassessment data fi-om four streams of the Plains 

 Ecoregions of north-central Montana. The streams were sampled for the first time in 1995 in an 

 attempt to form a baseline against which to compare the data resulting fi-om future collections. 



METHODS 



Aquatic macroinvertebrates were sampled by personnel of the Montana 

 Department of Environmental Quality (DEQ) from four Plains Ecoregions streams on July 19 

 and 20, 1995. The traveling kick-net method described by Bukantis (1997) was utilized. Single 

 samples fi-om six reaches were collected; the resulting samples are described and dated as 

 follows: 



1. Corral Creek, near mouth. July 19, 1995. 



2. Corral Creek, at mouth of headwaters. July 19, 1995. 



3. Marias River, upstream of Dead Indian Coulee. July, 19, 1995. 



4. Pondera Coulee, south of Cheek's bridge. July 20, 1995. 



5. Pondera Coulee, '/2 mile fi-om Marias River. July 20, 1995. 



6. Sage Creek, near headwaters. July 20, 1995. 



Macroinvertebrate Sample Processing and Identiflcation 



Laboratory and data analyses were contracted to BlueStem Incorporated. Benthic 

 macroinvertebrate samples were processed by BlueStem Incorporated personnel using the U.S. 

 Environmental Protection Agency's techniques for RBP III (Plafkin et al. 1989). Taxonomic 

 identification of benthic macroinvertebrates was subcontracted by BlueStem Incorporated to 

 EcoAnalysts, Incorporated. Chironomidae and Oligochaeta identifications were subcontracted to 

 Michael J. Mcbride. 



Sample processing consisted of obtaining approximately a 300-organism subsample and 

 was consistent with RBP III (Plafkin et al. 1989). Organisms were enumerated and identified 

 whenever possible to the taxonomic level specified in the Montana DEQ SOP (Bukantis, 1996). 



