METHODS 



Aquatic invertebrates were sampled by Pat Newby of the Montana Department of 

 Environmental Quality (MT DEQ). Two sites on Shields River were sampled; Table 1 

 gives site locations. Both sites lie within the Montana VaUeys and Foothill Prairies 

 (MVFP) ecoregion.The sampling method employed is described in the MT DEQ 

 Standard Operating Procedures for Macroinvertebrate Sampling (Bukantis 1998). In 

 addition, habitat quality was evaluated by scoring various instream, streambank and 

 riparian zone parameters using a DEQ-modified version of the U.S. EPA's Rapid 

 Bioassessment Protocols. Aquatic invertebrate samples and associated habitat assessment 

 data were delivered to Rhithron Biological Associates, Missoula, Montana, for laboratory 

 and data analyses. 



Table 1. Sampling locations on Sliields River. August 2000. 



Sampling 

 station 



McCloud 

 Johnstone 



Latitude Longitude 



46° 09' 56" 110° 34' 05'" 

 45° 57' 21" 110° 37' 57" 



In the laboratory, the Montana DEQ-recommended sorting method was used to 

 obtain subsamples of at least 300 organisms from each sample. Organisms were 

 identified to the lowest possible taxonomic levels consistent with Montana DEQ 

 protocols. 



To assess invertebrate communities in this study, a multimetric index developed 

 in previous work for streams of western Montana (Bollman 1998) was used. Multimetric 

 indices result in a single numeric score, which integrates the values of several individual 

 indicators of biologic health. Each metric used in this index was tested for its response or 

 sensitivity to varying degrees of human influence. Correlations have been demonstrated 

 between the metrics and various symptoms of human-caused impairment as expressed in 

 water quality parameters or instream, streambank and stream reach morphologic features. 

 Metrics were screened to minimize variability over natural environmental gradients, such 

 as site elevation or sampling season, which might confound interpretation of results. The 

 multimetric index used in this report incorporates multiple attributes of the sampled 

 assemblage into an integrated score that accurately describes the benthic community of 

 each site in terms of its biologic integrity. In addition to the metrics comprising the index, 

 other metrics, which have been shown to be applicable to biomonitoring in other regions 

 (Kleindl 1995, Patterson 1996, Rossano 1995), were used for descriptive interpretation of 

 Shields River results. These metrics include the number of "dinger" taxa, long-lived taxa 

 richness, the percent of predatory organisms, and others. They are not included in the 

 integrated bioassessment score, however, since their performance in the ecoregions of 

 Montana is unknown. However, the relationship of these metrics to habitat conditions is 

 intuitive and reasonable. 



The six metrics comprising the bioassessment index used in this study were 

 selected because both individually and as an integrated metric battery, they are robust at 

 distinguishing impaired sites from relatively unimpaired sites (Bollman 1998). In 

 addition, they are relevant to the kinds of impacts that are present in the Shields River 

 drainage, and they have been demonstrated to be more variable with anthropogenic 



