is also less tolerant, suggesting that water quality is not as degraded here as it is farther 

 downstream. Some very sensitive taxa were collected here, including a high abundance of the 

 mayfly Cinygmula sp. (17% of the sampled community), as well asAmeletus sp. The dominant 

 taxon is the filter-feeding blackfly Prosimulium sp.(63% of the sample), though, giving some 

 indication that fine organic particles are suspended in a rapid flow. 



Sage Creek near its headwaters had a somewhat higher biotic index score, but, compared 

 to the Plains Ecoregions reference, the site was rated slightly impaired. A high relative abundance 

 of the stonefly Hesperoperla pacifica and the caddisfly Brachycentnis sp. suggested that water 

 quality was not a major limitation to biotic health here. Sediment impacts, or other habitat 

 limitations, however, can not be ruled out, almost 63% of the sampled community was comprised 

 of midges. I'rif. ■■ 



Moderate impairment was indicated at the lower Pondera Coulee site; it received the 

 lowest bioassessment score of any stream in this study (37% of reference). The mayfly Caenis sp. 

 dominated the benthic community here, comprising 69% of the sampled assemblage, and 

 indicating that heavy sediment deposition may severely limit the health of this portion of Pondera 

 Coulee. Warm water temperatures are also indicated. Most of the diversity at this site comes fi"om 

 the twelve taxa of highly tolerant midges collected here. A high biotic index score (6.90) suggests 

 that organic and/or nutrient inputs add to the habitat limitations here. 



Farther upstream, the Pondera Coulee benthic assemblage indicates slight-to-moderate 

 impairment. Greater diversity was found here than at the downstream site, but the community was 

 still quite tolerant (biotic index = 6.26), with midges, especially Tanytarsus sp. and Cricotopiis 

 spp. making up 65% of the sample. Some sediment impacts are suggested by the composition of 



the community, but 



Figure 2. Bioassessment scores, compared to an internal reference. there IS probably a 



Plains ecoregions streams, 1995. Stronger impact from 



100 I organic and/or 



nutrient inputs; six 

 filter-feeding taxa 

 were collected here, 

 including 

 hydropsychid 

 caddisflies and a 

 fairly high abundance 

 (13%) of the blackfly 

 Sinmlium sp. 



Cotnl CIc *t hesdwaten I Pondera Coulee >. of bridge I S«ge Ck. nr he«dwatei IntemSI 



ConrBl Ck. nr. mouth Mariai R. tbove Dead Indian C. Pondera Coulee V^ mi. fr. Marias R. rf^rprPliri^ 



Four of the 

 six sites in this study received similar ratings when compared to an internal reference as they did 

 when the Plains Ecoregions reference was used. Figure 2 displays total bioassessment scores for 

 all sites, based on comparison to the internal reference derived fi"om the 1995 data for these 

 streams reported here. Differences between the sites in terms of their overall biotic health became 



