TA8 Field-Based Effects Measures
A105 & A106
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() A reference stream approach for identifying resource injury in the South Fork Coeur d Alene River, Idaho.

Reiser, D1, Jeanes, E1, Woodward, D2, Harper, D2, Farag, A2, 1 R2 Resource Consultants, Sammamish, Washington, USA2 U.S. Geological Survey, Jackson Hole, Wyoming, USA

ABSTRACT- From 1994 to 1996 we conducted a study in support of a Natural Resource Damages Assessment that was focused on the release of hazardous substances from historic and existing mining operations in the South Fork (SF) Coeur d Alene basin in Idaho. This work was conducted under contract to the U.S. Fish and Wildlife Service. Because there were no suitable upstream control areas in the upper SF that represent conditions and anthropogenic impacts similar to those in the lower river, we used a reference watershed/stream approach from which to make comparisons of biotic and abiotic parameters at five paired sites. We selected the St. Regis River (RG) in Montana as the reference stream, based in part on watershed location and its similarity to the SF in a number of geomorphological and hydrological characteristics, and the type of land-use impacts. We used a paired study site approach; five sites were located on each stream at about 1.6, 13, 26, 39 and 52 km upstream of their mouths. Biotic (trout abundance, fish species composition, benthic invertebrates, biofilm) and abiotic (water, sediment, habitat quality and quantity; land-use activities) parameters were assessed at each paired site. In addition, in situ bioassay exposures of 10 to 16 westslope cutthroat trout (Oncorhynchus clarki lewisi) were performed at each of the paired sites to assess fish injury. Study results suggested that wild trout populations were controlled primarily by heavy metals concentrations in the lower three sites (SF 1-3), a combination of physical habitat and channel alteration, and perhaps a downstream metals avoidance response at SF-4, and primarily watershed and channel characteristics in the upper site (SF-5).

Key words: salmonids, bioassay, reference, metals

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