Bioassessment of a Reclaimed Placer Mined Stream: Recovery of Benthic Macroinvertebrate Communities

The upper reaches of Elk Creek, Granite County, Montana, have been placer mined for more than 100 years. Recent efforts at restoring trout habitat in these reaches included reconstruction of portions of the stream channel, resulting in improved morphology, the return of surface flows in some areas, and introduction of riparian vegetation to denuded streambanks. Prior to reconstruction, In this study, biotic health of these reaches of Elk Creek was evaluated. A comparison of benthic macroinvertebrate communities and bioassessment metrics between reconstructed and control sites was made over three years, using a battery of bioassessment metrics shown to be reliable indicators of anthropogenic impacts. For reconstructed sites, time to recovery was demonstrated, where recovery was defined as achievement of bioassessment scores equivalent to those of control sites. Even after recovery of reconstructed sites, all sites continued to show improvement in biotic health. Continued improvement may have been due to facilitation of macroinvertebrate colonization from upstream sites, made possible by the restoration of surface flow throughout the studied reaches