Macroinvertebrate Community Analysis on lower Hood River Before and During the Removal of Powerdale Dam: A Baseline Study

摘要

Powerdale Dam was an 87-year-old hydroelectric complex on lower Hood River in northern Oregon which was decommissioned in 2010. Macroinvertebrate samples were collected in 2009, before the removal process began, and in 2010, near the end of the demolition project, at one site upstream and three sites downstream of the dam. Macroinvertebrate communities were analyzed using both multi-metric (Benthic Index of Biotic Integrity [B-IBI]) and multivariate (Predictive Assessment Tool for Oregon [PREDATOR]) approaches, as well as EPT and Functional Feeding Group (FFG) analysis. All analytical approaches indicated declines in habitat quality in 2010 relative to 2009, and showed increasing impairment in the downstream sites in 2010, with sediment implicated as an impairment factor. Pollutants such as pesticides released from the impoundment might also contribute to downstream disturbance levels. The upstream, control site showed habitat quality declines in 2010 relative to 2009, indicating a possible upstream source of impairment. The demolition project did not physically impact upstream areas, and tributary turbidity does not appear to have been elevated relative to other years; however, the Hilsenhoff Biotic Index indicates an increase in upstream nutrient pollution in 2010 relative to 2009. Future research will be able to establish rate and extent of post-removal habitat recovery relative to these baseline data.