Geomorphic and ecological disturbance and recovery from two small dams and their removal

PLoS One. 2014 Sep 18;9(9):e108091. doi: 10.1371/journal.pone.0108091. eCollection 2014.

Abstract

Dams are known to impact river channels and ecosystems, both during their lifetime and in their decommissioning. In this study, we applied a before-after-control-impact design associated with two small dam removals to investigate abiotic and biotic recovery trajectories from both the elimination of the press disturbance associated with the presence of dams and the introduction of a pulse disturbance associated with removal of dams. The two case studies represent different geomorphic and ecological conditions that we expected to represent low and high sensitivities to the pulse disturbance of dam removal: the 4 m tall, gravel-filled Brownsville Dam on the wadeable Calapooia River and the 12.5 m tall, sand and gravel-filled Savage Rapids Dam on the largely non-wadeable Rogue River. We evaluated both geomorphic and ecological responses annually for two years post removal, and asked if functional traits of the macroinvertebrate assemblages provided more persistent signals of ecological disturbance than taxonomically defined assemblages over the period of study. Results indicate that: 1) the presence of the dams constituted a strong ecological press disturbance to the near-downstream reaches on both rivers, despite the fact that both rivers passed unregulated flow and sediment during the high flow season; 2) ecological recovery from this press disturbance occurred within the year following the restoration action of dam removal, whereas signals of geomorphic disturbance from the pulse of released sediment persisted two years post-removal, and 3) the strength of the press disturbance and the rapid ecological recovery were detected regardless of whether recovery was assessed by taxonomic or functional assemblages and for both case studies, in spite of their different geomorphic settings.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Conservation of Natural Resources
  • Ecosystem
  • Geologic Sediments / chemistry
  • Insecta
  • Oregon
  • Particle Size
  • Rivers*
  • Seasons

Grants and funding

The authors gratefully acknowledge funding support from the Oregon Watershed Enhancement Board, award number 207-091 and the National Oceanic and Atmospheric Association (NOAA), National Marine Fisheries Service, award number NA07NMF4630201 [DT, CW]. The funders played no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.