Allyce R. Miller | Search USGS

USGS2026

From sediment pulse to ecological recovery: A nine-year study of benthic macroinvertebrate response to Elwha River dam removal

Large dam removals are increasingly important river restoration actions, but long-term ecological responses remain poorly understood, especially for removals involving large sediment releases. We evaluated benthic macroinvertebrate (BMI) responses following removal of the Elwha and Glines Canyon dams on the Elwha River, Washington, USA. At the time of removal (2011–2014), these were the largest dams to be dismantled worldwide. Dam removal reconnected over 90% of the watershed to anadromous fish, released more than 20 megatonnes of reservoir sediment downstream, and restored natural sediment and wood transport processes. Using nine years of monitoring data spanning periods before, during, and after dam removal, we quantified changes in BMI density, taxa richness, and community composition across five river sections exposed to different combinations of sediment disturbance, reservoir succession, and fish reintroduction. Sediment release substantially altered downstream physical habitat and was accompanied by pronounced declines in BMI density and richness, particularly downstream of both dams. Density declined by up to 95% during active dam removal but rebounded to near baseline levels within three years after peak sediment transport subsided. In contrast, taxa richness and community composition remained significantly altered three years after dam removal, with persistent reductions particularly evident among Trichoptera and long-lived taxa. Fine sediment was the environmental variable most strongly associated with changes in BMI community structure. Our results demonstrate that large dam removal can cause severe but largely transient reductions in BMI abundance while producing longer-lasting changes in taxonomic diversity and community composition. These findings highlight the importance of distinguishing between numerical and ecological recovery and suggest that recovery trajectories following large dam removal extend well beyond the period of active sediment release.

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USGS2023

Community and citizen science on the Elwha River: Past, present, and future

This report reflects on the past, present, and potential future of community and citizen science (CCS) in the Elwha River watershed, with particular focus on the years before and after a major restoration event: the removal of two dams that had impacted the river system for a century. We ask: how does CCS feature in the Elwha story and how could it feature? We use the term CCS to reference the broad range of ways in which members of the public might participate in authentic science and monitoring processes, including students and both paid and unpaid interns: participants are individuals contributing to scientific projects without prior formal training in the topic. Removal of the Elwha dams was a large-scale, complex project, and communities had an important role to play: the Lower Elwha Klallam Tribe (LEKT) and other local groups were a large part of the original drive to remove the dams. Some funding and policy requirements for monitoring are ending, but there is still much to learn from the changes happening in the Elwha, requiring ongoing research and monitoring. In 2022, the Elwha scientific community came together in a multifaceted effort called the “Elwha ScienceScape” to mark the ten-year anniversary of dam removal and to plan for future monitoring. One of ScienceScape’s priorities is expanding CCS efforts, and because the Elwha dam removal is a powerful international symbol of large-scale watershed restoration, ScienceScape is well-positioned to inform and emphasize the potential role of CCS in dam removal worldwide. This report presents insights about Elwha CCS from an academic literature review and discussions with scientists and many others that have been working in the Elwha. We found that the history of CCS on the Elwha is important but understated, with few scientific papers acknowledging support by volunteers of various kinds. Recent and ongoing CCS projects on the Elwha tend to be focused on biological phenomena, and most are associated with educational opportunities (across many types of institutions) and paid internships. We also noted that most Elwha CCS projects required volunteers with particular pre-existing skill sets (e.g., botanical knowledge) or time to impart specialized training (e.g. boat use), leading many projects towards engagement with a smaller number of volunteers. Partners working in the Elwha are considering a wide range of potential new CCS projects, and these ideas are in varying stages of development. Many new projects would broaden public involvement in terms of the opportunities available and increase the variety of focal topics for research and monitoring. This increased breadth is promising: there are indications that the local community’s interests also range widely, from fish recovery after dam removal to dam removal impacts on humans. Elwha CCS projects have encountered some challenges and barriers, including the administrative burden of coordinating volunteers and managing liability concerns. But Elwha ScienceScape scientists are committed to the value that CCS brings both to the research itself as well as to those who participate in these projects. CCS can be a way to increase equity in science and engage people who would not otherwise participate in research, and in many cases the research simply wouldn’t be possible without their help. Support with project administration, volunteer management, and data management could help in expanding CCS efforts and broadening their inclusivity. More systematic tracking of CCS projects to assess how they contribute to research and to community and participant benefit could be helpful in establishing and maintaining a long-term CCS strategy in the Elwha.

Wshington↗