Coastal vegetation responses to large dam removal on the Elwha River
IntroductionLarge dam removals provide a restoration opportunity for shrinking coastal wetland habitats. Dam removal can increase sediment delivery to sediment-starved river deltas and estuaries by restoring natural sediment transport and mobilizing reservoir-impounded sediment. However, rapid mobil...
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2023-09-01
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| Series: | Frontiers in Ecology and Evolution |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fevo.2023.1233903/full |
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| author | Laura G. Perry Laura G. Perry Patrick B. Shafroth Samuel J. Alfieri Ian M. Miller |
| author_facet | Laura G. Perry Laura G. Perry Patrick B. Shafroth Samuel J. Alfieri Ian M. Miller |
| author_sort | Laura G. Perry |
| collection | DOAJ |
| description | IntroductionLarge dam removals provide a restoration opportunity for shrinking coastal wetland habitats. Dam removal can increase sediment delivery to sediment-starved river deltas and estuaries by restoring natural sediment transport and mobilizing reservoir-impounded sediment. However, rapid mobilization of massive quantities of sediment stored behind large dams also constitutes a major ecological perturbation. Information is lacking on coastal habitat responses to sediment pulses of this magnitude.MethodsRemoval of two large dams along the Elwha River (Washington, USA) in 2011–2014 released ~20.5 Mt of impounded sediment, ~5.4 Mt of which were deposited in the delta and estuary (hereafter, delta). We used time series of aerial imagery, digital elevation models, and vegetation field sampling to examine plant community responses to this sediment pulse across seven years during and after dam removal.ResultsBetween 2011 and 2018, the Elwha River delta increased by ~26.8 ha. Vegetation colonized ~16.4 ha of new surfaces, with mixed pioneer vegetation on supratidal beach, river bars, and river mouth bars and emergent marsh vegetation in intertidal aquatic habitats. Colonization occurred on surfaces that were higher and more stable in elevation and farther from the shoreline. Compared to established delta plant communities, vegetation on new surfaces had lower cover of dominant species and functional groups, with very low woody cover, and lower graminoid cover than dunegrass and emergent marsh communities. Over time following surface stabilization, however, vegetation on new surfaces increased in species richness, cover, and similarity to established communities. By 2018, ~1.0 ha of vegetation on new surfaces had developed into dunegrass or willow–alder communities and ~5.9 ha had developed into emergent marsh. At the same time, dam removal had few discernible effects on established delta plant communities.DiscussionTogether, these results suggest that rapid sediment mobilization during large dam removal has potential to expand coastal wetland habitat without negatively affecting established plant communities. However, as sediment loads declined in 2016–2018, new delta surfaces decreased by ~4.5 ha, and ~1.6 ha of new vegetation reverted to no vegetation. Long-term persistence of the expanded coastal habitat will depend on ongoing erosional and depositional processes under the restored natural sediment regime. |
| first_indexed | 2024-04-24T23:58:52Z |
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| id | doaj.art-f85e9b45438f43f1a8c34debf4b90e5e |
| institution | Directory Open Access Journal |
| issn | 2296-701X |
| language | English |
| last_indexed | 2024-04-24T23:58:52Z |
| publishDate | 2023-09-01 |
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| series | Frontiers in Ecology and Evolution |
| spelling | doaj.art-f85e9b45438f43f1a8c34debf4b90e5e2024-03-14T10:51:12ZengFrontiers Media S.A.Frontiers in Ecology and Evolution2296-701X2023-09-011110.3389/fevo.2023.12339031233903Coastal vegetation responses to large dam removal on the Elwha RiverLaura G. Perry0Laura G. Perry1Patrick B. Shafroth2Samuel J. Alfieri3Ian M. Miller4Biology Department, Colorado State University, Fort Collins, CO, United StatesU.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, United StatesU.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, United StatesU.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, United StatesWashington Sea Grant, University of Washington, Port Angeles, WA, United StatesIntroductionLarge dam removals provide a restoration opportunity for shrinking coastal wetland habitats. Dam removal can increase sediment delivery to sediment-starved river deltas and estuaries by restoring natural sediment transport and mobilizing reservoir-impounded sediment. However, rapid mobilization of massive quantities of sediment stored behind large dams also constitutes a major ecological perturbation. Information is lacking on coastal habitat responses to sediment pulses of this magnitude.MethodsRemoval of two large dams along the Elwha River (Washington, USA) in 2011–2014 released ~20.5 Mt of impounded sediment, ~5.4 Mt of which were deposited in the delta and estuary (hereafter, delta). We used time series of aerial imagery, digital elevation models, and vegetation field sampling to examine plant community responses to this sediment pulse across seven years during and after dam removal.ResultsBetween 2011 and 2018, the Elwha River delta increased by ~26.8 ha. Vegetation colonized ~16.4 ha of new surfaces, with mixed pioneer vegetation on supratidal beach, river bars, and river mouth bars and emergent marsh vegetation in intertidal aquatic habitats. Colonization occurred on surfaces that were higher and more stable in elevation and farther from the shoreline. Compared to established delta plant communities, vegetation on new surfaces had lower cover of dominant species and functional groups, with very low woody cover, and lower graminoid cover than dunegrass and emergent marsh communities. Over time following surface stabilization, however, vegetation on new surfaces increased in species richness, cover, and similarity to established communities. By 2018, ~1.0 ha of vegetation on new surfaces had developed into dunegrass or willow–alder communities and ~5.9 ha had developed into emergent marsh. At the same time, dam removal had few discernible effects on established delta plant communities.DiscussionTogether, these results suggest that rapid sediment mobilization during large dam removal has potential to expand coastal wetland habitat without negatively affecting established plant communities. However, as sediment loads declined in 2016–2018, new delta surfaces decreased by ~4.5 ha, and ~1.6 ha of new vegetation reverted to no vegetation. Long-term persistence of the expanded coastal habitat will depend on ongoing erosional and depositional processes under the restored natural sediment regime.https://www.frontiersin.org/articles/10.3389/fevo.2023.1233903/fullcoastal wetland restorationdam removalecological successionpioneer geomorphic surfacesriparianriver delta |
| spellingShingle | Laura G. Perry Laura G. Perry Patrick B. Shafroth Samuel J. Alfieri Ian M. Miller Coastal vegetation responses to large dam removal on the Elwha River Frontiers in Ecology and Evolution coastal wetland restoration dam removal ecological succession pioneer geomorphic surfaces riparian river delta |
| title | Coastal vegetation responses to large dam removal on the Elwha River |
| title_full | Coastal vegetation responses to large dam removal on the Elwha River |
| title_fullStr | Coastal vegetation responses to large dam removal on the Elwha River |
| title_full_unstemmed | Coastal vegetation responses to large dam removal on the Elwha River |
| title_short | Coastal vegetation responses to large dam removal on the Elwha River |
| title_sort | coastal vegetation responses to large dam removal on the elwha river |
| topic | coastal wetland restoration dam removal ecological succession pioneer geomorphic surfaces riparian river delta |
| url | https://www.frontiersin.org/articles/10.3389/fevo.2023.1233903/full |
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