Type of Presentation

Oral

Session Title

General Habitat Topics

Description

Processes occurring at varying temporal and spatial scales shape ecosystem structure and functioning. Disturbance events, in particular, can alter these processes and drive significant change in ecosystems. The emplacement and removal of the Elwha and Glines Canyon dams on the Elwha River in Washington, USA, can each be considered large-scale disturbance events. One hundred years of dam emplacement withheld 30 million tonnes of sediment from river, coastal, and nearshore habitats. Over 14 million tonnes of sediment were released during the three-year dam removal process (2011 to 2014). Here we show the physical and biological response of the Elwha estuary ecosystem and river delta during the dam removal process to sediment movement and deposition. The first large sediment deposition event during dam removal started a cascade of ecosystem shifts beginning with substrate composition that quickly progressed to estuarine water quality and ultimately to community composition of aquatic macroinvertebrates, fish, and vegetation. The significant shifts in fish and macroinvertebrate community assemblages in the estuary are consistent with substrate fining, decreased salinity, and increased turbidity, as well as reconnection to the upper watershed. The expansion of early-successional plants associated with the expanding delta dominated changes in terrestrial vegetation. The overall habitat characteristics of the existing and newly formed estuary are continuing to change as the river delta is reshaped during sediment deposition and erosion events. The dynamic nature of this ecosystem is likely to continue for the foreseeable future, highlighting the importance of long-term studies to increase our understanding of how ecosystems respond to large-scale disturbance events.

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Cascading ecosystem changes as a result of dam removal on the Elwha River, Washington

2016SSEC

Processes occurring at varying temporal and spatial scales shape ecosystem structure and functioning. Disturbance events, in particular, can alter these processes and drive significant change in ecosystems. The emplacement and removal of the Elwha and Glines Canyon dams on the Elwha River in Washington, USA, can each be considered large-scale disturbance events. One hundred years of dam emplacement withheld 30 million tonnes of sediment from river, coastal, and nearshore habitats. Over 14 million tonnes of sediment were released during the three-year dam removal process (2011 to 2014). Here we show the physical and biological response of the Elwha estuary ecosystem and river delta during the dam removal process to sediment movement and deposition. The first large sediment deposition event during dam removal started a cascade of ecosystem shifts beginning with substrate composition that quickly progressed to estuarine water quality and ultimately to community composition of aquatic macroinvertebrates, fish, and vegetation. The significant shifts in fish and macroinvertebrate community assemblages in the estuary are consistent with substrate fining, decreased salinity, and increased turbidity, as well as reconnection to the upper watershed. The expansion of early-successional plants associated with the expanding delta dominated changes in terrestrial vegetation. The overall habitat characteristics of the existing and newly formed estuary are continuing to change as the river delta is reshaped during sediment deposition and erosion events. The dynamic nature of this ecosystem is likely to continue for the foreseeable future, highlighting the importance of long-term studies to increase our understanding of how ecosystems respond to large-scale disturbance events.