Elucidating patterns of channel erosion, sediment deposition, and vegetative regrowth on the restored Nisqually River Delta
Presentation Abstract
Tidally-influenced salt marshes are an ideal habitat for a variety of species including overwintering waterfowl and outmigrating juvenile salmon. Post-restoration salt marsh formation is dependent upon several factors such as frequency and duration of tidal inundation, sediment input from upstream sources, and local prevalence of halophilic plant species. Here we present five years of monitoring data to examine biophysical and vegetative changes on the restored Nisqually River Delta in Puget Sound, Washington, USA. We used these data to evaluate tidal channel morphology, marsh elevation, and vegetative community structure through time. Overall, major channel area increased 42% and major channel length increased 131% from pre- to post-restoration conditions across the Delta, with channel bed erosion occurring at rates of 6.5 cm/year on average. Furthermore, our analyses suggested that mudflat elevations in the restoration area were increasing at a rate of 0-3 cm/year, with Sloughs closer to the mouth of the Nisqually River experiencing more rapid sediment accretion rates as a result of higher initial elevations. These factors interacted to determine vegetative community composition on the Delta. Low marsh, saline-tolerant species were prevalent at newly colonizing restored sites, while high marsh halophilic and brackish species were dominant at two unaltered reference sites. Vegetation colonization occurred faster at sites with higher initial elevations, although species diversity still increased slightly (about 10%) through time at low elevation sites closer to open water. This integrative approach can be used as a tool for scientists and managers to evaluate the immediate effects of dike or levee removal. By incorporating multiple years of monitoring data into a spatially explicit model, we can provide simple projections of geomorphological changes following restoration.
Session Title
General Habitat Topics
Conference Track
Habitat
Conference Name
Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)
Document Type
Event
Start Date
2016 12:00 AM
End Date
2016 12:00 AM
Location
2016SSEC
Type of Presentation
Oral
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Restoration ecology--Washington (State)--Nisqually River Delta; Salt marsh ecology--Washington (State)--Nisqually River Delta; Watershed restoration--Washington (State)--Nisqually River Delta
Geographic Coverage
Salish Sea (B.C. and Wash.); Nisqually River Delta (Wash.)
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
Elucidating patterns of channel erosion, sediment deposition, and vegetative regrowth on the restored Nisqually River Delta
2016SSEC
Tidally-influenced salt marshes are an ideal habitat for a variety of species including overwintering waterfowl and outmigrating juvenile salmon. Post-restoration salt marsh formation is dependent upon several factors such as frequency and duration of tidal inundation, sediment input from upstream sources, and local prevalence of halophilic plant species. Here we present five years of monitoring data to examine biophysical and vegetative changes on the restored Nisqually River Delta in Puget Sound, Washington, USA. We used these data to evaluate tidal channel morphology, marsh elevation, and vegetative community structure through time. Overall, major channel area increased 42% and major channel length increased 131% from pre- to post-restoration conditions across the Delta, with channel bed erosion occurring at rates of 6.5 cm/year on average. Furthermore, our analyses suggested that mudflat elevations in the restoration area were increasing at a rate of 0-3 cm/year, with Sloughs closer to the mouth of the Nisqually River experiencing more rapid sediment accretion rates as a result of higher initial elevations. These factors interacted to determine vegetative community composition on the Delta. Low marsh, saline-tolerant species were prevalent at newly colonizing restored sites, while high marsh halophilic and brackish species were dominant at two unaltered reference sites. Vegetation colonization occurred faster at sites with higher initial elevations, although species diversity still increased slightly (about 10%) through time at low elevation sites closer to open water. This integrative approach can be used as a tool for scientists and managers to evaluate the immediate effects of dike or levee removal. By incorporating multiple years of monitoring data into a spatially explicit model, we can provide simple projections of geomorphological changes following restoration.
