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Increasing Salt Marsh Elevation Using Sediment Augmentation: Critical Insights from Surface Sediments and Sediment
Elizabeth Fard1, Lauren N Brown2,3, Richard F Ambrose4
1Department of Geography, University of California, 1255 Bunche Hall, Box 951524, Los Angeles, CA, 90095, USA. efard@ucla.edu.
Environmental Management
|November 1, 2023
Summary
Sediment augmentation can help tidal wetlands combat sea-level rise, but applied sediment characteristics and thickness must match historic conditions for successful vegetation recovery and resilience.
Area of Science:
- Coastal ecology
- Wetland restoration
- Climate change adaptation
Background:
- Tidal wetlands face significant threats from sea-level rise, especially in areas with steep topography or human development.
- Sediment augmentation is a proposed strategy to increase wetland elevation and prevent habitat loss.
- Limited understanding exists on optimal sediment augmentation approaches and their long-term effectiveness in mimicking natural processes.
Purpose of the Study:
- To assess a southern California marsh case study on sediment augmentation.
- To determine the characteristics of pre-existing sediments and site variability.
- To evaluate the applied sediments in relation to the augmentation experiment.
Main Methods:
- Analysis of sediment cores to understand historical sediment composition over 1500 years.
- Comparison of applied sediment grain size and organic content with historical data.
- Measurement of experimental sediment application rates and post-augmentation accretion rates.
Main Results:
- Applied sediments were significantly coarser (100% sand) than historical sediments (max 76% sand).
- Experimental sediment application rate (~25 cm in 2 months) far exceeded historical natural accretion rates.
- Post-augmentation accretion rates at the experimental site were slower than pre-augmentation or control site rates.
Conclusions:
- A mismatch in sediment characteristics and application thickness compared to historical conditions likely hindered vegetation recovery.
- While sediment augmentation can be useful, slow recovery may occur if applied sediments do not match natural conditions.
- Testing adaptive strategies for wetland elevation is crucial for mitigating sea-level rise impacts, with lessons applicable to other sites.
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