Estuarine Wetland Restoration Impacts on Carbon Sequestration in the Oldest Projects Along the West Coast

Mitigating carbon dioxide's impact on our climate has become an important area of study. One such mitigation technique includes enhancing and protecting the earth's natural carbon sinks. Estuarine wetlands, though occupying a small fraction of the Earth's surface, are recognized for their significant carbon storage capacity. This thesis investigates the long-term impacts of estuarine wetland restoration on carbon sequestration by comparing mature restoration sites (20+ years post-restoration) with natural reference sites along California, Oregon, and Washington coasts. This study included 12 estuarine wetlands that each contained at least one reference site and one restoration site. Carbon sequestration rates were determined by collecting and processing 2-4 soil cores from each sample site. Soil accretion rates were determined by 210Pb profiles. Carbon sequestration rates were then calculated by multiplying the carbon density by the soil accretion rates. We found that both soil accretion rates and carbon density were not significantly different between restored and natural sites. All study sites save for Sonoma Baylands, Heerdt Marsh, and Nisqually Pilot and Phase 1 were meeting or exceeding relative sea level rise. Lastly, a linear mixed effects model was used to find carbon sequestration rates of restored and natural sites were not significantly different and therefore supports the effectiveness of restoration efforts. However, the variability of soil accretion and carbon sequestration across sites suggests site-specific assessments and emphasizes the importance of long-term monitoring.