Without a substantial reduction in the billions of tons of anthropogenic greenhouse gases emitted annually our planet can expect a wide variety of deleterious effects. The restoration, enhancement, and conservation of coastal “blue carbon” habitats, including tidal salt marshes, have received increasing attention as a potential component of climate change mitigation because of their high carbon storage capacity.
This study presents the results of an investigation of soil carbon sequestration within a degraded Mediterranean-type climate tidal salt marsh in southern California, the Ballona Wetlands. Results from the Ballona Wetlands soil analyses and data from existing tidal marsh studies are used to estimate the change in soil carbon accumulation resulting from the proposed Ballona Wetlands Restoration Project (Ballona Project) as compared to the existing condition. Finally, this study demonstrates the process of using an existing carbon market methodology, VCS Methodology for Tidal Wetland and Seagrass Restoration VM0033 (2015, V 1.0), to calculate the number of carbon credits that could potentially be generated for the Ballona Project.
The results presented in Chapter 3 show that the existing tidal marsh habitats of the Ballona Wetlands contain soil organic carbon densities ranging from 0.018 to 0.030 g/cm3. Averaging SOC densities by habitat type resulted in a range of 0.022 to 0.027 g C/cm3, which is similar to natural tidal marshes around the world. Percent organic carbon is highest in low marsh habitat and decreases with increasing marsh habitat elevation (low > mid > high). However, carbon density is lowest in low marsh habitat and increases with increasing habitat elevation (low < mid < high). Carbon content is highest near the soil surface in all vegetated habitats and decreases rapidly due to decomposition of organic matter near the surface before stabilizing at lower soil depths. Higher levels of carbon at the soil surface of the existing habitats shows that even in its degraded condition the soils continue to accumulate organic carbon.
Chapter 4 presents a method to calculate carbon accumulation rates using the soil carbon densities measured in Chapter 3 along with soil accretion rates estimated from data in existing studies of tidal marsh habitat. Carbon accumulation rates estimated for habitats of the proposed Ballona Project are similar to rates reported in other tidal marsh studies. Results showed that the proposed restoration of a 600-acre degraded tidal marsh would increase the amount of carbon the habitats accumulate and store by an estimated 286 metric tons of carbon dioxide equivalents (CO2e) per year (range 110 – 680 mt CO2e/yr). This represents a 270% increase from the carbon accumulation estimated for the existing habitats.
The evaluation presented in Chapter 5 indicates that depending on project area, scope of restoration activities, and market value of a carbon credit (where 1 carbon credit = 1 mt CO2e), restoring tidal marsh habitat in general could be a viable component in a carbon trading market and climate change mitigation. However, due to its small area, high construction costs and emissions, and the currently low value of a carbon credit (approx. $13.50 in early 2017), the Ballona Project is not by itself financially feasible in a carbon market. The annual funding from carbon credit generation of the Ballona Project is estimated at approximately $2,538 per year (range $420 – $7,338) and is unlikely to even cover the monitoring and reporting costs associated with carbon market participation.