Carbon Sequestration in Tidal Salt Marsh Restoration Projects in Northern Humboldt Bay, California

We provide here a literature review and methodology for quantifying carbon sequestration associated with the restoration of tidal salt marshes and construction of a proposed living shoreline structure in Humboldt Bay, California. The rate of carbon sequestration can be used by the City of Arcata to quantify the benefits of restored tidal wetlands and for the City’s own carbon balance documentation. This work scope focused on a) gathering and analyzing existing data sets to estimate carbon sequestration in restoring local tidal salt marshes, b) assessing existing carbon sequestration models to quantify carbon sequestration rates; and c) performing a literature search to inform approaches to quantify carbon sequestration and identify key factors that affect rates. This memo summarizes the results of our review in two sections: Section (1) presents estimates of carbon sequestered for two restoring salt marshes and a proposed Living Shoreline project in Humboldt Bay; Section (2) utilizes the Marsh Equilibrium Model (MEMIII) to quantify carbon sequestration rates in evolving tidal salt marshes coordinately with sea level rise scenarios. Further analysis is presented in Appendix 1 with discussion and literature review of factors that may improve predictive power of current carbon sequestration modeling and a summary of published carbon sequestration values; Appendix 2 presents a parameter sensitivity analysis for the Marsh Equilibrium Model (MEMIII) to illustrate which parameters exert the most influence on calculated carbon sequestration rates using this model. We conclude that upon restoration of the two tidal salt marshes and proposed living shoreline in Humboldt Bay to mature salt marsh vegetation, approximately 100 metric Tons per year of carbon will be sequestered above current condition