Quantifying blue carbon for the largest salt marsh in southern British Columbia: implications for regional coastal management

Abstract

Understanding blue carbon storage and accumulation prior to engineering projects is essential for assessing the potential co-benefit of carbon storage for natural climate solutions. This study collected sediment cores from the western portion of Boundary Bay, Delta, British Columbia (BC), where implementation of a living dike pilot project is planned to alleviate impacts of sea level rise. Total carbon stocks were 10,034 ± 3,148 Mg C for the western 140 ha of marsh, with stocks averaging 83.3 ± 29.3 Mg C/ha (high marsh) and 39.3 ± 24.2 Mg C/ha (low marsh). Carbon accumulation rates (CARs) exhibited substantial variability, ranging from 19.5 to 454 g C/m2/yr (median 70.1 g C/m2/yr). Both stocks and accumulation rates were at least 45% lower than globally averaged estimates, likely due to the shallow depth and dominant vegetation type of the marsh. Despite historical modifications to the marsh, our study indicates that the western marsh has expanded by about 20% since 1930, which we estimate increased carbon stocks by about 1,549-1,698 Mg C. This study’s quantification of carbon stocks and CARs is an important first step towards leveraging the co-benefit of salt marshes for improved management, restoration, and preservation. However, additional data are needed to document the greenhouse gas budgets for carbon accounting purposes, along with exploration of law and policy issues related to carbon stewardship in a multi-jurisdictional coastal environment. We outline subsequent research needed for salt marshes such as Boundary Bay to be included in voluntary carbon markets in British Columbia.