Improved carbon monitoring with identification of two-loss processes in salt marsh ecosystems with very high-resolution satellite imagery and <i>in situ</i> elevation data

Abstract Blue carbon refers to carbon-dense coastal wetland ecosystems with high carbon burial rates and large soil organic carbon (SOC) stocks. These critical ecosystems are changing rapidly due to anthropogenic and natural drivers. Remote sensing is the basis for many local, regional, and global carbon monitoring systems. These remote sensing-based monitoring systems often simplify complex loss processes into a single emission estimate. In this study, we propose that the amount of SOC lost depends on the type of loss which can be, in part, determined based on the location of the loss. The two-loss processes (TLP) dominant in our study site are edge erosion and interior drowning. We examine differences between the TLP and potential carbon emissions using remote sensing, in situ elevation data, and SOC estimates. We utilize very high-resolution Worldview-2/3 and GeoEye-1 satellite data acquired between 2018 and 2024 to map salt marsh extent and change for the Mid-Atlantic’s barrier islands from Sandy Hook, NJ to Chincoteague, VA. We determine the impact of edge erosion and interior die-off, on the loss of SOC. We utilize remote sensing maps of vegetation change, SOC estimates, and GPS RTK estimates of marsh platform elevation to estimate that loss depths were 8.8 ± 1.3 cm and 48.9 ± 2.3 at the interior and edge, respectively. The change analysis estimated 12 835 ± 1,018 ha (CI 95%), 6,146 ± 823 ha (CI 95%) edge and interior change, respectively. Interior loss represented approximately 1/2 of the total loss but only 15.9% of the total emissions due to the low depth of loss. These findings demonstrate that location-specific loss processes significantly affect carbon emission estimates, suggesting that remote sensing monitoring systems should differentiate loss types rather than using uniform emission factors. This approach provides a framework for coastal carbon accounting and identifies interior salt marsh restoration as a priority for reducing future emissions.