Coastal wetland ecosystems are increasingly exposed to saltwater intrusion. Resilience to saltwater intrusion among coastal wetlands depends largely on how biogeochemical changes alter net ecosystem carbon (C) balance. Coastal forests and marshes are characterized by high net ecosystem productivity, making these ecosystems a global conservation priority for C storage. These ecosystems store up to 50× more C than terrestrial forests per unit area, yet account for less than 1% of earth’s land area. Manipulative experiments among multiple coastal wetlands in North America that test ecosystem responses to elevated salinity are finding divergent effects on above and belowground C storage, soil biogeochemistry, and microbial processes. The objective of this oral session is to bring together research from across multiple coastal wetland ecosystems to characterize the biogeochemical attributes of saltwater intrusion that most contribute to changes in C fluxes (storage and losses) from multiple ecosystem compartments (e.g., soils, aquatic biofilms, vascular plants). We will specifically address how changes in C storage and losses are driven by variation in saltwater intrusion, sea level rise, and associated biogeochemical changes. Understanding how the magnitude and variance in biogeochemical attributes of saltwater influence ecosystem-level C processes is critical given imminent sea level rise.