PNNL

Abstract

Coastal wetlands, including seagrass meadows, emergent marshes, mangroves, and temperate tidal swamps, can efficiently sequester and store large quantities of sediment organic carbon (SOC). However, SOC stocks may vary by ecosystem type and along environmental or climate gradients at different scales. Quantifying such variability is needed to improve blue carbon accounting, conservation effectiveness, and restoration planning. We analyzed SOC stocks in 1284 sediment cores along > 6500 km of the Pacific coast of North America that included large environmental gradients and multiple ecosystem types. Tidal wetlands with woody vegetation (mangroves and swamps) had the highest median stocks to 1 m depth (329 and 349 Mg ha-1, respectively), about 50% higher than marshes (230 Mg ha-1), and about 500% higher than seagrass (66 Mg ha-1). Unvegetated tideflats, though not often considered a blue carbon ecosystem, had noteworthy stocks (133 Mg ha-1). Stocks increased with tidal elevation and with fine (