Citation:

Janousek, C., J. Krause, J. Drexler, K. Buffington, K. Poppe, E. Peck, F. Adame, E. Watson, J. Holmquist, S. Bridgham, S. Jones, M. Ward, C. Brown, L. Schile-Beers, M. Costa, H. Diefenderfer, A. Borde, L. Sheehan, J. Rybczyk, C. Prentice, A. Gray, A. Hinojosa-Corona, A. Ruiz-Fernandez, J. Sanchez-Cabeza, K. Kohfeld, P. Ezcurra, J. Ochoa-Gomez, K. Thorne, M. Pellatt, A. Ricart, A. Nahlik, L. Brophy, R. Ambrose, M. Lutz, C. Cornu, S. Crooks, L. Windham-Myers, M. Hessing-Lewis, F. Short, S. Chastain, T. Williams, T. Douglas, E. Fard, L. Brown, AND M. Goman. Blue Carbon Stocks Along the Pacific Coast of North America Are Mainly Driven by Local Rather Than Regional Factors. Global Biogeochemical Cycles. American Geophysical Union, Washington, DC, 39(3):e2024GB008239, (2025). https://doi.org/10.1029/2024GB008239

Impact/Purpose:

Coastal blue carbon ecosystems such as seagrass meadows, marshes, mangroves, and other tidal wetlands efficiently accumulate and store organic carbon in their sediments. For the west coast of North America, we investigated whether the amount of carbon stored in the sediment (carbon stock) differed by ecosystem type, and whether differences were linked to local-scale factors such as elevation and plant type or regional-scale factors such as latitude and average climate conditions. We found the highest sediment carbon stocks in mangroves in Mexico and tidal swamps in the Pacific Northwest, both ecosystems dominated by woody vegetation. Unvegetated tideflats had stocks at least as high as seagrass meadows, while marshes were intermediate among all ecosystems. Overall, differences in stocks were more related to factors like a site’s elevation or the identity of the wetland sampled than broad geographic-scale differences in climate conditions. Knowing how soil carbon stocks differ across a range of coastal conditions will help those leading conservation and restoration efforts to incorporate blue carbon information into planning and decision-making.

Description:

Coastal wetlands, including seagrass meadows, 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 necessary to improve blue carbon accounting, conservation, and restoration planning. We synthesized SOC stock data from 1282 sediment cores along > 6500 km of the Pacific coast of North America, across environmental gradients and among ecosystem types. Tidal wetlands with woody vegetation (mangroves and temperate swamps) have 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, have noteworthy stocks (133 Mg ha-1). Stocks increased with tidal elevation and fine (< 63 µm) sediment content in mudflats and seagrass meadows but not in mangroves or marshes. Stocks also vary somewhat by dominant plant species within individual ecosystem types. Regionally, stocks are lower in the Sonoran Desert ecoregion of northern Mexico but otherwise show little correlation with ecoregion or latitude. Most variability in SOC stocks occurs among ecosystem types and at spatial scales no larger than individual estuaries or watersheds. These patterns may inform coastal wetland conservation and restoration priorities in regional estuaries where preserving stored carbon helps avert greenhouse gas emissions and maintains other ecosystem services. 

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