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<p>The Association of Southeast Asian Nations (ASEAN) region contains approximately one-third of the world’s mangrove forests and extensive seagrass meadows, making it a globally significant reservoir of coastal “blue carbon.” Yet these ecosystems face increasing pressure from land-use change and climate-driven stressors, raising concerns about the potential release of long-stored soil and sediment carbon. This study provides the first harmonized, region-wide assessment of blue carbon in soil stocks and fluxes across all 10 coastal ASEAN member states (Laos, as a landlocked country, does not support mangrove or seagrass ecosystems and is excluded from quantitative accounting) using a dual-framework approach. We integrate a probabilistic Net Ecosystem Carbon Balance (NECB) model—incorporating geomorphology- and salinity-stratified methane (CH₄) offsets—with a National Inventory method aligned with IPCC Tier 1 guidelines. Mangrove and seagrass ecosystems in ASEAN cover approximately 7.26&#xa0;million ha, storing an estimated 853 Mt C in coastal soils. The Inventory assessment indicates a Net Climate Benefit of 44.6 Mt CO₂e yr⁻¹, derived from gross sequestration minus emissions from anthropogenic disturbance. In contrast, the NECB model yields a more conservative median sink of 5.5 Tg C yr⁻¹ (95% CI: 3.8–7.1 Tg C yr⁻¹), reflecting substantial methane emissions in deltaic systems. Oceanic/Fringing systems exhibit low methane penalties (&lt; 15%), whereas Deltaic/Estuarine systems show high offsets (50–80%), often negating much of the carbon burial. These findings reveal strong but spatially heterogeneous climate-mitigation potential across the region. By providing country-specific carbon balance sheets and quantifying the divergence between policy-based and biophysical estimates, this study offers a scientific foundation for strengthening Nationally Determined Contributions (NDCs) and guiding high-integrity blue carbon investment in ASEAN.</p>

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Mangrove and Seagrass Blue Carbon Stocks and Fluxes Across ASEAN: A Dual-Framework Assessment of Soil Carbon Dynamics and Policy Implications

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月15日

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  • Tri Ngearnlek,
  • Wei-Ta Fang

摘要

The Association of Southeast Asian Nations (ASEAN) region contains approximately one-third of the world’s mangrove forests and extensive seagrass meadows, making it a globally significant reservoir of coastal “blue carbon.” Yet these ecosystems face increasing pressure from land-use change and climate-driven stressors, raising concerns about the potential release of long-stored soil and sediment carbon. This study provides the first harmonized, region-wide assessment of blue carbon in soil stocks and fluxes across all 10 coastal ASEAN member states (Laos, as a landlocked country, does not support mangrove or seagrass ecosystems and is excluded from quantitative accounting) using a dual-framework approach. We integrate a probabilistic Net Ecosystem Carbon Balance (NECB) model—incorporating geomorphology- and salinity-stratified methane (CH₄) offsets—with a National Inventory method aligned with IPCC Tier 1 guidelines. Mangrove and seagrass ecosystems in ASEAN cover approximately 7.26 million ha, storing an estimated 853 Mt C in coastal soils. The Inventory assessment indicates a Net Climate Benefit of 44.6 Mt CO₂e yr⁻¹, derived from gross sequestration minus emissions from anthropogenic disturbance. In contrast, the NECB model yields a more conservative median sink of 5.5 Tg C yr⁻¹ (95% CI: 3.8–7.1 Tg C yr⁻¹), reflecting substantial methane emissions in deltaic systems. Oceanic/Fringing systems exhibit low methane penalties (< 15%), whereas Deltaic/Estuarine systems show high offsets (50–80%), often negating much of the carbon burial. These findings reveal strong but spatially heterogeneous climate-mitigation potential across the region. By providing country-specific carbon balance sheets and quantifying the divergence between policy-based and biophysical estimates, this study offers a scientific foundation for strengthening Nationally Determined Contributions (NDCs) and guiding high-integrity blue carbon investment in ASEAN.