Estimating potential greenhouse gas emissions from degraded seagrass meadows: A case study from Thailand's seagrass ecosystems

Abstract

Seagrass meadows are critical organic carbon sinks and play a significant role in mitigating climate change. However, the ongoing degradation of seagrass meadows in Thailand reduces their ability to sequester carbon effectively, potentially contributing to greenhouse gas (GHG) emissions. This study examines variations in carbon storage, carbon metabolism, and GHG emissions across degraded, healthy seagrass and bare sand areas along the Andaman Sea coast of Thailand. The average carbon storage within the surface sediment (top 10 cm) varies across seagrass categories, with the highest carbon storage in heavily degraded areas (365.2 ± 206 g C m⁻²), followed by bare sand (289.5 ± 236 g C m⁻²) and healthy seagrass areas (86.47 ± 5.8 g C m⁻²). Furthermore, degraded seagrass and bare sand exhibited heterotrophic ecosystem functions with an average Net Community Production (NCP) value of 0.44 ± 0.49 and 0.13 ± 0.79 mmol C m⁻² d⁻¹, respectively. Conversely, healthy seagrass maintained autotrophic ecosystem functions with an NCP of 1.30 ± 0.508 mmol C m⁻² d⁻¹. The average total carbon sequestration varied among seagrass categories, with the highest sequestration in degraded seagrass areas (4328 ± 2395 CO₂-eq m⁻² d⁻¹), compared to bare sand (3981 ± 4120 CO₂-eq m⁻² d⁻¹) and healthy seagrass areas (1630 ± 0 CO₂-eq m⁻² d⁻¹). The study also revealed that methane (CH₄) emissions dominated GHG emissions in all seagrass categories, with the highest mean CH₄ emissions recorded in degraded seagrass meadows (1.16 ± 0.51 μmol m⁻² h⁻¹), followed by bare sand areas (1.02 ± 0.41 μmol m⁻² h⁻¹) and healthy seagrass meadows (0.48 ± 0.07 μmol m⁻² h⁻¹). On the other hand, carbon dioxide (CO₂) and dinitrogen (N₂) emissions remained consistently low in both healthy and degraded seagrass meadows and in bare sand areas. These findings are important indicators and provide the baseline of GHG emissions for degraded tropical seagrass meadows.