Estimating the Potential Greenhouse Gas Emission from Degraded Seagrass Meadows: A Case Study from Thailand's Seagrass Ecosystems

The seagrass meadows are critical for organic carbon storage and play a significant role in mitigating climate change. However, the ongoing degradation of the 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 Andaman Sea, Thailand. The average carbon storage within the surface sediment (top 10 cm) varies across seagrass conditions, with the highest carbon storage in heavy degraded (365.2 ± 206 g C m^-2), followed by bare sand (289.5 ± 236 g C m^-2) and healthy seagrass (86.47 ± 5.8 g C m^-2). Furthermore, degraded seagrass and bare sand exhibited heterotrophic ecosystem functions with an average 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 NCP 1.30 ± 0.508 mmol C m⁻² d⁻¹. The average total carbon sink varied among seagrass conditions, with the highest in degraded seagrass (4328 ± 2395 CO₂-eq m⁻² d⁻¹), compared to bare sand (3981 ± 4120 CO₂-eq m⁻² d⁻¹) and healthy seagrass (1630 ± 0 CO₂-eq m⁻² d⁻¹). The study also revealed that CH₄ emissions dominated GHG fluxes in all seagrass conditions, with the highest mean CH₄ fluxes recorded in degraded seagrass (1.16 ± 0.51 µmol m⁻² h⁻¹), followed by bare sand (1.02 ± 0.41 µmol m⁻² h⁻¹) and healthy seagrass (0.48 ± 0.07 µmol m⁻² h⁻¹). On the other hand, the CO₂ emissions remained consistently low in both seagrass meadows (healthy and degraded) and bare sand areas. These findings are important to indicate and provide the baseline of GHG emissions for healthy and degraded tropical seagrass meadows.

Keywords: Blue carbon, Climate Change, Emission, Greenhouse gas, Seagrass meadows