Comparative study of methane emission in the reclamation-restored wetlands and natural marshes in the Hangzhou Bay coastal wetland

Wetlands play a crucial role in reducing global warming potential in response to global climate change. Large-scale reclamation and artificial restoration of coastal wetlands significantly affect the greenhouse gas methane emissions of coastal ecosystems. To comprehensively understand the difference in methane emissions between natural and reclamation-restored wetlands, the natural bare mudflat (BM – bare mudflat) in Hangzhou Bay, three types of natural vegetation wetlands (SM - Scirpus mariqueter, PA – Phragmites australis, and SA – Spartina alterniflora), and four types of reclamation-restored P. australis wetlands with different water levels (RW0 – Water level at 0 cm; RW10 – Water level at 10 cm; RW20 – Water level at 20 cm; RW30 – Water level at 30 cm) were selected to analyze the relationship between methane emissions and environmental factors through field observations and laboratory experiments. The results showed that the methane emission flux and methane production potential (MPP) of reclamation-restored wetlands were notably higher than those of natural wetlands, and the monthly dynamics in the different types of wetlands were consistent with temperature. The methane emission flux increased rapidly from April to July (summer), and reached a monotonic peak in July. Among the natural wetlands, the methane emission flux and MPP of SA were significantly higher, which was mainly driven by the soil organic carbon (SOC). In the reclamation-restored wetlands, the methane emission fluxes did not significantly differ between RW10, RW20, and RW30, but were remarkably higher than those of RW0 and natural wetlands, which was mainly driven by the water level and salinity. The differences in the MPP of the different soil layers were mainly affected by the SOC and water levels. Especially in the 0–5 cm surface soil layer of the reclamation-restored wetlands, the MPP was significantly higher, which was mainly driven by the SOC. Therefore, during the later stages of artificial reclamation-restored wetlands, appropriate water level and salinity management and other effective engineering measures should be explored to manage methane emissions during wetland restoration.