Methane emissions from China’s natural wetlands: measurements, temporal variations and influencing factors

Background/Question/Methods

Natural wetlands received increased attention for their ecosystem services and high methane (CH₄) emissions. Natural wetland has been proposed to be the single largest CH₄ source based on recent estimates combining bottom-up and top-down fluxes, and global observations of atmospheric CH₄ concentrations in a three dimensional Atmospheric Transport and Chemical Model (ATCM) simulation. Although available reviews have analyzed the processes and factors influencing CH₄ emissions worldwide, few investigations carried out in China have been included because of the difficulty to access to those reports written in Chinese. In recent years, field measurements of CH₄ emissions from wetlands have been conducted covering different types and locations of wetlands. Considering that China is the largest global CO₂ emitter and most populous country with rapid economic development and significant changes in land use, it is required to review CH₄ emissions from wetlands in China. In this study, the area and CH₄ emission rates of wetlands in China were reviewed, and a national estimate of CH₄emissions from wetlands was carried out based on the best data available.

Results/Conclusions

In China, the total area of wetlands is about 38 million ha (M ha), accounting for about 4% of the land. Natural wetlands include peatlands (35.6%), coastal wetlands (15.4%), rivers (21.3%), lakes (21.7%) and reservoirs (6.7%). Human activities and settlement development have drastically reduced wetland areas worldwide. A recent estimate showed that 33% were lost between 1978 and 2008, and land reclamation accounted for more than 70% of the total loss in China. The available results showed that mean CH₄ emissions were 6.0 (range 1.0-15.6) mg CH₄ m^-2 h^-1 for peatlands, 1.6 (0.5-2.4) mg CH₄ m^-2 h^-1 for coastal wetlands, 3.1 (0.9-9.7) mg CH₄ m^-2 h^-1 for lakes and 0.2 (0.1-0.3) mg CH₄ m^-2 h^-1 for reservoir. The annual CH₄ emissions from natural wetlands in China was estimated to be 10.5 Tg CH₄ yr^-1 (1 Tg = 10¹² g), which accounted for 7.3% (145 Tg CH₄ yr^-1) of the global emissions from wetlands and 171% (6.147 Tg CH₄ yr^-1) of the CH₄ emission from rice paddies in China. The significant contribution of CH₄ emission from natural wetlands should be taken into account in national greenhouse gas inventory.