Methane Emissions from China’s Natural Wetlands: Measurements, Temporal Variations and Influencing Factors

Abstract

Natural wetlands received increased attention for their ecosystem services and high methane (CH4) emissions. 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. Effects of human activities on wetlands in China were studied at 16 sites across the country, i.e., 6 peatlands, 3 coastal wetlands, 5 lakes and 2 reservoirs. The 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 year−1 (1 Tg = 1012 g), which accounted for 7.3% (145 Tg CH4 year−1) of the global emissions from wetlands and 171% (6.147 Tg CH4 year−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.