Huai Chen
College of Forestry, Northwest A&F University

Methane (CH4) greatly impacts the chemical components of the atmosphere as well as the climatic system of the earth. Sources of CH4 become highly variable for countries undergoing a heightened period of development due to both human activity and climate change. An urgent need therefore exists to budget key sources of CH4 sensitive to such changes such as wetlands (rice paddies and natural wetlands) and lakes. For this study, references in relation to CH4 emissions from rice paddies, natural wetlands, and lakes in China were first reviewed and then re-estimated based upon the review itself. Total emissions from the three CH4 sources under investigation were 11.25 Tg CH4 yr-1 (ranging from 7.983 to 15.16 Tg CH4 yr-1, approximately 2% of the global estimate of all CH4 sources) after the re-estimation was carried out. 8.105 Tg CH4 yr-1 (ranging from 5.195 to 11.36 Tg CH4 yr-1) derived from rice paddies, 2.688 Tg CH4 yr-1 (ranging from 2.463 to 3.204 Tg CH4 yr-1) derived from natural wetlands, and 0.459 Tg CH4 yr-1 (ranging from 0.325 to 0.592 Tg CH4 yr-1) derived from lakes (including reservoirs and ponds). Plentiful water and warm conditions make rice paddies in southeastern China the greatest overall source of CH4, approximately 55% of total paddy emissions (Table 5). Due to the high CH4 emission rate, rice paddies in this region emitted approximately 2.117 Tg CH4 alone. Moreover, natural wetland estimates were slightly higher than the other sources owing to the higher CH4 emissions recorded within Qinghai-Tibetan Plateau peatland, making peatland the largest source of CH4 in China overall (1.254 Tg CH4 yr-1). Available measurements prove that salt marshes are an important source of CH4 in China (0.213 Tg CH4 yr -1). This study, however, found that wetlands that are flooded seasonally are the primary source of CH4, consisting 63.4% of wetland emissions in China. Total CH4 emissions from lakes were the first to be estimated for this study. It was found that 0.325 Tg CH4 yr -1 (ranging from 0.191 to 0.458 Tg CH4 yr-1) was being emitted from the littoral zone and only 0.133 Tg CH4 yr -1 from lake surfaces. Rice paddies, natural wetlands, and lakes are not constant sources of CH4 but decreasing ones owing to anthropogenic activity and climate change factors.  A new progress-based model used in conjunction with inverse modeling will help obtain better estimates and insights with regard to CH4 emissions deriving from wetlands and lakes in China.
Key words: CH4 budget; anthropogenic activity; Qinghai-Tibetan Plateau; agriculture; climate change