Spatial variations in methane emissions from natural wetlands in China

Abstract

Natural wetlands are thought to be one of the largest natural sources of atmospheric methane concentrations. Although numerous studies referred to the rate of methane fluxes in different geophysical regions, only a few had estimates of the overall geographical methane emissions in China. This study estimated the spatial variations of annual methane emissions with the pixel size of 1 km 9 1 km from natural wetlands, excluding water surface, in China. The natural wetland areas were extracted from the database of the 2000 land covers, and geophysical divisions were used to represent different climate conditions. Methane emission in every geophysical region was calculated based on methane release factors obtained from an extensive overview of published literature and the data of elevation and vegetation proportion. The estimated annual methane emissions ranged from 0 to 5,702.8 kg per pixel within the area of 1 km 2 , and the spatial variation in methane emissions was strongly correlated with proportion of wetlands in the area. The total methane emission from natural wetland in China ranged from 3.48 to 7.16 Tg (terrogram, unit of weight) per year, with the mean value of 4.94 Tg per year, based on the area 133,000 km 2 of natural wetlands. Specifically, the wetland in Northeast China had the highest contribution in China (39 %). Inner Mongolia and Qinghai-Tibet highland represented for about 25 and 21 %, respectively. The other 15 % of the measured methane was released in Northwest, North, Central, and South China.

Modeling CH4 Emissions from Natural Wetlands on the Tibetan Plateau over the Past 60 Years: Influence of Climate Change and Wetland Loss

“…Jin [60] estimated an area of 13.4 M ha based on the soil wet extent [76]. Our area estimate was based on remote sensing data [15] and was consistent with both Xu and Tian's study [62] and Zhang and Jiang's study [74].…”

“…The variation may have been due to the estimation method. Most previous studies used the survey wetland area (e.g., [18,19,74]). Jin [60] estimated an area of 13.4 M ha based on the soil wet extent [76].…”

CH4 exchanges of the natural ecosystems in China during the past three decades: The role of wetland extent and its dynamics

“…The simulation with Niu2012 suggested that China's wetlands emitted 3.86 ± 1.09 Tg CH 4 yr −1 in the 2000s, which falls within the reported range of previous studies (Table ). It was found that NE China plays a dominant role of 49% of CH 4 emissions, while the TP contributes only 25%, consistent with most simulations using various wetland maps in the present study (except GLWD) and other previous studies [ Ding et al, ; Xu and Tian , ; Zhang and Jiang , ]. In contrast, a previous bookkeeping survey [ Chen et al, ] estimated that the TP plays a dominant role of 45.6% of China's CH 4 emissions with 1.25 Tg CH 4 yr −1 , while NE China contributes only 25.3% with 0.59 Tg CH 4 yr −1 .…”

“…Building on these measurements, several groups conducted bookkeeping estimations of the CH 4 budget of China's natural ecosystems. However, a huge range has been reported for the magnitude of wetland CH 4 emissions, i.e., 1.30 to 5.71 Tg CH 4 yr −1 [ Wang et al, ; Ding et al, ; Cai , ; Chen et al , ; Zhang and Jiang , ]. For CH 4 uptake, Cai [] estimated that grasslands and forests take up −1.73 and −0.60 Tg CH 4 yr −1 , respectively, while Wang et al 's [] estimates of −0.65 and −0.68 Tg CH 4 yr −1 , respectively, were much less, also indicating significant uncertainty.…”

Methane Emission from Pineapple Cultivation on a Tropical Peatland at Saratok, Malaysia

“…Methane is released into the atmosphere through: molecular diffusion (peat pore spaces), ebullition (a process where bubbles in gas are formed from a dissolved state in water and channel their way to surface to the atmosphere) at the water table interface, and vascular plants with aerenchymous porous tissues which transport gases through plant roots into the atmosphere (Dinsmore, Skiba, Billett, & Rees, 2009;Watanabe, Purwanto, Ando, Kakuda, & Jong, 2009;Farmer, Matthews, J. Smith, P. Smith, & Singh, 2011;Zhang & Jiang, 2014). Methane can also be emitted through non-microbial CH 4 production from soil organic matter under favorable conditions such as high temperature, UV radiation, and reactive oxygen species (B. Wang, Hou, Liu, & Z. Wang, 2013).…”