Evaluation of CH4MOD<sub>wetland</sub> and Terrestrial Ecosystem Model (TEM) used to estimate global CH<sub>4</sub> emissions from natural wetlands

Abstract

Abstract. Wetlands are the largest and most uncertain natural sources of atmospheric methane (CH4). Several process-based models have been developed to quantify the magnitude and estimate spatial and temporal variations in CH4 emissions from global wetlands. Reliable models are required to estimate global wetland CH4 emissions. This study aimed to test two process-based models, CH4MODwetland and Terrestrial Ecosystem Model (TEM), against the CH4 flux measurements of marsh, swamp, peatland and coastal wetland sites across the world; specifically, model accuracy and generality were evaluated for different wetland types and in different continents, and then the global CH4 emissions from 2000 to 2010 were estimated. Both models showed similar high correlations with the observed seasonal/annual total CH4 emissions, and the regression of the observed versus computed total seasonal/annual CH4 emissions resulted in R2 values of 0.81 and 0.68 for CH4MODwetland and TEM, respectively. The CH4MODwetland produced accurate predictions for marshes, peatlands, swamps and coastal wetlands, with model efficiency (EF) values of 0.22, 0.52, 0.13 and 0.72, respectively. TEM produced good predictions for peatlands and swamps, with EF values of 0.69 and 0.74, respectively, but it could not accurately simulate marshes and coastal wetlands (EF <0). There was a good correlation between the simulated CH4 fluxes and the observed values on most continents. However, CH4MODwetland showed no correlation with the observed values in South America and Africa. TEM showed no correlation with the observations in Europe. The global CH4 emissions for the period 2000–2010 were estimated to be 105.31 ± 2.72 Tg yr−1 by CH4MODwetland and 134.31 ± 0.84 Tg yr−1 by TEM. Both models simulated a similar spatial distribution of CH4 emissions globally and on different continents. Marshes contribute 36 %–39 % of global CH4 emissions. Lakes/rivers and swamps are the second and third greatest contributors, respectively. Other wetland types account for only approximately 20 % of global emissions. Based on the model applicability, if we use the more accurate model, i.e., the one that performs best as evidenced by a higher model efficiency and a lower model bias, to estimate each continent and wetland type, we obtain a new assessment of 116.99–124.74 Tg yr−1 for the global CH4 emissions for the period 2000–2010. Our results imply that performance at a global scale may conceal model uncertainty. Efforts should be made to improve model accuracy for different wetland types and regions, particularly hotspot regions, to reduce the uncertainty in global assessments.

Methane Emissions from Wetlands in China and Their Climate Feedbacks in the 21st Century

“…As the model combination was fully parametrized and validated at multiple inland and coastal wetland sites across China and around the world, we followed the parametrization in previous studies. , The calibrated parameters are mainly related to the different capabilities of CH 4 production, oxidation, and transportation between herbaceous and woody plants, as well as the influence of salinity in coastal wetlands. The DISCover database was used to assign the woody or herbaceous plants.…”

Methane Anaerobic Oxidation Potential and Microbial Community Response to Sulfate Input in Coastal Wetlands of the Yellow River Delta

“…Although the total surface area of natural wetlands is only a small part of the land area, they are the largest source of global CH 4 emissions. Global wetland CH 4 emissions are approximately 116.99-124.74 Tg•yr −1 , which has a huge impact on global climate change according to the latest estimation models [7]. CH 4 produced in nature will reduce its emissions due to the oxidation-reduction reaction between microorganisms and various electron receptors under aerobic or anaerobic conditions before being discharged into the atmosphere [8].…”

“…Previous studies have shown that the AOM process involves several different electron acceptors, including sulfate (SO 4 2− ), nitrate/nitrite (NO 3 − /NO 2 − ), and metal ions (Mn 4+ , Fe 3+ ), called sulfate-based methane anaerobic oxidation (SAMO), nitrate-based methane anaerobic oxidation (n-DAMO), metal-ionic methane anaerobic oxidation (Metal-AOM), and direct interspecies electron transfer (DIET), respectively. Current domestic and international studies on AOM processes in natural wetlands have mostly focused on peatlands [18][19][20], mangrove wetlands [21], rice fields [7,[22][23][24], Yangtze River crossing wetlands [25,26], and the Minjiang River estuary wetlands [27,28]. In contrast, the Yellow River Delta is the youngest and most complex coastal wetland in the warm temperate zone of China.…”