Introduction to special section on Synthesis of Recent Terrestrial Methane Emission Studies

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, G00A02, doi:10.1029/2008JG000749, 2008 Introduction to special section on Synthesis of Recent Terrestrial Methane Emission Studies Q. Zhuang 1 and W. S. Reeburgh 2 Received 7 April 2008; revised 20 May 2008; accepted 2 June 2008; published 10 July 2008. Citation: Zhuang, Q., and W. S. Reeburgh (2008), Introduction to special section on Synthesis of Recent Terrestrial Methane Emission Studies, J. Geophys. Res., 113, G00A02, doi:10.1029/2008JG000749. 1. Introduction [ 1 ] Methane (CH 4 ) is a potent greenhouse gas, second in importance to carbon dioxide (CO 2 ) [Intergovernmental Panel on Climate Change (IPCC), 2007]. Biogenic sources account for 70% of global emissions – wetlands, rice paddies, livestock, landfills, forests, oceans and termites. Natural wetlands and rice paddies are the largest CH 4 sources, and account for 20– 60% of the total natural and anthropogenic emissions. While the existing estimates of emissions from these known sources still have great uncer- tainty, recent studies reveal a number of new sources contributing to the atmospheric CH 4 burden. For example, the bubble emissions due to thawing lake sediments from north Siberia alone were estimated to release 3.8 Tg CH 4 yr 1 [Walter et al., 2006]. Permafrost thawing also increases the CH 4 emissions from wet soils [e.g., Wickland et al., 2006]. To adequately quantify total CH 4 emissions and reconcile atmospheric CH 4 concentrations with the earth surface emissions, the mechanisms of and controls on these CH 4 sources need to be further understood. [ 2 ] The last synthesis effort of studying CH 4 emissions focused on data compilation and data analysis at site-levels [Ojima et al., 2000]. Our current synthesis continues the data compilation effort and incorporates new more sophis- ticated biogeochemistry and atmosphere transport models in quantifying regional and global CH 4 emissions. Specif- ically, recent CH 4 studies have focused on the following areas: (1) Understanding the processes and mechanisms of CH 4 production and consumption in different environments through field observations, environmental manipulations, and using isotopic analyses; (2) Measuring the emission fluxes from natural sources and observing atmospheric CH 4 concentrations and profiles using flask measurements and satellite instruments [e.g., Dlugokencky et al., 2001; Bergamaschi et al., 2007]; and (3) Refining the estimates of CH 4 emissions and their effect on the atmosphere with process-based biogeochemistry models and atmospheric transport and inversion models [e.g., Zhuang et al., 2004, 2006, 2007; Walter et al., 2001; Chen and Prinn, 2005, Department of Earth and Atmospheric Sciences and Department of Agronomy, Purdue University, West Lafayette, Indiana, USA. Department of Earth System Science, University of California, Irvine, California, USA. Copyright 2008 by the American Geophysical Union. 0148-0227/08/2008JG000749 2006]. This section resulted from a project supported by the National Center for Ecological Analysis and Synthesis (NCEAS) and presents results from new field studies, new instruments, and new approaches to the above areas. The section specifically addresses the issues of methane emis- sions in both natural and managed ecosystems, which are undergoing anthropogenic and natural perturbations of water table, permafrost thaw, volcanic deposition, sulfur deposition, and manure/fertilizer amendment. To better quantify the regional and global CH 4 emissions, these effects and controls need to be considered in biogeochemistry models. The continuous and long-term observations of CH 4 fluxes impacted by those factors and processes should still be a priority for the CH 4 research community. 2. Contents of This Special Section [ 3 ] Wetland constitutes the largest single source of CH 4 emissions with emissions ranging from 100 to 231 Tg CH 4 yr 1 [IPCC, 2007]. The climate variability and change modify the wetland distribution, soil wetness, water table depth, and soil temperature, affecting CH 4 emissions. The first two papers in this section involve field manipulations of soil temperature and water table depth in northern peat- lands [Turetsky et al., 2008; White et al., 2008]. The Turetsky et al. study involved an ecosystem-scale manipu- lation of water table and soil surface temperature in a moderate rich fen located in interior Alaska. Methanogen populations were found to respond rapidly to changes in soil moisture and temperature changes. White et al. studied the effects of water table, soil warming, and wetland type on production, oxidation, and emission of CH 4 in northern peatlands. Acetate fermentation was found to be the princi- pal methanogenic pathway in these systems. The White et al. paper does not appear in the print version of this section, but will be electronically linked to the section in the online version. [ 4 ] Arctic wetlands account for about half of the world’s wetland area and store about one-third of earth’s soil carbon [Gorham, 1995]. Thawing permafrost and fire disturbances change the conditions and transitions of wetlands and uplands, resulting in complex CH 4 emission patterns. In addition, the presence of permafrost promotes the formation and persistence of lakes in the Arctic [Smith et al., 2007], and the CH 4 emissions from these lakes have not been well quantified. Using data from Siberia and Alaska, a recent study estimated that arctic lakes emit 15 – 35 Tg of G00A02 1 of 3