Portland State University PDXScholar Physics Faculty Publications and Presentations Physics 2-3-2009 Global Methane Emissions From Wetlands, Rice Paddies, and Lakes Qianlai Zhuang Purdue University John M. Melack University of California, Santa Barbara Sergey Zimov North-East Science Station, Cherski Katey Marion Walter University of Alaska, Fairbanks Christopher Lee Butenhoff Portland State University See next page for additional authors Follow this and additional works at: https://pdxscholar.library.pdx.edu/phy_fac Part of the Physics Commons Let us know how access to this document benefits ou.y Citation Details Zhuang, Q., J. M. Melack, S. Zimov, K. M. Walter, C. L. Butenhoff, and M. A. K. Khalil (2009), Global Methan Emissions From Wetlands, Rice Paddies, and Lakes, Eos Trans. AGU, 90(5), 37, doi:10.1029/ 2009EO050001. This Article is brought to you for free and open access. It has been accepted for inclusion in Physics Faculty Publications and Presentations by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. Authors Qianlai Zhuang, John M. Melack, Sergey Zimov, Katey Marion Walter, Christopher Lee Butenhoff, and M. A. K. Khalil This article is available at PDXScholar: https://pdxscholar.library.pdx.edu/phy_fac/5 Eos, Vol. 90, No. 5, 3 February 2009 VOLUME 90 NUMBER 5 3 FEBRUARY 2009 EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION PAGES 37–44 accurately quantify global methane emis- Global Methane Emissions From sions with these models [e.g., Dlugokencky et al., 2003]. Instrumentation for monitoring methane fluxes and concentrations should Wetlands, Rice Paddies, and Lakes be a priority. Controls on, and processes of, biogenic PAGES 37–38 surveys of vegetation and wetland types methane emissions are not well understood. should be continued as a means to further We suggest the following research priorities: The current concentration of atmospheric develop data on global lake and wetland dis- (1) elucidate the role of permafrost degrada- methane is 1774±1.8 parts per billion, and tribution and extent. tion in methane emissions; (2) further exam- it accounts for 18% of total greenhouse gas Methane flux measurements, which are ine the effects of the atmospheric deposition radiative forcing [Forster et al., 2007]. Atmo- lacking from a variety of ecosystems, as of nitrogen and sulfate on methane produc- spheric methane is 22 times more effec- noted below, are needed to improve emis- tion and consumption; (3) investigate the tive, on a per- unit- mass basis, than carbon sion estimates and the accuracy of biogeo- microbial community structure and distri- dioxide in absorbing long- wave radiation chemical models and atmospheric transport bution of those microbes responsible for on a 100- year time horizon, and it plays an inversion models [e.g., Zhuang and Ree- methane production and consumption; and important role in atmospheric ozone chem- burgh, 2008]. Data acquisition of in situ and (4) investigate the role of different vegetation istry (e.g., in the presence of nitrous oxides, satellite atmospheric concentrations and types in affecting the exchanges of methane tropospheric methane oxidation will lead their profiles should be maintained to more between wetlands and the atmosphere. to the formation of ozone). Wetlands are a large source of atmospheric methane, Arc- tic lakes have recently been recognized as a major source [e.g., Walter et al., 2006], and anthropogenic activities—such as rice agriculture—also make a considerable contribution. However, the quantification of methane emissions still has large uncertainties. In this article, we identify some causes for the uncertainty; illustrate the challenges of reduc- ing the uncertainty; and highlight opportu- nities for research from the global perspec- tive and also from the perspective of three principal sources of methane: the Arctic, the Amazon basin, and rice paddies. Global Perspective Accurately mapping the global distribu- tion and dynamics of lakes and wetland types is challenging. Currently, estimates of global wetland areas from ground and sat- ellite instruments vary from 1 to 12 million square kilometers. Some existing estimates do not account for small lakes, resulting in underestimates of lake areas by a factor of Fig. 1. (a) In the Siberian north, the polygonal net of ice wedges is ubiquitous. In Pleistocene- aged more than 2 [e.g., Walter et al., 2007]. Fur- (1.8 million to 10,000 years before present) yedoma (an organic- rich loess with about 2% car- ther, global characterizations of wetlands bon by mass and with ice content of 50–90% by volume [see Walter et al., 2006]), the tops of and lakes are too coarse to represent signifi- ice wedges are usually situated directly beneath the active layer, so the active layer growth will cant differences in methane emission rates, lead to ice wedge melting and the appearance of the polygonal net of deep channels. Ponding and data on seasonal and interannual wet- of water in these channels causes deep thaw of permafrost, leading to the formation of methane- land inundation derived from satellite sen- producing thermokarst lakes. (b) In the Arctic lakes, open holes in early winter lake ice due sors need to be further developed. Satel- to seeps of methane bubbling are visible from airplanes and in TerraSAR- X satellite imagery. lite data in combination with ground- level (c) Floodable area (black) for the Amazon basin below the 500- meter contour, derived from Japanese Earth Resources Satellite 1 (JERS 1) synthetic aperture radar mosaics. Floodable areas are not all inundated simultaneously and may include areas not floodable that are not visible at BY Q. ZHUANG , J. M. MELACK , S. ZI M OV , K. M. the scale of the image. These floodable areas are important to methane emissions in the Amazon WALTER , C. L. BUTENHOFF , AND M. A. K. KHALIL basin [from Melack and Hess, 2009]. Eos, Vol. 90, No. 5, 3 February 2009 Challenges and Opportunities in the Arctic have large uncertainties, and many tropi- 40 milligrams of methane per hour per cal systems lack measurements of emis- square meter. In part, this range reflects the The carbon- rich Arctic soils and lakes sions. For the Amazon basin, Melack et al. different ecosystems under which rice is are underlain with either continuous or dis- [2004] combined passive and active micro- grown (e.g., irrigated, rain- fed, deepwater, continuous permafrost, which is a large res- wave remote sensing of the temporally vary- and so forth), and water management (e.g., ervoir of carbon containing 700– 950 pen- ing extent of inundation and vegetation with continuous versus intermittently flooded), as tagrams of carbon in its top 1– 25 meters field measurements to estimate that meth- longer inundation periods produce higher (Figure 1a) [Zimov et al., 2006]. Currently, ane emissions are 22 teragrams per year. fluxes. It also reflects differences in input methane is released from both thaw lakes Further improvements in these estimates will organic matter, soil type, and crop phenol- and soils (Figure 1b) [Walter et al., 2006]. require field campaigns in undersampled ogy, among other variables. In addition, An increase in permafrost degradation environments including extensive savannas, SAFs from the same field in side- by- side and the shoreline erosion of existing lakes high- elevation wetlands, narrow riparian plots are observed to vary over the emis- along with the formation of new permafrost- zones along streams, and small rivers. sion season by a factor of 2 to 4, evidently thawing lakes is expected, and these Another important area in northern owing to field inhomogeneities. Sampling of changes could increase methane emissions South America is the upper Negro River methane flux in paddies using the standard from these lakes by several orders of magni- basin, because it includes an approximately method of three replicates can produce tude [Walter et al., 2007]. 80,000- square- kilometer area with season- SAFs that vary by 40–60% [Khalil and Buten- As permafrost thawing develops, ally flooded emergent grasses and sedges, hoff, 2008]. increased linear erosion associated with areas with shrubs or palms, and flooded Paddy emissions are sensitive to farm- thaw lake expansion and migration could forests— all of which are methanogenic ing practices that can change in response lead to stream channel erosion and lake habitats. Year- round measurements of dif- to economic and political pressures [Khalil drainage. For instance, in the discontinuous fusive and bubble emissions of methane in and Rasmussen, 1993]. In China, conserva- permafrost zone of West Siberia, this process these organic- rich environments, and the tion has reduced the amount of water used has already begun to lead to a decrease in influences of habitat, water depth, variation for paddy irrigation, while bans on biomass lake area. In West Siberia’s far north, deep, in hydrostatic pressure, dissolved oxygen, burning have returned otherwise burnt crop cold ice wedges comprise more than 80% and temperature, have recently been deter- residue to the field. Manure use has declined of permafrost volume and are often covered mined by Belger [2007]. Similar measure- in favor of inorganic fertilizers. Quantifying with only 0.5 meters of soil. Minor increases ments are needed in the Pantanal in central these changes is vital for determining accu- in summer soil active layer thickness will ini- South America, the Llanos de Moxos, largely rate inventories, but it remains challenging. tiate the thaw of ice wedges in permafrost. in eastern Bolivia, the Roraima savannas Many farming practices are not officially Once the melting process begins, the dis- of northern Brazil, and the swamps of low- recorded and are available only through per- appearance of these large ice bodies will land Peru, although many of the wetlands sonal communication. Interviews with farm- result in dramatic changes in land surface in these areas are situated in interfluvial ers have yielded important information, but driven by active thaw erosion, thawing tens regions, making access very difficult.