Ninth International Conference on Permafrost ... - IARC Research

Carbon Dynamics of the Permafrost Regime, North Slope of AlaskaYongwon Kim<strong>International</strong> Arctic Research Center, University of Alaska Fairbanks, USAKeiji KushidaInstitute of Low Temperature Science, Hokkaido University, JapanMasato ShibuyaGraduate School of Agriculture, Hokkaido University, JapanHiroshi EnomotoDepartment of Civil Engineering, Kitami Institute of Technology, JapanIntroductionThe terrestrial ecosystems, including tundra and borealforest regions of the Arctic, cover a little less than 18% ofEarth’s land surface, but they contain more than 40% of allcarbon present in the terrestrial biomes (Kasischke 2000),demonstrating about one-third of the carbon sequesteredin Pan-Arctic tundra and boreal forests. High-latitudeecosystems are particularly vulnerable to climate changedue to the large carbon pools in northern latitude soils. Thesoil carbon pool estimated for the combined tundra-borealforest ranges from 21% (Raich & Schlesinger 1992) to 30%(Post et al. 1982) of the global carbon pool.Recently, Zimov et al. (2006) addressed carbonsequestration from thawing permafrost in the Arctic. Thesoils of the permafrost region of North America contain 213Gt of organic carbon—approximately 61% of the carbon inall soils of North America. The soils of the permafrost regionof North America are currently a net sink of approximately11 MtC/yr. The soils of the permafrost region of NorthAmerica have been slowly accumulating carbon for the last5–8 thousand years. More recently, increased human activityin the region has resulted in permafrost degradation and atleast localized loss of soil carbon.Considering the wide distribution of permafrost in Alaska’sNorth Slope, the observations of the fluxes of soil CO 2(e.g.,soil respiration) and CH 4, and of the soil carbon/nitrogencontents are extremely significant for a better understandingFigure 1. Microbial respiration in subalpine tundra.of soil organic carbon turnover time with the remarkableArctic climate change (ACIA 2004) on the permafrostregime of Alaska’s tundra ecosystem.Material and MethodDescription of study areaThe observation sites are shown in Kim & Tanaka (2001),which are coastal tundra (CT) near Deadhorse, uplandtundra (UT) north of Toolik Lake station, and subalpinetundra (SaT) north of the Brooks Range along the Trans-Alaska Pipeline during the growing season of 2000/2001.Flux measurements of CO 2and CH 4using chambers, soildensity, soil water content, and dominant vegetation typeand content of soil organic carbon/nitrogen in each site wereexamined. The chambers used were of two types: one madeof transparent material and the other, of nontransparentmaterial. The former is called light and the latter is darkchamber in this study.Results and DiscussionSoil respiration and CH 4fl uxSoil respiration consists of heterotrophic (microbial) androot respiration. The average fluxes of CO 2and CH 4rangedfrom -0.058±0.012 (±SE; standard error) in coastal tundrato 0.41±0.08 gCO 2-C/m 2 /d in upland tundra, and from-1.50±0.33 in subalpine tundra to 1.42±0.23 mg/CH 4-C/m 2 /din coastal tundra, respectively. The negative values of CO 2and CH 4fluxes indicate photosynthesis and atmospheric CH 4oxidation. In terms of soil carbon during the growing season,accumulated soil respiration was equivalent to 16±12 and35±24 gC/m 2 for light and dark chambers, respectively. Itis difficult to estimate seasonal carbon emission for CH 4flux due to CH 4oxidation. Gilblin et al. (1991) reportedthat the soil respiration ranged from 6 to 20 gC/m 2 in arctictundra soils during the growing season, and Oechel et al.(1997) measured soil respiration of 4.4 to 44 gC/m 2 in arctictussock and wet sedge tundra of Alaska, which is similar toour data during 2000/2001. Figure 1 shows a snapshot of theheterotrophic respiration by soil microbe of soil respirationin alpine tundra using Landsat ETM+ image analysis as wellas in situ soil respiration data.Biomass, soil carbon, and nitrogenThe average content of biomass, carbon and nitrogen,137