Ninth International Conference on Permafrost ... - IARC Research

Impact of Permafrost Degradation on Carbon and Nitrogen Stocks Related toPedogenesis and Ecosystem FunctioningFrank BaumannInstitute of Geography, University of Tuebingen, Tuebingen, GermanyJin-Sheng HeDepartment of Ecology, College of Environmental Sciences, Peking University, Beijing, ChinaPeter KühnInstitute of Geography, University of Tuebingen, Tuebingen, GermanyThomas ScholtenInstitute of Geography, University of Tuebingen, Tuebingen, GermanyIntroductionThe Qinghai-Xizang (Tibetan) Plateau is a key areaconcerning the environmental evolution of the earth atregional as well as global scales and proves to be particularlysensitive to anthropogenic global change, especially inareas affected by permafrost. It is the youngest, largest, andhighest plateau in the world, comprising an area of morethan 2.4 million km² with an average altitude exceeding4000 m a.s.l. and containing the largest high-altitude andlow-latitude permafrost area on Earth with 54.3% of its totalsurface affected by permafrost (Cheng 2005). These areas arecharacterized by strong diurnal patterns, high radiation on thesurface, as well as a distinct geothermal gradient (Wang &French 1994) that mainly control the permafrost distributionand, thus, soil temperature and soil moisture conditions.Further, the proposed decay of Tibetan permafrost will havea strong impact on soil hydrology. Global environmentalchange, largely caused by human activities, affects climateas well as soils, and consequently reassigns their role inecosystem functioning (Vitoussek et al. 1997). The majorparameters in this context are the organic carbon (C org) stockof soils and the decomposition of organic matter, whereas theQinghai-Xizang (Tibetan) Plateau stores the highest amountof C organd total nitrogen (N t) in Chinese soils (Wang & Zhou1999). Therefore, periglacial environments of Central Chinaplay a major role in the global C and N cycles, especiallydue to the pronounced sensitivity of this region to climatechanges.During two expeditions in 2006 and 2007, in total 60 siteswere investigated on the central-eastern Tibetan Plateaualong a 1500 km long northeast–southwest transect. Theresearch focused exclusively on alpine steppe and meadowgrassland vegetation. Sites containing continuous ordiscontinuous permafrost as well as areas without or heavilydegraded permafrost were studied for comparison of soildynamics under changing environmental settings. The mainobjective was to figure out how carbon and nitrogen contentsof the investigated soils on the Tibetan Plateau respond toother pedological parameters, such as texture, acidity andcarbonate content, since the sites along the transect show adistinct variety of climate conditions, relief locations andgeology. Another major goal was to assess impact of globalchange on permafrost and its implication concerning thecarbon and nitrogen cycles related to the above-mentionedfeedback paths. Permafrost, pedogenesis, and ecosystemfunctioning are, therefore, closely linked. Study of theirdetangled feedback processes and mechanisms allows a betterunderstanding of the role of geological and anthropogenicfactors controlling the development and the functioning ofTibetan Plateau ecosystems.MethodsAt each site a soil profile pit was established reaching theparent material of soil formation or permafrost, respectively.The detailed field investigations included soil profiledescription according to FAO (2006) and WRB IUSS WorkingGroup (2007). Soil moisture was determined in the field byTDR-probes connected with a moisture meter type HH2(Delta-T Devices Ltd, UK). Aboveground and belowgroundbiomass as well as soil respiration and temperature wereinvestigated. Moreover, on-site 1 M KCl extractions for thedetermination of mineralized N (N min) were carried out.The laboratory analysis included a combined sieving andpipette grain-size analysis. Electrical conductivity (EC) andacidity (pH) were determined potentiometrically. CaCO 3wastested volumetrically with HCl treatment. N tand C orgweremeasured by heat combustion (CNS-elemental analyzerVARIO EL III, Elementar, Germany). The KCl extractionswere analyzed photometrically for N min(Continuous FlowAnalyzer SAN Plus, Skalar, Netherlands). Water contentwas determined gravimetrically.Climate data for each site was calculated by Kriging out ofa 50-year time series of 680 climatic stations in China (1951–2000) (He et al. 2006). The whole dataset was investigatedby descriptive statistics, one-way ANOVA, as well ascorrelation and regression analysis (SPSS for Windows, R)for the relationships of variables.Results and DiscussionHighest C and N contents occur in permafrost andgroundwater-influenced soils. The lower amount in soils notinfluenced by permafrost can be explained by shorter durationof pedogenesis and different temperature-moisture regimes.Pedogenesis is described here by acidity, carbonates, grainsize distribution, and other soil parameters. Particularly atsites with initial soil formation, frequently influenced by19