Ninth International Conference on Permafrost ... - IARC Research

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Effects of Increased Snow Depth on Ecosystem CO 2Fluxes in Arctic TundraLina TanevaEnvironment and Natural Resources Institute, University of Alaska AnchoragePatrick F. SullivanDepartment of Biology, University of Alaska AnchorageBjartmar SveinbjornssonDepartment of Biology, University of Alaska AnchorageJeffrey M. WelkerEnvironment and Natural Resources Institute, University of Alaska AnchorageIntroductionShrub expansion into arctic tundra has been documented(Tape et al. 2006) and climate warming and alteredprecipitation regime have been proposed as possible driversof plant community composition changes (Sturm et al. 2005).Increases in winter precipitation and deeper snowpack canalter the soil microclimate, leading to warmer soils anddeeper active layer, potentially resulting in changes in thecarbon, water, and nutrient cycles of arctic ecosystems.Associated changes in plant community composition intundra ecosystems can further lead to altered ecosystemfunction. The Arctic represents a large carbon reservoir inthe global carbon cycle, and changes in the cycling of carbonin tundra ecosystems with observed changes in biotic andabiotic conditions could have important implications foratmospheric CO 2accumulation.The objective of this study was to evaluate the shorttermand long-term effects of deeper winter snow depth onecosystem carbon cycling during the growing season.MethodsThis research was conducted during the 2007 growingseason at three moist tussock tundra sites near Toolik Lake,in the northern foothills of the Brooks Range, Alaska, USA.Plant community composition is dominated by the tussockgrass Eriophorum vaginatum, the shrubs Betula nana, andSalix pulchra, as well as other short-stature vegetation,mosses and lichens. Snow fences were constructed in 1994(n = 1) and 2006 (n = 3), in order to increase snow depthin the treatment plots during winter/spring. A naturallyoccurring shrub patch was used as a reference.Ecosystem CO 2flux measurements were taken using aclear plexiglass chamber, connected to a Licor 6200 infraredgas analyzer.ResultsNo significant changes in ecosystem C uptake or respirationafter one year of snow depth increase were observed, withthe ecosystem representing a C source for part of the growingseason (Fig. 1). Long-term (13 yr) snow depth increaseresulted in greater C uptake rates in treatment plots, whereasno significant changes in ecosystem respiration rates wereobserved, and both treatment and control plots were a C sinkduring the growing season (Fig. 1). Ecosystem C fluxes ina nearby naturally occurring shrub patch were lower thanthose in tussock tundra under ambient or increased wintersnow depth, and NEE was near zero (Fig. 1).141210GPPTusscok CTLInter-Tuss CTLTussock Int DriftInter-Tuss Int DriftGPPCTLDriftGPP8642014Ecosystem RespiraitonEcosystem RespirationEcosystem Respiration-1 s -22m121086mol µ CO420121086420-2-4-6-8NEE5/21 6/4 6/18 7/2 7/16 7/30 8/13Date 2007Tussock CTLInter-Tuss CTLTussock Int DriftInter-Tuss Int DriftNEE5/21 6/4 6/18 7/2 7/16 7/30 8/13Date 2007NEE5/21 6/4 6/18 7/2 7/16 7/30 8/13 8/27Date 2007Figure 1. Ecosystem CO 2fluxes (gross ecosystem productivity [GEP], ecosystem respiration, and net ecosystem CO 2exchange [NEE]) intussock tundra after 1 and 13 years of snow accumulation increase, and in a site dominated by shrub (B. nana) vegetation without any snowtreatments.309
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tRelative growth rate (cm/day)0 .01 .61 .41 .21 .00 .80 .60 .40 .2G ro w th o f B . n a n a a n d E . v a g in a t u m1 .6 B . n a n a C T L1 y r S n o w T r t m n tE . v a g in a t u m C T LB . n a n a D rift1 .4E . v a g in a tu m D rift1 .21 .00 .80 .60 .40 .20 .01 .6 S h r u b p lo tB . n a n a1 .41 .21 .00 .80 .60 .40 .20 .01 3 y rs o f S n o w T rtm n t5 / 2 1 / 0 7 6 / 4 / 0 7 6 / 1 8 / 0 7 7 / 2 / 0 7 7 / 1 6 / 0 7 7 / 3 0 / 0 7 8 / 1 3 / 0 7 8 / 2 7 / 0 7D a teFigure 2. Growing season growth rate of B. nana and E. vaginatumin a tussock tundra ecosystem after 1 and 13 years of snowaccumulation increase, and in a shrub-dominated plot with no snowdepth manipulation.The growth rate of E. vaginatum was higher than that ofB. nana, with no significant changes in growth rates after 1yr of snow depth increase (Fig. 2). Long-term snow depthmanipulation led to a stimulation in B. nana growth rate anda trend towards lower E. vaginatum growth rates, relativeto ambient snow plots (Fig. 2). Rates of B. nana growth inthe long-term treatment plots were higher than those in theshrub-dominated plot, while growth rates at ambient snowwere comparable at tussock tundra and shrub sites (Fig. 2).AcknowledgmentsThis research was funded by an <strong>International</strong> Polar Yeargrant #0612534 through the Office of Polar Programs at theNational Science Foundation. We gratefully acknowledgethe staff at Toolik Field Station for camp maintenance andoperation. We thank Jeremy Chignell for his help in thefield.ReferencesJones, M.H., Fahnestock, J.T., Walker, D.A., Walker, M.D.& Welker, J.M. 1998. Carbon dioxide fluxes in moistand dry Arctic tundra during the snow-free season:Responses to increases in summer temperature andwinter snow accumulation. Arctic and Alpine Research30(4): 373-380.Oberbauer, S.F., Tweedie, C.E., Welker, J.M., Fahnestock,J.T., Henry, G.H., Webber, P.J., Hollister, R.D.,Walker, M.D., Kuchy, A., Elmore, E. & Starr, G.2007. Tundra CO 2fluxes in response to experimentalwarming across latitudinal and moisture gradients.Ecological Monographs 77(2): 221-238.Sturm, M., Schimel, J., Michaelson, G., Welker, J.M.,Oberbauer, S.F., Liston, G.E., Fahnestock, J. &Romanovsky, V.E. 2005. Winter biological processescould help convert Arctic tundra to shrubland.Bioscience 55(1): 17-26.Tape, K., Sturm, M. & Racine, C. 2006. The evidence forshrub expansion in northern Alaska and the Pan-Arctic. Global Change Biology 12(4): 686-702.Wahren, C-H.A., Walker, M.D. & Bret-Harte, M.S. 2005.Vegetation responses in Alaskan arctic tundra after8 years of a summer warming and winter snowmanipulation experiment. Global Change Biology11: 537-552.ConclusionsLong-term increases (13 yr) in winter snow cover andassociated changes in plant community composition (i.e.,increases in shrub abundance; Wahren et al. 2005) convertedthis tundra ecosystem from a source of C to the atmosphere(as reported in Jones et al. 1998 and Oberbauer et al. 2007after 2, 3, and 4 years of treatment) to a C sink.Enhanced GEP with deeper snow cannot be explainedby increases in shrub abundance alone and suggests alteredwinter soil processes under deeper snow that may alleviateecosystem nutrient limitation.Changes in plant community composition in tundraecosystems can potentially translate to altered C inputs,storage, and turnover rates in these C-rich and warmingsensitiveecosystems, with subsequent implications for theglobal C cycle.310
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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