Ninth International Conference on Permafrost ... - IARC Research

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