Ninth International Conference on Permafrost ... - IARC Research

Comparison of Thermal Regimes in Tundra Virgin and Post-Agricultural Soils ofthe European NortheastDmitry KaverinKomi Science Center, Russian Academy of Sciences, Syktyvkar, RussiaIntroductionIn tundra, agricultural activity transformed the soils andtheir properties including temperature conditions. Soilthermal regimes are considered to change into ones having noanalogues among virgin soils. We studied thermal propertiesof tundra post-agricultural and virgin soils. Revealinginterannual and seasonal temperature dynamics in these soilsis important in view of present climate change.Regional BackgroundThe research was conducted in upland tundra near the townof Vorkuta (67°30′N; 64°02′E) in the east-European RussianArctic. The terrain is a rolling plain covered generally withsilty loams. The area is attributed to the subzone of southerntundra characterized by the distribution of relatively highshrubs: birch and willow. The area under study belongsto the zone of discontinuous permafrost (Oberman &Mazhitova 2003). Massive islands of permafrost occupyslightly dissected hill slopes and hill summits covered withdwarf-shrub/moss vegetation. Permafrost temperatures varyaround -1°C.Mean annual air temperature (MAAT) is -5.8°C, meanannual thawing degree days (DDT) 1005°C-days, and meanannual precipitation 513 mm.Objects and MethodsSoil temperature regimes were studied in 2 post-agriculturaltundra soils. Two undisturbed soils, one permafrost-affectedand another one permafrost-free, served as controls.Grassland soils are located in the landscape position similarto that of the control virgin soils.Soils under study(1) Abandoned overgrowing sown grassland, soil EpigleyicGelisol, grass/dwarf-shrub community, willow covers 7–8%of the site area (2005). Permafrost is at 1.35 m depth.(2) R2 site of the Circumpolar Active Layer Monitoringnetwork, dwarf-shrub/moss tundra, soil Histi-Turbic Cryosol(Reductaquic), permafrost depth is 100 cm;(3) Abandoned overgrowing arable land, soil Endogleyi-Stagnic Cambisol, grass-moss community, willow covers only2% of the site area (2005), no permafrost within 2 m depth.(4) Shrub-moss tundra, soil Dystri-Stagnic Cambisol, nopermafrost within 2 m depth.Post-agricultural sites were abandoned about 10 yearsago, and tall shrubs cover up to 10% of the area. Beforeabandonment, since 1970s the grasslands were annuallyharvested with periodic rototilling and fertilizing.The records were conducted with digital Hobo loggersprogrammed for 8 measurements daily. Loggers were set atdepths of 0, 20, 50, and 80 cm and in the upper layer ofpermafrost in case of its presence. The study was conductedin the period of 2005–2007.Results and DiscussionBy now, there is not much data about the temperatureregime of tundra soils in the European Northeast.Kononenko (1986) studied summer temperatures in virginand agricultural soils but winter thermal regime was quitepoorly characterized. Thermal regimes of the soils were notstudied at landscape level.Continuous soil temperature measurements have beenconducted in the area since 1996 by Galina Mazhitova. Itwas revealed that MAST (mean annual air temperature) in allsoils of the area is strongly correlated with snow thickness inwinter, with permafrost occurring only in the sites with snowthickness less than 50 cm. A progressive increase in shrubcoverage is, therefore, the major MAST-controlling factor.Shrubs effectively intensify snow accumulation, catchingthe snow redistributed by winds (Mazhitova 2001, 2008).As in previous years during our study, MAST at depth0–50 cm was commonly above 0°C in all permafrost-freesoils. Negative mean annual temperatures in permafrostaffectedsoils and positive ones in permafrost-free soilsare quite typical for discontinuous permafrost zone (Burn2004).Studied permafrost-affected soils (No. 1, 2) are locatedat the southern windward hill slopes. Shallow snow cover(30–40 cm) and quite thick peat layer (10–20 cm) preservepermafrost within the soil profile. Soils of northern slopeslocated in the same landscape have no permafrost. Such aninversion is resulted from strong winds blowing in winter.Until 2006, the site with coldest permafrost-affected soil(No. 2) was characterized with negative MAST down allthe profile (Mazhitova 2001, 2008). MAST at a depth of20 cm was -1.9…0.4°C, 50 cm -0.5…-1.9°C. MAST in theupper permafrost layer was -1.2°C with minimum (-4.4°C)in April.According to MAST and freezing degree days at depthsof 0–50 cm the permafrost-affected soil of the abandonedgrassland No. 1 was warmer than the virgin soil No. 2. ThusMAST at a depth of 50 cm was -0.35°C versus -0.5°C in thecontrol soil (2006).The post-agricultural soil (No. 3) was developed in theformer shrubby site similar to that of the soil No. 4. It hadlower temperatures in comparison with profile No. 4. Despitethe absence of thick shrub vegetation, this grassland soilstill had no permafrost and was characterized with positiveMASTs at depths of 20 cm and 50 cm (+1 +2°C).123