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Soil Organic Carbon Pools in a Periglacial Landscape; a Case Study from the Central Canadian Arctic
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
2010 (English)In: Permafrost and Periglacial Processes, ISSN 1045-6740, E-ISSN 1099-1530, Vol. 21, no 1, 16-29 p.Article in journal (Refereed) Published
Abstract [en]

We investigated total storage and landscape partitioning of soil organic carbon (SOC) in continuous permafrost terrain, central Canadian Arctic. The study is based on soil chemical analyses of pedons sampled to 1-m depth at 35 individual sites along three transects. Radiocarbon dating of cryoturbated soil pockets, basal peat and fossil wood shows that cryoturbation processes have been occurring since the Middle Holocene and that peat deposits started to accumulate in a forest-tundra environment where spruce was present (∼6000 cal yrs BP). Detailed partitioning of SOC into surface organic horizons, cryoturbated soil pockets and non-cryoturbated mineral soil horizons is calculated (with storage in active layer and permafrost calculated separately) and explored using principal component analysis. The detailed partitioning and mean storage of SOC in the landscape are estimated from transect vegetation inventories and a land cover classification based on a Landsat satellite image. Mean SOC storage in the 0–100-cm depth interval is 33.8 kg C m−2, of which 11.8 kg C m−2 is in permafrost. Fifty-six per cent of the total SOC mass is stored in peatlands (mainly bogs), but cryoturbated soil pockets in Turbic Cryosols also contribute significantly (17%). Elemental C/N ratios indicate that this cryoturbated soil organic matter (SOM) decomposes more slowly than SOM in surface O-horizons.

Place, publisher, year, edition, pages
2010. Vol. 21, no 1, 16-29 p.
Keyword [en]
soil organic carbon pools, tundra land cover classification, peatlands, cryoturbation, permafrost
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-38632DOI: 10.1002/ppp.677ISI: 000275776100002OAI: oai:DiVA.org:su-38632DiVA: diva2:311643
Available from: 2010-04-22 Created: 2010-04-22 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Soil organic carbon in permafrost terrain: Total storage, landscape distribution and environmental controls
Open this publication in new window or tab >>Soil organic carbon in permafrost terrain: Total storage, landscape distribution and environmental controls
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

High latitude terrestrial ecosystems are considered key components in the global carbon (C) cycle and hold large reservoirs of soil organic carbon (SOC). To a large degree, this SOC is stored in permafrost soils and peatlands and is vulnerable to remobilization under future global warming and permafrost thawing. Recent studies estimate that soils in permafrost regions store SOC equivalent to ~ 1.5 times the global atmospheric C pool. Ecosystems and soils interact with the atmospheric C pool; photosynthesis sequesters CO2 into SOC whereas microbial decomposition releases C based trace gases (mainly CO2 and CH4). Because of the radiative greenhouse properties of these gases, soil processes also feedback on the global climate system. Recent studies report increases in permafrost temperatures and under future climate change scenarios permafrost environments stand to undergo further changes. As permafrost thaws and surface hydrology changes, there is concern that periglacial tundra and peatland ecosystems will switch from being sinks for atmospheric C into sources, creating a potential for positive feedbacks on global warming. The magnitude of change in C fluxes resulting from climate warming and permafrost thawing depends on the remobilization processes affecting SOC stores, the size of SOC stores that become available for remobilization and the lability of the SOM compounds in these stores. While the large size and potential vulnerability of arctic SOC reservoirs is recognized, detailed knowledge on the landscape partitioning and quality of this SOC is poor.

Paper I of this thesis assesses landscape allocation and environmental gradients in SOC storage in the Usa River Basin lowlands of northeastern European Russia. The Russian study area ranges from taiga region with isolated permafrost patches to tundra region with nearly continuous permafrost. Paper II of this thesis investigates total storage, landscape partitioning and quality of soil organic carbon (SOC) in the tundra and continuous permafrost terrain of the Tulemalu Lake area in the Central Canadian Arctic. Databases on soil properties, permafrost, vegetation and modeled climate are compiled and analyzed. Mean SOC storage in the two study regions is 38.3 kg C m-2 for the Usa River Basin and 33.8 kg C m-2 for Tulemalu Lake (for 1m depth in mineral soils and total depth of peat deposits). Both estimates are higher than previous estimates for the same study areas. Multivariate gradient analyses from the Usa Basin show that local vegetation and permafrost are strong predictors of soil chemical properties, overshadowing the effect of climate variables. The results highlight the importance of peatlands, particularly bogs, in bulk SOC storage in all types of permafrost terrain. In the Tulemalu Lake area significant amounts of SOC is stored in cryoturbated soil horizons with C/N ratios indicating a relatively low degree of decomposition. As this pool of cryoturbated SOC is mainly stored in the active layer, no dramatic increases in remobilization are expected following a deepening of the active layer. However, recent studies have demonstrated the importance of SOC storage in deep (>1m) cryoturbated horizons. Perennially frozen peat deposits in permafrost bogs constitute the main vulnerable SOC pool in the investigated regions. Remobilization of this frozen C can occur through gradual but widespread deepening of the active layer with subsequent talik formation, or through more rapid but localized thermokarst erosion.

Publisher
24 p.
Identifiers
urn:nbn:se:su:diva-31249 (URN)
Presentation
2009-06-08, 00:00 (English)
Opponent
Supervisors
Available from: 2009-12-07 Created: 2009-11-09 Last updated: 2010-04-22Bibliographically approved
2. Quantity and quality of soil organic matter in permafrost terrain
Open this publication in new window or tab >>Quantity and quality of soil organic matter in permafrost terrain
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High latitude terrestrial ecosystems are considered key components in the global carbon (C) cycle and hold large reservoirs of soil organic carbon (SOC). Much of this is stored as soil organic matter (SOM) in permafrost soils and peat deposits and is vulnerable to remobilization under future global warming. While the large size and potential vulnerability of arctic SOM reservoirs is recognized, detailed knowledge on its landscape partitioning and quality is poor. This thesis describes total storage, landscape partitioning and lability of SOM stored in permafrost areas of Canada and Russia. Detailed studies of SOC partitioning highlight the importance of especially permafrost peatlands, but also of O-horizons in moist tundra soils and cryoturbated soil horizons. A general characterization of SOM in an area of discontinuous permafrost shows that >70% of the SOC in the landscape is stored in SOM with a low degree of decomposition. Projections of permafrost thaw predict that the amount of SOC stored in the active layer of permafrost soils in this area could double by the end of this century. A lateral expansion of current thermokarst lakes by 30 m would expose comparable amounts of SOC to degradation. The results from this thesis have demonstrated the value of high-resolution studies of SOC storage. It is found that peat plateaus, common in the sporadic and discontinuous permafrost zones, store large quantities of labile SOM and may be highly susceptible to permafrost degradation, especially thermokarst, under future climate warming. Large quantities of labile SOM is also stored in cryoturbated soil horizons which may be affected by active layer warming and deepening. The current upscaling methodology is statistically evaluated and recommendations are given for the design of future studies. To accurately predict responses of periglacial C pools to a warming climate detailed studies of SOC storage and partitioning in different periglacial landscapes are needed.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology (INK), Stockholm University, 2011. 38 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 26
Keyword
carbon, soil organic matter, soil organic carbon, permafrost, arctic, upscaling, peat plateau, cryoturbation, active layer, thermokarst, carbon/nitrogen ratio, stable isotopes, humification
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-54041 (URN)978-91-7447-207-3 (ISBN)
Public defence
2011-02-25, De Geer salen, Geovetenskapens hus, Svante Arrhenius väg 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3, 4 and 5: Manuscripts.Available from: 2011-02-03 Created: 2011-01-25 Last updated: 2012-01-13Bibliographically approved

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