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Soil organic carbon in permafrost terrain: Total storage, landscape distribution and environmental controls
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
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.

Place, publisher, year, edition, pages
2009. , 24 p.
Identifiers
URN: urn:nbn:se:su:diva-31249OAI: oai:DiVA.org:su-31249DiVA: diva2:275889
Presentation
2009-06-08, 00:00 (English)
Opponent
Supervisors
Available from: 2009-12-07 Created: 2009-11-09 Last updated: 2010-04-22Bibliographically approved
List of papers
1. Landscape partitioning and environmental gradient analyses of soil organic carbon in a permafrost environment
Open this publication in new window or tab >>Landscape partitioning and environmental gradient analyses of soil organic carbon in a permafrost environment
2009 (English)In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 23, no GB3006Article in journal (Refereed) Published
Abstract [en]

This study investigates landscape allocation and environmental gradients in soil organic carbon (C) storage in northeastern European Russia. The lowlands of the investigated Usa River Basin range from taiga with isolated permafrost to tundra vegetation on continuous permafrost. We compile and analyze databases on soil properties, permafrost, vegetation, and modeled climate. Mean soil C storage is estimated at 38.3 kg C m−2, with similar amounts in taiga and tundra regions. Permafrost soils hold 42% of the total soil C in the area. Peatlands dominate soil C storage with 72% of the total pool and 98% of permafrost C. Multivariate gradient analyses show that local vegetation and permafrost are strong predictors of soil chemical properties, overshadowing the effect of climate variables. This study highlights the importance of peatlands, particularly bogs, in bulk soil C storage. Soil organic matter stored in permafrost has higher C:N ratios than unfrozen material. Permafrost bogs constitute the main vulnerable C pool in the region. 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.

Keyword
Soil Carbon
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-31242 (URN)10.1029/2008GB003419 (DOI)000267935700002 ()
Projects
CARBO-North
Available from: 2009-11-09 Created: 2009-11-09 Last updated: 2017-12-12Bibliographically approved
2. Soil Organic Carbon Pools in a Periglacial Landscape; a Case Study from the Central Canadian Arctic
Open this publication in new window or tab >>Soil Organic Carbon Pools in a Periglacial Landscape; a Case Study from the Central Canadian Arctic
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.

Keyword
soil organic carbon pools, tundra land cover classification, peatlands, cryoturbation, permafrost
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-38632 (URN)10.1002/ppp.677 (DOI)000275776100002 ()
Available from: 2010-04-22 Created: 2010-04-22 Last updated: 2017-12-12Bibliographically approved

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