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Controls on the storage of organic carbon in permafrost soil in northern Siberia
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography. Helmholtz Centre for Polar and Marine Research, Germany.
Stockholm University, Faculty of Science, Department of Physical Geography.
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2016 (English)In: European Journal of Soil Science, ISSN 1351-0754, E-ISSN 1365-2389, Vol. 67, no 4, 478-491 p.Article in journal (Refereed) Published
Abstract [en]

This research examined soil organic carbon (SOC), total nitrogen (TN) and aboveground phytomass carbon(PhC) stocks in two areas of the Taymyr Peninsula, northern Siberia.We combined field sampling, chemical and14C radiocarbon dating analyses with land cover classifications for landscape-level assessments. The estimatedmean for the 0–100-cm depth SOC stocks was 14.8 and 20.8 kgCm−2 in Ary-Mas and Logata, respectively. Thecorresponding values for TN were 1.0 and 1.3 kgNm−2. On average, about 2% only (range 0–12%) of the totalecosystem C is stored in PhC. In both study areas about 34% of the SOC at 0–100 cm is stored in cryoturbatedpockets, which have formed since at least the early Holocene. The larger carbon/nitrogen (C/N) ratio of thiscryoturbated material indicates that it consists of relatively undecomposed soil organic matter (SOM). Thereare substantial differences in SOC stocks and SOM properties within and between the two study areas, whichemphasizes the need to consider both geomorphology and soil texture in the assessment of landscape-level andregional SOC stocks.

Highlights

• This research addresses landscape-scale and regional variation in SOC stocks.

• Landform and soil texture are taken into account in the analysis.

• The contribution of phytomass to total ecosystem C stored is limited.

• Large SOC stocks are susceptible to decomposition following permafrost thaw.

Place, publisher, year, edition, pages
2016. Vol. 67, no 4, 478-491 p.
Keyword [en]
soil organic carbon, total nitrogen, phytomass carbon, permafrost, cryoturbation, C/N ratios, radiocarbon dating, landscape inventories
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-115705DOI: 10.1111/ejss.12357ISI: 000384745900012OAI: oai:DiVA.org:su-115705DiVA: diva2:798982
Projects
The ESF CryoCARB projectthe Nordforsk NCoE DEFROST projectthe EU FP7 PAGE21 project
Funder
European Science Foundation (ESF)EU, FP7, Seventh Framework Programme
Available from: 2015-03-27 Created: 2015-03-27 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Storage, landscape partitioning and lability of soil organic matter in permafrost terrain
Open this publication in new window or tab >>Storage, landscape partitioning and lability of soil organic matter in permafrost terrain
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Recent estimates indicate that soils in the northern circumpolar permafrost region store substantial amounts of soil organic carbon (SOC). This reservoir has accumulated over 10-100.000 years and is often preserved in a relatively undecomposed state because frozen and often water-logged conditions prevented microbial degradation. Under a projected future climate change caused by rising greenhouse gases, permafrost thaw and rapid decomposition of vulnerable soil organic matter (SOM) could provide a positive feedback on global warming by releasing large amounts of carbon dioxide and/or methane into the atmosphere.

SOC pools have large regional and landscape-level variability depending on topographic, ecoclimatic and edaphic factors. As a consequence, large scale maps and even regional data sets describing SOC storage should be taken with caution since they are highly simplified. The purpose of this thesis is to improve our knowledge on quantity and quality of SOM in different areas of continuous permafrost and provide regional high quality data from hitherto under-sampled regions for future assessment of the potential remobilization of SOC under global warming. A special focus is put on SOC partitioning within the landscape and soil horizon levels as well as on soil forming processes under periglacial conditions. Throughout the five different study areas presented in this thesis the landscape mean SOC storage ranges between 8 and 30 kg C m-2, while site differences are in the order of 0 to 80 kg C m-2. Paper I presents new SOC data from contrasting areas in continuous permafrost: a mountainous High Arctic site in Zackenberg (NE Greenland) and lowland sites in Shalaurovo and Cherskiy lower Kolyma (NE Siberia). The main difference is that about 60% of the Zackenberg area is higher elevation terrain with mostly barren ground and very low SOC content, resulting in a much lower landscape-level mean SOC storage compared to the Siberian sites. In addition, Paper II shows that even when comparing two lowland sites located only 150 km apart in Taymyr Peninsula (N Siberia) the mean SOC storage differs with 40% between the areas. This emphasizes that even in lowlands on a regional scale not only different landforms and land cover but also microrelief, soil moisture and especially parent material play a very important role for obtaining more accurate SOC storage estimates.

Throughout this thesis a special emphasis is put on understanding the role of cryoturbation for SOC storage. Signs of cryoturbation were observed at all sites and 14C dates show that this process is occurring since at least the early Holocene. On average, 30% of all SOC in the top meter of soil is located in buried C-enriched pockets. The only exception is Zackenberg, with only 12%, where slope processes were the dominant mechanism for burying C-enriched material into deeper layers.

We use the weight ratio of Carbon/Nitrogen (C/N) to gain information about SOM decomposability. Generally, all sites show the same trend that the C/N ratio decreases with soil depth. Top organic soil and peat samples have always the highest C/N ratios, suggesting little decomposed SOM. Except for the Zackenberg site, the buried C-enriched pockets have significantly higher C/N ratios than the adjacent mineral subsoil samples. We assume that this C-enriched material was exposed over longer time periods to aerobic decomposition and was therefore relatively well decomposed before it was buried by reactivated slope processes.

Place, publisher, year, edition, pages
Stockholm: Stockholm University, 2015
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-115707 (URN)
Presentation
2015-04-24, Ahlmannsalen, 13:00 (English)
Opponent
Supervisors
Available from: 2015-05-27 Created: 2015-03-27 Last updated: 2016-12-22Bibliographically approved
2. Landscape partitioning and burial processes of soil organic carbon in contrasting areas of continuous permafrost
Open this publication in new window or tab >>Landscape partitioning and burial processes of soil organic carbon in contrasting areas of continuous permafrost
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recent studies have shown that permafrost soils in the northern circumpolar region store almost twice as much carbon as the atmosphere. Since soil organic carbon (SOC) pools have large regional and landscape-level variability, detailed SOC inventories from across the northern permafrost region are needed to assess potential remobilization of SOC with permafrost degradation and to quantify the permafrost carbon-climate feedback on global warming.

This thesis provides high-resolution data on SOC storage in five study areas located in undersampled regions of the continuous permafrost zone (Zackenberg in NE Greenland; Shalaurovo and Cherskiy in NE Siberia; Ary-Mas and Logata in Taymyr Peninsula). The emphasis throughout the five different study areas is put on SOC partitioning within the landscape and soil horizon levels as well as on soil forming processes under periglacial conditions. Our results indicate large differences in mean SOC 0–100 cm storage among study areas, ranging from 4.8 to 30.0 kg C m-2, highlighting the need to consider numerous factors as topography, geomorphology, land cover, soil texture, soil moisture, etc. in the assessment of landscape-level and regional SOC stock estimates.

In the high arctic mountainous area of Zackenberg, the mean SOC storage is low due to the high proportion of bare grounds. The geomorphology based upscaling resulted in a c. 40% lower estimate compared to a land cover based upscaling (4.8 vs 8.3 kg C m-2, respectively). A landform approach provides a better tool for identifying hotspots of SOC burial in the landscape, which in this area corresponds to alluvial fan deposits in the foothills of the mountains. SOC burial by cryoturbation was much more limited and largely restricted to soils in the lower central valley. In the lowland permafrost study areas of Russia the mean SOC 0–100 cm storage ranged from 14.8 to 30.0 kg C m-2. Cryoturbation is the main burial process of SOC, storing on average c. 30% of the total landscape SOC 0–100 cm in deeper C-enriched pockets in all study areas. In Taymyr Peninsula, the mean SOC storage between the Ary-Mas and Logata study areas differed by c. 40% (14.8 vs 20.8 kg C m-2, respectively). We ascribe this mainly to the finer soil texture in the latter study area. Grain size analyses show that cryoturbation is most prominent in silt loam soils with high coarse silt to very fine sand fractions. However, in profiles and samples not affected by C-enrichment, C concentrations and densities were higher in silt loam soils with higher clay to medium silt fractions.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University, 2017
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 61
Keyword
soil organic carbon, total nitrogen, permafrost, cryoturbation, geomorphology, land cover classification, slope processes, texture, upscaling, carbon/nitrogen ratio
National Category
Physical Geography Climate Research
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-136383 (URN)978-91-7649-610-7 (ISBN)978-91-7649-611-4 (ISBN)
Public defence
2017-02-10, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
European Science Foundation (ESF), 282700EU, FP7, Seventh Framework Programme, 282700Nordic Council of Ministers, 23001
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-01-18 Created: 2016-12-05 Last updated: 2017-01-17Bibliographically approved

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