Organic Carbon Pools in Permafrost-Affected Soils of Siberian Arctic Regions

184 Pages·2013·9.57 MB·English

by  Sebastian Zubrzycki

Organic Carbon Pools in Permafrost-Affected Soils
of Siberian Arctic Regions

Dissertation
zur Erlangung des Doktorgrades
der Naturwissenschaften im Fachbereich Geowissenschaften
der Universität Hamburg

vorgelegt von
Sebastian Zubrzycki
aus
Starogard in Polen

Hamburg 2013
Als Dissertation angenommen vom Fachbereich Geowissenschaften der Universität Hamburg
auf Grund der Gutachten von Prof. Dr. Eva-Maria Pfeiffer
und Prof. Dr. Lars Kutzbach

Hamburg, den 23.01.2013

Prof. Dr. Christian Betzler
Leiter des Fachbereichs Geowissenschafen
Contents

Contents

I Summary......................................................................................................................VII
II Zusammenfassung..........................................................................................................X
III List of Tables..............................................................................................................XIII
IV List of Figures............................................................................................................XIII
V List of Symbols and Abbreviations............................................................................XVI

1. Introduction ......................................................................................................................... 1
1.1 Aims and objectives ................................................................................................... 3
1.2 Chapter overview ....................................................................................................... 3
1.3 Authors’ contribution ................................................................................................. 4
2. Permafrost-Affected Soils and their Carbon Pools – State-of-the-Art ................................ 7
2.1 Introduction ................................................................................................................ 7
2.2 Permafrost-affected soils as carbon stores ............................................................... 14
2.3 Current level of knowledge of the carbon pool in permafrost-affected soils ........... 21
2.4 Research requirements ............................................................................................. 27
3. Diversity of Permafrost-Affected Soils in Northern Siberia ............................................. 29
3.1 Introduction .............................................................................................................. 29
3.2 Investigation area ..................................................................................................... 30
3.3 Material and methods ............................................................................................... 36
3.4 Results and discussion .............................................................................................. 38
3.4.1 First River Terrace and Floodplains ..................................................................... 38

III
Contents

3.4.2 Second Terrace ..................................................................................................... 43
3.4.3 Third Terrace ........................................................................................................ 46
3.4.4 Hinterland: Polygonal Tundra .............................................................................. 63
3.4.5 Hinterland: Tundra-Taiga-Transition Zone .......................................................... 67
3.4.6 Hinterland: Northern Taiga .................................................................................. 69
3.4.7 Discussion of soil properties ................................................................................ 74
3.4.8 Soil assessment and conclusions .......................................................................... 80
4. Soil Organic Carbon and Nitrogen Stocks in the Lena River Delta ................................. 83
4.1 Introduction .............................................................................................................. 83
4.2 Study area ................................................................................................................. 85
4.3 Methods .................................................................................................................... 88
4.3.1 Drilling frozen soils .............................................................................................. 88
4.3.2 Soil-chemical analyses ......................................................................................... 94
4.3.3 Soil organic carbon and nitrogen stock calculations ............................................ 95
4.3.4 Synthesis of existing soil information .................................................................. 95
4.3.5 Organic carbon and total nitrogen pool calculations ............................................ 96
4.3.6 Satellite data and image processing ..................................................................... 96
4.3.7 Statistics ............................................................................................................... 98
4.4 Results .................................................................................................................... 100
4.4.1 Soil properties .................................................................................................... 100
4.4.2 Soil organic carbon stocks .................................................................................. 105
4.4.3 Holocene river terrace and the active floodplain ............................................... 105
4.4.4 Polygon centres, polygon rims, and soil units .................................................... 107
4.4.5 Nitrogen stocks ................................................................................................... 111

IV
Contents

4.4.6 Classifications and upscaling ............................................................................. 113
4.5 Discussion .............................................................................................................. 118
4.5.1 Soil organic carbon pools on the Holocene river terrace and the floodplains .... 118
4.5.2 Soil organic carbon storage in the patterned ground and the soil subgroups ..... 119
4.5.3 Vertical distribution of the soil organic carbon storage within the soil ............. 119
4.5.4 Permafrost soil organic carbon storage .............................................................. 120
4.5.5 Nitrogen stocks and nitrogen storage ................................................................. 122
4.6 Conclusions ............................................................................................................ 123
5. Soil Organic Carbon in the Active Layer in Soils from a Latitudinal Transect .............. 125
5.1 Introduction ............................................................................................................ 125
5.2 Investigation area ................................................................................................... 127
5.3 Materials and methods ........................................................................................... 129
5.4 Results .................................................................................................................... 130
5.5 Discussion and conclusions .................................................................................... 134
6. Synthesis and conclusions ............................................................................................... 139
7. References ....................................................................................................................... 145
8. Acknowledgements ......................................................................................................... 165

V
VI
Summary

I. Summary
Permafrost-affected soils of the Lena River Delta (Northern Siberia) and its hinterland are
characterized by a high diversity. The three main soil groups of the permafrost-affected soils,
which are organic-rich Histels, cryoturbated Turbels and mineral and non-cryoturbated
Orthels, include a large variety of subgroups. This variability formed while time, temperature,
and water saturation strongly slowed the soil-forming processes. These diverse North-
Siberian soils have been only scarcely investigated by soil scientists so far, although they play
a major role in global long-term carbon sequestration. Permafrost-affected soils started to
attract broader attention since increasing knowledge about the carbon storage of these soils
has been coupled with future climate trend projections indicating the potential of a positive
feedback loop of warming when the predicted release of “permafrost carbon” will increase the
greenhouse effect. Despite their small thickness of few decimetres, these soils and their
carbon storage might play an important role in affecting the future climate when one
considers the projected increases of temperature and recent models of the active layer depth
development. The question if they are still sequestering carbon is still controversially
discussed and will have different answers for different permafrost regions.
Approaches to determine the carbon source and sink functions of permafrost-affected soils
require robust knowledge of the recent carbon storage of these soils, which is where this
thesis begins. Here the author provides the first robust estimates of the carbon storage of the
modern, Holocene geomorphologic units of the Lena River Delta as well as estimates of the
carbon stocks of the seasonally thawed layer from a latitudinal transect in Northeast-Siberia
extending from the Lena River Delta into its hinterland. For the area of the Lena River Delta,
he also reports total nitrogen stocks.
The Lena River Delta, which is the largest delta in the Arctic, extends over an area of
32,000 km² and likely holds the major part of the soil organic carbon mass stored in the seven
major deltas in the northern permafrost regions. The geomorphologic units of the Lena River
Delta, which were formed by true deltaic sedimentation processes are a Holocene river terrace
and active – still regularly flooded – floodplains. Their mean soil organic carbon stocks for
the upper 1 m of soils were estimated at 29 kg m-2 ± 10 kg m-2 and at 14 kg m-2 ± 7 kg m-2,

VII
Summary

respectively. For the depth of 1 m, the total soil organic carbon storage of the Holocene river
terrace was estimated at 121 Tg ± 43 Tg, and the soil organic carbon storage of the active
floodplains was estimated at 120 Tg ± 66 Tg. The mass of soil organic carbon stored within
the observed seasonally thawed active layer was estimated at about 127 Tg assuming an
average maximum active layer depth of 50 cm. The soil organic carbon mass that is stored in
the perennially frozen ground below the average maximum active layer, which is excluded
from intense biogeochemical exchange with the atmosphere, was estimated at 113 Tg. The
mean nitrogen stocks for the upper 1 m of soils were estimated at 1.2 kg m-2 ± 0.4 kg m-2 for
the Holocene river terrace and 0.9 kg m-2 ± 0.4 kg m-2 for the active floodplain levels,
respectively. For the depth of 1 m, the total nitrogen storage of the river terrace was estimated
at 4.8 Tg ± 1.5 Tg, and the total nitrogen storage of the floodplains at 7.7 Tg ± 3.6 Tg.
Considering the projections for deepening the seasonally thawed active layer up to 120 cm in
the Lena River Delta region within the 21st century, these large carbon and nitrogen stocks
could become increasingly available for decomposition and mineralization processes.
Twelve sites along a north-south latitudinal transect in Siberia were investigated to classify
the soils and to determine their soil organic carbon stocks in the top 30 cm of the seasonally
thawed layer, which was shallower compared to the intensive delta study mentioned above.
There was a distinct arrangement into three groups of increasing soil organic carbon stocks
along the transect with decreasing latitude. The greatest stocks, with mean values of
24 kg m-2 ± 9 kg m-2 were identified for the southern group of forest tundra and taiga sites on
the ancient Central Siberian Plateau. The soils of Lena River Delta’s first and third river
terraces had stocks of on average 12 kg m-2 ± 3 kg m-2 whereas the sand-dominated north-
western part of the delta, the second river terrace, stored only 4 kg m-2 ± 2 kg m-2 in the top
30 cm of the soils. The climatological gradient with changing vegetation productivity and
different parent materials result in varying pedogenetic processes and were identified as key
controls on the soil organic carbon stocks.
Using the linear increase of the cumulative soil organic stock size with increasing soil depth
determined for the investigated Lena River Delta soils in a regression model, the organic
carbon stocks of soils investigated within the latitudinal transect are likely to reach up to
80 kg m-2 within a depth of 100 cm. The results of the pilot study encourage continuing the

VIII
Summary

organic carbon quantification studies within this region to gain a more detailed knowledge
about the soils of the unique and various landscapes of Northeast-Siberia.

IX
Summary

Zusammenfassung
Die von Permafrost beeinflussten Böden des nordostsibirischen Lenadeltas und seines
Hinterlandes sind durch eine sehr hohe Diversität charakterisiert. Die drei
Bodenhauptgruppen der von Permafrost beeinflussten Böden, die organikreichen Histels, die
kryoturbierten Turbels und die mineralischen und nicht-kryoturbierten Orthels, umfassen eine
große Variabilität an untergeordneten Bodeneinheiten. Diese Variabilität entstand, obwohl
Zeit, Temperatur und Wassersättigung die bodenbildenden Prozesse stark verlangsamten.
Diese diversen, von Permafrost beeinflussten sibirischen Böden wurden bisher nur
unzureichend bodenwissenschaftlich untersucht, obwohl sie bei der globalen Langzeit-
Kohlenstoff-Sequestrierung eine entscheidende Rolle spielen. Sie gewannen erst an
Bedeutung als das wachsende Wissen über die Kohlenstoffvorräte dieser Böden im
Zusammenhang mit den aktuellen Projektionen zum zukünftigen, globalen Klima betrachtet
wurden. Diese könnten in einem sich selbst verstärkenden Kreislauf resultieren, wenn
freigesetzter „Permafrost-Kohlenstoff“ den Treibhauseffekt verstärken würde. Obwohl nur
wenige Dezimeter mächtig, werden diese Böden mit ihren Vorräten an Kohlenstoff
möglicherweise eine entscheidende Rolle bei der Entwicklung des zukünftigen Klimas
spielen, wenn die aktuellen Projektionen zum Temperaturanstieg und die aktuellen Modelle
zur Entwicklung der Mächtigkeit der saisonalen Auftauschicht betrachtet werden. Die Frage,
ob diese Böden immer noch Kohlenstoff sequestrieren, wird noch kontrovers diskutiert und
wird wahrscheinlich unterschiedliche Antworten aus unterschiedlichen permafrost-
beeinflussten Regionen liefern.
Ansätze zur Beantwortung der Frage nach einer Kohlenstoff-Quellen- und Kohlenstoff-
Senkenfunktion der von Permafrost beeinflussten Böden brauchen belastbares Wissen über
die rezenten Kohlenstoffvorräte dieser Böden. Und genau hier setzt diese Arbeit an. Der
Autor liefert eine erste robuste Abschätzung der Kohlenstoffvorräte in den modernen
holozänen geomorphologischen Einheiten des Lenadeltas und darüber hinaus eine
Abschätzung der Kohlenstoffgehalte in der saisonalen Auftauschicht entlang eines Nordsüd-
Transekts im Nordosten Sibiriens, welcher sich vom Lenadelta bis zu seinem Hinterland
erstreckt. Für den Bereich des Lenadeltas werden auch die Stickstoffvorräte geschätzt.

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