25th International Meeting on Organic Geochemistry IMOG 2011

P-502
Soil organic matter characteristics in the permafrost terrain,
European Russian Arctic: lability, storage, and impact of
thawing
Joyanto Routh 1,5 , Gustaf Hugelius 2 , Timothy Filley 3 , Patrick Crill 4 , Peter Kuhry 2
1 Department of Earth Sciences, IISER-Kolkata, Mohanpur, India, 2 Department of Physical Geography and
Quaternary Geology, Stockholm University, Stockholm, Sweden, 3 Department of Earth and Atmospheric
Sciences, Purdue University, West Lafayette, United States of America, 4 Department of Geological Sciences,
Stockholm University, Stockholm, Sweden, 5 MTM, Örebro University, Örebro, Sweden (corresponding
author:joyanto.routh@iiserkol.ac.in)
Soils in high latitude terrestrial ecosystems store huge
stocks of organic carbon because the low
temperature and anoxic conditions from water logging
reduce decomposition rates. Redistribution of these
huge reservoirs of surface carbon pools driven by
climate change poses a challenge. Particularly, the
soils in permafrost regions including peatlands are
most vulnerable to remobilization because of thawing
and change in hydrologic conditions (1). The net C
flux from these reserves however depends on the size
and lability of the soil organic matter (SOM) pools.
Here, we have characterized the SOM stored in soils
representative of major land cover and soil types in
the discontinuous permafrost terrain of European
Russian Arctic. We are using an array of chemical
analyses involving elemental ratios (C, N, and H),
stable isotopes (C and N), and specific biomarkers (nalkanes,
sterols, and lignin). The detailed
characterization of SOM is supposed to yield
information about: 1) the major components of SOM
and it sources, 2) chemically labile vs. refractory
fractions in SOM, and 3) OM preservation affected by
depth/age in the soil profile in relation to permafrost
conditions and/or changes in the active layer depth.
Samples were collected from the tundra near Seida in
the Usa Basin, west of the Ural Mountains. The mean
annual temperature and precipitation are –6.1°C and
538 mm, respectively. The landscape is underlain by
discontinuous permafrost (70-90%). The peat
plateaus are underlain by nearly continuous
permafrost, whereas permafrost-free sections are
found in uplands and along river/stream valleys.
Shrubs, lichens and mosses characterize the upland
tundra on mineral soils. Isolated stands of spruce and
downy birch can be found on permafrost -free ground.
Peat plateaus were sampled near thermally eroding
edges. Permafrost soils were cored using steel pipes
hammered into the frozen peat. Permafrost-free fens
were sampled using Russian corers. The samples
were sectioned and freeze-dried. Radiocarbon
analysis of bulk SOM samples was done at the
Poznan Radiocarbon Laboratory, Poland. Elemental
and stable isotope (C and N) analyses were done in
decarbonated samples. Lipids were extracted and the
samples were further cleaned/fractioned and
derivitized (2) for analyses of n-alkanes, alkanols, and
sterols. Lignin was analyzed using the CuO method
(3). The OM extracts were analyzed on a GCMS.
Basal peat ages range from 1500 (fens) to 9000 (peat
plateaus) cal years B.P. Organic matter deposited is
immature. The biomarkers indicate that higher plants
are the primary source of OM. The concentrations of
different biomarkers (e.g., n-alkanes sterols and
lignin) increase with depth before reaching the
mineral soil interface. The trend coincides with
increase in age and humification. The low
concentration of different biomarkers in upper
samples results from OM degradation in surface
exposed to thawing. The biomarker profiles vary
suggesting dominance of one or more higher plant
types in the peats or soils (e.g. Sphagnum vs.
Equisetum). There is little indication of SOM
degradation in the peats with depth. High
Acid/Aldehyde ratio in lignin, which suggests OM
degradation only occurs in surface sediments. In
contrast, the permafrost free non-peatland soils
indicate more decomposed material with increasing
depths. The more labile components such as sterols
and alkanols show greater variability in concentration
with depth than n-alkanes and lignin.
References:
1. Tarnocai, C., Canadell, J., Mazhitova, G., Schuur,
E.A.G., Kuhry, P., and Zimov, S. (2009) Global
Biogeochemical Cycles 23, GB2023.
2. Wakeham, S.G., Peterson, M.L., Hedges, J.I., Le,
C. (2002) Deep-Sea Research II 49, 2265–2301.
3. Filley, T.R., Freeman, K.H., Bianchi, T.S.,
Baskaran, M., Colarusso, L.A., and Hatcher, P.G.
(2001) Organic Geochemistry 32, 1153-1167.
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