compound-specific stable-isotopes to investigate soil
TRANSCRIPT
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Compound-specific stable-isotopes
to investigate soil organic carbon source/sink
relocations between areas of land degradation
and deposition areas in a mountainous
watershed in Northwest Vietnam
C. Brandta, F. Raschea, H. Fröhlicha, N.T. Lamb, T. D. Vienb and G. Cadischa
a Hohenheim University, Department of Plant Production and Agroecology in the Tropics and
Subtropics, Stuttgart, Germany b Center for Agricultural Research and Ecological Studies (CARES), Hanoi, Vietnam
FAO/IAEA International Symposium on Managing Soils for
Food Security and Climate Change Adaptation and Mitigation
23 – 27 July 2012, Vienna
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1. Problem definition
2. Concept of CSSI
3. Objectives
4. Study area
5. Preliminary results
6. Conclusion
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Contents
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Land degradation in
South East Asia
Population pressure
Agricultural commercialization
Deforestation
Expansive maize production
From traditional shifting
cultivation systems to
continuous monocropping
Problem definition
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Problem definition
Sediment deposition and
siltation of reservoirs
Land use intensification in upland areas
Soil degradation on slopes
Soil relocation
Movement of SOC
and Nutrients
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Problem definition
Maize Teak
Cassava
Bamboo
Mix of different
sources
Which are the hot spots of
critical land degradation?
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Identification of hot spots of critical land degradation
for a cost-effective implementation of precision
conservation measures
How to apportion the source soils of sediments?
Compound specific stable isotope (δ13C)
approach and CSSI based mixing models
Main goal
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Problem definition
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Concept of CSSI
Marker compounds
Land-use fingerprint
Plants produce a range of organic compounds that leach
from leaves or stems or exude from roots
Different photosynthetic fixation pathways for CO2 (C3,C4)
Genetic and environmental factors influencing stomata
conductance as well as nutrient status
Same organic compounds of different plants have slightly
different δ13C isotopic signature (‰)
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Long-chain fatty acids (C12:0 – C24:0)
Abundant in environment
Highly polar (acids)
Fatty acid - clay mineral associations in upper soil
Concept of CSSI
Marker compounds of choice
Palmitic acid; C16:0
Stearic acid; C18:0
Lignoceric acid; C22:0
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Significant differences of δ13C values of fatty acids in
source-soils of various land uses can be utilized to
identify the provenances of sediments.
Therefore it is possible to trace soil organic carbon
source/sink relationships in a small agricultural
catchment on a spatial level.
Concept of CSSI
Hypothesis
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Sediment
sample
Land use
4
Land use
3
Land use
2
Land use
1
Sediment source ascription
δ13C value
3
δ13C value
2
δ13C value
1
δ13C value
4
Reference database of
source soils
Concept of CSSI
Gas Chromatography Combustion Isotope Ratio Mass Spectrometry (GC/C/IRMS)
Mixture of source soils of unknown proportions
Soil preparation (max 50°C/<2mm)
Fatty acid extraction and fractionation
Methylization FA FAME
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Significant differences between isotopic ratio of δ13C
of individual fatty acids in source soils
Proportional contributions of source soils to colluvial
sediment can then be estimated by mixing models
(Isosource, SIAR)
Concept of CSSI
Sediment source ascription
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Are CSSI and CSSI-based mixing models applicable to
identify and trace SOC source/sink relationships in a
small tropical catchment?
Development of a standard procedure combining an
optimized fatty acid extraction and measurement
strategy and the implementation of statistical
analyses and mixing models
Implementation of the CSSI-approach at catchment
level
Objectives
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Introduction – Study Area Study area
13/23
Chieng Khoi
catchment
Son La Province
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Introduction – Study Area Study area
0 250 500 Meters
Upland land use sites
in Chieng Khoi [M] Maize
[C] Cassava
[SBF] Sec. Forest and Bamboo
[PNF] Protected natural forest
[MFP] Mixed fruit plantation
[TW] Timber plantation
Soil sampling plot [10 - 20m²]
Sediment sampling site [4 - 10m²]
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Introduction – Study Area Study area
Maize
Cassava
Teak
Bamboo
0 50 100 Meters
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Preliminary results
Cassava field
Teak plantation
Maize field
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A
B
C
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Fatty acids (δ13
C ‰) Source soils (δ13
C ‰; SEM)
Maize Cassava Teak
C16:0 Methyl palmitate -23,5 ±0,36 -28,9 ±0,48 -29,7 ±0,33
C16:1 Methyl palmitoleate -22,5 ±0,35 -27,6 ±0,46 -27,9 ±0,61
C18:0 Methyl stearate -21,6 ±0,71 -27,2 ±0,50 -29,0 ±0,10
C18:1 Methyl oleate -21,8 ±0,74 -27,5 ±0,54 -27,8 ±0,51
C18:2 Methyl linoleate -23,4 ±0,36 -30,9 ±2.64 -28,3 ±0,44
C18:3 Methyl linolenate -33,1 ±0,58 -28,3 ±3,37 -39,5 ±3,35
17/22
Maize
Cassava
Teak
Preliminary results
Identification of fatty acids which are present in
all investigated soil and sediment samples
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Maize
Cassava
Teak
Preliminary results
C M T
24
26
28
30
C M T
25
30
35
40
45
Cassava Maize Teak Cassava Maize Teak
δ1
3C
(‰
)
C16:0 C18:3
Selection of suites of δ13C - FAME marker with
significant differences - Tukey HSD (Honest
Significant Difference)
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Preliminary results
Proportional contributions of potential sources
estimated by SIAR
0.0
0.2
0.4
0.6
0.8
1.0
Proportions by group: 1
Source
Pro
po
rtio
n
M T C
0.0
0.2
0.4
0.6
0.8
1.0
Proportions by group: 1
Source
Pro
po
rtio
n
M T C
0.0
0.2
0.4
0.6
0.8
1.0
Proportions by group: 1
Source
Pro
po
rtio
n
M T CCassava Maize Teak
Sediment A
Cassava Maize Teak Cassava Maize Teak
Sediment C Sediment B
Pro
portion
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1. Different land uses show contrasting δ13C signatures for
identical soil fatty acids
2. At least one suite of marker with sufficient discriminatory
power exists to describe distinct isotopic fingerprint
profiles
promising for the use of the CSSI-FAME
approach in a small tropical watershed
20/21
Conclusions
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The Uplands Program SFB 564
Acknowledgements
Thank you for your attention