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. Brandt a , F. Rasche a , H. Fröhlich a , N.T. Lam b , T. D. Vien b and G. Cadisch a 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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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
1. Problem definition
2. Concept of CSSI
3. Objectives
4. Study area
5. Preliminary results
6. Conclusion
2/21
Contents
Land degradation in
South East Asia
Population pressure
Agricultural commercialization
Deforestation
Expansive maize production
From traditional shifting
cultivation systems to
continuous monocropping
Problem definition
3/21
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
4/21
Problem definition
Maize Teak
Cassava
Bamboo
Mix of different
sources
Which are the hot spots of
critical land degradation?
5/21
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
6/21
Problem definition
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 (‰)
7/21
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
8/21
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
9/21
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
10/21
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
11/21
Are CSSI and CSSI-based mixing models applicable to
identify and trace SOC source/sink relationships in a