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| Titel |
Assessment of methods for organic and inorganic carbon quantification in carbonate-containing Mediterranean soils |
| VerfasserIn |
Marcos Apesteguia, Iñigo Virto, Alain Plante |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094641
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| Publikation (Nr.) |
 EGU/EGU2014-10067.pdf |
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| Zusammenfassung |
| Quantification of soil organic matter (SOM) stocks and fluxes continues to be an important
endeavor in assessments of soil quality, and more broadly in assessments of ecosystem
functioning. The quantification of SOM in alkaline, carbonate-containing soils, such as those
found in Mediterranean areas, is complicated by the need to differentiate between organic
carbon (OC) and inorganic carbon (IC), which continues to present methodological
challenges. Acidification is frequently used to eliminate carbonates prior to soil OC
quantification, but when performed in the liquid phase, can promote the dissolution and loss
of a portion of the OC. Acid fumigation (AF) is increasingly preferred for carbonate removal,
but its effectiveness is difficult to assess using conventional elemental and isotopic analyses.
In addition, the potential effects of AF on SOM are not well characterized. The objective of
the current study was to apply a multi-method approach to determine the efficacy of
carbonate removal by AF and its effects on the residual SOM. We selected a set of 24
surface agricultural soils representing a large range of textures, SOM contents and
presumed carbonate contents. For each soil, OC was determined using wet combustion
(Walkley-Black) and IC was determined using the calcimeter method. Samples were then
subjected to elemental (total C) and isotopic (δ13C) analyses by dry combustion
using a Costech autoanalyzer coupled to a Thermo Finnigan Delta Plus isotope
ratio mass spectrometer (IRMS) before and after AF. IC was equated to total C
determined after fumigation, and OC was estimated as the different in total C before
and after AF. Samples were also subjected to ramped oxidation using a Netzsch
STA109 PC Luxx thermal analyzer coupled to a LICOR 820A infrared gas analyzer
(IRGA). Quantification of OC was performed using evolved gas analysis of CO2
(CO2-EGA) in the exothermic region 200-500°C associated with organic matter
combustion. IC was quantified by CO2-EGA in the endothermic region 500-800°C
associated with carbonate decomposition. Finally, changes in SOM composition
or structure were assessed qualitatively through observed changes in the shapes
of the exothermic regions of the CO2-EGA and DSC thermograms. Preliminary
results of the thermal analysis indicate that acid fumigation is a highly effective
method for soil carbonate removal, but also generates substantial changes in SOM
composition/structure. Overall, our multi-method approach provided an excellent means of
assessing methods for OC versus IC quantification in carbonate-containing Mediterranean
soils. |
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