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| Titel |
A sequential extraction and hydrolysis approach to understand the chemical nature of soil water repellency |
| VerfasserIn |
Jiefei Mao, Stefan C. Dekker, Klaas G. J. Nierop |
| 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 |
250089274
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| Publikation (Nr.) |
 EGU/EGU2014-3471.pdf |
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| Zusammenfassung |
| Soil water repellency (SWR) biomarkers (SWR-biomarkers) are defined as hydrophobic
organic compounds in soils causing SWR and originating from vegetation or microbes (Doerr
et al., 2000). Free lipids and ester-bound biopolymers (cutins and suberins) are usually seen
in the aliphatic part of soil organic matter (SOM) (Nierop, 1998). The method of sequential
extraction can divide hydrophobic compounds into individual fractions with different
characteristics.
We aim to find out the SWR-biomarkers in soils within different fractions, investigate the
effects of fractions on SWR and link them to their original sources. To extract free and
ester-bound lipids from sandy soils, DCM (dichloromethane)/MeOH (methanol) and
IPA(isopropanol)/NH3 were used in sequential steps. As a result, three fractions were
obtained during these sequential experiments: a DCM/MeOH soluble fraction (D), a
DCM-MeOH soluble (AS) fraction of IPA/NH3 extracts and its insoluble (AI) fraction. To
date, research was limited to (organic) extractable fractions only. To investigate
the DCM-MeOH insoluble part of IPA/NH3 extracts they were depolymerised by
trans-methylation using BF3-MeOH. All fractions were analysed by gas chromatography-mass
spectrometry.
After DCM/MeOH extraction, water repellency of 80% of the soils studied increased
while SWR of the other soils remained at the same level. Straight-chain fatty acids, alcohols
and alkanes were the main compound groups in the D fractions. The distribution of fatty
acids (C20-C32) and alcohols (C20-C32), both of which with an even-over-odd predominance
suggest their source were higher plants, and so did the odd-over-even predominated alkanes.
After extraction by IPA/NH3 , most soils became non-repellent. Both fatty acids (C16-C32)
and alcohols (C16-C30) with an even-over-odd predominance were also found in the AS
fractions, whereas no alkanes were detected. There were four main component
groups identified in the AI fractions: fatty acids, alcohols, Ï-hydroxy fatty acids
and α,Ï-dicarboxylic acids. Aside from fatty acids and alcohols, the latter two
compound groups were considered as the main groups of monomers released from
suberins. Therefore, suberin-derived compounds were most abundant in the AI
fractions suggesting that plant roots could be the main source of AI fractions. We
will present some of the relations between fractions/compounds and SWR to show
that this approach may be an effective tool to improve our understanding of SWR
mechanisms.
We present relations between fractions/compounds from SOM with SWR to determine
SWR-biomarkers. By assessing the origin of these biomarkers, we are able to understand how
SWR is formed and in which circumstances they are mainly from leaves or roots (i.e. cutin or
suberin).
References:
Doerr, S.H., Shakesby, R.A., Walsh, R.P.D., 2000. Soil water repellency: its
causes, characteristics and hydro- geomorphological significance. Earth-Sci. Rev. 51,
33–65.
Nierop, K.G.J., 1998. Origin of aliphatic compounds in a forest soil. Organic
Geochemistry 29, 1009–1016. |
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