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Molecular descriptors of water repellency in forest fire affected soils. A chemometric approach

AuthorsJiménez Morillo, N. T. ; Almendros Martín, Gonzalo ; Zavala, Lorena M.; Jordán, A.; González-Vila, Francisco Javier ; González-Pérez, José Antonio
Issue Date3-Oct-2017
PublisherSociedad Española de Cromatografía y Técnicas Afines
Citation15 Jornadas de Análisis Instrumental 2017 3-5 Oct. (2017) Barcelona (Spain)
AbstractSoil water repellency (SWR), is a property of complex origin attributed to the accumulation and traslocation of hydrophobic compounds, mainly lipids [1, 2]. However, the extraction of soil lipids does not always suppress SWR and unextractable macromolecular fractions may also be responsible for SWR [3]. This may be the case with soils after wildfires, which alter SWR in different grades [4]. Burnt (B) and unburnt (UB) sandy soils under Quercus suber forest (Doñana National Park, Spain) were studied. SWR of bulk and of six size fractions were assessed by-droppenetration- time test (WDPT). The molecular composition of soil organic matter (SOM) was studied by analytical pyrolysis (Py-GC/MS). Partial least squares regression (PLS) was used to check whether SWR may be forecasted by total abundances of pyrolysis compounds and several indices were calculated to illustrate the extent to which individual compounds could be used as proxies for SWR, viz: a) factor loadings of PLS models, b) Pearson¿s R-squared coefficients, and c) subtraction of average values of samples with extreme WR values. The indices were represented as density surfaces in van Krevelen diagrams [5]. The PLS models for whole samples showed that SWR depends on SOM composition and that this can be predicted from pyrochromatographic data. Nonetheless, the significance of PLS models highly improved (P<0.01) when samples from UB and B soils were processed as independent sets which is interpreted as the structural factors associated with soil WR are different in B and UB samples. Pyrolysis compounds associated with SWR in UB soil, suggested an origin from fatty acids, peptides, carbohydrates and lignin. In contrast, B soil showed a prevalence of n-alkanes and aromatic compounds, and a lignin depletion. In general, SWR cannot be explained by few major compounds or compound families, but by several constituents, none of them having the control of the SWR alone. This suggest that SWR is a complex emergent property depending on characteristic patterns of compounds varying with the impact of fire. Therefore, the combination of pyrolysis with appropriate chemometric treatments is a valid and powerful approach to define crucial features of SWR which might have been oversimplified in classical studies focusing in extractable hydrophobic SOM constituents. References [1] A. Jordán, LM. Zavala, J. Mataix-Solera, et al. Catena 108 (2013) 1-8 [2] NT. Jiménez-Morillo, JA. González-Pérez, A. Jordán, et al. Land Degrad. Dev. 27 (2016) 1413-1423 [3] E. De Blas, M. Rodríguez-Alleres, G. Almendros. Geoderma 155 (2010) 242-248 [4] S.H. Doerr, RA. Shakesby, W.H. Blake, et al. J. Hydrol 319 (2006) 295-311 [5] G. Almendros, P. Tinoco, J.M. de la Rosa, et al. J. Soils Sediments (2017) (doi: 10.1007/s11368-016-1595)
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(MNCN) Comunicaciones congresos
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