Inferring changes in soil organic matter in post-wildfire soil burn severity levels in a temperate climate

Agustín Merino; María T Fonturbel; Cristina Fernández; Bruno Chávez-Vergara; Felipe García-Oliva; Jose A Vega

doi:10.1016/j.scitotenv.2018.01.189

Inferring changes in soil organic matter in post-wildfire soil burn severity levels in a temperate climate

Sci Total Environ. 2018 Jun 15:627:622-632. doi: 10.1016/j.scitotenv.2018.01.189. Epub 2018 Feb 3.

Authors

Agustín Merino¹, María T Fonturbel², Cristina Fernández³, Bruno Chávez-Vergara⁴, Felipe García-Oliva⁵, Jose A Vega⁶

Affiliations

¹ Unit of Sustainable Forest Management (Soil Science and Agricultural Chemistry), Escuela Politécnica Superior, Universidad de Santiago de Compostela, 27002 Lugo, Spain. Electronic address: agustin.merino@usc.es.
² Centro de Investigación Forestal. Lourizán, Consellería de Medio Rural, Xunta de Galicia, P.O. Box 127, 36080 Pontevedra, Spain. Electronic address: maria.teresa.fonturbel.lliteras@xunta.es.
³ Centro de Investigación Forestal. Lourizán, Consellería de Medio Rural, Xunta de Galicia, P.O. Box 127, 36080 Pontevedra, Spain.
⁴ Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, México, 58090 Morelia, Mexico; Departamento de Edafología, Instituto de Geología, Laboratorio Nacional de Geoquímica y Mineralogía (LANGEM), Universidad Nacional Autónoma de México, México, 04510 Ciudad de México, Mexico. Electronic address: chavezvb@geologia.unam.mx.
⁵ Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, México, 58090 Morelia, Mexico. Electronic address: fgarcia@cieco.unam.mx.
⁶ Centro de Investigación Forestal. Lourizán, Consellería de Medio Rural, Xunta de Galicia, P.O. Box 127, 36080 Pontevedra, Spain. Electronic address: jose.antonio.vega.hidalgo@xunta.es.

PMID: 29426186
DOI: 10.1016/j.scitotenv.2018.01.189

Abstract

Simple, rapid and reliable methods of assessing soil burn severity (SBS) are required in order to prioritize post-fire emergency stabilization actions. SBS proxies based on visual identification and changes in soil organic matter (SOM) content and quality can be related to other soil properties in order to determine the extent to which soil is perturbed following fire. This task is addressed in the present study by an approach involving the use of differential scanning calorimetry-thermogravimetric analysis (DSC-TGA) to determine changes in SOM generated in soils subjected to different levels of SBS. Intact topsoil monoliths comprising the organic horizons and the surface mineral soil (alumic-humic umbrisols) were collected from a representative P. pinaster stand in NW Spain. The monoliths were experimentally burned in a combustion wind tunnel to simulate different fire conditions (fuel bed comprising forest pine litter and wood; air flow, 0.6 m s^-1). Changes in OM properties in the soil organic layer and mineral soils samples (0-2 cm) at the different temperatures and SBS levels were identified. For both duff and mineral soil, the data revealed a temperature-induced increase in aromatic compounds and a concomitant decrease of carbohydrates and alkyl products. However, for a given temperature, the degree of carbonization/aromatization was lower in the mineral soil than in the duff, possibly due to the different composition of the OM and to the different combustion conditions. The low degree of aromatization of the organic matter suggests that this soil component could undergo subsequent biological degradation. SOM content and thermal recalcitrance (measured as T50) discriminated the SBS levels. Use of visual identification of SBS levels in combination with DSC-TGA enables rapid evaluation of the spatial variability of the effects of fire on SOM properties. This information is useful to predict soil degradation process and implement emergency soil stabilization techniques.

Keywords: (13)C NMR spectroscopy; Forest fire; SOM quality; Soil burn severity; Thermal analysis.