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SOIL PHYSICS

Application of Thermal Analysis to Elucidate Water-Repellency Changes in Heated Soils

^a Dep. of Soil Science, Faculty of Natural Sciences, Comenius Univ., Mlynska dolina B-2, 842 15 Bratislava, Slovak Republic
^b Dep. of Geography, Univ. of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
^c CSIRO Land & Water, GPO Box 1666, Canberra ATC 2601, Australia
^d Institute of Chemistry, Slovak Academy of Sciences, Dubravska cesta 9, 845 38 Bratislava, Slovak Republic
^e Institute of Landscape Ecology, Slovak Academy of Sciences, Stefanikova 3, 81499 Bratislava, Slovak Republic
^f GEA– Grupo de Edafología Ambiental, Dep. of Agrochemistry and Environment, Univ. Miguel Hernández, Avda de la Universidad s/n, E-03202 Elche, Alicante, Spain

^* Corresponding author (dlapa{at}fns.uniba.sk).

It is well established that during wildfires, the volatilization and condensation of hydrophobic compounds, as well as the thermal energy input itself, can markedly change the wettability of soils. This study evaluated the effects of thermal energy input on soil water repellency of sandy forest soils from Slovakia and explored the processes underlying the changes observed using thermal analysis. Initial sample water drop penetration time values ranged from <1 to >43,200 s. Heating induced distinct increases in water repellency to >3600 s in most samples, with its elimination occurring at 175°C or higher. The thermal analysis allowed evaluation of the relationship between the destruction of soil water repellency and thermal changes affecting soil organic matter (SOM). Differences in the thermal resistance of soil water repellency correspond to the thermal stability of SOM. Kinetic analysis showed that water repellency elimination due to soil heating is linked with thermal decomposition of a more thermally labile pool of SOM. The results suggest that under nonisothermal conditions, the degree of SOM decomposition depends on both the soil temperature reached and the soil heating rate. The temperature at which a certain level of SOM decomposition is reached increases with increasing heating rate. Heating experiments and the kinetic evaluation of thermogravimetric data for isothermal conditions also demonstrated an exponential relationship between heating durations and temperature thresholds.

Abbreviations: DTA, differential thermal analysis • DTG, derivative thermogravimetric analysis • SOM, soil organic matter • TGA, thermogravimetric analysis • WDPT, water drop penetration time