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.
Kořenková L., Šimkovic I., Dlapa P., Juráni B., Matúš P. (2015): Identifying the origin of soil water repellency at regional level using multiple soil characteristics: The White Carpathians and Myjavska pahorkatina Upland case study. Soil & Water Res., This paper evaluates the relationship between water repellency and multiple characteristics of topsoil samples belonging to seven Reference Soil Groups, taken from the area of the White Carpathians and the Myjavska pahorkatina Upland. In order to quantify water repellency, the Water Drop Penetration Time test and the Molarity of an Ethanol Droplet test were performed on 210 soil samples. The water repellency data were confronted with a number of categorical and numerical soil variables. It was observed that the particular land-use type and the nature of soil parent material, both are related towards detected water repellency of soil samples. All samples taken from the agricultural (tilled) and grassland soils were wettable. On the contrary, all samples which exhibited water repellency, belonged to the group of forest soils, although, not all forest soils were water repellent. Samples which showed considerable repellency were soils developed either on consolidated sedimentary rocks (sandstones, limestone-dolomitic rocks, flysch) or unconsolidated sediments of aeolic or polygenetic origin. On the other hand, the great majority of soils developed on recent alluvial deposits were clearly wettable. Correlation and regression analyses showed that susceptibility of forest topsoil to exhibit water repellency generally increases with increasing sand and organic carbon contents, and with a simultaneous decrease of soil pH value. An interesting observation came out regarding CaCO 3 and water repellency relation. Although certain soils with higher CaCO 3 exhibited water repellency (Rendzic Leptosols and Cambisols), all soils that developed on loose sediments and contained CaCO 3 were wettable.
Soil hydraulic properties are very sensitive to land-use in regions susceptible to physical degradation. Intensive agricultural practices often lead to soil compaction and erosion in the investigated area. The main goal of this paper was to evaluate the impact of land-use on the pore size distribution and water retention in loamy soils. The soil water retention curve (SWRC) combined the total porosity and the water retention of the undisturbed sample at 3, 10, 31, 100, 310, and 1000 hPa suctions and the disturbed sample at 1.5 MPa. The triple-exponential model approximated the curve's course, and its derivative defined the distinct macro-, structural, and textural pore maxima, with characteristic suctions corresponding to SWRC inflection points. The soil organic carbon content had the greatest influence on the content of all three pore classes. The water retention properties followed the hierarchical pore size distribution in the four research plots and decreased in the identical orchard > forest > grassland > arable soil order. These results show that the orchard and forest areas are the most appropriate land uses with respect to porosity and water retention, while the grassland has not fully recovered after its conversion from arable soil and remains relatively poor, and the arable soil properties are the worst.
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