Abstract
The influence of the severity of soil heating on aluminium and iron leaching was analysed, as well as its relationship with the solubility of organic matter. For this purpose, laboratory experiments were carried out under microcosm conditions where unaltered soil blocks were submitted to thermal shock and subsequently to rainfall simulation (300 mm), collecting the surface (0 cm) and subsurface runoff (12 cm). Soil heating was carried out using infrared lamps reaching temperatures of 222 and 401 ºC at a depth of 1 cm, similar to those reached in moderate and high intensity fires respectively. The analysis of the drainage waters showed that the leaching of Al increased with the severity of the thermal shock, whereas for Fe perceptible effects were only seen at the highest temperature. Geochemical modelling with Visual MINTEQ indicated that Al and Fe were fundamentally mobilised and associated with dissolved organic matter. Weak interactions (electrostatic binding) predominated in the case of Al and strong interactions (bidentate complexes with dissolved organic matter) in the case of Fe. Only towards the end of the leaching experiment, when the concentration of dissolved organic carbon decreased, was there a perceptible mobility of Al and Fe in the inorganic form, in the subsurface leachate of the moderate temperature treatment.
Highlights
Forest fires cause drastic changes to the properties of the upper layers of soils affected by heat, altering their physical (Imeson et al 1992; Everett et al 1995; Robichaud 2000), chemical (Covington et al 1991; Naidu and Srivasuki 1994; Knicker et al 1996; Hernández et al 1997; Cancelo-González et al 2013) and biological characteristics (DeBano et al 1998; Prieto-Fernández et al 1998; Choromanska and DeLuca 2002; Carballas et al 2009; Díaz-Raviña et al 2010)
An extensive review of the works describing these effects on forest soils is found in Certini (2005), who states that severe fires, such as wildfires, generally have several negative effects on soil
Heating of a soil subjected to different severities of thermal shock (222 °C and 159.7 DH; 401 °C and 413.8 DH at 1 cm depth) under controlled conditions affects Al and Fe leaching when the heated soil is subjected to simulated rainfall
Summary
Forest fires cause drastic changes to the properties of the upper layers of soils affected by heat, altering their physical (Imeson et al 1992; Everett et al 1995; Robichaud 2000), chemical (Covington et al 1991; Naidu and Srivasuki 1994; Knicker et al 1996; Hernández et al 1997; Cancelo-González et al 2013) and biological characteristics (DeBano et al 1998; Prieto-Fernández et al 1998; Choromanska and DeLuca 2002; Carballas et al 2009; Díaz-Raviña et al 2010). An extensive review of the works describing these effects on forest soils is found in Certini (2005), who states that severe fires, such as wildfires, generally have several negative effects on soil. They cause significant removal of organic matter, deterioration of both structure and porosity, considerable loss of nutrients through volatilisation, ash entrapment in smoke columns, leaching and erosion, and a marked alteration of both quantity and specific composition of microbial and soil-dwelling invertebrate communities. Due to the effect of heating, soil organic matter (SOM) undergoes changes in its structure and properties (Almendros et al 1988; Alcañiz et al 1994; Fernández et al 1997; Guinto et al 1999). Ash plays an important role in the recovery of these burnt areas as it acts as a reserve of available nutrients for plant growth (Úbeda et al 2009; Pereira et al 2011a, 2011b; Pereira et al 2012)
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