Effect of burning temperature on water repellency and aggregate stability in forest soils under laboratory conditions

Two forest soils rich in organic matter but differing in texture (sandy loam and silty loam) were heated under controlled laboratory conditions in order to examine the consequences of the heating effect that accompanies the passage of a fire on the physical properties of soil. Three samples of both soils were heated for 30 min in a muffle furnace at temperatures of 25, 170, 220, 380 and 460°C. At each temperature, the following parameters were determined: dry aggregate size distribution, water aggregate stability, total porosity, pore size distribution, water repellency and hydraulic conductivity. Heating the soils at 170 and 220°C caused no significant changes in aggregate size distribution or total porosity but increased water aggregate stability and the volume of pores 0.2–30 μm. Also, increased water repellency and strongly decreased the hydraulic conductivity. All parameters underwent much more dramatic changes at 380 and 460°C that can be ascribed to the combustion of organic matter. At such temperatures, water repellency was destroyed and the low hydraulic conductivity can be attributed to the aggregate breakdown observed under dry and wet conditions.

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Role of water repellency in aggregate stability of cultivated soils under simulated raindrop impact

Eurasian Soil Science ◽

10.1134/s1064229315070054 ◽

2015 ◽

Vol 48 (7) ◽

pp. 754-758 ◽

Cited By ~ 6

Author(s):

Lucia Kořenková ◽

Peter Matúš

Keyword(s):

Aggregate Stability ◽

Water Repellency ◽

Raindrop Impact ◽

Cultivated Soils

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Effects of a Canary pine forest wildfire (Tenerife, Canary Islands, summer 2007) on selected soil properties and their relationship with short- to medium-term soil water repellency .

Spanish Journal of Soil Science ◽

10.3232/sjss.2013.v3.n1.04 ◽

2014 ◽

Vol 2 ◽

Author(s):

Alexis Hernández ◽

Natalia Rodríguez ◽

Marcelino del Arco ◽

Carmen Dolores Arbelo ◽

Jesús Notario del Pino ◽

...

Keyword(s):

Soil Properties ◽

Soil Water ◽

Forest Fires ◽

Sampling Site ◽

Aggregate Stability ◽

Water Repellency ◽

Pine Forest ◽

Soil Water Repellency ◽

Soil Hydrophobicity ◽

The Impact

Forest fires modify the soil environment, often triggering severe soil degradation. In this paper, we studied the impact of a large northern Tenerife Canariy pine forest wildfire on a set of relevant soil properties, focusing on their evolution in time and relationship with soil water repellency. To do this, soils were sampled at four sites (burned and non-burned) and several soil physical and chemical parameters were measured. The results show significant variations for soil pH, electric conductivity (CE1:5), and NH4+-N between burned and non-burned samples, whereas non-significant increases were found in burned soils for oxidizable carbon (Cox), total nitrogen (Ntot) , Ca2+, Mg2+, Na+ and K+, and soil hydrophobicity. The differences caused by the fire were no longer evident one year later. Furthermore, in one sampling site (Vitric Leptosols under low pine forest with a mixed heath/beech tree understory) a wide variation in the content of Cox and Ntot and high water repellency was observed relative to the other sites. These differences can be attributed to the composition of the understory vegetation. Significant correlations between soil hydrophobicity with CE1:5, aggregate stability and the contents of Cox, Ntot, NH4+-N, Ca2+, Mg2+, Na+ and K+ were found.

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Wildfires in Grasslands and Shrublands: A Review of Impacts on Vegetation, Soil, Hydrology, and Geomorphology

Water ◽

10.3390/w11051042 ◽

2019 ◽

Vol 11 (5) ◽

pp. 1042 ◽

Cited By ~ 4

Author(s):

Ilan Stavi

Keyword(s):

Environmental Sustainability ◽

Ground Surface ◽

Aggregate Stability ◽

Water Repellency ◽

Livestock Grazing ◽

Moderate Intensity ◽

Structure Stability ◽

Water Runoff ◽

Ash Deposition ◽

Soil Aggregate Stability

Wildfires are prevalent in grasslands and shrublands. The objective of this study is to provide land managers with a general overview, by assessing the main impacts of wildfire, including those on plant communities (e.g., secondary succession and species invasion), soil characteristics (e.g., water repellency (hydrophobicity), aggregation and structure stability, and contents of organic carbon and nutrients), and surface processes (e.g., ash deposition, ground surface clogging, water runoff, soil erosion, hillslope debris flow, and dry ravel). Additionally, the study discusses the effects of livestock grazing on the functioning of post-fire grasslands and shrublands. Although mesic regions are mentioned, this review focuses on drylands. The comparatively low-to-moderate fuel loads that characterize grasslands and shrublands generate wildfires of relatively moderate intensity, resulting in moderate burn severity. Yet, it seems that because of decreased soil aggregate stability following burning, the hoof action of livestock that access burnt lands shortly after the fire increases the shearing and detachment of mineral material from the ground surface; this increases soil erodibility, with the possible risk of accelerated land degradation. The review ends with an assessment of general implications for environmental sustainability and health, and provides recommendations on wildfire control in rangelands, and on restoration of burnt lands.

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Does drought alter hydrological functions in forest soils?

Hydrology and Earth System Sciences ◽

10.5194/hess-20-1301-2016 ◽

2016 ◽

Vol 20 (3) ◽

pp. 1301-1317 ◽

Cited By ~ 11

Author(s):

Katharina F. Gimbel ◽

Heike Puhlmann ◽

Markus Weiler

Keyword(s):

Forest Soils ◽

Preferential Flow ◽

Water Drop ◽

Coniferous Forest ◽

Water Repellency ◽

Climatic Conditions ◽

Antecedent Soil Moisture ◽

Dye Tracer ◽

Infiltration Behavior ◽

Tracer Experiments

Abstract. Climate change is expected to impact the water cycle and severely affect precipitation patterns across central Europe and in other parts of the world, leading to more frequent and severe droughts. Usually when projecting drought impacts on hydrological systems, it is assumed that system properties, like soil properties, remain stable and will not be affected by drought events. To study if this assumption is appropriate, we address the effects of drought on the infiltration behavior of forest soils using dye tracer experiments on six sites in three regions across Germany, which were forced into drought conditions. The sites cover clayey-, loamy- and sandy-textured soils. In each region, we compared a deciduous and a coniferous forest stand to address differences between the main tree species. The results of the dye tracer experiments show clear evidence for changes in infiltration behavior at the sites. The infiltration changed at the clayey plots from regular and homogeneous flow to fast preferential flow. Similar behavior was observed at the loamy plots, where large areas in the upper layers remained dry, displaying signs of strong water repellency. This was confirmed by water drop penetration time (WDPT) tests, which revealed, in all except one plot, moderate to severe water repellency. Water repellency was also accountable for the change of regular infiltration to fingered flow in the sandy soils. The results of this study suggest that the drought history or, more generally, the climatic conditions of a soil in the past are more important than the actual antecedent soil moisture status regarding hydrophobicity and infiltration behavior; furthermore, drought effects on infiltration need to be considered in hydrological models to obtain realistic predictions concerning water quality and quantity in runoff and groundwater recharge.

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How are mineral and organic phases regulating burning-induced soil water repellency? Unravelling the crucial dynamics occurring in the Alps even at moderate fire intensities.

10.5194/egusphere-egu21-3533 ◽

2021 ◽

Author(s):

Sara Negri ◽

Beatrice Giannetta ◽

Daniel Said-Pullicino ◽

Luisella Celi ◽

Eleonora Bonifacio

Keyword(s):

Water Drop ◽

Aggregate Stability ◽

Water Repellency ◽

Beech Forest ◽

Mineral Surfaces ◽

Litter Cover ◽

Coarse Texture ◽

Fe Speciation ◽

Ft Ir ◽

Terrestrial Biomes

Wildfires play the role of ecosystem shapers in the majority of terrestrial biomes, altering canopy and litter cover and imposing strong modifications on soils. Organic matter (OM) content and composition, mineralogy, pH, aggregate stability and water repellency (WR) are among the main edaphic properties to be affected by heat. Various studies dealt with occurrence, extent and persistence of burning-induced soil WR, but the dynamics at the basis of its formation (and loss) are still widely unclear. In addition, the vast majority of research on this topic has been carried out in the Mediterranean, even if alpine environments are far from being untouched by fires. Our aims were therefore to provide insight into the key mechanisms regulating WR thermal alterations in a relatively understudied environment.Our sampling design aimed at collecting soils representative of the Western Italian Alps. Charring was simulated in the lab, at increasing temperatures (up to 300&#176; C), on a set of A soil horizons developed under pine and beech forest covers. Water drop penetration time (WDPT) was employed to test WR persistence. Soils were analyzed in terms of organic carbon (OC) and nitrogen contents, pH, texture and iron (Fe) oxides composition (Fe-DCB and Fe-pyrophosphate extracted). Fe-speciation and OM composition of some selected samples were further characterized using Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and Fourier transform-infra red (FT-IR) spectroscopy, respectively.WR was found to be extremely variable, event at room temperature. For samples exhibiting an increase in WR upon burning intensity, maximum repellency was observed at 200&#176; C. OC abundance (%) and coarse texture were found to be the main drivers of hydrophobicity in soil. WR was drastically lost when samples were exposed to temperatures higher than 200&#176;C. Above this threshold, pH systematically increased and OC (%) sharply decreased. The increasingly negative charge of mineral surfaces, mirrored by pH increase, seems to result in a significant C volatilization by OM desorption, eventually leading to a super-hydrophilic behavior in soil.Fe EXAFS allowed to evaluate different thermal-dictated pathways of Fe-speciation. The formation of more crystalline Fe-forms (e.g. hematite, meghemite) was observed above 200&#176; C. Even though a reduction in surface area should be expected when observing an increase in crystallization degree (potentially giving rise to greater WR), OM adhesion to mineral surfaces seems to be inhibited by the change induced in their charge. A reduction in the OM-bound Fe pool (pyrophosphate extracted) above 200&#176; C could be appreciated, supporting the interpretation of oxy-hydroxides transformations and OC (%) loss. &#160;The current investigation has been carried out to capture an in-depth picture of wildfire impacts on alpine soils, targeting factors responsible for WR enhancement and shred. Identifying the mechanisms regulating wildfire-related WR is a key issue, as the formation of hydrophobic layers in soil highly favors its erosion. Addressing such matters is crucial to tackle the issue of ecosystems recovery, considering that climate-change-related alterations in wildfires regimes are already causing the occurrence of more frequent and disruptive fires.

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