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| Titel |
Wildfire Ash: Chemical Composition, Ash-Soil Interactions and Environmental Impacts |
| VerfasserIn |
Anna Brook, Seham Hamzi, Lea Wittenberg |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101570
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| Publikation (Nr.) |
 EGU/EGU2015-734.pdf |
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| Zusammenfassung |
| Of the five classical factors of soil formation, climate, parent material, topography, time,
organisms, and recently recognized human activity, it is the latter factor which discretely
includes fire and post-burn impact. However, it is considered that soil undergoing fire just
experience a temporary removal of the top organic horizon, thus slightly modified and often
labeled as ’temporarily disturbed’ soil or soil ’under restoration/rehabilitation’. In fact the
suggested seventh factor, post-burned produced ash, can act both dependently and
independently of the other soil forming factors (Levin et al., 2013; Certini 2013). They are
interdependent in cases where ash influences occur on time scales similar to ‘natural’ soil
formation (Keesstra et ai., 2014) such as changes in vegetation. On the other hand, in post-fire
areas a strong dependency is expected between soil–water retention mechanism, climate and
topography.
Wild-land fires exert many changes on the physical, chemical, mineralogical,
biological, and morphological properties of soil that, in turn, affect the soil‘s hydrology
and nutrient flux, modifying its ability to support vegetation and resist erosion.
The ash produced by forest fires is a complex mixture composed of organic and
inorganic particles characterized by vary physical-chemical and morphological
properties.
The importance of this study is straightforwardly related to the frequency and large-scales
wildfires in Mediterranean region. In fact, wildfires are major environmental and land
management concern in the world, where the number and severity of wildfires has increased
during the past decades (Bodi, 2013). Certini (2013) assumed that cumulatively all of
the vegetated land is burned in about 31 years annually affecting 330–430 Mha
(over 3% of the Earth’s surface) and wide range of land cover types worldwide
including forests, peatlands, shrublands and grasslands. Whereas, the fire is identified
as an important factor in soil formation, the produced ash has significant and not
always constructive pedological, ecological, hydrological and geomorphological
effects and impacts (Shakesby, 2011). Abundant scientific information is assembled
either from control fires by collecting samples before and after wildfire event, or
conducting laboratory experiments exanimating data under truly isolated conditions
(Lugassi et al., 2013). However, an integration and synthesis of the knowledge
about ash including deeper understanding of inter-correlation between chemical,
physical and morphological compounds in open post-burn environment and its
possible interactions in soil formation or impact on soil composition are highly
needed.
The main aim of the presented study was to advance the science of soil-fire relationship
by recognizing the remains ash as a new soil-forming factor, on par with the traditionally
recognized factors: parent material, topography, time, climate, organisms, and recently
recognized human activity as the sixth factor. This research was conducted to develop new
methods to assess impacts and quantify the contributions/influences of post-fire products,
mainly ash, on soil composition and soil properties in post-burned environment. We
conducted several controlled experiments using 40 soil samples (typical Mediterranean
Rendzina soil, pH 6.84, a grayish-brown, humus- and free calcium carbonate- rich,
intra-zonal). The samples include bare soils and different types and loads of forest litter, were
exposed to different temperatures (200Ë C, 400Ë C and 600Ë C) in a muffle furnace for 2
hours (Pereira et al. 2011) as fire temperature plays a key role in determining ash
properties. The ash produced at a low temperatures (50%
carbon and retains many of the structural characteristics of the parent material. At
higher temperatures, the residue ash is greyish, consisted of very fine particles that
preserve almost none of the original structural characteristics of the fuel (Woods
and Balfour, 2008) creating gradient of layered ash with diverse physicochemical
properties.
The obtained post-burned soils were processed as following: 1. loss of mass (ML); 2. ash
layers sampling – the produced ash layers were collected separately; 3. grinding; 4. color –
the Munsell colour chart; 5. spectroscopy– each sample was analysed by two spectrometer,
first is the Ocean Optics USB4000 (0.35-1.05 μm) portable system across visible and near
infrared (VNIR) region using contact Halogen illumination, second is the Bruker Tensor II
(2.35-25 μm) across mid infrared (MIR) region by Furrier transform IR (FTIR) system using
the Pike EasiDiff diffuse reflectance spectroscopy (DRS) optical bench; 6. pH and electrical
conductivity (EC) including total dissolve solids (TDS) and salinity (S) measurements. The
result of high concentration of carbonates, oxides, and hydroxides of basic cations decreasing
EC levels caused by high pH (>8) there the CaCO3 surfaces are negatively charged and
variation of mineralogical composition introducing very detailed list of minerals (high
concentration of Nickeline NiAs, Cuprite Cu2O, Rehodochrosite MnCO3 and Nitrolite
Na2Al2Si3O102H2O in the top-layers and mixtures e.g. Kaolinite/Smectite (85%
Kaol.) Al2Si2O5(OH)4+(Na,Ca)0.33(Al,Mg)2Si4O10(OH)2nH2O and Mesolite +
Hydroxyapophyllite Na2Ca2Al6Si9O308H2O + KCa4Si8O20(OH,F)8H2O between ash and
post-burn top-soil layers.
Bodí M.B., Muñoz-Santa I., Armero C., Doerr S.H., Mataix-Solera J., Cerdà A., 2013.
Spatial and temporal variations of water repellency and probability of its occurrence in
calcareous Mediterranean rangeland soils affected by fires. Catena, vol. 108, pp.
14-24.
Certini G., Scalenghe R., Woods W.W., 2013. The impact of warfare on the soil
environment. Earth-Science Reviews, vol. 127, pp. 1-15.
Keesstra S.D., Temme A.J.A.M., Schoorl J.M., Visser S.M., 2014. Evaluating the
hydrological component of new catchment-scale sediment delivery model LAPSUS-D.
Geomorphology, vol. 212, pp. 97-107.
Levin N., Levental S., Morag H., 2013. The effect of wildfires on vegetation cover and
dune activity in Australia’s desert dunes: a multisensor analysis International Journal of
Wildland Fire, vol. 21 (4), pp. 459-475.
Lugassi R., Ben-Dor E., Eshel G., 2013. Reflectance spectroscopy of soils
post-heating—Assessing thermal alterations in soil minerals. Geoderma, vol. 231, pp.
268–279.
Pereira P., Úbeda X., Martin D., Mataix-Solera J., Guerrero C. 2011. Effects of a low
prescribed fire in ash water soluble elements in a Cork Oak (Quercus suber) forest
located in Northeast of Iberian Peninsula, Environmental Research, vol. 111(2), pp.
237–247.
Shakesby R.A., 2011. Post-wildfire soil erosion in the Mediterranean: Review and future
research directions Earth Science Reviews, vol. 105, pp. 71-100.
Woods, S.W., Balfour, V.N. 2010. The effects of soil texture and ash thickness on the
post-fire hydrological response from ash-covered soils, Journal of Hydrology, vol. 393, pp.
274–286. |
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