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| Titel |
Formation of Soil Water Repellency by Laboratory Burning and Its Effect on Soil Evaporation |
| VerfasserIn |
Sujung Ahn, Sangjun Im |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032823
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| Zusammenfassung |
| Fire-induced soil water repellency can vary with burning conditions, and may lead to
significant changes in soil hydraulic properties. However, isolation of the effects of soil water
repellency from other factors is difficult, particularly under field conditions. This study was
conducted to (i) investigate the effects of burning using different plant leaf materials and (ii)
of different burning conditions on the formation of soil water repellency, and (iii) isolate the
effects of the resulting soil water repellency on soil evaporation from other factors. Burning
treatments were performed on the surface of homogeneous fully wettable sand soil
contained in a steel frame (60 x 60 cm; 40 cm depth). As controls a sample without
a heat treatment, and a heated sample without fuel, were also used. Ignition and
heat treatments were carried out with a gas torch. For comparing the effects of
different burning conditions, fuel types included oven-dried pine needles (fresh
needles of Pinus densiflora), pine needle litter (litter on a coniferous forest floor, P.
densiflora + P. rigida), and broad-leaf litter (Quercus mongolica + Q. aliena + Prunus
serrulata var. spontanea + other species); fuel loads were 200 g, 300 g, and 500 g;
and heating duration was 40 s, 90 s and 180 s. The heating duration was adjusted
to control the temperature, based on previous experiments. The temperature was
measured continuously at 3-second intervals and logged with two thermometers.
After burning, undisturbed soil columns were sampled for subsequent experiments.
Water Drop Penetration Time (WDPT) test was performed at every 1 mm depth of
the soil columns to measure the severity of soil water repellency and its vertical
extent.
Soil water repellency was detected following all treatments. As the duration of heating
increased, the thickness of the water repellent layer increased, whilst the severity of soil
water repellency decreased. As regards fuel amount, the most severe soil water
repellency was formed at a fuel load of 300 g. Pine needle litter formed the most
severe soil water repellency and fresh pine needle formed the thickest water repellent
layer, whilst broad-leaf litter did only cause water repellency on the surface of the
sand.
The soil evaporation rate was measured by a gravitational method at an isothermal
condition. Undisturbed soil columns were sealed after adding 50 ml of tap water through the
bottom. After twelve hours of stabilization, the columns were opened and covered with filter
paper. The rate of soil evaporation through the soil surface was measured by the hourly
weight change at 45Ë C. The initial 65 hours’ evaporation rate was analyzed, while the slope
of cumulative evaporation over time maintained its linearity. It was found that as the thickness
of the water repellent layer increased, the evaporation rate tended to decrease. These two
variables showed a good correlation (Pearson’s correlation coefficient =-0.8916,
p=0.0170) and a large coefficient of determination (R2=0.795) in the linear regression.
This suggests that a layer of water repellent soil can affect water evaporation rate
and that the rate is negatively correlated with the thickness of the repellent layer. |
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