Temporal fluctuations in soil water repellency following wildfire in chaparral steeplands, southern California

2005 ◽  
Vol 14 (4) ◽  
pp. 439 ◽  
Author(s):  
K. R. Hubbert ◽  
V. Oriol
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Water Repellency ◽  
Weather Conditions ◽  
Antecedent Rainfall ◽  
Soil Water Repellency ◽  
Soil Wetness ◽  
Moisture Conditions ◽  
East West ◽  
Seasonal Weather

Soil water repellency is particularly common in unburned chaparral, and its degree and duration can be influenced by seasonal weather conditions. Water repellency tends to increase in dry soils, while it decreases or vanishes following precipitation or extended periods of soil moisture. The 15 426 ha Williams Fire provided an opportunity to investigate post-fire fluctuations in water repellency over a 1-year period. Soil water repellency was measured at the surface, and at 2-cm and 4-cm depths along six east–west-positioned transects located within the chaparral-dominated San Dimas Experimental Forest. During the winter and spring, seasonal variation in the degree of surface water repellency appeared to be inversely proportional to antecedent rainfall and soil moisture conditions. Precipitation through December reduced the proportion of surface ‘moderate or higher repellency’ from 49 to 4% as soil wetness increased to 12%. Throughout the summer, soil wetness remained below 2%; however, surface soils remained ‘wettable’, with the proportion of surface ‘moderate or higher repellency’ never returning to the early post-fire amount of 47%. Interestingly, at the 4-cm depth, the proportion of ‘moderate or higher repellency’ remained at levels >25% throughout the summer dry season.

scholarly journals Spatially variable soil water repellency enhances soil respiration rates (CO<sub>2</sub> efflux)

2017 ◽  
Author(s):  
Emilia Urbanek ◽  
Stefan H. Doerr
Keyword(s):  
Soil Moisture ◽  
Soil Respiration ◽  
Soil Water ◽  
Water Distribution ◽  
Preferential Flow ◽  
Water Repellency ◽  
Water Repellent ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Soil Water Repellency

Abstract. Soil CO2 emissions are strongly dependent on water distribution in soil pores, which in turn can be affected by soil water repellency (SWR; hydrophobicity). SWR restricts infiltration and movement of water, affecting soil hydrology as well as biological and chemical processes. Effects of SWR on soil carbon dynamics and specifically on soil respiration (CO2 efflux) have been studied in a few laboratory experiments but they remain poorly understood. Existing studies suggest that soil respiration is reduced in water repellent soils, but the responses of soil CO2 efflux to varying water distribution created by SWR are not yet known. Here we report on the first field-based study that tests whether soil water repellency indeed reduces soil respiration, based on in situ field measurements carried out over three consecutive years at a grassland and pine forest site under the humid temperate climate of the UK. CO2 efflux was reduced on occasions when soil exhibited consistently high SWR and low soil moisture following long dry spells. However, the highest respiration rates occurred not when SWR was absent, but when SWR, and thus soil moisture, was spatially patchy, a pattern observed for the majority of the measurement period. This somewhat surprising phenomenon can be explained by SWR-induced preferential flow, directing water and nutrients to microorganisms decomposing organic matter concentrated in hot spots near preferential flow paths. Water repellent zones provide air-filled pathways through the soil, which facilitate soil-atmosphere O2 and CO2 exchanges. This study demonstrates that SWR have contrasting effects on CO2 fluxes and, when spatially-variable, can enhance CO2 efflux. Spatial variability in SWR and associated soil moisture distribution needs to be considered when evaluating the effects of SWR on soil carbon dynamics under current and predicted future climatic conditions.

Quantifying the effect of post-wildfire soil water repellency on runoff

2021 ◽  
Author(s):  
Rose Shillito ◽  
Markus Berli ◽  
Ian Floyd ◽  
Li Chen ◽  
Teamrat Ghezzehei
Keyword(s):  
Soil Water ◽  
Water Repellency ◽  
Silica Sand ◽  
Watershed Model ◽  
Soil Water Repellency ◽  
Physically Based Model ◽  
San Gabriel Mountains ◽  
Physically Based ◽  
Dry Soil ◽  
Moisture Conditions

&lt;p&gt;Several factors are believed to contribute to post-wildfire flooding and debris flows. One contributing factor&amp;#8212;the occurrence of post-wildfire soil water repellency&amp;#8212;lacks a quantitative mechanism to incorporate the effects in physically-based runoff models. For this study, a physically-based model was developed linking the contact angle (degree of water repellency) to sorptivity. The model was verified in laboratory experiments using a silica sand proxy. The effects of water repellency on infiltration were illustrated. Further, the effect of water repellency on runoff was simulated using the AGWA-KINEROS2 watershed model with data from rainfall following the 2009 Station fire in the San Gabriel Mountains of southern California, USA. Results show water repellency has a quantifiable effect on runoff production, an effect enhanced by the dry soil moisture conditions common after wildfires.&lt;/p&gt;

Soil Water Repellency: A Method of Soil Moisture Sequestration in Pinyon-Juniper Woodland

2010 ◽  
Vol 74 (2) ◽  
pp. 624-634 ◽  
Author(s):  
David A. Robinson ◽  
Inma Lebron ◽  
Ronald J. Ryel ◽  
Scott B. Jones
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Water Repellency ◽  
Soil Water Repellency ◽  
Juniper Woodland

Soil water repellency under dry and wet antecedent weather conditions for selected land-cover types in the coastal zone of central Portugal

Soil Research ◽  
2005 ◽  
Vol 43 (3) ◽  
pp. 297 ◽  
Author(s):  
J. J. Keizer ◽  
C. O. A. Coelho ◽  
M. J. S. Matias ◽  
C. S. P. Domingues ◽  
A. J. D. Ferreira
Keyword(s):  
Land Cover ◽  
Soil Water ◽  
Arable Land ◽  
Late Summer ◽  
Soil Surface ◽  
Water Repellency ◽  
Weather Conditions ◽  
Individual Plant ◽  
Soil Water Repellency ◽  
Land Cover Types

This paper reports on the first systematic inventory of soil water repellency in Portuguese coastal dune sand areas. Since water repellency is widely associated with certain vegetation types or individual plant species, this inventory concerned arable land as well as 6 natural and semi-natural land-cover types representative for the vegetation zonation in the study area. Since water repellency further is a feature that commonly varies through time, disappearing when soils become wet, initial sampling was carried out during late summer 2000 and later repeated, at 1 of the 2 sites per land-cover type, during early spring 2001. Water repellency was principally measured in the field using the Molarity of an Ethanol Droplet (MED) test. Under the dry summer conditions, water repellency was a widespread phenomenon at and immediately below, the soil surface and numerous significant differences in ethanol classes existed between the land-cover types. The transient nature of water repellency was confirmed by many instances of significantly lower spring than summer ethanol classes. These significant differences were in general accompanied by a significant negative correlation of the summer and spring ethanol classes with volumetric soil moisture content. The sites’ overall repellency levels under dry antecedent weather conditions were significantly correlated with their overall levels of soil organic matter.

scholarly journals The Relationship between Soil Moisture and Soil Water Repellency Persistence in Hydrophobic Soils

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2322 ◽  
Author(s):  
Mohamed Bayad ◽  
Henry Wai Chau ◽  
Stephen Trolove ◽  
Jim Moir ◽  
Leo Condron ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Soil Water ◽  
Water Drop ◽  
Water Repellency ◽  
Soil Water Repellency ◽  
Sigmoidal Curve ◽  
New Equation ◽  
Two Parameters ◽  
The Relationship ◽  
Penetration Time

In this work, we modelled the response of soil water repellency (SWR) persistence to the decrease in moisture in drying soils, and we explored the implication of soil particle size distribution and specific surface area on the SWR severity and persistence. A new equation for the relationship between SWR persistence and soil moisture (θ) is described in this paper. The persistence of SWR was measured on ten different hydrophobic soils using water drop penetration time (WDPT) at decreasing levels of gravimetric water content. The actual repellency persistence showed a sigmoidal response to soil moisture decrease, where Ra(θ)=Rp/1+eδ(θ−θc). The suggested equation enables one to model the actual SWR persistence (Ra) using θ, the potential repellency (Rp) and two characteristic parameters related to the shape of the response curve. The two parameters are the critical soil moisture θc, where the Ra increase rate reaches its maximum, and the parameter δ affecting the steepness of the curve at the inflexion point of the sigmoidal curve. Data shows that both soil carbon and texture are controlling the potential SWR in New Zealand pastures.

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