Severity Of Soil Water Repellency Research Articles

Organic carbon and silt determining subcritical water repellency and field capacity of soils in arid and semi-arid region

Soil water repellency (SWR) is frequently observed in different types of land use and climates. Since SWR potentially enhances the difficulty of water infiltration in soil, the phenomenon can severely impact the water use of plants in arid regions. Therefore, understanding the origin of SWR is crucial in arid and semi-arid regions. This study investigated the fundamental and hydrological properties of soils in three arid ecosystems (desert, farmland, and forest). Analysis was done to determine any potential links between these properties, vegetation cover, and the severity of SWR. It was found that SWR was positively correlated with soil organic carbon (SOC), silt content, and field capacity of soil, where the SWR was in subcritical SWR range. The linear correlation and hierarchical clustering analysis confirmed that the SOC and silt content was the critical factor affecting the occurrence and persistence of SWR. The major source of organic carbon and nutrients to the soil was vegetation, which also had an impact on the distribution of soil carbon. The most striking observation was that the silt content was strongly correlated with both field capacity (r = 0.817, p = 0.001) and SWR (r = 0.710, p = 0.010), which can be attributed to the SOC on silt. In arid and semi-arid regions, the specific surface area of silt was relatively larger than that of sand. Meanwhile, compared to the clay in soil, the proportion of silt was much higher. The results imply that silt could significantly affect the soil hydrological properties and that silt content could serve as a new proxy for predicting water repellency in arid and semi-arid regions.

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

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.

Water repellency of soils on unpaved roads in coniferous forests

Forest roads play a crucial role in commercial forestry. Most of them are unpaved and exposed to increased surface runoff and the occurrence of soil erosion. Therefore, these roads constantly require repairs and maintenance, which are associated with the high cost of earthworks. Soil water repellency causes retardation of water infiltration into soil, which affects the generation of surface runoff, leading to the destruction of the active road layer. This phenomenon is well recognized in forest habitat soils, but poorly investigated in terms of soils constituting roads and communication routes. Therefore, the aims of this research were to determine the severity and persistence of potential water repellency in the case of soil collected from two unpaved roads in coniferous forest and to investigate the dependence between the severity of soil water repellency and its persistence. Soil samples (Dystric Brunic Arenosols) were collected from three points of the roadway, i.e., centre line, rut and roadside, from two different sites located in fresh coniferous and fresh mixed coniferous forest (Poland). The severity of soil water repellency was assessed, based on measured values of the wetting contact angle (Wilhelmy plate method) and the critical and 90° surface tensions. For this purpose, contact angle measurements of the solid phase, wetted by water–ethanol mixtures, were used and data results were analysed using the Zisman approach. The persistence of potential soil water repellency was assessed using the water drop penetration time test. The severity and persistence of soil water repellency depend on the forest habitat type surrounding the road and point locations on the road cross section. The soil samples collected from the roadside were more water repellent than samples taken from the centre line or rut. A strong relationship was found between the water drop penetration time and the advancing contact angle, the critical surface tension and the 90° surface tension.

The effect of biochar on severity of soil water repellency of crude oil-contaminated soil.

Crude oil contamination adversely affects soil water repellency. In this study the effect of biochar on this soil characteristic has been investigated in the laboratory. Soil sample was collected from a field located near Pars Oil Company, at the top depth of 0-15cm below surface. After air-drying and passing through a 2-mm sieve, the soil was artificially contaminated with four levels of crude oil (1:0, 1:25, 1:16.6, and 1:12.5 ratios). Biochars used in this research were generated from beechwood and maize residues at three different pyrolysis temperatures (350°C, 550°C, and 750°C). Chemical functionality of all biochar samples was determined using Fourier-transform infrared spectrometry. Sufficient amounts of beechwood and maize biochars, passed through a 0.053-mm and 2-mm sieves, were mixed into crude oil-contaminated soil at the rate of 0, 0.5, 1, and 2% of total dry soil weight. The mixed samples were then laboratory incubated for 90days at 24°C and 10% soil moisture. Water repellency was measured using water drop penetration time (WDPT). The experimental results showed that functional groups on the biochars' surfaces produced at the studied temperatures were distinct. Beechwood and fine size of biochar showed more ability in reducing the hydrophobicity. The produced biochars, at higher temperature, had more potential to alleviate water repellency due to the strong interactions between functional groups of biochars and crude oil. The highest amount of biochar used (2%) significantly alleviated water repellency.

The influence of surfactant-application method on the effectiveness of water-repellent soil remediation

Soil water repellency (SWR) has a substantial effect on soil–water hydrology: it hinders infiltration, leading to enhanced surface runoff and soil erosion, and causes preferential flow in the soil profile beyond that from the soil's natural heterogeneity. SWR is associated with soil organic matter content, the latter added to the soil by vegetation exudates, litter and residues, forest fires, and replacement of fresh water by treated wastewater for irrigation. Surfactants are surface-active substances composed of organic molecules with hydrophobic tails and hydrophilic heads that can reduce the surface tension (γ) of the aqueous solution, thereby reducing SWR, via adsorption to soil particles. Surfactants are commonly used to remediate water-repellent soils. We investigated the role of two surfactant-application methods on the efficacy of SWR remediation. Aqueous solutions of two commercial surfactants had a substantial effect on parameters used to characterize the persistence and severity of SWR. However, the efficacy of these surfactants in remediating sandy soils rendered water-repellent by irrigation with treated effluent was substantially affected by their application method. Whereas application of aqueous surfactant solution to the surface of water-repellent soil, the commonly used remediation method, formed finger-like plumes similar to those obtained for water application, bulbous-like plumes were formed when the soil was premixed with the aqueous surfactant solution prior to water application. These differences were attributed to the significant role of the rate-limited surfactant adsorption to the soil particles.

The Relation between Soil Water Repellency and Water Content Can Be Predicted by Vis‐NIR Spectroscopy

The severity of soil water repellency (SWR) varies nonlinearly with water content (w), and it is extremely laborious to obtain complete SWR‐w curves, which are needed to predict the occurrence of SWR. In this study, we combined a three‐parameter moisture‐dependent SWR (MD‐SWR) model with visible near‐infrared spectroscopy (vis‐NIRS) as a fast and novel method to estimate the SWR‐w curve. The method was applied to a data set of SWR‐w curves determined for 71 soil samples (organic carbon [OC] content: 0.021–0.147 kg kg‐1, clay: 0.000–0.520 kg kg‐1). The degree of SWR was measured on air‐dried soil samples (SWRAD) and on soil samples with increasing water contents until the water content at which the soils became wettable (wNON) was reached. The three‐parameter MD‐SWR model was fitted to the measured SWR‐w curves between the water content at air‐dry conditions (wAD) and wNON. The total SWR was then calculated as the trapezoidal integrated area underneath the SWR‐w curves (SWRAREA). Air‐dried soil samples were scanned with a vis‐NIR spectrometer. Each of the three MD‐SWR model parameters was correlated to vis‐NIRS spectra using partial least squares regression. The SWRAREA was predicted using two approaches. For Approach I, the SWRAREA calculated from the MD‐SWR model was predicted with a single vis‐NIRS model. Approach II utilized predicted MD‐SWR model parameter values to obtain vis‐NIRS‐predicted SWR‐w curves between wAD and wNON, and the SWRAREA was calculated from these curves. Results show that vis‐NIRS can predict the shape of the SWR‐w curves as well as the SWRAREA (R2 = 0.58 and 0.56 for Approach I and II, respectively) across a highly variable dataset from a single vis‐NIRS scanning and one SWR measurement at air‐dried conditions.

Water repellency in Japanese coniferous forest soils as affected by drying temperature and moisture

Soil water repellency occurs where the attraction between solid and liquid phases is weak. The objective of this study was to examine the occurrence and behavior of water repellency in Japanese coniferous forest soils as affected by drying temperature and moisture. Soil samples were obtained from forest soils under Chamaecyparis obtusa (CYP) and Cryptomeria japonica (CED), and an uncultivated land (weed and grass cover) in the Field Science Center of Ibaraki University (FSC) in Ibaraki prefecture, Japan. The persistence of soil water repellency (SWR) was estimated using the water drop penetration time (WDPT) test and the severity of SWR using the molarity of ethanol droplet (MED) test. In Experiment 1, soil samples were exposed to 25 °C and 35 °C temperatures for a period of 30 d. SWR and moisture contents were measured at weekly intervals. In Experiment 2, moisture-dependent repellency was examined in a drying process. CED soil was extremely repellent (WDPT>3600 s; contact angle>106°) and FSC soil was non-repellent (WDPT<1 s). The CYP soils were strongly (35 °C) to severely (25 °C) repellent compared with CED soils, and more prone to significant changes caused by temperature and duration. In CED soil, the changes in contact angles were slight while moisture content variations were significant. In CYP soils, the changes in repellency were significant while moisture content variations were slight. The integrated area below the water-dependent repellency curve (SWR) was greater in CED soil (~140 log s g 100 g−1) than in the CYP soils (~60 log s g 100 g−1). Slight changes in moisture content may or may not cause severe changes in SWR depending on the level of moisture content. These alterations in moisture content in the surface soils may occur as a result seasonal environmental changes and contribute to topsoil loss in mountain areas with high slopes.

Soil Water Repellency Severity and its Spatio‐Temporal Variation in Burnt Eucalypt Plantations in North‐Central Portugal

AbstractSoil water repellency (SWR) is a dynamic soil property that influences soil hydrology. The main goal of this work was to determine in situ spatial and temporal variations in SWR in six recently burnt eucalypt stands with different pre‐ and post‐fire management. The severity of SWR was measured in the field using the “molarity of an ethanol droplet test” during 1–2 years, at intervals of 1–2 weeks. Measurements were taken for the ash layer, soil surface and three different soil depths (2–3, 7–8 and 14–16 cm). The volumetric soil moisture content (SMC) was measured at the three deepest layers. The results showed that ploughing operations carried out several years before the fire did not have major impacts on the severity of SWR. The ash layer was predominately wettable, whereas the other soil layers were dominated by strong to extreme severity SWR. Furthermore, and starting at a soil depth of 3 cm, the severity of repellency decreased with increasing depth. The spatial variability within a slope was significant on half of the sampling days, indicating that wettable patches were present under median severely repellent conditions, possibly increasing hydrological connectivity within the slopes. Temporal SWR patterns were inversely related to antecedent rainfall and SMC. The SWR patterns were similar between sites, as well as for the different sampling depths within each site. Major changes in the median levels of repellency were registered in periods as short as 1–2 weeks, but measured rainfall and/or soil moisture conditions were insufficient to explain these changes. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Patterns of soil water repellency in response to coarse woody debris and fire: implications for eucalypt regeneration in dry forests

The severity of soil water repellency (WR) is affected by fire in dry eucalypt forests in Australia. This study aimed to investigate the variability of soil WR and moisture in and around typical seedling microsites after fire: in ashbeds near coarse woody debris (CWD). Values of soil WR severity and moisture content were measured adjacent to and at multiple distances from CWD in ashbeds and in unburnt soils. Soils were measured at depths of 0 to 5 cm in 1 cm increments for 8 individual CWD samples in ashbeds. Data were analysed to determine whether WR varied significantly among soil depths and distances from CWD. In microsites subjected to a severe burn, WR differed significantly among depths but not distance from CWD. Next to CWD, soil was wettable for 1–2 cm below the surface and this wettable layer was underlain by a severely water repellent layer of at least 1 cm thickness with less repellent soil below that. In areas of less severe and no burn, surface layers were moderately to extremely water repellent. The interaction between fire and CWD and the resultant severe burn, leads to spatially restricted regions where surface soil WR is reduced, moisture accumulates and seedling establishment is promoted.

Organic Matter Fractions Controlling Soil Water Repellency in Sandy Soils From the Doñana National Park (Southwestern Spain)

AbstractThe relationship between soil organic matter (SOM) content and organic molecular assemblages (n‐alkane/alkenes pairs and n‐fatty acids) with soil water repellency (WR) in different sieve fractions (1–2, 0·25–1, 0·05–0·5 and &lt;0·05 mm) was studied in sandy soils from the Doñana National Park (SW Spain) under four vegetation species: Quercus suber (QS), Pteridium aquilinum (PA), Pinus pinea (PP) and Halimium halimifolium (HH). The severity of soil WR [assessed according to the water drop penetration time (WDPT) test] was ordered according to the sequence QS &gt; PA &gt; PP &gt; HH. A positive correlation was found between soil WR from each sieve fraction and SOM content. Most severe soil WR was detected in QS for all sieve fractions, followed by the finer fractions (&lt;0·05 mm) from PA, PP and HH samples. The finer fraction had the highest SOM content, ranging between 20·9% (PP) and 46·9% (QS). Coarser PA, PP and HH soil fractions (1–2 mm) showed the highest long‐chain‐even C numbered fatty acids in the order PP &gt; PA &gt; HH. A significant correlation was observed between SOM content and the severity of soil WR in QS samples and finer fractions of soil under other vegetation (PA, PP and HH). Coarser fractions (1–2 mm) from PP, PA and HH 1–2 mm sieve fractions showed high severity of WR and relatively low SOM contents that could be explained by a low degree of evolution of the organic residues as seen by analytical pyrolysis, that is, higher alkane/alkene carbon preference index values and the presence of a higher diversity of fatty acid structures. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Natural soil water repellency in different types of Mediterranean woodlands

Water repellency (WR) is a property of some soils that reduces infiltration rates, enhances runoff generation and increases soil erosion risk. Although wildfires are considered a triggering factor, the characteristics of plant residues and soil properties may contribute to the development of soil WR. Because of its impacts, soil WR must be considered when modeling soil erosion risk and hydrological processes. Although many studies on WR from Mediterranean soils exist, relatively few studies have contributed to the knowledge of the natural baseline of soil WR in wide areas. The objective of this paper is to study the natural background soil WR in Mediterranean soils from south-western Spain under three representative forest types (pines, eucalypts and holm oaks) and its relation with plant cover (trees, shrubs and herbaceous plants) and soil properties. Field sampling was carried out in August 2013 in 15 areas from Huelva (SW Spain) under the studied forest types. Vegetation cover (trees, shrubs and herbaceous plants) was determined using transects at each case. The water drop penetration time test was used for assessing soil WR, and main soil properties were determined (texture, pH, organic C, N, Extractable P, exchangeable base cations – Ca2+, Mg2+, K+ and Na+ – and cation exchange capacity). According to results, soil WR was observed in all areas, increasing according to the sequence soils under holm oaks<eucalypts<pines. The severity of soil WR was always higher under the canopy of trees and usually decreased in bare areas, although bare soils under pine forest showed a proportion of slight to strong water-repellent cases. Severity of WR from soils under eucalypts and holm oaks increased with the presence of shrubs and herbaceous plants, but similar levels were not reached out of the tree-covered areas. Soils under vegetation in pine forests were always water-repellent, and wettability was observed only in some bare areas, suggesting a high potential of pines for induction of WR. Soil pH and the proportion of clay showed negative correlations with soil WR. A negative correlation between WR class and the proportion of exchangeable K+ was found, suggesting that K deficiency for trees and shrubs restricts the input of hydrophobic substances in soil.

Relationship between the severity, persistence of soil water repellency and the critical soil water content in water repellent soils

Soil water repellency (SWR) causes reduced soil water storage and enhanced runoff and reduced ecosystem productivity. As such, characterization of SWR is a prerequisite for effective environmental management. The objectives of this study were to determine the relationship between the severity of SWR and its persistence and to determine the soil critical water content (CWC). Soils were collected from thirteen soil sites; five from natural jack pine (Pinus banksiana) ecosites (AE1, AE2, SV 10, 26 and 27), six from reclaimed/disturbed sites (ALFH, CPA, SS trial, ATS, SCB, and SW30) located in the Athabasca Oil Sands region and two from agricultural sites (Goodale and Melfort) in Central Saskatchewan, Canada. The severity of SWR as a function of persistence was assessed by measuring the change of water drop contact angles (modified sessile drop method) with time (WDPT, water drop penetration time). The CWC was determined for all the soils by measuring water drop contact angles on soils with predetermined water contents from oven dried to 20% (kgkg−1). In natural, reclaimed and agricultural soils, a high severity (contact angle) of repellency does not necessarily denote long persistence (WDPT) or high CWC. Measurement of severity and persistence is related to the differences and changes in surface energy between water and the soil surface respectively. Although the CWC gives us the water content at which above it SWR is negligible, the trend between contact angle and increasing water content proved to be more informative. Characterizing and understanding the severity, persistence and CWC together are valuable when determining the effects of SWR on hydrological processes as they have different mechanisms compared to one another.

Ameliorating water repellency under turfgrass of contrasting soil organic matter content: Effect of wetting agent formulation and application frequency

Abstract Water conservation strategies are being developed in regions of the world expected to experience decreases in water resources due to changing climates. Strategies advocated for improving water-use efficiency may increase the incidence of soil water repellency in sandy-textured soils. We evaluated the effect of soil wetting agent formulation, and application frequency, on water repellency in sandy soil with two contrasting organic matter (OM) contents under kikuyugrass [Pennisetum clandestinum (Holst. Ex Chiov)], and irrigated at 60% replacement of net evaporation in a climate subject to hot, dry summers. The randomized plot design included two turfgrass ages [established from 20 week (7.7% OM) or 20 year old (30% OM) turfgrass in 2005, the latter included a 50 mm ‘mat’ layer], two soil wetting agent formulations (granular or liquid); two application frequencies (one or two applications per irrigation season); and plots of both turfgrass ages that did not receive any wetting agent (nil control). Both wetting agent formulations contained the same active ingredient (propylene oxide–ethylene oxide block polymer), and all wetting agent treatments received the same rate (69 L active ingredient ha−1). Water repellency in the surface soil (0–5 mm), measured using the molarity of ethanol droplet test (MED), ranged from 1.09 M to 4.32 M during the irrigation season, and was more severe in the soil with high OM (average MED, 3.3 M) than low OM content (average MED, 2.7 M). Applying one application of either granular or liquid soil wetting agent at the commencement of the irrigation season decreased the severity of soil water repellency by up to 30% in the high OM soil and by up to 60% in the low OM soil during the summer, and without the need for a second application. The decline in soil water repellency in response to soil wetting agent application was not matched by an increase in soil VWC in summer, and turfgrass quality was considered acceptable throughout the study. The soil wetting agents were less effective at treating water repellent sand containing a significant amount of OM than sand with low OM content.

The kinetics and energetics of transitions between water repellent and wettable soil conditions: a linear free energy analysis of the relationship between WDPT and MED/CST

AbstractSoil water repellency is commonly assessed using the Water Droplet Penetration Time (WDPT) and Molarity of Ethanol (MED) or Critical Surface Tension (CST) tests. The former is a kinetic measurement indicating the persistence of water repellency; the latter, a thermodynamic measurement, gives the initial severity of water repellency. This study aims to provide a theoretical framework to understand (i) what determines differences in persistence and initial severity of soil water repellency and (ii) correlations between such data. A linear free energy relationship between Solution Droplet Penetration Time (SDPT) and the difference between the surface tension of the droplet solution, γsol, and the Critical Surface Tension of the soil, γcx, has been derived. Here: γsol is the surface tension of water (for WDPT) or the solution being used (SDPT); N is the number of adsorbed molecules per unit area; k the Boltzmann constant; T the temperature; A is 1/SDPT when γcx = γsol; and f is an experimentally determined parameter. WDPT, SDPT (ethanol/water and propan‐1‐ol/water), and CST measurements for a group of sandy soils support this analysis. The value of f obtained (4·2 ( ± 0·4)), suggests that the surface free energy contribution to the free energy of activation of wetting is given by the difference between the cohesive energy of the molecular film adsorbed on the soil grains and that of the wetting solution.In this interpretation: γcx is determined by the cohesive energy of the organic film adsorbed on the soil; WDPT is determined by the difference in cohesive energies between this adsorbed film and the droplet solution; and soil‐to‐soil variations in both WDPT and γcx are due to organic films of different cohesive energies present on the soil particles. For aqueous solutions of simple linear alcohols and ketones, SDPT depends on γsol but is independent of the compound used to control γsol. Copyright © 2007 John Wiley &amp; Sons, Ltd.