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1.
Recent research shows that most soils are more or less water repellent. Already subcritical water repellency may cause incomplete soil wetting and preferential flow. Both processes potentially reduce the residence time of water and solutes in the vadose zone, resulting in an enhanced risk of groundwater contamination. The objective of the present paper is, therefore, to evaluate the impact of reduced soil wettability on the soil water infiltration rate and to investigate the tendency towards preferential flow with the analysis of the immobile water content in the infiltration zone. In november 2002, a field experiment was done in a coniferous forest, 30 km N of Hannover, Germany. Soil hydrophobicity was quantified by measuring the contact angles. The hydraulic conductivity of the podsolic sandy soil was measured depth‐dependent with a double‐ring tension infiltrometer in three soil horizons. To quantify possible preferential‐flow effects, a LiBr‐Tracer was added to the infiltrating water to evaluate the mobile water‐content fraction after infiltration. Additionally, infiltration rates of water were compared with infiltration rates of ethanol which were determined after water infiltration at the same locations. Results show that the actual water repellency of field‐moist soil was mainly subcritical (contact angle <90°). Water infiltration rates were reduced due to subcritical repellency by a factor of 3–170 compared with ethanol infiltration rates (exclusion of wetting effects). This spatially variable infiltration behavior was not clearly reflected neither by the small‐scale contact‐angle measurements nor by the analysis of the average immobile soil water content in the infiltration zone. We conclude that this specific infiltration behavior of water caused by small‐scale wettability effects may temporarily reduce the local connectivity of water‐flow pathways. 相似文献
2.
岷江上游干旱河谷旱地土壤斥水性特征初步研究 总被引：1，自引：0，他引：1
土壤斥水性是土壤颗粒不易被水滴浸润的现象,对土壤水分特征曲线、土壤溶质运移、土壤优先流、土壤导水率以及地表径流和土壤侵蚀等具有重要影响。研究结果表明,3月份岷江上游干旱河谷0-5cm土层具斥水性的土壤在空间上的分布概率约为34%,其中强度斥水性土壤分布比例为5%;在时间分布上,土壤斥水性主要表现在7月,轻度以下斥水性概率为91%,强度以上斥水性概率为58%;从各粒级土壤斥水性的研究结果来看,斥水性与土壤粒级呈显著负相关,粒级越小,土壤斥水性越高。因此,岷江上游干旱河谷旱地土壤斥水性具有明显的时空分布差异,并且粒级越小土壤斥水性越强,7月份土壤表层的土壤斥水性强度与分布比例高。这可能是导致干旱河谷严重水土流失、土壤砂砾化的一个重要原因。 相似文献
3.
The potential of biochar to ameliorate soil water repellency has not been widely studied. Previous studies have focused on the potential for biochar to induce or exacerbate existing water repellency rather than alleviate it. This study investigates the effect of adding wettable biochar to water‐repellent soil by comparing the water drop penetration times (WDPTs) of a control and biochar‐amended soil. The potential of wettable biochar to act as a physical amendment to water‐repellent soil was evaluated by mixing coarsely‐ground biochar (CGB, particle size range 250–2000 µm) or finely‐ground biochar (FGB, particle size range < 250 µm) with one strongly and one severely naturally water‐repellent soil in various quantities, and then measuring the WDPT for each mixture. When biochar particles did not fall within the size range of existing soil particles, an initial increase in both mean WDPT (WDPTM) and variation in WDPT was observed with small additions of biochar. These effects possibly result from increased surface roughness and inhibition of infiltration by the suspension of drops above the average soil–air interface at a few hydrophobic points. Both CGB and FGB reduced soil water repellency, FGB more effectively than CGB. The addition of 10% w/w FGB reduced soil WDPT by 50%, and 25% FGB eliminated repellency. Direct absorption of water by biochar and an increase in soil surface area in contact with water are the predominant physical mechanisms involved. This exploratory study suggests biochar has the potential to amend water‐repellent soil. 相似文献
4.
Soil water repellency is usually unstable, as exemplified by the common method of quantifying repellency degree – the water drop penetration time (WDPT) test. Dynamic penetration and infiltration of water into repellent soils is generally attributed to either reduction of the solid‐liquid interfacial energy (γSL) or reduction of the liquid‐vapour interfacial energy (γLV), or both. The reduction of γSL can result from conformation changes, hydration, or rearrangement of organic molecules coating soil particle surfaces as a result of contact with water, while the reduction of γLV can result from dissolution of soil‐borne surface active organic compounds into the water drop. The purpose of this study was to explicitly test the role of the second mechanism in dynamic wetting processes in unstably repellent soils, by examining the drop penetration time (DPT) of water extracts from repellent soils obtained after varying extraction times and at different soil : water ratios. It was indeed found that soil extracts had lower surface tensions (γLV approx. 51–54 mN m−1) than distilled water. However, DPT of the soil extracts in water repellent soils was generally the same or greater than that of water. Salt solutions with the same electrical conductivity and monovalent/divalent cation ratio as the soil extracts, but lacking surface active organic substances, had the same DPT as did the extracts. In contrast, DPT of ethanol solutions prepared with the same γLV, electrical conductivity, and monovalent/divalent cation ratio as the soil extracts, was much faster. Ethanol solutions are usually used as an agent to reduce γLV and as such, to reduce DPT. It is concluded that the surface‐active, soil‐derived organic substances in aqueous soil extracts do not contribute to wetting dynamics, and as such, this mechanism for explaining kinetics of water penetration into water repellent soils is rejected. It is also concluded that the rapid penetration of ethanol solutions must be due not only to changes in γLV, but to also to changes in either or both γSL and the solid‐vapour interfacial energy (γSV). These results stand in sharp contrast to well‐accepted logical paradigms. 相似文献
5.
Wettability parameters determined for individual soils often show a considerable variation depending on the kind of sample (aggregated or homogeneous material) and the method used. To investigate the causes of this variation, we assessed wettability of both intact and crushed aggregates and bulk soil using different methods. Wettability of intact aggregates was characterized by a modified technique where the specific infiltration rates of water and a completely wetting liquid were used to define a repellency index. Contact angles were determined on crushed aggregates and bulk soil using the Wilhelmy plate and capillary rise methods. The repellency index was found to be sensitive to slight differences in wettability and was in good agreement with Wilhelmy plate contact angles. Contact angles measured with the capillary rise method showed a strong deviation from those determined with the Wilhelmy plate method. This can be ascribed to the underlying assumptions of the capillary rise method (i.e. cylindrical and parallel capillaries) resulting in an over‐estimation of contact angle, particularly for the small‐sized particle fraction because of the impact of inertia and pore structure. No significant differences were found between intact and crushed aggregates whereas the bulk soil was slightly more water‐repellent, probably because of a somewhat larger organic carbon content. We conclude that the contact angle determined by the Wilhelmy plate method and the repellency index are appropriate parameters for characterizing soil water repellency because they detected small changes in wettability over a wide range extending from subcritical water repellency to hydrophobicity. 相似文献
6.
Considerable soil water repellency has been observed at a wide range of locations worldwide. The soil exhibiting water repellency is found within the upper part of the soil profile. The reduced rate of water infiltration into these soils leads to severe runoff erosion, and reduction of plant growth. Soil water repellency is promoted by drying of soil, and can be induced by fire or intense heating of soil containing hydrophobic organic matter. Recent studies outside soil science have shown how enhancement of the natural water repellency of materials, both porous and granular, by surface texture (i.e. surface roughness, pattern and morphology) into super‐hydrophobicity is possible. The similarities between these super‐hydrophobic materials and observed properties of water‐repellent soil are discussed from a non‐soil scientist, materials‐based perspective. A simple model is developed for a hydrophobic granular surface and it is shown that this can provide a mechanism for enhancement of soil water repellency through the relative size and spacing of grains and pores. The model provides a possible explanation for why soil water repellency should be more prevalent under dry conditions than wet. Consequences for water runoff, raindrop splash and soil erosion are discussed. 相似文献
7.
Occurrence, prediction and hydrological effects of water repellency amongst major soil and land-use types in a humid temperate climate 总被引：1，自引：1，他引：1
S. H. Doerr R. A. Shakesby L. W. Dekker & C. J. Ritsema 《European Journal of Soil Science》2006,57(5):741-754
Knowledge of soil water repellency distribution, of factors affecting its occurrence and of its hydrological effects stems primarily from regions with a distinct dry season, whereas comparatively little is known about its occurrence in humid temperate regions such as typified by the UK. To address this research gap, we have examined: (i) water repellency persistence (determined by the water drop penetration time method, WDPT) and degree (determined by the critical surface tension method, CST) for soil samples (0–5, 10–15 and 20–25 cm depth) taken from 41 common soil and land‐use types in the humid temperate climate of the UK; (ii) the supposed relationship of soil moisture, textural composition and organic matter content with sample repellency; and (iii) the bulk wetting behaviour of undisturbed surface core samples (0–5 cm depth) over a period of up to 1 week. Repellency was found in surface samples of all major soil textural types amongst most permanently vegetated sites, whereas tilled sites were virtually unaffected. Repellency levels reached those of the most severely affected areas elsewhere in the world, decreased in persistence and degree with depth and showed no consistent relationship with soil textural characteristics, organic matter or soil moisture contents, except that above a water content of c. 28% by volume, repellency was absent. Wetting rate assessments of 100 cm3 intact soil cores using continuous water contact (–20 mm pressure head) over a period of up to 7 days showed that across the whole sample range and irrespective of texture, severe to extreme repellency persistence consistently reduced the maximum water content at any given time to well below that of wettable soils. For slightly to moderately repellent soils the results were more variable and thus hydrological effects of such repellency levels are more difficult to predict. The results imply that: (i) repellency is common for many land‐use types with permanent vegetation cover in humid temperate climates irrespective of soil texture; (ii) supposedly influential parameters (texture, organic matter, specific water content) are poor general predictors of water repellency, whereas land use and the moisture content below which repellency can occur seem more reliable; and (iii) infiltration and water storage capacity of very repellent soils are considerably less than for comparable wettable soils. 相似文献
8.
F.B. Pierson P.R. Robichaud C.A. Moffet K.E. Spaeth C.J. Williams S.P. Hardegree P.E. Clark 《CATENA》2008,74(2):98-108
Millions of dollars are spent each year in the United States to mitigate the effects of wildfires and reduce the risk of flash floods and debris flows. Research from forested, chaparral, and rangeland communities indicate that severe wildfires can cause significant increases in soil water repellency resulting in increased runoff and erosion. Few data are available to document the effects of fire on the spatial and temporal variability in soil water repellency and potential impacts on infiltration and runoff on sagebrush-dominated landscapes. Soil water repellency, infiltration and runoff were assessed after two wildfires and one prescribed fire in three steep, sagebrush-dominated watersheds with coarse-textured soils. Water repellency was generally greater on unburned hillslopes and annual variability in water repellency had a greater impact on infiltration capacity than fire effects. The most significant impact of fire was canopy and ground cover removal on coppice microsites. Infiltration rates decreased on coppice microsites after fire even though soil water repellency was reduced. Fire-induced reduction in infiltration resulted from the combined effect of canopy and ground cover removal and the presence of naturally strong water repellent soils. Removal of ground cover likely increased the spatial connectivity of runoff areas from strongly water repellent soils. The results indicate that for coarse-textured sagebrush landscapes with high pre-fire soil water repellency, post-fire increases in runoff are more influenced by fire removal of ground and canopy cover than fire effects on soil water repellency and that the degree of these impacts may be significantly influenced by short-term fluctuations in water repellent soil conditions. 相似文献
9.
四种入渗模型对斥水土壤入渗规律的适用性 总被引：4，自引：6，他引：4
土壤斥水性影响入渗,进而影响作物产量。国外学者进行了一定的研究,但在中国研究的还很少。该文基于实测资料探讨几种常规的入渗模型在斥水土壤中的适用性。采用室内土柱进行积水入渗试验,对比了不同积水高度和斥水度条件下的土壤入渗规律,并采用4种模型分析了土壤入渗率变化特征。结果表明,累积入渗量随入渗历时的变化可用幂函数描述,不斥水土壤累积入渗量明显大于斥水土壤;累积入渗量与湿润锋推进距离呈良好的线性关系;利用Green-Ampt模型、Philip模型、Kostiakov公式和指数公式对入渗率与入渗历时间的关系进行拟合,其中Kostiakov公式更接近于实测值,其他模型拟合效果因斥水程度等因素的不同而异。 相似文献
10.
微咸水灌溉对斥水土壤水盐运移的影响 总被引：10，自引：4，他引：6
土壤斥水性影响着作物的产量,为了研究微咸水灌溉对斥水土壤水盐运移的影响,进行了室内土柱微咸水入渗试验。对比了不同矿化度和斥水程度对两种土质水盐运移的影响,探讨了微咸水入渗后土壤斥水性的变化特征。结果表明,不斥水土壤的入渗能力随矿化度的增加而增加。亲水和斥水土壤的入渗率均可采用Kostiakov公式简单模拟。斥水土壤入渗能力在矿化度为1?g/L时达到最大,超过1?g/L后则随矿化度的增大而减小。微咸水入渗的累积入渗量与湿润锋推进距离呈良好的线性关系,斥水性土壤中的相同剖面水盐的含量比不斥水的减小。微咸水入渗后土壤产生了一定的斥水性。该研究表明微咸水灌溉对盐渍化土壤的水盐分布和斥水性均有一定程度的影响。 相似文献
11.
作者运用所建立的斥水土壤中水热运动的数值模型，模拟分析了以下因素对沟中时苗床不分散失与温度的影响：（１）不同的沟垄尺寸；（２）湿润剂；（３）镇压；（４）沟垄的走向。以此为当地的耕种工程设计提供了依据。一般认为土壤斥性严重影响产量，但采用沟种后，表层的斥水土壤形成的不透不的垄能促进雨水渗入沟中，又能阻止水分的蒸发，降低沟中的温度，有利于种子发育出苗，从而使不利因素变化成有利条件。 相似文献
12.
A small increase in soil organic matter (SOM) content can change soil hydrological properties from a completely wettable to a partially water‐repellent state. Although considerable research describes hydrophobic compounds as a primary driver of this shift, the influence of pore shape has only been considered in a few studies and none of these has emphasized the role of different carbon compounds. Using a capillary bundle model of non‐cylindrical (wavy) capillaries, we described measured hydrological properties of five agricultural soils that have a small degree of water repellency and textures ranging from coarse sand to heavy clay. To isolate the influence of SOM, it was removed by combustion to provide an SOM‐free treatment. Water and methanol sorptivities quantified infiltration rates and soil‐water wetting angles in packed soil cores. Different cores were sectioned to measure wetting profiles and calculate diffusivity. The results from natural soils were supplemented by measurements carried out on model ‘soils’ consisting of quartz particles (50–200 µm) with four different hydrophobic states. Soil organic matter removal increased water sorptivity from about 60% for a coarse sandy soil (Haplic Arenosol) to about 290% for a heavy clay soil (Haplic Leptosol), corresponding to a decreased apparent wetting angle of 20–30°. Application of the wavy pore model suggests that the apparent wetting angle resulting from SOM removal can be several times smaller than its Young value. Generally, SOM removal increased water diffusivity values by one to two orders of magnitudes. The SOM components having the greatest impact on contact angle were hexanedioic acid and heneicosanoic acid (both hydrophilic) and docosane (hydrophobic). 相似文献
13.
14.
斥水程度对脱水土壤水分特征曲线的影响 总被引：2，自引：3，他引：2
为研究斥水程度对土壤水分特征曲线的影响,该文基于滴水穿透时间法,人工配置7种斥水程度的黏壤土(L0~L6)和6种斥水程度的砂土(S0~S5),用高速离心机测定其土壤水分特征曲线,应用van Genuchten-Mualem(VG)模型进行拟合,得出VG模型水力参数。结果表明:在同一吸力条件下,斥水黏壤土的含水率比斥水砂土的高;随着斥水程度增加,在相同吸力情况下,土壤含水率随斥水程度增大而减小;斥水黏壤土的残余含水率随着斥水程度增加而减小,斥水砂土S0~S3的残余含水率没有差异,S4、S5的残余含水率显著减小;斥水黏壤土和砂土进气值的对数与斥水剂添加量呈负线性相关;随着斥水程度增加,田间持水率减小,凋萎系数没有明显差异,重力水增加,有效水和易有效水减小,易利用水比例随着斥水程度增加而减小;对于斥水黏壤土,微孔隙(0.3~5μm)和小孔隙(5~30μm)含量随着斥水程度的增加明显减小,土壤空隙(≥100μm)随着斥水程度的增加急剧增加;对于斥水砂土,中等孔隙(30~75μm)的含量随斥水程度的增加明显增加。该研究成果可为斥水土壤的入渗、蒸发和数值模拟提供理论支持。 相似文献
15.
再生水灌溉对农田土壤水流运动影响的研究进展 总被引：2，自引：1，他引：1
再生水灌溉农田既可节约宝贵的水资源、缓解农业用水紧缺,同时再生水中的多种营养元素和微量元素可促进作物生长、提高粮食产量。但再生水中的物质进入农田后将引起土壤孔隙结构、团聚体结构、黏粒分散特征和水土作用关系等一系列的变化,进而引起土壤入渗性能和导水性能的改变,增大环境污染风险。该文综述了再生水中的悬浮无机固体、大分子有机质、油脂、表面活性剂和盐分对农田土壤水流运动的影响及其作用机理,指出受灌农田土壤结构性质演化过程与驱动机制、受灌农田土壤与灌溉入渗水流之间的相互作用关系为该领域亟需开展的2个研究方向。文章对再生水农田灌溉制度制定、污染风险控制和生态环境保护均有参考价值。 相似文献
16.
坡耕地地表糙度对降水分配的实验研究 总被引：1，自引：0，他引：1
地表糙度指地表微小的高低起伏变化,是人为土地管理与土壤侵蚀共同作用的结果,可以影响降雨过程中水分转化与土壤侵蚀过程。该文以直线坡为对照,借助3种常见耕作管理措施（人工锄耕、人工掏挖与等高耕作）产生不同水平的地表糙度,结合人工模拟降雨试验研究地表糙度水分转化效应。结果表明:长历时人工降雨条件下,地表糙度可以强化降雨向土壤水分转化。其强化入渗作用表现为:增加地表填洼量,增大入渗水头与入渗深度,滞后产流时间,削减径流量,进而提高入渗率及水分转化率。坡耕地地表糙度与填洼量成指数关系,与平均入渗率及水分转化率成对数关系。 相似文献
17.
砾石覆盖厚度对斥水土壤入渗特性的影响及模型优选 总被引：1，自引：1，他引：1
基于室内一维垂直入渗土柱试验,研究砾石覆盖厚度(0,3,6,9,12 cm)对斥水土壤积水入渗及水分再分布的影响,并利用不同入渗模型进行拟合。结果表明:砾石覆盖显著增加斥水土壤湿润锋运移距离(p<0.05);同一时段内,各处理累积入渗量皆高于对照组(p<0.05),斥水性红壤累积入渗量与砾石覆盖厚度呈正相关关系;斥水性红壤初渗率与稳渗率随砾石覆盖厚度变化均可用指数函数来描述,决定系数分别为0.91和0.87,砾石覆盖使得斥水性潮土初渗率与稳渗率增大,其中稳渗率与砾石覆盖厚度呈二次函数关系,决定系数为0.78,覆盖6 cm时稳渗率达到最大;砾石覆盖明显提高斥水土壤剖面平均含水率,斥水性红壤和潮土最大分别增长180.8%和57.6%;隔绝蒸发条件下,再分布过程斥水土壤湿润体含水率表现为停渗时刻>再分布1天>再分布3天>再分布7天;Horton模型对砾石覆盖斥水土壤入渗过程的拟合效果最好,是分析和预测砾石覆盖斥水土壤水分入渗特征的适宜模型。 相似文献
18.
The effect of dairy sewage sludge amendment on repellency and hydraulic conductivity of soil aggregates from two depths of Eutric Cambisol 
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下载免费PDF全文 Appropriate management of sewage sludge is an important worldwide issue due to the still growing amount of wastewaters. In the study we examined to what extent the addition of dairy sewage sludge compared with mineral fertilization affects porosity, repellency index, and hydraulic conductivity of variously sized aggregates from two soil depths of Eutric Cambisol derived from loess: 5–15 cm and 25–35 cm. The repellency index was calculated as a ratio of ethanol and water sorptivity. Data on water and ethanol sorptivities of initially air‐dry soil aggregate fractions were obtained from steady state flow measurements using an infiltration device. Hydraulic conductivity was determined by measuring water infiltration at five pressure heads: –8, –6, –4, –2, and 0 cm of water column with the same device as for sorptivity determination. Addition of sewage sludge to the soil decreased the soil repellency index by an average of 27% in topsoil and 32% in subsoil for both aggregate sizes, respectively, and increased hydraulic conductivity about four times in both layers. Smaller aggregates (15–20 mm diameter) from soil amended with sewage sludge, in comparison with larger ones (30–35 mm diameter), had a higher repellency index by 36 and 24% in topsoil and subsoil, respectively. As for aggregates from soil with mineral fertilization, those differences were smaller and equal to 15% in subsoil, in topsoil smaller aggregates even had slightly lower repellency index (by 5%). Aggregates taken from the upper soil layer were more water repellent and had smaller hydraulic conductivity than those taken from subsoil, regardless of soil treatment and aggregate size. 相似文献
19.
J. Poulenard J.C. Michel F. Bartoli J.M. Portal & P. Podwojewski 《European Journal of Soil Science》2004,55(3):487-496
Water repellency of volcanic ash soils from the Ecuadorian páramo was studied by a combination of extraction and analysis of water‐repellent products, Molarity Ethanol Droplet values, water contact‐angle measurements by capillary rise, and N2 adsorption isotherms. The undried samples studied are hydrophilic, but exhibit water repellency after moderate drying (48 hours at 30°C). The advancing water contact‐angle measured by capillary rise varies from 78° to 89°. These water contact‐angles decrease strongly after extraction of organic materials by an isopropanol–water mixture. Elemental analysis, infrared spectra and gas chromatography‐mass spectrometry analyses were used to characterize the extracts. The results show that long‐chain fatty acids and more complex non‐polar alkyl components (waxes) are the main water‐repellent materials. The deposition of such extracted materials onto hydrophilic sand leads to the rapid increase of water contact‐angle until values close to those measured on the soil samples are achieved. Assuming a coating of the mineral surface by organic hydrophobic products and using Cassie's law, the water contact‐angle of extracted materials was computed. The values ranged from 100° to 157°. Nitrogen specific surface areas of the soils studied were very small, indicating a low adsorbent–adsorbate interaction on hydrophobic surfaces. These results partially validate the hypothesis of water‐repellent materials that occur as coatings at least after a drying process. 相似文献
20.
Droplet infiltration and organic matter composition of intact crack and biopore surfaces from clay‐illuvial horizons 下载免费PDF全文
下载免费PDF全文 The organic matter (OM) in biopore walls and aggregate coatings may be important for sorption of reactive solutes and water as well as for solute mass exchange between the soil matrix and the preferential flow (PF) domains in structured soil. Structural surfaces are coated by illuvial clay‐organic material and by OM of different origin, e.g., earthworm casts and root residues. The objectives were to verify the effect of OM on wettability and infiltration of intact structural surfaces in clay‐illuvial horizons (Bt) of Luvisols and to investigate the relevance of the mm‐scale distribution of OM composition on the water and solute transfer. Intact aggregate surfaces and biopore walls were prepared from Bt horizons of Luvisols developed from Loess and glacial till. The mm‐scale spatial distribution of OM composition was scanned using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The ratio between alkyl and carboxyl functional groups in OM was used as potential wettability index (PWI) of the OM. The infiltration dynamics of water and ethanol droplets were determined measuring contact angles (CA) and water drop penetration times (WDPT). At intact surfaces of earthworm burrows and coated cracks of the Loess‐Bt, the potential wettability of the OM was significantly reduced compared to the uncoated matrix. These data corresponded to increased WDPT, indicating a mm‐scaled sub‐critical water repellency. The relation was highly linear for earthworm burrows and crack coatings from the Loess‐Bt with WDPT > 2.5 s. Other surfaces of the Loess‐Bt and most surfaces of the till‐derived Bt were not found to be repellent. At these surfaces, no relations between the potential wettability of the OM and the actual wettability of the surface were found. The results suggest that water absorption at intact surface structures, i.e., mass exchange between PF paths and soil matrix, can be locally affected by a mm‐scale OM distribution if OM is of increased content and is enriched in alkyl functional groups. For such surfaces, the relation between potential and actual wettability provides the possibility to evaluate the mm‐scale spatial distribution of wettability and sorption and mass exchange from DRIFT spectroscopic scanning. 相似文献