Preferential Flow Features Research Articles

Morphological and structural characteristics of preferential flow and its influencing factors on colluvial deposits of Benggang

AbstractPreferential flow plays a vital role in infiltration processes in structured soil. However, knowledge of preferential flow in colluvial deposits of Benggang remains limited. In this study, three typical colluvial deposits with different formation times were selected. The formation times of colluvial deposits A, B and C increased in sequence. Water infiltration in colluvial soil was visualized through Brilliant Blue dye experiments (a total of 90 photos from the dyed soil profiles). The dye morphological characteristics of preferential flow were analysed, and the influencing factors were explored. The dye morphological parameters confirmed the occurrence of preferential flow in the colluvial deposits. The dye coverage of colluvial deposit A was the greatest (61.12%), followed by colluvial deposits B (50.41%) and C (46.81%). The matrix flow depth, preferential flow fraction and length index of colluvial deposits A and B were greater than those of colluvial deposit C. Preferential flow was more notable in colluvial deposits A and B than in colluvial deposit C. The migration process of dyed water varied spatially. There were more preferential flow paths at a 10 cm horizontal width. In addition to the bulk density and saturated hydraulic conductivity, the soil particle composition, especially the gravel content (r = 0.740), was closely related to the observed dye coverage. According to the principal component analysis results, the soil particle composition imposed the greatest influence on the formation of preferential flow in the colluvial deposits, with a contribution of 45.24%. The results provide a theoretical reference for explaining the mechanism of soil infiltration processes and a systematic basis for the treatment of colluvial deposits.

A comparison of preferential flow characteristics and influencing factors between two soils developed in the karst region of Southwest China

A comparison of preferential flow characteristics and influencing factors between two soils developed in the karst region of Southwest China

Variation in preferential flow features induced by desiccation cracks in physical crusts

Studies have shown that preferential flow induced by cracks establishes multiple features such as morphology in different soil profiles. However, there has been little experimental evidence of the contribution of physical crust towards crack features and preferential flow. Essentially, this investigation focused on physical crusts (structural and deposition crust) of Lou soil, a loam and silt loam-textured soil, to demarcate the formation of cracks and preferential flow under artificial rainfall. The crack initiation and propagation processes were defined as the formation of primary cracks in the initial phase and narrow cracks around primary cracks, respectively. The cylindrical soil containers and cubical stainless-steel boxes were employed to trace preferential flow in the horizontal and vertical profile, respectively. The cracks in structural and deposition crusts were dominated by initiation and propagation cracks, respectively. The area, length, and width of the cracks in the structural crusts (5.7 cm2, 815, and 1.44 mm) were notably larger than deposition crusts (1.7 cm2, 604, and 0.96 mm). The maximum dyed depths of the structural and deposition crusts reached 35, 45, and 65 mm, and 35, 55, and 75 mm under the infiltration amounts of 10, 30, and 50 mm, respectively. The uniform infiltration depth, length index and PF-fr of structural crusts were in the ranges of 6.7 ∼ 25.5 mm, 19 ∼ 46 %, and 83 ∼ 111 %, respectively. Corresponding values for deposition crusts were 7.2 ∼ 26.2 mm, 10 ∼ 46 %, and 87 ∼ 103 %, respectively. The preferential flow in the soil profiles with structural crusts was superior to deposition crust. An assessment of the potential function of the physical crust for preferential flow is a supplement to study the effect of soil surface morphology on hydrological process.

Preferential Flow and Preferential Path Characteristics of the Typical Forests in the Karst Region of Southwest China

The ecological environment in the karst region of southwest China is fragile, and vegetation degradation is considered the main cause of this phenomenon. Vegetation growth is affected by preferential flow due to a large number of fissures and macropores in the soil. Therefore, the preferential flow and preferential paths in local typical vegetation need to be studied. The distribution and developmental characteristics of preferential flow and preferential paths in three typical local stands were obtained by conducting field staining tracer experiments and using image processing techniques. The results showed that there was preferential flow movement in the soil moisture of the local understorey and that there was a high degree of preferential flow development and high variability. The degree of preferential flow in several typical forests can be expressed, from highest to lowest, in the following order: secondary forests, Cupressus duclouxiana Hickel (Hickel., 1814) forest, and Pinus massoniana (Lamb., 1803) forest. The preferential paths in the soil were mainly distributed above 15 cm, and the number of preferential paths with a small influence radius was much greater than that with a large influence radius. The preferential paths with an influence radius of 2.5~5 mm accounted for the largest proportion. The total number of preferential paths in the P. massoniana forest was small. The preferential paths in the secondary and C. duclouxiana Hickel forests were similar in number, but the secondary forests had more preferential paths with a large influence radius. This study investigated the characteristics of preferential flow and preferential paths in the typical forests of the karst region in southwest China, and it can provide data and research directions for the study of hydrological processes in local forest vegetation.

A novel UNet segmentation method based on deep learning for preferential flow in soil

Accurate binary images based on dye-tracing experiments are fundamental for understanding preferential flow in soil. Nevertheless, general image-processing software, such as Photoshop, Image-Pro Plus, and ImageJ, cannot automatically and accurately binarize dye-strained regions for the areas with uneven staining and blurred boundaries, causing errors in the subsequent analysis of preferential flow characteristics. Therefore, this study aimed to develop a novel UNet segmentation method based on a dual-scale attention residual module (DARM-UNet), to improve the segmentation accuracy of preferential flow images and assist in digital soil descriptions. The proposed method is a two-level nested U-structure, i.e., a dual-scale attention residual module (DARM) on the lowest level and the typical architecture of UNet at the top level. On the lowest level, the DARM obtained improved contextual information and expand the receptive field based on the attention mechanism and the dual-scale convolution, which was used to improve the recognition ability of uneven dye and low-contrast regions. At the top level, the typical architecture of the UNet model was followed to fuse feature maps of different resolutions, in which each stage is filled by a DARM block. Compared with general image processing software and deep learning methods, the DARM-UNet method showed higher preferential flow segmentation accuracies (95.71% and 93.29%), recall rates (91.91% and 89.29%), and harmonic means (92.72% and 91.82%) for the natural secondary and hazelnut shrub forests, respectively. The four preferential flow indicators indicated that the flow patterns of the natural secondary and hazelnut shrub forests varied with soil depth. In natural secondary forests, the preferential flow started from the surface and was of the primary flow type, whereas in hazelnut shrub forests, it occurred only in the deeper layer, following the matrix flow and concentrating in the 0–16 cm soil layer. This study demonstrated that the proposed DARM-UNet method could effectively identify and segment preferential flow of different forests, especially the areas with uneven staining and blurred boundaries.

Visualization study on preferential flow in highly saturated and super hydrophilic porous media by combining dye tracking and infrared imaging

• New method to track finger flow in highly saturated superhydrophilic porous media. • Preferential flow recurrence was observed at high saturation. • The preferential flow was found to impair desalination efficiency. • The temperature distribution was controlled by preferential flow. Air-gap diffusion distillation (AGDD) is a practical desalination technique. The highly saturated super hydrophilic porous medium as its evaporation surface has a decisive influence on the desalination efficiency of AGDD. In experiments, we found preferential flow in porous media. However, the preferential flow in highly saturated super hydrophilic porous media has not been studied, and the effect of preferential paths on evaporation from porous media surfaces remains poorly understood. The method of combining dye tracking and infrared imaging was used to visualize the process of thermal seepage in highly saturated super hydrophilic porous media. Under the condition of uniform and continuous liquid supply on the upper surface, the preferential flow characteristics of hot stream seepage in porous media are tracked; Point source infiltration experiments were carried out at room temperature to compare the difference between preferential flow in super hydrophilic porous media and general soil (sand). The experimental results of thermal seepage showed that the preferential flow greatly influences the uneven temperature distribution of the porous media, which directly impairs the desalination efficiency of AGDD. According to the coefficient of variation (CV), the preferential flow development process can be divided into three stages: stable development, exponential development, and high-speed growth. As the seepage flow is stabilized, the influence of preferential flow on the flow field and temperature field still exists and is affected by these three stages. Preferential flow characteristics were also captured in the saturated capillary rise zone at the bottom of the porous medium (below the phreatic level). The point source infiltration experiment found that the preferential flow in superhydrophilic porous medium will reappear at high saturation, which is completely different from the soil (sand) studied by previous studies. In addition, the effects of inlet temperature, flow rate, thickness, and hydrophilic, hygroscopicity on preferential flow were discussed. Increasing the flow rate and inlet temperature and reducing the thickness of the porous media can weaken the influence of preferential flow on the temperature field. But increasing the temperature only superficially weakens the preferential flow. Increasing hydrophilicity and hygroscopicity can also reduce the preferential flow.

A comparative evaluation of soil preferential flow of mulched drip irrigation cotton field in Xinjiang based on dyed image variability versus fractal characteristic parameter

Preferential flow in soil has a potential impact on the maintenance of the agricultural ecosystem. The aim of this study was to quantify and evaluate the characteristics of preferential flow in drip irrigation cotton fields in Xinjiang. We applied the dye tracer method, addressed the variability in stained images, collected soil samples in the excavated soil profile, and calculated the fractal parameters in four key growth stages of cotton in 2021. According to the dyeing mode, the dyed area ratio tended to keep decreasing from the soil surface; a down movement of points which drastically dropped to zero appeared at pace with the growth of the cotton (from −10 cm to −30 cm). Statistics obtained from the staining images showed that the preferential flow degree was highest at the boll opening stage; no significant difference in non-uniformity emerged from different treatments at the same growing stage (p > 0.05). Conversely, the fractal feature parameters in the active region model probed that the preferential flow degree was developed at the flowering & bolling stage in treatments with opaque oxidation-biodegradable film mulching (B,W), and at boll opening stage with plastic film mulching (P). During the same growth period, a significant difference (p < 0.05) existed between different groups. In comparison, the fractal feature parameter was found more adequate and effective in evaluating the characteristics of preferential flow in drip irrigation cotton fields. This research will provide practical information for the local department to adjust some agronomic measures to reduce the risk of low irrigation water utilization efficiency.

基于探地雷达的滨河带藤本和次生乔木林土壤优先流特征

PDF HTML阅读 XML下载 导出引用 引用提醒 基于探地雷达的滨河带藤本和次生乔木林土壤优先流特征 DOI: 10.5846/stxb202103260800 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（32071839） Characteristics of preferential flow of liana and secondary arbor forests along riverside based on Ground Penetrating Radar Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:滨河带是河流生态系统和森林生态系统的过渡带，该区域林分的土壤优先流特征对流域的地表水文过程会产生重要影响。探究土壤异质性与优先流的关系，为当地地下水安全和河流上下游水生态安全提供参考。本研究以永定河滨河带的藤本和次生乔木林两种植被为研究对象，结合传统亮蓝（Brilliant Blue FCF）染色示踪法，利用探地雷达（Ground Penetrating Radar，GPR）技术进行测线扫描。提取探地雷达图像的单道波形图，对反射波各参数与染色面积比进行拟合，并结合优先流染色特征进行分析。染色形态特征表明，藤本样地土壤染色形态呈现断离式零散分布，优先流发育带为土壤表层以下5-30 cm的土层深度，而次生乔木林土壤呈现大面积斑块状分布，优先流发育较为迟缓，其发育带为土壤表层以下10-25 cm的土层深度，且平均染色面积比藤本小1.68%。探地雷达测线表明，土层深度为0-15 cm时，最大振幅和总振幅面积均随土层的深度增加而下降，土层深度为15-35 cm时，两参数开始波动变化，且藤本样地的最大振幅和总振幅面积大于次生乔木林样地。经拟合发现，染色面积比与最大振幅呈y=25.104lnx+25.137（R2=0.8697）的对数关系，染色面积比与总振幅面积呈y=23.874lnx-26.862（R2=0.6173）的对数关系。以上分析可知，次生乔木林地土壤比藤本覆盖下的土壤紧实度更好，其电磁波在经历物理过程中损失的电磁信号较少，而藤本样地的电磁信号波动较大，可见藤本覆盖下土壤层次间结构差异变化比次生乔木林更明显，从而导致藤本覆盖下的土壤优先流程度更高。为保护地下水安全，对于滨河床地带和丘前的低洼地这类排水不良的区域，可对藤本植被茂盛的地带采取适当适量的伐藤措施来抑制藤本覆盖下的优先流过度发育，同时也可通过避免强降雨前施肥降低藤本植被覆盖下的地下水污染。 Abstract:The riparian zone is a transition zone between river ecosystem and forest ecosystem. The characteristics of preferential flow in forest belt along riverside have an important influence on the surface hydrological process of the watershed. Therefore, study of the relationship between soil heterogeneity and preferential flow is of great significance to local groundwater security and water ecological security of upstream and downstream rivers. In this paper, using the technique of Ground Penetrating Radar (GPR) combined with the traditional staining tracing method, the liana and secondary arbor forest sample plots along Yongding Riverside (the junction of Beijing and Hebei) were detected. The single channel oscillogram of the GPR image was extracted, and then the parameters of reflected wave and dye area ratio were fitted. Finally, the key step was to analyze the preferential flow staining features. The staining morphological characteristics showed that the preferential flow segment of liana sample plot was 5-30 cm below the soil surface, while the secondary arbor forest sample plot was 10-25 cm below the soil surface. The average dye area of the secondary arbor was 1.68% smaller than that of liana. The GPR lines results showed that the maximum amplitude and the total amplitude area decreased with the increase of soil depth at 0-15 cm. At 15-35 cm below the soil surface, the two parameters began to fluctuate. The maximum amplitude and total amplitude area of liana plot both were larger than that of secondary arbor plot. It was found that the dye area ratio was logarithmic with the maximum amplitude and the total amplitude area. The logarithm relationship between the dye area ratio and the maximum amplitude was y=25.104lnx+25.137 (R2=0.8697), and the logarithm relationship between the dye area ratio and the total amplitude area was y=23.874lnx-26.862 (R2=0.6173). The soil compactness of secondary arbor forest was better than that of liana. Therefore, there was less electromagnetic signal lost in the secondary arbor forest during the physical process. The electromagnetic signal of liana plot fluctuated greatly and lost more signals. It could be seen that the difference of soil structure between different layers of liana vegetation was more distinct than that of the secondary arbor, which led to preferential flow more frequently under liana coverage. In order to protect the safety of groundwater, it is necessary to cut down lianas appropriately and moderately in areas with poor drainage such as riverside bed zone and low-lying depression in front of hills. It could inhibit the over-development of preferential flow in soil under lianas coverage. 参考文献 相似文献 引证文献

Effects of straw returning to movement characteristics of soil preferential flow in sugarcane fields

The measures of returning straw to the field can change soil environment in the field and affect crop growth. In order to explore the impacts of different straw returning measures on the preferential flow in the field, we investigated the movement characteristics of preferential flow in sugarcane fields under different straw returning measures [straw mulching (CM), straw burning mulching (BM), and non-straw mulching (CK)] in Guangxi by combining image analysis techniques with ecological landscape pattern analysis methods. The results showed that under the same external water supply environment, soil staining morphology of non-straw mulching sugarcane fields differentiated into finger-like and clump-like. Both straw mulching and straw burning mulching were mainly differentiated into clump-like. The mean total staining area ratio was significantly higher than that of non-straw mulching (26.0%). The ratio of surface staining area decreased rapidly under non-straw mulching. The water movement range decreased rapidly under straw mulching and straw burning mulching in the depth of 15-30 cm. The change rate of straw mulching staining area ratio was the lowest in the deep soil. The shape index of non-straw mulching was 15.54. The water flow movement was more concentrated. The average sub-circular index of straw mulching and straw burning mulching was 0.67 in the sugarcane field, with a higher degree of preferential flow bending, an average proximity index of 0.87, and better water flow connectivity. The average substrate flow depth (3.52 cm) and edge density index (11.51) were the smallest under non-straw mulching, but the priority flow ratio was the largest (73.2%), and the spatial development degree of preferential flow was the highest. The straw returning measures reduced the preferential flow in the sugarcane fields, with positive effects on water conservation.

宁夏荒漠草原不同林龄人工柠条林地土壤优先流研究

土壤优先流作为土壤中常见的水分流动方式，会造成土壤水分流失、地下水污染及坡面土体稳定性降低等问题。以位于宁夏盐池县的典型荒漠草原为研究区域，通过土壤水分入渗染色法、CT扫描法、图像处理技术相结合的分析方式，选取人工营造9、14、24、35年的柠条灌丛林地，以空白草地作为对照，探究不同恢复年限人工柠条林土壤优先流特征及其与土壤大孔隙与根系的关系。结果表明：（1）不同林龄柠条林地土壤优先流特征及大孔隙度具有显著差异，表现为随着种植年份的增加，土壤大孔隙度逐渐升高，土壤入渗染色深度随之加深，同时染色面积比随着柠条林林龄的增加而增大。（2）土壤基质流深度表现为随着种植年份的增加而增大，人工柠条林地的土壤优先流程度显著高于草地。（3）随着人工柠条林龄的增加，土壤根系数量增加，而灌丛生长发育过程中的根系活动使得灌丛林地土壤具有更多迂曲度低、连通性强的大孔隙，这些大孔隙是导致土壤水分优先迁移的主要因素。因此，植物根系和土壤大孔隙变化是影响荒漠草原人工柠条恢复过程中土壤水分分布的关键因素，合理配置人工林以改善根系及土壤结构特征，或可有效提高荒漠草原地区的土壤水分利用效率。;Soil preferential flow is a common way of water flow in the soil, which causes soil water loss, groundwater pollution, and reduces slope soil stability. This paper takes a typical desert grassland as the research area in Yanchi County, Ningxia. And we selected artificially constructed shrubland (9, 14, 24, and 35 ages) as the research objects and used blank grassland as the control group, which explored the characteristics of soil preferential flow and its relationship with soil structure by soil water infiltration combining dyeing method, CT scanning method, and image processing technology. The results showed that:(1) there were significant differences in soil preferential flow characteristics and macroporosity. Soil macroporosity gradually and color depth of soil infiltration increased with the increase of planting years. Meanwhile, the ratio of dyeing area increased with the increase of Caragana korshinskii forest age. (2) The depth of soil matrix flow increased with the increase of vegetation planting years, and the soil priority degree of artificial Caragana korshinskii forest was significantly higher than that of grassland. (3) With the increase of the age of Caragana korshinskii plantation, the number of soil roots improved. The root activity in the process of shrub growth and development made the soil to have much lower tortuosity and stronger connectivity macropores, which were the main factors to lead to the preferential migration of soil water. Therefore, the changes of plant roots and soil macropores are the key factors to effect the soil water distribution in the process of artificial Caragana korshinskii restoration in desert steppe. The reasonable allocation of artificial forest plantation could improve soil water use efficiency in desert steppe effectively owing to its role in root system and soil structure characteristics modification.

Solute transport in permeable porous media containing a preferential flow feature: Investigation of non-Darcian flow effects

Fractures, faults, karstic features and/or interbedded layers of coarse sediment often manifest in the form of preferential flow features (PFFs). Previous investigations into the effects of PFFs on solute plume distributions within otherwise permeable host rocks have treated flow in PFFs as Darcian. However, flow through faults and fractures is known to exhibit non-Darcian flow behavior. The current study extends previous investigations of the effects of PFFs (e.g., a fault or fracture) on solute plumes in permeable aquifers that assume Darcian flow in the fault/fracture. The finite-element model COMSOL Multiphysics was applied to examine how non-Darcian flow in a single PFF influences flow fields and steady-state solute plume distributions in permeable aquifers, compared with the Darcian flow assumption. The Forchheimer equation was applied within numerical models to represent flow in the PFF for a variety of PFF-permeability contrasts, PFF apertures and matrix flow directions. The refraction of flow lines at matrix-PFF interfaces and the specific discharge in the PFF were found to be smaller in non-Darcian models, leading to larger peak solute concentrations (by up to 160%) and narrower plumes compared to Darcian models. In addition, the impact of non-Darcian flow on flow fields and solute plumes was greater with smaller matrix hydraulic conductivity, larger PFF aperture and larger incidence angle at the matrix-PFF interface. Upstream dispersion at the matrix-PFF interface, observed in previous matrix-PFF studies of solute transport as the result of steep solute concentration gradients opposing head gradients, was found to be reduced when non-Darcian flow was considered in PFFs. This study highlights that non-Darcian flow effects may be significant in the simulation of flow and solute transport within high-permeability PFFs embedded in otherwise porous aquifers.

Investigating colloid-associated transport of cadmium and lead in a clayey soil under preferential flow conditions

Abstract Colloids have a high adsorption capacity and can be mobile under preferential flow, and so may facilitate heavy metal migration. Heavy metal migration with soil colloids in a clayey soil under preferential flow conditions was investigated through experiments. Adsorption tests were carried out to determine the adsorption of Cd2+ and Pb2+ to the clay and colloids. The preferential flow characteristics in the soil column were investigated by dye tracing tests. The mobility of soil colloids in the soil column was studied by breakthrough tests. Leaching tests of cadmium and lead with and without colloids were carried out. The adsorption tests showed that soil colloids adsorbed more cadmium and lead than the silty clay. The dye tracing tests showed that moderate preferential flow in the soil column can be obtained by choosing clod-size distribution and dry density. The co-leaching test showed that the outflow of cadmium and lead was 1.49 and 33.88 times greater with colloids than without, respectively. The heavy metals adsorbed onto clay and the pore concentrations were both lower with colloids than without, indicating more heavy metals migrated downward with colloids. The migration of cadmium and lead was greatly enhanced by colloids under preferential flow conditions.

Influence of alternated drying and wetting on the characteristics of soil preferential flow formation in Honghe Arid Valley.

To clarify the effects of alternation of drying and wetting on the formation of soil preferential flow in arid valley, taking the wasteland in the arid valley of Honghe River as the research object, we analyzed the soil preferential flow characteristics before and after the simulation of drying and wetting alternation based on dyeing tracer method, water breakthrough curve, and image processing technology. The results showed that, under the simulated alternation of drying and wetting, the matrix flow occurred in the 0-10 cm soil layer, the dyeing depth reached 35 cm, the horizontal width of the preferred path was only 3-10 cm, and the dyeing area curve fluctuated little. Simulated alternation of drying and wetting led to significant increases in the steady effluent, macropores number, and macroporosity. In the 0-20 cm soil layer, the steady effluent after alternation of drying and wetting was about 0.27 cm3·s-1 higher than that non-alternation of drying and wetting, macropores number in dyeing area was about 1.4 times higher, and the macroporosity was 13.4% higher. The macropores number was positively correlated with stable flow rate. After simulated alternation of drying and wetting, the number of macropores from large to small was 0.6-0.8 mm＞0.8-1.0 mm＞1.0-1.5 mm＞1.5-2.0 mm＞2.0-3.7 mm, while under non-alternation of drying and wetting, it was 0.8-1.0 mm＞0.6-0.8 mm＞1.0-1.5 mm＞2.0-3.7 mm＞1.5-2.0 mm. The macropores number in each pore size range was significantly correlated with the dyeing area ratio. After simulated alternation of drying and wetting, the correlation increased, and the dominant factor affecting the occurrence of preferential flow changed from the macropores number in the pore size range of 1.5-2.0 mm to that of 0.8-1.0 mm. Therefore, the alternation of drying and wetting would affect the characteristics of macropores, which caused the soil to be more prone to preferential flow and with higher magnitude.

Effects of Infiltration Amounts on Preferential Flow Characteristics and Solute Transport in the Protection Forest Soil of Southwestern China

Preferential flow has an important role as it strongly influences solute transport in forest soil. The quick passage of water and solutes through preferential flow paths without soil absorption results in considerable water loss and groundwater pollution. However, preferential flow and solute transport under different infiltration volumes in southwestern China remain unclear. Three plots, named P20, P40 and P60, were subjected to precipitation amounts of 20, 40 and 60 mm, respectively, to investigate preferential flow and solute transport characteristics via field multiple-tracer experiments. Stained soils were collected to measure Br− and NO3− concentrations. This study demonstrated that precipitation could promote dye tracer infiltration into deep soils. The dye tracer reached the maximum depth of 40 cm in P60. Dye coverage generally reduced with greater depth, and sharp reductions were observed at the boundary of matrix flow and preferential flow. Dye coverage peaked at the soil depth of 15 cm in P40. This result demonstrated that lateral infiltration was enhanced. The long and narrow dye coverage pattern observed in P60 indicated the occurrence of macropore flow. Br− and NO3− were found at each soil depth where preferential flow had moved. Increasing precipitation amounts increased Br− and NO3− concentration and promoted solute movement into deep soil layers. Solute concentration peaked at near the end of the preferential flow path and when preferential flow underwent lateral movement. These results indicated that the infiltration volume and transport capacity of preferential flow had important effects on the distribution of Br− and NO3− concentrations. The results of this study could help expand our understanding of the effects of preferential flow on solute transport and provide some suggestions for protection forest management in southwestern China.

Determining the influencing factors of preferential flow in ground fissures for coal mine dump eco-engineering.

Ground fissures (GF), appearing in front of dumps, are one of the most obvious and harmful geological hazards in coal mining areas. Studying preferential flow and its influencing factors in the ground fissures of dumps may provide basic scientific support for understanding the rapid movement of water and vegetation restoration and reconstruction in mining areas. Based on field surveys of ground fissures, three typical ground fissures were selected in the studied dump. The morphological characteristics of preferential flow for ground fissures were determined through field dye tracing, laboratory experiments, and image processing technology. The results indicated that the lengths of the three ground fissures ranged from 104.84 cm to 120.83 cm, and the widths ranged from 2.86 cm to 9.85 cm. All of the ground fissure area densities were less than 10%, and the proportion of ground fissure surface area was small in the dump. The maximum fissure depth was 47 cm, and the minimum was 16 cm. The ground fissure widths ranged from 0 cm to 14.98 cm, and the fissure width and fissure width-to-depth ratios decreased with increasing soil depth. The stained area was greater than 90% in the 0–5 cm soil layers of the three fissures, and water movement was dominated by matrix flow. The stained width decreased from 90 cm to 20 cm with increasing soil depth. The preferential flow was mainly concentrated on both sides of the fissure, which was distributed as a “T” shape. The preferential flow stained area ratios were 27.23%, 31.97%, and 30.73%, respectively, and these values decreased with increasing soil depth. The maximum stained depths of the preferential flow among the three fissures were different, and the maximum stained depth of GF II was significantly larger than that of GF I and GF III (P < 0.05). The stained path numbers of the three fissures ranged from 0 to 49. With increasing soil depth, the stained path number first increased and then decreased. The stained path widths of the three fissures ranged from 0 cm to 90 cm. With the increase in soil depth, the stained path width decreased. The stained area ratio was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter, and sand content and was significantly negatively correlated with soil water content and clay content. The stained path number was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity and soil organic matter. The stained path width was significantly positively correlated with the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter and sand content and was significantly negatively correlated with clay content. Plant roots could significantly increase the stained area ratio, stained path number, and width and promote the formation and development of preferential flow.

黄河三角洲刺槐群落土壤优先流及养分分布特征

黄河三角洲湿地面临严重的水资源短缺、湿地退化、土壤盐碱化等问题，湿地土壤干旱缺水，土壤收缩产生裂隙等优先流路径，在小尺度上改变湿地内部以及湿地板块之间水文连通性，小尺度水文效应往往制约大尺度水文连通性，基于当前社会对湿地修复的迫切需求，从小尺度对水文连通研究有必要加以重视。然而，目前的研究多集中在大尺度水文连通的阐述，为进一步明确黄河三角洲湿地小尺度水文连通和养分随优先流路径运移分布情况，以此区域典型刺槐群落为研究对象，基于室外染色示踪实验和室内图像处理技术，分析土壤优先流形态和分布特征，并探究优先流和土壤养分含量之间的关系。结果表明：（1）刺槐群落染色面积比随土壤深度变化主要包括2个阶段，第一阶段：优先流和基质流相互影响作用显著，第二阶段：优先流和基质流相互作用不显著，优先流强度逐渐增强，明显存在指流现象，极少部分管流现象。（2）刺槐群落染色面积比、基质流深度和百分之五十染色深度的数值较大，优先流区染色面积比较小，基质流深度发生在土壤深10-15 cm区间，该类型植被群落水流均匀入渗深度较大，优先流和基质流相互作用程度大，水文连通性较高。（3）优先流区土壤有机碳、有机质、全氮、全磷和有效磷含量值均高于基质流区；（4）土壤优先流区染色面积比与5种养分指标均呈负相关关系，有机碳、有机质和有效磷含量受优先流路径影响显著。（5）土壤中有机碳、有机质和有效磷含量在一定程度上可以衡量土壤优先流发育水平。研究结果可为黄河三角洲湿地生态系统保护和管理提供参考。;More serious environmental problems including water shortage, wetland degradation, and soil salinization are gradually recognized in the Yellow River Delta wetland. Due to water deficiency of wetland soils, preferential pathways including soil cracks occur as soil shrinkage which changes the hydrological connectivity of inside wetlands or between wetlands at small scale, and small scale hydrological processes tend to affect the large scale hydrological cycle, depending on our urgent needs to restore wetlands, it is necessary to pay attentions to the study of hydrological connectivity research from microcosmic perspectives to promote the understanding of connotation of hydrological connectivity. However, most of the current studies focused on the hydrological connectivity from macroscopical perspectives. In order to clarify the small-scale hydrological connectivity in the Yellow River Delta, the morphology and distribution characteristics of preferential flow in soil were analyzed based on outdoor dyeing tracer experiment and indoor image processing technology. The relationship between preferential flow and soil nutrient content was explored. The results show that:(1) There are two stages in the variation of the dry coverage of Robinia pseudoacacia Linn community with soil depth. The first stage:the interaction between preferential flow and matrix flow is significant; the second stage:the interaction between preferential flow and matrix flow is not significant, and the intensity of preferential flow is gradually increasing, finger flow phenomenon and a small part of pipe flow phenomenon is observed. (2) Vertical soil-profile indexes (dry coverage, dry coverage of preferential pathway, depth of diffusion area, and depth of 50% dry coverage) reveal a strong interaction between preferential flow and matrix flow, and depth of diffusion area occurs in the range of 10-15cm in the soil, which indicates that this type of vegetation community has large depth of water infiltration flow uniformly and the hydrological connectivity is high; (3) The contents of soil organic carbon, organic matter, total nitrogen, total phosphorus and available phosphorus in preferential flow area were higher than those in matrix flow area; (4) The dye coverage ratio of preferential flow area was negatively correlated with the five nutrient indexes, and the contents of organic carbon, organic matter and available phosphorus were significantly affected by preferential pathway. (5) The content of organic carbon, organic matter and available phosphorus in soil can measure the development level of preferential flow to a certain extent. These results can provide references for wetland ecosystem protection and management in the Yellow River Delta.

Study on the Preferential Flow Characteristics under Different Precipitation Amounts in Simian Mountain Grassland of China

Understanding the response of preferential flow paths to water movement is an important topic in soil hydrology. However, quantification of the complicated distribution patterns of preferential flow paths remains poorly understood. Therefore, dye experiments were conducted to investigate preferential flow characteristics under three different precipitation amounts (20, 40 and 60 mm, numbered as the G20, G40 and G60, respectively) in Simian Mountain grassland, Chongqing province, China. O-ring statistics were used to analyze the spatial distribution characteristics and the spatial correlation of preferential flow paths. Results revealed that precipitation could promote dye tracer infiltration into deeper soils, reaching the maximum depth of 55 cm in G60. The number of preferential flow paths in G60 plots was 3.0 and 7.4 times greater than those of G40 and G20, respectively. Structural distribution of the preferential flow paths showed a gradually clumped pattern with the increase of precipitation, which was conducive to enhancing the correlation between preferential flow paths in each pore size range. These results could expand our understanding of the effects of precipitation on the characteristic of preferential flow paths in grassland, which is helpful to evaluate the water movement in the study area.

Inferring Subsurface Preferential Flow Features From a Wavelet Analysis of Hydrological Signals in the Shale Hills Catchment

AbstractPreferential flow (PF)‐dominated soil structure is often considered a unique system consisting of micropores and macropores and thus supposed to provide dual‐pore filtering effects on hydrological signals, through which smoothing effects are likely to be stronger for matrix flow and weaker for PF via macropores. By using time series of hydrological signals (precipitation, canopy interception, throughfall, soil moisture, evapotranspiration, water storage in soil and groundwater, and catchment discharge) propagating through the Shale Hills Catchments and representative soil series, the filtering effects of the catchment and soil profiles were tested through the wavelet analysis. Typical filtering effects, that is, the characteristic of the role of soil and the groundwater table as a buffer, were observed from the wavelet spectrum, gradually smoothing off the precipitation signal. The hypothesized dual‐pore style filtering effects of the soil profile were also confirmed through the coherence spectra and phase differences, rendering them applicable for possible use as “fingerprints” of PF to infer subsurface flow features. We found that PF dominates the catchment's discharge response at the scales from 3 to 12 days, which contributes to the catchment discharge mainly as subsurface lateral flow at upper or middle soil horizons. Through subsurface PF pathways, even the hilltop is likely hydrologically connected to the valley floor, building connections with or making contributions to the catchment discharge. This study highlights the potential of wavelet analysis for retrieving and characterizing subsurface flow processes based on the revealed dual‐pore filtering effects of the soil system. Although some limitations and uncertainties still exist, we believe that wavelet methods provide a highly potential but underexplored approach to studying subsurface hydrology.

Velocities, Residence Times, Tracer Breakthroughs in a Vegetated Lysimeter: A Multitracer Experiment

AbstractFlow velocities, residence times, and tracer breakthroughs at the lysimeter scale are affected by matrix properties and preferential flow. Despite their relevance to transport processes, however, the relative timing of preferential flow, and its link to transit times through the soil block, is still poorly described. Here we present and analyze tracer data from a 2.5 m3 vegetated lysimeter experiment where 18 mm of isotopically labeled water was added as a pulse and then followed with a series of tracer‐free controlled rainfall events for 5 months. A solution of two fluorobenzoid acid tracers was also injected and tracked. Time series of soil water samples at three different depths and bottom drainage samples were collected and analyzed. Unlike past lysimeter experiments, a willow tree grown within the lysimeter exerted strong evapotranspiration fluxes. By comparative analysis of soil water and bottom drainage samples, we show the presence of both translatory and preferential flow features reflecting the interplay of slow vertical percolation and fast recharge through macropores. We found that water ponding and evaporating from the top of the lysimeter after irrigation prompted samples to be highly and irregularly fractionated. Comparative analyses of multitracer breakthroughs (adjusted by removing fractionation effects) showed that fluorobenzoid acid tracers reached the bottom of the lysimeter earlier than the isotopes, likely due to the effect of plant uptake. Our results underscore the essential role of models to interpret tracer behavior and, critically, the importance of future experiments aimed at measuring the ages of the water abstracted by vegetation.

Preferential flow characteristics of reclaimed mine soils in a surface coal mine dump

There are a large number of macropores/tubular channels of a few centimeters and plant roots in reclaimed dump soils, which are the main reasons for the formation of soil macropores and soil preferential flow. To systematically study the morphological characteristics and variation of soil preferential flow for different reclaimed vegetations in a dump, a dye-staining experiment and physical and chemical analysis were carried out to investigate the formation mechanism and influencing factors of soil preferential flow in the vegetation restoration process. The results indicate that there were differences in the soil water breakthrough curves for different plots. The macropore effluent rate generally increased at first and then tended to stabilize. The soil steady effluent rate decreased with increasing soil depth, which reached the maximum and minimum values at the depths of 0∼5cm (0.0193∼0.0315mms-1) and 50∼60cm (0.0028∼0.0035mms-1), respectively. Furthermore, the radius of soil macropores under different types of reclaimed vegetation ranged from 0.03 to 4.71mm, most of which ranged from 0.11 to 2.36mm. The soil macroporosity of different reclaimed vegetation types ranged from 0.03 to 16.58%, which was significantly greater than 5%. The soil macroporosity determined 65% of the variation in the steady effluent rate and 42% of the variation in the saturated hydraulic conductivity. Furthermore, the dye coverage ratio decreased as the soil layer depth increased in different plots, and there were some differences in each plot. The maximum dye coverage ratio occurred in the 0∼5cm soil layer, which reached 90.37%. The dye coverage ratio at a depth of 0∼60cm in six plots followed the order of Robinia pseudoacacia (26.48%)>Ulmus pumila (20.12%)>mixed forest (17.32%)>farmland (15.06%)>shrub (13.97%)>weeds (10.07%). The soil preferential flow mostly occurred in the 0∼40cm soil depth layer, which occupied more than 93% of the total soil profile (0∼60cm). Moreover, a Pearson correlation was used to analyze the relationship between environmental factors (soil, water, and plant factors) and the dye coverage ratio. The dye coverage ratio of soil preferential flow under different reclamation vegetations was very significantly or significantly positively correlated with the gravel content, mean radius of soil macropores, soil saturated hydraulic conductivity, root weight density, and root length density, which promoted the formation and development of soil preferential flow. This study will provide a scientific basis for understanding the formation mechanism and perfecting the research system of soil preferential flow, vegetation restoration, and reconstruction in a dump; furthermore, this research offers significance guidance in the construction of green mines and the development of regional economics.