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Felix Naef - One of the best experts on this subject based on the ideXlab platform.
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simulating surface and subsurface initiation of Macropore flow
Journal of Hydrology, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Abstract Initiation of Macropore flow either from the soil surface or from a saturated soil layer at depth is a first order control on water flow in Macropores and water transfer from Macropores into the surrounding soil matrix. Nevertheless, these initiation processes have not been well documented. We surveyed surface topography at four field sites with permanent grass vegetation with grid spacing of 10 cm and applied Kriging to derive the spatial correlation structure. We then simulated the water flux into Macropores based on different combinations of surveyed surface micro-topographies, spatial earthworm burrow distributions, and the soil properties, to examine more fully the role of Macropore drainage area (MDA) on Macropore flow initiation. The spatial distributions of the earthworm burrows were derived from horizontal soil sections extracted from each study profile. The MDA was calculated for different sets of surface topography and Macropore density using a flow accumulation algorithm. The resulting MDA of each Macropore was used to calculate the total relative MDA, which is equal to the proportion of overland flow draining into Macropores, and the MDA probability distribution. The results showed that the Macropore density primarily controlled the total MDA and that surface micro-topography strongly influenced the probability distribution of the MDA. Only a few Macropores contributed significantly to the total Macropore flow whereas the majority of Macropores received little water; a phenomenon especially pronounced for a rough surface topography and for a low soil surface gradient. The simulated probability distribution of subsurface initiation was very different from the distribution derived for surface initiation; more symmetrical, less variable and slightly influenced by the roughness and the gradient of the interface between the saturated and the low permeable soil layer. We conclude that the different amount of water supplied to each Macropore further alters the percolation depth and transport of solutes in macroporous soils and should be considered for modelling infiltration in macroporous soils.
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an experimental tracer study of the role of Macropores in infiltration in grassland soils
Hydrological Processes, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Water flow in Macropores is an important mechanism of infiltration in natural soils and, as such, is crucial for the prediction of runoff generation. The major flow processes controlling Macropore flow are the initiation of Macropore flow (water supply into Macropores) and the water transfer from the Macropores into the surrounding soil matrix (interaction). The water movement during infiltration and the resulting flow paths were studied with combined sprinkling and dye tracer experiments under different rainfall intensities and initial soil moisture conditions. The dye tracer was continuously applied with the sprinkling water on 1 m2 plots. After the sprinkling, horizontal and vertical soil sections were prepared for surveying dye patterns, which showed the cumulated flow pathways in the soils. These experiments were carried out on four hillslope sites covered with grassland, where earthworms mainly built the Macropore system. The evaluation of the flow processes in the soil was based on classified dye patterns and measurements of water content and matric potential. The results illustrate how flow in earthworm channels influences general hydrological flow processes during extreme rainfall events. Macropore flow was initiated from the soil surface or from a saturated or partially saturated soil layer. Transfer of water from the Macropores into the soil matrix was mainly influenced by the soil properties and soil water content. The permeability of the underlying bedrock in combination with this transfer of water controlled the drainage of the Macropores. Finally, major effects of Macropore flow processes on the hydrological response were extracted. Infiltration excess overland flow was reduced if water bypassed the less permeable layer through Macropores, saturation excess overland flow was less affected by Macropores, and subsurface flow was activated very rapidly because the infiltrated water bypassed the soil matrix. This study highlights the most important processes that have to be considered in order to understand better and to model infiltration in natural soils in the future. Copyright © 2003 John Wiley & Sons, Ltd.
Markus Weiler - One of the best experts on this subject based on the ideXlab platform.
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Macropores and preferential flow—a love‐hate relationship
Hydrological Processes, 2016Co-Authors: Markus WeilerAbstract:Preferential flow is of high relevance for runoff generation, transport of chemicals and nutrients, and the transit time distribution of water in the soil or watershed. However, preferential flow effects are generally ignored in lumped hydrological models. And even most physically-based models ignore Macropores and preferential flow features at the soil and hillslope scale. Keith Beven was never satisfied with this situation and he tried again and again to convince the scientific community to focus their research on the complex topic of Macropore and preferential flow. Although he recognized how difficult it is to correctly include preferential flow in hydrological models, he made substantial progress defining and describing Macropore flow and showing its relevance, developing models to simulate preferential flow, and in particular, the interaction between Macropores and the soil matrix. In this short commentary, I reflect on these achievements and outline a vision for research in preferential flow experiments and modeling.
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simulating surface and subsurface initiation of Macropore flow
Journal of Hydrology, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Abstract Initiation of Macropore flow either from the soil surface or from a saturated soil layer at depth is a first order control on water flow in Macropores and water transfer from Macropores into the surrounding soil matrix. Nevertheless, these initiation processes have not been well documented. We surveyed surface topography at four field sites with permanent grass vegetation with grid spacing of 10 cm and applied Kriging to derive the spatial correlation structure. We then simulated the water flux into Macropores based on different combinations of surveyed surface micro-topographies, spatial earthworm burrow distributions, and the soil properties, to examine more fully the role of Macropore drainage area (MDA) on Macropore flow initiation. The spatial distributions of the earthworm burrows were derived from horizontal soil sections extracted from each study profile. The MDA was calculated for different sets of surface topography and Macropore density using a flow accumulation algorithm. The resulting MDA of each Macropore was used to calculate the total relative MDA, which is equal to the proportion of overland flow draining into Macropores, and the MDA probability distribution. The results showed that the Macropore density primarily controlled the total MDA and that surface micro-topography strongly influenced the probability distribution of the MDA. Only a few Macropores contributed significantly to the total Macropore flow whereas the majority of Macropores received little water; a phenomenon especially pronounced for a rough surface topography and for a low soil surface gradient. The simulated probability distribution of subsurface initiation was very different from the distribution derived for surface initiation; more symmetrical, less variable and slightly influenced by the roughness and the gradient of the interface between the saturated and the low permeable soil layer. We conclude that the different amount of water supplied to each Macropore further alters the percolation depth and transport of solutes in macroporous soils and should be considered for modelling infiltration in macroporous soils.
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an experimental tracer study of the role of Macropores in infiltration in grassland soils
Hydrological Processes, 2003Co-Authors: Markus Weiler, Felix NaefAbstract:Water flow in Macropores is an important mechanism of infiltration in natural soils and, as such, is crucial for the prediction of runoff generation. The major flow processes controlling Macropore flow are the initiation of Macropore flow (water supply into Macropores) and the water transfer from the Macropores into the surrounding soil matrix (interaction). The water movement during infiltration and the resulting flow paths were studied with combined sprinkling and dye tracer experiments under different rainfall intensities and initial soil moisture conditions. The dye tracer was continuously applied with the sprinkling water on 1 m2 plots. After the sprinkling, horizontal and vertical soil sections were prepared for surveying dye patterns, which showed the cumulated flow pathways in the soils. These experiments were carried out on four hillslope sites covered with grassland, where earthworms mainly built the Macropore system. The evaluation of the flow processes in the soil was based on classified dye patterns and measurements of water content and matric potential. The results illustrate how flow in earthworm channels influences general hydrological flow processes during extreme rainfall events. Macropore flow was initiated from the soil surface or from a saturated or partially saturated soil layer. Transfer of water from the Macropores into the soil matrix was mainly influenced by the soil properties and soil water content. The permeability of the underlying bedrock in combination with this transfer of water controlled the drainage of the Macropores. Finally, major effects of Macropore flow processes on the hydrological response were extracted. Infiltration excess overland flow was reduced if water bypassed the less permeable layer through Macropores, saturation excess overland flow was less affected by Macropores, and subsurface flow was activated very rapidly because the infiltrated water bypassed the soil matrix. This study highlights the most important processes that have to be considered in order to understand better and to model infiltration in natural soils in the future. Copyright © 2003 John Wiley & Sons, Ltd.
Mingan Shao - One of the best experts on this subject based on the ideXlab platform.
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application of x ray tomography to quantify Macropore characteristics of loess soil under two perennial plants
European Journal of Soil Science, 2016Co-Authors: Tongchuan Li, Mingan ShaoAbstract:Summary With the advent of large-scale restoration of vegetation in the Loess Plateau, northwest China, there has been an increase in concern about the suitability of loess soil to support permanent vegetation cover. The quantification of soil Macropore characteristics could be critical in determining the architecture and hydrological processes of loess soil on the plateau. In this research, we compared the effects of Purple alfalfa (Medicago sativa L.) and Korshinsk peashrub (Caragana korshinskii K.) on the Macropore characteristics of a soil profile on the plateau with computed tomography (CT). To achieve this, undisturbed cores of soil were excavated from beneath purple alfalfa (ALF), 22-year-old Korshinsk peashrub (KOP22) and 40-year-old Korshinsk peashrub (KOP40) vegetation types in the Liudaogou watershed for evaluation. The soil Macropore characteristics (including macroporosity, largest pore area, amounts of Macropores, circularity, surface area density, branch density, junction density and connectivity) were determined with image analysis software. Soil under KOP22 and KOP40 treatments had approximately the same amounts of Macropores (17 per 6359-mm2 area), which was three times greater than those under ALF plants. Macroporosity ratios of soil under KOP22 and KOP40 plants to that under ALF plants were 2.3 and 3.6, respectively. Compared with KOP22, KOP40 had a larger macroporosity and the largest pore area at the 100–300-mm soil depth. The KOP plants, in particular KOP40, apparently improved the Macropore network structure of the soil more than ALF. However, the Macropores under ALF were much rounder at the 100–300-mm soil depth than those under the other two plants. There was no correlation between Macropore characteristics and organic matter content of the soil at 100–400-mm depth. Nevertheless, macroporosity was strongly correlated with the largest pore area. The findings of this research are critical for developing strategies for the restoration of vegetation in the Loess Plateau through improvement of the hydrological process of loess soil. Highlights We examined Macropore characteristics of loess soil on the Loess Plateau in China. We determined the effects of different plants on soil Macropore characteristics. Soil under Korshinsk peashrub had better Macropore structure than that under Purple alfalfa. Long-term recovery of KOP benefits the Macropore structure most on the northern Loess Plateau.
H Foll - One of the best experts on this subject based on the ideXlab platform.
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crystal orientation dependence and anisotropic properties of Macropore formation of p and n type silicon
Journal of The Electrochemical Society, 2001Co-Authors: M Christophersen, J Carstensen, Silke Ronnebeck, Ch Jager, W Jager, H FollAbstract:The dependence of Macropore morphology on the orientation of p- and n-type silicon samples was studied for various organic and aqueous electrolytes containing hydrofluoric acid. Scanning electron microscopy was used studying the morphology of the maeropores. The results show that the Macropore formation in p- and n-type silicon is a strongly anisotropic process. Depending maeropores. The results show that the Macropore formation in p- and n-type silicon is a strongly anisotropic process. Depending on the substrate orientation and preferred growth directions could be observed. The mierostructure of Macropores was studied by analytical and high-resolution transmission electron microscopy. The surface of Macropores in n- and p-type Si(001) shows {111} facets indicating that {111} planes are stabilized against further dissolution. Breakthrough pores show very specific anisotropic properties independent of the electrolyte. These pores consist of periodic arrangements of truncated octahedral voids with {111} walls strung up in directions. The erystal orientation dependence of pore formation reflects specific properties of the pore formation mechanism and one of the important electrolyte parameters is the ability to form an anodic oxide. Macropores formed in more strongly oxidizing electrolytes tend to have smoother Macropore walls.
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Macropore formation on highly doped n type silicon
Physica Status Solidi (a), 2000Co-Authors: M Christophersen, J Carstensen, H FollAbstract:Using specially “designed” electrolytes, it is possible to obtain Macropores even in highly doped n-type silicon (0.020–0.060 Ωcm) without illumination. Based on predictions of the “current-burst-model” [phys. stat. sol. (a) 182, 63 (2000), this issue], HF-containing electrolytes were systematically modified with strongly oxidizing components and evaluated with respect to their ability to produce Macropores. Well developed Macropores with depths up to 10 μm and pore diameters between 200 nm and 2 μm could be obtained in several cases. The Macropore nucleation starts with a facetting of the surface on {111} planes.
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Macropore Formation on Highly Doped n‐Type Silicon
Physica Status Solidi (a), 2000Co-Authors: M Christophersen, J Carstensen, H FollAbstract:Using specially “designed” electrolytes, it is possible to obtain Macropores even in highly doped n-type silicon (0.020–0.060 Ωcm) without illumination. Based on predictions of the “current-burst-model” [phys. stat. sol. (a) 182, 63 (2000), this issue], HF-containing electrolytes were systematically modified with strongly oxidizing components and evaluated with respect to their ability to produce Macropores. Well developed Macropores with depths up to 10 μm and pore diameters between 200 nm and 2 μm could be obtained in several cases. The Macropore nucleation starts with a facetting of the surface on {111} planes.
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crystal orientation and electrolyte dependence for Macropore nucleation and stable growth on p type si
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2000Co-Authors: M Christophersen, J Carstensen, A Feuerhake, H FollAbstract:Abstract Macropore formation in moderately doped p-type Si was studied in mostly galvanostatic experiments (2–10 mA cm −2 ) with various fluoride containing electrolytes and substrate orientations [(100), (511), (5 5 12), (111)] from the nucleation phase to the phase of stable pore growth. Macropores on p-type Si always grow anisotropically in 〈100〉- and 〈113〉-directions. The most important parameter of the electrolyte is its ability to supply oxygen and hydrogen. Whereas oxygen is necessary for smoothing the pore tips, hydrogen is the decisive factor for the anisotropic growth and the passivation of Macropore side walls. Based on a better theoretical understanding of the electrode processes in general pore formation in particular, etching conditions could be optimized for the generation of Macropores in p-type Si with better aspect ratios, better stability, and smaller diameters than those in n-type Si.
J Fredericia - One of the best experts on this subject based on the ideXlab platform.
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flow and transport processes in a macroporous subsurface drained glacial till soil i field investigations
Journal of Hydrology, 1998Co-Authors: Karen G Villholth, K H Jensen, J FredericiaAbstract:Abstract The qualitative and quantitative effects of Macropore flow and transport in an agricultural subsurface-drained glacial till soil in eastern Denmark have been investigated. Three controlled tracer experiments on individual field plots (each approximately 1000 m 2 ) were carried out by surface application of the conservative chloride ion under different application conditions. The subsequent continuous long-term monitoring of the rate and chloride concentration of the drainage discharge represented an integrated and large-scale approach to the problem. In addition, point-scale determination of Macropore structure and hydraulic efficiency, using image analysis and tension infiltration, and of soil water content, level of groundwater table, and chloride content of soil water within the soil profile yielded insights into small-scale processes and their associated variability. Macropore flow was evidenced directly by the rapid (within 10 mm of water input) and abrupt chloride break-through in the drainage water at 1.2 m depth in two of the tracer experiments. In the third experiment, the effect of Macropore transport was obvious from the rapid and relatively deep penetration of the tracer into the soil profile. Dye infiltration experiments in the field as well as in the laboratory supported the recognition of the dominant contribution of Macropores to the infiltration and transport process. The soil matrix significantly influenced the tracer distribution by acting as a source or sink for continuous solute exchange with the Macropores. An average field-determined active macroporosity constituted 0.2% of the total porosity, or approximately 10% of the total macroporosity.
