Development Of Preferential Flow Research Articles

Forest restoration effects on soil preferential flow in the paleo-periglacial eastern liaoning mountainous regions, China

To provide a practical reference index for the protection of water conservation forests and the establishment of vegetation in different forest restoration areas, we seek to clarify the preferential flow development and its influencing factors under different rainfall events in the forest restoration areas of paleo-periglacial landform in eastern Liaoning Province of China. To quantify the preferential flow development (PFI) in soil profile-scale through soil profile indexes, we carried out dual-tracer experiments with dyeing in two types of forest restoration lands (plantation forest, PF, and natural secondary forest, NSF) in the paleo-periglacial landform forestland to obtain the soil water infiltration trajectories and water-solute transport characteristics. The indexes of preferential flow morphology and pathway diversity (solute migration) were integrated to construct a more complete evaluation system of the PFI. In addition, we explored factors affecting the PFI through soil physical properties and root characteristics. The results showed that: (1) There were obvious preferential flows in both PF and NSF. Compared with NSF, preferential flow in PF diverged earlier, had greater non-equilibrium degree, more paths and higher development degree, and preferential flow was the main infiltration form. (2) Changes in infiltration amount played a key role in altering the PFI, i.e., increasing infiltration amount reduced the PFI, especially in PF (p < 0.05); (3) After water infiltration, the solute Br− diffusion range of the soil profile was wider than that of Brilliant Blue tracer, thus the development of preferential flow was better synthetical reflected by the indexes of water flow morphology and solute distribution characteristics; (4) Differences in the PFI can be explained by variations in clay content, total porosity (TP), and root volume density (RVD), with total path coefficients of 0.824, 0.462, and 0.624, respectively. In addition to establishing different forest restoration types in similar areas, it would be worthwhile to strengthen the prevention and control measures of soil and water loss in NSF, and properly manage PF in a near-natural model to enhance ecologically sustainable development of forest land. The results of this study contribute to the understanding of the hydrological processes of forest ecosystems in paleo-periglacial landforms, and provide theoretical support for the proposed forest management strategies.

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.

Effects of Grass and Forests and the Infiltration Amount on Preferential Flow in Karst Regions of China

Preferential flow is an important water infiltration phenomenon in karst regions. The response of preferential flow to vegetation restoration requires urgent investigation due to the special soil structure of karst regions. In order to study the effect of vegetation restoration on water movement in karst regions, four kinds of ponded water infiltration experiments were carried out in Pinus Yunnanensis plantation forestland, secondary forestland, and natural grassland. A brilliant blue dyeing experiment was conducted to visualize the distribution of water infiltration in soil (a total of 150 stained images from vertical soil slices). Results showed that the average depth of matrix flow in natural grassland was approximately six times those in plantation and secondary forestlands. An increase in matrix flow will have a negative effect on the development of preferential flow. Water transported in preferential flow paths affects the distribution of nutrients and organic matter in the soil. However, preferential flow in grassland can promote the accumulation of available nutrients, and preferential flow in plantations can inhibit the loss of organic matter. Preferential flow in grasslands and forest plantations is less than that in native forests soils. Preferential flow increases the percolation of water in soils. The effect is that preferential flow can obstructs water uptake by the roots under low rainfall conditions, and decreases surface runoff before soil saturation under high rainfall conditions. In the process of nutrient element migration, preferential flow has a good contribution, which is conducive to the migration and accumulation of elements required for surface vegetation growth. The contribution of preferential flow needs to be considered in studies on vegetation restoration planning and land degradation.

Preferential Flow in Different Soil Architectures of a Small Karst Catchment

Core Ideas Macropores and cracks are preferential channels in karst depression and downslope locations Heterogeneity of soil property results in finger flow in karst mid‐ and upslope locations High Ks and soil layering weaken preferential flow in mid‐ and upslope locations Preferential flow degree and infiltration rate can be independent in karst regions In karst regions, soil architecture varies along topographical locations, resulting in marked differences in infiltration rates. However, the relationship between soil architecture and preferential flow (PF) is still unclear. In this study, dye tracing was used to investigate PF and the dominant effects of five types of soil architecture in a small karst catchment. These soil architectures included deep clay soil in farmland (CSF) and deep clay soil in shrubland (CSS) in the depression; shallow clay soil with minimally weathered, slanted bedrock on downslope locations (CSWD); shallow sandy loam soil with highly weathered bedrock on midslope locations (SLSM); and sandy loam soil with rock fragments on upslope locations (SLSU). The results showed that macropores and cracks were the major channels that resulted in a high degree of PF in depressions and downslope locations. Preferential flow also continued along the rock–soil interface in the downslope locations. Finger flow mainly appeared in mid‐ and upslope locations, and cracks mainly appeared in the surface soil layer. However, down‐ and upslope locations showed lower PF. We observed that PF might not contribute to the different infiltration rates in different topographical locations. Tillage in depressions damages macropores, thereby minimizing vertical percolation. The high saturated hydraulic conductivity (Ks) of the soil matrix covered the development of PF in the mid‐ and upslope locations, and the decrease in Ks weakened the formation of PF as a result of heterogeneity of soil properties. These findings demonstrate that infiltration‐excess runoff may occur in depressions and downslope locations and that saturation‐excess runoff may occur in mid‐ and upslope locations.

Liquid water infiltration into a layered snowpack: evaluation of a 3-D water transport model with laboratory experiments

Abstract. The heterogeneous movement of liquid water through the snowpack during precipitation and snowmelt leads to complex liquid water distributions that are important for avalanche and runoff forecasting. We reproduced the formation of capillary barriers and the development of preferential flow through snow using a three-dimensional water transport model, which was then validated using laboratory experiments of liquid water infiltration into layered, initially dry snow. Three-dimensional simulations assumed the same column shape and size, grain size, snow density, and water input rate as the laboratory experiments. Model evaluation focused on the timing of water movement, thickness of the upper layer affected by ponding, water content profiles and wet snow fraction. Simulation results showed that the model reconstructs relevant features of capillary barriers, including ponding in the upper layer, preferential infiltration far from the interface, and the timing of liquid water arrival at the snow base. In contrast, the area of preferential flow paths was usually underestimated and consequently the averaged water content in areas characterized by preferential flow paths was also underestimated. Improving the representation of preferential infiltration into initially dry snow is necessary to reproduce the transition from a dry-snow-dominant condition to a wet-snow-dominant one, especially in long-period simulations.

The role of heterogeneous lithology in a glaciofluvial deposit on unsaturated preferential flow – a numerical study

Abstract An understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous glaciofluvial deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.

森林生态系统林木根系对优先流的影响

The study of the transportation of soil water and solutes,especially preferential flow,is a hot topic in pedology,ecology,and related environmental fields. Preferential flow,now recognized as a common pedological phenomenon,generally occurs without reaching equilibrium or as a non-uniform,random,highly variable process both spatially and temporally and is essentially unpredictable. Preferential flow and soil matrix flow are two typical permeating patterns of water flow and solute transport. Flow in soil matrix pores at the pedon scale results from spatial variation in soil texture and bulk density; it is affected by the presence of stones or rock fragments and by the ability of some substrates to repel water.Flow in large,continuous pores or macropores at the pore scale arises from different soil interactions such as biopores formed by root systems and macrofauna,cracks formed by freeze and thaw or shrink / swell circles,as well as voids formed by irrigation,cultivation,and tillage. Consequently,preferential flow results in complex flow patterns that bypass the normal soil matrix patterns; this increases the risk that pollutants( e. g. heavy metals,radionuclides) will reach greater soil depths than would otherwise occur or that this also may allow pollutants to even reach the groundwater. Many factors control preferential flow including soil bulk density,soil structure,soil moisture content,rainfall intensity and tillage systems.Plant roots and other abiotic factors are some of the most important factors influencing preferential flow. In particular,the growth of plant roots influences the process of preferential flow. Obviously,root growth is a dynamic process and involvesthe formation of a continuous macropore network; plant roots may also create a series of well-connected pores that enhance preferential flow. Plant roots are widely known to play a key role in the development of preferential flow at the plot scale,but a quantitative description of the interaction between plant roots,the development of micropores and preferential flow is still a major challenge in preferential flow studies. This study investigated a forest ecosystem located in Jiufeng National Forest Park,Beijing,China,with the goal of characterizing and quantifying the effects of plant roots on preferential flow and the related complex interactions. Field dye tracing methods and laboratory experiments were applied to confirm and evaluate changes in root length density and root biomass along preferential pathways as well as in the soil matrix. Results indicated that 1) root length density,in general,decreased with an increase in soil depth. Root length density was larger in preferential pathways than in the surrounding soil matrix and was 66. 7%,88. 9% and 88. 3% for plant roots with a diameter( d) of 1 mm,1 d 3 mm and 3 d 5 mm respectively. 2) The contribution of plant roots d 1 mm to preferential flow was almost 94. 8% for all experimental plots,while it was 4. 3% and 0. 9% for plant roots 1 d 3 mm and 3 d 5 mm,respectively. 3) The proportion of root biomass in the preferential pathways larger than in the soil matrix was 66. 7% for all experimental plots. Evaluating the effects of plant roots on preferential flow will help researchers to better understand the factors controlling soil water and solute transportation and may prevent subsurface flow and groundwater being polluted for forest ecosystems containing relatively more plant roots and stones,especially allowing for protection of the environment from pollution.

Affecting factors of preferential flow in the forest of the Three Gorges area, Yangtze River

In order to study the factors affecting preferential flow, a 2.9 m-long, 2.6 m-deep soil profile was dug in the Quxi watershed, Yangtze River. To analyze the influence of rainfall on preferential flow, the preferential flow process was observed when the rainfalls were recorded. Soil physical and infiltration characteristics were also measured to study their effect on preferential flow. The results showed that the rainfall amount that could cause preferential flow was over 26 mm. There are four types of rainfall in the Three Gorges area, namely gradually dropping rain, even rain, sudden rain and peak rain. Preferential flow process was found to be relevant to the rainfall process. It was determined that with different rainfall types, preferential flow appeared at different times, occurring first in peak rain, followed by sudden rain, gradually dropping rain, and then even rain. Preferential flow would appear when the rainfall intensity was over 0.075 mm/min. In the studied area, the coarse soil particles increased with the soil depth, and for the deeper soil layer, the coarse particles promote the formation of preferential flow. Preferential flow accelerates the steady infiltration rate in the 83–110 cm soil horizon, and the quickly moving water in this horizon also enhanced the further formation and development of preferential flow.