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1.
The distribution law of averaged coefficients of aeration is established for the aeration zone in accelerated turbulent flows in prismatic channels, and a technique is proposed for the evaluation of the length of this zone. Both the results are in agreement with the data of special laboratory studies. The estimation of the length of the aeration zone is based on relationships derived by the author and verified for flow-controlling parameters varying within wide limits. The law of increasing air content was also confirmed by field measurement data.  相似文献   

2.
Organized spatial distribution of plants (plant zonation) in salt marshes has been linked to the soil aeration condition in the rhizosphere through simplistic tidal inundation parameters. Here, a soil saturation index (ratio of saturation period to tidal period at a soil depth) is introduced to describe the soil aeration condition. This new index captures the effects of not only the tidal inundation period and frequency but also the flow dynamics of groundwater in the marsh soil. One‐dimensional numerical models based on saturated flow with the Boussinesq approximations and a two‐dimensional variably saturated flow model were developed to explore the behaviour of this new soil aeration variable under the influence of spring‐neap tides. Simulations revealed two characteristic zones of soil aeration across the salt marsh: a relatively well aerated near‐creek zone and a poorly aerated interior zone. In the near‐creek zone, soils undergo periodic wetting and drying as the groundwater table fluctuates throughout the spring‐neap cycle. In the interior, the soil remains largely water saturated except for neap tide periods when limited drainage occurs. Although such a change of soil aeration condition has been observed in previous numerical simulations, the soil saturation index provides a clear delineation of the zones that are separated by an ‘inflexion point’ on the averaged index curve. The results show how the saturation index represents the effects of soil properties, tidal parameters and marsh platform elevation on marsh soil aeration. Simulations of these combined effects have not been possible with traditional tidal inundation parameters. The saturation index can be easily derived using relatively simple models based on five non‐dimensional variables. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

3.
Soil rhizosphere aeration status is an important aspect of soil quality and soil ecology. The objective of the current study was to determine the appropriate moisture environment that facilitates rhizosphere soil aeration and ensures normal root respiration in tomato. In the potted experiment, five treatments of soil aeration were used (0.4, 0.8, 1.2, 1.6 ventilation volume of 50% porosity of soil, and no ventilation) under conditions of the different soil moisture upper limits. The effects of different rhizosphere soil aerations on the physiological indicators and water absorption of tomato were studied. Under the same soil moisture condition, plant growth and root vitality initially increased, and then decreased when the soil ventilation volume increased. The combination of soil moisture with 80% of field capacity and 0.8 ventilation volume with 50% soil porosity raised the chlorophyll content by 29.98% and the root vitality by 61.55%, as compared with the non‐ventilated treatment. Therefore, the appropriate volume of rhizosphere ventilation can effectively improve the capacity of water absorption in tomato. The result provides a new view about soil quality and soil ecology in terms of soil–root system.  相似文献   

4.
Sampling of soil pore moisture in the vadose zone underneath land disposal facilities (landfills and surface impoundments) for hazardous waste has been suggested as an "early warning system" to detect leakage from these facilities. Some states require vadose zone moisture sampling at such sites. Given a leak of a particular size, mathematical models can estimate the necessary moisture sample volume collection times and lysimeter spacings to guarantee detection of the leak in a homogeneous medium. Examination of 47 hazardous waste sites existing in 1984 indicated the most were located in areas with water tables too shallow to permit vadose zone detection monitoring. Several of the 47 sites had soils that could be described as loamy sand, silt loam or silty clay. Using these three soils as examples, the process of lysimeter leak-detector network design has been illustrated. For a particular loamy sand with a saturates hydraulic conductivity of 10-6 cm/ sec, the maximum ceramic lysimeter spacing is 15.5 feet at a depth of 30 feet to collec a moisture sample of 10 mL in one week from a 1 ft2 leak. For a silt loam, maximum lysimeter spacing would be 17 feet at depth of 15 feet. For silty clays, the maximum lysimeter spacing is 7 feet at a depth of 2 feet; maximum emplacement depth is about 9 feet. Calculations show that in some soils, suction lysimeters will not be able to collect usable moisture samples. Since soil properties vary widely and lysimeter spacing is strongly dependent on soil-moisture characteristics appropriate soil measurements and modeling must be performed at each disposal facility to estimate lysimete performance and to select locations for emplacement.  相似文献   

5.
This work was undertaken for two main purposes. One was to examine spatial and temporal variability in surface water repellency under field conditions in sandy loam forest soils of NW Spain, and its relationship to weather and soil moisture conditions. The other purpose was to get further inside in the dynamics of soil water repellency by studying a wetting–drying cycle under controlled laboratory conditions. Both for the field and laboratory study, water repellency was determined using the Water Drop Penetration Time test. Soil water repellency under field conditions was found to exhibit a seasonal pattern, i.e. it peaked during the summer and was absent between November and May. The time required for repellency to become re‐established during the spring was shorter under eucalyptus than under pine. Spatial variability peaked at an early stage of soil drying and was minimal during the wet period when soils were hydrophilic as well as at the end of the summer, when repellency was strongest. Spatial and temporal variability in water repellency was found to be negatively correlated with soil moisture and, to a lesser extent, with antecedent rainfall. The moisture range of the so‐called transition zone (below which the soil is hydrophobic and also above which it is hydrophobic) differed for the pine (21–50%) and eucalyptus plantations (17–36%). The lower and upper bounds of the transition zone agreed well with the soil moisture contents at the permanent wilting point and at field capacity, respectively. The laboratory results with samples in the wetting phase confirmed those of the field tests. Water repellency increased slightly during the drying phase, but not so much as in the field. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
A spatial pattern of relative solutional denudation is described for a hillslope hollow and adjacent spurs at Bicknoller Combe, Somerset. The pattern was obtained from a network of micro-weight loss rock tablets emplaced in the soil. The results show that the hollow is the main locus of solutional denudation. The soil moisture distribution over the hollow indicates that it is a transmission zone for acid soil water percolating from the adjacent spurs to the saturated wedge at the base of the hollow. The wetter acid soils in the hollow are responsible for the relatively higher solutional denudation taking place in the hollow.  相似文献   

7.
Karimova  O. A. 《Water Resources》2003,30(1):103-108
The procedure of evaluating pesticide travel time through the aeration zone to the groundwater table is presented. It is found that the time of pollutant travel through rocks of the aeration zone depends on the thickness and composition of rocks of this zone, the porosity of rocks, distribution factor, volumetric humidity, and the infiltration recharge. As shown, the most vulnerable are the valleys of principal rivers of the area of Caucasian Mineral Water, where the Recent and Middle Quaternary aquifers confined to these valleys are intensely used for domestic and drinking needs.  相似文献   

8.
镉(Cd)是目前三峡库区消落带主要的污染物之一,其迁移和形态转化直接威胁水环境安全.选择库区丰都-忠县段消落带,按照高程差异分别于不同土地利用类型(农田、林地、果园和村庄)下采集土壤样品,利用化学连续提取法测定Cd的形态组成,探讨影响消落带土壤中Cd及其形态空间分布的关键因素.结果表明,消落带土壤中Cd的平均含量为0.65 mg/kg,可交换态及碳酸盐结合态是土壤中Cd的主要形态,占比达到41.21%,残渣态和铁锰氧化物结合态次之,有机物及硫化物结合态占比最低.不同土地利用类型下消落带土壤Cd的含量整体上不存在显著性差异,表明当地人类活动对土壤Cd的直接贡献较弱.消落带土壤Cd及其形态的含量与高程呈显著负相关,且在160～165 m区域发生明显转变,水位变化导致的泥沙沉积可能是控制消落带Cd空间分布的主要因素.此外,土壤理化性质,尤其是细颗粒泥沙对Cd及其形态分布具有明显影响,将来需重点关注泥沙理化属性对Cd迁移及形态转化的影响.  相似文献   

9.
Belousova  I. A.  Kosterin  A. V. 《Water Resources》2004,31(2):221-225
The problem of migration of a hydrocarbon liquid through aeration zone to groundwater table is formulated and solved analytically. The aeration zone is represented by fractured–porous rocks, and the pollution source is a shallow pool that has formed due to a spill. Two schemes of liquid infiltration from fractures into rock blocks—piston-like and kinetic—are considered. The trajectory of pollution front in fractures and its distribution in the rock blocks are found.  相似文献   

10.
《水文科学杂志》2013,58(2):316-326
Abstract

Nitrate contamination in groundwater originates mainly from excessive use of fertilizers and uncontrolled discharge to land of incompletely-treated wastewater associated with agricultural activities. A systematic field investigation was carried out in a sub-catchment of Dianchi Lake, Kunming, Yunnan, China, into the hydrological, biological and geological processes of nitrogen transport and transformation in the aeration zone and aquifer system. In situ experiments showed that the quantity of NO3-N recharged into groundwater was related to fertilization. Nitrification and denitrification behaved quite differently but were affected by moisture content and Eh value. The vertical infiltration rate was controlled by the groundwater table and hydraulic conductivity of the soil. The existence of a zero-flux plane reflected the dynamics of water fluxes in the soil profile and Eh was measured in the aeration zone. In response to these factors, the nitrification rate was greatest in the top soil and reduced with the depth of soil; it was 6.53 mg/(kg·h) in the vegetated plot and 0.2–0.3 mg/(kg·h) in the unvegetated one. The denitrification rate in the unvegetated plot was 6.36 mg/(kg·h), and it was 2.79 mg/(kg·h) in the vegetated one.  相似文献   

11.
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12.
Perchlorate and nitrate in vadose‐zone soil can be continuing sources of groundwater contamination and technologies for remediation of these sources are limited. Gaseous electron donor injection technology (GEDIT) is an in situ approach that was demonstrated at a site in California. A mixture of hydrogen, carbon dioxide, liquefied petroleum gas (LPG), and nitrogen was injected into the vadose zone over a period of 5 months followed by 3 months of LPG alone. Perchlorate and nitrate plus nitrite nitrogen concentrations were reduced by over 90% and both were capable of being reduced to nondetectable concentrations. Hydrogen was required for perchlorate destruction, although concentrations as low as 0.5% were effective. Hydrogen was not required for nitrate destruction. Contaminant destruction was observed in both fine‐grained and coarse‐grained soils ranging from clay to gravel. Hydrogen was an effective electron donor because of its low molecular weight and high diffusivity which likely promoted its penetration into low‐permeability formations. Contaminant destruction was also observed in moisture contents ranging from 6.8% to 36% demonstrating that GEDIT was effective in low‐ and high‐moisture soils. The radius of influence (ROI) for perchlorate destruction was approximately 3.0 to 4.6 m while that for nitrate was greater than 17 m. The ROI was limited by use of a single injection location. Use of a grid injection system is anticipated to greatly increase efficiency. This research represents the first demonstration of GEDIT for treatment of contaminants in the vadose zone.  相似文献   

13.
Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well‐developed biological soil crusts than in physical or poorly developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared with the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

14.
Experiments involving six soil types indicated that the production of miniature ice lenses is dependent on soil moisture content and grain size with lenses being produced in finer-grained soils at lower moisture contents than is possible in coarser soils. Explanation of the results involves consideration of the unsaturated hydraulic conductivity of the unfrozen soil through which water migrated to the freezing plane to allow ice lens growth.  相似文献   

15.
The recent transformation of wetlands into farmland in East Africa is accelerating due to growing food-demand, land shortages, and an increasing unpredictability of climatic conditions for crop production in uplands. However, the conversion of pristine wetlands into sites of production may alter hydrological attributes with negative effects on production potential. Particularly the amount and the dynamics of plant available soil moisture in the rooting zone of crops determine to a large extent the agricultural production potential of wetlands. Various methods exist to assess soil moisture dynamics with Frequency Domain Reflectometry (FDR) being among the most prominent. However, the suitability of FDR sensors for assessing plant available soil moisture has to date not been confirmed for wetland soils in the region. We monitored the seasonal and spatial dynamics of water availability for crop growth in an inland valley wetland of the Kenyan highlands using a FDR sensor which was site-specifically calibrated. Access tubes were installed within different wetland use types and hydrological situations along valley transects and soil properties affecting soil moisture (organic C, texture, and bulk density) were investigated. There was little variation in soil attributes between physical positions in the valley, and also between topsoil and subsoil attributes with the exception of organic C contents. With a root mean squared error of 0.073 m3/m3, the developed calibration function of the FDR sensor allows for reasonably accurate soil moisture prediction for both within-site comparisons and the monitoring of temporal soil moisture variations. Applying the calibration equation to a time series of profile probe readings over a period of one year illustrated not only the temporal variation of soil moisture, but also effects of land use.  相似文献   

16.
Soil moisture data of 45 years from European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and the in situ observational data are used to study the temporal and spatial characteristics of the soil moisture in boreal spring in the area to the east of 100°E in China. Results show that ERA-40 soil moisture well reproduces the temporal and spatial features of observations. ERA-40 data capture the spatial pattern that the soils in Northeast China and Southwest China are wetter than those...  相似文献   

17.
Soil-gas surveys are becoming more widely accepted as a tool for the preliminary determination of the extent of soil and ground water contamination by volatile organic compounds (VOCs). The interpretation of the results of published soil-gas surveys has been necessarily limited and qualitative due to a lack of adequate models. There has been considerable effort in the recent past to characterize the transport and fate of pesticides in soil. However, the behavior of pesticides generally differ substantially from those of VOCs.
This paper presents a computer model developed to simulate the diffusive transport of VOC vapor through unsaturated soils using a two-dimensional, finite-difference, solution to Fick's second law of diffusion. An effective diffusion coefficient that incorporates the effects of tortuosity, moisture content, and soil organic carbon content is computed. Although the model has not been validated due to the unavailability of adequate field or laboratory data, nevertheless, sensitivity analyses demonstrate the importance of soil moisture and, secondarily, organic matter content in controlling the migration of VOC vapor through the unsaturated zone. The interpretation of soil-gas surveys can be complicated by unknown spatial heterogeneities in soil moisture and organic carbon content, temporal variations in moisture content, extent of contaminant migration as a non-aqueous phase liquid and by the unknown extent of VOC liquid and contaminated ground water.  相似文献   

18.
Infiltration of water into two frozen engineered soils of different gradation was studied in laboratory soil columns 1.2 m long and 0.1 m in diameter. Prior to testing, the soil moisture was adjusted to two levels, described by the gravimetric water content of 5% or 10%, and soils were compacted to about 80–90% of the maximum dry density and refrigerated to temperatures ranging from ?8 to ?2 °C. Water with temperatures 8–9 °C was thereafter fed on the top of columns at a constant head, and the times of water breakthrough in the column and reaching a steady percolation rate, as well as the percolation rate, were recorded. The soil water content was a critical factor affecting the thawing process; during freezing, soil moisture was converted into ice, which blocked pores, and its melting required high amounts of energy supplied by infiltrating water. Hence, the thawing of soils with higher initial water content was much slower than in lower moisture soils, and water breakthrough and the attainment of steady percolation required much longer times in higher moisture soils. Heat transfer between infiltrating water, soil ice, and frozen soil particles was well described by the energy budget equations, which constitute a parsimonious model of the observed processes. The finer grained soil and more compacted soil columns exhibited reduced porosity and required longer times for soil thawing. Practical implications of study results for design of bioretention facilities (BFs) in cold climate include the use of coarse engineered soils and fitting bioretention facilities with a drain facilitating soil drainage before the onset of freezing weather. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
In this study, it was aimed to determine the effect of various aeration rates on composting to supply the optimum aeration rate for a successful and economic composting. For this aim, vegetable–fruit wastes (VFW) were composted at various aeration rates (0.37, 0.49, 0.62, 0.74, 0.86, and 0.99 L/min kg VS) and moisture, temperature, pH, electrical conductivity, C/N, and cellulose were investigated. Moistures of the reactor that had the highest aeration were generally lower than those of the others. Reactor that had the lowest aeration reached thermophilic phase earlier than the others and stayed more days. This situation was opposite for the reactor that had the highest aeration. pH variations with aeration rates were not significant. Although electrical conductivity did not differ significantly with aeration rates, at the beginning of the thermophilic phase it generally increased with the increase in aeration. The highest C/N reduction was observed in the reactor that had an aeration of 0.62 L/min kg VS. The final cellulose contents were close to each other. It could be said that aeration rates used were efficient on composting of VFW. Taking the C/N into account which is the parameter of the indicator of the stabilization in composting, it could be said that the optimum aeration rate for forced aerobic composting of VFW was 0.62 L/min kg VS.  相似文献   

20.
In this paper, we investigate the possibility to improve discharge predictions from a lumped hydrological model through assimilation of remotely sensed soil moisture values. Therefore, an algorithm to estimate surface soil moisture values through active microwave remote sensing is developed, bypassing the need to collect in situ ground parameters. The algorithm to estimate soil moisture by use of radar data combines a physically based and an empirical back‐scatter model. This method estimates effective soil roughness parameters, and good estimates of surface soil moisture are provided for bare soils. These remotely sensed soil moisture values over bare soils are then assimilated into a hydrological model using the statistical correction method. The results suggest that it is possible to determine soil moisture values over bare soils from remote sensing observations without the need to collect ground truth data, and that there is potential to improve model‐based discharge predictions through assimilation of these remotely sensed soil moisture values. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

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