Modelling water flow through undisturbed soil cores using a transfer function model derived from 3HOH and Cl transport

Large undisturbed soil cores (20 cm diam. × 25–30 cm long) were irrigated at rates of 0.5–4 cm h^?1 with 0.005 M CaCl₂ solution labelled with ³HOH. The cores were used at varying initial water contents and flow in all cases was unsaturated. Breakthrough curves for Cl and ³HOH were markedly asymmetric and unlike those reported for columns of packed aggregates. The data could be satisfactorily described using a density distribution function of the logarithm of cumulative drainage D. The mean and standard deviation of In D were estimated by a curve-fitting procedure from Cl and ³HOH effluent concentrations in each core. The mean pore water velocity and fraction of the soil water that participated in solute transport (the mobile volume) were also calculated. The apparent velocity of Cl movement was always greater than that of ³HOH which suggested that the mobile volume involved in convective and diffusive transport of Cl was less than that for ³HOH. We suggest that Cl and ³HOH diffused at different rates out of flowing water films in a relatively few large conducting channels into essentially immobile water within the surrounding soil matrix. The difference in mobile volume for Cl and ³HOH was used to calculate the perimeter of voids in any horizontal cross-section of the soil through which water flowed, assuming a planar interface between the mobile and immobile water.     

Effect of water flow on the mobility of the root-knot nematode Meloidogyne incognita in columns filled with glass beads, sand or andisol

In the present study, the migration of nematodes was studied in columns filled with three materials of different textures and chemical properties. The role of soil pores that enable root-knot nematode (Meloidogyne incognita) second stage juveniles (J2) to escape rapid water flow in soil was demonstrated using columns filled with glass beads, sand or andisol that maintained a constant water flow. Under a constant flow flux of 36 cm h⁻¹, living J2, dead J2 or anion bromine tracer (Br⁻) was injected in the middle of the column and then drainage water equivalent to two pore volumes (PV) was collected. The passive transport of the anion tracer in water flow could be explained by a convection dispersion equation. The dead J2 showed a pattern similar to that of Br⁻. However, the living J2 resisted movement in the water flow and remained in the column even at the highest water flow rate of 93.3 cm h⁻¹ in glass beads. The mobility of living J2 was affected by the filling materials; the number of J2 passing through the column was much lower in the andisol-filled column than in the other two columns but the total number of J2 in drainage water was 5% or less of the number injected for all columns. We suggest that J2 were affected not only by soil water flow but also by soil pore structure and have the ability of withstanding or avoiding movement in soil water flow.     

Beitrag zum Elementaustrag mit dem Sickerwasser unter verschiedenen Ökosystemen im nordwestdeutschen Flachland

Contribution to the element output with seepage under different ecosystems in the flat plains of Northwest Germany Over a period of one year samples of seepage water were taken from 3 different ecosystems of the pleistocene lowlands of Northwest Germany. A mixed crop of oak, a pure pine forest and a heathland area were chosen. The ions H, Na, K, Ca, Mg, Mn, Fe, Al, PO₄, SO₄, Cl, NO₃ and NH₄ were analysed. A balance calculation was done based on measurements or estimations of total evaporation and on measurements of element input with rainfall. The data indicate different interception (dry deposition) rates of air pollutants for the 3 stands. Al-ions were found in the soil solution under the pine stand and under the heathland area in a depth of 1.2 m. This status has not yet developed in the soil of the oak stand, but seems to be reached soon.     

Mobility and Availability of Copper in Agricultural Soils Irrigated from Water Treated with Copper Sulfate Algaecide

A mesocosm system was designed to study evaporation kinetics and transport of TCE in flowing surface water. The airtight unit, with a total internal volume of 52.01?×?10^?2 m³, was fabricated with glass and Teflon material, and was provided with 8.53 m long channel to simulate water flow in an open channel. The peristaltic pumps, connected to the inlet and the outlet of the mesocosm, provided a constant water flow through the channels. The experimental studies were conducted at two different velocities, 9.42?×?10^?3 and 4.71?×?10^–3 m/s, respectively. For both the velocities, a tracer (NaBr) test confirmed uniform water flow in the channels. The total length and the length between the sampling ports were found sufficient to record gradual decrease in TCE concentrations along the direction of the flow in the channels. The volatilization coefficient for TCE was found to be 0.49 and 1.07 h^?1 for the experiments conducted at lower and higher water velocities, respectively. The TCE evaporation half life (t 1/2) and the corresponding evaporation half distance (d 1/2) were 1.41 h and 23.98 m for lower velocity, and 0.65 h and 21.96 m for higher velocity, respectively.     

Soil water balance and nitrate leaching in winter wheat–summer maize double‐cropping systems with different irrigation and N fertilization in the North China Plain

Field experiments over a 3 y period were conducted in a winter wheat‐maize double‐cropping system at the Dongbeiwang Experimental Station, Beijing, China. Three different treatments of irrigation (sprinkler “suboptimal” and “optimized”; conventional flood irrigation) and N fertilization (none, according to N_min soil tests, conventional) were studied with respect to effects on soil water balance, nitrate leaching, and grain yield. Under sprinkler irrigation, evaporation losses were higher due to a more frequent water application. On the other hand, in this treatment nitrate leaching was smaller as compared to flood irrigation, where abundant seepage fluxes >10 mm d^–1 along preferential flow paths occurred. For quantifying nitrate leaching, passive samplers filled with ion‐exchange resins appeared to be better suited than a method which combined measurements of suction‐cup concentrations with model‐based soil water fluxes. As a result of the more balanced percolation regime (compared to that under conventional flood irrigation), there was a tendency of higher salt load of the soil solution in the rooting zone. Given a seepage rate of 50 mm, a winter wheat grain production of 5–6 t ha^–1 required a total water addition of about 430 mm. Fertilizer treatments >100 kg N ha^–1 did not result in any additional yield increase. An even balance between withdrawing and recharge of groundwater cannot be achieved with “optimized” irrigation, but with a reduction of evapotranspiration losses, adapted cropping systems, and/or by tapping water resources from reservoirs in more distant areas with surpluses.     

基于HYDRUS模型的华北平原小麦种植区水盐运移模拟

土壤中水分和盐分是影响作物生长的两个关键因素,揭示水盐运移机制对阐明作物利用土壤水过程具有重要意义。本研究以华北平原典型农田——中国科学院禹城综合试验站为试验地,基于试验站内冬小麦种植地的长期土壤水分观测数据及室内土柱试验,应用HYDRUS-1D模型分别阐明土壤水分及盐分变化规律及分布特征,探究影响水盐运移的驱动因素,并评价HYDRUS-1D模型对研究区水盐运移模拟的适用性。水分运移模拟结果表明:浅层土壤水分运移模拟因受外界因素的剧烈影响而较深层土壤产生更大的误差,10cm、20 cm、30 cm、40 cm和60 cm处水分运移模拟结果的均方根误差分别为0.0348 cm~3·cm~(-3)、0.0179 cm~3·cm~(-3)、0.0179cm~3·cm~(-3)、0.0122cm~3·cm~(-3)和0.0053cm~3·cm~(-3);水分运移模拟的纳什效率系数平均值为0.826,变异系数为0.0560,表明模拟结果与实测土壤水分变化过程一致性较好。土柱试验结果显示:灌水8 L,入渗12 h、24 h、40 h、45 h和48 h后,各时刻土壤盐分含量在垂向上整体呈现先增大后减少的分布规律,均方根误差分别为0.181 g·kg~(-1)、0.131 g·kg~(-1)、0.120 g·kg~(-1)、0.034 g·kg~(-1)和0.027 g·kg~(-1),平均误差的平均值为0.174 g·kg~(-1)。受蒸发、耕作、根系等影响,理化性质变异性较大导致浅层土壤盐分运移模拟值与实测值偏差增大,纳什效率系数的变异系数达9.71。灌水8 L、16 L、24 L,入渗48 h后分别在土壤23 cm、26 cm、29 cm处出现盐分含量峰值,表明增加灌水量可加强盐分淋洗效果。此研究可为深入探究华北平原冬小麦土壤水盐运移规律、优化农田水资源管理、提高水资源利用效率提供一定理论基础。     

Calculation of nitrogen mineralization and leaching in fallow soil using a simple dynamic model

Simple models describing nitrogen processes are required both to estimate nitrogen mineralization in field conditions and to predict nitrate leaching at large scales. We have evaluated such a model called LIXIM, which allows calculation of nitrogen mineralization and leaching from bare soils, assuming that these are the dominant processes affecting N in bare soil. LIXIM is a layered, functional model, with a 1-day time step. Input data consist of frequent measurements of water and mineral N contents in soil cores, standard meteorological data and simple soil characteristics. The nitrate transport is simulated using the ‘mixing-cells’ approach. The variations in N mineralization with temperature and moisture are accounted for, providing calculation of the ‘normalized time’. An optimization routine is used to estimate the actual evaporation and the N mineralization rates that provide the best fit between observed and simulated values of water and nitrate contents in all measured soil layers. The model was evaluated in two field experiments (on loamy and chalky soils) including treatments, lasting 9–20 months. The water and nitrate contents in soil were satisfactorily simulated in both sites, and all treatments, including a ¹⁵N tracer experiment performed in the loamy soil. In the chalky soil, the calculated water balance agreed well with drainage results obtained in lysimeters and independent estimates of evaporation. At both sites, N mineralization was reduced by the incorporation of crop residues (wheat or oilseed rape straw); the amounts of nitrogen immobilized varied between 20 and 35 kg N ha^?1. In the treatments without crop residues, the mineralization rate followed first-order kinetics (against normalized time) in the loamy soil, and zero-order kinetics in the chalky soil. In the latter soil, the mineralization kinetics calculated in situ were close to the kinetics measured in laboratory conditions when both were expressed against normalized time.     

盘塘水源地渗流井取水方式下地下水允许开采量计算

介绍了渗流井的结构和井流特征,通过引入等效渗透系数,构建"渗流—管流"耦合模型,建立了渗流井取水的数学模型。以陕西省神木县盘塘水源地为例,用地下水流三维有限差分法对水源地地下水允许开采量进行了计算。结果表明,盘塘水源地渗流井开采方式下,地下水允许开采量为92 400m3/d,枯水期允许开采量为56 200m3/d。通过对比不同取水方式下的允许开采量,认为渗流井取水方式较管井、辐射井等取水方式具有出水量大,易管理等优势。在干旱半干旱的地区,渗流井具有明显优于其他取水结构的特点。     

基于热传递过程的薄层水流流速测量方法及装置

基于薄层水流中的热传递过程，提出测量水流流速的示踪方法，并设计对应的测量系统。在室内试验坡面上，设计不同试验工况(坡度为5°,10°,20°,流量为2,5,8 L/min),以盐示踪法为对照，研究热示踪测量薄层水流流速的可行性及其影响因素。结果表明，测量系统能准确地测得热示踪剂的运移过程；热与盐2种示踪剂测得流速范围为0.408～1.522 m/s,线性拟合斜率为1.006,R²为0.993,表明两者具有显著的线性关系，热示踪法具有较高的可靠性；由于物理属性差异，部分水力工况下示踪剂的释放方式对盐和热的测量结果影响显著，表明此时2种示踪剂测量流速的代表性不同；可采用盐与热联合示踪的方法，取二者测量结果的均值作为薄层水流的平均流速，以提高测量结果的代表性。研究结果可为复杂下垫面、盐渍化和禁用化学成分等特殊坡面上薄层水流流速的准确测量提供新方法和理论参考。薄层水流流速的准确测量对地表水文和土壤侵蚀领域的研究具有重要意义。     

Short‐term transport of cadmium during a heavy‐rain event simulated by a dual‐continuum approach

The transport of solutes in soils, and its intensification due to preferential flow, plays crucial role when problems related to the groundwater pollution are dealt with. The objective of this study was to examine transport of cadmium (Cd) in response to an extreme rainfall event for three different soils using numerical modeling. The ^115mCd²⁺ concentration profile had been measured in the Bodiky reference site (Danubian Lowland, Slovakia) by the radioactive‐tracer technique and used for the calibration of the dual‐continuum model S1D. The Cd transport during a single rain event was predicted with the S1D model for light, medium‐heavy, and heavy soil in the same region. The Cd transport through the soil profile was simulated by the one‐dimensional dual‐permeability model, which assumes the existence of two pore domains: the soil‐matrix domain and the preferential‐flow domain. The model is based on Richards' equation for water flow and advection‐dispersion equation for solute transport. A modified batch technique enables to distinguish process of adsorption in the matrix domain and the preferential pathways. Modeling with classical single‐permeability approach and dual‐continuum approach without considering the particle‐facilitated transport led to negligible Cd penetration. The rainfall event with extremely high rainfall intensity induced deep penetration of Cd in the medium‐heavy and heavy soil, which may indicate increased vulnerability to shallow groundwater pollution for the respective sites in Danubian Lowland region. The highest Cd leaching was predicted for heavy clay soil, where the preferential particle‐facilitated transport of Cd through the soil profile was significant due to the contrasting properties of the soil‐matrix domain and the preferential‐flow domain. The results of the sensitivity analysis suggested only slight effect of the transfer rate coefficients on simulated Cd leaching.     

Mobilization of cesium in organic rich soils: Correlation with production of dissolved organic carbon

A study of the downward movement of ¹³⁷Cs in an undisturbed forest soil is presented. Seasonal variations and depth profiles of ¹³⁷Cs activities were measured in seepage water, which is the transport medium for the downward movement of anthropogenic substances in soils. Furthermore the correlation of ¹³⁷Cs mobilization and production of dissolved organic carbon (DOC) was investigated. Seasonal variations of both ¹³⁷Cs and DOC fluxes in the seepage water in a depth of 5 cm depth were observed, where the maximum fluxes in the summer months were about one order of magnitude higher than the minimum fluxes in the winter months. ¹³⁷Cs fluxes are found to be correlated with DOC fluxes with a correlation coefficient of r = 0.63, and both are highly correlated with soil temperature. This indicates that cesium is bound to soil organic material. The production of DOC is controlled by microbial decomposition of soil organic matter and we assume that this holds true for the ¹³⁷Cs release as well. The actual transport velocity (0.2 ± 0.14 mm/a) of ¹³⁷Cs (calculated by the weighed mean of ¹³⁷Cs concentration in the seepage water and the total ¹³⁷Cs content of the soil) is about one order of magnitude less than the mean transport velocity (1.2 ± 0.3 mm/a) over the past 25 years (calculated from the ¹³⁷Cs depth profile). It is possible that the transport velocity of ¹³⁷Cs in undisturbed soils decreases with time as it binds to aged organic material which is less easily decomposable than fresh organic material.     

Effect of non-linear adsorption on the transport behaviour of Brilliant Blue in a field soil

The food dye Brilliant Blue FCF (Color Index 42090) is often used as dye tracer in field studies for visualizing the flow pathways of water in soils. Batch studies confirmed findings of other researchers that non‐linear sorption is important for Brilliant Blue, especially at small concentrations (< 10 g l^?1 for our soil), and that retardation increases with decreasing concentrations as well as with increasing ionic strength of solutions. Therefore, it is not obvious if it can be used as an indicator for water flow paths as is often done. In this study, we compared the mobility of Brilliant Blue in a field soil (gleyic Luvisol) with that of bromide. Brilliant Blue and potassium bromide were simultaneously applied as a 6‐mm pulse on a small plot in the field, and the tracers were displaced with 89 mm of tracer‐free water using a constant intensity of 3.9 ± 0.2 mm hour^?1. Both tracer concentrations were determined on 144 soil cores taken from a 1 m × 1 m vertical soil profile. The transport behaviour differed in both (i) mean displacement and (ii) spatial concentration pattern. We found the retardation of Brilliant Blue could not be neglected and, in contrast to the bromide pattern, a pulse splitting was observed at the plough pan. Numerical simulations with a particle tracking code revealed that the one‐dimensional concentration profile of bromide was represented fairly well by the model, but the prediction of the double peak in the Brilliant Blue concentration profile failed. With additional assumptions, there were indications that Brilliant Blue does not follow the same flow paths as bromide. However, the question of Brilliant Blue taking the same flow pathways as bromide cannot be adequately answered by comparing both concentration distributions, because we look at two different transport distances due to the retardation of Brilliant Blue. It became obvious, however, that Brilliant Blue is not a suitable compound for tracing the travel time of water itself.     

土壤混掺生物炭对微咸水蒸发特性的影响

为探究不同生物炭混掺量对微咸水蒸发特性的影响,采用离心机试验和室内土柱模拟试验,设置3个生物炭质量添加比例(B₀、B₂、B₄)和4个微咸水矿化度(W₀、W₁、W₃、W₅),分析不同处理对微咸水蒸发下的土壤水分特征曲线、孔隙分布、累积蒸发量、盐分运移、土壤温度日变幅的影响,并应用蒸发模型进行拟合分析。结果表明:生物炭和微咸水联合应用下能提高土壤持水能力,增加土壤中的较大孔隙和较小孔隙的比例;土壤累积蒸发量随着生物炭混掺量的增加先减少后增加,生物炭混掺量为2%时可以更好地抑制微咸水蒸发;Rose蒸发模型可以较好地拟合微咸水蒸发;土壤中混掺生物炭可以降低盐分表聚,使其在土壤中均匀分布;混掺生物炭可以有效降低土壤温度日变幅;相同生物炭施用量下,矿化度为3 g/L的微咸水,可以降低0—10 cm土层土壤平均温度,提高10—50 cm土层土壤平均温度。综合考虑各项指标,处理B₂W₃的生物炭和微咸水更适宜农田施用,为西北干旱地区更好地利用微咸水灌溉提供理论依据。     

土壤扩蓄增容肥对冬小麦棵间蒸发和水分利用效率的影响

利用农田水量平衡公式计算了冬小麦耗水量,用微型蒸渗仪测定了农田土壤棵间蒸发状况,在此基础上通过对比试验研究了土壤扩蓄增容肥条件下不同水分处理冬小麦生长期间农田棵间蒸发与水分利用效率.结果表明,施加土壤扩蓄增容肥后冬小麦生育期平均耗水量较对照平均减少了491.67 m3/h㎡,可明显降低冬小麦棵间蒸发,同时可降低播种到拔节期阶段棵间蒸发占阶段耗水量的比例;灌水量2250 m3/h㎡3理(T2)水分利用效率达2.62 kg/m3;灌水量1950 m3/h㎡的处理(T3)可增产32.68%.     

Does transport of water to roots limit water uptake of field crops?

The question was examined under which conditions the water extraction rate of plant roots in the field can be limited by water transport to the roots. For this purpose we used a numerical solution of the single root model. Scenario calculations were carried out in order to investigate the general model behaviour. A sensitivity analysis showed that initial volumetric water content and root length density are of greater importance than root diameter in determining the maximum water transport rate to the roots. Data from a field experiment were taken, describing root length density, volumetric water content and water uptake rates under oats (Avena saliva L.) and faba beans (Vicia faba L.) as model input parameters. With this data the model calculated the water content difference between the bulk soil and the root surface which is necessary to induce a water flow to the roots matching the observed water uptake rate. Root length densities below the grain legume crop faba beans are one order of magnitude lower compared to that of the cereal crop oats. The therefore higher specific water influx rates of faba beans roots resulted in a higher decrease in water content near the root surface. However, water uptake by faba beans was controlled by the water flow towards the roots probably only in deeper soil layers with very low root length density. For the given conditions no transport limitation of water uptake was calculated, when rooting densities were higher than about 0.1 cm.cm^?3.     

黄淮海平原三种土壤中优势流现象的试验研究

在黄淮海平原选择三种不同质地类型的土壤（砂壤土、淤土、风沙土）,各设１．５ｍ×１．５ｍ两个小区,其中一个小区在试验开始前两癸灌水约５６ｋｇ,以获得不同的初始含水量。将１００ｍｍ含有染色剂亮蓝的水灌入小区,一天之后,开挖１ｍ×１ｍ的剖面拍照,进行图像分析处理,计算剖面中染色百分比随深度的变异,研究所形成的优势流的状况与土壤类型、土壤初始含水量的关系。结果表明：不同土壤发生优势流的程度不同,结构发育好     

A model of ammonia volatilization from applied urea. V. The effects of steady-state drainage and evaporation

Rachhpal-Singh & Nye's model of ammonia volatilization is expanded to account for the effects of steady-state water movement by drainage or evaporation when the soil does not dry out to any great extent. The model shows how upward movement of water during evaporation increases volatilization by carrying urea-derived NH₄⁺ and HCO₃^? ions upward, thereby increasing the concentration of ammonia gas at the surface. Conversely, water drainage reduces volatilization by carrying the dissolved solutes into the soil. The model is used to assess the effects on volatilization of evaporating conditions and of irrigation or rainfall.