Soil moisture movement and groundwater recharge by tritium tracer tagging technique

The paper deals with the study of rate of soil moisture movement and recharge to groundwater system at Indian Agricultural Research Institute (IARI) farm for the years 1973, 1974 and 1975. The utility of artificially injected tritium, experimental techniques adopted and a quantitative determination of recharge and moisture movement rates are discussed. Corrections for upward movement of moisture after the end of monsoon have been used to calculate the average rates of water movement below the injection level and groundwater recharge. Average rates of soil moisture movement and recharge are 9.4 mm/d and 27.4% (193 mm) of monsoon precipitation for three years respectively. Under favourable conditions the diffusion coefficients for soil water system are calculated assuming Gaussian distribution of tritium concentrations in the soil profiles. The average value of diffusion coefficient is 2.5 × 10^?5 cm²/s for the sandy loam soils. The variation in recharge is mainly due to inherent variability in soil physical properties and vegetative cover. The technique is not found reliable for higher water table conditions on account of lateral flow.     

Ground water recharge in Western Uttar Pradesh

The downward movement of water in the soil due to 1971 monsoon precipitation and supplemental surface irrigation has been traced at about forty-five sites in Western Uttar Pradesh, using a thin layer of moisture tagged with tritiated water. The tritiated layer was found to move down to different depths at different sites. The movement, averaged over the forty sites is found to be 96 cm, indicating that the average recharge for the year 1971 (a year of normal monsoon) was 21.5 cm of water.     

The measurement of tritium activity in natural waters

The concentrations of tritium have been determined in wet precipitations occurring over the Indian subcontinent during 1961–64, using a sensitive method for counting of tritium activity discussed in Part I* of this paper. The tritium concentrations varied significantly during the period of observation; highest concentrations were observed during 1963. An analysis of the data reported here, in conjunction with those available for concentrations of H³ and Sr⁹⁰ in rains at higher latitudes, reveals that these nuclides which were originally placed at high altitudes in the polar regions during late 1962, were deposited chiefly at 30°–90° latitudes during 1963 and 1964 respectively in relative proportions of 1 and 0·6. The data show that the largest gradients in their zonal deposition occur at about 35°–40° N latitude and that to a first approximation, their deposition per unit area in 1963 or 1964 was practically uniform, separately in the 30°–90° and 0°–30° latitude regions. This observation suggests the existence of two well-defined cells, which are internally well mixed: the meridional transport to low latitudes occurs as a result of interaction between these cells. The annual deposition rates of Sr⁹⁰ as observed during 1963 and 1964 suggest a mean time of 3 months for exchange of air between the two cells, in good agreement with the values deduced for mid-months of the year on the basis of analysis of bomb produced C¹⁴ data. The tritium and strontium data for the inland, coastal and island stations are analysed to evaluate the importance of (i) the re-evaporation of tritium from continents, and (ii) the molecular exchange of atmospheric tritium with oceanic water. Process (i) probably plays a significant role over the continents throughout the year; its effect, however, is experimentally visible only during June to September. The estimated concentration of H³ in evaporated water suggests that the precipitated water mixes very slowly with that in the soil; limits on the equivalent amount of exchangeable soil water are given. It is shown that the relative wet deposition of H³ and Sr⁹⁰ atisland andcoastal stations is similar to their estimated concentration ratio in upper level tropospheric air. Furthermore, the relative concentrations of H³ and Sr⁹⁰ at continental and occanic stations differ only to the extent expected due to reinjection of H³ over continents. Thus, if one takes into account the recycling of H³ at continental stations (which results in about a 50% higher apparent deposition on an annual basis), one is led to the conclusion that process (ii) is rather unimportant; an upper limit of 30% on the fraction of tritium removed over oceans by molecular exchange is deduced. The mean annual concentration of Sr⁹⁰ in wet precipitation is lower at oceanic stations compared to that at continental stations. This could be due to meteorological effects peculiar to oceanic areas,e.g., higher rainfall and quick recycling of evaporated water. Otherwise, one must postulate a significant removal of Sr⁹⁰ (and H³) by ocean spray and jet action.     

豫南山区典型森林类型土壤水分变化规律研究

采用连续定位观测的研究方法,对豫南低山区天然落叶阔叶林土壤水分变化规律进行了研究.结果表明,10cm,20cm,30cm,50cm四个不同测定深度处的土壤水分随季节变化均发生明显的周期性变异,土壤水分含量50cm20cm30cm10cm;变异幅度随深度增加而增加,即50cm30cm20cm10cm;垂直变化差异显著.土壤水分含量与降雨量存在显著的回归关系,10cm,20cm,30cm,50cm四个测定深度土壤水分含量与降雨量的线性回归方程相关系数分别达到0.727,0.772,0.786,0.626.     

电磁波在三相土介质中的传播

研究电磁波(EM波)在土中的传播特性,必须获得如介电常数和磁导率等基本电磁参数.在麦克斯韦方程组的基础上,提出了等效模型来计算土体介电常数.利用该模型的计算结果与实测数据符号很好,可以为利用电磁波法测量土体含水量,土体的CT分析以及土工环境监测奠定理论基础.     

Analytical solutions for time-dependent heat conduction equation of soil moisture

We present the analytical solutions for time-dependent heat conduction equation of soil moisture. Solutions for four different types of initial, final and boundaries are obtained by use of moisture content as the primary variable. Our results are tested numerically and the agreements are excellent.     

Spectral decompositions in nonlinear coupled diffusion

The solutions of a coupled, linear and nonlinear diffusion equationin a semi-infinite medium are derived using series methods.In addition, perturbation techniques allied to the spectraldecomposition of matrices are used to simplify the analysisand to find semianalytic solutions. The discussion is motivatedby the transmission of heat, moisture, and solute through thestrongly nonlinear medium of soil. Under boundary conditionsrepresenting the daily or seasonal fluctuations, it is shownusing spectral decomposition, despite the nonlinearities, howthe period of oscillation is preserved on passage through themedium. It is also shown how n³ partial differential equationsmay be solved for each of the n coupled variables to determineclosed forms for the first- and second-order perturbation effects.Examples of the solutions are given for the case of the coupledtransport of heat and moisture in soil.     

非饱和水流问题的混合元法及其数值模拟

1.引 言 均质土壤中的地下水流动可归结为非饱和土壤水的流动,是土壤水未完全充满孔隙时的流动,是多孔介质流体运动的一种重要形式.非饱和流动的预报在大气科学、土壤学、农业     

土壤水流与溶质耦合运移问题的混合元-迎风广义差分法研究

本文研究了一维非饱和土壤水流与溶质耦合运移问题的数学模型, 建立了求其数值解的守恒混合元-迎风广义差分格式. 对非线性土壤水分入渗方程, 采用守恒混合元法进行离散模拟, 同时得到了土壤含水量和水分通量; 而对对流-扩散形式的溶质运移方程, 利用迎风的广义差分法离散求解. 且分析了解的存在唯一性, 并讨论了误差估计. 最后给出数值算例, 模拟结果表明利用本文格式来求解非饱和土壤水流与溶质耦合运移问题是可靠的, 且该格式具有稳定性和可实用性.     

春小麦水分敏感指数与有限水量生育期的最优分配

通过不同的受旱处理，确定了Jensen模型中的春小麦水分敏感指数。介绍了运用生态规划模型实现有限水量生育期最优分配的方法与步骤，并以辽西地区春小麦为例，确定了不同初始含水量和生育期可利用灌溉水量下的最优分配决策。     

Identification of the Rain Rate for a Boundary Value Problem of a Rainfall Infiltration in a Porous Medium. II. Determination of the Conditions of Optimality

This paper deals with the determination of the conditions of optimality for a control problem related to a rain history identification from available moisture observations in the soil.     

矿区土壤中含水率及重金属迁移转化的数值模拟

本文基于由连续性方程和达西定律所推出的土壤中水分运动基本方程,以一维垂向水分方程为研究对象,构造稳定收敛的有限差分格式,运用MATLAB数学工具,对地面饱水情况下土壤水分运动的一维垂向方程进行了数值模拟,得到了土壤中水分的迁移规律;同时,综合考虑对流扩散作用以及土壤对重金属的吸附解吸作用,利用非饱和土壤中重金属离子迁移转化模型,对锌离子在矿区土壤中的迁移转化进行了数值模拟,展示了锌离子在矿区土壤中的浓度分布规律．     

Compartmental model for nitrogen dynamics in citrus orchards

A simple model that represents the soil nitrogen dynamics in a citrus orchard is studied. This model consists of several compartments of organic and inorganic nitrogen representing the main processes that occur among the compartment of the soil column. Some of these processes are coupled to the carbon dynamics in the soil, thus, the evolution of organic carbon in the soil has been also described in the model. The dependence of these processes with soil moisture requires the coupling of a nitrogen model with a model of soil water dynamics. A compartmental model for the water has been used to simulate the dynamics of water in the root profile.The proposed model has been used to predict the soil mineral nitrogen content and the nitrate leaching in a citrus orchard placed in the area of Valencia and the obtained results have been compared with the results obtained with the nitrogen component of the widely used Leaching Estimation and Chemistry Model (LEACHM).     

Hierarchical Low Rank Approximation of Likelihoods for Large Spatial Datasets

Datasets in the fields of climate and environment are often very large and irregularly spaced. To model such datasets, the widely used Gaussian process models in spatial statistics face tremendous challenges due to the prohibitive computational burden. Various approximation methods have been introduced to reduce the computational cost. However, most of them rely on unrealistic assumptions for the underlying process and retaining statistical efficiency remains an issue. We develop a new approximation scheme for maximum likelihood estimation. We show how the composite likelihood method can be adapted to provide different types of hierarchical low rank approximations that are both computationally and statistically efficient. The improvement of the proposed method is explored theoretically; the performance is investigated by numerical and simulation studies; and the practicality is illustrated through applying our methods to two million measurements of soil moisture in the area of the Mississippi River basin, which facilitates a better understanding of the climate variability. Supplementary material for this article is available online.     

Classical and weak solutions for one-dimensional pseudo-parabolic equations with typical boundary data

Summary In this paper we consider the pseudo-parabolic equations arising in the filtration of water in media with double porosity and moisture transfer in soil. The existence, uniqueness and stability for both classical and weak solutions are studied.     

回归分析在土壤水份测定中的应用

针对现实中土壤水分含量测定困难的问题,应用回归分析方法,找到反映土壤水分含量的相关因素,推导出回归方程,从而计算出土壤水分含量.这样简便了测定方法,便于在实际中运用.     

Existence for a time-dependent rainfall infiltration model with a blowing up diffusivity

A difficulty in the modelling of water infiltration into an unsaturated soil is due to the presence of a diffusion coefficient that blows up at the moisture saturation value. This is put in evidence in some well-known hydraulic models like those of Broadbridge and White and van Genuchten. In this paper, we obtain results concerning the existence, uniqueness and regularity properties of the solution of unsaturated water flow determined by a time-dependent rainfall, with a nonlinear flux boundary condition on the outflow boundary and a singular diffusion coefficient. Some considerations related to the possibility of saturation occurrence and the extension of the results to the model describing the infiltration into an nonhomogeneous stratified soil are finally made.     

无界域上一类非线性积分微分方程解的存在性

在比较宽松的条件下,研究了无界域上一类非线性积分微分方程解的存在性.通过引进等价的范数,利用递归法、Tonelii近似序列和局部凸拓扑,建立了新的存在性定理,改进了定义在有界域上的非线性湿气迁移方程的相应结果.     

Theoretical studies on solid heterogenous targets thickness in muon catalyzed fusion using transport theory and its comparison with available experimental values

Muon catalyzed fusion in solid heterogeneous H/D/T layers has been studied in recent years. When a negative muon enters the protium layer with a small admixture of tritium, the muonic atom is formed. molecular ion formation is highly dependent on the energy of the muonic tritium atom, μt, and this energy itself depends on the thickness of H/T and D₂ layers. In this paper, the transport theory is used to study the effect of the thickness of different layers (H/T and D₂) on the output kinetic energy of the μt atom. The calculated thickness by the used theoretical method are compared with the available experimental values and it is shown that they are in a good and acceptable agreement, and represents the reliability of used theoretical method.     

湿气迁移方程的非线性初边值问题

In this paper,combining Riemann's method with the fixed point theory effectively,we proved that the migration equation of the moisture in soil with nonlinear initial boundary value problem has unique classical solution.