【作者】 王子龙；

【导师】 付强；

【作者基本信息】 东北农业大学 ， 农业水土工程， 2010， 博士

【摘要】 在我国东北、西北和西南等广大地区,冬季通常会有一层相对稳定的雪被覆盖于冻结土壤表面,雪被覆盖条件下的季节性冻土水分运移和热量传输具有独特的性质,需将雪被和季节性冻融土壤视为一个联合体进行整体研究。同时,水分、热量在雪被-土壤联合体中的运移、存储和转化是自然界水循环中的一个重要环节,在农业、水资源、环境系统中占有极其重要的地位,对农业生产具有重要意义。然而,在理论基础、技术方法、实际应用等各方面,面向农业的雪被覆盖条件下季节性冻土水热运移的研究还存在许多问题亟待解决。针对雪被覆盖条件下季节性冻土水热运移研究中存在的问题,结合哈尔滨市科技创新人才研究专项资金资助项目“雪被覆盖条件下农田土壤水热耦合运动规律及其数值模拟研究(No.RC2010XK002013)”,本文以雪被-土壤联合体中的水分和热量为研究对象,通过田间试验与理论分析相结合的方法,深入研究了联合体中水热耦合运移的变化规律、数学模型及数值模拟。本文的主要研究内容、具体方法、分析结果及研究结论如下:(1)根据野外试验实测资料,运用对比分析和统计分析的方法,对季节性冻土水分运移的驱动力、土壤季节性冻融过程中地面温度的变化规律、地面温度与土壤中温度场的关系、土壤剖面温度、总含水量及液态含水量的变化规律、雪被覆盖对土壤温度、含水量的影响等问题进行了详细探讨。结果表明:季节性冻土水分沿土水势减小的方向运移,地面温度与气温相关性较高且对土壤表层温度影响较大,冻融期日平均地面温度总体上呈开口向上的抛物线型,而地面温度日变化则在不同时期表现出不同的变化规律,土壤已冻层中的总含水量、液态含水量的变化与土壤冻结、融化过程密切相关,季节性冻土区土壤冻融作用导致了土壤水分的重分布,雪被覆盖对土壤与大气之间的热交换具有阻滞作用,对土壤剖面(特别是土壤表层)热状况影响显著,而雪被覆盖仅在融化期才对土壤表层含水量有显著影响。以上分析结果与结论可为数学模型构建及数值模拟计算中合理假设条件的制定、初始及边界条件的简化、水热运移参数的确定等提供重要依据。(2)运用地统计学的理论与方法,通过季节性冻土水分半方差分析及空间分布图的绘制,分别对季节性冻土区土壤冻融过程中剖面总含水量及液态含水量的空间变异结构和空间分布规律进行了分析和研究。结果表明:季节性冻土总含水量与液态含水量具有良好的空间结构和空间相关性,土壤冻融过程影响两种含水量的空间相关性和变程,受冻融过程影响冻结状态下土壤两种含水量均表现出一定的空间分布规律,土壤融化后表层含水量的空间分布表现出较大的随机性。地统计学理论能够很好的刻画季节性冻土水分的空间变异性,可为冻土水分运移的机理研究提供新的思路。(3)从季节性冻土水热运移的机理出发,基于质量守恒原理、能量守恒定律、非饱和土壤水流动的达西定律、热传导理论及一定的假设条件构建了季节性冻土水热耦合运移数学模型,运用有限差分法对季节性冻土一维垂向水热耦合运移进行了数值模拟及结果检验。结果表明:一维季节性冻土水热耦合运移的数值模拟结果存在一定误差,但模拟值与实测值的平均相对误差较小,并且土壤剖面含水量和温度模拟值的变化规律与实测值基本一致。数值模拟效果表明本文所建立的季节性冻土水热耦合运移模型合理、参数确定及数值模拟方法比较可靠。(4)在充分分析雪被-土壤联合体水热运移机理的基础上,根据前人研究成果构建了一维雪被-土壤联合体水热耦合运移模型,制定了模型参数化方案,并进行了数值模拟分析和验证。结果表明:一维雪被-土壤联合体水热耦合运移数值模拟存在较大误差,但模拟值与实测值的绝对误差尚可接受且变化规律相近,本文所建立的一维雪被-土壤联合体水热耦合运移模型及参数化方案尚需进一步改进。综上所述,对季节性冻土区雪被-土壤联合体水热耦合运移规律、数学模型及数值模拟的研究,不仅能揭示季节性冻土区雪被覆盖条件下的土壤水热耦合运移规律、刻画冻融过程中的土壤水热状况,而且能为季节性冻土区农业土壤水热资源的有效利用,地表水、地下水资源评价,水土保持,环境保护等方面的研究提供理论支撑和科学依据。更多还原

【Abstract】 Snow cover is a widespread and relatively stable coverage type on soil surface during the winter of vast areas of northeast, northwest and southwest China. Snow cover and seasonal freezing-thawing soil need to be studied unitedly for water movement and heat transfer of seasonal frozen soil have distinctive properties under the coverage condition of snow cover. Movement, storage and transformation of water and heat in snow cover and soil union are the important link of nature water cycle, play an important role in the systems of agriculture, water resources and environment and have significances to agricultural production. However, studies on water-heat movement in seasonal frozen soil under snow cover still have many problems at the aspects of theory basis, technical method, practical application, etc. to be solved, particularly in the studies towards agriculture.Aiming at the problems in the studies on water-heat movements in seasonal frozen soil under snow cover and combining with the project“Study on farmland soil water-heat coupling movements and numerical simulation under snow cover”(No.RC2010XK002013) subsidized by Harbin Science and Technology Innovation Talents Research Special Funds, the thesis taking the water and heat in snow cover and soil union as study objects, studied the change laws, mathematical model and numerical simulation of water-heat coupling movements in the union by using the methods of field experiments and theory analysis.The study contents, specific methods, analysis results and conclusions of the thesis are as follows:(1) On the basis of the data measured in field experiments, some basic topics were studied by using comparison and statistics methods, including the driving force of water movement in seasonal frozen soil, change law of soil surface temperature during seasonal freezing-thawing process, correlation between soil surface and profile temperature, variations of soil profile temperature, total and liquid moisture and the influence of snow cover on soil temperature and moisture. The results indicated that water in seasonal frozen soil moved along the direction on which soil-water potential decreased, soil surface temperature had high correlation with air temperature and strongly affected surface soil temperature, daily average soil surface temperature assumed an upward opening parabola while its daily changes have various laws in different periods, the changes of frozen soil total and liquid moisture have high correlations with soil freezing-thawing process, soil freezing-thawing action redistributed soil water, snow cover blocked the heat exchange between soil and atmosphere and affected surface soil heat condition significantly, but only in thawing period have significant effects on surface soil moisture. All the above results and conclusions can provide an important basis for making reasonable hypothesis, simplifying initial and boundary conditions, ascertaining water-heat movement parameters, etc. of model establishment and numerical simulation.(2) Spatial variation structures and distributions of soil profile total and liquid moisture during freezing-thawing process were studied according to semivariance and spatial distribution analysis of seasonal frozen soil water using geostatistics. The results indicated that seasonal frozen soil total and liquid moisture have good spatial structures and correlations, freezing-thawing process affected the spatial correlations and ranges of the two type soil moisture, the spatial distributions of the two type soil moisture have good laws affected by freezing-thawing process, after thawing the spatial distributions of surface soil moisture have major randomicity. Geostatistics can effectively characterize the spatial variation of seasonal frozen soil water and provide a new way to study the movement mechanism of frozen soil water.(3) Seasonal frozen soil water-heat coupling movement model was established based on water-heat movement mechanism, conservation of matter and energy, Darcy’s law, heat conduction theory and some hypotheses. Then the process was simulated numerically using finite difference method and the results were tested. The results indicated that simulation values have some error with the measured values, but the average relative error between them is small and they have the same trend. Therefore, the seasonal frozen soil water-heat coupling model established in the thesis was reasonable. The methods of parameter confirmation and numerical simulation were reliable.(4) One-dimension snow cover and soil union water-heat movement model and parameterization scheme were established based on water-heat movement mechanism and previous research results. Then numerical simulation analysis and test were conducted. The results indicated that the simulated values have major error with the measured values, but the absolute error between them can be accepted and they have similar trend. Thus, the one-dimension snow cover and soil union water-heat movement model and parameterization scheme need to be improved further.To conclude, the study on laws, model and numerical simulation of snow cover and soil union water-heat coupling movement in seasonal frozen soil region can not only reveal the soil water-heat movement law with snow cover and characterize the water and heat conditions during soil freezing-thawing process, but also provide theory support and science basis for effective utilization of soil water and heat resources, evaluation of surface and underground water, soil and water conservation, environmental protection, etc. in seasonal frozen soil region.更多还原