【作者】 史文娟；

【导师】 沈冰； 汪志荣；

【作者基本信息】 西安理工大学 ， 水文学及水资源， 2005， 博士

【摘要】 由于涉及水资源、农业、环境等诸多方面的问题,土壤中水和溶质运移的研究历来为人们所重视。本文针对我国西北地区土壤剖面多呈层状和春季强烈返盐季节土壤多处于裸露状态的特点,以室内土柱模拟实验为主,研究同一潜水位和矿化度(3g/l)条件下不同大气蒸发能力时夹砂层强化盐渍土壤的水盐运动规律及其迁移机制。实验分毛管水上升和水分蒸发两个阶段进行,主要分析了砂土层厚度、层位、质地等因素对水盐运动的影响及作用机制,所得主要结论如下:1. 均质土毛管水上升速度和地下水补给速率均与时间呈非线性幂函数关系,二者之间可近似为线性关系,其斜率表示此期间土壤剖面含水量:变化量。入渗条件下的Green-Ampt模型也可用于模拟地下水埋深较浅时均质土壤毛管水分运动特性。2. 与均质土相比,砂层对毛管水的上升既有促进也有抑制作用。具体情况取决于砂层的层位。在本实验条件下,砂层的层位大于5cm(相对层位为0. 1) 时,砂层会抑制水分运动。经分析认为,砂层层位对水分蒸发由促进到抑制的转折点为砂土和壤土导水率的相对大小发生变化之时。此外,砂层的抑制作用随砂层层位的升高、厚度的增加以及级配的变差而增大。3. 夹砂层土壤毛管水最大上升高度以及各层土壤含水量的分布是否会受到影响主要取决于砂层的质地、层位、厚度及其相互间的关系,同时还与同剖面中其它土壤的质地有关。其它土壤质地一定时,若砂层的有效粒径或不均匀系数满足西安理工大学博士学位论文Dlo之1 4.0632一1462尸三0 .06821261则毛管水的最大上升高度以及各层土壤含水量的分布均会被抑制。 4.对于盐渍土的蒸发来说,由于盐壳形成后对水分蒸发的抑制,不同大气蒸发能力条件下地下水埋深为50cm时,短历时(<15d)的潜水蒸发为稳定蒸发,而长历时(>15d)则为非稳定蒸发。对于盐渍土潜水稳定蒸发强度的计算,阿维里杨诺夫公式不再适用,而清华大学雷志栋公式较好。同时也可估算不同大气蒸发能力条件卜的非稳定蒸发强度,但两种情况下公式中系数刀的下限值均比规定值小,需要做近一步调整。 5.砂层对潜水蒸发强度、土表返盐量以及盐溶液浓度的影响与砂层对毛管水上升速度的影响规律基本相同,当砂层层位大于35cm(相对层位为0.7)时,砂层对水盐的抑制作用可达70一80%。同时盐分在土砂上下界面均有滞留现象,且砂层层位越高或有效粒径越大,其滞留量越大。因而砂层对盐分的抑制率大于对水分的抑制率。这对于盐碱地的改良和作物的生长非常有利。 6.以均质土壤潜水稳定蒸发强度计算模型为基础,建立了适用于不同蒸发能力条件下各层位夹砂层土壤以及同层位不同质地夹砂层十壤稳定蒸发强度计算的雷志栋公式,并提出其非稳定蒸发强度计算的方法及条件。砂层的相对层位和相对有效粒径可分别作为预测不同层位和质地夹砂层稳定蒸发强度的重要参数。 7.不同大气蒸发能力时各层位夹砂层土壤以及不同质地夹砂层土壤土表Zcm和10cm的累积蒸发量与全盐量呈明显的线性关系,但层位人于35cm(相对层位为0.7)的夹砂层土壤应与小于35cm的夹砂层土壤分别进行处理。 8.砂层对不同离子运动的影响不同。对地下水和土壤中均存在的Na+和Cl一而言,其表聚情况最为强烈,同时受砂层的影响也最人,且在蒸发后期砂层对Na+的抑制作用大于cl一。对于仅土壤中存在的50户、ca2+和HcO3一三种离子来说,随水分向上迁移的主要是5042一和ca2+,且砂层层位的变化对ca2+的影响更大一些;而HCO3一则不随水分而运动,即砂层对HC03一无明显影响,但不同处理在接近地卜水位处出现了次生碱化的现象(即HC03一含量明显增大),且随蒸发历时的延长以及大气蒸发能力的增加而加重。外界大气蒸发强度越大,砂层对离子的抑制作用越大。 9.均质土壤剖面Cl一和全盐量之间呈线性关系,而Na+与全盐量则旱_对数函数摘要关系,且离子与全盐量的关系不受大气蒸发能力影响;不同层位夹砂层土壤剖面全盐量和两种离子的关系与均质土相同;不同质地夹砂层土壤剖面全盐量与Cl’呈指数型关系曲线,而与Na+呈直线关系。同一大气蒸发能力条件下离子与全盐量的关系不受砂层层位以及砂层质地的影响。 10.敏感性分析结果表明,忽略参数b将使理论计算的潜水极限蒸发强度比实测值大,且土壤质地越轻,忽略参数b时所计算的潜水极限蒸发强度越大;同一质地时,则参数b的大小对潜水极限蒸发强度的影响与潜水理深有关。对于盐渍土来说,由于盐壳的影响,理论计算的潜水极限蒸发强度均比实测值大。 11.将层状土壤各土层以均质土来看待,并以此为基础来计算层状土壤的稳定蒸发强度,对于层位较低的夹砂层土壤较为适用,但对于层位较高的夹砂层土壤还必须考虑砂层对水分的“阻抗作用”,否则会产生较大的偏差。 以上研究结果对于预测层状土壤稳定蒸发强度、防止次生盐碱化,以及灌溉和排水的设计均有重要作用。 关键词:夹砂层土壤;毛管水分运动特性;蒸发强度;返盐量;盐分分布:离子运动特性;理论计算。 本研究得到国家自然科学基金项目《黄土区土壤溶质迁移机制及祸合模型研究))(59879022)和《西北地区城市雨水利用及其生态环境效应》(40271022)?更多还原

【Abstract】 Owing to the problems involved in water resources, agriculture, environment and so on, the study on the transport of water and solute in soil is always pay attention to. In addition, considering the fact that most soil profiles assume layered structure in the field and that most bare soils are exposed to the atmosphere when salt accumulation in the surface soil is very rapid in spring, a laboratory investigation was conducted for capillary water rise in, and evaporation from different sand-layered soil columns under different atmospheric evaporation powers in the presence of shallow water table. The groundwater fluid was mineral water containing 3g/l NaCl. The effect of the thickness, the position, the particle size and its distribution of the sand layer on transport of water and salt and the estimated method of evaporation rate were studied, its mechanism was further examined. And the theory evaporation rate was calculated and its results were discussed. The main results are as follows:1. The results showed that there was linear function relationship between the capillary water rise velocity and the capillary water supply rate for the uniform soil and an non-linear power function relationship between them and the time, Green-Ampt model can be applied in simulating capillary water movement for the uniform soil in the presence of the shallow water table.2. The sand-layered soil had an important effect on the upward capillary water movement compared to the uniform soil column. The movement can be not only restrained but speeded as well. This is mainly related to the relationship of the hydraulic conductivity of the two soils in the profile i.e. whose conductivity will be larger. In the paper, the rate of the capillary water rise were limited by the sand layer when the distance between the low boundary of the sand layer and the water table ismore than 5cm, and the effect was intensified not only by the thicker sand layer and the higher sand layer position, but also by the worse sand particle size distribution. The change of the capillary water rise velocity and the capillary water supply rate for the layered soil were behaved by the relative position (i. e. the ratio of the position to the buried depth of water table), the effective particle diameter (i. e. D10, particle diameter with 10%) and the no uniform coefficient (i. e. , the ratio of the particle diameter with 60 % to the particle diameter with 10%) respectively.3. Whether the maximum height of the capillary water rise and water content of each layer soil for layered soil were changed or not were mainly determined by the sand soil texture, position, thickness, and their mutual relationship, and they also were closer connected with other soil texture in the profile. When the soil profile was certain, they will decrease when the sand layer meets with the conditions, i.e. 4. As far as evaporation from the high-salt soil with 50cm depth of water table was concerned, the evaporation rate remained steady with less than the 15d evaporation duration, and tended to be no steady with more than 15d duration under different atmospheric evaporation power, this was related to the formation of salt crust which in turn restricted water evaporation.5. The calculated steady rates by the empirical equation presented by Averiyanov had a large difference with the measured ones, and the calculated ones by the equation proposed by Lei et al (1988) had a well agree with the measured data, but the low limited value of the coefficient P for later equation needed further modify. In addition, the equation proposed by Lei et al was also proved to be suitable for calculating the no steady phreatic evaporation rate when coefficient was less than the stated value.6. The phreatic evaporation rate, the accumulative salt amount and salt concentration in the topsoil from the layered soils were smaller significantly than that from uniform soils except for the treatment whose distance of the sand layer to the water table was 0, this was更多还原