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咸水滴灌条件下塔里木沙漠公路防护林土壤水盐时空动态及数值模拟
丁新原
学位类型硕士
导师周智彬
2015
学位授予单位中国科学院大学
学位授予地点北京
学位专业生态学
关键词咸水滴灌 土壤水分特征曲线 水盐时空动态 数值模拟 塔里木沙漠公路防护林
摘要土壤水作为荒漠生态系统水分的主要存在形式,是制约植被生长的最大限制因子,不仅对沙地土壤的发生、演化和土地生产力产生重大影响,而且在荒漠生态系统的结构稳定性保持和功能正常性发挥等方面具有重要意义。塔里木沙漠公路防护林生态工程纵贯塔克拉玛干沙漠,由于该地区的高强度蒸发,其沙地土壤水分很难维持一个相对平衡状态,从而无法满足大多数植物的正常用水需求,故防护林生态工程的核心便是解决水的问题。然而,长期利用咸水尤其是高矿化度咸水灌溉植被引起的土壤积盐甚至盐渍化问题等,已成为防护林后期建设与维护的重要障碍性因子。基于此,对其开展水盐动态及其数值模拟研究等很有必要。本研究通过野外土壤水盐实时监测揭示了该区土壤水盐的时空动态规律,并分析了其主要影响因子;同时基于室内土壤水分特征曲线试验等进行了土壤水盐运移的数值模拟,并分析了其沙质土壤的水分物理性质。本研究可为区域土壤盐渍化防治、土壤水盐动态预报等提供科学支撑,同时也对防护林后期建设与维护及其灌水制度的进一步优化等具有重要指导意义。 (1)防护林土壤水盐时空动态规律性显著 咸水滴灌下,防护林土壤水盐动态具有显著的周期性规律。时间变化方面:在灌水周期间(4-7月),水分随月变化整体呈下降趋势,而盐分整体有所上升;一个灌水周期内(1-15 d),水分先后经历了快速下降(1-4 d)、缓慢变化(4-10 d)和基本稳定(10-15 d)三个时期,整体呈幂函数递减规律(y=8.746t-0.270,t=1, 2, 3…);盐分则先后经历了脱盐(1-7 d)和积盐(7-15 d)两个阶段,整体变化规律符合抛物线函数(y=0.009t2-0.138t+2.269,t=1, 2, 3…)。空间分布方面:水平0~60 cm距离内的土壤水分呈一元线性递减分布,而盐分呈一元线性递增分布;垂直0~120 cm距离内的土壤水分表现为较明显的单峰曲线,其峰值位于20 cm土层处,而盐分分布满足逆函数模型,并在表土层距滴头45~60 cm处有显著积盐现象,含盐量高达10~20 gkg-1。 (2)防护林土壤水分特征曲线实测与拟合效果优良 各土层土壤水分特征曲线的表现不尽相同。其中,表土层(0~5 cm)处的曲线除与中间层曲线(40~60 cm)的差异性不明显外,与其它土层曲线的差异性均较显著(P<0.05),而其它各土层之间的曲线差异性均不显著(P>0.05)。同时,各土层水分曲线特征反映出的差异与其表现出的基本物理性质差异一一对应,即容重较小、粉粘粒含量较多的土层的曲线位置较高,对应的持水性较强,饱和含水率和凋萎含水率也较高,反之则较低。模型拟合方面,三种曲线模型均可用于拟合防护林试验地的土壤水分特征曲线,但各有优缺点。其中,在拟合精度上,VG模型和BC模型在低吸力段的拟合精度均较高,Gardner模型在中吸力段的拟合精度稍高,但VG模型和BC模型的整体拟合效果优于Gardner模型。 (3)防护林土壤水分物理性质表现出一定层间差异性 防护林土壤各土层持水性由强至弱依次为:0~5 cm,40~60 cm,100~150 cm,60~100 cm和5~40 cm;各土层供水性由强至弱依次为:5~40 cm,60~100 cm ,0~5 cm,40~60 cm和100~150 cm,且整体在低于1.5×105 Pa吸力值时表现较强;各土层有效水含量和进气吸力值均自上而下递减,均值分别为17.3%和13.0 cm H2O。饱和持水量、毛管持水量和田间持水量也随土层自上而下呈同步下降趋势,并与容重成显著一元线性负相关。有效水范围内,防护林地土壤有效水上限对应0.3×105 Pa的吸力值,易效水与难效水的临界点吸力值以1.5×105 Pa为宜;各土层的易效水均多于难效水,总体上,前者均值为13.1%,是后者的3倍;5~40 cm和60~100 cm土层的易效水多,0~5 cm和40~60 cm土层的难效水多,二者比例均为同类最高;同层内易效水比例与土壤持水性之间负对应。 (4)基于根系吸水模型的防护林土壤水盐运移数值模拟具有一定可靠性 在土壤根系密度分布方面:水平方向(0~60 cm)上,梭梭的根长密度分布特征满足指数函数形式;垂直方向(0~120 cm)上,梭梭根长密度函数在0~30 cm土层内呈线性递增,而在30~120 cm土层内呈线性递减。在土壤水盐运移数值模拟方面:基于含根系吸水项的一个灌水周期内防护林土壤水盐运移的数值模拟具有一定的可靠性。其中,土壤水分运移的数值模拟精度整体相对稍好(RSME均值约为0.01),而土壤盐分运移的模拟精度则相对稍差(RSME均值约为0.17)。整体而言,该模拟可用以进行区域土壤水盐动态的预报。
其他摘要As a dominant existing form of water, soil water is the biggest factor which limits to the growth of vegetation in desert ecosystem. Not only does it can make an important impact on the occurrence, evolution and productivity of sand soil, but also it can play a significant role in maintaining the structure stabile and functioning properly for desert ecosystem. Ecological engineering protection-forest along the Tarim desert highway runs through the Taklimakan desert, due to a high evaporation intensity of this region, it is very difficult to maintain a state of relative balance for the sandy soil moisture, the normal water demands for most plants can not be met. Consequently, the key problem of ecological engineering of shelterbelt is to solve the problem of water. However, the soil salinization caused by the saline water irrigation, especially the high salinity saline water irrigation, which has been used to irrigate the vegetation of this region for a long-term, has become an important barrier factor for the construction and maintenance of the shelterbelt. Based on this, it is very necessary to carry out the dynamics of soil water and salt and its numerical simulation and so on in this region. On the one hand, in order to reveal the spatial and temporal dynamic laws of the soil water and salt for the artificial shelterbelt in the center of Taklimakan Desert under saline water drip-irrigation, the temporal characteristics and two-dimensional spatial distributions for its soil water and salt among four irrigating cycles of months from April to July had been measured and the related main factors were analyzed. On the other hand, the soil water characteristic curves for different depths of the soil in Tarim desert highway shelterbelt were measured and studied, which were used to provide the soil hydraulic parameters for the numerical simulation of soil water and salt transport and analyzed the soil physical water properties for different depths of sand soil of the shelterbelt. This paper can not only provide theoretical basis for controlling soil salinization and predicting dynamics of soil water and salt in this region, but also can make a good influence on developing and maintaining the shelterbelt and optimizing further its irrigation regulation in later stage. The main results showed as follows: (1) The dynamic regularity of soil water and salt of shelterbelt was obvious. ①The dynamics of the soil water and salt on space and time for the artificial shelterbelt took obviously cyclical laws. When it referred to the temporal changes of the soil water and salt, on the other hand, in an irrigating cycle, the dynamics of soil water displayed three changeable stages which were divided into the rapidly decreasing period(1-4 d), the slowly changing period(4-10 d) and the almost stable period(10-15 d), respectively, while the dynamics of soil salt content undergone two changeable stages which were divided into the desalting process(1-7 d) and the salt accumulation process(7-15 d). Meanwhile, it took a decreasing law along with days according with Power Model(y=8.746t-0.270, t=1, 2, 3…) for the soil water, but the relationship between the soil salt and the time was consistent with Parabolic Function(y=0.009t2-0.138t+2.269, t=1, 2, 3…). ②When it referred to the spatial distributions of the soil water and salt, the average soil moisture content was reduced by One-Linear Regression Function while the average soil salt content was increased by One-Linear Regression Function along with the distance on the horizontal space(0~60 cm). On the vertical space(0~120 cm), it showed an approximate unimodal curve for the distribution of soil water, and its peak was at the depth of 20 centimeters in the vertical space. However, for the soil salt, its characteristics of distribution were conformed with Reciprocal Function, and it presented marked phenomenon of salt accumulation at the surface of soil, especially in the ranges of horizontal distance which was away 45~60 cm from the irrigating drips, where the content of salt was up to 10~20 g/kg. (2) The effects of measured and fitted soil water characteristic curves of the shelterbelt were good. ①The soil water characteristic curves of different depths of the soil were not all the same. Among them, the topsoil (0~5 cm) curve is very different from the other curves(P<0.05) which from 0 cm to 150 cm of the soil profile, except the middle depth (40~60 cm), while the other curves were little different from another one(P>0.05), besides the middle depth (40~60 cm). ②The structural differences among the depths of the soil profile could be reflected by the measured soil water characteristic curves, resulting from the correspondence between the features of the curves and the soil basic physical properties in different depths of soil. Briefly, the characteristics that the capacity of soil water retention was stronger, the saturated moisture content and residual moisture content were higher, which were consistent with the features that the soil bulk was smaller and the proportion of the silts and clays were higher. ③The fitted precision of van Genuchten Model and Brooks-Corey Model were higher in the low suction less than 1.0×105 Pa while the fitted precision of Gardner Model was a little higher in the above suction from 1.0×105 Pa to 15.0×105 Pa. However, on the whole, the formers were superior to the latter on fitting the soil water characteristic curves, because the results of correlation coefficients and root-mean-square errors between simulated values and measured values of soil moisture content by van Genuchten Model and Brooks-Corey Model were better than the values calculated by Gardner Model. Summarily, the three models can be used to fit the soil water characteristic curve of this region. (3)The soil water physical properties among the soil layers of shelterbelt showed some differences. ①From strong to weak, the capacity of soil water retention for different depths were followed respectively by 0~5 cm, 40~60 cm, 100~150 cm, 60~100 cm, 5~40 cm while the soil water supply were followed respectively by 5~40 cm, 60~100 cm, 0~5 cm, 40~60 cm, 100~150 cm, and it took on a strong water supply under the soil suction on Pressure which was less than 1.5×105 Pa. The available moisture content of soil was decreased gradually from the upper depth to the lower depth and its average was 17.3%. ②Saturated moisture capacity, capillary moisture capacity and field moisture capacity were also showed a synchronized decreasing trend from the upper depth to the lower depth;on the other hand, the relationship was closed between three kinds of soil moisture holding-capacity and soil bulk, which was consistent with one-linear regression function. ③The upper limit of available water was the soil moisture content corresponding to the suction of 0.3×105 Pa and it was suitable to take the value which was 1.5×105 Pa as the boundary point of suction for readily available water and resistant available water. The readily available water content in all the depths were more than the resistant available water content, and the value of former was 13.1%, which was three times of the latter. Compared with the others, the readily available water content in the depths of 5~40 cm and 60~100 cm took the most supreme proportion while the resistant available water content in the depths of 5~40 cm and 60~100 cm took the highest proportion in the range of available soil water content, and both the values of them were the biggest. (4)The result for the numerical simulation of soil water and salt transport had certain reliability based on the root water absorption model. ①In terms of the soil root density distribution, the feature of distributions of the root length density on the horizontal space(0~60 cm) for Haloxylon ammodendron was according with Exponential Function along with the distance on the horizontal space(0~60 cm), while the feature of distributions of the root length density for Haloxylon ammodendron was according with One-Linear Regression Function along with the distance on the vertical space (0~120 cm), including the reduced distribution along with the distance from 0 cm to 30 cm and the increased distribution along with the distance from 30 cm to 120 cm. ②In terms of the numerical simulation of soil water and salt transport, the result for the numerical simulation of soil water and salt transport of the shelterbelt in an irrigating cycle had certain reliability based on the root water absorption model. Specifically, the precision(the average value of RSME is close to 0.01) for the numerical simulation of soil water transport was a little better while the precision(the average value of RSME is close to 0.17) for the numerical simulation of soil salt transport was a little worse on the whole. Overall, this numerical simulation could be applied to predict the dynamics of soil water and salt for this region.
学科领域生态学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14643
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
推荐引用方式
GB/T 7714
丁新原. 咸水滴灌条件下塔里木沙漠公路防护林土壤水盐时空动态及数值模拟[D]. 北京. 中国科学院大学,2015.
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