【作者】 赵培培；

【导师】 邵明安；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 土壤学， 2010， 博士

【摘要】 黄土高原水土流失是世界瞩目的生态环境问题,其水土保持影响到我国黄土高原地区的农业发展,生态环境以及黄河两岸安全等等。为了保持水土,黄土高原大面积打坝淤地。坝地不仅可以控制水土流失,也可以作为种植作物的农田。截止到2003年,在黄土高原地区已经建成淤地坝11.35万座,形成了3,340 km2的坝地,淤积了2.1×1010 m3的泥沙,控制的坡地面积达9,247 km2。按照《黄河流域黄土高原地区水土保持淤地坝规划》,到2020年底前,黄土高原地区的坝地面积将翻一番。因此,加强对坝地相关科学问题研究,显得非常紧迫和重要。鉴于黄土高原淤地坝坝地的土壤水分和泥沙研究对粮食生产、坝体安全、防洪,以及人畜用水的重要性,本论文以黄土高原六道沟小流域的几座典型坝地为研究对象,基于野外试验观测,结合地统计学方法、经典统计、模型模拟等手段,对坝地土壤水分和泥沙分布特征进行了研究,探讨了坝地土壤水分、泥沙、植物多样性、地上生物量等之间的相关关系,坝地表层和浅层土壤水分变化规律,表层土壤容重和饱和导水率分布特征等问题,得到了以下的主要研究成果:(1)淤地坝坝地表层(0-6 cm)土壤水分具有很好的空间结构性,高斯模型可以很好的拟合其半方差函数的实际值,但其空间分布具有各向异性,主要呈带状分布。普通Kriging插值和序贯高斯条件模拟可以很好的表现坝地表层水分的空间分布特征。在坝地样带上的表层土壤水分研究也表明其有很好的空间结构,结果表明坝地样带上的土壤水分采集可以采用2 m的采样间距。(2)坝地由多种异质土壤组成,本论文中研究中的两座坝地有四种质地的土壤组成:砂壤土、粉质壤土、壤质砂土和砂土,并且土壤呈现层状分布,这对土壤水分分布和运移造成了很大的影响。在坝地,土壤水分会因为和土壤颗粒的相关性呈现层状分布,土壤水分入渗的时候会形成漏斗流。正因为优先流的存在,使得坝地土壤水分入渗过程中的湿润锋不稳定。通过空间相关性分析,层状水流的速度可以达到7 m/天,比垂直入渗的速度(0.3 m/天)快。但这只是在降雨后的第一天和特定的降雨条件、坝地环境下,因此这个速度并不是固定不变的。(3)Pearson分析表明坝地表层土壤的饱和导水率和土壤质地、饱和含水量、土壤容重等显著相关。坝地中部的饱和导水率最大,这是因为粗泥沙的沉积和频繁的动物活动。而坝体前离淤积最远处的饱和导水率最小,这主要是因为颗粒的沉降规律:细颗粒会随着径流在较远的地方沉积。(4)坝地土壤颗粒组成具有很好的单一分形特征,分形维和土壤质地呈S型曲线关系。但是多重分形分析方法的应用受到限制,可能是因为坝地土壤颗粒组成内部信息混乱。通过对14个颗粒组成参数模型的适用性评价,结果表明二参数的Weibull模型可以用来坝地土壤颗粒分布的估测和插值。(5)淤地坝坝地除了保持水土,固碳外,还能保持植物多样性。坝地内物种和控制坡地上的基本相同。在土壤物理性指标中,土壤水分和砂粒含量是影响植物多样性最重要的两个指标,前者为显著负相关,而后者为显著正相关(P<0.05)。坝地表层土壤水分具有空间相关性,这意味着Kriging插值,自相关模型等都可以用于表层水分研究以获得更多的信息。坝地内发生优先流可能会携带病毒、杀虫剂或者除草剂等进入浅层地下水体,从而污染地下水。层状流也因为其相对较快的运动速度,应引起足够的重视。坝地土壤水分除了接受天然降雨外,汇集坡面径流势必造成其水分运动活跃。土壤扰动会增加饱和导水率,加强未耕作坝地的扰动是增强坝地防洪能力的一个措施。作为一个新环境,注重坝地内的物种多样性,也是保护生态环境的一个重要方面。有研究表明,适度放牧和割草有利于物种多样性保护,因此,坝地内可以进行适当的放牧和割草以保护其植物生物多样性。坝地的土壤水分和泥沙特征对于淤地坝环境影响评价、坝地粮食种植以及人畜用水安全都有重要影响,同时对其研究也能对淤地坝建设规划有所帮助和启示。本文在野外试验研究的基础上,研究了坝地水分和泥沙等的科学问题,以期对黄土高原淤地坝坝地科学问题的研究,以及土壤水分和泥沙相关问题的探索深入等提供借鉴,对小流域坝地的利用和农业生产提供一定的指导。在整个黄土高原进行淤地坝坝地碳累积,粮食产量研究、淤地坝坝地对地下水水质水量的影响,以及控制泥沙和植被的关系等,应该是淤地坝科学问题研究的方向之一。更多还原

【Abstract】 The Loess Plateau of China was more famous with the most serious soil loss in the world than the biggest area. Lots of check-dams were built to hold sediment and conserve water widely and quickly. As a consequence, the widespread dam farmlands, which were believed to be to the last barrier to control soil and water losses, were formed quickly due to the serious soil and water losses. In addition, the dam farmland also can be grown plant to increase the crop yield with higher value than the sloping farmland. By 2002, there were about 113,500 check-dams which formed 3,340 km2 dam farmland, held 2.1×1010 m3 of sediments, and controlled 9,247 km2 drainage areas on the Loess Plateau of China. The number of check-dams and the area of dam farmlands are expected to be doubled by 2020. Many plans also showed that more check-dam should be built to conserve the soil and water for their great achievement. Consequently, it is necessary to pay more attention to the dam farmland for the aim of serving agriculture production and ecological protection.The spatial distribution of the soil water content and sediment in the dam farmland is very important to the crop yield, flood control, and water consuming and so on. The objectives of this dissertation were to explore the spatial distribution of soil water content and sediment in the dam farmlands. The study dam farmland located in the Liudaogou catchment of the northwest of Shaanxi province. The soil water content was measured by neutron tube and soil auger. The soil textures of the samples were measured by Mastersizer2000. Classic and geostatistic tools were combined to study the soil water content in the dam farmlands. In addition, fractal theory and parametric model were also introduced to study the soils taken from the dam farmlands.The major results of the present study in the dam farmland on the Loess Plateau of China are listed below: (1) The soil water content (0-6 cm) of the surface layer showed good spatial structure in the dam farmland. Gaussan model could fit the semivariance well. However, the semivariance showed anisotropism. The results showed that the Kriging and condition simulation could be well used in the study of soil water content of surface layer in the dam farmland.(2) The soil texture in the study dam farmland included silt loam, sandy loam, loamy sand, and sand. The soil water contents showed layered distribution corresponding to the particle size. The funnel flow was only found in the shallow soils with layered soil structure of the dam farmland after rainfall. The instability of an unsaturated wetting front as it passes from fine to coarse layers was demonstrated in the dam farmland. The soil water moved laterally in the dam farmland proved by the spatial correlation analysis. However, the water movement mainly happened on the first day after rainfall with a velocity of about 7 m day-1 which was quicker than the infiltration rate.(3) Analysis using Pearson correlation coefficients showed that the spatial variation in KS (at the observation scale) was significantly correlated with the spatial distributions of soil texture, saturated water content, and bulk density at both the filled dam farmland and the silting dam farmland under natural silting conditions. The areas with lowest KS values corresponded to the areas with the highest clay content, silt content, and saturated water content, indicating that the uplands of the dam farmlands are more prone to surface runoff. The area with the highest KS value was found at the middle portion of the dam farmlands with relative higher sand content and bulk density values (not the highest) which can benefit floodwater and runoff control.(4) The relationship between fractal feature and soil texture of the soils in dam farmlands was shown by sigmoid curve. However, the multifractal tool was invalid to predication soil degradation or soil desertification for the disordered intrinsic particle-size information. In addition, Weibull model was recommended to interpolate the soil particle-size distribution for the soils in the dam farmlands from the comparison among 14 models.(5) The dam farmlands without tillage contributed to the plant biodiversity. The plant species in dam farmland was similar with the sloping land. The collected data showed that soil water and sand fraction were important determinants of plant species. The local environment condition was very important for the establishment of the biodiversity in dam farmland.Some methods related to auto-correlation could be used to study topsoil water content for exploring more information. The existence of wetting front instability, carrying water rapidly and deeply in layered soils, might have great practical importance to the hydrologic process and environment protection. Not only the preferential flow, but also the layered water flow should be considered in case of possible contamination in the dam farmland. More attention should be paid to the preferential flow and layered flow aiming at water resource management and contamination control. As the water cycling of the dam farmland was more active due to the acceptation of runoff, the protection and the study was more urgent and important. Moreover, our results suggest focusing on environmental site conditions in order to better explain plant diversity in dam farmland. To the forage resource in filled dam farmland without tillage should be given more attention for it is an additional and potential resource. To encourage the local farmers to graze at a low stocking rate in dam farmland of no tillage could contribute to the biodiversity. If the terrain of dam farmland is too steep to decline the accessibility, advisable mowing is also encouraged.The spatial distribution of soil water and sediment content in the dam farmlands had important effects on the environmental impact assessment of check-dam, crop yield, water quality, and the layout of the check-dam. Based on the field observation, a little work about the soil water and sediment in the dam farmland was studied. The results were expected to be helpful on the related research about dam farmland. However, some science problems were still unclear, such as the accumulation of soil organic carbon, crop yield, the quality and quantity of the groundwater, the transport of the chemicals, and the relationship between sediment control and vegetation in the dam farmland. Those may be the direction of the study on the dam farmland in the future.更多还原