黄土坡耕地地表粗糙度对入渗、产流及养分流失的影响研究

发布时间：2018-05-08 08:45

本文选题：地表粗糙度 + 入渗过程　；参考：《西北农林科技大学》2017年博士论文

【摘要】：黄土高原是我国坡耕地的主要分布区之一。由于降雨集中、坡度大、土壤抗侵蚀性弱及人们耕作管理活动等因素,该区也是水土流失主要的策源地。坡耕地严重水土流失,导致土壤及养分流失,降低土壤肥力和土地生产力,流失养分造成水体富营养化。坡耕地经耕作管理后形成的高低起伏、凹凸不平的微地形,称之为地表粗糙度,其特征与坡面土壤侵蚀密切相关。研究坡耕地地表粗糙度对入渗、产汇流过程及养分流失的特征,有助于探明地表粗糙度对土壤侵蚀机理的影响以及为坡耕地水土流失治理提供科技支撑。因此,本研究在系统总结国内外相关研究资料基础上,以点种、锄耕、等高耕作和犁耕等4种耕作措施形成的地表粗糙度为研究对象,并以平整直线坡为对照组,采用室内外人工模拟降雨试验的方法,观测了不同耕作方式下粗糙坡面微地形特征,以及对入渗、产流产沙与养分流失及泥沙颗粒机械组成特征等。获取了以下主要结论。(1)通过三维激光扫描仪获取耕作后粗糙坡面高程模型(DEM),利用Arc GIS分别提取了微地形坡度与坡向因子。分析表明相对于平整坡面,粗糙坡面微地形坡度分在范围为0°-80°之间。其中,点种坡面微地形坡度主要集中在10°-15°、20°-40°范围内,其临界坡度分别为20°;同样地,锄耕坡面微地形坡度主要集中在10°-15°、20°-40°范围内,其临界坡度分别为20°;犁耕坡面微地形坡度主要集中在5°-30°,其临界坡度为15°。等高耕作坡面微地形坡度主要集中在5°-30°,其临界坡度为30°。随着坡面坡度的增加,小于临界坡度的栅格数随坡面坡度的增大而减少,而大于临界坡度的栅格数增加。另外,点种、锄耕、等高耕作和犁耕坡面微地形坡向栅格数主要以南、西南或东南为主,即与试验径流小区出流口方向一致。同时随坡面坡度增加,粗糙坡面微地形南、西南或东南坡向的栅格数逐渐增加,而其他坡向的栅格数逐渐减小。(2)通过室内人工模拟降雨试验,利用土壤水分实时监测技术获取微地形特征点(凸处、凹处、平整处)、微坡面(cm~2)与平整坡面(m~2)的土壤含水量变化过程。研究结果表明粗糙坡面上凸处、洼处、平整处等在降雨过程中洼处稳定土壤含水量高于凸处与平整处。可见,低洼处具有蓄积、促进降水入渗的能力。另外不同深度的土壤水分变化趋势表明降雨过程中粗糙坡面土壤水分活动层为0-15cm,而平整坡面为0-10cm,进一步说明粗糙度促进坡面降水入渗深度。同时粗糙坡面上微坡面(cm~2)与平整坡面(m~2)的土壤水分变化过程相类似,这表明了微坡面与平整坡面产流方式一致。与平整坡面不同的是,粗糙坡面上微坡面产生的薄层径流汇集在低洼处,从而延迟了坡面初始产流时间。(3)通过室内人工模拟降雨试验,粗糙坡面与平整坡面产流点位沿径流方向的分布范围分别为12-181 cm、42-180cm之间。同时两处理坡面产流点位沿径流方向上的变异系数分别为34.4%-52.1%、15.5%-31.1%。研究表明粗糙坡面产流点位较平整坡面在坡面空间分布更为分散。通过径流小区人工模拟降雨试验,可以看出相比于平整坡面,地表粗糙度具有推迟坡面初始产流时间的效应。但是推迟产流效应随着坡度、雨强的增大而逐渐减弱。预测初始产流时间与实测初始产流时间比值为2.2%-36.2%,表明地表粗糙度影响坡面初始产流时间的主导过程为通过增加入渗的间接作用,从而确定了地表粗糙度延迟坡面初始产流主导作用。(4)通过三维激光扫描仪获取降雨后各粗糙坡面高程模型(DEM),利用Arc GIS提取坡面汇流流向、汇流密度等特征。结果表明在平整坡面汇流方向均为连续沿坡面向下流动,汇流密度值为13.08-17.06 m/m~2之间。且随着降雨强度、坡度的增大而增大。粗糙坡面汇流流向多变,增加了汇流的蜿蜒度,汇流密度较小,其值为6.85-11.44 m/m~2之间。相比于平整坡面,粗糙坡面汇流密度降低了31.7-51.5%。另外,由坡面径流系数变化过程可知,粗糙坡面的径流系数均少于平整坡面。将坡面汇流流向、汇流密度结合坡面径流系数变化过程可知地表粗糙度通过蓄积水分,促进降水入渗和增加坡面汇流流向多样,降低汇流密度,从而造成坡面径流连通性降低,径流系数减少。但是随着降雨强度、坡度增加,地表粗糙度聚集坡面径流,有利于坡面径流连通的作用,导致粗糙坡面与平整坡面的径流系数差异逐渐减少。因此,该结果为解释地表粗糙度对坡面径流连通的影响提供依据。(5)通过室内人工模拟降雨试验,对比研究3种粗糙坡面处理分别为凸地、凹地和平整坡面上产流产沙、泥沙颗粒机械组成及其随径流和泥沙流失的可溶态和吸附态养分流失过程。结果表明总体而言,粗糙坡面可溶态养分流失量为凸地洼地平整坡;吸附态养分流失量为凸地平整坡洼地。径流中养分流失主要以吸附态为主,可溶态养分流失总量与坡面总产流量呈幂函数关系,吸附态氮流失总量与总产沙量呈幂函数关系,吸附态磷流失总量与总产沙量呈线性正相关关系。同时泥沙颗粒中粘粒含量为洼地凸地平整坡,相对于试验原土,具有明显的富集特征。粉粒、沙粒含量大小为凸地平整坡洼地。产沙过程中粘粒部分逐渐减少,粉粒和沙粒部分含量逐渐增加,随着降雨历时进行,泥沙颗粒组成趋近于原土壤,进一步阐明了粗糙度对坡面泥沙颗粒的侵蚀、搬运与沉积过程的影响。另外,吸附态氮、磷与泥沙颗粒中粘粒富集率(Er)、中值粒径(d50)、比表面积(SSA)成相关性,因此,粗糙坡面中吸附态养分流失差异主要受泥沙颗粒分布特征影响。
[Abstract]:The Loess Plateau is one of the main distribution areas of Sloping Farmland in China. Due to the concentration of rainfall, the high slope, the weak soil erosion resistance and the management activities of people, the area is also the main source of soil erosion. The serious soil erosion of the sloping farmland leads to the loss of soil and nutrients, the lowering of soil fertility and the productivity of land, and the loss of nutrients caused by water. The high and low undulating and uneven terrain formed by the management of sloping cultivated land, which is called the surface roughness, is closely related to the soil erosion of the slope. The study of the surface roughness of the sloping land on infiltration, the process of runoff production and the loss of nutrients will help to explore the effect of the surface roughness on the soil erosion mechanism. As well as providing scientific and technical support for soil and water erosion control in sloping land, based on the systematic summary of relevant research data at home and abroad, the research object is the surface roughness formed by 4 kinds of tillage measures, such as seed planting, hoeing ploughing, high tillage and plow tillage, and using the flat straight slope as the control group, the indoor and outdoor simulated rainfall experiments are adopted. The characteristics of the rough slope micro topography under different tillage methods, the infiltration, the runoff and sediment, the loss of nutrient and the mechanical composition of sediment particles were observed. The following main conclusions were obtained. (1) the elevation model of the rough slope after cultivation (DEM) was obtained by the three-dimensional laser scanner, and the slope and slope of the micro topography were extracted by using the Arc GIS. Factor analysis shows that the gradient of the rough slope of the rough slope is divided in the range of 0 -80 degrees relative to the flat slope. Among them, the gradient slope of the slope surface is mainly concentrated in the range of 10 -15 and 20 -40 degrees, and the critical slope is 20 degrees respectively. Similarly, the slope degree of the sloping surface is mainly concentrated in the range of 10 degrees -15 and 20 -40. The degree of the gradient of the plough slope is mainly concentrated at 5 -30 degrees, and its critical slope is 15 degrees. The slope degree of the slope is mainly concentrated at 5 -30 degrees, and the critical slope is 30 degrees. With the increase of the slope, the number of grids less than the critical slope decreases with the increase of the slope, but the number of grids larger than the critical slope increases. In addition, the number of grid grids in high tillage and ploughing slope surface is mainly South, southwest or southeast, which is the same as the outlet direction of the experimental runoff plot. At the same time, with the increase of the slope gradient, the rough slope surface is south, the number of grid numbers in the south-west or South-East slopes gradually increases, while the number of other slopes gradually decreases. (2) Through the indoor simulated rainfall experiment, the soil moisture content change process of micro terrain feature points (convex, concave, flat), micro slope surface (cm~2) and flat slope surface (m~2) is obtained by the real-time monitoring technology of soil moisture. The results show that the soil moisture content in the rough slope surface, such as the convex place, the depression, the leveling place, and so on, is higher than that in the rainfall process. It is obvious that the low lying area has the capacity of accumulating and promoting the infiltration of precipitation. In addition, the trend of soil moisture change at different depths indicates that the soil moisture activity layer of the rough slope in the rainfall process is 0-15cm, while the flat slope is 0-10cm, which further indicates that the roughness promotes the infiltration depth of the slope surface and the micro slope surface (cm~) on the rough slope surface. 2) it is similar to the process of soil moisture change on the flat slope (m~2), which indicates that the slope surface and the flat slope are in the same way of runoff production. Different from the flat slope surface, the thin surface runoff produced on the surface of the rough slope is collected in the low-lying place, which delays the initial flow time between the slope surface. (3) the rough slope surface is simulated by indoor artificial rainfall experiment. The distribution of runoff point along the runoff direction is 12-181 cm and 42-180cm, respectively. At the same time, the variation coefficient of the flow point along the runoff direction is 34.4%-52.1%, respectively. The 15.5%-31.1%. study shows that the flow point position of the rough slope is more dispersed on the slope surface than the flat slope surface. Compared with the flat slope surface, it can be seen that the surface roughness has the effect of postponing the initial flow time of the slope, but the delayed yield effect gradually decreases with the increase of the gradient and the rainfall intensity. The ratio of the initial runoff time to the measured initial runoff time is 2.2% -36.2%, indicating that the surface roughness affects the initial runoff yield. The dominant process of time is to determine the initial flow leading role of the surface roughness delayed slope by increasing the indirect effect of infiltration. (4) the rough slope elevation model (DEM) after the rainfall is obtained by the three-dimensional laser scanner, and the flow direction and the density of the slope surface are extracted by Arc GIS. The flow density is between 13.08-17.06 m/m~2 and continuous slope along the slope. The flow density increases with the increase of rainfall intensity and slope. The flow direction of the rough slope is changeable, and the sinuous degree of the confluence is increased. The density of the confluence is less than that of 6.85-11.44 m/m~2. Compared with the flat slope, the density of the confluence of the rough slope is reduced by 31.7-51. 5%. also, from the change process of slope runoff coefficient, the runoff coefficient of the rough slope is less than that of the flat slope. The flow direction of the slope and the flow density combined with the change process of the slope runoff coefficient can be seen that the surface roughness is accumulated through accumulating water, which promotes precipitation infiltration and increases the flow direction of slope surface to various and reduces the density of confluence, thus causing the slope surface. The runoff connectivity is reduced and the runoff coefficient decreases. However, with the increase of rainfall intensity and the increase of slope, the surface roughness aggregates the runoff on the slope surface, which is beneficial to the function of the slope runoff connectivity, which leads to the decrease of the runoff coefficient between the rough slope and the flat slope. Therefore, this result provides the basis for explaining the influence of the surface roughness on the slope runoff connectivity. (5) through indoor simulated rainfall experiments, 3 kinds of rough slopes were treated to produce miscarriage sand, the mechanical composition of sediment particles and the loss of soluble and adsorbed nutrients with runoff and sediment loss. The results showed that in general, the dissoluble nutrient loss of the rough slope was convex DIWA. The amount of nutrient loss in runoff was mainly adsorbed state, the total amount of soluble nutrient loss and total runoff yield showed a power function relationship. The total amount of adsorbed nitrogen loss and total sediment yield showed a power function relationship, and the total amount of adsorbed phosphorus loss and total sediment yield showed linear positive correlation. At the same time, the content of clay particles is convex and leveling in the low-lying land, which has obvious enrichment characteristics compared with the test original soil. The size of grain and sand grain is a convex flat and whole slope depression. The content of clay particles gradually decreases and the content of grain and sand part increases gradually during the process of sediment production, and the composition of sediment particles is closer to the original soil as the rainfall goes on. Further clarifies the influence of roughness on the erosion, transport and deposition of sediment particles on the slope. In addition, the adsorption nitrogen, the concentration of clay particles in the phosphorus and sediment particles (Er), the median particle size (D50), and the specific surface area (SSA) are related. Therefore, the difference of the adsorption and shunt loss in the rough slope is mainly influenced by the distribution characteristics of sediment particles.

【学位授予单位】：西北农林科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S157

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