【作者】 陈宝群；

【导师】 赵景波；

【作者基本信息】 陕西师范大学 ， 自然地理学， 2007， 博士

【摘要】 摘要：针对黄土高原的土壤干层现象和人们对黄土高原植被建设存在问题的关注本文以陕北黄土高原为研究区,以土壤含水量的测量为主要研究手段,综合运用野外考察和实验分析,对土壤干层的评价标准、土壤干层的形成原因、土壤干层的形成机制和空间分异、土壤干层形成的动态过程、土壤干层的补偿与恢复、黄土高原环境退化的自然背景、黄土高原植被建设途径等进行了系统研究。期望能为黄土高原尤其是陕北黄土高原的植被建设提供决策依据。通过研究,获得的主要进展和新认识包括：(1)陕北黄土高原人工林地普遍有土壤干层发育,榆林地区土壤干层的发育强度高于延安地区。土壤干层的空间分异在年降水量550mm和400mm附近表现出两个突变现象,具体表现是：在年降水量400mm的榆林靖边县荒地没有土壤干层发育,而年降水量329mm的定边县荒地有土壤干层发育；在年降水量500mm延安北部延川县18龄苹果林地出现接近稳定凋萎湿度的强烈干层,而年降水量550mm的甘泉县20龄苹果林地出现的是较弱的干层。(2)洛川人工林地土壤水分的动态过程表现为春季显著失墒期、夏季显著增墒期、秋季稳定失墒期和冬季稳定增墒期。由于春季降水少、气温高、蒸发蒸腾作用强,春季失墒现象表现尤其突出,失墒现象以17龄中老龄苹果林地最为显著。土壤含水量的下降不仅在地表2米以上表现明显,在2米以下同样很显著。春季显著失墒期是土壤干层的主要形成时期。(3)2004年1月的土壤含水量测定结果表明,洛川地区极端丰水年的降水入渗使得人工林地土壤水分得到了较好恢复。17龄乔化苹果林地、17龄矮化苹果林地和8龄乔化苹果林地土壤水分恢复深度分别达到4米、5米和6米,不同的恢复深度取决于土壤干层的发育深度和发育强度。连续一年的土壤含水量测定表明,极端丰水年降水能够在短期内将土壤干层恢复到田间持水量水平,但是只具有2至3年的短期补偿效应,并不能从根本上减轻或消除土壤干层的危害。(4)实验分析表明,重力水带土层在充分湿润或者比较湿润的情况下,土壤水的运动可以到达较大深度,能够补给薄膜水带的土壤水分亏缺,不会形成土壤干层,因此黄土高原土壤干层的形成原因在于土壤表层干旱。土壤表层干旱一方面使得重力水的入渗深度在正常降水条件下保持在2米深度范围内,重力水带含水量较低也导致薄膜水的运动速度变得很慢,使得薄膜水带的土壤水分一旦被利用就很难得到补给最终导致土壤干层的形成。(5)研究了陕西扶风全新世黄土剖面的土壤学和地层学特征,全新世古土壤S0与黄土L0之间显著的界面代表了一次季风气候转型。3100a BP是全新世大暖期结束的时间,黄土L0磁化率低,而pH值很高,表明在其堆积形成过程中气候比较干旱,土壤水分缺乏。这次气候转型标志着黄土高原由全新世大暖期相对暖湿的气候转变为相对干冷的气候,这就导致了黄土高原3100年以来水分不足的状况,这样的状况延续到现今,加上当今暖干化的影响,就不可避免地导致黄土高原植被的退化和土壤干层的发育。(6)经过对前人详细的土壤干层评价标准进行系统分析,发现不同土壤地带土壤水分常数和土壤干层评价标准之间存在吻合得很好的比例关系,由此提出土壤干层指数(土壤干层指数=土壤稳定湿度÷土壤含水量)作为土壤干层的定量化指标。以1.0、1.3、1.6、1.9、2.2作为划分非干层、弱干层、较弱干层、中等干层、较强干层和强干层的分级标准,并且以生长更新速率和生长发育过程的受影响程度为依据,对五种类型土壤干层的特点进行了分析。(7)通过对洛川地区土壤水分动态研究提出了耗水指数Ic=(W1-W2)/W1,其中,Ic表示耗水指数,即植被对土壤水分的消耗程度,w1和W2分别表示研究时段初始含水量和终了含水量。运用耗水指数这一指标可以对每一个测量深度的土壤含水量进行分析计算,从而反映每一深度层次土壤水分的差别。耗水指数意义明确、计算方便,是土壤水分动态研究和土壤水分分异研究中的一个定量化分析指标。(8)陕北黄土高原林场空间分布与河流存在密切的空间关系,是黄土高原森林植被非地带性的显示。长安县少陵塬修建水平梯田的坡地土壤水分含量存在斜坡下部较高而斜坡上部较低的现象,说明降水产生的径流在坡面上的重新分配是一个普遍现象。黄土高原土壤水分的坡下富集特点导致森林植被常延沟谷分布。(9)环境胁迫、水分胁迫和人口胁迫造成了黄土高原生态环境恶化,黄土高原生态建设与经济建设脱离造成了生态环境建设的缓慢。黄土高原地区应以退耕还林还草为契机,以特色农业、林果业和草畜业等生态适宜型产业基地建设为重点,全面实施产业结构调整战略,建立以土壤水分植被承载力为依据的生态适宜型产业结构模式,实现生态经济可持续发展的根本目标。更多还原

【Abstract】 Abstract:Aim at serious phenomenon of dried soil layer and concern about vegetation construction in the Loess Plateau, a series of questions, such as assessing standards, forming reasons, regional distribution, formation mechanism, renew condition of dried soil layer, had been discussed, by measuring soil moisture content, field investigation and experimental analysis in northern Shaanxi, which located in the middle part of the Loess Plateau, expecting to serve decision basis of vegetation construction in the Loess Plateau,especially for northern Shaanxi.The main achievements and cognitions concluded as follows:1.Dried soil layers in Yulin are stronger than in Yan’an, and spatial differentiation show sudden changes when precipitation are about550mm/year or about400mm/year. The details are as follow:in wild land, there are dried soil layers in Dingbian county(precipitation is329mm/year), there are no dried soil layer in Jingbian county(precipitation reaches400mm/year).in apple orchard about20year, there are strongest dried soil layers in Yanchuan county(precipitation is500mm/year) wherever there are weakest dried soil layers in Ganquan county(precipitation reaches550mm/year).2. The dynamic process of soil moisture in Luochuan county can be separated into notable decreasing stage of soil moisture in spring, notable increasing stage of soil moisture in summer, stable decreasing stage of soil moisture in autumn and stable increasing stage of soil moisture in winter. Mainly caused by higher temperature, higher evaporation and lower precipitation in spring, it was notable decreasing in spring. Soil moisture decreased notably not only in the depth of2meters but also under the depth of2meters. The results show spring is the main season, in which man-made plantation leads to dried soil layer.3. It was shown that the soil moisture content of artificial forest increased greatly after2003, the rainy year. The soil moisture content of dried layer in17-aged arboreal apple trees,17-aged dwarf apple trees and8-aged arboreal apples recovered respectively reached4meter,5meter and6meter, which was decided by the depth and strength of the dried soil layer. The precipitation in uttermost rainy year can enhance the soil moisture content in dried layer to field moisture capacity, which last for2or3years. The shortdated equalize can’t uproot even lighten the harm of dried layer.4.On measuring soil water unsaturated flow rate and pellicular water move rate of soil near Xi’an, it shows that soil moisture under2meters can be recharged if soil is most or more wet in gravity water zone in the depth of2meters, there would be no dried soil layer, so dried soil layers of the Loess Plateau in the semi-humid and semi-arid zone are mainly caused by shallow dried soil layer, because of lower precipitation and higher evaporation. Shallow dried soil layer leads to smaller infiltration depth, less unsaturated flow and slower pellicular water movement than in humid areas, which to be the mechanism of dried soil layer, can described as the surface-driven model of dried soil layer.5. The integrative pedological and sedimentary study was carried out in a Holocene loess profiles on the Zhouyuan loess tableland in Fufeng County, Shaanxi Province.The distinct interface between the Holocene Soil SO and loess LO indicate a monsoon climatic change. The Holocene climatic optimum was ended at3100B.P. The low magnetic susceptibility and high pH in loess mean that it was opposite dry and soil moisture was lacking during the loess deposited. The climate change indicated the climate changed from the opposite warm and humid into the opposite cold and dry, which caused the soil moisture lacking in Loess Plateau from then on. Joined with warm-dry climate, it was unavoidable that the plant degradation and dried soil layer developed.6. Drought degree of dried soil layer can be measured by Id which means index of dried soil layer and can be defined as steady moisture to soil moisture content. Soil layers can be classified as non dried soil layer, weakest dried soil layer, weaker dried soil layer, medium dried soil layer, stronger dried soil layer and strongest dried soil layer by1.0,1.3,1.6,1.9,2.2according to the score of Id. Characters of each type of dried soil layer are described by situations of growth and reproduction rate of vegetations. The construction of Id and its assessing standards provides a unified and convenient quantitative evaluation means when research dried soil layers of different area in the Loess Plateau.7. To research soil moisture dynamics, we define water-consuming index as follows: Ic=(W1-W2)/W1 As above, Ic means soil moisture consuming degree by vegetation.W1means initial soil moisture content or soil moisture content of reference profile,W2means terminal soil moisture content or soil moisture content of researching profile. When score of Ic in each depth are calculated, differences between two profiles will be showed clearly. The water-consuming index will be a useful index when we research soil moisture dynamic process or analyze soil moisture character of different plantations.8. There is a close spatial relationship between forest distribution and river location in Yan’an and Yuling of northern Shaanxi by our surveys, it shows forest have more non zonal character than zonal character in northern Shaanxi. The phenomenon is mainly caused by water redistribution, which result much more soil water can be got in lower space. Enrichment mechanism of soil moisture in lower space to be a general situation, it were testified in one slope at Chang’an district in Xi’an, where terrace were constructed. Enrichment mechanism of soil moisture in lower space leads to forest distributed along valleys in most part of the Loess Plateau.9. The stress from environment, water resources and population caused ecological deterioration in the Loess Plateau. Solely vegetation construction separated from economic development leads to lower speed and lower efficiency. The construction in the Loess Plateau should take the opportunity of reforestation, build the eco-industrial model, that according to the vegetation carrying capacity of soil water resource, focused on special agriculture, fruit industry and grass-stock industry. Thus, the sustainable eco-economic development would come true.更多还原