我国水土流失典型区土壤表土结皮敏感性

表土结皮是降雨与土壤共同作用下的产物,某一土壤是否结皮、结皮的敏感程度如何,取决于该土壤的性质及所处地区的降雨情况。我国广泛分布着多种理化性质迥异的土壤,尤其是黄土、紫色土、红壤和黑土分布在我国水土流失严重的区域。但是,土壤发育表土结皮的敏感性很少见报道。本文通过分析模拟降雨试验结果及前人研究结论,提出了影响表土结皮发育敏感性的3个关键因素,并基于此对我国四大水土流失典型区土壤表土结皮的敏感性进行了分析。研究表明:细颗粒,尤其是粉粒是表土结皮发育的物质基础;团聚体稳定性是表土结皮发育快慢及程度的决定因素;高强度降雨是表土结皮发育的必要条件。黄土高原地区土壤极易发育表土结皮,四川紫色土区土壤发育表土结皮的概率大,南方红壤区除花岗岩、页岩外其他母岩上发育的土壤很难发育表土结皮,东北典型黑土不发育表土结皮,而非典型黑土易发育表土结皮。     

An investigation of periglacial slope stability in relation to soil properties based on physical modelling in the geotechnical centrifuge

Results are presented from eight scaled centrifuge modelling experiments designed to investigate mass movement processes on thawing ice-rich slopes. Four pairs of simple planar slope models were constructed, one in each pair being of sufficient gradient to promote slope failure during soil thaw and the second having a gradient below the threshold for instability. Four frost susceptible soils were used, three were normally consolidated and had different clay contents (2%, 12% and 20%) and the fourth comprised the 20% clay soil, but was over consolidated prior to model testing. Modelling protocols included freezing from the surface downwards under an open hydraulic system, and thawing from the surface downwards under an enhanced gravitational field within the geotechnical centrifuge, thereby utilising scaling laws to simulate correct prototype self weight stresses during thaw. Slopes below the stability threshold gradient were subjected to between 2 and 4 cycles of freezing and thawing, simulating annual cycles. Those above the stability threshold were subjected to only one cycle, since they failed during the first thaw phase. Thermal conditions, pore water pressures, surface movements, and profiles of displacement are reported. Measured pore pressures are used in slope stability analyses based on a simple planar infinite slope model. Profiles of solifluction shear strain and mechanisms of slope failure are both shown to be sensitive to small changes in soil properties, particularly clay content and stress history. In all cases, pore pressures rose rapidly immediately following thaw, remained below the threshold for failure in low gradient models, but exceeding the threshold to trigger landslides on steeper slopes. Upward seepage of melt water away from the thaw front contributed to loss of shear strength. Mechanisms of slope failure differed between test soils, ranging from mudflow in non-cohesive silt to active layer detachment sliding in over consolidated silt–clay. During solifluction, shear strain was greatest at the surface in non-cohesive silt and decreased rapidly with depth, but in test soils containing clay, the zone of maximum shear strain was located lower in the displacement profiles.     

Structural analysis and design of frost resistance function for subgrade of high-speed railway ballasted track in cold regions

According to the technical characteristics of short fixed wheelbase of a high-speed carriage, a subgrade-track integrated space mechanical response analysis model is proposed for trains under the action of biaxial load after the comparison of the stress distribution characteristics of the ballast track subgrade bed structures for high-speed railway under the action of uniaxial load and biaxial load. The loading threshold value (high-cycle long-term dynamic strength) under the circumstance where the cumulative deformation of subgrade structure gradually develops and finally reaches the convergent state, and its relationship with the foundation coefficient K₃₀ were deduced, based on the characteristics of cumulative deformation evolution obtained from the unit structure filling model test under the action of cyclic loading. In view of structure stability and frost resistance requirements of the railway subgrade in cold regions, technical conditions to maintain good service performance of subgrade structure of high-speed railway ballasted track are discussed and analyzed. Study results show that the additive effect manifests itself obviously for railway train bogies under the action of biaxial load than uniaxial load, which has a significant dynamic effect on the subgrade bed bottom and a slight effect on the surface layer. Thus, the adoption of a biaxial load model in the design of a high-speed railway subgrade accurately reflects the vehicle load. Pursuant to the structure design principle, the design method of the subgrade structure of high-speed railway ballasted track is proposed to meet the technical requirements such as structural strength, bearing stiffness and high-cyclic and long-term stability. Technical indicators are obtained for the variation of thickness of the surface layer of reinforced subgrade bed in the double-layer subgrade mode along with the change of K₃₀ at the subgrade bed bottom. The double-layer structure mode of "closure on the upper layer and drainage on the lower layer" was proposed in order to meet the waterproofing and drainage requirements of the upper layer of the subgrade bed in cold regions. A dense-framework graded gravel filler with weak water permeability at a coefficient of 10^-4 cm/s is used on the upper layer and the void-framework graded gravel filler at the water permeability coefficient of 10^-2 cm/s is adopted on the lower layer.     

沙坡头地区固沙植被土壤水分动态研究

沙坡头地区始建于1956年的无灌溉人工固沙植被,是我国交通干线防沙体系的成功模式。利用40余年的土壤水分定位观测数据,分析了不同期间建立的固沙植被土壤水分的时空变化特征及对植被的影响。结果表明,固沙植被发展至9~10a后土壤含水量开始明显下降,特别是较深层(>100cm)的含水量下降明显;0~40cm层土壤水分含量与降水相关显著,而降水对40~300cm层土壤水分的含量影响不显著;深根系固沙植物对根际区域水分的利用,进一步恶化了固沙区土壤深层的水分状况,进而抑制了这些植物的生长和生存,间接地影响了原有固沙植被组成和稳定性;经过40多年的演变,固沙植被中优势灌木种的盖度从最大盖度47.6%降至6%~9%,群落中草本和微生物结皮层得到发育。当深根系灌木的盖度降低至6%~9%时,深层土壤可维持一个相对稳定的低含水量。     

表土结皮形成影响因素述评

西北干旱半干旱地区,表土结皮普遍发育,其形成受诸多因素影响。土壤质地是影响表土结皮形成的最重要因素。此外,团聚体稳定性、表面粗糙度、矿物质和交换性离子浓度、降雨历时、降雨强度、前期含水量、湿润速度等因素同样对结皮的形成具有重要影响。结皮的形成可以简要归纳为两个主要过程,一是团聚体的分散,二是分散后的粘粒阻塞土壤孔隙。因此团聚体稳定性和粘粒含量是影响表土结皮形成的关键。研究发现,土壤中粘粒含量为20%～30%时,极易形成结皮,当粘粒含量超过40%时,团聚体变得较为稳定,结皮形成受到一定抑制。此外,土壤中如果富含蒙脱石矿物,或者土壤溶液具有较低的交换性钠离子和电解质浓度,则表土结皮易于形成。前期含水量和湿润速度对结皮形成也同样具有重要影响。试验表明,粘粒含量较高的试样在较低的前期含水量情况下更容易形成结皮,因为稳定性较高的团聚体在干燥条件下更容易因迅速湿润而崩解。湿润速度对表土结皮的影响作用随着粘粒含量的增加而增大,但在土壤结构不稳定条件下,其影响作用受到很大限制。影响结皮形成的各因素并不是孤立的,它们之间互相作用、互相影响,这给定量研究和分析结皮形成敏感性带来很大难度,如何对各影响因子的临界值进行确定以及定量研...     

20年来部分黑土耕层有机质和全氮含量的变化

黑土有机质含量的变化一直倍受社会关注。根据第二次全国土壤普查的采样记录,2001年在吉林省黑土区采集了27个土壤样品,分析测定了耕层土壤(深度与第二次土普数据相同)的有机质和全氮含量。与第二次土普查数据对比发现,过去20年间,吉林省黑土土壤有机质和全氮含量有增有减,但平均水平无明显变化。与已有的研究对比分析,高产玉米生产条件下的根系碳输入量可能抵消矿化损失的有机质量,使水土流失不严重区域的黑土土壤有机质水平维持平衡,有机质含量下降的土壤可能是水土流失的结果。而在水土流失不严重地区土壤有机质则可能增加。     

云南省元谋干热河谷土壤水分的动态变化

用波谱分析法的研究结果表明,当地旱雨季土壤含水量差异较大:旱季土壤含水量<凋萎湿度,土壤水分严重亏缺。因受降水量的影响,土壤含水量呈周期为1a的波动变化。用谐波分析法还计算了各层次土壤含水量的谐波展开式,由此可预报土壤含水量变化趋势。     

Stability of streambanks formed in partially saturated soils and effects of negative pore water pressures: the Sieve River (Italy)

Streambanks of alluvial channels are usually composed of loose materials, which are unsaturated in ambient conditions. Unsaturated soils are subject to negative pore water pressures, which cause an apparent cohesion. The latter is the main factor in allowing the stability of near-vertical banks. Even during moderate in-bank flow events, the apparent cohesion can be strongly reduced as the material approaches full saturation; therefore, during the drawdown phase, as the confining pressure of the water in the channel disappears, a bank failure is likely to occur. Channel bed-level lowering along the Sieve River, Central Italy, has caused widespread bank instability. A geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks. Interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils, in order to obtain relations between bank angle and height in limit equilibrium conditions. A stability chart was obtained with curves for different apparent cohesion values, and a stability analysis was performed taking into account the effects of flow events. In order to investigate the pore pressure effects, a series of piezo-tensiometers were installed in a streambank of the Sieve River. Data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall, evapotranspiration, and water stage variations. A planar failure with a tension crack occurred in the upper cohesive part of the bank during December 1996. The safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material. Safety factor variations through time are therefore shown as a function of seasonal variations in matric suction.     

黑河流域土壤退化研究

在黑河流域干旱土纲中采集5个典型土壤剖面以研究该地区干旱土壤的演化。同时，为了了解土壤养分含量、土壤干旱化和土壤盐化的变化趋势，测定了高台县西北盐池地区主要盐土类型各剖面中的盐分含量和流域内主要土类中水分含量的分布。结果表明，干旱区内陆河流域土壤的退化主要表现为干旱化、盐渍化和土壤肥力的退化。在流域内干旱化随流域上中下游降水量和干燥度的变化而变化，土壤随距河流的距离及地下水位的高低而变化。流域内土壤从潜育土向雏形十、干旱雏形土和干旱土的方向变化。盐渍化与土壤水分含量和地下水位有关，并与水分的蒸发有密切的关系。在一定范围内，距水源越远，盐分含量一般越高。土壤肥力的退化表现为土壤有机质含量降低，阳离子代换量降低等理化性质的退化，这一退化过程是其它过程的综合反映。质地的退化虽受风沙化的影响，但与土壤的形成母质有一定的关系。     

南亚热带丘陵赤红壤理化性质变化及其原因

本文研究了南亚热带丘陵赤红壤物理、化学性质变 (退 )化的特征及其原因。结果表明 ,丘陵赤红壤在物理性质退化方面 ,主要表现在土壤团聚体稳定性下降、土壤孔隙性和土壤水分性能变劣 ;在化学性质退化方面 ,主要表现在养分贫瘠化、保肥供肥能力降低。植被破坏会引起土壤养分减少、保肥供肥能力降低 ,有机质的减少是丘陵赤红壤物理性质退化的主要原因。有必要保护植被、提高土壤有机质含量 ,以防止丘陵赤红壤理化性质退化     

古尔班通古特沙漠风沙土土壤蒸发特征

土壤表面蒸发是降水的无效损失,其大小直接决定着降水转化为有效土壤水的效率,从而间接决定了植物可利用水分的多寡。在降水稀少的沙漠区,定量认识土壤蒸发的大小和其所占降水的比例显得尤为重要。在2004年全生长期(5~9月)应用自制的微型蒸渗仪(Micro-Lysime-ter)测定了风沙土(有结皮覆盖的丘间低地和裸露沙丘顶部)和对照的荒漠盐碱土的土壤蒸发。结果表明:在相似的气象条件下,风沙土区的丘间低地和荒漠盐碱土的日平均蒸发量分别约是裸露沙丘(风沙土区)的2倍和3倍。整个生长期裸露沙丘的累积蒸发量为18.7mm,丘间低地为38.8mm,荒漠盐碱土为52.1mm。根据整个观测期的累积蒸发量和累积降雨量计算得出的蒸发降雨比分别为:裸露沙丘0.20,丘间低地0.42,荒漠盐碱土0.62,表明裸露沙丘由降水转化为土壤水而储存的比率最高。同时,从数据分析中可以看出:在风沙土区0~5cm土层的含水量对土壤蒸发起决定作用,而盐碱土区的土壤蒸发则受到更深层次土壤水分的影响。裸露沙丘低的土壤蒸发、高的降水转化效率,为植被恢复奠定了良好的基础。因此,裸露沙丘的低蒸发量可以视为植被状况对生态水文过程的一种良性反馈。     

黄土丘陵小流域土壤物理性质的 空间变异

黄土丘陵小流域土壤物理性质在景观尺度上的空间变异以质地、容重和饱和含水量最小，稳定入渗率最大，团稳性与粘结力居中，不同土地利用类型之间诸项物理性质都存在显著差异，土壤质地以林地的砂粒含量显著偏低但粉粒含量显著高于其它土地利用类型，休闲地的粉粒含量显著较低；容重以林地显著偏大，耕地较小；饱和含水量以灌木地较大，林地显著偏低，土壤团稳性以林地显著偏高，耕地显著偏低；土壤粘结力以灌木地，林地，荒地和休闲地显著较强，耕地显著较弱；稳定入渗率以灌木地显著较高，间作地显著较低，就坡形来说，垂直与水平凹形坡的砂粒含量都显著较低而粉粒含量比较高，相反直形坡的砂粒比较高而粉粒含量显著较低；饱和含水量与稳定入渗率都是以垂直直形坡较高，垂直凹形坡则较低，就坡向而言，偏东坡的土壤粘结力显著低于偏西坡；偏北坡土壤质地比偏南坡粘性强，但稳定入渗率低，稳定入渗率还随坡度的增大而增高，随着海拔的升高，土壤砂粒含量与稳定入渗率增高，而粘粒含量与团稳性呈降低趋势。     

Population explosion in Africa: further implications

A serious problem associated with the population explosion in Africa is the widespread degradation of vegetation and soils. Various factors such as climate, animal overgrazing, overcultivation, fires, and soil erosion contribute to the social and economic impact in some areas. An increase of droughts due to lack of precipitation has damaged grasslands. In addition, increased animal population due to animal disease control, increased water supply, and social custom of measuring wealth in terms of herd size cause near wastelands from overgrazing. Also, overcultivation of commercial crops due to an increasing population has accelerated soil erosion by allowing shorter fallow periods, which causes lower crop yields and soil deterioration. Firing woodlands and grasslands to suppress new woody growth is damaging soil as well as encouraging the growth of coarse grasses that have little value for grazing animals. The barren land due to firing causes soil erosion both by water and wind; a total estimated drift of dust from western Africa is 60 million tons/year. These conditions indicate that deterioration will continue resulting in lower carrying capacities and lower productivity from cultivated land.     

流沙固定过程中土壤-植被系统演变

包兰铁路横穿腾格里沙漠沙坡头段,全长45 km,年降水量186 mm;流动沙丘相对高度20 m,以每年4 m的速度向东南方向移动。无灌溉条件下、工程措施与生物措施相结合的防沙固沙工程体系始建于1956年,近半个世纪以来该体系确保了包兰铁路畅通无阻。几十年的土壤植被系统演变正影响着整个防护体系。植被在从人工系统向自然系统的演变中经历了覆盖度从增加到减少的自疏过程、从灌木到半灌木到草本的变化;土壤从流动风沙土向钙积旱成土发育,地表生物结皮发育;降水在生态系统中的再分配过程已经彻底改变,新的水分平衡格局明显影响现有防沙固沙体系。     

SOME FEATURES OF CARBON CYCLES IN KARST SYSTEM AND THE IMPLICATION FOR EPIKARSTIFICATION —An Example of Yaji Karst Experimental Site in Guilin,China

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西藏土壤有效铁含量及其影响因素

根据西藏土壤18个供试土类169个剖面有效铁(Fe)的分析资料,探讨土壤有效Fe含量变化及其影响因素。结果表明,西藏供试土壤表层有效Fe含量平均为83 mg/kg,但各类土壤变化很大,其中50~238 mg/kg的土壤面积占35.2%,<50 mg/kg的土壤面积占61.5%,只有少部分土壤有效Fe低于缺乏临界值5 mg/kg。有效Fe高的土壤几乎都是有机质丰富的酸性土,而有效Fe较低的土壤大多是有机质缺乏的碱性钙质土。土壤有效Fe含量受pH、铁的形态、有机质和粘粒等因素的综合影响。土壤有效Fe随pH的升高而降低。土壤有效Fe与全Fe、游离Fe无关,而与活性Fe、络合Fe呈极显著正相关,据此推论有效Fe来自活性Fe包括其中络合Fe与非络合活性Fe两部分。土壤有效Fe与有机质、粘粒含量呈极显著正相关,有机质对有效Fe的贡献在于其作为络合剂形成络合Fe和作为阳离子吸附载体吸持活性Fe离子;粘粒的贡献则是作为阳离子吸附载体吸持活性Fe离子,但其贡献远不如有机质。     

Water table control on rill initiation and implications for erosional response

On sloping sandy agricultural soil sites near Toronto, Canada, summer storms adequate to generate runoff occur frequently, but rill development occurs mainly in spring when snowmelt or rainfall-induced runoff occurs above frozen subsoil. This suggests that on low and moderate slopes on these soils rill initiation is controlled primarily by hydraulic impedance close to the surface, rather than critical hydraulic conditions in runoff. Laboratory flume experiments were carried out on 10 m slopes at 1.5°, 5° and 9° with loamy sand/clay composite soil sample to test this hypothesis. Runoff with hydraulic conditions adequate for rill initiation occurred rapidly in most tests, but on 1.5° and 5° slopes little knickpoint scour or sediment transport occurred before water table development. This coincided with reduced surface soil strength, knickpoint scour and marked increase in sediment discharge, particularly on 5° slopes where increase was 20- to 30-fold. Further increase in sediment discharge occurred when water tables reached the surface. On 9° slopes runoff occurred more quickly, with higher hydraulic values. Significant rill incision and sediment discharge occurred well before water table development, and ultimately reached much higher values than on lower slopes. Results show that soil erodibility can change dramatically over short time periods during storms due to soil moisture conditions, and that the presence of a hydraulic impedance close to the surface which causes a perched water table to develop can strongly influence rill incision and sediment transport. The influence is unlikely to be marked on soils which are very erodible regardless of moisture conditions, or on extremely resistant soils. It will also be limited on very gentle or steep sites, but can be a significant factor in rill development on intermediate slopes.     

The differences of water balance components of Caragana korshinkii grown in homogeneous and layered soils in the desert–Loess Plateau transition zone

Soil texture greatly influences soil water movement, thus may affect the water balance and vegetation growth in the desert–Loess Plateau transition zone. This study is to determine if the water balance differs in homogeneous and layered soils with Caragana korshinkii stands in semiarid region. Soil water measurements up to 500-cm depth were taken in 2006 and 2007 on homogeneous sandy soil, homogeneous silt loam soil, and layered soil with sand overlying silt loam. HYDRUS-1D was used to simulate the soil water balance. The results indicated the annual water balance components were greatly affected by soil layering. The ratio of average actual evapotranspiration (ET_a) to precipitation (P) during the two years in the layered soil was slightly lower than that in homogeneous soils. The ratios of annual actual transpiration (T_r) to evapotranspiration were 50.9%, 41.2% and 30.6% in layered soil, homogeneous sandy soil, and homogeneous silt loam soil, respectively. C. korshinkii grown in layered soil had deeper soil water recharge and higher T_r/ET_a ratio, thus had more available water for transpiration than that in homogeneous soils. This study suggested the layered soil with sand overlying silt loam is more favorable to C. korshinkii growth in terms of water use than homogeneous soils in the desert–Loess Plateau transition zone.     

Soil-geographical characteristics of the western part of the democratic People’s Republic of Korea

The specific character of soil cover in the territory of the Democratic People’s Republic of Korea (DPRK) is revealed, and the soil interpretation schemes in the key areas are compiled. It is established that the main soil resource for agriculture within the region’s low and middle mountains is provided by areas of weakly developed brown forest soils in the lower parts of slopes as well as by alluvial soils along the valleys of large and medium-sized rivers. Specifically, brown forest soils of slopes are used largely in dry farming and forestry, while soils along river valleys are utilized in rice cultivation. Soils of terraced slopes and rice fields have been transformed anthropogenically to the greatest extent.     

Roadbed, embankment, tower support and culvert stability problems on permafrost

The history of railway and highway construction in permafrost zones in Russia, the United States, Canada, and China spans more than 110 years. Nonetheless, no railway track or highway has yet been built in such area that is impervious to deformation caused by subsidence resulting from the thawing of ice-rich subgrade soils. This paper presents data on the roadbed states of the Transbaikalian and the Baikal-Amur Railways as well as the Russian "AMUR" Chita-Khabarovsk Highway. It also discusses the feasibility of roadbed stability maintenance using methods based on the reduction of the mean annual ground temperature and roadbed preservation in a permafrost state by means of the natural cooling and heating factors ratio regulation resulting in a reduction of the heat generation in the roadbed and the adjoining area accompanied by an increase of heat consumption with help of the sun-precipitation protective sheds (awnings), rock covers, dolomite powder (reflective paint), cooling tube and thermosyphons as well as tower supports and corrugated pipe culverts stability.