工程堆积体坡面侵蚀泥沙分选特性与运移机制研究

为揭示工程堆积体陡坡坡面在径流驱动下侵蚀泥沙颗粒分选特征及搬运机制,设计了3种上方来水流量(10,20,30 L/min)下的野外模拟径流冲刷试验,对杨凌弃土工程堆积体陡坡坡面(32°)侵蚀泥沙的颗粒分布特征进行分析。结果表明:侵蚀泥沙(分散前)中黏粒、细粉粒较原始土壤明显增加,易产生侵蚀;径流对团粒破碎作用影响侵蚀泥沙黏粒含量,当径流功率＜1.71 N/(m·s)时,黏粒含量与径流功率呈负相关,＞3.89 N/(m·s)时则呈正相关;侵蚀泥沙中细粉粒、粗粉粒主要以单粒的形式搬运,而黏粒以及砂粒多以团粒的形式搬运;侵蚀泥沙中黏粒表现为富集,砂粒表现为贫化;泥沙颗粒粒径决定其主要搬运形式,＜0.11 mm的泥沙颗粒以悬移/跃移搬运为主,＞0.11 mm的泥沙颗粒以滚动搬运为主;滚动搬运的贡献率随径流搬运能力的增强呈先增大后减小。研究结果将有助于揭示工程堆积体坡面水蚀过程机理,为提高工程堆积体陡坡坡面水蚀模型预测精度提供科学依据。     

A simultaneous model for ultrasonic aggregate stability assessment

Aggregate stability is a difficult to quantify, complex soil property. Ultrasonic processing of soil–water suspensions enables quantifiable and readily reproducible assessment of the level of mechanical energy applied to soil aggregates. Here, we present a method of investigating the stability and comminution of soil aggregates by simultaneously modeling the redistribution of particles throughout any arbitrarily-selected set of soil particle-size intervals as ultrasonic energy is applied to a soil–water suspension. Following model development, we demonstrate its application to 5 particle-size subgroups (0.04–2000 μm) of a Dystroxerept subject to 12 levels of ultrasonic energy between 0 and 5800 J g^− 1 (750 mL^− 1). Laser granulometry was used for particle-size distribution (PSD) analysis, providing precise, non-disruptive measurements of changes in the volume of PSD subgroups in both the microaggregate (< 250 μm; 3 subgroups) and macroaggregate (> 250 μm; 2 subgroups) fractions throughout ultrasonic treatment. Two groups of aggregates were detected exhibiting significantly (p < 0.05) different ultrasonic stability: a group composed exclusively of macroaggregates ranging 250–2000 μm in size, and a finer, relatively stable group ranging 20–1000 μm. The PSD of particles liberated from two aggregate groups significantly (p < 0.05) differed: the coarser, less-stable group liberated 13% clay (0.04–2 μm), 53% fine silt (2–20 μm), and 34% coarse silt and sand (20–250 μm); while the finer, more-stable group liberated 26% clay and 74% fine silt. The ultrasonic energy required to disrupt 25%, 50%, and 75% of all aggregates within a given PSD interval significantly (p < 0.05) differed between all selected intervals, showing a trend of declining stability with increasing particle-size. Both the flexibility of the proposed model and the extension of ultrasonic stability assessment to simultaneous analysis of both microaggregate and macroaggregate subgroups can facilitate broader application of ultrasonic methods to soil processes related research.     

黄土高原黄土团粒组成及其与碳酸钙关系的研究

通过团粒分析、电子显微镜 (SEM/EDX)扫描等元素分析扫描方法和手段 ,对黄土高原西北部自然黄土中的团粒数量及其与碳酸钙的溶解量的关系、团粒表面和内部碳酸钙的分布进行了研究。结果表明 :碳酸钙大约参与了 99%的团粒形成 ,呈现团粒越大 ,碳酸钙含量越多的趋势 ;反之 ,团粒数量与碳酸钙的溶解量成反比 ;随着团粒表面碳酸钙分布的减少 ,附着在团粒表面的微团粒及粉粒、粘粒减少 ;在团粒内部 ,碳酸钙与矿物颗粒之间存在 3种胶结方式 ,分别为碳酸钙附着在矿物颗粒表面、碳酸钙分布于矿物颗粒之间以及碳酸钙表面附着矿物颗粒。实验结果证明了黄土团粒的主要胶结物是碳酸钙这一理论。     

Late quaternary drift deposits of north central Nigeria examined by scanning electron microscopy

Samples of drift were studied by mechanical analysis and scanning electron microscopy of individual grains and compared with nearby fixed dunes and present-day pedisediment. Results indicate that the drift is well sorted and has the textural characteristics of a loess (modal grain size + 4 − + 5 Ø, 62-31 μm), this differs markedly from the fixed dunes (modal grain size + 2 − + 3 Ø, 250-125 μm), SEM micrographs show that the drift contains grains with a wide variety of morphologies, although they are predominantly angular to sub-angular with only limited evidence of abrasion by aeolian and/or fluvial transport and some ovegrowths of secondary silica. This suggests that much of the drift material is of local origin, and was deposited by aeolian reworking of alluvium and coarse surface soil horizons when sand dunes were forming further north. It is envisaged that concomittant with aeolian activity was periodic reworking of the drift by slopewash associated with individual storms and a wet season of reduced duration and intensity.     

The Impact of Agriculture on Soil Texture Due to Wind Erosion

Wind erosion produces textural changes on topsoil of semiarid and arid environments; however, the selection of particles on different textured soils is unclear. Our objectives were to evaluate textural changes induced by wind erosion on cultivated soils of different granulometry and to asses if textural changes produced by wind erosion are linked to aggregation of granulometric particles into different sizes of aggregates formed in contrasting textured soils. Considering this, we studied the particle size distribution (PSD) with full dispersion (PSD_F) of 14 cultivated (CULT) and uncultivated (UNCULT) paired soils and, on selected sites, the PSD with minimum dispersion (PSD_MIN) and the quotient PSD_MIN/F. Results showed that the content of silt plus clay was lower in CULT than in UNCULT in most of the sites. The highest removal of silt was produced in soils with low sand and high silt content; meanwhile, the highest removal of clay was observed in soils with medium sand content. According to PSD_MIN, particles of 250–2,000 μm predominated in the sandy soil, in the loamy soil particles between 50 and 250 μm and in the silty loam soil particles between 2 and 50 μm. For clay sized particles, PSD_MIN/F was lower than 1 in all soils and managements, but this quotient was higher in CULT compared with UNCULT only in the loamy soil. This means a decrease of clay accumulation in aggregates of larger sizes produced by agriculture, which indicates an increase in the risk of removal of these particles by wind in loamy soils. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparing surface erosion processes in four soils from the Loess Plateau under extreme rainfall events

This research aims to improve erosion control practice in the Loess Plateau, by studying the surface erosion processes, including splash, sheet/interrill and rill erosion in four contrasting soils under high rainfall intensity (120 mm h⁻¹) with three-scale indoor artificial experiments. Four contrasting soils as sandy loam, sandy clay loam, clay loam and loamy clay were collected from different parts of the Loess Plateau. The results showed that sediment load was significantly impacted by soil properties in all three sub-processes. Splash rate (4.0–21.6 g m⁻²∙min⁻¹) was highest in sandy loam from the north part of the Loess Plateau and showed a negative power relation with the mean weight diameter of aggregates after 20 min of rainfall duration. The average sediment load by sheet/interrill erosion (6.94–42.86 g m⁻²∙min⁻¹) was highest in clay loam from middle part of the Loess Plateau, and the stable sediment load after 20 min showed a positive power relation with the silt content in soil. The average sediment load increased dramatically by rill and interrill erosion (21.03–432.16 g m⁻²∙min⁻¹), which was highest in loamy clay from south part of the Loess Plateau. The average sediment load after the occurrence of rill showed a positive power relation with clay content and a negative power relation with soil organic matter content. The impacts of slope gradient on the runoff rate and sediment load also changed with soil properties. The critical factors varied for different processes, which were the aggregate size for splash erosion, the content of silt particles and slope gradient for sheet/interrill erosion, and the content of clay particles, soil organic matter and slope gradient for rill erosion. Based on the results of the experiments, specific erosion control practices were proposed by targeting certain erosion processes in areas with different soil texture and different distribution of slope gradient. The findings from this study should support the improvement of erosion prediction and cropland management in different regions of the Loess Plateau.     

Influence of fertilization and organic amendments on organic‐carbon fractions in Heilu soil on the loess plateau of China

The influence of fertilization on organic‐carbon fractions separated by density and particle size in Heilu soil (Calcic Kastanozems, FAO) was investigated in a 20‐year (1979–1999) long‐term experiment on the Loess Plateau of China. Compared to an unfertilized treatment, N application alone did not increase total organic carbon (TOC) and its fractions of density and particle size. However, the treatment of N + P fertilization significantly increased salty‐solution–soluble organic carbon (SSOC), microbial biomass C (MB‐C), and organic C associated with fine silt. When manure was applied alone and in combination with N and P fertilizer, the light fraction of organic C (LFOC), SSOC, and MB‐C were increased significantly, and the TOC was as high as that of a native Heilu soil. Organic C associated with different particle‐size fractions was also increased significantly, and the allocation of C among the fractions was altered: the proportions of C in sand (>50 μm), coarse‐silt (20–50 μm), and fine‐clay (<0.2 μm) fractions were increased whereas fine‐silt (2–20 μm) and coarse‐clay (0.2–2 μm) fractions were decreased. It is concluded that N fertilizer alone is not capable of restoring organic‐matter content in the Heilu soils of the Loess Plateau and that C‐containing material like manure and straw is necessary to produce significant increase in soil organic carbon in these soils.     

利用土壤颗粒的沉降粒级研究泥沙的迁移与分布规律

了解不同粒径泥沙迁移运动规律,有助于深入理解侵蚀条件下碳、氮、磷等元素的生物地球化学过程。土壤营养元素的迁移转化与泥沙颗粒的运动规律密切相关,而泥沙的运动规律由颗粒大小、性状、孔隙度和密度等因素共同决定。依据泥沙颗粒沉降速度分选的原理,针对中国两种典型侵蚀土壤(红壤和黄绵土),分别进行了土壤机械组成(矿质土粒分选)和沉降速度分选测定。结果表明,土壤颗粒的沉降粒级可有效区分红壤和黄绵土中不同粒径团聚体的沉降速度,能够更加准确地反映出同一粒径颗粒因性状、密度和孔隙度的差异而形成的不同沉降速度。相对于质地疏松的黄绵土,红壤的机械组成显示,有86.9%的有机碳与≤32μm的矿物颗粒相结合,很有可能随悬移过程汇入下游水体。但土壤颗粒沉降速度分布表明,约有90.5%的红壤有机碳与等效石英粒径≥63μm的团聚体相结合,易在经历较短的迁移过程后,快速沉积于下坡面。这表明,现有的土壤侵蚀模型大多利用土壤机械组成(即矿质粒径大小)在反映泥沙运动或元素迁移规律方面存在片面性。土壤的团聚过程可有效缩减有机碳和无机碳的迁移距离,从而使其更易沉积于陆生环境。土壤颗粒的沉降速度分级对认识泥沙颗粒和养分元素在侵蚀—迁移—沉积过程中的生物地球化学过程提供了新的途径和视角。     

Genesis and micromorphology of loess-derived soils from central Kansas

The genesis and micromorphology of three Harney soils from different precipitation regions (from 540 mm to 715 mm) (fine, smectitic, mesic Typic Argiustolls) in the Smoky Hills of central Kansas were investigated. The objectives were to (1) examine the morphological, chemical, physical and mineralogical characteristics of Harney soils formed in loess; (2) determine the clay mineral distribution with depth and the origin of the clay minerals present; and (3) investigate the relationship between the clay mineralogy and other soil properties such as soil plasmic fabric, COLE values and fine clay/total clay ratios. Mineralogical and micromorphological techniques were used to evaluate the characteristics of the loess-derived soils. The first pedon was formed in 88 cm of Bignell loess over Peoria loess and the other two pedons were formed from Peoria loess. The chemical properties were similar for the pedons studied. Differences were observed in physical properties, especially in particle size distribution, oven-dry bulk density and coefficient of linear extensibility values. Although the soils were mapped in the same soil series, the geomorphic positions of the pedons and the nature of the parent material affected the characteristics of the soils. Smectite was the predominant clay mineral, especially in the fine clay fraction, regardless of the location in the precipitation gradient. The dominance of smectite increased in the C-horizons. This implies a detrital source of smectite in the B-horizons formed in both Bignell and Peoria loess units. The presence of randomly interstratified mica-smectite and the micromorphological observations of weathering biotite indicate that weathering also plays an important role in the mineralogy of Harney soils. The high content of clay mica in the surface horizons was caused by dust fall in the study area. Thick and continuous argillans were observed when FC/TC and COLE values were low and crystalline smectite was present. In the lower part of the soil profiles, the plasmic fabric was mostly ma-skelsepic (granostriated b-fabric) and smectite was more crystalline as indicated by sharper X-ray diffraction peaks.     

Relative importance of sorption versus aggregation for organic matter storage in subsoil horizons of two contrasting soils

Soil organic matter (OM) stabilization by the mineral phase can take place through sorption and aggregation. In this study we examined both of these processes, (i) organic carbon (OC) sorption onto clay‐sized particles and (ii) OC occlusion in silt‐size aggregates, with the objective of evaluating their relative importance in OM storage and stabilization in soil. We studied two loamy soil profiles (Haplic Luvisol and Plinthic Cambisol) currently under agricultural use down to a depth of 2 m. Our approach was based on two parallel fractionation methods using different dispersion intensities; these methods isolated a free clay fraction (non‐occluded) and a clay fraction occluded within water‐stable silt‐size aggregates. The two clay fractions were analysed for their C content and ¹⁴C activity. The proportion of sorbed OC was estimated as OC loss after hydrofluoric acid (HF) demineralization. Our results showed an important contribution to SOM stabilization by occlusion of OC into silt‐size aggregates with depth through both soil profiles. In the Haplic Luvisol, OC associated with clay and located in silt‐size aggregates accounted for 34–64% of the total soil OC, whereas in the Plinthic Cambisol this occluded material represented 34–40% of total OC. In the Haplic Luvisol, more OC was located in silt‐size aggregates than was sorbed onto clay‐size minerals, suggesting that silt‐size aggregation plays a dominant role in OC storage in this soil. In the Plinthic Cambisol, the abundance of sorbed OC increased with depth and contributed more to the stored C than that associated with silt‐size aggregates. Radiocarbon dating of both clay fractions (either occluded within silt‐size aggregates or not) suggests, in the case of the Plinthic Cambisol, a preferential stabilization of OC within silt‐size aggregates.     

Effect of clay content and silt—clay fabric on stability of artificial aggregates

The influence of clay content and silt–clay fabric on aggregate stability was investigated. Two silt—clay fabrics were produced in the laboratory by mixing silt particles with a clay phase: (i) a loose packing of the silt particles with clay aggregates, and (ii) a close packing of the silt particles with the dispersed clay phase, the latter coating and bridging the silt particles. Porosity and pore size distribution were measured, and the silt—clay fabric was described using scanning electron microscopy. The aggregate stability was measured under three treatments corresponding to different wetting conditions and energy levels: fast wetting, mechanical breakdown and slow wetting. Our results show that aggregate stability is related to both clay content and silt—clay fabric. Comparison of fragment size distributions and their mean weight diameter amongst the three treatments enabled identification of mechanisms responsible for the variation of aggregate breakdown. The compression of trapped air was the predominant breakdown mechanism for both fast and slow wetting and was related mainly to porosity characteristics. For the mechanical breakdown, the degree of disintegration depended on the cohesion of the silt–clay fabric, which is related to the continuity of the solid phase.     

雨型和坡长对侵蚀泥沙粒径特征的影响

为揭示降雨和坡长对侵蚀泥沙粒径特征的影响,以不同坡长野外观测试验小区为对象,结合82场降雨资料,以降雨量(P,mm)、最大30 min雨强(I₃₀,mm/h)和降雨侵蚀力[R,MJ·mm/(hm²·h)]为降雨特征指标,利用系统聚类法进行雨型划分(A雨型：大雨量、高雨强、高侵蚀力;B雨型：中雨量、小雨强、中等侵蚀力;C雨型：低雨量、中雨强、中低等侵蚀力),分析了11场降雨事件中侵蚀泥沙的粒径分布特征。结果表明：(1)研究区侵蚀泥沙粒径特征受不同雨型影响,有效黏粒和最终黏粒含量在C雨型下最高,有效砂粒和最终砂粒含量在B雨型下最高,而有效粉粒和最终粉粒含量分别在A和C雨型下最高。(2)坡长对侵蚀泥沙粒径特征的影响存在临界坡长效应(14 m),小于临界坡长时,黏粒级和粉粒级颗粒含量随坡长增加而降低;超过临界坡长后,黏粒级和粉粒级颗粒含量随坡长增加而增加,该效应在最终粒径下更为显著。(3)有效砂粒输移形式受雨型和坡长影响较大,在B雨型下主要以团粒形式输移,在A,C雨型下达临界坡长时以单粒形式输移。侵蚀泥沙的有效粒径颗粒比原坡面土壤细,而最终粒径颗粒则...     

黄土丘陵区小流域淤地坝泥沙沉积特征

了解淤地坝泥沙沉积特征是坝地泥沙输移过程及规律研究的基础和前提。该文通过对黄土丘陵区小流域淤地坝不同位置泥沙沉积剖面中各沉积旋回层厚度及粒径组成变化的分析,研究了淤地坝次洪水沉积过程中泥沙的再分布特征。结果表明:坝地内次洪水泥沙沉积过程为非均匀分布,各沉积旋回层厚度在纵剖面和横剖面都存在一定差异,早期沉积层厚度的起伏变化要大于后期的起伏变化。坝地泥沙粒径组成以粉粒为主,黏粒、粉粒和沙粒的平均含量分别为4.66%、58.78%和36.56%。坝地泥沙沉积过程中,各旋回层中黏粒、粉粒和沙粒的平均含量变化较小,但在坝地不同位置,土壤粒径组成发生了一定程度的分选。从坝尾到坝前,土壤质地粗化度显著下降,土壤粒径组成呈逐步细化的趋势。     

Particle size fractionation of fungal and bacterial biomass in subalpine grassland and forest soils

Characterization of soil aggregates according to particle size fractions is a useful tool in process-oriented research into soil organic matter and biological properties. Substrate-induced respiration (SIR) inhibition was used to quantify microbial, fungal and bacterial biomass in particle size fractions of soils ranging from forest to grassland in a subalpine region of central Taiwan. In addition, ergosterol content was determined in the same samples to verify fungal biomass measured by SIR inhibition technique. Surface soil (0–10 cm) was fractionated into four particle size fractions: coarse sand (250–2000 μm), fine sand (53–250 μm), silt (2–53 μm) and clay (0.2–2 μm). The larger sized fractions (>250 μm and 53–250 μm) contained higher levels of fungal ergosterol than the smaller sized ones (2–53 μm and 0.2–2 μm). The largest particle size fraction (250–2000 μm) from all studied habitats showed the highest level of microbial biomass, with no clear trend in microbial biomass level among the other size fractions. SIR-calculated fungal biomass level and ergosterol converted fungal biomass content were positively correlated (r=0.71, p<0.05), and such correlation decreased as biomass levels were high. Ratios of fungi to bacteria ranged between 0.6 and 1.3 in fractions obtained in this study. This study indicates a high variability of microbial (fungal and bacterial) biomass level among particle size fractions in soil, and that the large-sized fractions tend to contain a high level of microbial biomass in a given ecosystem.     

降雨驱动下红壤团聚体的溅蚀特征及周转过程

[目的]研究降雨驱动作用下土壤团聚体受雨滴打击发生破碎和形成的过程,丰富土壤侵蚀研究机理。[方法]基于稀土元素示踪法,对各粒径土壤团聚体同时进行标记。在90 mm/h降雨溅蚀条件下,通过各粒径土壤团聚体(2～5 mm, 0.25～2 mm, 0.053～0.25 mm,<0.053 mm)在不同降雨特征参数(降雨历时、雨滴大小)下的质量变化和稀土元素含量变化,定量分析了团聚体间的周转路径和溅蚀颗粒特征。[结果]降雨驱动作用下,溅蚀量和溅蚀率会随着降雨动能的增加而变大,溅蚀颗粒主要分布于0.25～2 mm粒径范围内;除>2 mm的颗粒为大团聚体直接飞溅产生,<0.25 mm粒级溅蚀颗粒均主要源于大粒级团聚体破碎形成,最高可达到73.83%,其次为该粒级直接被击飞形成,同时会有小粒级颗粒吸附黏结形成;在残余团聚体的动态周转过程中,主要是相邻级别的团聚体间形成和破碎过程占比较高,其中大团聚体破碎产生小团聚体和粉黏粒团聚形成小团聚体分别对原粒级团聚体的破碎和形成方向的贡献率较高,分别达到24.06%～42.15%和36.83%～70.76%,且随着降雨时间的变化,大团聚体首先...     

Straw incorporation and soil organic matter in macro-aggregates and particle size separates

Two field experiments in which straw has been removed or incorporated for 17 yr (loamy sand) and 10 yr (sandy clay loam) were sampled to examine the effect of straw on the C and N contents in whole soil samples, macro-aggregate fractions and primary particle-size separates. The particle size composition of the aggregate fractions was determined. Aggregates were isolated by dry sieving. Straw incorporation increased the number of 1–20 mm aggregates in the loamy sand but no effect was noted in the sandy clay loam. Straw had no effect on the particle size composition of the various aggregate fractions. After correction for loose sand that accumulated in the aggregate fractions during dry sieving, macro-aggregates appeared to be enriched in clay and silt compared with whole soil samples. Because of the possible detachment of sand particles from the exterior surface of aggregates during sieving operations, it was inferred that the particle size composition of macro-aggregates is similar to that of the bulk soil. The organic matter contents of the aggregate fractions were closely correlated with their clay + silt contents. Differences in the organic matter content of clay isolated from whole soil samples and aggregate fractions were generally small. This was also true for the silt-size separates. In both soils, straw incorporation increased the organic matter content of nearly all clay and silt separates; for silt this was generally twice that observed for clay. The amounts of soil C, derived from straw, left in the loamy sand and sandy clay loam at the time of sampling were 4.4 and 4.5 t ha^?1, corresponding to 12 and 21% of the straw C added. The C/N ratios of the straw-derived soil organic matter were 11 and 12 for the loamy sand and sandy clay loam, respectively.     

Recognition and characterisation of the aeolian component in soils in the Girilambone Region,north western New South Wales,Australia

Characterisation of aeolian material in the Girilambone Region of New South Wales (600 km NW of Sydney), using particle size analysis, mineralogy, geochemistry and micromorphological analysis, shows that it consists of spheroidal, highly abraded 70 μm quartz grains. Although relatively pure aeolian accessions are found on top of Tertiary leucitite flows, the aeolian material is generally admixed with residual and transported soil to a depth of 0.3 m throughout the region. This study has established a set of criteria for identifying the aeolian contribution to soils in the Girilambone region of north western New South Wales where it is difficult to distinguish. These include: a characteristic particle size of 70 μm of the quartz grains; highly abraded and spherical morphology; presence of thin clay coats on well-rounded grains; and gradational patterns in particle size distribution, mineralogy and geochemistry through the soil profile. These types of soils, with a high content of silt and fine sand, do not readily form aggregates, particularly where they have low organic content. To improve the sustainability of cropping and pastoral activities on these soils, their management should aim to maintain or increase structural stability, for example by addition of organic material. Mineral exploration procedures should avoid the diluting aeolian component by sampling the > 150 μm fraction from surficial soils or material from below 0.3 m.     

坡面覆沙后侵蚀泥沙颗粒分选特性

侵蚀泥沙颗粒大小的分布在一定程度上影响着侵蚀泥沙的搬运和沉积,了解侵蚀泥沙的分选作用将有助于解释泥沙的侵蚀和沉积过程。该文以覆沙坡面为研究对象,采用室内模拟降雨的方法,选取坡度12°、雨强1.5 mm/min的黄土坡面上分别覆盖0.5、1.0、1.5 cm的沙层进行试验。结果表明:坡面覆沙后,坡面粗颗粒物质大部分在产流开始0~10 min内便被冲刷带走;侵蚀泥沙颗粒主要以粉粒为主;坡面覆沙后,在细沟间侵蚀阶段,径流优先搬运大于0.054 mm的颗粒,在细沟侵蚀阶段和细沟侵蚀及细沟间侵蚀的组合阶段,径流搬运的泥沙颗粒以小于0.054 mm的颗粒为主;同时,在产流前期(0~10 min)侵蚀泥沙颗粒主要以大于0.054 mm的颗粒为主;而在产流后期(10 min以后)侵蚀泥沙则主要以小于0.054 mm的颗粒为主。坡面覆沙后,黏粒以团聚体的形式存在,粉粒以单粒的形式存在,而沙粒以细颗粒聚集体的形式存在。该文为进一步研究泥沙沉积后风蚀对水蚀的影响提供数据支撑。     

Geographic variations in particle size distribution of the last interglacial pedocomplex S1 across the Chinese Loess Plateau: Their chronological and pedogenic implications

Due to northwestward attenuation of the summer monsoon and northwestward intensification of loess deposition during the last interglacial, the last interglacial pedocomplex S1 gradually differentiated from the northwest to the southeast. The three paleosols (S1S1, S1S2, S1S3) corresponding to the marine isotope sub-stages 5a, 5c, and 5e and the two intercalated loess units (S1L1, S1L2) corresponding to the marine isotope sub-stages 5b and 5d are completely preserved at northwestern sections. Towards southeast, both the S1L1 and S1L2 were annexed by the subsequent paleosol development (S1S1 and S1S2) and the three paleosols (S1S1, S1S2, and S1S3) were partially welded. At the southeasternmost site, the three soil-forming events (S1S1, S1S2, and S1S3) repeatedly occurred in a single paleosol profile. The three observed orders of particle-size variations are interpreted to have imprinted important chronological and pedogenic signatures. First-order variations, i.e., a remarkable difference between the interglacial pedocomplex S1 and the glacial loess units (L1 and L2), implies that the S1 parent material was considerably finer in the source areas or/and the proximity to the source areas was much farther during interglacial period than during the preceding (L2) and following (L1) glacial periods. Second-order variation, i.e., the parenthetical trends in > 63 μm and < 10 μm fraction curves, might have resulted from the delayed response of the source material supplies to the climate changes. The third-order variations in < 10 μm fraction correspond well to the variations in frequency-dependent magnetic susceptibility, suggesting that pedogenically formed finer particles (i.e., < 10 μm fraction) and the associated ultra-fine paramagnetic minerals as expressed by the frequency-dependent susceptibility occurred only as a minor component of the < 10 μm fraction. The third-order variations seem to be obscured by soil welding and annexation at southeastern sections where the paleosols within the S1 were partially or completely welded. The laboratory data-indicated < 10 μm fraction peaks of the third-order and field-observed clay coatings on ped-faces, together with carbonate leaching and accumulation, in the paleosols within the S1 indicate occurrence of within-S1 material translocation. To sum up, it is unrealistic to reconstruct high-resolution climatic records from the S1 pedocomplex because a number of factors might have undermined the validity of the particle size as a winter monsoon proxy. These factors include weathering in the source areas, in situ post-depositional weathering and fine fraction translocation, and downward penetration of soil formation into underlying previously deposited materials on stable land surfaces.     

黄土地区土壤物理性质及与黄土成因的关系

该文主要讨论了在陕、甘、宁境内作为黄土风成成因的主要颗粒组成从北向南或从西向东的分布规律,以砂粒、粗粉粒、粘粒及物理性粘粒四种粒级作为黄土风成成因的主要指标粒级,并讨论了随着土壤颗粒的变化,而产生的土壤一系列物理性质的变化:土壤比重愈向南愈大;土壤容重则是最南部及最北部最大,而中间过渡地带较小;对于破坏土壤(无结构的土壤),土壤质地愈粘重,渗透性能愈差,质地愈轻则渗透性能愈好,而对于有结构的原状土壤则恰好相反。另外,黄土地区的土壤水分常数如最大吸湿水、凋萎湿度、自然含水量及田间持水量亦是从北向南相应的逐渐递增变大,然而毛管持水量则是最南部及最北部较小,而中间过渡地带最大,和土壤粗粉粒分布规律恰相吻合。