Characteristics of a paleosol and its implication for the Critical Zone development,Rocky Mountain Front Range of Colorado,USA

Activity and stability phases as well as geomorphic processes within the Critical Zone are well known. Erosion and deposition of sediments represent activity; soils represent geomorphic stability phases. Data are presented from a 4 m deep sediment section that was dated by luminescence techniques. Upslope erosion and resulting sedimentation started in the late Pleistocene around 18 ka until 12 ka. Conditions at the study site then changed, which led to the formation of a well-developed soil. Radiocarbon dating of the organic matter yielded ages between 8552 and 8995 cal. BP. From roughly 6.2 to 5.4 ka another activity phase accompanied by according sediment deposition buried the soil and a new soil, a Cambisol, was formed at the surface. The buried soil is a strongly developed Luvisol. The black colors in the upper part of the buried soil are not the result of pedogenic accumulation of normal organic matter within an A-horizon. Nuclear magnetic resonance spectroscopy clearly documents the high amount of aromatic components (charcoal), which is responsible for the dark color. This indicates severe burning events at the site and the smaller charcoal dust (black carbon) was transported to deeper parts of the profile during the process of clay translocation.     

Soil genesis and clay mineralogy on Aliabbas River Alluvial Fan, Kerman Province

Alluvial fan is among the important geomorphic positions in arid and semi-arid environments, and the history of settlement in central parts of Iran plateau has significantly been related to this landform. Soil properties are also related to the stability and the position of geomorphic surfaces. To study and compare clay mineralogy and soil physicochemical responses to geomorphic positions, 11 representative pedons on stable and unstable alluvial fan surfaces and plain geomorphic position in a transect from Sarcheshmeh Mountains toward Rafsanjan Plain were studied. Soil moisture and temperature regimes of the area were aridic and mesic, respectively. Smectite, kaolinite, chlorite, illite, and palygorskite clay minerals were found in almost all the studied soils. More salinity was investigated in stable alluvial fan surfaces than unstable positions. Evidence of a more humid paleoclimate shown by buried Bt horizons in plain surface was observed. Transformation of palygorskite to smectite in surface horizon of unstable alluvial fan position and preservation of palygorskite associated by gypsum crystals in By horizon of stable fan surfaces were among the important findings of the research. There was a significant and mutual relationship between geomorphology and physicochemical and mineralogical properties of soils under study.     

新疆博斯腾湖东岸盐渍土分布特征

新疆焉耆盆地博斯腾湖东岸几种不同地貌单元中,盐渍土发育强烈。在研究区内自北至南50km的地段呈线性分布。以刻槽法分5层连续采取0～1．00m深度土壤样品,分析易溶盐含量,判断盐渍土的含盐类型。平面上,从冲洪积扇前缘的细土平原到冲积-湖积平原,盐渍化程度呈增高趋势。盐渍土的含盐类型,沙垅段主要为硫酸盐,东南岸冲积-洪积平原主要发育亚硫酸盐和硫酸盐,其余地段盐渍土类型以氯盐和亚氯盐为主。剖面上,除沙垅段外,各个地貌单元土壤盐渍化表聚性特征明显。     

Spatial variability of reconstructed soil properties and the optimization of sampling number for reclaimed land monitoring in an opencast coal mine

Drastically disturbed soils caused by opencast mining can result in the severe loss of soil structure and increase in soil compactness. To assess the effects of mining activities on reconstructed soils and to track the changes in reclaimed soil properties, the variability of soil properties (soil particle distribution, penetration resistance (PR), pH, and total dissolved salt (TDS)) in the Shanxi Pingshuo Antaibao opencast coal-mine inner dump after dumping and before reclamation was analyzed using a geostatistics method, and the number of soil monitoring points after mined land reclamation was determined. Soil samples were equally collected at 78 sampling sites in the study area with an area of 0.44 km². Soil particle distribution had moderate variability, except for silt content at the depth of 0–20 cm with a low variability and sand content at the depth of 20–40 cm with a high variability. The pH showed a low variability, and TDS had moderate variability at all depths. The variability of PR was high at the depth of 0–20 cm and moderate at the depth of 20–40 cm. There was no clear trend in the variance with increasing depth for the soil properties. Interpolation using kriging displayed a high heterogeneity of the reconstructed soil properties, and the spatial structure of the original landform was partially or completely destroyed. The root-mean-square error (RMSE) can be used to determine the number of sampling points for soil properties, and 40 is the ideal sampling number for the study site based on cross-validation.     

Geospatial approach in mapping soil erodibility using CartoDEM – A case study in hilly watershed of Lower Himalayan Range

Soil erodibility is one of the most important factors used in spatial soil erosion risk assessment. Soil information derived from soil map is used to generate soil erodibility factor map. Soil maps are not available at appropriate scale. In general, soil maps at small scale are used in deriving soil erodibility map that largely generalized spatial variability and it largely ignores the spatial variability since soil map units are discrete polygons. The present study was attempted to generate soil erodibilty map using terrain indices derived from DTM and surface soil sample data. Soil variability in the hilly landscape is largely controlled by topography represented by DTM. The CartoDEM (30 m) was used to derive terrain indices such as terrain wetness index (TWI), stream power index (SPI), sediment transport index (STI) and slope parameters. A total of 95 surface soil samples were collected to compute soil erodibility factor (K) values. The K values ranged from 0.23 to 0.81 t ha^?1R^?1 in the watershed. Correlation analysis among K-factor and terrain parameters showed highest correlation of soil erodibilty with TWI (r ²= 0.561) followed by slope (r ²= 0.33). A multiple linear regression model was developed to derive soil erodibilty using terrain parameters. A set of 20 soil sample points were used to assess the accuracy of the model. The coefficient of determination (r ²) and RMSE were computed to be 0.76 and 0.07 t ha^?1R^?1 respectively. The proposed methodology is quite useful in generating soil erodibilty factor map using digital elevation model (DEM) for any hilly terrain areas. The equation/model need to be established for the particular hilly terrain under the study. The developed model was used to generate spatial soil erodibility factor (K) map of the watershed in the lower Himalayan range.     

Hornblende etching and quartz/feldspar ratios as weathering and soil development indicators in some Michigan soils

Weathering can be used as a highly effective relative age indicator. One such application involves etching of hornblende grains in soils. Etching increases with time (duration) and decreases with depth in soils and surficial sediments. Other variables, related to intensity of weathering and soil formation, are generally held as constant as possible so as to only minimally influence the time-etching relationship. Our study focuses on one of the variables usually held constant—climate—by examining hornblende etching and quartz/feldspar ratios in soils of similar age but varying degrees of development due to climatic factors. We examined the assumption that the degree of etching varies as a function of soil development, even in soils of similar age. The Spodosols we studied form a climate-mediated development sequence on a 13,000-yr-old outwash plain in Michigan. Their pedogenic development was compared to weathering-related data from the same soils. In general, soils data paralleled weathering data. Hornblende etching was most pronounced in the A and E horizons, and decreased rapidly with depth. Quartz/feldspar ratios showed similar but more variable trends. In the two most weakly developed soils, the Q/F ratio was nearly constant with depth, implying that this ratio may not be as effective a measure as are etching data for minimally weathered soils. Our data indicate that hornblende etching should not be used as a stand-alone relative age indicator, especially in young soils and in contexts where the degree of pedogenic variability on the geomorphic surface is large.     

基于微结构模拟的土体自相关距离分析

土体具有显著的空间变异性,描述土体空间变异性的重要指标是自相关距离。提出基于土体微结构模拟的方法来求解土体的自相关距离。在生成土体的微结构数值模型时,对四参数随机生长法（QSGS法）进行改进,考虑土体的粒径分布信息,使得生成的土体微结构更加合理。改进的四参数随机生长法（MQSGS法）所需的输入参数可以结合土体的扫描电镜试验及粒径分析试验获取。基于生成的土体微结构数值模型,即可计算土体的2点自相关函数,再通过曲线拟合即可求解土体的自相关距离。研究表明：与QSGS法相比,采用MQSGS法生成的土体微结构更加符合自然界的真实土体;基于MQSGS法生成的微结构数值模型计算得到的土体自相关距离略小于QSGS法得出的自相关距离。     

Utilisation of loess for soil amelioration

In Hungary loess has long been used for soil reclamation. The main steps of the method are: horizon A and B are removed from a suitable area and their material is stockpiled at the margins of the resulting pit. The loess (horizon C), this way exposed, is excavated and spread over the salt affected soils to be improved then mixed with their upper layer. The pit is named in Hungarian digó (pit). The name of the reclamation process is the digo method or spreading of yellow earth. Digó method is mainly used for the amelioration of salt affected soils with an acid A horizon and its benefits are as follows:

1. The acidity of the horizon A is eliminated
2. The soil structure is improved
3. The amount of calcium (a plant nutrient) is increased
4. Soil fertility is improved continuously
5. The soil depth is extended which adds to the relative volume of the ground water table.

     

Accuracy of cosmogenic ages for moraines

Analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38% between the oldest and youngest boulders from each moraine. This range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform. The wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders. A diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders (n = 3-7) will always yield a lower age limit for the moraine. The model indicates that for identical dating accuracy, six to seven boulders are needed from old and tall moraines (40,000-100,000 yr, 50-100 m initial height) but only one to four boulders from small moraines (20,000-100,000 yr, 10-20 m). By following these guidelines the oldest obtained boulder age will be ≥90% of the moraine age (95% probability). This result is only weakly sensitive to a broad range of soil erosion rates. Our analysis of published boulder ages indicates that <3% of all moraine boulders have prior exposure, and 85% of these boulders predate the dated moraine.     

Statistical analysis of the temporal stability of soil moisture in three desert regions of northwestern China

Soil moisture and its variations are key factors for understanding hydrological processes, which are characterized by a high temporal variability at different scales. The study was conducted at three field stations in the desert regions of northwestern China, where soil moisture measurements with gravimetric method were used to characterize the temporal stability of soil moisture using various statistical parameters and an index of temporal stability (ITS). The soils are a gray–brown desert soil at the Linze station, an aeolian sandy soil at the Fukang station, and a brown desert soil at the Cele station. Soil textures are accordingly sandy loam at Linze and Cele, and loamy sand at Fukang. The dynamic variation in soil moisture depends strongly on the rainfall pattern (amount and frequency) in these desert ecosystems. Soil moisture content is low and significantly different among the three desert ecosystems, with the maximum at the Linze station (6.61 ± 2.08 %), followed by the Cele (4.83 ± 0.81 %) and Fukang (3.46 ± 0.47 %) stations. The temporal pattern exhibits high variability because soil moisture is characterized by low temporal stability and a high coefficient of variation (CV). The standard deviation, CV, and ITS increase significantly with increasing soil moisture. Soil moisture displays a skewed frequency distribution that follows a logarithmic function at lower soil moisture but a log-normal distribution at higher values.     

Cumulative probability functions and their role in evaluating the chronology of geomorphological events during the Holocene

Cumulative probability functions (CPFs) for large numbers of radiocarbon age determinations are increasingly being used by scientists as a methodology to discern environmental histories. While the recent compilation of regional databases of the radiocarbon dating control for fluvial sediment sequences has been beneficial for identifying gaps in knowledge and stimulating new research, there are a number of problems that critically undermine the use of these CPFs as sensitive hydroclimatic proxies. (i) The CPF method is underpinned by the assumption that each radiocarbon measurement is a true age estimate for a point in time, whereas each measured age in fact forms a scatter around the true age of the sample; (ii) calibration of radiocarbon ages is responsible for much of the structure in CPFs and compounds the problem of scatter and smears the chronological control; (iii) the databases incorporate multiple types of environmental changes differing chronological relationships between the ¹⁴C measurements and the dated events, with pre‐dating, dating or post‐dating chronological control each displaying variable length temporal lags all mixed together in the same analysis; and (iv) the radiocarbon ages from individual case studies need to be more robustly tested before being incorporated into regional databases. All these factors negate the value of CPFs as sensitive proxies of environmental change, because peaks in probability for individual radiocarbon measurements are likely to be an incorrect estimate for the age of a geomorphological event and this problem is compounded by combining probabilities for multiple unrelated events. In this paper we present a critical analysis of CPFs and their interpretation before suggesting alternative approaches to analysing radiocarbon geochronologies of geomorphic events, which include: (i) Bayesian age modelling of river terrace development; (ii) developing regional databases that test specific geomorphic hypotheses; (iii) Bayesian age modelling of palaeoflood records; and (iv) analysis of sedimentation rates. Copyright © 2011 John Wiley & Sons, Ltd.     

Radiocarbon Dating of Soil Organic Matter

Radiocarbon ages of soil organic matter are evaluated with a model which incorporates the dynamics of the¹⁴C content of soil organic matter. Measured¹⁴C ages of soil organic matter or its fractions are always younger than the true ages of soils due to continuous input of organic matter into soils. Differences in soil C dynamics due to climate or soil depth will result in significantly different¹⁴C signatures of soil organic matter for soils of the same age. As a result, the deviation of the measured¹⁴C age from the true age of soil formation could differ significantly among different soils or soil horizons. Our model calculations also suggest that¹⁴C ages of soil organic matter will eventually reach a steady state provided that no climatic or ecological perturbations occur. Once a soil or a soil horizon has reached a steady state,¹⁴C dating of soil organic matter will provide no useful information regarding the age of the soil. However, for soils in which steady state has not been reached, it is possible to estimate the age of soil formation by modeling the measured¹⁴C contents of soil organic matter. Radiocarbon dating of buried soils could, in general, overestimate the true age of the burial by as much as the steady-state age of the soil or soil horizon.     

TDR测定喀斯特地区石灰土含水量的标定研究

土壤含水量是气候、水文、土壤侵蚀等研究中的一个重要参数。TDR法因具有方便、快速、精确且不扰动土壤等优点而得到广泛应用,但因受土壤质地、容重、温度等物理因素的影响而必须对其进行标定。本研究采用室内标定(壤土)和田间标定(粗、中、细质土以及三者的组合)相结合的方式,对用TDR法测定的喀斯特地区不同质地石灰土含水量进行了标定。结果表明:（1)TDR法测定的土壤含水量比烘干法测定值要小,两者最大绝对偏差在室内标定条件下为10.6%,田间标定为12.2%;相应的相对偏差最高分别可达60.3%和32.8%。因此,必须在使用前对TDR进行标定。（2)标定后TDR法测定的土壤含水量精度明显提高,平均绝对偏差低至1.4%~3.1%;室内标定曲线精度略低于田间标定曲线。（3)不同质地组合的TDR法土壤含水量标定曲线的标定精度较高(平均绝对偏差为1.5% ~ 2.6%),可用于不同质地土壤含水量标定。本研究结果可用于修订校正研究区及类似区域TDR法测定土壤含水量的结果。      

Prediction of spatial soil organic carbon distribution using Sentinel-2A and field inventory data in Sariska Tiger Reserve

Dynamic and vigorous top soil is the source for healthy flora, fauna, and humans, and soil organic matters are the underpinning for healthy and productive soils. Organic components in the soil play significant role in stimulating soil productivity processes and vegetation development. This article deals with the scientific demand for estimating soil organic carbon (SOC) in forest using geospatial techniques. We assessed distribution of SOC using field and satellite data in Sariska Tiger Reserve located in the Aravalli Hill Range, India. This study utilized the visible and near-infrared reflectance data of Sentinel-2A satellite. Three predictor variables namely Normalized Difference Vegetation Index, Soil Adjusted Vegetation Index, and Renormalized Difference Vegetation Index were derived to examine the relationship between soil and SOC and to identify the biophysical characteristic of soil. Relationship between SOC (ground and predicted) and leaf area index (LAI) measured through satellite data was examined through regression analysis. Coefficient of correlation (R ²) was found to be 0.95 (p value < 0.05) for predicted SOC and satellite measured LAI. Thus, LAI can effectively be used for extracting SOC using remote sensing data. Soil organic carbon stock map generated through Kriging model for Landsat 8 OLI data demonstrated variation in spatial SOC stocks distribution. The model with 89% accuracy has proved to be an effective tool for predicting spatial distribution of SOC stocks in the study area. Thus, optical remote sensing data have immense potential for predicting SOC at larger scale.     

The role of pore water in the mechanical behavior of unsaturated soils

Deformation and failure of soils are governed by the stresses acting on the soil skeleton. The isotropic stress acting on the soil skeleton can be divided into two components. One is the stress component which is transmitted through the soil skeleton. This skeleton stress is influenced by the pore water (bulk water) in the soil. The other is the internal stress component which does not contribute to equilibrium with a given external force. The internal stress is induced by the capillary tension of meniscus water clinging to the contact point of soil particles and acts so as to connect the soil particles tightly. Therefore, in modeling the stress and strain relations for unsaturated soils, it is of much importance to quantitatively evaluate how the pore water exists in the soil. This paper discusses the role of pore water on the mechanical behaviour of the soil. In particular, the significance of the water retention curve is emphasized from a mechanical viewpoint. Essential features required in modeling of the constitutive relations for unsaturated soils are discussed and presented.     

Genesis of pedons with discontinuous argillic horizons in the Holocene loess mantle of the southern Pampean landscape,Argentina

Soil development in the plain landscape of the southern Argentinean Pampa is related to pulses of aeolian accretion of calcareous loess during the Holocene epoch. Such plain relief is associated with landform stability that favors pedogenesis. In some sectors of the Holocene loess mantle, detailed soil surveys show a great variability of soil morphology in short distances (<7 m), such that pedons with Bt horizon (Ap-Bt-C-2Ckm) coexist with pedons with an AC horizon (Ap-AC-C-2Ckm) in a plain landscape, within identical loess parent material over a tosca layer (2Ckm-calcrete-petrocalcic horizon), and in a similar pedoclimate. This article studies the origin of this spatial variation. Loess parent materials directly overlie the relic tosca layer, exhumed after erosion of preexisting soils of the Late Pleistocene. The contrast in soil morphology between the petrocalcic horizon and the overlying Holocene soils reflects the effect of polygenesis. The complex soil spatial distribution pattern over the tosca layer appears unrelated to its paleomicrotopography, because soils with Bt horizons are identified in positive and depressed microlandforms of the tosca. The absence of Bt horizons might be caused by formerly intense biological activity related to a stable pattern of two natural vegetation covers or a surface paleomicrotopography that supported distinct vegetation types depending on the soil moisture in each paleomicrolandform.     

一种非饱和土表层蒸发过程的预测方法

探索了一种由土壤基本物性指标、气象数据预测非饱和土表层蒸发过程的方法。通过土壤基本物理性质（颗粒分布、土粒相对密度、干密度）预测出土-水特征曲线（SWCC）,进而得到土壤气相对湿度与含水率的关系,采用Penman-Wilson模型预测出了非饱和土表面的蒸发曲线。通过该方法,只需实地采取土样,获取其基本物理性质,由任意时刻土壤的含水率及气象数据就能预测出该时刻土表的蒸发速率。采用自制的自动蒸发测量系统进行浅层土蒸发试验,得到了蒸发曲线,与预测结果进行比较发现预测蒸发过程与实测结果一样皆由临界含水率和风干含水率将其分为3个阶段：稳定阶段、减速阶段和残余阶段,且蒸发量吻合,证明了所提出方法的准确性和实用性,对工程界估计土表蒸发量,确定水流量边界有重要意义。     

Geochronology and geochemistry of a dyke–host rock association and implications for the formation of the Bavarian Pfahl shear zone, Bohemian Massif

To place constraints on the formation and deformation history of the major Variscan shear zone in the Bavarian Forest, Bavarian Pfahl zone, SW Bohemian Massif, granitic dykes and their feldspar-phyric massive host rock (so-called palite), zircons were dated by the U–Pb isotope dilution and Pb-evaporation methods. The dated samples comprise two host rocks and four dykes from a K-rich calc-alkaline complex adjoining the SW part of the Bavarian Pfahl shear zone. The palites, which appear to be the oldest magmatic rocks emplaced in the shear zone, yield ages of 334±3, 334.5±1.1 Ma (average ²⁰⁷Pb/²⁰⁶Pb-evaporation zircon ages) and 327–342 Ma (range of U/Pb zircon ages) suggesting a Lower Carboniferous age for the initiation of the Pfahl zone. Absence of inherited older cores in all investigated zircons indicates that incorporation of crustal zircon material has played virtually no role or that the melting temperature was very high. Determination of the dyke emplacement age is complicated by partial Pb-loss in most of the fractions analysed. This Pb-loss can be ascribed to higher U content of the dyke zircons compared to those from host rock. Upper discordia intercept ages of the different dykes range from 322±5 to 331±9 Ma. The dykes are pre- to synkinematic with respect to penetrative regional mylonitisation along the Pfahl zone, and the upper intercept ages provide a maximum age for this tectonic event.     

A loess-paleosol record of climate and glacial history over the past two glacial-interglacial cycles (~ 150 ka), southern Jackson Hole, Wyoming

Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric ¹⁰Be accumulation in soils, and cosmogenic ¹⁰Be surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8, 7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (~ 76-69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (~ 43-51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada.