Natural Soil Profiles Research Articles

FEATURES OF THE GENESIS OF ANTHROPOGENIC SOILS OF LVIV

FEATURES OF THE GENESIS OF ANTHROPOGENIC SOILS OF LVIV

3D Numerical Assessment of Rammed Aggregate Pier Performance under Dynamic Loading in Liquefiable Soils

Ground improvement (GI) techniques have shown promise in effective liquefaction mitigation, but the physical mechanisms governing their three-dimensional (3D) response during dynamic loading are not yet fully understood. To evaluate the 3D performance of one GI technique, the rammed aggregate pier (RAP), in-situ site characterization, full-scale field test data, and calibrated baseline constitutive soil model parameters are combined to model the 3D fully coupled hydromechanical response of natural (unreinforced) and improved (reinforced) soil profiles. To the authors’ knowledge, this contribution represents the first 3D model of a columnar-reinforced soil profile being calibrated using full-scale field testing. The field observations from the comprehensive ground improvement testing (GIT) program in New Zealand and insights from two-dimensional (2D) finite-difference analyses using constitutive model parameters calibrated against the field measurements were used. The developed 3D models were subjected to dynamic loads simulating the excitation generated by a vibroseis truck at one of the in-situ test sites of the GIT program, as well as unidirectional and bidirectional earthquake ground motions from the Canterbury Earthquake Sequence events. The 3D simulations showed that the improved soil profiles experienced reduced excess pore pressures and reduced dynamically induced shear strains compared to the natural, unreinforced soil models. The developed 3D finite-element predictions were compared and validated vis-à-vis the field observations of the GIT program. Compared to 2D analyses, 3D analyses provide a more accurate description of actual field conditions, and, for instance, it was observed that multidirectional shaking has a significant effect on liquefaction triggering, particularly for natural soil profiles. Finally, it was shown that soil densification around the installed pier elements and the lateral earth pressure increase within the densified soil and are the primary ground improvement mechanisms contributing to the reduction of dynamically induced shear deformations and excess pore pressure generation during earthquake shaking. It was also found that the permeability and shear stiffness of the installed RAP piers did not have a significant influence on the pore pressure response and shear strains developed along the centerline of the improved area.

Use of sediments and soils (paleosols) in construction fills of La Joya archaeological site, Veracruz, Mexico: micromorphological evidence

In this paper, we study the materials used for the construction of earthen structure in the La Joya archaeological site, on the Gulf of Mexico coast, built on top of a paleodune, from the Late Preclassic (400 BC) to the Classic period (AD 100-1000). The first constructions arise around 100 BC, on a paleodune top rising slightly above the surrounding alluvial terraces of the Jamapa river; then it grows into a 15-ha monumental compound. The total construction volume reaches 250,000 m3, all made of earth, surrounded by large artificial water pounds (reservoirs). To understand the kind of components found in the structures and their provenance, we compare the micromorphological features of the materials from the earthen constructions with the sediments and paleosols located in the surrounding areas. Samples were taken from the fills of three first building stages, as well as from a natural soil profile and the natural paleosol horizons found beneath the structures. Micromorphological features found in fills permit to establish the correlation between them and their parent material. The fills from the first stage of construction have fragments of a Btb horizon, mixed with an A horizon, compacted and crushed, in which abundant artifacts are identified. However, these artifacts were not intentionally incorporated to the fills, but had been accumulated on the pre-occupation A horizon as residential and agriculture trash. Particular attention was paid to a gley material occurring in the third building stage, that was believed to come from the sediments accumulated in the original borrow pits transformed into water reservoirs, enclosing the main architectural compound. These reservoir fills share properties of the natural sediments and paleosols but transformed by the waterlogging conditions. In consequence, these materials are interpreted as a case of anthropogenic pedogenesis, where the gley micromorphology indicates waterlogging conditions, but in artificially made reservoirs, as they do not have dark organic sediments that would result of the vegetation typical of a natural pond in a humid tropical environment.

Mercury background values in soils and saprolites in the gold-rich greenstone belt of Suriname, Guiana Shield: The role of parent rock and residual enrichment

In order to develop criteria to distinguish polluted from unpolluted materials in areas subjected to artisanal small-scale gold mining, background mercury values were established in 62 natural soil and saprolite profiles on 16 different parent rock types in the greenstone belt of Suriname. Hg values in pristine topsoils often amount to up to 200 μg/kg, about 100 times higher than Hg in common parent rocks. Additional analyses of 40 major and trace elements in two pilot profiles show that Hg values are strongly correlated to Fe, Cr and V values, which suggests that just as those elements Hg is residually enriched in topsoils by laterisation processes. In the deeper pallid zones of the profiles, Hg has often been leached almost completely together with iron by reducing groundwater action. In this way the range of Hg values within a single profile can be greater than between profiles. Maximum and average Hg values of 196 samples from the 16 different parent rock types fall apart into two main groups. Felsic parent rocks with predominance of quartz and feldspar have maximum Hg values around 100 μg/kg and averages around 50 μg/kg, mafic ones with less silica and higher Fe, Mg and Ca have maximum values around 250–300 μg/kg and averages around 150 μg/kg. In general the natural soil and saprolite Hg values are in the same order of magnitude as many published mine tailings and stream sediments, and therefore cannot be used to separate polluted from unpolluted materials.

Mineralogy and geochemical signatures as indicators of differential weathering in natural soil profiles from the West Asturian-Leonese Zone (NW Iberia)

This paper presents detailed mineralogical results together with a geochemical characterization for a sequence of six natural soil profiles. Bedrock samples (R series) and overlying soil samples (S series) were characterized. The soil profiles are distributed in a series of Paleozoic lithological units from lower Ordovician to upper Carboniferous in age (Iberian Massif, NW Iberia). The lithological influence on mineral properties and geochemical composition and, how different weathering may be occurring under very similar temperate and acidic conditions, have been studied. Field observations together with laboratory analyses were indicative of differential weathering. So, a series of selected chemical indices and relations were applied to clarify this assumption. The mineralogy was analysed by Scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD) of rock powder and soil oriented aggregates. X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectroscopy (ICP-MS) were applied to analyse chemical composition. The first results showed how major elements, SiO2, Al2O3 and Fe2O3, slightly enriched in the soil profiles, are consistent with the dominant mineralogy: quartz, chlorite, muscovite and/or illite, together with kaolinite and albite. The bases K2O, Na2O, CaO and MgO are also coherent with mineral composition and experience little variation, but are gradually removed in the profiles. The mobility of major elements leads to a general loss of bases and, in general, a slight enrichment in silica and sesquioxides. SiO2 is enriched, firstly accumulated in soils and partially depleted by dissolution as colloidal form. Al2O3 in some soils is slightly less than in former rocks, so other physical processes are expected to take place, involving clay removal with consequent aluminium depletion too. A special emphasis has been given to albite coexisting with kaolinite, firstly supposed to be directly inherited from parent substrates when present, but finally the chemical index PIA shows it was mainly due to mineral alteration of plagioclases. The best correlations to explain the albite alteration and kaolinitization progress were obtained with chemical indices PIA, CIW, CIA and Al2O3/Na2O ratio. This together with mineralogical signatures, suggest that kaolinite is the result of gradual dissolution due to the acid hydrolysis of albite in such acidic environments, which may also be attributed to the organic matter influence.

Heavy Metal Concentrations in Orchard Soils with Different Cultivation Durations and Their Potential Ecological Risks in Shaanxi Province, Northwest China

The heavy metal pollution of soils, resulting from long-term fertilizing activity, is becoming serious in many countries, endangering ecological safety and human health. This study employed inductively coupled plasma-mass spectrometry (ICP-MS) to investigate concentrations of eight heavy metal elements (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in five apple orchard soil profiles after different cultivation durations, one modern intercropping farmland soil profile, and one natural soil profile from Baishui County, in Shaanxi Province, Northwest China. The potential risk associated with the presence of heavy metals in the soils was assessed by the single-factor pollution index (Pi), Nemerow comprehensive index (NCI), and potential ecological risk index (RI). Results showed that the average concentrations of Cr, Ni, As, Pb, and Hg in the farmland soil were higher than those in the apple orchard soils. The average concentrations of Ni, Cu, As, and Hg in the apple orchard soils reached the highest after 25 years of cultivation. The results imply that concentrations of heavy metals will increase with increasing cultivation time. The farmland soil had the highest NCIs, while the NCIs of the apple orchard soils also increased with cultivation time. Compared with the quality standards of pollution-free orchards and green food production areas, all Pis and NCIs were less than 1 and 0.7, respectively, indicating that the soils were in healthy condition. The RI results also suggest that the soils have a low ecological risk (RI < 150). Although the potential ecological risk is currently low, predicting and reducing heavy metal input should be considered.

Translocation of Phytoliths Within Natural Soil Profiles in Northeast China.

Phytoliths are a reliable paleovegetation proxy and have made an important contribution to paleoclimatic studies. However, little is known about the depositional processes affecting soil phytoliths, which limits their use for paleoclimate and paleovegetation reconstructions. Here, we present the results of a study of the vertical translocation characteristics of phytoliths in 40 natural soil profiles in Northeast China. The results show that phytolith concentration decreases within the humic horizon of the soil profiles and that ∼22% of the phytoliths are translocated below the surface of the studied soils. In addition, we find that the translocation rate of phytoliths varies markedly with phytolith type and that phytolith size and aspect ratio also have a significant effect. Phytoliths with length >30 μm and with aspect ratio >2 and those with length <20 μm and aspect ratio <2 are preferentially translocated compared to those with length >25 μm and aspect ratio <2. Our results demonstrate that differential translocation of phytoliths within soil profiles should be considered when using soil phytoliths for paleoclimate and paleovegetation reconstruction.

Patterns of variation magnetic properties and chemical elements of soil profile in landslide area of South East Sulawesi Indonesia

Applications of the magnetic properties of rock continue to be developed because of its ability to integrate the understanding of the variation patterns of minerals and chemical elements in the process of soil formation and also their influence due to external factors . The primary objective of this study is to knowlege how the trends of variations of the magnetic properties and chemical elements on soil profile in landslide area, and how the association between the element as welpalal as the association between chemical elements and magnetic properties. Eleven soil profiles are the focus for the study of magnetic properties (parameter of magnetic susceptibility) and their elemental content (i.e., using the X-Ray Fluorescence, XRF). From the soil profiles studied, one hundred and twenty-four samples were taken and analyzed for their magnetic properties and elemental content. The results of this finding show that the trend of variation in magnetic susceptibility and chemical elements in soils differs from the normal soils and soils affected by human activity. The linear correlation between χLF and χFD values indicates that the soil profile in this study is a natural soil profile even though it has undergone changes due to landslides.

The Impact of Climate Change on the Water Balance of Oil Sands Reclamation Covers and Natural Soil Profiles

Abstract The design of reclamation soil covers at oil sands mines in northern Alberta, Canada, has been conventionally based on the calibration of soil–vegetation–atmosphere transfer (SVAT) models against field monitoring observations collected over several years, followed by simulations of long-term performance using historical climate data. This paper evaluates the long-term water balances for reclamation covers on two oil sands landforms and three natural coarse-textured forest soil profiles using both historical climate data and future climate projections. Twenty-first century daily precipitation and temperature data from CanESM2 were downscaled based on three representative concentration pathways (RCPs) employing a stochastic weather generator [Long Ashton Research Station Weather Generator (LARS-WG)]. Relative humidity, wind speed, and net radiation were downscaled using the delta change method. Downscaled precipitation and estimated potential evapotranspiration were used as inputs to simulate soil water dynamics using physically based models. Probability distributions of growing season (April–October) actual evapotranspiration (AET) and net percolation (NP) for the baseline and future periods show that AET and NP at all sites are expected to increase throughout the twenty-first century regardless of RCP, time period, and soil profile. Greater increases in AET and NP are projected toward the end of the twenty-first century. The increases in future NP at the two reclamation covers are larger (as a percentage increase) than at most of the natural sites. Increases in NP will result in greater water yield to surface water and may accelerate the rate at which chemical constituents contained within mine waste are released to downstream receptors, suggesting these potential changes need to be considered in mine closure designs.

Мониторинг почв земельных участков как информационное обеспечение реестра почвенных ресурсов на локальном уровне

The results of large-scale (1 : 5000) soil mapping of allotments (garden non-commercial partnerships) located on the territory of Meshchera lowland of Noginsk district of Moscow region are considered. The investigations showed that the initial soils located on the territory of the allotments have suffered the significant transformation since the allotments were created. Predominantly soddy podzolic soils with the different degree of surface or ground gleization, and also boggy soils were transformed into the agro-soddy podzolic soils and agrozems. The most significant changes occurred within soils in areas of intensive development where the implementation of organo-mineral fertilizers, green manures, formed agrogenic (hummock) micro-topography, manmade microstructure of the soil cover. Compared to the natural soil profile, they are characterized by a neutral pH, high and medium content of mobile phosphorus, poor in exchange potassium. Soils with the medium humus content (3–5% humus) prevail in this area. We separated clusters characterized by the agro-chemical and morphological properties of soils reflecting the classification at the level of subtype. The revealed changes reflect the growth of productivity and quality of the allotment soils and determine the expediency of soil parameters consideration in the basic documents providing the register of soil resources at the local level.

An alternative method for interpreting JET erosion test (JET) data: Part 2. Application

AbstractThis paper reports the results of jet tester experiments on soil samples of uniform properties which allow quantitative application of the new theory proposed in part 1 of these publications. This theory explores the possibly that a more adequate indicator of soil erodibility may be obtained by using the mass (and so volume) of soil eroded by the jet and the depth of scour penetration, rather than by using penetration depth alone, as assumed in the commonly‐used data interpretation method. It is shown that scour geometry can be well described using a generalized form of the Gaussian function, defined by its standard deviation and maximum depth. Using a published expression for jet kinetic energy flux, the new theory divides this flux into that used to erode soil, and the remainder which is dissipated in a variety of ways. Jet experiments on a specially‐prepared uniform soil sample are reported which provide the key to determining the spatial variability in the profile resistance to erosion offered by field soils. This resistance is expressed in the work required to erode unit mass of soil, denoted as J (in J/kg). The paper also gives results obtained on the profile variation in J for jet tests carried out at riverine sites on the upper Brisbane River, Queensland, Australia. As expected in most natural soil profiles, the results show an increase in J with depth in the profile. The soil resistance (J) is compared to the traditional interpretation of soil erodibility, (kd). The graphical comparison of these two indicators illustrates the inverse type of relationship between them which is expected from their respective definitions, but this relationship is associated with significant scatter. Possible reasons for this scatter are given, together with comments on jet tester experience in a wide variety of soil types. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Streamflow recession patterns can help unravel the role of climate and humans in landscape co-evolution

Abstract. Traditionally, long-term predictions of river discharges and their extremes include constant relationships between landscape properties and model parameters. However, due to the co-evolution of many landscape properties more sophisticated methods are necessary to quantify future landscape–hydrological model relationships. As a first step towards such an approach we use the Brutsaert and Nieber (1977) analysis method to characterize streamflow recession behaviour of ≈ 200 Swedish catchments within the context of global change and landscape co-evolution. Results suggest that the Brutsaert–Nieber parameters are strongly linked to the climate, soil, land use, and their interdependencies. Many catchments show a trend towards more non-linear behaviour, meaning not only faster initial recession but also slower recession towards base flow. This trend has been found to be independent from climate change. Instead, we suggest that land cover change, both natural (restoration of natural soil profiles in forested areas) and anthropogenic (reforestation and optimized water management), is probably responsible. Both change types are characterised by system adaptation and change, towards more optimal ecohydrological conditions, suggesting landscape co-evolution is at play. Given the observed magnitudes of recession changes during the past 50 years, predictions of future river discharge critically need to include the effects of landscape co-evolution. The interconnections between the controls of land cover and climate on river recession behaviour, as we have quantified in this paper, provide first-order handles to do so.

Modeling water flow and nitrate–nitrogen transport on golf course under turfgrass

Golf courses are constructed from artificial layers on top of natural soil as the goal is to rapidly drain excess water through the soil profile using subsurface tile drainage system. Golf turf is one of the most intensively managed systems due to the high use of fertilizer and irrigation. Leaching and runoff of nitrogen (N) from turf can pollute surface- and groundwaters. Our objective was to understand the fate of water and nitrate–N in constructed golf course turf. We conducted a modeling study for system 1 with tile drainage and artificial soil layers and system 2 with a natural soil profile using HYDRUS 2D. Experimental data from a planned golf course in Istria, Croatia for natural soil were used. Artificial layers were constructed according to United States Golf Association (USGA) recommendations. Urea was used as the fertilizer N source at three application rates (50, 75, and 100 kg ha−1). Water flow modeling showed a large amount of tile drainage outflow in system 1, where tile drains aided in lowering the pressure head in the soil above the tile drains. In system 2, low permeability of the natural soil and lack of drainage resulted in lower pressure head in the topsoil with surface runoff during high rainfall. Results of solute simulations using HYDRUS 2D revealed that at 100 kg ha−1 scenario, 66 % of ammonium–N, and 39 % of nitrate–N were leached through tile drains rather than infiltrate into the subsoil. The distribution of the nitrate–N was predominantly influenced by the highly permeable layers and tile drainage system. However, in the absence of drainage, modeling revealed that a large amount of nitrate–N can reach bottom of the soil profile and thus leach into groundwater. The modeling study revealed that using a USGA recommendation for golf course construction can reduce nitrate–N leaching into subsoil and consequently groundwater. The presence of tile drains provided a rapid conduit for transmission of water and nutrients (N species in this specific case), thus limiting infiltration of water and associated solutes into subsoil layers. Subsurface drainage systems are typically installed only on golf greens and not on the entire golf course area, while fertilizers are applied across entire golf course, which can lead to greater leaching of nitrate–N.

引黄灌区土壤有机碳密度剖面特征及固碳速率研究

PDF HTML阅读 XML下载 导出引用 引用提醒 引黄灌区土壤有机碳密度剖面特征及固碳速率 DOI: 10.5846/stxb201211051537 作者: 作者单位: 南京师范大学地理科学学院,南京师范大学地理科学学院,南京师范大学地理科学学院,中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室,中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室,中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划“973”资助项目（2010CB950702）；中国科学院战略性先导科技专项资助项目（XDA05050507）；博士后基金资助项目（1202051C） Profile distribution patterns of soil organic carbon and the rate of carbon sequestration in Ningxia Irrigation Zone Author: Affiliation: College of Geographical Science,Nanjing Normal University,College of Geographical Science,Nanjing Normal University,College of Geographical Science,Nanjing Normal University,State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences,State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences,State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为揭示灌溉耕作对土壤有机碳密度剖面（0-100 cm）分布产生的影响，通过在宁夏引黄灌区进行实地调查与采样，以无灌溉耕作的自然土壤作为对照，研究不同灌溉耕作时间序列下灌区土壤有机碳密度的剖面分布特征，并估算其平均固碳速率。结果表明：灌区土壤有机碳含量具有随土层深度增加而下降的剖面分布特征，灌溉耕作对增加表层土壤有机碳含量作用最明显；灌区土壤剖面碳密度与灌溉耕作时间和土壤类型均显著相关（P < 0.01），相关系数分别为0.63和 0.74，且因灌溉耕作时间和土壤类型的不同，土壤有机碳密度差异性显著（P < 0.05）；灌溉耕作影响的土层深度及剖面土壤有机碳密度的增加量因灌溉耕作时间长短的不同而异；引黄灌区5类土壤的平均固碳速率为0.53 MgC · hm-2 · a-1。引黄灌溉耕作在增加农田土壤固碳中发挥着重要作用。 Abstract:To reveal the effect of irrigation with sediment laden water from the Yellow River on soil organic carbon (SOC) distribution in profile (0-100 cm), Ningxia Irrigation Zone was selected as the study area to carry out the research. Totally, 40 soil profiles of five soil types (Irrigation-silted soils, Fluvo-aquic soils, Sierozem soil, Aeolian sandy soil and Alluvial soils) were collected, including 34 cropland profiles with the irrigated durations ranged from 10 to 2200 years and 6 natural soil profiles never irrigated and cultivated, to analyze profile distribution patterns of SOC content and density under different durations of irrigation and cultivation. The natural soil profiles were used as control profiles and their irrigation duration were set to zero. Pearson correlation coefficients were calculated to determine relationships between SOC density and irrigation durations and soil types. SOC content and density were subjected to analysis of variance (ANOVA) to test difference of irrigation effects from irrigation years and soil types at 5% probability level, respectively. SOC sequestration rate was also estimated by comparing irrigated soils with control ones.Results indicated that SOC content of irrigated cropland showed a decreasing trend with the deepening of soil layers in profile. SOC content of surface layer (0-20 cm) affected mainly by irrigation and cultivation increased more rapidly than those of deeper layers affected mainly by soil parent material. When the irrigated duration was about 50 years, the SOC content showed the most significant difference among the five soil types. The irrigation-silted soil layer formed by irrigation and cultivation activities, usually thicker than 50 cm, were found in those areas with such activities of 50 years over. The depth influenced by irrigation and the increment of SOC density both are different due to the difference of irrigation durations. SOC density was significantly related with irrigation durations and soil types, the correlation coefficients were 0.63 (P < 0.01) and 0.74 (P < 0.01), respectively. SOC density in the profile depth were significant different (P < 0.05) among varied irrigation durations and soil types. SOC density increment was significantly and positively correlated with irrigation durations shorter than 50 years. On average, the SOC density increment of the cropland soils in depth of 0-20, 20-30, 30-60 and 60-100 cm were 14.69, 4.52, 9.84 and 9.52 Mg/hm2 more than the corresponding soil layers of their control profiles. SOC density increment of irrigation-silted soils formed under the long-term alternate activities of irrigation, manure addition, silting and cultivation, was more than other four soil types in Ningxia Irrigation Zone. The linear relationships between SOC density increments and irrigation durations inferred that average SOC sequestration rate reached 0.53 MgC · hm-2 · a-1 from the five soil types in Ningxia Irrigation Zone. The SOC sequestration rate varied among soil types.Results discussion indicated, by stimulating plant and root growth as well as soil biotic activity,irrigation could potentially enhance SOC sequestration of cultivated land in the arid and semi-arid area. In addition, irrigation with sediment laden Yellow River water via sediment with organic matter silting, make the irrigation-silted soil layer thicker at the top of profile, and SOC increased accordingly. Overall, irrigation by the Yellow River water plays an important role in increasing SOC density. 参考文献 相似文献 引证文献

Numerical Modeling of Gas Flow in the Suncor Coke Stockpile Covers

The occurrence of thermally driven convective air flow within waste rock or natural soil profiles has been well established; however, the potential impact that convective air flow may have on water storage within reclamation soil covers has not been previously explored. We conducted a numerical modeling study to evaluate the effect that convective air flow may have on stored water within a soil reclamation cover placed over a coke stockpile at an oil sands mine in Alberta, Canada. Coke is a carbon, sand‐like byproduct of heavy oil processing. Two‐dimensional simulations of thermally driven convective air flow were conducted for two different field sites based on available field data. The elevated temperature within the coke stockpile resulted in the development of strong convective air flow cells that drew in drier atmospheric air over the lower slope positions while releasing it across the upper slope and plateau areas of the cover. The magnitude of the gas flux and the intensity of the convection within the cell were a function of the air permeability of the coke and cover material, the depth of the coke, and the slope of the stockpile. It was estimated that convective air movement through the cover could produce as much as 1 to 2 mm/d of enhanced drying of the cover in lower slope positions. Field observations of water content distributions within the cover provided corroboration that the cover has undergone enhanced drying at lower slope positions.

Determination of dose rate from Chernobyl-derived radiocaesium in Estonian soil

The deposition and vertical depth distribution of 134Cs and 137Cs in the natural undisturbed soil profiles down to 20–25 cm were studied at locations in the North Eastern Estonia, which were most strongly affected by the Chernobyl fallout in 1986. The total depositions were estimated based on summing the sampled and measured activities of 134Cs and 137Cs in all sections of soil profiles. The Chernobyl 137Cs deposition values varied considerably from site to site and the range was from 3.9 kBq m−2 to 50.2 kBq m−2, with the average of 22.8 kBq m−2 for the region (reference data May 1, 1986). The ratio of total activities, A(134Cs)/A(137Cs), varied in the range from 0.47 to 0.55. Using a compartment model and the observed data on the 134Cs and 137Cs activity concentrations (Bq m−2) in four compartments, 0–1 cm, 1–5 cm, 5–15 cm and 15–30 cm, of soil collected in 1991–2003, the approximate residence half-times of radiocaesium in soil were determined. The latter increased from 3.7 y in the top-most compartment to 8.6 y and 36.4 y in the deeper compartments, respectively. The time dependence of the external gamma-dose rate at the height of 1 m above a flat ground area arising from the deposited and migrating radiocaesium was calculated using the modeled data on the 134Cs and 137Cs activity in soil compartments. Considering the total depositions of radiocaesium in soil from the Chernobyl 1986 accident, the 50 year effective doses caused by external gamma exposure varied in the range from 0.13 mSv to 1.74 mSv, with the mean of 0.79 mSv in the region.

Controls and Frequency of Preferential Flow Occurrence: A 175‐Event Analysis

Despite the widespread acceptance of hydrologic importance, controls on the initiation of preferential flow in natural soil profiles and the frequency of its occurrence at different times of year remain elusive. This study determined the controls and frequency of preferential flow occurrence in the Shale Hills Critical Zone Observatory. Soil moisture profiles and precipitation were monitored at 10 sites along a topographic gradient for &gt;3 yr, encompassing 175 precipitation events. For each event and each site, the flow regime was classified as either preferential flow, sequential flow, or nondetectable flow based on the sequence of soil moisture response at various depths within the same site. Preferential flow here specifically refers to out‐of‐sequence soil moisture response, with a deeper horizon responding to precipitation earlier than a shallower horizon. Indices describing antecedent precipitation, precipitation characteristics, precipitation timing, and initial soil moisture were examined to determine the characteristics of events that resulted in preferential flow vs. those that resulted in sequential flow. Analyses showed that preferential flow was common throughout the catchment, occurring during 17 to 54% of the 175 events at each of the 10 monitored sites. Preferential flow occurred in at least one site during 90% of the 175 events. While the frequency of preferential flow appeared insensitive to topographic position, the controls on preferential flow initiation varied with landscape position. Analysis of subsets of the time series data showed that while the frequency of preferential flow can be determined from 1 yr of real‐time monitoring, the controls on preferential flow require much longer (≥3 yr) monitoring to be reliably identified.

Use of a soil moisture network for drought monitoring in the Czech Republic

Since 2000, the network of stations that make up the Czech Hydrometeorological Institute (CHMI) has measured the soil moisture content at the 0- to 0.9-m layer using sensors placed within the natural soil profile under closely cropped grass cover. Using information from 8 years of continuous observation at seven stations throughout the Czech Republic, we verified the usefulness of the Soil Moisture Index (SMI). The SMI is a potentially useful index for calculating the water deficit in the Czech Republic and Central Europe. During this period, a statistically significant decrease in moisture content was detected, and negative SMI values predominated. There were frequent occurrences of flash drought, defined as a very rapid decline in soil moisture during a 3-week period. The CHMI can use SMI values below −3 in the Integrated Warning Service System. The routine calculation of SMI values can alert agricultural producers to the development of flash drought conditions and provide them with information regarding the effectiveness of recent rainfall events. An increase in soil moisture, in contrast, could serve as a warning sign for hydrology because it creates the preconditions for flooding. The complex study of soil humidity regimes is becoming more significant in connection with current global climatic change warnings in hydrological cycles.

Infiltration and drainage processes in multi-layered coarse soils

Huang, M., Barbour, S. L., Elshorbagy, A., Zettl, J. D. and Si, B. C. 2011. Infiltration and drainage processes in multi-layered coarse soils. Can. J. Soil Sci. 91: 169–183. Infiltration and drainage processes in multi-layered soils are complicated by contrasting hydraulic properties. The objective of this study was to evaluate the performances of the hysteretic and non-hysteretic models to simulate the infiltration and drainage processes from three different natural soil profiles containing as many as 20 texturally different layers. Hydraulic properties were estimated from soil textures using pedotransfer functions and were calibrated and validated using measured water contents during infiltration and drainage phases, respectively. The results supported the use of the Arya-Paris pedotransfer function to estimate the wetting curve when contact angles are incorporated. The unique Kozeny-Carmen equation parameter was evaluated by optimizing the estimated saturated hydraulic conductivity. The calibrated numerical model (Hydrus-1D) accurately simulated soil water content profiles and water volumes during the infiltration and drainage phases. The mean error of prediction (MEP) between the measured and estimated soil water contents varied from –0.030 to 0.010 cm3 cm−3, and the standard deviation of prediction (SDP) from 0.003 to 0.057 cm3 cm−3. The simulation was improved for more heterogeneous soil profiles when hysteresis was taken into account. The measured and simulated results indicated that the soil profile with vertical heterogeneity in soil texture can store more water than the similar textured vertically homogeneous soils under drained conditions.

Carbon isotopic composition, turnover and origins of soil CO2 in a monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir, South China

Carbon isotopic compositions of soil CO2 in rainy season (July) from two natural soil profiles (DHLS & DHS) in the monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir (DBR), South China, are presented. Turnover and origins of soil CO2 are preliminarily discussed in this paper. Results show that the content of soil CO2 varies between 6120 and 18718 ppmv, and increases with increasing depth until 75 cm, and then it declines. In DHLS, soil CO2 δ 13C ranges from −24.71‰ to −24.03‰, showing a significant inverse correlation (R 2=0.91) with the soil CO2 content in the same layer. According to a model related to soil CO2 δ 13C, the soil CO2 is mainly derived from the root respiration (>80%) in DHLS. While in DHS, where soil CO2 δ 13C ranges from −25.19‰ to −22.82‰, soil CO2 is primarily originated from the decomposition of organic matter (51%–94%), excluding the surface layer (20 cm, 90%). Radiocarbon data suggest that the carbon in soil CO2 is modern carbon in both DHLS and DHS. Differences in 14C ages between the “oldest” and “youngest” soil CO2 in DHLS and DHS are 8 months and 14 months, respectively, indicating that soil CO2 in DHLS has a faster turnover rate than that in DHS. The Δ14C values of soil CO2, which range between 100.0‰ and 107.2‰ and between 102.5‰ and 112.1‰ in DHLS and DHS, respectively, are obviously higher than those of current atmospheric CO2 and SOC in the same layer, suggesting that soil CO2 is likely an important reservoir for Bomb-14C in the atmosphere.