Fine Soil Particles Research Articles

Predicting the particle size distribution of eroded sediment using artificial neural networks.

Water erosion causes soil degradation and nonpoint pollution. Pollutants are primarily transported on the surfaces of fine soil and sediment particles. Several soil loss models and empirical equations have been developed for the size distribution estimation of the sediment leaving the field, including the physically-based models and empirical equations. Usually, physically-based models require a large amount of data, sometimes exceeding the amount of available data in the modeled area. Conversely, empirical equations do not always predict the sediment composition associated with individual events and may require data that are not always available. Therefore, the objective of this study was to develop a model to predict the particle size distribution (PSD) of eroded soil. A total of 41 erosion events from 21 soils were used. These data were compiled from previous studies. Correlation and multiple regression analyses were used to identify the main variables controlling sediment PSD. These variables were the particle size distribution in the soil matrix, the antecedent soil moisture condition, soil erodibility, and hillslope geometry. With these variables, an artificial neural network was calibrated using data from 29 events (r2=0.98, 0.97, and 0.86; for sand, silt, and clay in the sediment, respectively) and then validated and tested on 12 events (r2=0.74, 0.85, and 0.75; for sand, silt, and clay in the sediment, respectively). The artificial neural network was compared with three empirical models. The network presented better performance in predicting sediment PSD and differentiating rain-runoff events in the same soil. In addition to the quality of the particle distribution estimates, this model requires a small number of easily obtained variables, providing a convenient routine for predicting PSD in eroded sediment in other pollutant transport models.

Association of Plutonium isotopes with natural soil particles of different size and comparison with 137Cs.

Information on how plutonium (Pu) isotopes associate with natural soil particles of different size is very important for the interpretation involved in the application of Pu isotopes as soil erosion tracers. This work investigated the association of Pu isotopes with different particle size fractions of natural soils and compared it with that of 137Cs. Ten bulk soils collected from two different areas were separated into different particle size fractions by a combination of wet sieving and centrifugation techniques and the sub-samples were analyzed for 137Cs, 239Pu and 240Pu. Results showed that the concentrations of both 239+240Pu and 137Cs increase with decreased particle sizes and are closely related to the specific surface areas of soil particles, which demonstrated a similar preferential association of Pu with finer soil particles as 137Cs. The activity ratios of 239+240Pu/137Cs in soil fractions increasing with increased particle size further indicated a less preferential transport of Pu with fine particles compared to 137Cs. These results not only highlight the suitability of Pu isotopes as soil erosion tracers, but also provide useful information for assessing the migration behavior of Pu in contaminated environments.

风速变化对草原生态系统的影响研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 风速变化对草原生态系统的影响研究进展 DOI: 10.5846/stxb201606161164 作者: 作者单位: 北京师范大学地表过程与资源生态国家重点实验室,北京师范大学地表过程与资源生态国家重点实验室,北京师范大学地表过程与资源生态国家重点实验室,北京师范大学地表过程与资源生态国家重点实验室,北京师范大学地表过程与资源生态国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金创新团队项目（41321001）；地表过程与资源生态国家重点实验室资助项目（2014-zy-04）；中央高校科研业务费专项资金资助（310421103） Research progress of the effects of wind speed change on grassland ecosystem Author: Affiliation: State Key laboratory of Earth Surface Progress and Resources Ecology,Beijing Normal University,State Key laboratory of Earth Surface Progress and Resources Ecology,Beijing Normal University,State Key laboratory of Earth Surface Progress and Resources Ecology,Beijing Normal University,State Key laboratory of Earth Surface Progress and Resources Ecology,Beijing Normal University,State Key laboratory of Earth Surface Progress and Resources Ecology,Beijing Normal University 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:在全球风速呈下降趋势的大背景下，研究风速变化对生态系统的影响具有重要意义，尤其是其重要组成部分——草原生态系统。近年来大量学者开始研究风速变化对草原生态系统的影响，主要集中在以下几个方面并得出相关的结论，（1）风速变化会影响植物的生长速率和叶片形态，适当的风速能够促进植物生长发育、提高植被初级生产力，而强风或持续大风不仅会对植物产生破坏作用，还会影响其生长发育；（2）风会最先带走地表细小颗粒，从而导致土壤质地变粗、水分下降、营养成分重新分配；（3）风引起地表边界层和大气边界层物质和能量的转移和交换，热量和水汽的交换导致地表微气候发生变化，如风速降低会导致地表温度升高；（4）风力作用使得土壤水分亏缺、营养成分变化，导致草原生态系统结构变化、草地覆盖度降低、物种生活型复杂化、耐旱植物增加；（5）大气稳定性、CO2交换速率和碳排放都会随着风速的增加而增加，碳吸收则相反，碳通量也因此发生变化。综上，风速降低对于草原生态系统的影响复杂且利弊相当，未来的发展趋势会更加侧重于以下几个方面的发展：研究对象的多样化、加强控制实验的定量化研究、综合多要素的相互作用机理研究、整体结构和功能性的研究。 Abstract:Under the context of wind-reducing worldwide, researching the effects of wind speed change on grassland ecosystem, which plays an important role in terrestrial ecosystem, has important significances. The experiment results over decades show that:(1) wind speed change impacts plant growth rates and leaf shapes. Appropriate wind speed can improve plant growth and enhance the primary productivity. But strong wind or continuous wind might damage plant; (2)Wind takes away soil fine particles (e.g., silt and clay) from soil surface first, which lead to soil structural change, soil moisture reduction and the redistribution of nutrients; (3)Wind induces the transfer and exchange of materials and energy between land surface and atmosphere, which can change the surface micro-climate. For example, soil surface temperature will rise due to reduced wind; (4) Wind can decrease the soil moisture and change the nutrient component, making grassland ecosystem structure varied, grassland cover decreased, plant life forms complicated and drought-tolerant plants increased; (5) Atmospheric stability, CO2 exchange rate and carbon emission increase with wind speed acceleration. Carbon absorption is the opposite. As a result, carbon flux also changes. Above all, It has its pros and cons for the effect of wind speed decrease on grassland ecosystem. In the future,the study will be more focused on the following aspects:Research object diversification; Quantitative study by strengthening the control of experiment; Comprehensive interaction mechanism of multi factor; the overall structure and functional study. 参考文献 相似文献 引证文献

Early cultivation and bioturbation cause high long-term soil erosion rates in tropical forests: OSL based evidence from Ghana

Soil erosion in forests is often considered negligible or minimal. In some tropical forest ecosystems, however, the combination of continuous surface exposure of fine soil particles at the upper slope by soil macrofauna and episodic precipitation can cause considerable downslope soil transport, and the introduction of slash and burn agriculture is often found to speed up soil erosion even more. Here we, for the first time, use OSL dating to quantify the long-term soil erosion rate along a hillslope in the moist semi-deciduous forest zone of Ghana. During the last ~4–5000years about 100cm of sediment has accumulated at an approximately constant rate of ~0.13–0.21mmyear−1 (1.95–3.15tha−1year−1). This is about an order of magnitude higher than literature estimates from similar environments, primarily obtained using short-term experimental setups; this suggests that care should be taken when extrapolating short-term erosion estimates to centennial or millennial timescales. We further deduce that an apparent acceleration in erosion began ~4500years ago. This may be due to the introduction of cultivation in the area, slightly earlier than previously suggested (2800–3500years ago). In this case the erosion rate based on deposition below 100cm (~0.05mmyear−1) can be taken to represent the (natural) erosion rate without human influence; this value is consistent with literature estimates. More retrospective studies of soil erosion rates are needed in order to confirm the validity of our methodology and results, as well as to test the reliability of extrapolated short-term erosion estimates.

Co-variation of fine-root distribution with vegetation and soil properties along a revegetation chronosequence in a desert area in northwestern China

This study investigated the changes in the distributions of fine roots and explored their responses to changes in vegetation and soil properties along a 46-year revegetation chronosequence in a desert area in northwestern China. Fine roots and soil samples at depths of 0–3.0m soil profile were obtained from revegetated sand-binding areas and compared with those from moving sand dunes, natural undisturbed vegetated dunes, and a desert steppe. The soil physicochemical properties in the top 0.8m layer were analyzed, and the soil water contents at depths of 0–3.0m soil profile were measured. Redundancy and regression analyses were conducted to explore the relationships between fine roots, vegetation and soil properties. Both the cumulative fine-root length and mass in the 0–0.4m layer and throughout the 0–3.0m profile increased along the revegetation chronosequence, and those of the 1.0–3.0m layer increased up to 29years and then decreased. Additionally, the proportion of fine roots in the 0–0.4m layer increased and the proportion of fine roots from 1.0–3.0m decreased along the revegetation chronosequence. The fine-root length in 0–0.4m layer was mainly influenced by herbaceous cover, while the fine-root mass at depth of 0–3.0m was affected by shrub cover and biomass. The amounts of fine soil particles, soil organic carbon, and total nitrogen were the main edaphic factors that influenced the distribution of fine roots. The fine-root length and mass in the 0–0.4m layer were weakly and positively correlated with soil water contents, while those in the 1.0–3.0m layer had strong negative relations with the soil water contents in corresponding layers. Our results demonstrated that the fine-root distribution in revegetated sand dunes was regulated by the succession of the vegetation-soil system after revegetation.

Glyphosate and AMPA distribution in wind-eroded sediment derived from loess soil

Glyphosate is one of the most used herbicides in agricultural lands worldwide. Wind-eroded sediment and dust, as an environmental transport pathway of glyphosate and of its main metabolite aminomethylphosphonic acid (AMPA), can result in environmental- and human exposure far beyond the agricultural areas where it has been applied. Therefore, special attention is required to the airborne transport of glyphosate and AMPA. In this study, we investigated the behavior of glyphosate and AMPA in wind-eroded sediment by measuring their content in different size fractions (median diameters between 715 and 8 μm) of a loess soil, during a period of 28 days after glyphosate application. Granulometrical extraction was done using a wind tunnel and a Soil Fine Particle Extractor. Extractions were conducted on days 0, 3, 7, 14, 21 and 28 after glyphosate application. Results indicated that glyphosate and AMPA contents were significantly higher in the finest particle fractions (median diameters between 8 and 18 μm), and lowered significantly with the increase in particle size. However, their content remained constant when aggregates were present in the sample. Glyphosate and AMPA contents correlated positively with clay, organic matter, and silt content. The dissipation of glyphosate over time was very low, which was most probably due to the low soil moisture content of the sediment. Consequently, the formation of AMPA was also very low. The low dissipation of glyphosate in our study indicates that the risk of glyphosate transport in dry sediment to off-target areas by wind can be very high. The highest glyphosate and AMPA contents were found in the smallest soil fractions (PM10 and less), which are easily inhaled and, therefore, contribute to human exposure.

Relationships between Artemisia ordosica communities and environmental factors following sand-dune stabilization in the Mu Us desert, northwest China

Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis (CCA) to examine the relationships between A. ordosica communities and environmental factors at three habitats: semi-fixed dune (SF), fixed dune with low-coverage biological soil crust (F), and fixed dune with high-coverage biological soil crust (FC) in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vegetation–environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0–20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs.

Briefing: Laboratory permeability determinations for biosolids

Biosolids/sewage sludge materials are the residue by-products of municipal wastewater treatment. Drainage of biosolids storage facilities is a critical aspect of their design. Laboratory permeability tests are widely performed for economical and practical reasons. Reported laboratory coefficient of permeability (k) values for these materials suggests very/extremely low permeability. However, limited field data reported for sewage sludge material would tend to suggest significantly greater k values. This briefing article explores issues related to the water permeability (filter size) of the porous media (discs) in contact with the specimen drainage boundaries during laboratory consolidation and permeability testing of biosolids/sewage sludge materials. These include clogging of their pores by fine soil particles and biogenic gas bubbles, bio-clogging, and the increase in viscosity of the pore liquid remaining within the test specimen due to filtering action. In applications where rates of flow (and consolidation) are measured, their effect can be to produce misleading results, potentially by many orders of magnitude. Recommendations on laboratory consolidation and permeability testing, including selection and verification of appropriate porous media, are presented. Issues relating to the analysis and interpretation of experimental consolidation data are discussed, with caution urged on the use of classical consolidation theory for these difficult and unconventional geomaterials.

Linking selected soil properties to land use and hillslope - A watershed case study in the Ethiopian Highlands

Deforestation of native forests for crop production in the Gumara-Maksegnit watershed, located in the Lake Tana basin, Ethiopia, dramatically increases the vulnerability of the soil for rainfall driven erosion. Hence, the central task of the study is to investigate general links of land-use and topography related to selected soil properties. The 53.7 km2 watershed was divided into a 500 × 500 m square grid to sample bulk density (ρd), pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), and texture of topsoil. Such properties were investigated with respect to the two main land-uses, forest and agriculture, and three different slope steepness classes, 0-10%, 10-30%, > 30%. Descriptive statistics and correlation analyses were undertaken to explore potential dependencies of the obtained soil parameters according to land-use and slope steepness. The study indicates higher SOC, TN, silt and sand content in forest soils compared to agricultural soils, while solely ρd is lower in the forest soil. Overall increases of SOC, TN, silt, and sand content from the gentle to the steep slopes have been observed for both land-uses. In contrast, clay content and ρd seem to increase from steep to gentle slopes on agricultural areas, which might be due to accumulation of particularly fine soil particles eroded from the steep areas. Basic correlations valid for all land-uses and slope steepness classes have not been detected. Nevertheless, the study suggests slope steepness as a tool to assess the potential drivers of soil depletion in the Ethiopian Highlands.

Modeling of Particle Migration in Porous Media: Application to Soil Suffusion

The suffusion phenomenon occurs when fine soil particles are detached by seepage flow and transported away from the matrix. This process is one of the main causes of failure of hydraulic structures and road embankments. This study aimed to build a numerical model for simulating the particles suffusion within a porous medium. This model combines a flow law and an erosion equation related to the evolution of soil porosity. In addition the dispersion and the deposition kinetics processes of eroded particles were combined with detachability process. The equations describe the evolution of the instantaneous concentration of the fluidized solid, and the variation of eroded mass. Sensitivity analysis allows highlighting the influence of the different parameters on suffusion, particularly that deposition kinetics starts acting only below a threshold of hydraulic gradient and beyond a given sample length. The adjustment results indicate that the suffusion process is strongly related to hydraulic conditions, physical soil characteristics and pore water chemicals. The comparison of numerical results with experimental data from laboratory tests provides a quite good agreement.

Heavy metal contamination characteristic of soil in WEEE (waste electrical and electronic equipment) dismantling community: a case study of Bangkok, Thailand.

Sue Yai Utit is an old community located in Bangkok, Thailand which dismantles waste electrical and electronic equipment (WEEE). The surface soil samples at the dismantling site were contaminated with copper (Cu), lead (Pb), zinc (Zn), and nickel (Ni) higher than Dutch Standards, especially around the WEEE dumps. Residual fractions of Cu, Pb, Zn, and Ni in coarse soil particles were greater than in finer soil. However, those metals bonded to Fe-Mn oxides were considerably greater in fine soil particles. The distribution of Zn in the mobile fraction and a higher concentration in finer soil particles indicated its readily leachable character. The concentration of Cu, Pb, and Ni in both fine and coarse soil particles was mostly not significantly different. The fractionation of heavy metals at this dismantling site was comparable to the background. The contamination characteristics differed from pollution by other sources, which generally demonstrated the magnification of the non-residual fraction. A distribution pathway was proposed whereby contamination began by the deposition of WEEE scrap directly onto the soil surface as a source of heavy metal. This then accumulated, corroded, and was released via natural processes, becoming redistributed among the soil material. Therefore, the concentrations of both the residual and non-residual fractions of heavy metals in WEEE-contaminated soil increased.

Effects of toposequence and land use-land cover on the spatial distribution of soil properties

Topographic properties can influence pedogenic processes, soil profile depth and spatial variations of soil properties. The objectives of this study were to determine the spatial variation of soil properties at different slope positions and land use-land cover and also the relationships among soil properties, slope and land use-land cover. The study area was divided into five topographic positions by an elevation transect from 935 to 1370 m. These positions were shoulder, flat plateau-1, flat plateau-2, lower back slope, and toe slope which were sampled at 10 × 20 m grid size. A total of 500 soil samples were collected from 0 to 20 cm depth. Soil properties showed significant variation among slope positions and land use-land cover type when analysed with ANOVA and post hoc multiple comparison tests. Slope was responsible for large discrimination effects compared to land use-land cover. It was also the main factor contributing to the transportation and accumulation of fine soil particles when soil organic matter content and water stable aggregates amount were low. Moreover, different land use-land cover type affected soil organic matter content and water stable aggregate amount and caused significant variance in them. Overall, the spatial variability of soil physico-chemical properties was strongly affected by pedogenic factors, slope and land use.

Iodine isotopes in precipitation: Four-year time series variations before and after 2011 Fukushima nuclear accident

Rainwater samples were collected monthly from Fukushima, Japan, in 2012–2014 and analysed for 127I and 129I. These are combined with previously reported data to investigate atmospheric levels and behaviour of Fukushima-derived 129I before and after the 2011 nuclear accident. In the new datasets, 127I and 129I concentrations between October 2012 and October 2014 varied from 0.5 to 10 μg/L and from 1.2 × 108 to 6.9 × 109 atoms/L respectively, resulting in 129I/127I atomic ratio ranges from 3 × 10−8 to 2 × 10−7. The 127I concentrations were in good agreement with those in the previous period from March 2011 to September 2012, whereas the 129I concentrations and 129I/127I ratios followed declining trends since the accident. Although 129I concentrations in five samples during the period of 2013–2014 have approached the pre-accident levels, 129I concentrations in most samples remained higher values in winter and spring-summer. The high 129I levels in winter and spring-summer are most likely attributed to local resuspension of the Fukushima-derived radionuclide-bearing fine soil particles deposited on land surfaces, and re-emission through vegetation taking up 129I from contaminated soil and water, respectively. Long-term declining rate suggests that contribution of the Fukushima-derived 129I to the atmosphere would become less since 2014.

Climate, soil texture, and soil types affect the contributions of fine-fraction-stabilized carbon to total soil organic carbon in different land uses across China

Mineral-associated organic carbon (MOC), that is stabilized by fine soil particles (i.e., silt plus clay, <53 μm), is important for soil organic carbon (SOC) persistence and sequestration, due to its large contribution to total SOC (TSOC) and long turnover time. Our objectives were to investigate how climate, soil type, soil texture, and agricultural managements affect MOC contributions to TSOC in China. We created a dataset from 103 published papers, including 1106 data points pairing MOC and TSOC across three major land use types: cropland, grassland, and forest. Overall, the MOC/TSOC ratio ranged from 0.27 to 0.80 and varied significantly among soil groups in cropland, grassland, and forest. Croplands and forest exhibited significantly higher median MOC/TSOC ratios than in grassland. Moreover, forest and grassland soils in temperate regions had higher MOC/TSOC ratios than in subtropical regions. Furthermore, the MOC/TSOC ratio was much higher in ultisol, compared with the other soil types. Both the MOC content and MOC/TSOC ratio were positively correlated with the amount of fine fraction (silt plus clay) in soil, highlighting the importance of soil texture in stabilizing organic carbon across various climate zones. In cropland, different fertilization practices and land uses (e.g., upland, paddy, and upland-paddy rotation) significantly altered MOC/TSOC ratios, but not in cropping systems (e.g., mono- and double-cropping) characterized by climatic differences. This study demonstrates that the MOC/TSOC ratio is mainly driven by soil texture, soil types, and related climate and land uses, and thus the variations in MOC/TSOC ratios should be taken into account when quantitatively estimating soil C sequestration potential of silt plus clay particles on a large scale.

Chemical compositional changes in archaeological human bones due to diagenesis: Type of bone vs soil environment

Diagenesis in human remains is a subject of growing interest due to the increase in bone chemical studies to reconstruct pre- and post-mortem features in archaeological and forensic sciences. The efforts made during the last decades have solidified our understanding of diagenetic processes; however, their high complexity demands more research to address them empirically, specifically considering factors such as types of soil substratum and skeletal element. In this work, a geochemical study of human remains from the archaeological site of A Lanzada (NW Spain) is performed to understand diagenesis (i.e. chemical alteration) and life environmental exposure. Three types of bone (thoracic, long and cranial) from 30 skeletons of two periods (9 Roman, 21 post-Roman) were analysed by X-ray fluorescence. Bones were recovered from burials located in slightly alkaline (Haplic Arenosol (calcaric)) and acidic (Cambic Umbrisol (humic)) soils. Principal components analysis was applied to extract the main chemical signatures, and analysis of variance to determine the influence of different factors.Bone composition was characterized by four chemical signals related to: i) alteration of bone bioapatite; ii) metal sorption from the soil solution; iii) presence of fine (silt–clay) soil particles; and iv) lead incorporation. Thoracic bones were found to be more sensitive to diagenesis and the burial environment; long bones and crania presented a similar response. Skeletons buried in the acidic soil were significantly poorly preserved. Lead content was higher in bones of the Roman period, which seems to be related to pre-mortem conditions. Previous investigations on palaeopollution in NW Spain enable us to hypothesize that Roman individuals may have been subjected to a high exposure of Pb due to elevated atmospheric metal contamination.

Discussion of “Drained Monotonic Responses of Suffusional Cohesionless Soils” by Lin Ke and Akihiro Takahashi

The authors have published many valuable articles related to suffusion and internal instability. In the paper under discussion, binary mixtures were made of Silica No. 3 (as a soil skeleton in the mixture) and Silica No. 8 (as the erodible fine grains) to investigate the effect of suffusion on their properties. Three mixtures were prepared, namely mixtures with 15, 25, and 35% fine grains (Silica No. 8). A simple discussion is presented here related to the mixture with 35% (FC 1⁄4 35%) which exceeds the maximum value of FC. Suffusion is related to bimodal soil structure, or is sometimes called clast-supported soils, where the soil has a main soil skeleton, composed of coarser particles, which carries all or most of the external loads; among the voids of these particles, there are fine loose particles under low or no stresses, as shown in Fig. 1(a). For a certain coarser skeleton, the amount of fine grains is important. If the fine grain content is increased beyond a certain level, the coarser particles would lose their contacts among each other; resulting in what is called a matrix-supported structure, as shown in Fig. 1(b). In another words, in a clast-supported structure, there is a shortage of fines, while in a matrix-supported structure, there is an excess of fines (Vaughan 1994). Provided that the diameter of the fine particles is smaller than the diameter of the pore throat, suffusion would occur if amount of fine soil particles is less than that is required to fill the voids of the main soil skeleton, Wan and Fell (2008). In contrast, soils with a matrix-supported structure have no susceptibility to undergo suffusion because the coarser particles cannot create a load-bearing roof through which finer particles can be washed out by the seepage forces (Ronnqvist 2010). Indraratna et al. (2011) suggested Eq. (1) to determine the maximum weight of fine soil grains that fill the voids of the main soil skeleton, Wlmax Wlmax 1⁄4 ec 1þ el Wc ð1Þ

The impact of soil and climatic factors on forest growth

This preliminary study reveals the relations between the forest growth (annual dendromass increment; ADMinc - as dependent variable) and some important soil factors, which have effect on plant growth, such as: groundwater level (GWL), groundwater composition (GWC), plant available water capacity (PAWC), depth of humus layer, texture (hyi) and pH of the soil, moreover the maximum concentration (MAX) of salt and CaCCb and the depth of its MAX in the soil profile. 17 plantations (Poplar, Common oak and Black locust) are included in the analysis investigated all over the Great Hungarian Plain. Correlation profile of the above parameters was created explaining that two abiotic parameters limit plant growth: if GWL is deeper than 5 m and if HCO3 concentration in groundwater is high (above 15 meq/L). Within the tested range (0.17 - 2.23 mS/cm for electrical conductivity (EC) and 0.5 /sand/ - 4.21 /clay loam/ for hyi), the higher magnitude of EC results in higher ADMinc and the higher hyi (higher proportion of fine soil particles) leads to higher ADMinc The positive relationship of ADMinc with EC suggests good nutrient supply of the soil, while the higher proportion of fine particles refers to better water management properties. Thickness of humus layer is an important soil factor: compared to shallow humus layer, deep one increases ADMinc exponentially. In case of Black locust, PAWC is the substantial factor for growing, unlike Poplar, whose growth depends on groundwater uptake (GWU). This phenomenon originates from the differences between the individual needs of the tree species and differences in root morphology. Merely 4 sampling plots were equipped with meteorological stations, thus the number of climatic parameter data were not enough for statistical analysis. So data for all 17 plots were collected from literature and a general, regionally calculated data were applied (mean rainfall in the vegetation period and aridity index). There was no significant correlation between climatic parameters and ADMinc Further studies and more field investigations are needed in order to clarify the results.

Simulating the role of gravel in freeze–thaw process on the Qinghai–Tibet Plateau

Soils containing gravel (particle size ≥2 mm) are widely distributed over the Qinghai–Tibet Plateau (QTP). Soil mixed with gravel has different thermal and hydrological properties compared with fine soil (particle size <2 mm) and thus has marked impacts on soil water and heat transfer. However, the most commonly used land models do not consider the effects of gravel. This paper reports the development of a new scheme that simulates the thermal and hydrological processes in soil containing gravel and its application in the QTP. The new scheme was implemented in version 4 of the Community Land Model, and experiments were conducted for two typical sites in the QTP. The results showed that (1) soil with gravel tends to reduce the water holding capacity and enhance the hydraulic conductivity and drainage; (2) the thermal conductivity increases with soil gravel content, and the response of the temperature of soil mixed with gravel to air temperature change is rapid; (3) the new scheme performs well in simulating the soil temperature and moisture—the mean biases of soil moisture between the simulation and observation reduced by 25–48 %, and the mean biases of soil temperature reduced by 9–25 %. Therefore, this scheme can successfully simulate the thermal and hydrological processes in soil with different levels of gravel content and is potentially applicable in land surface models.

Multiscale effects on biological soil crusts cover and spatial distribution in the Monte Desert

Biological soil crusts (BSC) play diverse roles in arid and semi-arid ecosystems such as increasing soil fertility and reducing soil loss due to aeolian and hydric erosion, but they are very sensitive to disturbances. These attributes point to the relevance of BSC for soil conservation and restoration. In order to use BSC for restoration of degraded soils, we need to understand the ecological drivers of BSC. In this study, we analyzed the effect of environmental factors on BSC cover at different spatial scales in the central Monte Desert (Argentina), including landform, slope, aspect, vascular plants, and disturbance intensity. We evaluated the effects of different factors with linear mixed effect models, comparing the adjustment of models of different complexity, which included different number of factors. First, at the landscape scale, we analyzed BSC cover in two geomorphological units with different soils, topography, and vegetation. BSC cover was higher in the old riverbed, which has a higher proportion of fine clay soil particles, than in the aeolian plain. Disturbance effects were apparent in the old riverbed, showing increasing BSC cover at higher distances from settlements, and BSC located both, under and outside plant canopies. At the mesoscale, we found no differences of BSC cover in dune flanks and inter-dune valleys of the aeolian plain. Finally, at the microscale, BSC patches of higher surface cover were found in association with vascular plants (Larrea divaricata, Bulnesia retama, Lycium sp.), on mounds, and in microsites of southern exposure and high slopes. Our findings suggest that BSC develop preferentially associated with vascular plants, which generate mounds and sloped microsites with southern exposure, where lower irradiances reduce desiccation in these extremely dry environments.

Experimental Study on Suffusion of Gravelly Soil

Although internal erosion causes serious hazards to embankments and dams, studies on the emission of fine soil particles and the development of non-uniform penetration of the soil foundation after suffusion do not go far enough. Given that suffusion development is random and complex, this study employed self-designed equipment to conduct tests under specific conditions. Twelve samples with three different pore size distributions were used to make a comparative analysis on aspects such as piezometric head, flow rate, coefficient of permeability, trend of fine particles, and accumulated sand emissions. Furthermore, the coefficient of permeability, void ratio, movement trend of fine particles in samples, and changes in content of the remaining fine particles were studied. Combined with theoretical calculations, correlations among the movement trend of fine particles in the samples, content of remaining fine particles and uneven changes in the permeability coefficient were shown. Using the relationship between permeability and porosity, we derived a theoretical formula was deduced from the changing amount of accumulated sand emissions over time under fixed upstream total head.