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Based on the perspective of flight technology and flight safety, the unsaturated clayey foundation soil of a high plateau airport in the mountainous area of southwest China is taken as the research object, and the calculation method of the composite modulus of CFG pile composite foundation with the soil between the piles as the unsaturated soil is established according to the relevant characteristics of unsaturated soil, and the calculation method of the composite foundation's settlement is carried out on the basis of this method. At the same time, Plaxis finite element analysis software is used to model the actual project and numerically analyze the settlement characteristics of the composite foundation. Finally, the calculation results of the two methods are compared and studied with the actual settlement monitoring values on site. The study shows that: 1) the theoretical analysis method is able to consider the effects of pile length, pile modulus, and matrix suction in unsaturated soil of rigid piles on the composite modulus, which is more in line with the reality than the conventional composite modulus method that does not consider the unsaturated nature of the soil between the piles; 2) the resultant values computed by the theoretical and numerical analysis methods recommended in this paper are both smaller than those measured at the site but the difference is within the range of 10%, so that in the actual plateau of the High Plains airports can choose the two analysis methods recommended in this paper to conduct related research. [ABSTRACT FROM AUTHOR]

Soil properties are crucial in forest ecological management and rare vegetation protection. In this study, Fanjing Mountain, a typical subtropical forest, was used to investigate and analyze the differences in soil properties and climate change characteristics of Fanjing Mountain in 1982 and 2014. Then redundancy analysis was used to analyze the influence of climate factors on soil properties. The results showed that: 1) Compared to 1982, the soil properties of Fanjian Mountain changed significantly in 2014. The soil texture evolved from a silty loam in 1982 to a silty clay loam in 2014. There was a significant increase in soil clay particles. In addition, the soil showed acidification, weakened cation exchange capacity, and relatively stable soil total nitrogen but significant loss of soil organic matter and total phosphorus nutrients. 2) In the past 32 years, the environmental climate of Fanjing Mountain has shown the characteristics of increasing annual average temperature and annual rainfall, frequent extreme temperature, widening the annual temperature range and decreasing annual relative humidity. 3) Soil type and maximum annual temperature have a highly significant effect on the evolution of soil properties, while annual rainfall and slope orientation significantly affect the evolution. Conclusion: The evolution of soil properties in subtropical forests is dominated by their type differences and climate warming. [ABSTRACT FROM AUTHOR]

Natural source zone depletion (NSZD) is the main process of LNAPL (Light Non-Aqueous Phase Liquid) removal under natural conditions. The NSZD rates assessed ranged from 0.55 to 11.55 kg·m−2·a−1 (kilograms per square meter per year) in previous studies. However, most of these data were obtained from sandy sites, with few clayey sites. To gain knowledge of NSZD in clayey soil sites, the study assessed the NSZD of a petroleum hydrocarbon-contaminated clayey soil site in China, combining the concentration gradient method with metagenomic sequencing technology. The results show that the abundance of methane-producing key enzyme mcrA gene in the source zone was more abundant than in background areas, which suggests that there was methanogenesis, the key process of NSZD. The concentration gradients of oxygen and carbon dioxide existed only in shallow soil (<0.7 m), which suggests that there was a thin methane oxidation zone in the shallow zone. The calculated NSZD rates range from 0.23 to 1.15 kg·m−2·a−1, which fall within the moderate range compared to previous NSZD sites. This study expands the knowledge of NSZD in clayey soil and enriches the attenuation rate data for contaminated sites, which is of significant importance in managing petroleum contaminants. [ABSTRACT FROM AUTHOR]

• Calibration of red clay with different water contents based on EDEM software. • The Hertz-Mindlin with JKR Cohesion model was used to model red clay soil's physical properties. • Experimental studies provide insights into the impact of soil moisture content on its properties. • Technical references for future research on soil-tool interactions were provided. Distinct physical properties of red clay soil in hilly and mountainous regions of southwest China, including high adhesiveness and density, challenge the operation of agricultural machinery. A scarcity of accurate discrete element simulation parameters for this soil type restricts computational modeling. The study was focused on red clay soil with a moisture content of 12.50% ± 1% and a measured repose angle of 35.54°. The soil's inherent physical properties were identified through experimental assessments. Soil contact mechanical parameters were obtained from the GEMM database, and optimal contact parameter ranges were determined using Steepest Ascent Experiments, with the simulated soil particle repose angle serving as the response value. A second-order regression model was developed using a quadratic regression rotation orthogonal combination test. By taking the actual repose angle as the optimization criterion, parameters were optimized. The optimal contact mechanical parameters in EDEM simulations were identified as: JKR surface energy at 8.981 J/m2, recovery coefficient at 0.474, dynamic friction coefficient at 0.196, and static friction coefficient at 0.45. The model yielded a repose angle of 36.21°, closely corresponding with the observed value, with a relative error of 1.80%. The parameters calibrated in this study offer a valuable reference for future soil-tool interaction studies and tillage implement optimization in these regions. [ABSTRACT FROM AUTHOR]

The Mg isotopic compositions of siliciclastic components (δ26Mgsili) of sediments and sedimentary rocks have been commonly used to constrain the intensity of continental weathering, based on observations of, (1) an upward enrichment of 26Mg in modern weathering profiles, (2) preferential uptake of 26Mg in soil clays, and (3) general positive correlations between weathering intensities and δ26Mgsili values. However, not all weathering profiles display an upward increase of δ26Mgsili, and not all soil clays enrich in 26Mg, complicating the interpretations of δ26Mgsili data of sediments and sedimentary rocks. To further explore the controls of δ26Mgsili of sediments and sedimentary rocks, here we measured δ26Mgsili, mineralogical compositions and major element compositions of deep sea sediments from South China Sea (SCS) and carbonate rock samples from two late Paleozoic sections in South China. Carbonate samples show decreasing trends of both normalized Mg concentration (Mgnorm) and δ26Mgsili values with the increase of weathering intensity, while SCS sediments samples do not show any correlation between Mgnorm or δ26Mgsili values and weathering intensity. A three-stages weathering model is developed to explain the observed Mgnorm and δ26Mgsili data. In the new model, weathering can be divided into three stages, (1) the preliminary weathering stage characterized by dissolution of primary minerals and formation of secondary clay minerals in saprolite, (2) the transitional stage with massive vermiculite and chlorite formation on the bottom of soil, and (3) the advanced stage showing dissolution of vermiculite and chlorite in the top of soil. The new model explains an δ26Mgsili increase and Mgnorm decrease with an increase weathering intensity in preliminary weathering stage and decrease of Mgnorm and δ26Mgsiliwith increase weathering intensity in advanced weathering stage. The revised weathering model warrants the application of Mg isotope in the study of continental weathering in deep time. [ABSTRACT FROM AUTHOR]

Soil salinization affects more than 25% of land globally. Subsurface pipe drainage is known for its effectiveness in improving saline–alkali land. The red clay layer (RCL) hinders soil improvement in the Hetao Irrigation District of Inner Mongolia, China. The soil water and salt migration rules at different buried depths and RCL were studied based on the field subsurface pipe drainage test and simulation using the DRAINMOD-S model (Version 6.1). The following implications can be drawn from the results: (1) Although the RCL affected the accuracy of the model, the calibrated statistical results met the application requirements, and the DRAINMOD-S model can be used to analyze subsurface pipe drainage under different distribution conditions of the RCL. (2) The RCL can reduce the drainage efficiency of the subsurface pipe, specifically when the distribution is shallow. (3) The soil desalting rate increased with an increase in the buried depth of the subsurface pipe. The desalination effect of shallow soil was better than that of deep soil. The RCL reduced the drainage and salt removal efficiency of the subsurface pipe. Burying the subsurface pipe as far above the RCL as possible should be considered. Thus, it is feasible to apply the DRAINMOD-S model to relevant studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil silt/clay and nutrients increased with increasing distance from the shelterbelt. • Downslope deposition lead to an increase in plow pan thickness and a decrease in bulk density. • Erosion rate was primarily affected by shelterbelt distance, followed by elevation. • Sites closer to shelterbelt warrant particular attention due to coarse-texture materials. Soil erosion is the most severe form of land degradation globally. Farmland shelterbelts are important for reducing erosion, especially erosion caused by the co-occurrence of water and wind. However, few studies have focused on how the distance from the shelterbelt associated with farmland topography affects the redistribution of soil quality indicators. The aims of this study is to reveal the relative importance of these two factors to soil quality under typical wind and water erosion conditions concurrent with the Songnen Plain, China. Topsoils (0–10 cm) were sampled at seven distances from the shelterbelt with three replicates, where topography heterogeneity was also considered. We found that the silt/clay content and soil nutrients at sites farther from the shelterbelt were significantly greater than those at sites closer to the shelterbelt (P < 0.05). Similarly, deposition was dominant at sites farther from the shelterbelt and downslope positions, while erosion was dominant at sites closer to the shelterbelt and upslope positions. Moreover, we discovered that the relative influence of distance from the shelterbelt and farmland elevation varied with individual soil quality indicators. Soil nutrients increased through the deposition of more fine-textured soil (silt/clay) positions farther from the shelterbelt. The downslope region responds to soil deposition by enhancing the plough pan thickness and lowering the bulk density and pH. Overall, distance from the shelterbelt and farmland elevation had interactive effects on soil quality, and erosion was primarily affected by distance from the shelterbelt (63.4 %), followed by elevation (22.7 %). Furthermore, the sites closer to the shelterbelt (i.e., 20 to 420 m) warrant particular attention due to the deposition of coarse-texture materials here. This work is crucial for an improved understanding of the synergistic effects of long-term water and wind co-occurrence on soil quality evolution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stream power and soil clay content were used to model soil erosion rate. • Sediment sorting and transport were controlled by the soil properties. • A linear function was developed to quantify the sediment clay content. • The relative contributions of different transport mechanisms were quantified. Understanding the sediment sorting and transport processes is is crucial for enhancing the understanding of soil erosion mechanisms and improving soil erosion prediction. However, quantitative studies based on the coupling effects of both hydraulic parameters and soil properties are still lacking. In this study, five loessial soils with varying physicochemical properties were collected in the Loess Plateau of China, and simulated rainfall experiments were carried out in a metal box with a slope of 20 degrees under rainfall intensities of 1, 1.5, and 2 mm min−1. Runoff samples were collected to analyze the variation in erosion rates and effective particle size distribution of eroded sediments during the rainfall process. The results showed that the stream power was the optimal parameter to model the erosion rate, and a power function incorporating the clay content and stream power could well predict the erosion rate of different soils. The enrichment ratio indicated the enrichment of fine particles and depletion of coarse particles. And the sediment sorting degree increased with increasing soil clay content. The critical particle size for distinguishing different transport mechanisms varied among soils, with more than 55.46 % of the total sediment transported by suspension/saltation. A linear function and power function including the original soil particle size distribution and stream power were developed to quantify the sediment clay content and the relative contribution of different transport mechanisms. This study could be helpful to improve the soil erosion prediction model and provide basic guidelines for regional soil and water conservation. [ABSTRACT FROM AUTHOR]

• Patchiness caused significant reduction of SOC and TN stocks. • Reduced vegetation input and increased erosion output accounted for SOC and TN loss. • Grasslands with high patchiness had a great potential for C and N sequestration. Patchiness acts as an indicator of terrestrial ecosystem degradation and can lead to considerable loss of soil organic carbon and total nitrogen. However, quantitative assessments of the effects of patchiness on soil organic carbon and total nitrogen stocks and their associated mechanisms remain limited. This study aimed to explore the influence mechanisms of patchiness on soil organic carbon and total nitrogen stocks and to project the quantitative contribution of the further expansion of patchiness and vegetation recovery. Soil properties, soil organic carbon and total nitrogen stocks were investigated using a combination of field sampling and aerial photography in four grassland types, alpine meadow, alpine steppe, temperate grassland, and desert grassland, at 47 sites in northwestern China. Soil organic carbon and total nitrogen densities in the bare patches were 34–54 % and 23–41 % lower, respectively, compared to the original vegetation. At the plot-scale, current soil organic carbon and total nitrogen stocks ranged from 30.85 to 77.80 T/ha and 3.26 to 10.19 T/ha, respectively, across grassland types; with a 10–27 % and 7–24 % potential loss of soil organic carbon and total nitrogen stocks, respectively, from the further expansion of patchiness but a 10–50 % and 9–37 % potential increase in soil organic carbon and total nitrogen stocks, respectively, from vegetation recovery. Soil organic carbon and total nitrogen stocks were positively correlated with vegetation biomass, soil clay content, and precipitation (p < 0.001), whereas they were negatively correlated with patchiness (p < 0.001). In summary, patchiness reduced soil organic carbon and total nitrogen stocks by decreasing vegetation inputs and increasing erosion outputs, while vegetation recovery showed potential for increasing carbon and nitrogen stocks. Our results highlight that maintaining intact vegetation cover is critical for preserving terrestrial ecosystem carbon and nitrogen storage. [ABSTRACT FROM AUTHOR]

Knowledge of soil organic carbon (OC) components and enzyme activities is essential to maintain soil health and for sustainable land use during long-term vegetation restoration. The effects of vegetation restoration on soil physicochemical properties have been widely documented; however, knowledge of the relationships among soil OC components, enzyme activities, and soil properties in restored ecosystems remains unclear. Here, the soil from four successional stages of restored Robinia pseudoacacia vegetation (10, 20, 30, and 40 years) were sampled in China's Loess Plateau. The soil water content (SWC), bulk density (BD), pH, total nitrogen (TN), soil microbial biomass C (MBC) and N (MBN) contents, OC components (labile and recalcitrant OC), and soil enzyme (hydrolytic and oxidase) activities were measured. We found that restoration time significantly affects soil physicochemical properties, OC components and enzyme activities. Across the restoration time, the SWC decreased from year 10 to year 30, then increased from year 30 to year 40. Soil OC and TN increased with restoration time, while soil clay content decreased with restoration time. Following 40 years of restoration, soil MBC and MBN significantly increased by 214% and 88%, respectively. For OC components, 40 years of restoration significantly increased recalcitrant C component rather than labile C component. Soil hydrolytic enzyme activities significantly increased by 76.9% and 80.3% in 40 years stand compared with that of in 10 years stand, respectively, while soil oxidase enzyme activities significantly decreased with restoration time. Correlation analysis demonstrated that the SOC and MBC content significantly influenced soil recalcitrant C component and hydrolytic enzyme activities, while MBC and clay content significantly influenced soil oxidase enzyme activities. These results provided useful insights on the responses of forest restoration on soil OC components and related OC degrading enzymes and the understanding of soil C sequestration in the restored ecosystems in such areas. [ABSTRACT FROM AUTHOR]