Search Results (522)

The Jianggang sand ridges (JSR) in the southwestern Yellow Sea are a radiating tidal sand ridge system that plays crucial roles in ecological preservation, coastal protection, and terrestrial resource supply. Clay and silt fractions constitute important sediment components of the Jianggang sand ridges. In this study, the Sr-Nd isotopes of clay fractions and the Pb isotopes of K-feldspar in the silt fractions, along with their elemental geochemistry, are investigated to reveal the provenance and transport patterns of clay-size and silt-size sediments in the study areas. The results show that in both the clay-size sediments and the K-feldspar of the silt-size sediments, Ba exhibits the highest content, with the ranges of 432.24 μg/g to 531.05 μg/g and 398.02 μg/g to 2822.36 μg/g, respectively. In contrast, Lu shows the lowest abundance (<0.5 μg/g and <0.1 μg/g, respectively). The ⁸⁷Sr/⁸⁶Sr and ε_Nd(0) values of the clay fraction vary from 0.7158 to 0.7265 and from −14.65 to −10.92, respectively. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb of K-feldspar in silt fraction are 17.959~18.429, 15.450~15.689, and 38.066~38.551, respectively. Through the MixSIAR model, it is suggested that the Yangtze River Mouth is the dominant contributor to clay-size sediments in both the onshore and offshore sand ridges (53.9 ± 8.8% and 51.9 ± 8.4%, respectively), followed by the Modern Yellow River Mouth and the Old Yellow River Delta (sum of contributions: <36%). For the silt fraction, the primary sediment sources of the onshore and offshore sand ridges are the Yangtze River Mouth (46.8 ± 5.5%) and the Old Yellow River Delta (42.4 ± 5.3%), while the Modern Yellow River contributes less than 16%. The Northern Chinese Deserts and the Korean rivers make only minor contributions to both fractions. Elemental and isotopic tracers indicate that the silt-size and clay-size sediments derived from the Modern Yellow River are transported southward along the Jiangsu coast by the Subei Coastal Current. Meanwhile, the silt fraction from the Yangtze River Mouth is carried northward along the coast under the influence of the Subei Coastal Current, whereas the clay fraction of it has another longer path, which moves through the central Yellow Sea and migrates southward along the Jiangsu coast to the Jianggang sand ridges under the influence of the Yellow Sea Warm Current. This study enriches the geochemical dataset of the southern Yellow Sea. Full article

Rotational tillage is considered a potential option to improve soil organic carbon (SOC) stock and mitigate climate change. However, the mechanisms underlying SOC sequestration under rotational tillage remain poorly understood due to insufficient data on SOC concentration and mineralization within soil aggregates. A 12-year field experiment was conducted in Northwest China to evaluate the effects of tillage on SOC stocks, soil aggregate stability, aggregate-associated OC concentrations and mineralization. The results showed that rotational tillage had more crop residue and less soil disturbance, thus improving soil aggregate stability, aggregate-associated OC concentrations and SOC stocks. The highest MWD and SOC stocks were found in no-tillage rotated with subsoiling (NS), which were 36.0–69.7% and 16.3% higher than plowing, respectively. Macroaggregates had higher cumulative OC mineralization and lower OC mineralizability, due to physical protection. Rotational tillage treatments with higher soil aggregation contributed to decreasing OC mineralizability and increasing SOC sequestration. Meanwhile, rotational tillage decreased OC mineralization loss, mineralizability, and decomposition rate within microaggregates and silt–clay fractions. Among all treatments, NS treatment had the lowest total OC mineralization, which was lower by 5.94–27.3% than plowing at 0–40 cm depths. Considering soil structure stability, SOC mineralization and sequestration, NS treatment was a promising strategy in semiarid regions. Full article

In the field of smart agriculture, soil property data at the field scale drives the precision decision-making of agricultural inputs such as seeds and chemical fertilizers. However, soil texture has significant spatial variability at the field scale, and traditional remote sensing monitoring methods have certain data intermittency, which limits small-scale prediction research. In this study, based on the Google Earth Engine platform, soil synthetic images were generated according to different time intervals using mean compositing and median compositing modes, image bands were extracted, and spectral indices were introduced; combined with the random forest algorithm, the effects of different compositing time windows, compositing modes, and compositing data types on prediction accuracy were evaluated; and three partitioning strategies based on crop growth, soil synthetic image brightness, and soil type were adopted to conduct local partitioning regression of soil texture. The results show that: (1) The use of mean compositing of multi-year May images from 2021 to 2024 can improve prediction accuracy. When this method is combined with the “band reflectance + spectral indices” dataset, compared with other compositing methods, the R² of clay particles, silt particles, and sand particles can be increased by 8.89%, 9.50%, and 2.48% on average. (2) Compared with using only image band data, the introduction of spectral indices can significantly improve the prediction accuracy of soil texture at the field scale, and the R² of clay particles, silt particles, and sand particles is increased by 4.58%, 3.43%, and 4.59% on average, respectively. (3) Global regression is superior to local partitioning regression; however, the local partitioning regression strategy based on soil type has good accuracy performance. Under the optimal compositing method, the average R² of soil particles of each size fraction is only 1.08% lower than that of global regression, which has great application potential. This study innovatively constructs a comprehensive strategy of “moisture spectral indices + specific compositing time window + specific compositing mode + soil type partitioning”, providing a new paradigm for soil texture prediction at the field scale in Northeastern China, and lays the foundation for data-driven water and fertilizer decision-making. Full article

The issue of formulating scientifically sound standards for mercury (Hg) content in Arctic soils is becoming increasingly pertinent in view of the rising human impact and climate change, which serve to augment the mobility of Hg compounds and their involvement in biogeochemical processes. In the absence of uniform criteria for regulating Hg concentrations, it is particularly important to determine its geochemical baseline values and the factors that determine the spatial and vertical distribution of the element in the soil profile. The study conducted a comprehensive investigation of Hg content and patterns of its distribution in various types of tundra soils in the European North-East of Russia. The mass fraction of total Hg was determined by atomic absorption spectrometry, and the spatial features of accumulation were analysed using geoinformation technologies. The distribution of Hg in the soils of the tundra zone was found to be distinctly mosaic in nature, determined by the combined influence of organic matter, granulometric composition, and hydrothermal conditions. It has been established that the complex influence of the physicochemical properties of soils determines the spatial heterogeneity of Hg distribution in the soils of the tundra zone. The most effective Hg accumulators are peat and gley horizons enriched with organic matter and physical clay fraction, while in Podzols, vertical migration of Hg is observed in the presence of a leaching water regime. In order to standardise geochemical baseline Hg values, a 95% upper confidence limit (UCL_95%) is proposed. This approach enables the consideration of natural background fluctuations and the exclusion of extreme values. The results obtained provide a scientific basis for the establishment of standards for Hg content in background soils of the Arctic. Full article

Refractory geopolymers derived from aluminosilicate sources and alkaline activation are a promising alternative to traditional fired bricks, particularly when low-cost, waste-derived raw materials are used. This study improves the workability of a refractory brick formulated with clays (Kaolin and Tepozan–Bauwer), seashell waste, sodium silicate, potassium hydroxide, and water by incorporating sodium lignosulfonate (LS) and polycarboxylate (PC) plasticizers. Clays from Comonfort, Guanajuato, Mexico, and seashells were ground and sieved to pass a 100 Tyler mesh. A base mixture was prepared and evaluated using the Mini Slump Test, varying plasticizer content from 0 to 2% relative to the solid fraction. Based on workability, 0.5% LS and 1% PC (by solids) increased the slump, and a blended plasticizer formulation (1.5% by solids, 80%PC+20%LS) produced the highest workability. These additives act through different mechanisms, with LS primarily promoting electrostatic repulsion and PC steric repulsion. Bricks with and without plasticizers exhibited thermal resistance up to 1200 °C. After four calcination cycles, compressive strength values were 354.74 kg_f/cm² for the brick without plasticizer, 597.25 kg_f/cm² for 1% PC, 433.63 kg_f/cm² for 0.5% LS, and 519.05 kg_f/cm² for 1.5% of the 80%PC+20%LS blend. Strength was consistent with changes in porosity and apparent density, and 1% PC provided a favorable combination of high workability and high compressive strength after cycling. Because the cost of clays and seashells is negligible, formulation selection was based on plasticizer cost per brick. Although 1% PC and the 1.5% of 80%PC+20%LS blend showed statistically comparable strength after cycling, 1% PC was selected as the preferred option due to its lower additive cost ($0.0449 per brick) compared with the blend ($0.0633 per brick). Stereoscopic microscopy indicated pore closure after calcination with no visible cracking, and SEM–EDS identified O, Si, and Al as the significant elements, with traces of S and K. Overall, the study provides an integrated assessment of workability, multi-cycle calcination, microstructure, and performance for refractory bricks produced from readily available clays and seashell waste. Full article

Soils represent the largest reservoir of organic carbon (OC) in terrestrial ecosystems, storing approximately 1500 Gt C. Forest and grassland ecosystems contribute 39% and 34% to global terrestrial carbon stocks, with soils holding about 44% and 89% of forest and grassland carbon, respectively. Land-use changes, such as the conversions between forest and grassland ecosystems, can strongly influence soil carbon accumulation, though the direction and magnitude remain uncertain. Comparative data from paired-plot studies of forest and grassland soils are still limited. In this study, we conducted pairwise comparisons of total OC and total nitrogen (TN) stocks in mature forest and climax grassland soils along a climatic and pedogenic gradient encompassing Retisols, Luvisols, and Chernozems. Relationships between OC and TN stocks (0–10 cm) and soil physicochemical properties—OC and TN contents, bulk density, pH, clay content, and humus fractional composition, as well as biological indicators—the abundance of culturable fungi and bacteria, microbial biomass carbon, potential metabolic activity, and activities of laccase and dehydrogenase, were evaluated. Strong positive correlations were found between OC and TN stocks and OC and TN contents (r = 0.62–0.99), pH (r = 0.79–0.81), clay content (r = 0.70–0.87), and the fraction of humic acids bound with calcium (r = 0.73). OC stocks also correlated strongly with dehydrogenase activity (r = 0.85–0.95). At 0–10 cm depth, OC stocks were higher in grassland soils than in forest soils by factors of 1.6–1.7 in Retisols and 1.4–1.5 in Chernozems. Similarly, TN stocks were 1.6–2.0 times greater in grasslands across all soil types. Community-level physiological profiling revealed higher potential metabolic activity in forest soils compared with grasslands, with the strongest differences in Retisols and Luvisols, while contrasts were attenuated in Chernozems. Overall, the results highlight the fundamental role of organo-mineral interactions and calcium binding in OC stabilization, as well as the likely involvement of dehydrogenase activity in the biogenic formation of calcium carbonates that contribute to this process. Full article

The mineral matter in coal has great significance for geological evolution, and clean and fractional utilization. The Laochang mining area is one of the largest anthracite coal production bases in Southern China, and the most important coal energy base in Yunnan province, China. This study investigates the composition and mode of occurrence of mineral matter in the Laochang coals to reveal the sediment provenance, sedimentary environment, and hydrothermal fluids. The predominant minerals in the Laochang coals include oxide (quartz, anatase), clay (kaolinite, illite/smectite mixed layer), sulfide (pyrite, sphalerite), phosphate (xenotime, monazite, goyazite–gorceixite), and carbonate (calcite, dolomite, sideroplesite, siderite). The minerals in the Laochang coals are dominated by quartz (2.4~54.8%) and kaolinite (3.4~39.2%), followed by illite, smectite, muscovite, calcite, pyrite, and anatase. Quartz and dolomite in SB-7+8 coal have the highest proportions, reaching 54.8% and 17.3%. The modes of occurrence of minerals reflect that the Laochang coals are affected by the epigenetic hydrothermal fluids and seawater. The chalcophile elements Hg, Pb, Se, and Cr, and lithophile elements Li, Nb, Ta, Zr, Hf, and REY are slightly enriched in XB-3 coal, which is attributed to the intrusion of seawater and the supply of terrestrial detrital materials, respectively. REY is dominated by LREY, followed by MREY, and a lower level of HREY in the Laochang coals, which have a high fractionation degree. The REY enrichment H-type is influenced by the hydrothermal fluids. Based on the relationship between Al₂O₃ and TiO₂, Al₂O₃/TiO₂ and Nb/Yb, and the negative anomaly Eu, the detrital material in the erosion source area of the Laochang coal is derived from the Emeishan Large Igneous Province basalt and felsic–intermediate rocks. Full article

Glyphosate is the most widely used herbicide in the world for weed control; however, due to lixiviation, wind and runoff effects, an important fraction can reach the soil, aquifers and surface waters, affecting environmental and human health. The behavior of glyphosate in two agricultural soils (C1: silty clay texture, and C2: silty loam texture) was analyzed in this study using a laboratory-scale model. Water transfer was modeled with the Richards equation, while glyphosate transport was modeled using the advection–dispersion equation, with both solved using finite difference methods. The glyphosate dispersion coefficient was obtained from laboratory concentration data derived from the soil profile via inverse modeling using a non-linear optimization algorithm. The goals of this study were to (i) quantify glyphosate retention in soils with different physical and chemical properties, (ii) calibrate a numerical model for the estimation of dispersivity and simulation of short- and long-term scenarios, and (iii) assess vulnerability to groundwater contamination. The results showed that C1 retained a greater amount of glyphosate in the soil profile, while C2 was considered more vulnerable as it liberated the contaminant more easily. The model accurately reproduced the measured concentrations, as evidenced by the RMSE and R² statistics, thus supporting further scenario simulations allowing for prediction of the fate of the herbicide in soils. The approach utilized in this study may be useful as a tool for authorities in environmental fields, enabling better control and monitoring of soil contamination. These findings highlight potential risks of contamination and reinforce the importance of agricultural management strategies. Full article

The characterization and biomedical modification of bentonite clays from the Kalzhat deposit (Kzh), which is situated in Kazakhstan’s Zhetysu region, are the main objectives of this work. In order to improve the raw material’s structural qualities, the montmorillonite fraction was enriched, and coarse impurities were eliminated using the Salo method. The presence of meso- and micropores that guarantee high dispersity and specific surface area, as well as the prevalence of montmorillonite and kaolinite, was all confirmed by physicochemical analysis. Particle size measurements indicated finely dispersed structures with a propensity to aggregate, whereas thermal analysis demonstrated resilience under heating. After effective functionalization with silver nanoparticles, a porous hybrid system with improved surface reactivity was produced. These enhancements demonstrate the modified bentonite’s usefulness as a multifunctional carrier for the immobilization and controlled release of pharmaceuticals, with potential uses in drug delivery systems, antimicrobial coatings, and wound-healing materials. The material has potential use in sorption and environmental protection technologies in addition to its biomedical application. Overall, Kzh’s structural and functional performance is greatly improved by the combination of purification and functionalization with silver nanoparticles, highlighting its promise as a useful element in the development of next-generation polymer–composite systems. Full article

Accurate porosity evaluation is critical for the assessment of continental shale oil reservoirs, yet remains challenging due to complex lithology and significant burial depth variations, as exemplified by the Lianggaoshan Formation in the Sichuan Basin. Conventional fixed-matrix-density models often yield unsatisfactory accuracy in porosity estimation from density logs. This study proposes a variable matrix-density logging method to improve porosity calculation. The approach integrates core X-ray diffraction and lithology scanning logs to convert mineral mass fractions into volumes, constructing a petrophysical model that accounts for crystalline minerals, clay minerals, kerogen, and fluids. A depth-dependent dynamic matrix density model was established by analyzing compaction effects across varying depths. By incorporating this model into the density-log response equation, shale porosity was quantitatively derived. Application to the Lianggaoshan Formation demonstrates that the method reduces the absolute error in porosity estimation by 2.55 porosity units compared to conventional approaches, while also addressing the limitations of NMR-based porosity evaluation in shales. The proposed method provides a reliable, applicable technique for porosity assessment in continental shale reservoirs with similar geological conditions. Full article

Shale reservoirs contain abundant organic matter, pyrite, and clay minerals, making them highly susceptible to fluid-sensitivity damage; consequently, conventional hydraulic fracturing often yields poor stimulation performance, with low fracturing fluid flowback and rapid post-treatment production decline. Oxidative dissolution, however, can significantly alter the physical properties of shale reservoirs and improve stimulation effectiveness. In this study, nuclear magnetic resonance (NMR), contact-angle measurements, and triaxial compression tests are combined to systematically evaluate the effects of oxidative dissolution on the pore structure, wettability, and mechanical properties of Wufeng Formation shale from the Sichuan Basin. Core-flooding experiments with NaClO solutions show that, as the oxidant dosage (pore volume) increases, shale permeability rises by 66.67–266.67% and porosity by 1.79–9.58%, while the hydrophilic surface fraction increases from 5.45% to 61.73%. These changes are accompanied by a steady reduction in rock strength: the compressive strength decreases by up to 57.8%, and the elastic modulus exhibits a non-monotonic response to oxidation. Oxidative dissolution preferentially enlarges micropores, improves pore connectivity, and strengthens water wetness by consuming oil-wet organic matter and pyrite, which also enhances gel-breaking efficiency. Based on the experimental results, a series of characterization models are developed for oxidized shale reservoirs, including quantitative relationships linking porosity to compressive strength, elastic modulus, and contact angle, as well as a model relating oxidant dosage to microscopic pore structure evolution and imbibition enhancement. Overall, the coupled modifications of pore structure, wettability, and mechanical behavior produced by oxidative dissolution synergistically broaden the effective action range of fracturing fluids, promote shale gas desorption, and improve hydrocarbon seepage, providing a theoretical basis and practical guidance for oxidation-assisted stimulation in shale reservoirs. Full article

To investigate the effects of long-term elevated atmospheric CO₂ (eCO₂) on the distribution and stability of soil aggregates and microbial characteristics in wetland soils and to reveal the mechanisms by which eCO₂ influences soil organic carbon (SOC) sequestration, a multi-temporal-scale eCO₂ control experiment was conducted in the Sanjiang Plain wetland with treatments at ambient CO₂ concentration (AC), 550 ppm, and 700 ppm CO₂. Soil aggregate fractionation, phospholipid fatty acid (PLFA) analysis, and redundancy analysis (RDA) were used to analyze changes in aggregate size distribution, stability indices (MWD, GMD), microbial biomass, and community structure. The results showed that eCO₂ significantly affected aggregate size distribution. Both short- and long-term exposure to low-concentration eCO₂ reduced the proportion of large aggregates. Over time, the proportion of silt and clay particles increased, while microaggregates decreased. Although CO₂ concentration did not directly affect MWD and GMD, long-term eCO₂ significantly reduced soil aggregate stability. Microbial biomass and diversity were not sensitive to CO₂ concentration but decreased significantly with prolonged exposure. In contrast, microbial community structure was significantly affected by both CO₂ level and exposure duration. RDA indicated that, under short-term eCO₂, aggregate fractions were positively correlated with microbial biomass, whereas, under medium- and long-term treatments, they were positively correlated with soil physicochemical properties. Macroaggregates were positively correlated with aggregate stability, while microaggregates and silt–clay fractions were negatively correlated—a relationship that strengthened with longer eCO₂ exposure. Thus, long-term eCO₂ altered soil aggregate structure and microbial communities, ultimately influencing SOC stability. These findings provide data and theoretical support for predicting soil carbon stability and ecosystem functioning in wetlands under climate change. Full article

The accurate mapping of soil texture, a key determinant of soil’s hydrological and nutritional behavior, is essential for agricultural drought assessment, yet the application of multi-temporal satellite data for this purpose remains largely unexplored. In this study, we first identified the optimal prediction period by evaluating the performance of single-date imagery (satellite images captured on individual observation dates). Subsequently, dual-phase imagery (DPI) was developed to increase mapping accuracy. Finally, these refined predictions quantified soil texture’s response to drought and its corresponding thresholds. Results demonstrated that: (1) the bare soil period in April provided peak prediction accuracy for all texture fractions (Sand: R² = 0.617, RMSE = 10.21%; Silt: R² = 0.606, RMSE = 8.648%; Clay: R² = 0.604, RMSE = 1.945%); (2) Significant accuracy gain from DPI using April-August imagery fusion (Sand: R² = 0.677, RMSE = 9.386%; Silt: R² = 0.660, RMSE = 8.034%; Clay: R² = 0.658, RMSE = 1.807%); (3) sand content was the most critical factor influencing crop drought stress, with a threshold of 31%. By integrating multi-temporal satellite observations with quantitative drought evaluation for high-resolution soil texture mapping and precision agricultural management in Northeast China’s black soil region. Full article

China possesses abundant tight conglomerate oil resources. However, these reservoirs are typically characterized by low porosity and permeability, high clay mineral content, and complex pore structures, resulting in poor performance of conventional waterflooding development. Challenges including insufficient energy replenishment and high flow resistance ultimately lead to low oil recovery factors. This study systematically investigates surfactant-assisted CO₂ huff-n-puff (SA-CO₂-HnP) for enhanced oil recovery in tight conglomerate reservoirs. For a tight conglomerate reservoir in a Xinjiang block, a fully implicit, multiphase, multicomponent dual-porosity numerical model was established. By integrating pore–throat distributions acquired through high-pressure mercury intrusion with a self-developed MATLAB PVT package, nanoconfinement-induced shifts in the phase envelope were rigorously embedded into the simulation framework. The calibrated model was subsequently employed to conduct a comprehensive sensitivity analysis, quantitatively delineating the influence of petrophysical, completion, and operational variables on production performance. Simulation results demonstrate that compared to conventional CO₂ huff-n-puff, the addition of surfactants increases the cumulative recovery factor by 3.5 percentage points over a 20-year production period. The enhancement mechanisms primarily include reducing CO₂–oil interfacial tension (IFT) and minimum miscibility pressure (MMP), improving reservoir wettability, and promoting CO₂ dissolution and diffusion in crude oil. Sensitivity analysis reveals that injection duration, injection pressure, and injection rate significantly influence recovery efficiency, while soaking time exhibits relatively limited impact. Moreover, an optimal surfactant concentration (0.0003 mole fraction) exists; excessive concentrations lead to diminished enhancement effects due to competitive adsorption and pore blockage. This study demonstrates that SA-CO₂-HnP technology offers favorable economic viability and operational feasibility, providing theoretical foundation and parameter optimization guidance for efficient tight conglomerate oil reservoir development. Full article

Triaxial suction-controlled relaxation tests were performed on unsaturated reticulated red clay from a highway cut slope to quantify the coupled influence of matric suction (50–200 kPa), net confining pressure (100–300 kPa), and axial strain (2–8%) on time-dependent stress decay. The results reveal that 60–80% of deviatoric stress dissipates instantaneously, with the remaining loss evolving nonlinearly toward a stable residual; higher suction or confinement raises residual capacity but enlarges absolute relaxation, whereas increasing strain accelerates damage and intensifies stress drop. A parsimonious three-element fractional Poynting–Thomson (FPTh) model that embeds Caputo-derived Koeller dashpot and the exponential damage variable of the viscous coefficient was formulated. The proposed model demonstrates a superior performance compared with the Merchant, Burgers, and Nishihara models (R² > 0.99 and RMSE < 3.5). The FPTh model faithfully reproduces the rapid and attenuating relaxation phases, offering a robust predictive tool for the long-term stability assessment of unsaturated clay slopes. Full article