Clay Fraction Research Articles

Insight into the dynamics of protected and non-protected carbon pools in four soils with different land uses

Abstract Background and aims To provide insight into the patterns of soil organic matter decomposition, changes in the quantity of biopolymers and the correlation between them were followed using 2D correlation spectroscopy (2DCOS) FTIR. Methods Soil organic matter fractions with different vegetation/land use (grass, spruce, oak and arable) were examined in a 1-year laboratory incubation. The non-protected organic matter fraction was calculated in terms of particulate organic matter (POM), the carbon stabilized in aggregates as S + A (sand + aggregates), and the mineral-associated organic matter (MAOM) as the s + c (silt and clay) fraction. Results Forest soils (spruce, oak) exhibited high C and N accumulation in the POM fraction (48, 43% and 29, 22% for spruce and oak, respectively) due to the limited decomposition, caused by low pH and high soil C/N ratio. The 2DCOS analysis revealed that carbohydrate-protein and carbohydrate-lignin correlations could be observed most frequently during incubation. The carbohydrate-protein correlation was negative in all cases, for all fractions and for all vegetation types, which suggests biogeochemical linkage between these biopolymers. The temporal order of the spectral changes was widely varied for the vegetation types and especially for the SOM fractions. Lipid/Lignin → Carbohydrate or Lipid → Lignin/Carboxyl/Protein sequences were found for the protected carbon pools (S + A and s + c), possibly because of the readily available abundant N compounds present in MAOM. Conclusion Although lipids and lignin are considered as chemically stable materials that commonly remain constant during decomposition, these compounds were found to be very susceptible in all the fractions.

Chemical weathering in the Mekong River Basin: Clay mineralogy and element geochemistry of lower-reach river sediments

Chemical weathering of parent rocks in river basins plays a significant role in controlling the global geochemical cycle and climate change, especially in the world’s largest river basins such as the Mekong River Basin in tropical regions. However, the chemical weathering process of the Mekong River Basin is still not well understood. In this study, clay mineralogy and major/trace-element geochemistry of fluvial sediments (clay, silt, and sand fractions) collected from the lower Mekong River Basin (Cambodia and Vietnam) were utilized to investigate the sediment provenance and chemical weathering process. The major-element compositions of the clay, silt, and sand fraction sediments from both the mainstream and tributaries consist of dominant SiO2, Al2O3, and Fe2O3, (84 wt.%, 89 wt.%, and 95 wt.%, respectively) and minor K2O, Na2O, MgO, CaO, TiO2, P2O5, and MnO. The clay mineral assemblages in mainstream sediments are high in illite (36 wt.%), moderate in kaolinite (28 wt.%) and chlorite (26 wt.%), and low in smectite (10 wt.%), whereas those in tributary sediments are high in smectite (37 wt.%), moderate in kaolinite (26 wt.%) and chlorite (22 wt.%), and low in illite (15 wt.%). The different clay mineral assemblages between mainstream and tributary sediments can be significantly related to the parent rock lithology and/or the weathering process in the source region. On the basis of clay mineralogy and elemental geochemistry, river sediments of the mainstream in the lower reach may be derived mainly from felsic rocks in the lower part of the middle reach of this basin, with secondary contributions from the upper and lower reaches as well as the upper part of the middle reach. Sediments in the Kampi and Speu tributaries highly originate from felsic rocks, whereas sediments in the Srepok, Ter, and Chhiong tributaries can be mostly weathering products of mafic rocks. The clay mineral proxies (smectite/(illite + chlorite) and kaolinite/(illite + chlorite)) combined with the elemental geochemistry (CIA, αAlE values, and weathering trends) of the clay fraction sediments indicate intensive chemical weathering in the lower and middle reaches. The high-relief topography and cold and dry climatic conditions in the upper reach result in high illite and chlorite contents in the soil and moderate chemical weathering. The chemical weathering intensity increases from the upper to middle reaches and further to the lower reach. Tectonics in the middle and upper reaches of the Mekong River Basin play the most important role in controlling weathering and erosion processes, whereas East Asian–Indian monsoon climate conditions with warm temperature and predominant rainfall throughout the year and lithology are the main forcing factors for the intensity of chemical weathering in the lower reach.

Deciphering Paleocene‐Eocene Thermal Maximum Climatic Dynamics: Insights From Oxygen and Hydrogen Isotopes in Clay Minerals of Paleosols From the Southern Pyrenees

AbstractThis study focuses on the Paleocene‐Eocene Thermal Maximum (PETM), a hyperthermal event characterized by a rapid increase in global temperature (5–8°C) over 20 ka, in the Southern Pyrenean Foreland Basin. Although there is evidence of increased flood discharge and erosion in the Southern Pyrenees, how paleoclimatic conditions and weathering evolved remains to be assessed. This study focuses on the catchment scale climatological changes recorded in the clay minerals of floodplain paleosols, giving insights into how rainfall affected the weathering regime during and after the hyperthermal event. The oxygen (δ18O) and hydrogen (δD) isotope compositions were analyzed in two clay fractions in paleosols of the Esplugafreda continental section. The clay minerals comprise a dominant smectite‐rich assemblage, which indicates a predominantly seasonal, semi‐arid climate throughout the section. Two positive excursions in the δ18O record during the Pre‐Onset Excursion (POE) and the Syn‐PETM support an increase in air near‐surface temperature. Using the δD and δ18O smectite fractionation factors, we estimate a Mean Annual Air Temperature (MAAT) of 24.2 ± 1.0°C for the POE and 27.0 ± 0.8°C for the Syn‐PETM. The δD values show a relatively stable composition during the climatic disturbance, which suggests that this mid‐latitude catchment was overall characterized by low yearly rainfall, with a peak in extreme events during the body of the PETM and a trend toward aridification during the recovery phase of the PETM, supported by the paleosol morphotype. These climatic conditions suggest a kinetically controlled weathering regime, where physical transport of the sediments played a primary role as a denudation mechanism.

Physicochemical characteristics of andisols and their correlation to potato yield based on land mapping units

The high phosphate retention in andisol soil is often associated with a decrease in potato yield. Additionally, identification of the physical and chemical characteristics of andisols and their correlation to potato yield through soil mapping units (SMUs) is necessary to facilitate field surveys. Therefore, this study aimed to identify the physicochemical characteristics of andisols with a focus on available phosphorus (P) and the correlation to potato production based on SMUs. The experiment was conducted in Karo District, North Sumatra, Indonesia, from July 2022 to February 2023. A descriptive-analytical method was used by overlaying maps of slope, soil types, and altitude until 10 SMUs were selected that were planted with potatoes. Soil physicochemical properties were identified, while Pearson correlation analysis was performed on available-P and potato yield using IBM SPSS software. The results showed that the silt and clay fractions positively correlated with available-P in andisols. All soil physical characteristics were categorized as very weak to weak in supporting potato yield. A total of four SMUs including 1, 5, 8, and 10 were found to have lower available-P and very low to moderate correlations with soil pH, organic-C, C:N ratio, cation exchange capacity (CEC), as well as total-P. Based on the results, potato yield could increase by 1.765 and 0.380 tons ha-1 through the addition of organic-C and C:N ratio in Karo District. Therefore, soil amendment is required as an alternative to improve andisols soil.

Enhancing Soil Texture and Bulk Density Mapping Using Soil Grids and Machine Learning: A Comparative Analysis with Observed Data

Digital soil mapping plays a crucial role in understanding soil variability and informing sustainable land management practices. This study focuses on the Kurdistan Region of Iraq (KRI), evaluating the accuracy of SoilGrids, a global-scale soil mapping initiative, and exploring the efficacy of machine learning algorithms in refining soil properties estimations. The aim of this research was to assess and represent the physical parameters of soils effectively by comparing ground truth soil sampling data with data obtained from SoilGrids regarding clay, silt, and sand fractions and bulk density. Comparative analyses were conducted between ground truth soil sampling data and SoilGrids predictions, revealing significant differences across soil mineral fractions including clay, silt, sand fractions, and bulk density. The results showed that the mean clay fraction in the ground truth dataset differed notably from SoilGrids estimation, with a Mean Absolute Deviation (MAD) of 124.0 g kg-1 and Root Mean Square Error (RMSE) of 152.5. However, the integration of machine learning algorithms, particularly the Extreme Gradient Boosting (XG Boost) algorithm, showed promising results in improving accuracy. The XG Boost algorithm exhibited a relatively low MAD of 97.9 g kg-1 for clay fractions, indicating a better approximation of observed values compared to SoilGrids. Significant percent improvements in RMSE and Mean Absolute Percentage Error (MAPE) values were observed across soil fractions and bulk density measurements, ranging from approximately 15% for clay to 35% for sand fractions and 20% for bulk density. These findings highlight the importance of integrating advanced mapping techniques and machine learning algorithms to enhance soil mapping methodologies. Moving forward, efforts to expand ground truth datasets through targeted soil sampling campaigns and develop international collaboration initiatives will be crucial for improving the accuracy and reliability of soil mapping products in the KRI. By incorporating advanced mapping approaches, we can better support sustainable land management practices and environmental conservation efforts in the region.

Evaluating the impacts of area closure on soil properties in south central highland of Ethiopia

Soil degradation affects its quality and productivity of the land. To control soil degradation, various soil and water conservation (SWC) measures, including area closure are implemented. Understanding the impacts of SWC measures could support planning and implementation of land management practices. This study aimed to investigate impacts of area closure on soil properties in south central highland of Ethiopia. To acquire the necessary data, we conducted interviews with 80 households. Furthermore, nine years old area closure with physical soil and water conservation (AC-SWC), open grazing with physical SWC (OG-SWC), and open grazing without physical SWC (OG) were identified and each divided into upper, middle, and lower slope positions. In each slope position, 3 sample plots were established at 25–50 m intervals. A total of 27 composite samples and other 27 core samples for bulk density (3 treatments∗3 slope position∗3 replications) were collected and analyzed for soil properties. The data were analyzed using descriptive statistics and one-way ANOVA. The results showed that about 98 % of the respondents perceived that area closure would be an effective way to restore degraded land. Majority of the farmers (86 %) believed that area closure could reduce soil erosion and replenish soil fertility and thus, is beneficial in improving land productivity. Soil test results revealed that AC-SWC had significantly greater (P < 0.05) clay fractions, pH, available potassium, and available phosphorus than OG-SWC and OG. Variations of soil organic carbon (SOC) and total nitrogen (TN) were more pronounced. The SOC in AC-SWC was 83 % and 314 % greater than OG-SWC and OG, respectively. In the AC-SWC, TN was three and seven times higher than that of OG-SWC and OG, respectively. This could be due to vegetation restoration that reduces erosion, and enhances organic matter, moisture, and nutrient. The SOC, TN, pH, available potassium, and clay were significantly greater (P < 0.05) at lower slope position than upper in all forms of land management, which could be due to deposition at downslope. About 12 % and 11 % variations of clay fractions and SOC were, respectively, observed in between upper and lower slope positions at AC-SWC, but they varied by 25 % and 57 %, respectively, in OG. These imply area closure has had a beneficial effect on soil properties even on sloping land. AC-SWC is an important option to integrate in land management for rehabilitation of degraded soil.

Predicting USCS soil texture classes utilizing soil spectra and deep learning

Abstract Purpose Soil texture identification is vital for various agricultural and engineering applications but generally involves rigorous laboratory work, especially for estimating USCS (Unified Soil Classification System) soil texture classes. Soil texture influences soil water storage capacity, soil fertility, compaction characteristics, and soil strength. Soil spectroscopy offers a reliable approach that is non-destructive, rapid, and cost-effective to estimate several soil properties including texture. For engineering applications, the USCS soil texture classes are preferred, but very few studies have focussed on estimating USCS soil texture using soil spectroscopy or remote sensing data in general. Methods Two large soil spectral libraries (SSLs), viz., Kellog Soil Spectral Library (KSSL) and Open-source Soil Spectral Library (OSSL), as well as three deep learning algorithms (VGG-16, ResNet-16, and Swin transformers), were used in this study to predict six USCS soil texture classes and three USCS soil texture groups. The USCS soil texture classes and groups were derived by grouping clay, sand, and silt fractions that are closely associated with the corresponding USCS soil texture classes. Results The results indicate that the Swin transformer model performed the best with an accuracy of 67% for six USCS soil texture class predictions and 81% for three USCS soil texture group predictions. Cohen’s kappa value implies a moderate agreement (0.55) for soil texture class predictions and a substantial agreement (0.64) for soil texture group predictions. Conclusion The proposed methodology offers a novel approach for USCS soil texture class predictions utilizing SSLs and deep learning techniques.

Enhancing forensic applications through the mineralogy of clays in surface soil horizon: A case study of baixada fluminense, Southeast Brazil

Clay minerals possess chemical, mineralogical, and crystallographic characteristics that make them potential forensic markers, as they can reflect geochemical and weathering processes on a detailed scale. Therefore, this study aims to use the mineralogy of the clay fraction to distinguish samples from the surface soil horizons in four municipalities in Brazil, to assess the possibility of geographical tracking for forensic applications. Studies characterizing clays in environments with a variety of soil types in forensic pedology are necessary but still in their early stages. Furthermore, due to the high incidence of homicides involving the displacement of bodies in the region and the low resolution of these crimes, this research is crucial for geoscientific applications, with the potential for global replication. The samples were separated by centrifugation and analyzed using X-ray diffractometry, X-ray fluorescence, and thermogravimetry. Minerals were determined through quantitative mineralogical analyses using Rietveld and Biscaye methods. Additionally, in conjunction with the crystallographic parameters of kaolinite (Full Width at Half Maximum – FWHM), it was possible to form 8 Clay Mineral Assemblages and Gibbsite (CMAG), whose geographical delimitation considered geological and hydrographic aspects. The determination of CMAGs is based on mineralogy and is defined as follows: CMAG 1: kaolinite+(illite); CMAG 2: kaolinite+(gibbsite); CMAG 3: kaolinite + illite + montmorillonite; CMAG 4: kaolinite + illite+(gibbsite); CMAG 5: ordered kaolinite+(illite)+(gibbsite); CMAG 6: kaolinite + gibbsite+(illite); CMAG 7: disordered kaolinite + illite + gibbsite; CMAG 8: kaolinite+(illite)+(chlorite). The results indicate that the quantification of clay minerals in samples from surface soil horizons, FWHM, and the % of Al in goethite can represent valuable tools for forensic pedology. Moreover, through the characterization of iron and titanium (hydr)oxides, it was possible to distinguish samples with a distance of 335 m between them, further expanding the capability to identify the geographical origin of samples, making them potential forensic markers.

Origin and distribution of clay minerals in semi-arid Sahelian soils: case of Kori Ouallam watershed, south-western Niger

Abstract This study examines the origin and distribution of clay minerals of the pedological horizons of Kori Ouallam watershed (south-western Niger). It is based on field sampling campaigns and a series of laboratory analyses. A total of 49 samples were analysed, 28 from surface horizons (0–10 cm depth) and 21 from pedological profiles (0–1 m depth). The samples were analysed by X-ray diffraction on bulk and clay (&lt;2 μm) fractions, X-ray fluorescence spectrometry, laser granulometry, organic matter and calcium carbonate content, macroscopic observations (binocular loupe) and scanning electron microscopy equipped with an energy-dispersive spectrometry system. The pedological horizons are characterized by low organic matter contents (&lt;1%) and no calcium carbonate. The particle-size distribution shows net textural differentiation, with a predominance of sandy loam to sandy clay loam textures in the upper horizons and clay loam to clay in the deep horizons. The main major oxides were SiO2 (46.3–89.0%), Al2O3 (5.0–24.2%) and Fe2O3 (1.0–27.9%). Kaolinite (64–98%) is the predominant clay mineral at all horizons, associated with low to moderate proportions of illite (1–34%) and traces of chlorite. Kaolinite is essentially inherited from the parent rock, whereas illite results from chemical alteration by bisialitization of the primary minerals initially rich in potassium feldspar contained in the parent rock. However, soil texture and organic matter vary independently with clay mineralogy. An extended study of all of the pedological facies that make up south-western Niger, combined with supplementary analyses, would further improve our understanding of clay mineralogy in the Sahelian zone.

Vegetation degradation reduces aggregate associated carbon by reducing both labile and stable carbon fraction in Northeast China

Vegetation changes can affect soil organic carbon (SOC) content and storage by altering the inputs of plant biomass and the catabolism and anabolism of soil microorganisms. However, influence of vegetation degradation on aggregate associated carbon fractions and the contribution of different aggregates to total SOC in bulk soil remains poorly understood. In this study, undisturbed soil samples were collected from three types of grassland in Songnen grassland: an undegraded grassland (LEY, Leymus chinensis), a moderately degraded grassland (CHL, Chloris virgata), and a severely degraded grassland (SUA, Suaeda heteroptera). Three soil aggregates including macroaggregate (> 0.25 mm), microaggregate (0.053–0.25 mm) and silt and clay fraction (< 0.053 mm) were separated using wet sieving. Contents of total SOC, soil labile and stable carbon in bulk soil and different soil aggregates were measured. Compared with LEY, the mean weight diameter and geometric mean diameter under the degraded vegetation communities reduced by 39.42 % and 28.47 %, respectively. The reduction in SOC contents in bulk soil, macroaggregate, microaggregate and silt and clay fraction resulting from vegetation degradation was 49.81 %, 26.00 %, 76.17 % and 43.65 %, respectively. Under the degraded vegetation communities, contents of soil labile and stable carbon in bulk soil (45.73 % and 52.61 %, respectively), macroaggregate (17.38 % and 31.61 %, respectively), microaggregate (77.83 % and 74.18 %, respectively), and silt and clay fraction (21.20 % and 53.45 %, respectively) were significantly lower than those under LEY. The contribution of macroaggregate, microaggregate and silt and clay fraction to total SOC was 13.27 %, 23.61 % and 63.12 %, respectively. The contribution of soil aggregates to total SOC following vegetation degradation reduced by 53.63 % for microaggregate, but increased by 47.10 % for silt and clay fraction. These findings collectively indicate that vegetation degradation reduces the aggregate associated carbon content by reducing both labile and stable carbon fraction in Songnen grassland, and sustainable vegetation restoration strategies are need to enhance soil carbon storage in Northeast China.

Prediction of thermal conductivity of frozen soils from basic soil properties using ensemble learning methods

Thermal conductivity is one of the important properties required for understanding the frozen soils behavior. There are several models available in the literature for the prediction of thermal conductivity of frozen soils based on the proportions of unfrozen water, ice, gas, and soil particles. In this study, two ensemble learning methods-based models; namely, the Random Forest (RF) model and the Least Squares Boosting (LSB) model, are extended to estimate the thermal conductivity of frozen soils. These models utilize basic soil properties as input parameters that include water content, dry density, temperature, and fractions of gravel, sand, silt, and clay, can be measured easily, or determined. Additionally, seven widely used thermal conductivity models, referred to as the traditional models for frozen soils, were evaluated. Both the RF and LSB models, as well as the traditional models, were assessed using data of 823 tests derived from 43 soils with different textures that were gathered from the literature. The results highlight that the traditional models have their strengths and limitations in terms of their use for different types of soils. In contrast, the proposed ensemble learning methods-based models provide higher prediction accuracy compared to the traditional models and can be applied to all soil types and temperature ranges. Furthermore, estimation from the ensemble learning methods-based models can be used to provide probability of multi-dimensional analysis of frozen soils.

Investigating concentrations and sources of polycyclic aromatic hydrocarbons in South and Central Texas bays and estuaries along the Gulf of Mexico, USA

Polycyclic aromatic hydrocarbons (PAHs) are among the most widespread organic contaminants in the environment, and anthropogenic activities can produce PAHs through a variety of pyrogenic or petrogenic means. Knowing the concentrations and sources of PAHs helps evaluate ecosystem health and manage natural resources. In this study, 16 US Environmental Protection Agency priority PAHs were analyzed in water and sediment samples collected from September 2021 to September 2023 in four bay systems along the south and central Texas coast, which are a hotpot of crude oil transportation in the United States. Our results indicated that the total concentration of PAHs ranged from 1.9 to 8.3 ng/mL in surface waters (&amp;lt; 0.5 m) and from 520 to 1257 ng/g in surface sediments (top 5 cm). Grain size analysis revealed that the sediment was dominated by silt (4 - 63 μm), followed by clay (&amp;lt; 4 μm) and sand (&amp;gt; 63 μm) fractions. Both organic carbon and clay content were shown to play a significant role in controlling the PAH content in sediments. Diagnostic ratios indicated that PAHs were primarily sourced via pyrolytic processes, such as the combustion of fossil fuels. Additional sampling at Port Bay, a shallow, secondary bay in the Mission-Aransas National Estuarine Research Reserve, implicated a strong role of resuspension in the distribution and composition of PAHs in the bay systems studied. Overall, these data offer insights into the concentration levels and sources of PAHs in this key region housing oil production and transportation in the United States.

Long-term Chinese milk vetch incorporation promotes soil aggregate stability by affecting mineralogy and organic carbon

Soil aggregates profoundly impact soil sustainability and crop productivity, and they are influenced by complex interactions between minerals and organics. This study aimed to elucidate the alterations in mineralogy and soil organic carbon (SOC) following long-term green manure incorporation and the effect on soil aggregates. Based on 5- and 36-year field experiments, surface soil samples (0-20 cm) were collected from Alfisol and Ferrisol soils subjected to rice-rice-winter fallow (CK) and rice-rice-Chinese milk vetch (MV) treatments to investigate aggregate stability, mineralogy, SOC composition, and soil microstructural characteristics. The results showed that high clay-content Ferrisol exhibited greater aggregate stability than low clay-content Alfisol. The phyllosilicates in Alfisol primarily comprised illite and vermiculite, whereas those in Ferrisol with high-content free-form Fe oxides (Fed) were dominated by kaolinite. Additionally, the clay fraction in Ferrisol contained more aromatic-C than the clay fraction in Alfisol. The 36-year MV incorporation significantly increased the Ferrisol macroaggregate stability (9.57-13.37%), and it also facilitated the transformation of vermiculite into kaolinite and significantly increased the clay, Fed, and aromatic-C contents in Ferrisol. Backscattered electron (BSE)-scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) revealed a compact aggregate structure in Ferrisol with co-localization of Fe oxides and kaolinite. Moreover, the partial least path model (PLS-PM) revealed that clay content directly improved macroaggregate stability, and that kaolinite and Fed positively and directly affected clay or indirectly modulated clay formation by increasing the aromatic-C levels. Overall, long-term MV incorporation promotes clay aggregation by affecting mineral transformation to produce more kaolinite and Fe oxides and retain aromatic-C, and it ultimately improves aggregate stability..

Quantifying the sediment sorption of organic ultraviolet filter chemicals using solvophobic theory

Hydrophobic organic chemicals (HOCs) that enter the aquatic environment often negatively impact organisms, endangering aquatic biodiversity. Understanding sediment sorption equilibria for these chemicals can properly direct mitigation efforts. In addition, many HOCs of environmental concern lack sufficient environmental fate data to adequately assess their risk to ecosystems and humans. In this study, a sorption method addressing solvophobic effects was used to quantify the sorption of an HOC of current environmental concern, OD-PABA (padimate O, 2-ethylhexyl-4-(dimethylamino)benzoate), to a variety of sediments. OD-PABA is an organic ultraviolet filter chemical used in commercial sun protection products; it has been shown to exhibit cytotoxic effects and is known to photochemically transform under natural sunlight conditions. Given its commercial use, it enters the aquatic environment via recreational use and wastewater treatment plant effluent. OD-PABA is strongly hydrophobic; to mitigate the adsorption of OD-PABA to the container walls during sorption experiments, a precise concentration of methanol was used to avoid solvophobic effects. This sorption method was used to determine the sorption capacities for OD-PABA of four sediment samples, each with unique geochemical characteristics. Sediment-water distribution coefficients (Kd) were quantified and were normalized to various sediment characteristics to assess the main driving force(s) for sorption of OD-PABA. Organic carbon content was found to be a main driving force, with organic carbon-normalized distribution coefficients (log Koc) ranging from 4.4 to 4.6 for sediments with total organic carbon (TOC) > 10%); the clay fraction was also found to be important, especially for sediments with low TOC. The sorption of para-aminobenzoic acid (PABA), a water-soluble analog of OD-PABA was also investigated to assess the experimental approach, yielding a log Koc of 2.1 for the sediment with the greatest TOC.

Impact of textural layers in soils on irrigation infiltration processes in an oasis farmland, northwestern China

AbstractThe Hexi Corridor Oasis in China is an important agricultural area supported by extensive irrigation. The sandy soil in the area exhibits textural layering, which has marked effects on its properties. Textural layered soils play an important role in distributing and regulating water regimes in irrigated fields. However, little is known about the textural layering‐dependent variability in soil water infiltration characteristics following irrigation and the potential effects on soil hydrology and water regimes in these soils. The objective of this study was to determine water infiltration processes and their influencing factors for six soil profile types in an oasis farmland. Six in situ constant‐head infiltration measurements (with three replications in each of six sites) were conducted with a single‐ring infiltrometer in different soil texture configurations, and Hydrus‐2D model was applied to evaluate soil water distribution. The results showed that the wetting front depth for all treatments was in the following order: ST‐1 &gt; ST‐5 &gt; ST‐6 &gt; ST‐3 &gt; ST‐2 &gt; ST‐4; the stable infiltration rate ranged from 1.2 to 3.3 cm/min during the investigation period in all treatments. The presence of a finer‐textured soil layer decreased water infiltration rates through the profiles, and the thickness and burial depth of textured layers had obvious effects on infiltration, compared with homogeneous sand profiles. Presence of a medium‐textured layer affected the infiltration characteristics and soil water spatial variability; driven by increased field capacity and the wilting point, hydraulic conductivity was correlated with soil variables that were related to soil structure, such as wilting point and field capacity, and less so with variables that were related to soil texture, such as the clay fractions (p &lt; 0.001). These results suggested that textural layering altered the soil structure and caused heterogeneous infiltration of water, with implications for the distribution of irrigation water and prevention of deep percolation in this oasis farmland. The result of this study offers a new analysis of ponded single‐ring water infiltrometer data that the soil water infiltration is also influenced by the type of textural layered than just the irrigation system, which supports crop irrigation management in study area and other regions with similar soil regimes.

In situ treatment of contaminated soil using persulfate activated by sulfidated zero-valent iron

Soil contamination with hazardous substances like phenol poses significant environmental and health risks. In situ soil mixing can be a promising technological solution to this challenge. A persulfate and sulfidated zero-valent iron (S-ZVIbm) system for remediating contaminated soil was developed and tested to be suited to in situ soil mixing. S-ZVIbm was synthesized using a ball mill process, and the optimal sulfur to iron molar ratio for effectively removing phenol from soil removal without pyrophoric risks was 0.12. Soil slurry experiments were performed, and the best phenol oxidation results (high stoichiometric efficiency and sustained oxidation after mixing) were achieved at a persulfate to S-ZVIbm molar ratio of 2:1 and a persulfate to phenol molar ratio of 8:1. A high organic matter content of the silty clay fraction of the soil strongly suppressed persulfate activation, so suppressed phenol removal and increased persulfate consumption. Electron spin resonance and radical scavenging tests confirmed that hydroxyl and sulfate radicals were present during the degradation of phenol. While sulfate radicals predominantly facilitated degradation in the soil, both sulfate and hydroxyl radicals were crucial in the aqueous phase in the absence of soil organic matter. In situ soil mixing simulation tests indicated that the persulfate and S-ZVIbm doses and the mixing rate and duration strongly affected the efficacy of the system, and the optimal conditions for phenol removal were determined. The results indicated that the persulfate/S-ZVIbm system could be tuned to achieve sustained persulfate activation and to remediate contaminated soil employing in situ soil mixing technique.

Effects of Chemical Alteration on Frictional Properties in a Deep, Granitic, Geothermal System in Cornwall: Direct Shear Experiments at Near In Situ Conditions

AbstractThe geochemical alteration of host rocks might affect the productivity and the potential for induced seismicity of geothermal systems. In addition to natural alteration, following production and heat extraction, re‐injected fluids at lower temperatures and different pressures may be in chemical disequilibrium with the rock, impacting mineral solubility and dissolution/precipitation processes. In this study, we investigate the effect of geochemical alteration on the frictional behavior of granites, and their seismogenic potential, by conducting direct shear experiments using samples with varying degrees of alteration. The samples originate from the Carnmenellis granite in Cornwall, SW England, and represent the formation used in the United Downs Deep Geothermal Power Project for heat extraction. Experiments were conducted on granite powders (referred to as gouges) at room temperature and 180°C, at simulated in situ confining and pore pressures of 130 and 50 MPa, respectively (∼5 km depth). With increasing degree of alteration, the frictional strength of the gouges decreases while frictional stability increases. At high temperature, frictional stability is reduced for all samples while maintaining the trend with alteration stage. Microstructural investigation of the sheared gouges shows alteration delocalizes shear by reducing grain size and increasing clay fraction, which promotes the formation of pervasive shear fabrics. Our work suggests that, within the range of tested pressures, more alteration of granite initially causes more stable shearing in a fault. This behavior with alteration is sustained at high temperatures, but the overall frictional stability is reduced which increases the potential for induced seismicity at higher temperatures.

Influence of the clay fractions from various horizons on the radiation shielding parameters of an Arenosol

Abstract This study examines the effects of the chemical composition of the clay fraction of various soil horizons on radiation shielding parameters. X-ray fluorescence (XRF) analysis did not reveal significant differences in the concentration of the most abundant oxides (Al2O3, SiO2, Fe2O3) among the various horizons. Consequently, the mass attenuation coefficient did not vary among the horizons in terms of the photon energies studied (15 keV–10 MeV). The mean free path (MFP), half-value layer (HVL) and tenth-value layer (TVL) did not differ for energies up to 100 keV. However, at higher energies, these parameters were mainly influenced by the differences in the densities of the soil horizons. The effective atomic number did not differ across the horizons for the various photon energies, nor did the mass attenuation coefficient. It is shown that slight differences in the chemical composition of the clay fraction of soil horizons do not affect radiation shielding parameters (MFL, HVL, TVL) for low photon energies (&lt;500 keV). Density is more important for radiation shielding than the chemical composition of the various horizons of the same soil type for higher energies (&gt;100 keV); hence, compacting the clay fraction might be more efficient for radiation shielding purposes at higher energies.

Interplay of natural and anthropogenic factors in sediment dynamics and trace element distribution in Güllük Gulf, western Türkiye: A comprehensive geochemical and hydrodynamic analysis

Güllük Gulf, located in the southeastern Aegean Sea, is significantly impacted by diverse human activities, including urban development, tourism, and intensive aquaculture. This study aims to assess the spatial distribution of trace metals in the Gulf's sediments, identify their sources, and evaluate their environmental impacts to inform effective management strategies. It also examines sediment transport patterns, which are crucial in influencing the distribution and concentration of pollutants. Establishing background concentration levels for various elements provides a baseline to assess pollution levels and identify deviations due to anthropogenic impact. Sediment samples were collected from 45 stations and analyzed for grain size, organic carbon, carbonate content, and concentrations of 26 elements. Contamination was assessed using indices such as Enrichment Factor (EF), Geoaccumulation Index (Igeo), Contamination Factor (Cf), Degree of Contamination (Cdeg), Pollution Load Index (PLI), Modified Pollution Index (MPI), and Toxic Risk Index (TRI). Statistical analyses, including Principal Component Analysis (PCA) and Cluster Analysis (CA), were used to identify pollution sources. Results indicated that Güllük Gulf's sediments are predominantly sandy, with significant silt and clay fractions in sheltered bays. Organic carbon content averaged 1.68%, with higher values near urban and aquaculture areas. Trace metal concentrations exhibited notable spatial variability, with elevated levels of Pb, Cu and Zn in specific areas, indicating both natural and anthropogenic sources. PCA identified five significant factors contributing to metal presence, linking them to lithogenic origins, aquaculture activities, and industrial inputs. TRI results showed moderate toxic risk in Asin Bay, primarily due to Ni, As and Cr. The sediment transport model of Güllük Gulf, crucial in understanding regional pollution dynamics, revealed a complex interplay of hydrodynamic forces. The study underscores the significant environmental impact of human activities on sediment quality in Güllük Gulf. Elevated trace metal levels near aquaculture sites emphasize the need for stringent environmental management practices. Effective strategies should include regular monitoring, sustainable aquaculture practices, and stakeholder engagement to mitigate environmental impacts and preserve the Gulf's ecological integrity. This comprehensive approach provides crucial insights for future research and environmental management policies aimed at addressing the complex challenges facing Güllük Gulf.

Exploring the Influencing Factors of Net Ecosystem Productivity (NEP) Based on Random Forest and SHAP

As global climate change intensifies, Net Ecosystem Productivity (NEP) serves as a crucial indicator for measuring the carbon absorption and release of ecosystems, playing a vital role in understanding the carbon cycle and shaping climate policy. The Northwestern region of China, characterized as a typical inland arid and semi-arid area, is particularly sensitive to global changes. Understanding the environmental drivers of NEP in this region is critical for both regional ecological protection and global environmental management. This study utilized environmental data from five provinces in Northwestern China, applying the Random Forest (RF) model and SHapley Additive exPlanation (SHAP) method to analyze the primary environmental factors influencing NEP. The research integrated climatic data (including temperature, precipitation, wind speed, and solar radiation), soil characteristics such as pH, organic carbon content, and soil texture, topographic attributes elevation and slope, and a Human Footprint. The RF model identified significant environmental factors impacting NEP, and SHAP values were used to explain the specific contributions of these factors. Furthermore, multiple linear regression analysis revealed interactions among environmental factors. The results indicate that solar radiation (Srad), precipitation, topsoil reference bulk density (T_REF_BULK), temperature, and the topsoil clay fraction (T_CLAY) significantly influence NEP. Notably, interactions between aspect and T_CLAY, aspect and T_REF_BULK, as well as the human footprint (HFP) and Srad, also show significant impacts on NEP. This study confirms that solar radiation, precipitation, soil characteristics, and human activities are the primary environmental drivers of NEP in the Northwest region of China, with solar radiation playing the most critical promotional role. The findings not only provide a scientific basis for the management of ecosystems in Northwestern China but also offer references for formulating global climate change mitigation strategies and estimating the global carbon budget. Future research should further explore the specific mechanisms and interactions of these drivers across different ecosystems to more comprehensively understand and predict the trends in NEP changes.