Top Soil Layer Research Articles

Evaluation of soil water content and bulk electrical conductivity across the U.S. Climate Reference Network using two electromagnetic sensors

AbstractSoil bulk electrical conductivity (BEC) was evaluated alongside soil volumetric water content (VWC) and soil temperature measurements using the HydraProbe (model HydraProbe, Stevens Water Monitoring Systems, Inc.) (hereafter called HP) with accuracy range of BEC ≤ 0.3 S m−1, and the time domain reflectometry (TDR)‐315L Probe (model TDR‐315L, Acclima, Inc.) (hereafter called AP) suitable for BEC up to 0.6 S m−1, at 23 stations of the U.S. Climate Reference Network. Previous evaluations revealed inconsistent performance of both sensors in some clay soils using manufacturer‐recommended calibrations in converting dielectric permittivity measurements to VWC. Here, we found that hourly values of BEC reached 0.6 S m−1 in high clay content soils and exceeded 2 S m−1 in high saline soils, and these high values of BEC were associated with poor performance and failures of both HP and AP sensors. Large values of BEC occurred in predominantly saturated soils where VWC values reached about 0.5 m3 m−3 for saline soils and about 0.7 m3 m−3 for clay soils, while low magnitudes of BEC were associated with low soil water content and seldomly saturated soils. Low hourly BEC values of less than 0.1 S m−1 were observed in wide variety of soil types, where sensor performance was typically excellent. The most influential factor on BEC was high soil water content conditions. Although dielectric permittivity measurements in estimating the soil water content were sensitive to BEC as some high clay content and high salinity soils increased BEC, the impact of large BEC on dielectric permittivity measurements was smaller in the well‐drained top soil layers than in deep soil layers that remained near saturation. Soil temperature had only a small impact on BEC. With high clay content and high salinity, the specific area of clay minerals was also associated with the magnitude of BEC.

Assessing leachate contamination and groundwater vulnerability in urban dumpsites: a case study of the Ipata Area, Ilorin, Nigeria

This study explores the extent of leachate contamination and groundwater vulnerability in urban dumpsites, with a specific focus on the Ipata area in Ilorin, Nigeria. The study employs a combination of 2D Electrical Resistivity Tomography (ERT), soil classification, and physicochemical analyses to investigate the percolation of leachate into groundwater and its potential environmental and health implications. The ERT data unveiled subsurface layers, highlighting the presence of decomposed topsoil down to approximately 1.2m. Beneath this layer, a low-resistivity zone (6.53 to 10.7 ?m) indicated the potential risk of leachate percolation into groundwater. Soil classification revealed a shallow topsoil layer with insufficient clay content to hinder leachate penetration, emphasizing the need for enhanced containment measures. Physicochemical analysis of leachate, well water, and soil displayed variations in key parameters such as pH, electrical conductivity, total dissolved solids, and anion concentrations. Leachate exhibited high pH and electrical conductivity, suggesting elevated total dissolved solids, while well water remained within acceptable pH limits for drinking water. Heavy metal concentrations exceeded permissible WHO limits in topsoil, leachate, and well water, with cadmium presenting a high ecological risk. The absence of persistent organic pollutants (POPs) in the samples indicates a current focus on heavy metals as a primary concern. In conclusion, this study underscores the urgent need for proactive pollution abatement measures in urban dumpsites like Ipata. Regular monitoring of surface and groundwater quality is essential to safeguard public health and the environment.

Enrichment and fractionation of rare earth elements (REEs) in ion-adsorption-type REE deposits: Constraints of an iron (hydr)oxide–clay mineral composite

Abstract Ion-adsorption-type rare earth element (REE) deposits are the source of more than 90% of global heavy REEs (HREEs). Thus, understanding the ore genesis of REEs, particularly the distribution characteristics and enrichment mechanisms of HREEs, is vital for efficient exploration and mining of ion-adsorption-type REE deposits worldwide. The characteristics and petrogenesis of bedrock, and the aqueous mobility of REEs, are known to be important factors controlling REE accumulation and fractionation in the weathering crust of REE deposits. However, the effect of REE adsorption on secondary minerals, which is a crucial step in deposit formation, remains poorly understood. This problem was addressed by the study described herein, which involved a systematic analysis of the complete weathering profile (78 m) of the Renju ion-adsorption-type REE deposit in South China and a simulated adsorption experiment. Clay minerals and iron (Fe) (hydr)oxides are the dominant REE adsorbents in the weathering crust and most are micro-to-nanosized particles. Thus, the fine particle fraction (< 2 μm) was separated from field samples, to better disclose their effects on the concentration and redistribution of REEs. Phase compositions and morphologies were characterized by X-ray diffraction, Mössbauer spectrometry, and scanning/transmission electron microscopy (SEM/TEM), which revealed that various clay minerals and Fe (hydr)oxides form composites along the profile of the deposit. Composites of ferrihydrite–kaolinite, goethite–kaolinite/halloysite, and hematite–kaolinite/halloysite were found to be distributed in the semi-weathered, completely weathered, and topsoil layers, respectively, with different sizes and shapes. The concentrations and partition patterns of REEs in different occurrence states were distinguished after sequential extraction. Ion-exchangeable-REEs were the major state and enriched in the upper completely weathered layer. These species were found to be adsorbed onto kaolinite and halloysite via electrostatic attraction, without obvious fractionation. Fe (hydr)oxides were determined to comprise ca. 20% of REEs at most depths and over 50% of REEs in the topsoil and semi-weathered layer. It was found that Fe (hydr)oxides scavenge REEs through complexation and oxidation, resulting in HREE enrichment and a positive cerium (Ce) anomaly, respectively. In addition, compared with crystalline Fe (hydr)oxides, amorphous Fe (hydr)oxides immobilize more REEs but exhibit weaker preferential adsorption of HREEs. The above-described findings are consistent with the results of simulated experiments for REE adsorption onto a clay mineral–Fe (hydr)oxide composite (Bt-60), which was obtained from hydrothermal processing of biotite. Furthermore, the distributions and stabilities of LREEs and HREEs were distinguished by TEM–energy–dispersive spectroscopy (EDS) of Bt-60 before and after REE extraction by ammonium sulfate. The phase transformation pathways of clay minerals and Fe (hydr)oxides, and their different enrichment and fractionation characteristics in REEs, were also discussed in terms of the structure and surface properties of minerals, adsorption mechanisms, and variations in chemical properties across the REE group. The results shed new light on how clay minerals and Fe (hydr)oxides affect the enrichment and fractionation of REEs in ion-adsorption-type deposits.

Optimizing organic fertilization towards sustainable vegetable production evaluated by long-term field measurement and multi-level fuzzy comprehensive model

Precision and efficient management of organic substitution fertilization is crucial in balancing soil health, environmental risks, and economic benefits for intensive crop cultivation. However, effectively determining the optimal organic substitution ratio in vegetable production remains uncertain and still relatively unexplored. We conducted a five-year vegetable field experiment and established four nitrogen-equivalent fertilization treatments: mineral fertilizer alone, and organic fertilizer substituting a quarter, half, and entirety of the mineral nitrogen. Employing a specialized multi-level fuzzy comprehensive evaluation model, our study assessed impacts of different organic substitution ratios on soil qualities, microbial diversity, vegetable yield and quality, environmental risks, and economic benefits in sustainable vegetable production of eastern China. Our results showed that the 50% organic substitution was optimal, significantly improving soil qualities and microbial characteristics, particularly in the topsoil layer. Compared to the control, this approach significantly reduced methane by 6.6–48.3%, nitrous oxide by 49.5–79.1%, and nitric oxide by 36.5–50.0%, while enhancing vegetable yield by 16.0–28.3% and its five-year average stability as well as quality as evidenced by increased protein, soluble sugar, and vitamin C contents. Economic analysis revealed that while it maximized environmental benefits, complete organic substitution did not consistently yield positive economic returns. In contrast, a 50% substitution ratio was identified as the most economically viable, representing a sustainable compromise that balances environmental health with economic feasibility. Further modeling analysis indicated an optimal comprehensive range between 42.9% and 64.5% for achieving the best balance of multiple objectives in vegetable fields. The study underscores the intricate organic substitution effects on intensive vegetable production, highlighting the necessity for tailored organic substitution strategies that integrate environmental sustainability with agricultural productivity and economic practicality.

Climatic impacts induced by winter wheat irrigation over North China simulated by the nonhydrostatic RegCM4.7

Quantification of the impact of winter wheat irrigation on the climate and the occurrence of extreme climatic events over North China is crucial for regional adaptation planning. Previous related studies mainly focused on the impact on surface processes; however, few focused on the effects of extreme events using high-resolution nonhydrostatic regional climate models. Here, the 9-km-resolution nonhydrostatic RegCM4.7 was coupled with a crop irrigation scheme and an updated winter wheat irrigation dataset to better simulate irrigation effects. Two experiments were conducted with and without winter wheat irrigation to isolate the effects of irrigation. Results showed that irrigation simulation reduces the model biases in temperature, precipitation, latent heat flux, soil moisture, sensitive heat flux, and top-layer soil moisture. Moreover, it also reduces the bias and increases the correlation with observations obtained in irrigated areas, especially in summer, indicating better representation of irrigation schemes. Winter wheat irrigation tends to cause substantial cooling of the local surface maximum, minimum, and mean air temperatures (by −1.68, −0.34, and −0.79 °C, respectively) over irrigated areas of North China, with the largest changes observed in relation to maximum temperature. Additionally, precipitation is found to increase during spring and summer, which is strongly related to water vapor transport in the lower levels of the atmosphere. Further analyses indicated that the number of annual mean hot days decrease (−13.9 d), whereas the number of both comfort days (+10.2 d) and rainy days (days with total precipitation greater than 1 mm: +6.6 d) increase over irrigated areas, demonstrating beneficial feedback to human perception and agriculture. Fortunately, although the heat wave risk increases (number of annual mean heat wave days: +5.8 d), the impact is limited to small areas within irrigated region. Additionally, no notable change was found in terms of heavy rainfall events and precipitation intensity, which might be an undereastimation caused by the less water use in model simulation. Although winter wheat irrigation does not have notable impact on the climate of the surrounding region, it is an important factor for the local-scale climate.

Soil Properties Variation Valued in Relation to Land Use and Management Practices in Vietnam

Background: Land use and management practices (LUMPs) have been accelerated globally to serve the increasing socio-economic requirements in recent decades. Methods: This study focuses to assess the impacts of the LUMPs on the properties and composition of soil in the Lam River Basin (LRB), Vietnam based on analysis of ninety-six soil samples collected in the soil profiles (0_60 cm). Result: The results indicated that the sand and clay ratios (34.0~35.7% and 16.2~19.9%) and bulk density (BD) (1.07±0.05~1.34 ± 0.06 Mg m-3) in the natural forest lands (NFLs) were lower and higher perturbed than the plantation forest lands (PFLs) (31.1~ 51.5%, 5.7~38.2% and 0.86 ± 0.03~1.12±0.05 Mg m-3) in the 0-20 cm topsoil layer. The soil texture is mainly sandy clay to clay loam and the BD tends slightly increase in the topsoil layer, then decrease in the 20-60 cm subsoil layer. There is no difference in soil pH between collected soil samples (CSSs) and tends to increase with increasing the subsoil layer. The base cations (BCs) (Ca2+, K+, Mg2+: 0.01~0.29, 0.06~0.11 and 0.06~0.07 Cmolc kg-1) and total organic contents (TOCs) (total carbon (TC), total nitrogen (TN), total phosphorus (TP): 24.11; 2.80 and 0.19 g kg-1) of the NFLs are higher than those of the CSSs (TC, TN, TP: 14.37~23.91, 1.62~2.28 and 0.08~0.17 g kg-1) in the topsoil layer while these values were not different in the topsoil layer.

Soil bacterial community characteristics and its effect on organic carbon under different fertilization treatments.

By implementing small-scale and efficient fertilization techniques, it is possible to enhance the activity of microorganisms, thereby improving soil carbon sequestration and ecological value in agriculture. In this study, field experiments were conducted using various types of fertilizers: organic fertilizer, microbial fungal fertilizer, composite fertilizer, and an unfertilized control (CK). Additionally, different dosages of compound fertilizers were applied, including 0.5 times compound fertilizers, constant compound fertilizers, 1.5 times compound fertilizers and CK. Using advanced technologies such as Illumina MiSeq high-throughput sequencing, PICRUSt2 prediction, Anosim analysis, redundancy analysis, canonical correlation analysis, and correlation matrix, soil organic carbon (SOC) content and components, bacterial diversity, metabolic functions, and interaction mechanisms were examined in different fields. The results showed pronounced effects of various fertilization modes on SOC and the bacterial community, particularly in the topsoil layer (0-20 cm). Organic fertilizer treatments increased the richness and diversity of bacterial communities in the soil. However, conventional doses and excessive application of compound fertilizers reduced the diversity of soil bacterial communities and SOC content. Additionally, different fertilization treatments led to an increase in easily oxidizable organic carbon (EOC) contents. Interestingly, the relationship between SOC components and soil bacteria exhibited inconsistency. EOC was positively correlated with the bacterial diversity index. Additionally, Chloroflexi exhibited a negative correlation with both SOC and its components. The influence of metabolismon primary metabolic functions on the content of SOC components in the soil was more notable. It included seven types of tertiary functional metabolic pathways significantly correlated with SOC components (p < 0.05). These findings enhance the understanding of the relative abundance of bacterial communities, particularly those related to the carbon cycle, by adjusting agricultural fertilization patterns. This adjustment serves as a reference for enhancing carbon sinks and reducing emissions in agricultural soils.

Using a novel vector length stability index (VLSI) to evaluate soil aggregate stability: A preliminary study

Soil aggregate stability is an important soil characteristic which can represent the improvement of soil structure after revegetation. Due to the high heterogeneity of soil, large-scale sampling is usually necessary to estimate the spatial variation of aggregate stability across landscapes. Although there are many methods and corresponding indices for analysis of aggregate stability, many of them are not suitable for investigations with a large number of samples due to time-consuming experimental practices. To avoid unnecessary costs of time and labor in the long-term land degradation and restoration monitoring across large regional scales, simple indices of aggregate stability would help monitoring across large regional scales. For this reason, we introduced a new, simple, and normalized index, the vector length stability index (VLSI) and its weighted form (wVLSI) to describe soil aggregate stability. The VLSI shares key information of aggregate size distribution with mean weight diameter (MWD), but it is naturally normalized and dimensionless. This new index was tentatively tested to describe soil aggregate stability of the 0–30 cm soil layers under artificial plantations, natural grassland, abandoned farmland, and farmland in production in a small watershed located in the Loess Plateau of China. The results showed that the aggregate stability of the 0–20 cm layers in abandoned farmland could be recovered near to the condition under artificial plantations just after 2-year abandonment, but the aggregate stability hardly changed in the 20–30 cm layer. The aggregate stability of the 0–10 cm layer in natural recovered grassland is close to that in top soil layers under artificial plantations, but the stability in the 10–30 layers appeared as low as that in farmland. Because of its simple form and low data requirements, the VLSI could be an alternative efficient tool for soil aggregate stability evaluation when a large number of samples are needed.

Biogeochemistry of dissolved organic matter and inorganic solutes in soil profiles of tropical pasturelands

Tropical soils play a critical role in the global biogeochemical cycles and are essential for maintaining the Earth's carbon balance. Understanding the dynamics of dissolved organic matter (DOM) is paramount due to its implications for ecosystem functioning and nutrient cycling. This study comprehensively evaluated the origin, distribution, and composition of DOM and inorganic solutes in Brazilian tropical agricultural soils. Multiple analytical techniques were utilized to assess DOM from soil profiles (0–100 cm depth) across a spectrum of land uses, including a native Atlantic Forest, a degraded pasture, as well as intensive grazing, extensive grazing, and silvopastoral systems. Inorganic elements were quantified to assess the coupling between the organic and inorganic biogeochemical cycles. The dominance of C4 carbon in topsoil layers suggested substantial contributions of organic matter from grasses to the soil organic matter pool. However, with increased depth, C3 carbon inputs became more prominent, indicating the influence of forest vegetation that existed prior to the implementation of agricultural managements. DOM concentrations decreased with soil depth due to reduced carbon inputs, sorption to minerals, or oxidation. DOM composition did not show significant changes among different land use and managements. Lignin was identified as the primary contributor to oxidized DOM with increasing soil depth. The composition of DOM exhibited a shift from more aromatic and higher molecular weight compounds in topsoil layers to smaller, more aliphatic compounds in subsoil layers. Our key findings revealed that aliphatic compounds, particularly fatty acids, tend to accumulate in deeper soil layers. This phenomenon was consistent in pastures dominated by grasses but not in soils near treed vegetation. Overseeding (from C3 plants) did not significantly impact DOM compositions, emphasizing the persistence of C4 plants in these systems. The presence of inorganic elements in soil water extracts showed minimal impact on DOM dynamics, suggesting decoupled organic and inorganic biogeochemical cycles in tropical pasturelands.

The spatial variability of physicochemical parameters of mangrove soil and mangrove species in Negombo Lagoon, Sri Lanka

Mangrove forests are unique and invaluable ecosystems due to their role in biodiversity, coastal protection, and carbon sequestration. This study examined spatial variability of selected physicochemical parameters of mangrove soil and species distribution at the Negombo lagoon. Eighteen sampling sites were selected based on judgmental sampling techniques. A 10 m x 10 m area was selected within the 1 km x 1 km grid to get the replicate soil samples from 0 − 15, 15–30 and 30–45 cm depths from the surface. Further, a vegetation survey was conducted to identify mangrove species in the same 10 m x 10 m area. Soil temperature, pH, salinity, and soil organic matter (OM) were analyzed using standard laboratory methods. Results show that temperature varied spatially from 25.2 °C to 30.0 °C, with the highest temperature recorded in the topsoil layer. Soil pH and salinity spatially varied from 5.39 to 8.31 and 0.56 % to 8.83 %, respectively. Soil organic matter spatially varied from 2.56 % to 15.7 % and increased with the increasing depth. Soils with high salinity tend to reduce OM by accelerating the mineralization of OM. Correlation analysis showed a positive relationship between salinity and OM (r = 0.57; P < 0.05). Rhizophora apiculata, Rhizophora mucronate and Avicennia marina were associated more in soils with high salinity (3.72 % − 7.15 %) and neutral to weakly alkaline pH. Bruguiera gymnorrhiza was more prevalent in soils with higher salinity (7.69 % − 8.83 %) and lower pH, while Lumnitzera racemosa was found in acidic to slightly alkaline pH but with low salinity (1.35 % − 1.92 %) soils. Sonneratia caseolaris was recorded in soils with the lowest salinity (0.83 % − 1.04 %). The findings offer valuable insights for decision-making processes for conserving and restoring mangrove forests, providing effective and sustainable environmental management strategies.

The Short-Term Responses of Forest Soil Invertebrate Communities to Typhoon Disturbances

Knowledge regarding the response of soil invertebrate communities to typhoon disturbance is limited, although it is known that soil invertebrates are sensitive to forest disturbances and that tropical cyclones (typhoons/hurricanes) are the most destructive natural disasters affecting the structure and function of forest ecosystems. To fill this knowledge gap, soil invertebrates in both litter and topsoil layers were investigated in four representative subtropical coastal forests of eastern China one week before the first typhoon (Hinnamnor) (T1), one day after the first typhoon (Hinnamnor) (T2), one day after the second typhoon (Muifa) (T3), and one week after the second typhoon (Muifa) (T4) in September 2022. Typhoon disturbances decreased the density and taxa abundance of soil invertebrate communities in litter layer, but the first typhoon disturbance increased these values in the topsoil layer. One week after the second typhoon disturbance, soil invertebrate communities in the litter layer showed a gradual recovery trend. Meanwhile, the soil invertebrate communities in the litter layer were more sensitive to typhoon disturbances than those in the topsoil layer. Furthermore, the responses of the soil invertebrate communities to the typhoon disturbances varied greatly with the forest types. The invertebrate densities in the litter layer decreased by 62.1%, 63.53%, 47.01%, and 46.92% in Chinese fir, second broad-leaved, mixed, and bamboo forests, respectively. Particularly, these two non-catastrophic typhoons significantly altered the functional group composition of detrital food webs in the short term, and the proportion of phytophages in detrital food webs in the litter layer increased after the typhoon disturbances. In conclusion, the effects of typhoon disturbances on soil invertebrate communities vary greatly with forest type and soil layer, and soil invertebrate communities can gradually recover after typhoon disturbances. The legacy effects of typhoon disturbances on the functional group composition of detrital food webs may influence carbon and nutrient cycling in forest ecosystems.

Combination of Lolium perenne L. and Festuca arundinacea Schreb. improve yields under low phosphorus availability

AbstractPhosphorus (P) is one of the main nutrients for all plants, including grasses. However, sources of P fertilizer are not renewable, are not evenly distributed and overfertilization can lead to serious environmental degradation. Smart combinations of grasses may be able to more efficiently take up P from soils through complementarity. In a two-year field mesocosm experiment, we compared the performance of Lolium perenne L. and Festuca arundinacea Schreb. in monocultures and in combination, as well as a mixture of both species with a tetraploid variety of Lolium perenne L and Phleum pratense L. Plants were grown in an unfertilized low P soil and in P fertilized soil for two growing seasons. We measured biomass production, root traits, nutrient uptake, microbial biomass and enzymatic activities. In the unfertilized plots the combination of Lolium perenne and Festuca arundinacea generated the highest cumulative yields (25,951 ± 4059 kg ha−1), relative total yield (&gt; 1) and P nutrition index (0.79). We related this to the complementarity found in root traits and lower intraspecific competition of Festuca arundinacea and Lolium perenne diploid. Festuca arundinacea produced higher root biomass than Lolium perenne diploid at deeper soil layers (98 vs. 44 g m−2; p &lt; 0.05). On the other hand, Lolium perenne diploid had significantly finer roots than Festuca arundinacea both at topsoil and bottom layers (0.19 vs. 0.22 mm and 0.19 vs. 0.23 mm at top and bottom layers respectively). The 4 species combination did not result in higher yields. Our results show that, in low P soils, combinations of grass species with contrasting root traits could lead to significantly higher yields than monocultures.

Effect of long-term compost fertilization on the distribution of organic carbon and nitrogen in soil aggregates

Soil fertility is mainly related to soil total organic carbon (C) that should be preserved in order to optimize soil quality and functionality. Consequently, the use of organic amendments could be a possible strategy to increase soil C and nitrogen (N) storage particularly in orchard systems where the disturbance of soil is reduced thus making favorable conditions for C and N stabilization.The aim of this study was to evaluate the distribution and stabilization of organic C and total N in aggregate fractions after a 14-years-period of compost application to a peach orchard. The trial was conducted in the south-eastern Po valley, on a commercial nectarine orchard and the following treatments were compared in a complete randomized block design with four replicates: 1. unfertilized control; 2. mineral fertilization; 3. compost at a rate of 10 Mg dry weight ha−1 yr−1. At the end of orchard lifetime, soil was sampled from the row at four depths (0–0.15, 0.16–0.25, 0.26–0.45, and 0.46–0.65 m) and physically fractionated to separate macroaggregates (> 250 μm), microaggregates (250–50 μm) and silt and clay (< 50 μm) that were analyzed for organic C, total N, δ13C, and δ15N.Compost addition induced a significant increase of macroaggregates (66%), no changes in microaggregates and a decrease of silt and clay (22%) compared to control and mineral fertilization. With compost the accumulation of organic C and total N content in the macroaggregates was four-five times higher than the other two treatments in all the depths, therefore almost 50% of the soil organic C was in this fraction, compared to 20–24% in the control and mineral. In the micro-aggregates more C and N accumulated only in the two top layers, while no effect was observed in the silt and clay fraction. From macro-to microaggregates to the silt and clay fraction, the C/N ratio shifted from 9 to 7.5 to 6 on average indicating that the C and N stabilized in the finer fractions is mainly of microbial origin. The enrichment in C and N isotopic composition from macro-to micro to silt and clay is also indicative of the isotopic fractionation due to microbial metabolism and the consequent stabilization of microbial residues in the finer fractions. In the control and mineral, only receiving orchard litter, this change was observed in all the layers, on the contrary, with compost similar δ13C and δ15N values characterized the fractions in the top soil layer suggesting the occlusion of compost in all the fraction. With depth the macroaggregates maintained the same δ13C and δ15N values indicating consistent redistribution of compost in deep soil layers, while the finest fractions showed a progressive enrichment of δ13C due to the presence of C fractionated during microbial metabolism and progressively stabilized. In conclusion, compost supply leads to positive effects on C and N accumulation and stabilization also in the deeper layers favoring the increase of long-term soil fertility and C storage.

Phytoremediation capacity of hybrid aspen at sites affected by industry and agriculture.

Fast-growing Populus spp. are well-acknowledged to restore contaminated soils from heavy metals in industrial areas. Thus far, there is no knowledge about the phytoremediation capacity of Populus spp. plantations in hemiboreal Estonia conditions to restore industrially polluted areas. The objective of this study was to assess the soil contamination rate of heavy metals (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb and Zn) and their uptake by mature hybrid aspen (Populus tremula × Populus tremuloides Michx.) in plantations in different industrial pollution areas (e.g. cement factory, oil shale mining). For the reference, industrially polluted plantations were compared with the low pollution area hybrid aspen plantation on former agricultural soil, which was influenced by fertilization and liming before afforestation. Twenty-one years after afforestation, soil samples were collected from the 0-10cm topsoil layer. Aboveground biomass sampling was performed for bark and stem wood by ingrowth cores to separate wood formed during early (1-10years) and late (11-21years) stand development. Two decades after the afforestation of industrially polluted areas, the heavy metal concentrations in the soil were higher than the reference plantation and the standard reference for unpolluted soils in most cases. The highest concentrations of heavy metals in woody biomass were in the oil shale quarry spoil; because of poor growth, the accumulated pools in aboveground biomass were low. Cd differed from other metals and accumulated less in wood and more in bark. The concentration of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni and Zn) was higher in the first decade of stand formation (1-10years) than in the last 10years (11-21years). High pools of heavy metals were accumulated in aboveground biomass in the reference plantation, indicating the considerable removal of heavy metal residues from the previous fertilization and liming source with harvest. Two decades of afforestation with hybrid aspen is too short for complete ecosystem restoration from heavy metals in industrially polluted areas.

Priming of Soil Organic Carbon Decomposition Induced by Exogenous Organic Carbon Input Depends on Vegetation and Soil Depth in Coastal Salt Marshes

The input of fresh organic carbon into soils can stimulate organic carbon mineralization via priming effects (PEs). However, little is known about the characterization of PEs in coastal wetlands. We investigated the PEs of two salt marshes (Suaeda salsa and Phragmites australis) in the Yellow River Delta by adding 13C-labeled glucose to soils collected from the 0–10 cm and 20–30 cm layers of both salt marshes. The addition of glucose produced a significant positive PE in both soil layers for both vegetation types. There were no differences in the PE of the topsoil layer between the two vegetation types (p &gt; 0.05), whereas the PE of S. salsa was 19.5% higher than that of P. australis in the subsoil layer (p &lt; 0.05). In addition, the topsoil layer showed a higher average PE of 29.1% compared to that of the subsoil layer for both vegetation types (p &lt; 0.05). The differences in the PEs between the two vegetation types and the two layers could be associated with a differential soil salinity, substrate availability, and microbial community structure. Our findings highlight the important role of PEs in regulating the soil carbon storage of coastal salt marshes, which should be considered when assessing and modeling the soil carbon cycling of coastal wetlands.

Resistivity Prospecting for Groundwater Potential at the Proposed Ibrahim Badamasi Babangida University Teaching Hospital, Lapai, Niger State

Resistivity methods have been increasingly used for aquifer characterisation due to their high level of effectiveness. In this study, electrical resistivity survey was carried out at the Proposed Ibrahim Badamasi Babangida University Teaching Hospital Lapai Niger State Nigeria in order to study the groundwater potential with a view of determining the depth to the bedrock and thickness of the overburden protective capacity. Vertical Electrical Sounding (VES) using Schlumberger array was used to occupy thirty (30) VES stations using ABEM Terrameter (SAS 300) for the acquisition of apparent resistivity data. The field data obtained was analysed using computer software (IPI2win) which gave the secondary geoelectric parameters of depth, layer thickness and layer resistivities. The results revealed heterogeneous nature of the subsurface geological sequence comprising top soil (clayey-sandy and sandy-lateritic), weathered layer, partly weathered (fractured basement) and fresh basement. The resistivity value for the topsoil layer varied from 20Ωm to 600Ωm with thickness ranging from 0.5 to 7.2 m. The weathered basement had resistivity values ranging from 15Ωm to 593Ωm while the thicknesses varied between 2.75 and 33.04m. The fractured basement had resistivity values ranging from 201Ωm to 835Ωm and thicknesses having values between 11 and 20.4m. The fresh basement (bedrock) had resistivity values ranging from 1161Ωm to 3115Ωm with infinite depth. The depth from the earth’s surface to the bedrock surface varied between 2.5 to 47.75m. The VES 10, 11 and 19 had very good overburden protective capacity and can serve as good sites for borehole drilling.

Experimental model updating of slope considering spatially varying soil properties and dynamic loading

AbstractThe widespread threat posed by slope structure failures to human lives and property safety is widely acknowledged. Additionally, natural soil often displays spatial variability due to geological deposition and other factors. Therefore, predicting the seismic response of slopes subjected to ground motions and inversely analyzing the spatial distribution of soils remains an unresolved issue. In the present work, a shaking table experimental test is first designed and carried out, in which a soft‐soil slope dynamic system is established. To capture the seismic response of the soft‐soil slope, specifically the experimental characteristic of acceleration and soil pressure response in both spatial domain and time domain, a series of sensors were pre‐embedded in the slope. Subsequently, a model updating approach is proposed for slope seismic analysis that incorporates spatial variability of soil. In addition, to enhance computational efficiency, the dimensionality reduction of Karhunen–Loève expansion method is introduced to reduce inverse analysis parameters. On the basis of 34 samples collected from experimental data, it is shown that near‐fault pulse‐like ground motions deliver greater concentrated energy, causing more severe damage to slope structures, especially the topsoil layer. Furthermore, using data obtained from a shaking table test subjected to ground motion Recorded Sequence Number 158H1 from the Pacific Earthquake Engineering Research Center NGA‐West2 database as an example, it is also shown that the proposed approach demonstrates high accuracy in predicting the spatial distribution of the maximum shear modulus in soil slope dynamic systems. The present work not only addresses the challenges posed by mainshock–aftershock effects but also highlights the potential of model updating approaches to enhance the understanding of slope behavior under seismic loading conditions.

Vertical bearing capacity of spun precast concrete pile in liquefiable soil: a case study

Spun precast prestressed concrete (SPC) pile has been used in many parts of the world as a viable foundation alternative. This study assesses the load-carrying capacity of SPC piles passing through a deep soft subsoil layer and resting on a dense sand layer. The vertical bearing capacity of the SPC pile has been estimated using various analytical methods and static pile load tests for the Jolshiri area of Dhaka. The liquefaction potential of the site has been assessed using local seismic site conditions, field and laboratory test data. The liquefaction analysis suggests that the topsoil layer is liquefiable to a depth of 4.5 m. The capacity obtained from the load test is compared with those obtained from the different methods, ultimate push-in load, and local design guidelines. Finite Element Analysis (FEA) was performed considering the hardening soil (HS) model using PLAXIS 3D to simulate field conditions. The load settlement response obtained from FEA shows a good agreement with the test results. The capacity examinations primarily suggest that the SPC pile can be a viable foundation solution for the subsoil conditions of Jolshiri Abasion area of Dhaka.

Desiccation of undamaged grasses in the topsoil causes Namibia’s fairy circles – Response to Jürgens & Gröngröft (2023)

In a novel study, Getzin et al. (2022) have excavated 500 grasses at four regions of the Namib to systematically investigate the temporal process of how the young grasses die in fairy circles. Based on measurements of the root lengths, statistical testing, and comparative photo documentations the authors showed that sand termite herbivory did not cause the death of the freshly germinated grasses within fairy circles (FCs). Roots of those dead grasses were initially undamaged and even longer than those of the living grasses outside in the vegetation matrix, which is contrary to termite herbivory. The dying annual grasses within FCs had significantly higher root-to-shoot ratios than the vital grasses in the matrix, both of which can be attributed to the same grass-triggering rain event. This indicates that they died from water stress because the desiccating grasses invested biomass resources into roots, trying to reach the deeper soil layers with more moisture, but they failed.Jürgens and Gröngröft (2023) commented on our research findings. Here, we shed light on their statements by investigating the existing data evidence on the Namib fairy circles, which includes a thorough literature review about the proposed termite-feeding mechanism, as well as describing the properties of soil water within and around the FCs. Our review shows that there is no single study to date that has demonstrated with systematic field evidence in the form of root measurements and data from several regions of the Namib that the green germinating grasses within the FCs would be killed by root herbivory of sand termites.We emphasize that the top 10 cm of soil in the FCs is very susceptible to drying out. In this topsoil layer, the freshly germinated grasses with their 10 cm long roots die quickly after rainfall due to lack of water, because these small plants cannot reach and utilize the higher soil moisture content, which is only found in deeper soil layers below the dry topsoil. Based on 400 measurements of soil moisture during the rainy season 2024, we show that the topsoil in the FCs is significantly drier than in the matrix outside. Finally, we show that the soil physical conditions allow a very high hydraulic conductivity that supports the “uptake-diffusion feedback” during the first weeks after grass-triggering rainfall. During the first two weeks, the soil moisture at 20 cm depth ranged for several rainfall events between 9% and 18% within the FCs, hence way above the 6–8% threshold below which the hydraulic conductivity strongly declines. Even 20 days after rainfall, soil moisture was still above 8%. During this biologically active period, new grasses germinate after about five days, the large perennial grasses along the FC edge resprout and strongly draw water with their established root system at 20–30 cm depth, and the freshly germinated grasses in the FCs desiccate and die within 10–20 days. With our continuous soil moisture measurements, we argue that the quickly greening and competitively superior grasses on the FC edge, as well as the vital matrix grasses, draw soil water from the FCs. This rapid depletion of soil water and drying out of the topsoil leads to the death of the new grasses in the fairy circles.

18O isotopic labelling and soil water content fluctuations validate the hydraulic lift phenomena for C3 grass species in drought conditions

Hydraulic lift is a functional characteristic observed in some plant species, often associated with their ability to withstand drought conditions. It involves capturing water from deep soil layers and redistributing it to shallower soil layers through the plant's roots. Bromus valdivianus Phil., Dactylis glomerata L., and Lolium perenne L. may perform hydraulic lift at varying rates. Using both direct (isotopic labelling - δ18O) and indirect (soil water content sensors) techniques, the study assessed and validated the hydraulic lift under extreme drought conditions on the soil top layer (below permanent wilting point), maintaining the bottom layer at high (20–25% filed capacity [FC]) and low (80–85% FC) levels of soil water restriction. Above- and below-ground biomass growth and morpho-physiological responses were evaluated. All species displayed some degree of hydraulic lift, with significant differences observed in the isotopic analysis and soil water content (p > 0.05). This illustrates that water was redistributed from the deep to shallower soil layer and validates that the hydraulic lift phenomenon is occurring in these C3 grasses. Bromus valdivianus presented the highest δ18O values (25.05‰) and highest increases in soil water content (µ=0.00626 m3 m−3; five events). Bromus valdivianus had a dry matter ratio of approximately 4:1 (0–20cm:20–40 cm). In contrast, L. perenne and D. glomerata had approximately 6:1 and 5:1, respectively. This difference in root morphology may explain the higher rate of hydraulic lift observed in B. valdivianus relative to L. perenne and D. glomerata. This paper validates the occurrence and provides initial insights into the hydraulic lift process occurrence of temperature grass species.