Soil Research Articles

Application of Gum Arabic on the Geotechnical Properties of Subgrade Materials

This study investigates the impact of Gum Arabic on the geotechnical properties of subgrade soil materials, a non-traditional soil stabilization technique. Given the need for sustainable and locally available alternatives in road construction, the study aims to assess how different percentages of Gum Arabic affect the physical and mechanical behavior of soil. The research aims to provide sustainable and locally available alternatives in road construction. Three soil samples were treated with varying percentages of Gum Arabic, (1.5%, 3%, 6% and 12%), and standard geotechnical tests were conducted under both soaked and unsoaked conditions. The results showed that the average natural moisture content of the soils was 7.9%, 2.2%, and 4.6%. The addition of Gum Arabic increased the peak maximum dry density of the soil samples by 8.02%, 1.88, and 7.88%. The maximum unsoaked California Bearing Ratio (CBR) values of soil samples were 32.1%, 81.7%, and 48.7%, respectively. Whereas, maximum soaked CBR values of soils S1, S2 and S3 obtained at 1.5%, 6% and 1.5% additions of gum Arabic were 8.4%, 28.7% and 16.9% respectively. The study recommends using 3% Gum Arabic to improve the CBR property of soil samples. The application of Gum Arabic showed significant improvements in soil behavior under both soaked and unsoaked conditions.

Composition and storage of soil inorganic carbon as well as the controlling factors in coastal area of the northern Jiangsu, China.

The sequestration of soil inorganic carbon (SIC) especially pedogenic carbonate (PC) is one of the important pathways reducing the concentration of atmospheric carbon dioxide and thus mitigating climate change in coastal areas. Using the technology of 13C stable isotope, we analyzed the differences in the composition and storage of SIC, and explored the key physicochemical properties influencing soil PC storage in different horizons (0-10, 11-20, 21-40, 41-60, 61-80 and 81-100 cm) from Suaeda salsa wetland (SS), Spartina alterniflora wetland (SA), young poplar plantation (YP), and mature poplar plantation (MP) in coastal area of the northern Jiangsu Province. The results showed that except for the surface (0-10 cm) soil in MP, the SIC content was higher than SOC in all soil horizons. Overall, neither the soil PC to SIC ratio nor the SIC storage were significantly different in SA and SS soils. Compared to wetland soils (0-40 cm), the soil PC to SIC ratio was reduced by 32.7% and 54.1% and the PC storage was reduced by 40.5% and 59.2%, the lithogenic carbonate (LC) storage changed little, while the SIC storage was reduced by 21.0% and 17.9%, respectively in the YP and MP soils. Compared to the YP soils (0-100 cm), both the soil PC to SIC ratio and the PC storage were significantly reduced while the LC storage was significantly increased, especially at the 41-100 cm soil horizons, meanwhile, the SIC storage was not significantly changed in the MP soils. Results of the structural equation modeling (SEM) indicated that key factors influencing soil PC storage were the ratio of PC to SIC, followed by the SOC content and bulk density. SOC could inhibit the formation of soil PC. Generally, the coastal wetlands have greater SIC storage and sequestration potential than poplar plantations, and the PC sequestration can be regulated by modulating the ratio of PC to SIC and SOC content.

Microbiodiversity Landscape Present in the Mine-Tailings of the “Sierra de Huautla” Biosphere Reserve, Mexico

Large-scale mining activities generate significant amounts of waste that accumulates in the environment. These wastes, known as mine tailings, contain high levels of heavy metals, posing risks to human health and causing severe damage to ecosystems. In this study, we determined the heavy metal content of mine tailings in the Sierra de Huautla Biosphere Reserve (REBIOSH), Mexico, and investigated their effect on microbial composition. One of the sites historically contaminated with metals was sampled in three different locations, labeled S1, S2, and S3. A fourth site free of heavy metals (S4) was also used as a control. Our results showed high levels of As, Pb, Cd, and Ag, potentially dangerous metals that exceed thresholds set by international regulatory agencies. Metal contamination indices indicated moderate to extreme enrichment for As, Cd, and Pb, posing potential ecological risks. A metagenomic study of mine tailings showed a core specie-specific microbiome covered by Sinimarinibacterium flocculans, Jiangella anatolica, Thiobacillus denitrificans, Fontimonas thermophile, Sphingomonas koreensis. These may be associated with the processing of heavy metals. A comparative study using the ALDEx2 revealed that less represented species like Variovorax paradoxus, Usitatibacter rugosus, Usitatibacter palustris, Sphingosinicella microcystinivorans, Sphingobium yanoikuyae, and Stella humosa may serve as microbial markers in metal-contaminated environments. In addition, we detected rare or low-abundance species belonging to the phylum Armatimonadota, Candidatus Melainobacteriota, Candidatus Saccharimonadota, Chlamydiota, Deinococcota, Elusimicrobiota, Bacillota, Rhodothermota and Verrucomicrobiota, which could play an important role in ecosystems contaminated with heavy metals. Also, we found site-specific taxonomic representatives such as Nitrososphaera gargensis and Nitrospira nitrificans dominating the S3 ecosystem; Ensifer aridi (S2 and S1), N. nitrificans (S2), while Reyranella soli dominate the S1 soil. These organisms could be crucial for nitrogen access in oligotrophic environments and underscore the adaptability of microbial life to extreme conditions. This is the first comprehensive study of the microbial composition in this important ecological site of the Mexican geography and can provide future guidance for the management and biological treatment of mining wastes.

Changes in root and nutrient uptake of chickpea affected by organic fertilizers and inoculation with arbuscular mycorrhizal fungi and Rhizobium

AbstractAlthough humans have studied biological nitrogen (N) fixation for nearly two centuries, our understanding of how legumes–microbiome interactions impact agroecosystem function is still evolving. To understand the effects of organic fertilizers and dual inoculation with Rhizobium and arbuscular mycorrhizal fungi (AMF) on root activity, N fixation and nutrient uptake of chickpea (Cicer arietinum), a two‐year greenhouse study was conducted in 2020–2021 at the research station of Ferdowsi University of Mashhad, Iran. The experiment design was a randomized complete blocks in the factorial arrangement with three replications. The first factor consisted of two seedbeds including S1 (field soil) and S2 (soil + humic acid + 40 ton ha−1 cattle manure). The second factor included inoculation with Rhizobium alone, mycorrhiza alone, both Rhizobium and mycorrhiza and non‐inoculated treatment. The results showed that the application of organic fertilizers increased the number of nodules, nodule weight, AMF colonization, leaf N content, leaf P content, root volume, root biomass and N uptake of chickpea, significantly. Also, the effect of seed inoculation was significant on all studied parameters where the highest root biomass (2 g), root volume (3.6 cm3) and leaf phosphorus (0.54%) were obtained in co‐inoculated treatments. There was no significant difference between the effect of single inoculation of Rhizobium and dual inoculation of mycorrhiza and Rhizobium on nodule number, nodule weight, leaf N and N uptake of chickpea. Generally, rhizobia and AMF can benefit nutrient uptake and root activity of chickpea, potentially leading to higher crop production.

Influence of Thermal Desorption Technology on Removal Effects and Properties of PAH-Contaminated Soil Based on Engineering Experiments

Polycyclic aromatic hydrocarbon (PAH) contamination in soil poses a serious threat to ecological safety, human life, and health. Thermal desorption is commonly used to remediate PAH-contaminated soil. Current thermal desorption research primarily focuses on parameters for engineering designs through in-house simulations. In this study, based on a PAH-contaminated site thermal desorption remediation project, the removal efficiency of PAHs in soil (S1, S2) after disposal at different heating temperatures (400, 450, 500, 550 °C) and different residence times (20, 25 min) was investigated, and changes in soil properties before and after disposal were analyzed. The removal rate of 16 PAHs from soil at two concentrations reached 100% after 20 min at 500 °C and 550 °C, respectively. The three-phase structural distances of S1 and S2 soils, respectively, increased by 1.65 and 2.99 times after disposal, sand content increased by 3.20% and 8.27%, water-stable macroaggregates decreased by 8.14% and 2.06%, organic carbon content decreased by 7.27% and 27.05%, heavy fraction organic carbon increased by 33.68% and 5.12%, pH decreased from 10.00 and 10.35 to 8.81 and 8.69, and cation exchange decreased by 13.79% and 26.65%. Soil nutrient content such as TP, AP, TK, and AK increased after thermal desorption, and TN content decreased; approximately 1.0 mg/kg of NO3−-N remained. Our results are expected to support the design of programs for soil reuse after disposal.

A combined landfarming-phytoremediation method to enhance remediation of mixed persistent contaminants.

Contamination of soil and water with petroleum hydrocarbons and metals can pose a significant threat to the environment and human health. This study aimed to investigate the establishment and growth of tall fescue and agropyron in two petroleum-contaminated soils (soil S1 and soil S2) with previous landfarming treatments, and to assess the phytoremediation potential for heavy metal removal from these polluted soils. The results showed that the presence of petroleum hydrocarbons significantly (P < 0.05) reduced plant growth, but plant development was facilitated in soils with prior landfarming treatments. Urease activity in the rhizosphere of agropyron for soil S1 was about 47% higher than the unplanted control soil. The rhizosphere of agropyron and tall fescue eliminated more than 40% and 20% of total hydrocarbon amounts in soil S1, respectively, compared to the unplanted soil. Moreover, the plants grown in the landfarming treatment exhibited higher concentrations of metals (Fe, Zn, Mn, Cu, and Ni) than the control. Based on the findings, the combination of landfarming and phytoremediation techniques can provide an optimal solution for removing mixed pollutants, including petroleum hydrocarbons and metals, from the environment.

Influence of Xanthan Gum-Based Soil Conditioners on the Geotechnical Properties of Soils

The impact of climate change has become increasingly severe in forests, where droughts and strong winds on the one hand and extreme rainfall events on the other hand can damage forest ecosystems. To mitigate the effects of drought and enhance soil water retention capacity, three types of soil conditioners (SCs), labeled SC_R, SC_CG, and SC_ZZC, were developed as part of the European project ONEforest. All the conditioners are based on Xanthan gum and have different types and amounts of fillers with diverse cellulose fiber lengths. These can offer the potential to optimize the SC characteristics, e.g., water absorption, water retention, and mechanical stability. This paper focuses on the influence of fillers in the SCs on the geotechnical properties of forest soils from Ljubelj in the Alpine part of Slovenia (S1), Catalonia, northeastern Spain (S2), and Heldburg, Germany (S3). The results show an increase of 53% to 100% in the water absorption of treated soil. A less favorable impact of the SCs was found on the drained shear strength and the compressibility. The drained shear strength of untreated forest soils in a saturated state was S1 c′ = 4.4 kPa, φ′ = 33.5°; S2 c′ = 1.4 kPa, φ′ = 30.0°; and S3 c′ = 12 kPa, φ′ = 28.0°. The addition of SCs results in a reduction in the drained shear strength of saturated mixtures. The reduction depends on the dosage of added SC—whether it is a low (L) or a high (H) dosage. For instance, when the soil S1 was treated with a low dosage of the soil conditioner SC_R, it demonstrated a cohesion (c′) of 11 kPa and a friction angle (φ′) of 27.0°. However, increasing the dosage of the SC_R led to a decrease in both the cohesion and the friction angle for the same soil (c′ = 7.7 kPa, φ′ = 25.0°). Additionally, the type of soil conditioner also impacts the drained shear strength. Among the mixtures with a high dosage of the SC_R, SC_CG, or SC_ZZC, those containing the SC_CG with the longest fibers stand out, demonstrating the highest friction angle. Therefore, longer fibers can be a promising component of the SCs to reduce the negative influence of XG on the mechanical properties of treated soils.

Degradation of pharmaceutical pollutants in different soils by photocatalytic treatment under solar irradiation

Pharmaceutical compounds are chemicals widely applied for the treatment and prevention of human/animal diseases. Wastewater treatment plants (WWTP) are identified as one of their main transfer pathways to aquatic environment since traditional wastewater treatments do not completely remove them. Agricultural irrigation with reclaimed water from WWTP effluents is a growing strategy in areas where water scarcity is a limiting issue. However, the residual presence of these compounds in wastewaters facilitates a new terrestrial route of environmental exposure, increasing the risks of soil pollution and giving rise to dangerous situations for human health and the environment. In this study we have evaluated the effectivity of TiO2 photocatalysis using solar irradiation for the degradation of four contaminants (diclofenac, ibuprofen, ketoprofen and sulfadiazine) in different soil matrices. Influential parameters of photocatalytic process (TiO2 dosage and soil moisture content) were optimized at laboratory scale using UV-LED lamps as light source. Solar remediation trial was performed exposing polluted soils to different treatments (in presence and absence of photocatalyst) during August 2023. After 50 h of solar exposure degradations of these pharmaceuticals reached 97.8–99.5 %, 99.7–100 % and 83.2–97.5 % for soils S1, S2 and S3 respectively. For all compounds, removal followed the order S2 > S1 > S3, in coincidence with the lesser organic matter content of soils. Results suggest that TiO2 photocatalysis under sunlight irradiation could be a useful tool for remediating soils polluted with pharmaceutical residues.

Rice rhizospheric effects and mechanism on soil cadmium bioavailability during silicon application

Exogenous Si mitigates the mobility and bioavailability of Cd in the soil, thereby alleviating its phytotoxicity. This study focused on specific Si-induced immobilisation effects within the rhizosphere (S1), near-rhizosphere (S2), and far-rhizosphere (S3) zones. Based on the rhizobox experiment, we found that applying Si significantly elevated soil pH, and the variation amplitudes in the S3 soil exceeded those in the S1 and S2 soils. Si-induced changes in the rhizosphere also included enhanced dissolved organic carbon and diminished soil Eh, particularly in the Si400 treatment. Meanwhile, the introduction of Si greatly enhanced the Fe2+ and Mn2+ concentrations in the S1 soil, but reduced them in the S2 soil. The rhizosphere effect of Si which enriched Fe2+ and Mn2+ subsequently promoted the formation of Fe and Mn oxides/hydro-oxides near the rice roots. Consequently, the addition of Si significantly reduced the available Cd concentrations in S1, surpassing the reductions in S2 and S3. Moreover, Si-treated rice exhibited increased Fe plaque generation and fixation on soil Cd, resulting in decreased Cd concentrations in rice tissues, accompanied by reduced Cd translocation from roots to shoots and shoots to grains. Structural equation modelling further highlighted that Si is essential in Cd availability in S1 and Fe plaque development, ultimately mitigating Cd accumulation in rice. Si-treated rice also exhibited higher biomass and grain yield than those of control groups. These findings provide valuable insights into Si-based strategies for addressing the Cd contamination of agricultural soils.

N2O consumption, uptake, and microbial reduction processes in flooded sandy loamy paddy soils

AbstractSandy loamy soils are widely distributed in fluvial floodplains and experience flooding events frequently, resulting in a large amount of nitrous oxide (N2O) emissions. This case is more serious when the soil use is changed to paddies. It is of great significance to figure out the N2O consumption and its influencing factors in sandy loamy paddy soils to mitigate N2O emissions. In this study, three sandy loamy paddy soils (0–5 cm) originated from lake deposits were selected (S1, S2, and S3) as objectives. A certain concentration of exogenous N2O was added at the bottom of the flooded soil column to monitor the dynamics of N2O and nitrogen (N2) on the soil surface. Total N2O consumption, N2O uptake, and N2 production were quantified, and the abundance of nitrous oxide reductase genes (nosZI, and nosZII) and other soil properties (ammonium‐nitrogen, nitrate‐nitrogen, and dissolved organic carbon [DOC] content) were analyzed. The results showed that the sandy loamy paddy soil column with a depth of 0–5 cm could intercept more than 95% of the exogenous N2O under the flooded anaerobic condition, indicating that the three sandy loamy paddy soils all had extremely strong N2O consumption capacities. And the increment of N2 accounted for 68.73%–76.09% of the total N2O consumption, which had a stronger relationship with the increase of nosZI gene abundance than nosZII gene. In addition, the total N2O consumption and N2 increment of S1 and S3 soils were significantly higher than those of S2 soil. This difference was mainly related to soil organic matter content, total nitrogen content, DOC consumption, and the increase of nosZI gene abundance (p &lt; 0.05). The strong N2O consumption potential of sandy loamy soils can provide feasible solutions for regulating N2O emissions in a wide range of similar environments in fluvial floodplains.

Responses and resistance capacity of Solanum nigrum L. mediated by three ecological category earthworms in metal-[Cd-As-Cu-Pb]-contaminated soils of North China

Earthworms play vital functions affecting plant growth and metal accumulation from downground to aboveground. Soil metal mobilization may be combined with use of earthworm and hyperaccumulator-Solanum nigrum to improve its remediation efficiency. Understanding the effects of specific-species earthworm belonging to different ecological categories on mechanisms underlying of S. nigrum is critical for metal-polluted remediation. However, seldom studies concerned earthworm-assisted phytoremediation of metal contaminated soil in Northern China. This study investigated the effects of earthworm (Eisenia fetida, Amynthas hupeiensis and Drawida gisti) on S. nigrum with exposure to uncontaminated and [Cd-As-Cu-Pb]-contaminated soil (referred to as S0 and S1) for 60 days, respectively. In S1 soil, A. hupeiensis (anecic) had stronger effects on growth and metal accumulation in the organs (root, stem, and leaf) of S. nigrum than D. gisti (endogeic) and E. fetida (epigeic), attributing to their ecological category. The BAF values of S. nigrum were generally ranking in Cd (0.66–5.13) > As (0.03–1.85) > Cu (0.03–0.06) > Pb (0.01–0.05); the BAFCd values were ranking in leaf (2.34–5.13) > root (1.96–4.14) > stem (0.66–1.33); BAFAs, BAFCu, and BAFPb were root (0.04–1.63) > stem (0.01–0.09) ≈ leaf (0.01–0.06). A. hupeiensis decreased the TF values of S. nigrum from the roots to the shoots. Co-effects of metal stress and earthworm activity on metal uptake by shoots suggested that A. hupeiensis increased the uptake of As, Cu, and Pb (by 56.3 %, 51.5 %, and 16.2 %, p < 0.05), but not Cd, which appeared to remain steady for prolonged durations. Alterations in the integrated biomarker response index version 2 (IBRv2) values demonstrated that A. hupeiensis (12.65) improved the resistance capacity (stimulated GSH, SnGS1, and SnCu-SOD) of S. nigrum under metal-containing conditions, compared with E. fetida and D. gisti (IBRv2 were 9.61 and 9.11). This study may provide insights into the patterns of ‘soil-earthworm-plant system’ on improving remediation efficiency of S. nigrum, from the perspective of earthworm ecological niche partitioning.

Effect of Fertilizer on the Growth and Yield of Boro and T. Aman Rice in the Soils of Industrially Polluted Agricultural Land Areas of Madhupur

A pot experiment was conducted during 2018-19 in a net house at the Department of Soil Science, Sher-e-Bangla Agricultural University, Dhaka, to determine fertilizer's effect on the growth and yield of Boro and T. Aman rice in the soils of industrially polluted agricultural land areas of Madhupur Tract. The study consisted of two factors, i.e., polluted soil viz., S1: Non-polluted soil, S2: polluted soil-1, S3: polluted soil-2, S4: polluted soil-3, and four fertilizer treatments viz., T0: Control, T1: N150P30K60S20Zn3.0 (100%RDCF), T2: N105P21K42S14Zn2.1 (70%RDCF) T3: N75P15K30S10Zn1.5(50%RDCF) The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. Among the soils, the highest Boro rice grain yield of 90.83 g pot-1 was found in S2 (polluted soil-1) soil, and the lowest 41.66 g pot-1 in soil S1 (Non-polluted soil). The treatment T3(50% RDCF) fertilizer treatment gave the highest plant height (84.12 cm), effective tillers (42.5 hill–1), straw (112.58g pot –1) and grain yield (80.03g pot−1) of Boro rice. The higher grain and straw yields of Boro rice were obtained from two industrially polluted soils (S2 and S4). The maximum grain yield (112.3g pot–1) of Boro was found in S2T3 (Contaminated soil 1 and 50% RDCF) , which was statistically similar to S4T2 and S4T3 and lowest in the S1T0 treatment combination. The maximum T. Aman grain yield (38.75gpot−1) was obtained in soil S2 (polluted soil-1), which at par to S4 (polluted soil-3). The maximum T. Aman rice grain yield (36.68 g pot−1) was found in the T2 treatment, which was closely by T1 treatment. Similarly, the maximum T. Aman grain yield was obtained in S2T1 (Contaminated soil 1 and 100% RDCF) which was statistically similar to S2T2, S4T1, and S4T2 and lowest in the S1T0 treatment combination. The highest T. Aman straw yield was found in the S3T1 and lowest in the S1T0 treatment combination.&#x0D; Bangladesh Agron. J. 2023, 26(1): 112-121

ASSESSMENT OF THE HEAVY METAL POLLUTION OF THE SOIL OF AJAOKUTA STEEL COMPANY, AJAOKUTA, KOGI STATE NIGERIA

Soil samples from different sections of Ajaokuta Steel Complex, Ajaokuta were collected randomly for the analysis of the concentration of selected heavy metals caused by the activities of the iron and steel complex. The results obtained were compared with WHO, NAFDAC and SON standards; and the parameters assessed fall within the permissible limits. The low concentration could be attributed to the fact that the Ajaokuta Steel Company has not been in operation for more than five years. The analysis was done using pH meter and atomic absorption spectrometric technique. The pH of the soil S1 (7.50), S2 (7.60), S3 (7.10) and S5 (7.20) were slightly basic and S4 (6.10) and S6 (6.90) were slightly acidic and the concentration of the heavy metals in ppm were within the permissible range except for Fe which is in a high concentration, which was found to range between 97.4to116.5 mg/Kg. Heavy metal pollutants in the environment are of immense concern globally, so there is need to study and enlighten the habitants of such environments where this giant company is situated as clarified in this study.

The Effect of Heating on Properties of Sandy Soils

Although burning grass and crop residues is prohibited in many countries, farmers perceive it as a quick and inexpensive way to eliminate unwanted biomass. The aim of this study was to estimate the impact of heating temperature (simulation of biomass burning) on the studied properties (soil organic carbon (SOC) content, pH(H2O), water drop penetration time, WDPT, and contact angle, CA) of acidic sandy soils. Soil samples were taken from the experimental sites S1, S2, and S3 at Studienka village in the Borská nížina lowland (southwestern Slovakia). Experimental site S1 was arable land, experimental site S2 was arable land abandoned for approximately 10 years, and experimental site S3 was arable land abandoned for approximately 30 years with scattered Scots pine (Pinus sylvestris L.) trees. It was found that all the soil properties studied were strongly affected by heating. A drop in SOC was observed in all the soils for the heating temperature between 20 and 600 °C. Due to the incomplete combustion of SOC, a small (0.1–0.7%) SOC content was recorded even in soils heated to between 600 and 900 °C. An increase in pH(H2O) was observed in all the soils for the heating temperature higher than 300 °C. Soil from the experimental site S1 was wettable (WDPT &lt; 5 s) for all of the heating temperatures. WDPT vs. heating temperature relationships for the soils from the experimental sites S2 and S3 were more complex. After a decrease in the heating temperature of 50 °C, an increase in WDPT for the heating temperature between 50 °C and 300 °C (for S3 soil) and 350 °C (for S2 soil) was registered. Finally, the WDPT dramatically dropped to 0 for the heating temperature of 350 °C (for S3 soil) and 400 °C (for S2 soil). CA started to decrease at 300 °C in all the soils and dropped to 0° for all the soils at 800 °C. CA &gt; 0° measured in soils for the heating temperature between 400 and 800 °C, as a consequence of the small SOC contents due to the incomplete combustion of SOC, is a novelty of this study which demonstrates that CA is more sensitive to the changes in subcritical water repellency than WDPT.

Cellular Cd2+ fluxes in roots confirm increased Cd availability to rice (Oryza sativa L.) induced by soil acidifications

Soil acidifications become one of the main causes restricting the sustainable development of agriculture and causing issues of agricultural product safety. In order to explore the effect of different acidification on soil cadmium (Cd) availability, soil pot culture and hydroponic (soil potting solution extraction) were applied, and non-invasive micro-test technique (NMT) was combined. Here three different soil acidification processes were simulated, including direct acidification by adding sulfuric acid (AP1), acid rain acidification (AP2) by adding artificial simulated acid rain and excessive fertilization acidification by adding (NH4)2SO4 (AP3). The results showed that for direct acidification (AP1), DTPA-Cd concentration in field soils in Liaoning (S1) and Zhejiang (S2) increased by 0.167 - 0.217 mg/kg and 0.181 - 0.346 mg/kg, respectively, compared with control group. When soil pH decreased by 0.45 units in S1, the Cd content of rice stems, leaves and roots increased by 0.48 to 6.04 mg/kg and 2.58 to 12.84 mg/kg, respectively, When the pH value of soil S1 and S2 decreased by 0.20 units, the average velocity of Cd2+ at 200 µm increased by 10.03 - 33.11 pmol/cm2/sec and 21.33 -52.86 pmol/cm2/sec, respectively, and followed the order of AP3 > AP2 > AP1. In summary, different acidification measures would improve the effectiveness of Cd, under the same pH reduction condition, fertilization acidification increased Cd availability most significantly.

Optimization of Soil-Sludge Mixtures by Compaction for Potential Use in Mine Site Reclamation

Studies have indicated the potential of mixtures of silty soil and sludge produced by active treatment of acid mine drainage for use in covers with capillary barrier effects for mine site reclamation. Very high water contents of sludge in the settling pond could negatively affect the required hydrogeotechnical properties of soil sludge mixtures with high sludge contents. The challenge is then to determine the optimum wet sludge content of soil-sludge mixtures with air entry values (AEV) and/or saturated hydraulic conductivity (ksat) required for use in mine site reclamation covers. This paper presents a method to determine the optimum wet sludge content βopt for obtaining the maximum dry density of compacted soil-sludge mixtures. Two types of soil (S1 and S2) and two types of sludge (A and W) were tested. It was observed that βopt can be determined when the initial water content of the soil used in the mixture is lower than the optimum water content determined from the Proctor curve of the soil alone (10 wt% and 6 wt% for soils S1 and S2, respectively) and that βopt does not change with increasing initial soil water content. Optimum wet sludge contents found were low (≈15 wt% and ≈7 wt% for mixtures containing soils S1 and S2, respectively) for the test conditions, indicting a limited quantity of reusable sludge in the mixtures. For all mixtures, the water content corresponding to βopt was close to the optimum water content of the soil alone. Results of soil water retention and saturated hydraulic conductivity (ksat) tests conducted on selected optimized mixtures indicated that the mixtures based on soils S1 and S2 have air entry values higher than 20 kPa and would be suitable for use in the moisture retention layer of covers with capillary barrier effects, while soil S2 and the derived mixtures exhibited ksat &lt; 10−7 cm/s and would be potential materials for the low permeability layer in low saturated hydraulic conductivity covers.

Assessing the suitability of three purple soils for aquaculture by physiological responses in freshwater bivalves (Hyriopsis cumingii)

Small-scale pond aquaculture is one of the fast-growing land use options in fragmented mountainous regions of southwest China. This study measured the quality of three purple soils from Kaizhou (S1), Bishan (S2), and Tongnan (S3) in the Sichuan Basin and assessed their potentials as aquaculture substrates through overlying water trials. The effects of the substrates on the immunity, metabolism, and thermal resistance of Hyriopsis cumingii were also investigated. Soil properties analysis showed that the three soils varied in pH, total organic matter, macro-nutrient, and micro-nutrient contents. The maximum total potassium and available potassium favorable for phytoplankton growth were observed in S3. The physicochemical parameters of the substrates in the overlying water trials concurred with the soil properties. Furthermore, soil enzymes may be used as indices of soil fishability. However, S1 and S2 soils were prone to leach noxious ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2−-N) in water columns. On the other hand, S3 soil maintained the dynamic balance of the antioxidant system in H. cumingii, activated the relative expression of their immune-related and metabolism-related genes, and improved their resistance to thermal stress. Principal component analysis suggested that NH4+-N and NO2−-N in the soil were key environmental factors that destroyed the antioxidant system and impeded the metabolic process of H. cumingii. Based on the findings, the soils were ranked in terms of their suitability for aquaculture as follows: S3 > S1 > S2. Our study will provide a scientific foundation for building inland aquaculture ponds and developing land use policies in China and around the world.

Arsenic mobility and toxicity on soil acid phosphatase activity increased with added phosphorus in contaminated mine soils

AbstractSoil phosphatase activity is identified as sensitive to arsenic (As) pollution and therefore, often used as an indicator to estimate As toxicity in soil. Nevertheless, the effect of As on soil phosphatase activity after its desorption by P is not adequately studied. This study employed sequential extraction procedure and ecological dose parameters to show As mobility and its toxicity to acid phosphatase (AcP). Results indicated that P application significantly increased As desorption ratio in the As ageing process. In S1 (As 2895 mg kg−1) soil, after P addition, the water‐soluble (FWS) fraction had the highest proportion of As, while for S2 (As 645 mg kg−1) and S3 (As 39 mg kg−1) it was residual (FRES) fraction. Additionally, P addition increased the As bioavailability in all soils. Generally, P addition significantly reduced soil AcP activity under all P concentrations and increased in the soil with minimum As content. The variation partitioning analysis indicated that for S1, P concentration was the major factor, for S2 and S3 soils, it was As desorption and ageing time, respectively, that influenced the AcP activity in soils. The calculated ecological dose (ED50) showed that in most cases, As toxicity increased at the end of ageing. Thus, it is essential to control the phosphorus fertilizer applications in silty soils with acid and neutral pH, since it can lead to increased As mobility and toxicity to soil AcP.

Vertical organization of microbial communities in Salineta hypersaline wetland, Spain.

Microbial communities inhabiting hypersaline wetlands, well adapted to the environmental fluctuations due to flooding and desiccation events, play a key role in the biogeochemical cycles, ensuring ecosystem service. To better understand the ecosystem functioning, we studied soil microbial communities of Salineta wetland (NE Spain) in dry and wet seasons in three different landscape stations representing situations characteristic of ephemeral saline lakes: S1 soil usually submerged, S2 soil intermittently flooded, and S3 soil with halophytes. Microbial community composition was determined according to different redox layers by 16S rRNA gene barcoding. We observed reversed redox gradient, negative at the surface and positive in depth, which was identified by PERMANOVA as the main factor explaining microbial distribution. The Pseudomonadota, Gemmatimonadota, Bacteroidota, Desulfobacterota, and Halobacteriota phyla were dominant in all stations. Linear discriminant analysis effect size (LEfSe) revealed that the upper soil surface layer was characterized by the predominance of operational taxonomic units (OTUs) affiliated to strictly or facultative anaerobic halophilic bacteria and archaea while the subsurface soil layer was dominated by an OTU affiliated to Roseibaca, an aerobic alkali-tolerant bacterium. In addition, the potential functional capabilities, inferred by PICRUSt2 analysis, involved in carbon, nitrogen, and sulfur cycles were similar in all samples, irrespective of the redox stratification, suggesting functional redundancy. Our findings show microbial community changes according to water flooding conditions, which represent useful information for biomonitoring and management of these wetlands whose extreme aridity and salinity conditions are exposed to irreversible changes due to human activities.

Experimental investigation of mechanical behavior of geosynthetics in different soil plasticity indexes

Nowadays, in-depth research is done to evaluate the behavior of geosynthetics in cohesive soil. However, it is still unclear how the plasticity index (PI) of soil affects the mechanical behavior of reinforced cohesive soil. The behavior of distinct geosynthetic types in soils having different PI is likewise uncertain. To bridge this gap, the mechanical behavior of three cohesive soils designated as S1, S2, and S3 reinforced with four types of geosynthetics (woven/non-woven geotextile, geocomposite, and geogrid) were studied by executing multiple triaxial compression and interface direct shear tests with and without reinforcement. The results show that the soils reinforced with woven geotextile (GTW) produce higher shear strength than other reinforcements because of their higher interface frictional resistance and tensile strength. It was found that three layers of GTW to S1 soil increased its stiffness, cohesion, and shear strength parameters by 150%, 307%, and 161%, respectively. On the other hand, the increase in shear strength caused by adding three layers of GTW to S2 and S3 soil was only about 59% and 37%, respectively. The interface properties indicate a strong interaction between GTW-S1 soil lasted, whereas a weak interaction between GTW-S2 or S3 soil existed. These findings demonstrate that an increase in the PI of soil significantly reduces the performance of reinforcements due to the reduction in interface friction, lateral constraint, and interlocking effect. The geosynthetic reinforcement performed better in lower plastic soil rather than in higher.