Reduction In Hydraulic Conductivity Research Articles

Volume Contraction and Reduction in Hydraulic Conductivity during Particle Crushing

Volume Contraction and Reduction in Hydraulic Conductivity during Particle Crushing

Statistical and machine learning analysis for the application of microbially induced carbonate precipitation as a physical barrier to control seawater intrusion

Seawater intrusion in coastal aquifers is a significant problem that can be addressed through the construction of subsurface dams or physical cut-off barriers. An alternative method is the use of microbially induced carbonate precipitation (MICP) to reduce the hydraulic conductivity of the porous medium and create a physical barrier. However, the effectiveness of this method depends on various factors, and the scientific literature presents conflicting results, making it challenging to generalise the findings. To overcome this challenge, a statistical and machine learning (ML) approach is employed to infer the causes for the reduction in hydraulic conductivity and identify the optimum MICP parameters for preventing seawater intrusion. The study involves data curation, exploratory analysis, and the development of various models to fit the input data (k-Nearest Neighbours – kNN, Support Vector Regression – SVR, Random Forests – RF, Gradient Boosting – XgBoost, Linear model with interaction terms, Ensemble learning algorithms with weighted averages – EnL-WA and stacking – EnL-Stack). The models performed reasonably well in the region where permeability reduction is sensitive to carbonate increase capturing the permeability reduction profile with respect to cementation level while demonstrating that they can be used in initial assessments of the specific conditions (e.g., soil properties). The best performing algorithms were the EnL-Stack and RF followed by XgBoost and SVR. The MICP method is effective in reducing hydraulic conductivity provided that the various biochemical parameters are optimised. Critical biochemical parameters for successful MICP formulations are the bacterial optical density, the urease activity, calcium chloride concentration and flow rate as well as the interaction terms across the properties of the porous media and the biochemical parameters. The models were used to identify the optimum MICP formulation for various porous media properties and the maximum permeability reduction profiles across cementation levels have been derived.

Evidence that variation in root anatomy contributes to local adaptation in Mexican native maize.

Mexican native maize (Zea mays ssp. mays) is adapted to a wide range of climatic and edaphic conditions. Here, we focus specifically on the potential role of root anatomical variation in this adaptation. Given the investment required to characterize root anatomy, we present a machine-learning approach using environmental descriptors to project trait variation from a relatively small training panel onto a larger panel of genotyped and georeferenced Mexican maize accessions. The resulting models defined potential biologically relevant clines across a complex environment that we used subsequently for genotype-environment association. We found evidence of systematic variation in maize root anatomy across Mexico, notably a prevalence of trait combinations favoring a reduction in axial hydraulic conductance in varieties sourced from cooler, drier highland areas. We discuss our results in the context of previously described water-banking strategies and present candidate genes that are associated with both root anatomical and environmental variation. Our strategy is a refinement of standard environmental genome-wide association analysis that is applicable whenever a training set of georeferenced phenotypic data is available.

Reductions in Hydraulic Conductivity of Sands Caused by Microbially Induced Calcium Carbonate Precipitation

Reductions in Hydraulic Conductivity of Sands Caused by Microbially Induced Calcium Carbonate Precipitation

Assessment of the yield and yield attributing characters of oat (Avena sativa L.) grown under different tillage methods and NPK fertilizer rates in semi-arid conditions

Field experiments were conducted to determine the effect of tillage practices and inorganic sources of different combinations of nitrogen, phosphorus, and potassium fertilizers on some physical properties of soil and the yield of oats. The main plots were tillage techniques of no-till (T1), tillage with a cultivator (T2), twice-disc harrow (T3), and moldboard plowing (T4). Split-plots were fertilizer treatments of F1 control without fertilizer, 70:45:50 kg ha−1 NPK (F2), 140:90:100 kg ha−1 NPK (F3), 210:135:150 kg ha−1 NPK (F4), and 280:180:200 kg ha−1 NPK (F5). Soil density, acidity, electrical conductivity, and soil organic carbon increased under T1, while saturated hydraulic conductivity decreased compared with other tillage practices. Soil bulk density and pH increased with increasing sampling depth, while electrical conductivity and soil organic carbon declined with depth. Results from this study indicated a reduction in saturated hydraulic conductivity with time. The highest grain yield was found in the T4 and T3. In contrast, the highest grain yield was observed under F4 and F5 fertilization treatments at location 1 and F5 and F4 treatments at location 2. There were significant differences in growth characteristics and yield components due to the influence of tillage practices and fertilization levels in both experiment locations.

A critical review of municipal solid waste hydraulic conductivity: A mini review.

This study is a critical review of municipal solid waste (MSW) hydraulic conductivity that includes investigation of the influence of vertical stress, dry unit weight and degradation. A total of 56 studies were compiled that included laboratory-, pilot- and landfill-scale hydraulic conductivity experiments. Compacting waste and increasing vertical stress reduce MSW hydraulic conductivity via reshaping the pore networks throughout the waste matrix, reducing the void ratio and increasing tortuosity. However, the magnitude of reduction in hydraulic conductivity is dependent on stress, waste composition and decomposition. Solid waste decomposition can have opposing effects on hydraulic conductivity. Some studies have indicated that an increase in MSW decomposition results in particle size reduction and settlement that reduces the void ratio and decreases hydraulic conductivity. Conversely, some studies indicate that waste decomposition reduces the solid mass, which increases the void ratio and creates larger flow paths that increase hydraulic conductivity. The data compilation, observations and key findings from this study are beneficial for solid waste practitioners to improve design, analysis and operation of MSW landfills.

Strengthening and permeability control in sand using Cr3+-crosslinked xanthan gum biopolymer treatment

Trivalent chromium (Cr3+), commonly used in reservoir conformance control, has recently been introduced as an innovative technique for enhancing the strength and durability of Xanthan gum (XG) biopolymer-based soil treatment via Cr3+-induced crosslinking. We investigated the effects of Cr3+-crosslinked XG (Cr-XG) biopolymer treatment on the strength, stiffness and hydraulic conductivity of sand through a comprehensive series of experiments, including unconfined compression, direct shear, constant-head permeability tests, and rheological yield stress measurements. The results revealed that gelation of Cr-XG hydrogel via crosslinking between cation and carboxyl groups in XG, leading to gel stiffening, enhances cohesion within the sand over time. Furthermore, the increased yield stress in the Cr-XG hydrogel, compared to clean XG hydrogel, contributes to a more enduring pore-clogging effect, particularly under elevated hydraulic gradient conditions. The addition of 1% Cr-XG biopolymer to the sand significantly increased the ultimate bearing capacity by 466% and resulted in a four-orders-of-magnitude reduction in hydraulic conductivity, in comparison to untreated sand. This study elucidated the soil strengthening mechanism and efficacy attributed to crosslinking-induced gelation in Cr-XG biopolymer treatment. It effectively addressed limitations inherent in previous biopolymer-soil treatments, thereby accentuating its potential as a rapid grouting material within geotechnical engineering.

Response of Liquid Water and Vapor Flow to Rainfall Events in Sandy Soil of Arid and Semi-Arid Regions

In arid and semi-arid regions, rainfall takes on a critical significance to both agricultural and engineering construction activities, and the transport process and driving mechanism of soil water under rainfall conditions are in need of further investigation. To clarify the variations in soil moisture, temperature, and liquid and vapor flux under various rainfall scenarios, the Mu Us Sandy Land was selected as the study region, and a water–vapor–heat transport model was established using the Hydrus-1D software with in situ observed soil and meteorological data. The simulated results were in good agreement with the measured data during both the calibration and validation periods, suggesting that the model was accurate and applicable to the study region. The variations in the selected dry and rainy periods proved the significant effect of rainfall events on soil matric potential, temperature, and driving forces. When rainfall occurred, the hydraulic conductivity for liquid water rose by three to five orders of magnitude, driving the liquid water flow downward. In contrast, the vapor flux played a vital role in soil water movement, accounting for about 15% of the total water flux in the shallow layer when the soil was dry, while it became non-significant during rainy periods due to the reduction in hydraulic conductivity for vapor and the temperature gradient. These results clarified the mechanisms of soil liquid water and vapor movement in arid areas, which could provide scientific support for future studies on vegetation restoration and ecosystem sustainability in ecologically fragile areas.

Effect of soil compaction and cover crop management on soil physical quality, biomass production and corn and soybean yield

ABSTRACT No-till with cover crop (CC) has been marketed to growers as a sustainable way to increase soil quality and crop yields. Our goal was to better understand the effect of CC management strategies on crop yield and mitigation of soil compaction. The compaction treatments were: four (C4) and eight (C8) wheel passes of a tractor, and without additional compaction (C0). CCs in autumn/winter were Italian ryegrass (IR) hay, IR as CC, and mix of IR and forage radish as CC. In the spring/summer, corn and soybean were cultivated. The reduction of hydraulic conductivity (0–6 cm depth) after first season in the IR hay was 74.9% in C4 and 96.2% in C8 comparted with C0. Overall, harvested CC has limited capacity to respond to compaction, decreasing root growth (root biomass of 2191, 2753, and 3744 kg ha−1, IR hay, IR CC, and mix, respectively). Further, the negative effects of compaction on crop yield were modest, probably because of the low axle loads and contact stresses; high inherent structural stability of Oxisols; and permanent no-till and CC roots which favored soil structure stability. Future works should use higher axle loads and surface stresses and a control treatment without CC.

Role of Soil Biofilms in Clogging and Fate of Pharmaceuticals: A Laboratory-Scale Column Experiment.

Contamination of groundwater with pharmaceutical active compounds (PhACs) increased over the last decades. Potential pathways of PhACs to groundwater include techniques such as irrigation, managed aquifer recharge, or bank filtration as well as natural processes such as losing streams of PhACs-loaded source waters. Usually, these systems are characterized by redox-active zones, where microorganisms grow and become immobilized by the formation of biofilms, structures that colonize the pore space and decrease the infiltration capacities, a phenomenon known as bioclogging. The goal of this work is to gain a deeper understanding of the influence of soil biofilms on hydraulic conductivity reduction and the fate of PhACs in the subsurface. For this purpose, we selected three PhACs with different physicochemical properties (carbamazepine, diclofenac, and metoprolol) and performed batch and column experiments using a natural soil, as it is and with the organic matter removed, under different biological conditions. We observed enhanced sorption and biodegradation for all PhACs in the system with higher biological activity. Bioclogging was more prevalent in the absence of organic matter. Our results differ from works using artificial porous media and thus reveal the importance of utilizing natural soils with organic matter in studies designed to assess the role of soil biofilms in bioclogging and the fate of PhACs in soils.

Hydraulic Conductivity of Mine Waste Treated Using Enzyme-Induced Calcite Precipitation Method Under Various Curing Conditions

The hydraulic conductivity of mine waste soil is considered moderately high attributed to the high percentage of pore spaces. One of the risks associated with this poor property ispossibleintrusion of contaminated acid drainage into the groundwater or river. Biocementation using enzyme-induced calcite precipitation is a relatively new, more inventive, and environmentally sustainable method compared to the other techniques in improving soil properties. However, limited available data on how this method can be applied in improving heavy-metal contaminated mining wastes. This paper summarizes the effectofthis treatment,includingdifferent cementation concentrations, degree of compaction, curing temperatures and curingdurations in reducing the hydraulic conductivity of mining waste. Results obtained indicate a greater effect of 1.0M compared to 0.5Mconcentration, a degree of compaction of 80% compared to 70%,acuring temperature of 25 °C compared to 15 °C and 5 °C, and immediate reaction effect after 1then slowed down after 3 and 7-day curing. When compared to control samples, the reduction in hydraulic conductivity ranged from75.66to 97.14%. The positive result is attained due to the production of calcite, CaCO3that biocemented the soil particles together and reduced the pore spaces, indicated by their content obtained,ranging from 2.0-5.15% in the treated soil. Visualimages through SEM and spectra of x-ray diffraction confirmed the presence of CaCO3in soil particles. This work contributedsignificantly to the study of the properties of copper mine tailings in Ranau, Sabah, including the first study on biocementation of copper mine tailings. The method couldbe used to reduce the hydraulic conductivity of mining waste soils contaminated with heavy metals. Various scenarios such as curing temperature, duration, cementation concentration and degree of compaction have been proposed to optimize the effectiveness of the treatment.

Effect of compaction water on strength and hydraulic properties of bentonite-based liner

The abundance of pond ash and its resemblance to natural sand encourages its use as a substitute for sand in sand–bentonite (SB) liner material. Compaction water content influences the geoengineering properties of cohesive soil to a great extent. Accordingly, the compaction, strength, permeability and shrinkage characteristics of both pond ash–bentonite (PAB) and SB mixes are investigated at standard and modified Proctor compaction energies at various water contents to support the recommendation of the PAB mixture as an alternative landfill liner. At similar compaction conditions, the PAB mix exhibits higher unconfined compressive strength (UCS) and hydraulic conductivity than the SB mix. The UCS values of mixes compacted on the dry side of optimum are higher than those of mixes compacted on the wet side. Dry-side compacted mixes exhibit a reduction in hydraulic conductivity with permeation time, whereas no substantial reduction in hydraulic conductivity is noticed for wet-side compacted mixes. Furthermore, the volumetric shrinkage of both PAB and SB mixes is within the permissible value of 4%, for a wide range of water variation from the dry to the wet side of optimum. The observed mechanical properties are correlated to the shape of coarse fraction particles and the corresponding microstructural arrangements of the compacted specimens.

Influence of biochar on improving hydrological and nutrient status of two decomposed soils for yield of medicinal plant - Pinellia ternata

Abstract The root tuber of Pinellia ternata has been used as a traditional therapeutic herbal medicine. It is reported to impart beneficial attributes in recovering COVID-19 patients. To meet an increasing demand of P. ternata, this study is intended to investigate the effects of biochar on the soil hydrological and agronomic properties of two decomposed soils (i.e., completely decomposed granite (CDG) and lateritic soil) for the growth of P. ternata. The plant was grown in instrumented pots with different biochar application rate (0%, 3% and 5%) for a period of three months. Peanut shell biochar inclusion in both soils resulted in reduction of soil hydraulic conductivity and increase in soil water retention capacity. These alterations in hydrological properties were attributed to measured change in total porosity, biochar intra pore and hydrophilic functional groups. The macro-nutrient (i.e., N, P, K, Ca, and Mg) concentration of both soils increased substantially, while the pH and cation exchange capacity levels in the amended soils were altered to facilitate optimum growth of P. ternata. The tuber biomass in biochar amended CDG at all amendment rate increases by up to 70%. In case of lateritic soil, the tuber biomass increased by 23% at only 5% biochar application rate. All treatments satisfied the minimum succinic acid concentration required as per pharmacopoeia standard index. The lower tuber biomass exhibits a higher succinic acid concentration regardless of the soil type used to grow P. ternata. The biochar improved the yield and quality of P. ternata in both soils.

Effects of Solids Accumulation on Greenhouse Gas Emissions, Substrate, Plant Growth and Performance of a Mediterranean Horizontal Flow Treatment Wetland

In treatment wetlands (TWs), solids accumulation can result in hydraulic malfunction, reducing the operation life, and it could enhance biological activity by favoring biofilm development. It is still unknown whether the solids accumulation can affect greenhouse gas (GHG) emissions. This study aims to evaluate the solid concentration along a horizontal flow (HF) TW, and its role in GHG emissions, hydraulics, treatment performance, and vegetation development (Phragmites australis (Cav.) Trin. ex Steud.). The study was carried out in an eight-year-old full-scale HF-TW located in the Mediterranean region (Sicily, Italy). To collect data inside the HF unit, nine observation points (besides the inlet and the outlet) along three 8.5-m-long transects (T1, T2, and T3) were identified. The first transect (close to the inlet zone) showed a hydraulic conductivity (Ks) reduction approximately one order of magnitude higher than the other two. Results highlighted that GHG emissions increased during the summer, when the temperature and solar radiation were higher than in the rest of the year, matching the macrophyte growth rate. Theoretical methane (CH4) emissions followed the trend of volatile solids (VS), which was around 3.5 and 4 times in T1 to T2 and T3. Pore clogging affected carbon dioxide (CO2) emissions, which decreased from T1 to T3, with maximum monthly values in T1 (21.4 g CO2·m−2·d−1) being approximately double with respect to T2 (12.6 g CO2·m−2·d−1) and T3 (10.7 g CO2·m−2·d−1) observed in July. The same trend for chemical oxygen demand (COD) removal efficiency, decreasing from T1 to T3, was observed. Notwithstanding this behavior, the final effluent quality was very satisfactory, with an average value of COD removal efficiency above 90%.

Modelling changes in soil structure caused by livestock treading

Increased soil compaction resulting from livestock treading and use of heavy machinery is a major environmental hazard often linked to degradation of the soil ecosystem and economic services. However, there is a weak quantitative understanding of the spatial and temporal extent of soil compaction and how it modifies soil properties and associated functions. To address this challenge, we developed a framework for systematic modelling soil compaction caused by grazing animals. We considered random movement of livestock in a confined field to describe the spatial variation in the soil that is discretized in square cells with given properties. We then used a rheology model based on Bingham’s law to infer compaction-induced changes in soil bulk density and porosity. An associated reduction of saturated hydraulic conductivity is obtained from soil porosity predictions by empirically accounting for macroporosity reduction using a dual-porosity permeability model. This model is coupled with an empirical model of soil structure recovery to account for biological activity (i.e., earthworms and roots). The modelling framework effectively captures primary effects of soil compaction on key soil properties despite lack of explicit consideration of complex effects of compaction such as redistribution of pore sizes and changes in pore connectivity. We tested the model using bulk density, macroporosity and saturated hydraulic conductivity data from a grazing study at the Tussock Creek experimental platform in New Zealand. Data were successfully reproduced by the model. Compaction and recovery trends can be interpreted in terms of model properties associated with management, soil texture and environmental conditions. If data are available for calibration of such properties, the model could be used in agro-ecosystem modelling applications to assess the environmental impacts (such as surface runoff and green-house gas emissions) of livestock-grazing systems and inform management strategies for ameliorating these.

Hydraulic and volume change behaviors of compacted highly expansive soil under cyclic wetting and drying

The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions. The results of this study demonstrate how seasonal climatic variation and stress and boundary conditions individually or collectively influence the hydraulic and volume change behavior of compacted highly expansive soils. The cyclic wetting and drying (CWD) process was applied for two boundary conditions, i.e. constant stress (CS) and constant volume (CV), and for a wide range of axial stress states. The adopted CWD process affected the hydraulic and volume change behaviors of expansive soils, with the first cycle of wetting and drying being the most effective. The CWD process under CS conditions resulted in shrinkage accumulation and reduction in saturated hydraulic conductivity ( k sat ). On the other hand, CWD under CV conditions caused a reduction of swell pressure while has almost no impact on k sat . An elastic response to CWD was achieved after the third cycle for saturated hydraulic conductivity ( k sat ), the third to fourth cycle for the volume change potential under the CV conditions, and the fourth to fifth cycle for the volume change potential under the CS conditions. Finally, both swell pressure ( σ s ) and saturated hydraulic conductivity ( k sat ) are not fundamental parameters of the expansive soil but rather depend on stress, boundary and wetting conditions.

Physiological response and photosynthetic recovery to an extreme drought: Evidence from plants in a dry-hot valley savanna of Southwest China

The frequency of extreme drought events has been rising worldwide, but due to its unpredictability, how plants will respond remains poorly understood. Here, we aimed to characterize how the hydraulics and photosynthesis of savanna plants respond to extreme drought, and tested whether they can subsequently recover photosynthesis after drought. There was an extreme drought in 2019 in Southwest (SW) China. We investigated photosynthetic gas exchange, leaf-, stem-, and whole-shoot hydraulic conductance of 18 plant species with diverse leaf habits (deciduous, semi-deciduous and evergreen) and growth forms (tree and shrub) from a dry-hot valley savanna in SW China for three rainy seasons from 2019 to 2021. We also compared photosynthetic gas exchange to those of a regular year (2014). We found that leaf stomatal and hydraulic conductance and maximum photosynthetic rate were significantly lower during the drought in 2019 than in the wetter years. In 2019, all studied plants maintained stomatal conductance at their minimum level observed, which could be related to high vapor pressure deficits (VPD, >2 kPa). However, no significant difference in stem and shoot hydraulic conductance was detected across years. The reductions in leaf hydraulic conductance and stomatal regulation under extreme drought might help keep the stem hydraulic function. Stomatal conductance and photosynthesis after drought (2020 and 2021) showed comparable or even higher values compared to that of 2014, suggesting high recovery of photosynthetic gas exchange. In addition, the response of hydraulic and photosynthetic traits to extreme drought was convergent across leaf habits and growth forms. Our results will help better understand the physiological mechanism underlying the response of savanna ecosystems to climate change.

Analysis of Biopolymer Solution Injectability Based on Pore Size Distribution and Injection Pressure Using Pore Network Model

Biopolymers used for ecofriendly ground improvement lead to various effects, such as strength increase, hydraulic conductivity reduction, and vegetation enhancement. However, related studies evaluate the mechanical performance of a biopolymer-stabilized soil by simple mixing of the biopolymer and the soil. In this study, the injection performance of a biopolymer solution was evaluated by pore network modeling based on the pore size distribution and the injection pressure. The developed pore network model applies the power law behavior to a modified Hagen-Poiseuille equation to consider the rheological properties of the biopolymer solution. The pore size distribution was obtained by changing the average and standard deviation of the overall pore size. The results showed that as the average pore size increased, the pore saturation and injectivity increased. However, as the standard deviation of the pore size distribution increased, the pore saturation decreased. In addition, as the injection pressure increased, the effects of the standard deviation on the pore saturation and the injectivity decreased. The pore network model developed in this study can predict the injection properties of a grout material into the ground considering rheological properties.

Influence of freezing directionality on the permeability of silty clay

During artificial ground freezing, freezing may undergo in directions either parallel or normal to the flow of water, which may result in different permeability for the water to flow. Therefore, it is of significant importance to observe the influence of freezing directionality on the permeability of soils. A set of laboratory permeation tests were performed in this study on specimens subjected to three freeze-thaw modes. Considerable change in hydraulic conductivity subsequent to freeze-thaw event was found even under condition where volume change was not allowed. Vertical freeze-thaw resulted in the lowest level of hydraulic conductivity as compared with the other two cases, irrespective of dry density and moisture content. The permeability of specimen subsequent to radial freezing was approximately 34 times in maximum greater than that subsequent to vertical freezing. The occurrence of vertical cracks was responsible for the dramatical increase in hydraulic conductivity of specimens after radial freeze-thaw. Vertical freeze-thaw, however, resulted in an apparent reduction in hydraulic conductivity because of the local consolidation of soil structure during the growth of horizontal ice lenses. Processes that larger pores became larger but smaller pores became smaller contributed to the increase in hydraulic conductivity of thawed specimens even though the total void ratio was unchanged.

Modeling moisture redistribution from selective non-uniform application of biochar on Palouse hills

Precision agriculture is most effective in areas where significant in-field variation occurs. The Palouse region of the Pacific Northwest in the US, a vast area of undulating fertile farmland, has relatively high in-field variation in water retention and crop yield due to regional topography and uneven soil erosion. The regional agricultural systems depend on the soil at or near field capacity towards the end of a wet spring to support crops throughout the summer drought period. Dryland agricultural systems and high in-field variation and changing climate make water retention management practices throughout the region critical. A finite element vadose zone transport model was developed and used to understand the benefits of the targeted application of biochar on water retention and water redistribution in a representative hillslope. The model utilizes measured soil hydraulic properties to predict soil moisture distribution over the dry season. A Redwood Sawdust and Wheat Straw biochar was amended at 4% and 7% concentrations by mass. Biochar amended soils showed an increase in water retention and apparent reduction in unsaturated hydraulic conductivity as the soil approached saturated conditions. After two months of bare field evaporation, the model showed that biochar impacts water redistribution in the soil profile, contributing to positive and negative changes and a net increase in water retention. Model outputs with biochar showed increased retention in and around the amendment area, although the magnitude between outputs varied, with some samples showing minimal effectiveness. Despite the differences in magnitude with targeted biochar amendment, these results indicate that biochar can change water redistribution (up to 0.5%) in a soil profile. Additionally, the developed model shows promise as a field and regional level management tool to determine the best return on investment from biochar application when applied in a targeted manner.