Low Permeability Soils Research Articles

Removal of Pb from Contaminated Kaolin by Pulsed Electrochemical Treatment Coupled with a Permeable Reactive Barrier: Tuning Removal Efficiency and Energy Consumption.

Lead contamination in soil has emerged as a significant environmental concern. Recently, pulse electrochemical treatment (PECT) has garnered substantial attention as an effective method for mitigating lead ions in low-permeability soils. However, the impact of varying pulse time gradients, ranging from seconds to hours, under the same pulse duty cycle on lead removal efficiency (LRE) and energy consumption in PECT has not been thoroughly investigated. In this study, a novel, modified PECT method is proposed, which couples PECT with a permeable reaction barrier (PRB) and adds acetic acid to the catholyte. A comprehensive analysis of LRE and energy consumption is conducted by transforming pulse time. The results show that the LREs achieved in these experiments were as follows: PCb-3 s (89.5%), PCb-1 m (91%), PCb-30 m (92.9%), and PCb-6 h (91.9%). Importantly, these experiments resulted in significant reductions in energy consumption, with decreases of 68.5%, 64.9%, 51.8%, and 47.4% compared to constant voltage treatments, respectively. It was observed that LRE improved with an increase in both pulse duration and voltage gradient, albeit with a corresponding rise in energy consumption. The results also revealed that corn straw biochar as a PRB could enhance LRE by 6.1% while adsorbing migrating lead ions. Taken together, the present data highlights the potential of modified PECT technology for remediation of lead-contaminated soil, which provides an optimal approach to achieve high LRE while minimizing energy consumption.

Influence of remediation by electrokinetic on the chemical and geotechnical properties of clayey soil contaminated by copper sulfate

The enhanced electrokinetic (EK) technique is an innovative approach and increasingly used in remediation of the fine-grained texture soils contaminated with different types of contaminant. In this study, the EK is enhanced by adding an intermediate compartment and using purging solutions at the electrode’s compartments. The natural clayey soil samples were obtained from Al-Ahadab oil field and artificially contaminated with two ratios of copper sulfate (66666.67 and 26666.67 mg/kg). The feasibility of using EK technique was evaluated by the efficiency of extracting copper from soil and the magnitude of recovery in the geotechnical properties of soil. The duration of remediation was continued for about 240-250 hours depending either on the continuity of electroosmosis flow or reach a constant rate of electrical current. The removal efficiency of copper from contaminated soil samples was ranged from 98.4% to 99.6%. The EK remediation technique proved a marginal impact on the specific gravity and Atterberg’s limits, but it has a significant effect on the shear strength parameters and compressibility of soil. Furthermore, the EK technique can be considered an efficient method for removing the low and high concentrations of copper sulfate from clayey soil of low permeability.

Enhancing hydraulic fracturing for in-situ remediation in low-permeability soils: A comprehensive investigation of fracture propagation

Enhancing the complexity of the hydraulic fractures to provide a wide channel for the injection of the agent is crucial for remediating low-permeability contaminated sites. This study involved a physical simulation experiment of large-scale true triaxial hydraulic fracturing in undisturbed soil, as well as field fracturing tests, to investigate fracture initiation mechanisms and the influence of different factors on fracture propagation. The study revealed a unique failure mode for low-permeability soils characterized by impact splitting, involving simultaneous tensile and shear failure. Three typical fracture propagation patterns emerged: (1) horizontal fracture, (2) parallel fracture, and (3) complex fracture. Silty clay predominantly exhibited horizontal fractures, while mucky clay facilitated the formation of complex fractures dominated by multiple transverse fractures. As the vertical stress difference coefficient increased from 1.0 to 1.5, the pressure on the fracture surface enhanced the connection between hydraulic fractures and natural fractures. Hydraulic fracturing in low-permeability soils necessitated large displacements and high-viscosity fracturing fluids to sustain fracture propagation. The field fracturing test results underscored that soil type and in-situ stress were the primary factors governing hydraulic fracture initiation and propagation. Identifying the optimal fracturing location was critical for achieving the maximum stimulated formation volume.

Enhancing Overland Flow Infiltration through Sustainable Well-Managed Thinning: Contour-Aligned Felled Log Placement in a Chamaecyparis obtusa Plantation

Contour felling is a restoration method used to decrease overland flow (OF) and soil erosion in the world. However, the impact of thinning and the placement of felled logs on OF remains inconclusive. Low ground cover and soil permeability promote OF in Chamaecyparis obtusa (Siebold et Zucc.) Endl plantations, making thinning a method for reducing runoff. We examined the relationship between OF and ground cover in a C. obtusa plantation in Japan. Event-based runoff was monitored in three plots from 2016 to 2021, with 40% thinning conducted in 2019. In plot T1, logs were randomly scattered, and, in T2, logs followed contour lines, while control plots stayed the same. After thinning, both treatment plots showed lower OF than the control plot. The ANCOVA test shows a significant slope reduction in treatment plots compared to the control plot from pre-thinning to post-thinning (T1: 0.67 to 0.26, T2: 0.66 to 0.12, p < 0.001, Tukey HSD test). However, in plot T2, OF remained stable for two years post-thinning, affirming the enduring effectiveness of contour-aligned log placement. This study backs the notion that aligning fallen logs with contour lines boosts long-term OF infiltration, supporting sustainable forest and soil management.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3mm and 0.4-0.6mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experimentsdepicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.

Sugarcane growth variation based on rainfall and soil permeability in Takalar, Indonesia

The germination and sprouting phases of sugar cane are critical periods that determine productivity. This phase occurs when the sugar cane is 1-3 months old and requires an adequate supply of water to support the formation of shoots. Poor soil conditions and high rainfall can cause the failure of bud formation. This study aims to determine the relationship between rainfall and soil permeability in successfully constructing sugarcane shoots. We divided the 1 ha research area into nine points (A, B, C, D, E, F, G, H, I) to observe plant growth and soil permeability. The growth factors measured included the number of stems, diameter, and plant height, measured by zigzag. Intact soil samples at a 0-15 cm depth were then analyzed in the laboratory using Darcy’s law to determine the value of soil permeability. The results showed variations in sugarcane growth in the nine study plots. The average number of sugarcane stalks is eight stalks/meter with a height of 159 cm and a diameter of 3 cm. The low soil permeability value of 0.13-0.5 cm/hour cannot compensate for the average rainfall during the budding phase, thereby suppressing plant growth by up to 50% of the average productivity that should be.

Effect of Different Irrigation Managements on Infiltration Equations and Their Coefficients

The main aim of this paper was to analyze the sensitivity of the five infiltration equations (Kostiakov, Kostiakov–Lewis, Philip, Horton and SCS) and their coefficients to various ponding depths and initial soil moisture under different irrigation managements. The treatments included three qualities of water (electrical conductivity = 6, 3 and 0.6 dS/m), two managements of irrigation (intermittent irrigation and daily irrigation) and three irrigation periods (100, 45 and 8 days). The HYDRUS-1D model was calibrated to simulate infiltration in various initial soil moistures and ponding depths. Evaluating the performance of infiltration equations showed that the Horton and Kostiakov–Lewis had better accuracy and Kostiakov and SCS had less accuracy than the other equations. The empirical coefficients of SCS and Kostiakov had the most and least sensitivities, respectively. Furthermore, Horton was the most sensitive equation, while SCS was the least sensitive one. The output parameters under daily management were the most sensitive to variations in infiltration coefficients, especially when the salinity and sodium contents of water and soil were higher. The results also showed that the effect of the initial soil moisture on the infiltration coefficient in high permeable soil (arising from daily management) was greater; but in low permeable soil (arising from intermittent management), the ponding depth was more effective. It is concluded that the infiltration equations (specifically the SCS equation) and their coefficients (specifically coefficient c) should be calibrated relative to the initial soil moisture, ponding depth, soil solution and water irrigation quality. Particularly in areas with high permeable soil (in the daily management), the calibration of the infiltration equation should be conducted with the initial soil moisture. In these areas, the irrigation period should be controlled. In areas with low permeable soil (in intermittent management), calibration should be carried out relative to the ponding depth. In these areas, the inflow rate should be controlled.

Seismic Performance of Drained Piles in Layered Soils.

The provision of drains to geotechnical elements subjected to strong ground motion can reduce the magnitude of shaking-induced excess pore pressure and the corresponding loss of soil stiffness and strength. A series of shaking table tests were conducted within layered soil models to investigate the effectiveness of drained piles to reduce the liquefaction hazard in and near pile-improved ground. The effect of the number of drains per pile and the orientation of the drains relative to the direction of shaking were evaluated in consideration of the volume of porewater discharged, the magnitude of excess pore pressure generated, and the amount of de-amplification in the ground's motion. The following main conclusions can be drawn from this study. Single, isolated piles and a group of drained piles were tested in three series of shake table tests. Relative to conventional piles, the drained piles exhibited improved performance with regard to the generation and dissipation of excess pore pressure and stiffness of the surrounding soil, with increases in performance correlated with increases in the discharge capacity of the drained pile. The acceleration time histories observed within the pile-improved soil indicated a coupling of the rate and magnitude of porewater discharge, excess pore pressure generated, and de-amplification of strong ground motion. The amount of de-amplification reduced with increases in the number of drains per pile and corresponding reductions in excess pore pressure. The improved performance should prove helpful in the presence of sloping ground characterized with low-permeability soil layers that inhibit the dissipation of pore pressure and have demonstrated the significant potential for post-shaking slope deformation.

The Influence of Electrokinetic Remediation Process on the Removal of Cationic and Anionic Dyes from Kaolinitic Soils

Low permeability soils possess specific mineralogical properties such as particle size, high buffer capacity, and high sorption capacity, which make them difficult to remediate and so pose serious environmental problems when polluted. The grain pores of these low permeability so ils trap in pollutants tightly, which are inaccessible and non-responsive to traditional technologies during remediation. Traditional technologies, some of which are ex-situ remediation techniques further compound these environmental problems through logistics and economic infeasibility. Electrokinetic Remediation (EKR) can offer certain advantages for treatment of various contaminants which include organic compounds, heavy metals, radionuclides, organic waste and some mixed inorganic species from a matrix with high salinity, low permeability and high buffering capacity. In addition, (EKR) is a clean and novel technique which accesses the grain pores of low permeability soils such as clays and silts, which have proven non-responsive to other soil remediation technologies such as soil flushing and soil washing. Among these fine soils, it has been proven that (EKR) is more effective on clay soil with particle size <2mm, moderate plasticity, lower cation exchange capacity (CEC) and lower buffering capacity which can be found in this order: kaolinite>illinite >bentonite.

Stable isotopes reveal the surface water-groundwater interaction and variation in young water fraction in an urbanized river zone

Based on 30 sampling campaigns on precipitation, river water and groundwater in Qingbaijiang urban catchment, southwest China, this study reports the spatio-temporal evolution of water isotopes under the impacts of human activities. The seasonal variation of groundwater-surface water interaction is quantitatively evaluated by isotope-aid hydrograph separation, and the young water fraction (Fyw) in river water at different spatial locations is estimated based on the seasonal periodicity of isotopes. The results show that the stable isotopes in river water and groundwater in Qingbaijiang urban catchment grow enriched from upstream to downstream, reflecting the transformation of the dominant water source from plateau river water to local precipitation and the influence of evaporation. The operation of water conservancy projects and construction of impervious surface in urban areas increase the evaporation intensity of river water. The results of the end-member mixing analysis (EMMA) demonstrates that the average annual contributions of river water to near-bank groundwater are 60.17%, 23.55% and 24.90% in the upper, middle and lower parts, respectively. The periodic storage and release of water led by the water conservancy projects enhances the groundwater recharge in the upstream river, while the water exchanges between river water and groundwater in the middle and lower parts of the catchment are reduced. The Fyw at 8 river sections of Qingbaijiang River estimated by the isotopic amplitude ratio method ranges from 0.067 to 0.194, with an overall increasing trend from upstream to downstream. The young water fraction is negatively correlated with mean elevation, mean slope and vegetation coverage, while positively correlated with the proportion of anthropogenic land use and the proportion of low-permeable soil. The construction of impervious surfaces and drainage systems in urban and rural areas is an important driver for the elevated young water fraction.

Air sparging remediation of VOCs contaminated low-permeability soil based on pressure gradient control

Air sparging (AS) is deemed unacceptable for remediating VOCs contaminated soil with low-permeability. To improve air flow and contaminant removal in sparging process, an original approach, termed as pressure gradient-enhanced air sparging (PGEAS) approach, is proposed by controlling pressure gradient in soil. Then the remediation efficiency, mass transfer characteristics, and remediation mechanism are investigated. Results showed that, the PGEAS approach accelerates gaseous contaminant exhaust, reduces residue contamination in soil, and promotes total contaminant removal, finally results in an improved remediation efficiency compared to the conventional approach. Controlled by sparging pressure and flow distance, the pressure gradient is created in soil, and a critical value needs to be exceeded to enhance the VOCs removal and mass transfer characteristics. The measured results of pore pressure and liquid saturation confirm a notable pressure gradient and drainage behavior in soil, which indicate the massive air subchannel formation during air sparging. At a two-dimensional scale, discrete distributions of contaminant concentrations in exhaust air and soil are presented, the removal extent and area are both enhanced using the PGEAS approach with a pressure gradient higher than the critical value. The reached conclusions are of great importance to contaminant removal in heterogeneous stratigraphy at sites.

Permeation grouting of low-permeability silty sands with colloidal silica

Permeation grouting is used to fill the voids in soils with particulates for the purpose of improving soil strength. The technique has been predominatly used for cohesionless soils, however due to nanotechnological advancements in colloidal silica, its application to other soil types has more recently gained attention. Given sands with high silt fractions are a common geotechnical deposit, permeation grouting using colloidal silica is potentially an attractive improvement technique, yet has received limited attention. Therefore, this paper seeks to investigate the transport properties of colloidal silica in low-permeability silty sand, in terms of the effective grouting penetration range and peak strength. To this end, permeation injection is applied on low-permeability silty sand in a laboratory setting and then direct shear tests are undertaken. The results indicate colloidal silica concentrations should be greater than 10% to meet water resistance and strength requirements, while lower than 30% to ensure a uniform distribution of grout and adequate penetration. A low injection pressure of between 45 and 55 kPa, and between 65 and 75 kPa, is found to be suitable for permeating 20% and 30% concentrations of colloidal silica, respectively. After 7 days of curing time, silty sand at natural moisture content and treated with a 20% concentration of colloidal silica shows an increase in peak strength of between 58.1% and 78.4%, which increases further with curing time. A 20% concentration of colloidal silica is recommended for treating silty sand with a coefficient of permeability in the range 10−6 m/s, based on both injection range and peak strength after treatment. These findings may guide the practice of permeation grouting for low-permeability soils.

Nitrate Migration and Transformation in Low Permeability Sediments: Laboratory Experiments and Modeling

The excessive application of fertilizers and the uncontrolled discharge of untreated wastewater on land contribute to the nitrogen pollution of groundwater. Low permeability sediment plays an important role in slowing down the migration of nitrate in groundwater systems. This study focuses on the mechanisms that affect nitrate transport in the low permeability layer. A soil column experiment was conducted and an MT3D transport model (a modular three-dimensional multispecies transport model) of nitrate was proposed. The results show that a low permeation layer could act as a strong barrier to nitrate migration and transportation, as demonstrated by the column soil experiment. The denitrification rates were controlled by many other factors, including nitrate concentration, flow rate, pH values and sediment particle characteristics. This indicated that denitrification is the most important factor in the attenuation of nitrate in low permeability sediments. This study clarified the law of migration and transformation of nitrate in low permeability soils and the factors that influence these processes. The results not only provide a basis for large-scale nitrate simulations, but also provide a reference for nitrate treatment in low permeability layers.

Approximate analytical solution to the axisymmetric model for PVD-enhanced in-situ flushing of double-layered contaminated soils

The in-situ soil flushing technique which utilizes prefabricated vertical drains (PVDs) is an effective remediation method for sandy, silt, and low-permeability clayey soils. It offers several advantages, such as reducing the seepage path, achieving uniform flushing of contaminated areas, and shortening the construction time. This paper proposes an axisymmetric analytical model for PVD-enhanced in-situ flushing remediation of double-layered contaminated soils considering the decay of the initial contaminant concentration along the depth. The derived solutions are then verified against experimental results and existing analytical solutions. The accuracy of the simplified solution is found to improve as the number of stratifications increases by vertically dispersing the initial contaminant concentration, as compared to the numerical results obtained from COMSOL Multiphysics. The study also reveals that a decrease in the spacing between adjacent injection and extraction PVDs or an increase in the injection/extraction rate enhances the flushing efficiency. However, the effects of the two parameters on soil remediation are non-linear and linear, respectively. Furthermore, the difference in the geotechnical properties of the upper soil layers in a bi-layered contaminated soil leads to a variation in the contaminant concentration at any depth and this variation grows larger with time until the soil is completely remediated.

Soil‐dependent β and γ shape parameters of the Haverkamp infiltration model for 3D infiltration flow

AbstractEstimating of soil sorptivity () and saturated hydraulic conductivity () parameters by field infiltration tests are widespread due to the ease of the experimental protocol and data treatment. The analytical equation proposed by Haverkamp et al. (1994) allows the modelling of the cumulative infiltration process, from which the hydraulic parameters can be estimated. This model depends on both initial and final values of the soil hydraulic conductivity, initial soil sorptivity, the volumetric water content increase () and two infiltration constants, the so‐called and parameters. However, to reduce the number of unknown variables when inverting experimental data, constant parameters such as and are usually prefixed to 0.6 and 0.75, respectively. In this study, the values of these constants are investigated using numerical infiltration curves for different soil types and initial soil water contents for the van Genuchten‐Mualem (vGM) soil hydraulic model. Our new approach considers the long‐time expansions of the Haverkamp model, the exact soil properties such as , and initial soil moisture to derive the value of the and parameters for each specific case. We then generated numerically cumulative infiltration curves using Hydrus‐3D software and fitted the long‐time expansions to derive the value of the and parameters. The results show that these parameters are influenced by the initial soil water content and the soil type. However, for initially dry soil conditions, some prefixed values can be proposed instead of the currently used values. If an accurate estimate of and is the case, then for coarse‐textured soils such as sand and loamy sand, we propose the use of 0.9 for both constants. For the remaining soils, the value of 0.75 can be retained for . For constant, 0.75 and 1.5 values can be considered for, intermediate permeable soils (sandy loam and loam) and low permeable soils (silty loam and silt), respectively. We clarify that the results are based on using the vGM model to describe the hydraulic functions of the soil and that the results may differ, and the assumptions may change for other models.

Regulating the electrokinetic delivery of Tween 80 and persulfate for remediating low-permeability phenanthrene contaminated soil: Importance of reducing unproductive consumption

Controllable delivery of persulfate (PS) and the enhancement of oxidative availability of pollutants in in-situ oxidative remediation of low-permeability polycyclic aromatic hydrocarbons (PAHs) contaminated soil are crucial. To tackle the above challenges, the coupling of Tween 80 solubilization enhanced oxidation of phenanthrene (PHE) in low-permeability soil under electrokinetic remediation (EKR) was proposed. Firstly, batch degradation experiments showed that the addition of Tween 80 significantly inhibited the degradation of PHE in soil under thermally activated PS, as the dosage of Tween 80 increased from 0 % to 1 % with the corresponding removal rate declining from 99.19 % to 40.90 %. Accordingly, in-situ electrokinetic delivery of Tween 80 and PS was regulated in further EKR, intending to reduce unproductive consumption. PS was more uniformly delivered to the whole remediation regions from the cathode chamber by electromigration, while Tween 80 was transported into the soil from the anode chamber by electroosmosis, which made Tween 80 solubilization and PS oxidation achieve synergistic effect. And the total removal rate of PHE reached 64.90 % under this strategy, which had increased by 415.90 % and 8.76 %− 130.14 % compared with only EKR or EKR coupling single enhanced technology, respectively. After further thermal activation of transported PS at 50 ℃ by electrical resistance heating, the total removal rate of PHE increased to 71.58 %. EPR spectrum indicated that SO4.- and OH. were responsible for the degradation of PHE.

Enhanced delivery of amendments in contaminated low-permeability soils by hydraulic fracturing

In-situ remediation of contaminated low-permeability sites remains to be a critical challenge due to severe mass transfer limitations. This work developed an analytical model for enhanced in-situ remediation by hydraulic fracturing in low permeability sites, considering the mechanisms of convection, diffusion, adsorption, and degradation of amendments. In this model, amendment-filled fractures were conceptualized as mass release sources, with the release process controlled by a dissolution-diffusion equation. Combining the Laplace and Fourier-cosine transformation techniques, the semi-analytic solutions in the two-dimensional spatial domain were obtained and then validated by COMSOL Multiphysics 6.0. Based on this model, the influence range, effective longevity, degradability, amendment reserves, and fracture spacing design of reactive fractures were investigated. Results show that (1) three reaction zones with different degradability will potentially form around the reactive fractures; (2) a larger reservoir of amendments effectively increases the influence range and effective longevity of reactive fractures; (3) the synergy of multiple fracture systems outweigh the sum of individual fracture properties, but the reasonable spacing design is decisive; (4) ignoring adsorption in low-permeability site remediation may overestimate the influence range of reactive fractures, leading to remediation failure. This work comprehensively analyzed the properties of reactive fractures, providing practitioners with a reference for the enhanced remediation of low-permeability contaminated sites.

Solute transport through undisturbed carbonatic clay soils in dry regions under differing water quality and irrigation patterns

The often-indispensable use of poor-quality irrigation water in drylands instigates diverse physicochemical dynamics leading to soil salinization and sodicity which are recognized as major contributors to land degradation. This study aimed to examine the effects of water quality and irrigation mode on solute transport conditions in terms of ion exchange of colloidal particles. Laboratory studies with undisturbed soil columns were carried out with two water treatments - tap and sodic waters - as well as two water flow velocities: fast leaching which corresponds to Darcy velocity equal to the saturated hydraulic conductivity and slow leaching equal to half the fast-leaching case. Results indicated that the flow velocities did not significantly influence pH, EC and ion concentrations due to the high calcium carbonate and clay contents of the soil which make the soil less permeable. However, flow velocity rapidly decreased in the fast leaching compared to that in slow leaching as the sodic water was applied. This reveals the destructive effect of Na+ in the soil. The EC rapidly dropped at the beginning of leaching for both water qualities opposite to pH, then became steady. All sodic applications caused an increase in Na+ till the end of treatments. This also resulted in variations in measured soluble anions. In general, sharp decreases in highly soluble anions were observed in all treatments, leading to an increase in HCO3–, especially for sodic treatments. Overall, sodicity caused significant changes in flow dynamics and ion concentrations and created favorable conditions for secondary salinization in this low permeable soil system.

Model-based assessment and mapping of total phosphorus enrichment in rivers with sparse reference data

Water nutrient management efforts are frequently coordinated across thousands of water bodies, leading to a need for spatially extensive information to facilitate decision making. Here we explore potential applications of a machine learning model of river low-flow total phosphorus (TP) concentrations to support landscape nutrient management. The model was trained, validated, and then applied for all rivers of Michigan, USA to identify potential drivers of nutrient variation, predict alteration in nutrient concentrations from minimally disturbed conditions, and explore reach-specific sensitivity to riparian agricultural change. A boosted regression tree model of low-flow TP concentrations trained on natural and anthropogenic landscape predictors accounted for 53 % of variation in cross-validation data, had good accuracy, little bias, and plausible relationships between predictors and response. Percent riparian agricultural cover accounted for the greatest root mean square error reduction in the modeled response (33.2 %), followed by riparian soil permeability (12.9 %), watershed slope (9.6 %), and percent urban cover (9.6 %). An apparent non-linear relationship between TP concentrations and percent riparian agricultural cover suggested steep positive increases in stream TP concentrations between 10 and 30 % upstream riparian agricultural cover. Predicted minimally disturbed TP concentrations were spatially variable and ranged from 7.0 to 48.5 μg/L, with the highest concentrations in watersheds draining low-permeability lake plain soils. Comparison of minimally disturbed predictions to those from the early 2000s suggested that much of northern Michigan existed close to the reference condition, while southern Michigan streams were often substantially enriched. Our predicted values of minimally disturbed condition generally agreed with previous studies but offer greater geographic specificity. Expanded application of machine learning modeling with landscape predictor data have great potential to inform stream nutrient strategy development in settings with sparse reference data.

A novel evaluation method of consolidation efficiency of electro-osmotic system

Energy consumption has emerged as a hot topic and cutting-edge research theme in the application of electro-osmotic consolidation of low-permeability soils. However, the resistance of circuits in an electro-osmotic consolidation system is complex, whereby electric energy can be converted into various forms of energy. Based on the law of energy conversion, this study proposes a new method for the quantitative evaluation of energy conversion in an electro-osmotic consolidation system. The most important energy created during electro-osmotic consolidation is the molecular migration kinetic energy, which can drive the drainage of water and cations and the consolidation of soil, which is referred to as the effective energy consumption (EEC). The second form of energy is interfacial thermal energy (ITE), which is associated with increasing interfacial resistance. The third form of energy is the soil thermal energy (STE), which is associated with the rising temperature of the system due to the passage of electric current. In the experiments conducted here, the EEC proportion was overestimated by 57–80% in the electro-osmosis process without considering the ITE and STE. The efficiency of electro-osmotic drainage can be considerably enhanced if appropriate measures can be taken to reduce the proportion of ITE and STE.