Soil Hydrophobicity Research Articles

Humic acid, dextran, and valeric acid representing macromolecules similar to compounds prevailing in treated wastewater induce soil hydrophobicity

Organic compounds originating from treated wastewater and soil texture have been reported to be the dominant factors influencing soil hydrophobicity. It is the aim of this investigation to elaborate the role of humic acid, dextran, and valeric acid, representing dissolved organic matter, polysaccharides, and fatty acids, respectively, as well as imitating their activity in inducing soil sub-critical water repellency induced by treated wastewater irrigation. The relationships between three model compounds imitating fractions of dissolved organic matter commonly found in treated wastewater, soil texture in relation to water repellency, were investigated. Three types of organic molecules, five soil mixtures with different specific surface areas, and three different organic compounds, as well as a mixture of the three, were tested. After 14–15 of wetting and drying cycles, low levels (sub-critical hydrophobicity) of water repellency developed in all soil mixtures were subjected to applications of several solutions of organic compounds, in comparison with a freshwater control. The highest degree of water repellency was exhibited by the soil with the lowest clay content (lowest specific surface area) and it decreased with increasing clay content (increasing specific surface area). The order of intensity of sub-critical water repellency levels induced by the organic compounds was consistent, yet independent of soil texture. However, soil texture exhibited large influence on soil hydrophobicity in response to the various organic chemicals. Humic acid, the closest in structure to organic matter prevailing in treated wastewater, exhibited the largest effect in inducing soil hydrophobicity.

Urban wastewater reuse in agriculture for irrigation in arid and semi-arid regions - A review

Purpose In recent years, attempts have been made to compensate irrigation water shortage through widespread wastewater application as a low-quality water resource for agriculture. The existing wastewater treatment plants do not have sufficient capacity to treat such a huge volume of wastewater. In arid and semiarid region, soil type as well as climate is different from the others, so the aim of this paper is the review of literature on the effects of wastewater reuse in agriculture. Methods An extensive literature review was conducted to evaluate urban wastewater effects on soil, plant and environment. Results One of the best methods for wastewater disposal is wastewater discharge into the soil. However, as it was revealed in this research, in most cases, this method would lead to increased salinity, SAR, organic matter content, permeability, and electric conductivity as well as reduced soil bulk density. Nevertheless, wastewater effect on soil physical properties depends on its characteristics and also its application period. For instance, in durations less than one year, wastewater has often no significant effect on some soil properties such as bulk density. The best wastewater usage approach is utilizing drip irrigation method, which can overcome the shortcomings resulted from its application. In most studies carried out in this field, wastewater irrigation has led to increased accumulation of heavy elements and nutrients in the soil and even sometimes in under-cultivation plants. It is noteworthy that these elements' accumulation in the fruit section is less than their accumulation in the vegetable part of the plants. Conclusion The use of wastewater without accurate management can extremely cause adverse environmental outcomes, including soil salinization, soil degradation, reduced soil hydraulic conductivity, soil hydrophobicity, poisoning, reduced yield of the crops, and surface/groundwater resources' contamination, and eventually the prevalence of diseases. Consequently, in order to reuse wastewater for agriculture, microbial contamination' reduction should be seriously considered in accordance with the standards determined by the Environmental Protection Agency or the World Health Organization guidelines. It is highly emphasized that after reaching the required standards, the wastewater can be used for irrigation. In conclusion, Pharmaceuticals presence in the wastewater are a growing global concern.

Vegetación arbórea de selvas bajas caducifolias en suelos litosoles y regosoles eutricos degradados

En México, las selvas bajas caducifolias (SBC) son perturbadas por actividades agrícolas. Su regeneración origina el restablecimiento de vegetación arbórea secundaria que, con menor cobertura vegetal y arraigo, produce suelos termófilos e hidrófobos vulnerables a la erosión, que impiden la regeneración de SBC. Se determinó la estructura, composición y diversidad de la vegetación arbórea en dos SBC en suelos litosoles y regosoles degradados en dos áreas de conservación ubicadas en el municipio de San Pedro Mixtepec (SBC-M) y la segunda en San Pedro Pochutla (SBC-P) de la costa de Oaxaca. En cada área se establecieron cuatro unidades de muestreo de 0.25 ha, divididas en 25 cuadros de 100 m² cada uno, en las que se midieron los individuos arbóreos con diámetro normal > 2.5 cm. Se determinó la composición de especies, la estructura vertical (altura) y horizontal (diámetro), el Índice de Valor de Importancia (IVI) y Valor forestal (IVF). La riqueza registrada se evaluó mediante estimadores paramétricos y no-paramétricos (Chao2), los índices de Simpson (1-Dp) modif icados por Pielou, Shannon-Weaver (H´), la equidad (JH´), dominancia y semejanza (IS) entre SBC. Se colectaron muestras de suelo de la SBC-M y se realizó la caracterización físico‑química. Los resultados indican que la riqueza de especies entre condiciones de desarrollo (SBC-M = 33; SBC-P = 47) tuvo diferencias significativas (P < 0.05). La estructura vertical fue entre 1 - 10 m y la horizontal se mantuvo en la clase diamétrica 5 (2.5 - 7.5 cm), para ambas condiciones. Las especies con mayor IVI e IVF fueron: Ceiba parvifolia, Heliocarpus donnell smithii, Dalbergia congestiflora y Amphipterygium adstringens. La SBC-M y SBC-P presentaron un índice I-Dp = 0.911 y 0.919 para H´ = 2.73 y 3.00, en ambas JH’ = 0.78; la dominancia fue de 0.157 a 0.219. La semejanza de especies entre selvas fue del 60%.

Karakteristik Emisi CO2 Tanah Gambut di Bawah Tegakan Kelapa Sawit

Penelitian ini bertujuan mengkaji karakteristik emisi CO2 dari tanah gambut di bawah tegakan kelapa sawit yang dihubungkan dengan faktor lingkungan spesifik lokasi penelitian di daerah Kabupaten Labuhan Batu, Sumatera Utara. Gas CO2 diambil dengan menggunakan close chamber technique, sedangkan konsentrasi gas tersebut diukur menggunakan portable micro Gas Chromatograph CP 4900. Faktor lingkungan sebagai variabel bebas yang diamati meliputi suhu tanah (TS), suhu atmosfer (TA), kelembaban tanah lapisan 0 – 5 cm (SM5), kelembaban tanah lapisan 0 – 30 cm (SM30), dan pH gambut (A). Model hubungan CO2 dengan faktor dianalisis menggunakan analisis korelasi Spearman dan regresi multivariant. Analisis regresi multivariant dilakukan menggunakan regresi stepwise untuk mengetahui faktor lingkungan yang mempunyai hubungan dengan CO2 pada taraf beda nyata 5%. Analisis variance inflation factor (vif) dilakukan untuk melihat multicollinearity dari model regresi multivariant. Berdasarkan analisis korelasi Spearman, faktor lingkungan A (pH gambut) mempunyai koefisiensi korelasi yang tegolong sedang (R = 0.637). Hasil regresi stepwise menunjukkan bahwa emisi CO2 nyata dipengaruhi oleh kelembaban tanah SM30 dan A (n = 216; p < 0.05) dengan nilai vif <3. Regresi multivariant, menghasilkan persamaan terbaik (R2 = 0.420) dimana emisi CO2 = 7.394*A – 0.008*SM30 – 16.659. Secara parsial, penelitian ini juga memperoleh model hubungan emisi CO2 dengan kelembaban tanah gambut, dimana emisi CO2 tertinggi dicapai pada kondisi kelembaban tanah sekitar kapasitas lapang (354 – 376% w w-1) dan menurun dengan meningkatnya kelembaban tanah di atas kadar air kapasitas lapangan. Emisi CO2 tanah gambut mengalami penurunan pada kondisi tanah gambut mengering di bawah zone kadar air kritis, hal ini karena hidrofobisitas tanah gambut meningkat.

Thermal imaging of a hydrophobic soil’s response to surfactant application at the Avon River Catchment Critical Zone Observatory

The hydrology of water repellent soil is poorly understood, in part because measuring hydrophobicity often interferes with subsequent water flow. Since soil surface temperatures provide information on near surface water content, thermography offers the potential to indirectly monitor this hydrology non-invasively. Using a near-infrared thermal camera, 15 plots, each 1 m2, of a hydrophobic sandy topsoil were recorded continuously for three weeks in the field. Treatments included plots with surfactant applied in bands from 16 cm to 100 cm width and a control (no surfactant). Soil sampling and continuous monitoring of soil moisture, soil temperature and weather conditions supplemented surface temperature measurements. Surface temperature and surface soil moisture were shown to be negatively correlated during the day and positively at night. Soil moisture probes indicated that water from three 10 mm irrigation events was largely restricted to depths less than 10 cm throughout the experiment. Dynamics of the semi-variance for treated plots were different to that of the control. Empirical orthogonal functionals (EOF) initially showed the dominant variability in spatial pattern reflected the surfactant application. During the course of the experiment, changes in the EOFs revealed the gradual re-emergence of background soil heterogeneity related to prior seeding rows. The monitoring did not reveal any lateral expansion of wetted areas from the edges of surfactant treated strips. Thermography was able to inform the dynamics of soil moisture related to spatial and temporal variability in hydrophobicity under field conditions. The approach offers the potential to non-invasively image dynamic soil hydraulic properties and to evaluate water repellence amelioration methods.

Hydrophobicity of peat soils: Characterization of organic compound changes associated with heat-induced water repellency

Boreal peatlands provide critical global and regional ecosystem functions including climate regulation and nutrient and water retention. Wildfire represents the largest disturbance to these ecosystems. Peatland resilience depends greatly on the extent of post-fire peat soil hydrophobicity. Climate change is altering wildfire intensity and severity and consequently impacting post-fire peat soil chemistry and structure. However, research on fire-impacted peatlands has rarely considered the influence of peat soil chemistry and structure on peatland resilience. Here we characterized the geochemical and physical properties of natural peat soils under laboratory heating conditions. The general trend observed is that hydrophilic peat soils become hydrophobic under moderate heating and then become hydrophilic again after heating for longer, or at higher, temperatures. The loss of peat soil hydrophilicity initially occurs due to evaporative water loss (250 °C and 300 °C for <5 min). Gently but thoroughly dried peat soils (105 °C for 24 h) also show mass losses after heating, indicating the loss of organic compounds through thermal degradation. Gas chromatography-mass spectrometry (GC–MS) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the chemistry of unburned and 300 °C burned peat soils, and various fatty acids, polycyclic compounds, saccharides, aromatic acids, short-chain molecules, lignin and carbohydrates were identified. We determined that the heat-induced degradation of polycyclic compounds and aliphatic hydrocarbons, especially fatty acids, caused dried, hydrophobic peat soils to become hydrophilic after only 20 min of heating at 300 °C. Furthermore, peat soils became hydrophilic more quickly (20 min vs 6 h) with an increase in heat from 250 °C to 300 °C. Minimal structural changes occurred, as characterized by BET and SEM analyses, confirming that surface chemistry, in particular fatty acid content, rather than structure govern changes in peat soil hydrophobicity.

Hydrophysical properties of sandy clay contaminated by petroleum hydrocarbon

The aim of the presented research was to assess the changes in hydro-physical properties of sandy clay under the influence of petroleum hydrocarbon contamination. An understanding of these changes is fundamental in the right remedial actions and for further use of soil. Laboratory tests of inherently wettable sandy clay showed that the petroleum hydrocarbon induced potential soil water repellency (SWR) of extremely repellent class at the contamination of 18 g kg−1. The relationship between soil water potential (pF) and SWR determined by the WDPT test for given hydrocarbon contamination, i.e., 6, 12, 18, 30, 100 g kg−1, showed that the critical soil moisture value (CSMC) corresponds to the pF = 1.0 ÷ 1.5. Soil retention characteristic (pF) showed that an increase in hydrocarbon contamination from 0 to 100 g kg−1 caused a reduction of total available water for plants from about 0.19 to 0.06 cm cm−3. At the same time, in the pF = 1.5 ÷ 2.0 range, intensive soil pore drainage was observed. Statistically, significant effect of hydrocarbon contamination and soil moisture potential on SWR was found. Soil hydrophobicity limits the addition of soil retention, because a significant part of the precipitation can be transformed by surface runoff. The carried out tests showed that at a hydrocarbon contamination of 30 g kg−1, total rainfall amount 14 mm with an intensity of 2 mm h−1 was transformed into a surface drain in approx. 40%. The conducted studies demonstrate the adverse impact of hydrocarbon contamination on the soil’s hydro-physical properties. The soil water retention reduction and launching of the surface outflow, as a result of limiting the water penetration process resulting from SWR, change the agrohydrological conditions of the contaminated area. It can result as the imbalance of the flow of energy and matter in the ecosystem. The scenarios of environmental effects, among others, depend on the type of soil, the degree of its pollution, the type of ecosystem, and supporting activities undertaken by man. It should be taken into account that the increasing frequency of drought occurrence associated with climate change is conducive to the phenomenon of SWR regardless of the reasons for its occurrence.

Effects of management measures on organic carbon, nitrogen and chemical structure of different soil fractions in Phyllostachys edulis plantations.

To examine the effects of management measures on carbon and nitrogen contents, as well as their distribution and structural characteristics of different soil fractions in Moso bamboo plantations, we compared three types of the bamboo forests (undisturbed, extensively managed, and intensively managed) and the control secondary broadleaved evergreen forest using the methods of physical fractionation, chemical and biological analysis and Fourier-transform infrared spectroscopy (FTIR). The results showed that soil total organic carbon (TOC) and total nitrogen (TN) content, as well as free particulate organic carbon and nitrogen, soluble organic carbon and nitrogen (DOC, DON), and mineral-associated organic carbon and nitrogen in the undisturbed and extensively managed Moso bamboo plantations were significantly increased compared with that in the control. The distribution ratio of free particulate organic carbon and nitrogen in the undisturbed Moso bamboo plantation significantly increased, with mineral-associated organic carbon being the largest reservoir of soil organic carbon (67.6%). Intensive management resulted in the decrease of soil organic carbon, total nitrogen storage, and the contents of each component, but significantly increased DOC/TOC, the ratio of microbial biomass nitrogen to TN as well as the ratio of microbial biomass carbon to TOC (microbial quotient). Management measures significantly affected the chemical structure of SOC. Compared with the control, the relative intensities of phenolic and alcoholic-OH, aliphatic methyl and methylene, aromatic C=C, and carbonyl C=O absorption were higher in the SOC of undisturbed and extensively managed Moso bamboo plantations, and soil hydrophobicity was significantly increased. Results from correlation analysis showed that soil hydrophobicity and the content of aliphatic and aromatic groups were negatively correlated with microbial quotient and positively correlated with TOC and TN content. In conclusion, the increased inputs of organic matter residues (such as litter and roots) could contribute to the relative accumulation of chemical resistance compounds with reduced human disturbance, which significantly enhanced chemical stability of soil organic carbon. Soil clay minerals played a key role in protecting soil organic carbon through the formation of mineral-organic compounds, which facilitate the stability of soil carbon storage and the long-term preservation of soil carbon.

Effect of wetting and drying on meniscus structures in hydrophobic sands

Hydrophobic soils can occur either naturally when particles are coated with plant-derived hydropho-bic organic compounds or if exposed to very high temperatures, or artificially if treated with contaminated water or chemicals in the laboratory. Hydrophobic soils can resist water infiltration, are associated with preferential flow and may lead to increased surface runoffand soil erosion. Traditional understanding of unsaturated hy-drophobic soils suggests that convex water menisci, and so positive water pressures, should form between soil particles, due to contact angles &gt; 90◦. However, experimental results do not support this theory. The objective of this work was to study the changes in meniscus structures in hydrophobic sand specimens, as well as the overall response of the sand to wetting and drying cycles. A very uniform, fine silica sand was mixed with Dimethyldichlorosilane to induce water repellence. Successive images captured in an environmental scanning electron microscope are presented, to examine the response of the sand in two distinct drying and wetting cycles. Preliminary results show that the non-spherical nature of the sand particles prevent or hinder the formation of convex liquid bridges, despite the high contact angles. Rather, water droplets appear to expand only through droplet coalescence, which prevents structures from contracting on drying.

Effect of late‐fall wetting agent application on winter survival of ultradwarf bermudagrass putting greens

AbstractPlant tissue desiccation and low‐temperature exposure are two common causes of winter injury to ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] putting greens. Unlike low‐temperature exposure, winter damage caused by tissue desiccation can occur regardless of temperature and may be worsened by soil hydrophobicity. Wetting agents are commonly applied to actively growing ultradwarf bermudagrass putting greens to remedy the negative effects of soil hydrophobicity. Less is known about the effect of wetting agent applications to dormant ultradwarf bermudagrass putting greens. This research aimed to quantify the effects of a late‐fall wetting agent application on winter injury and the soil volumetric water content of a sand‐based ultradwarf bermudagrass putting green. Single applications of three wetting agents at two rates were made in early December of 2015, 2016, and 2017 to a ‘TifEagle’ ultradwarf bermudagrass putting green and were compared with an untreated control. Spring green‐up and soil volumetric water content were monitored from March to May of each season. Water drop penetration time tests were conducted twice each season to quantify reductions in hydrophobicity compared with the untreated control. On multiple dates, wetting agent treatments had significantly more green turfgrass coverage than the untreated control. In general, wetting agents reduced water drop penetration times in the top 2 cm of the soil profile. This research suggests that late‐fall or winter applications of a wetting agent can reduce injury and enhance spring recovery of sand‐based ultradwarf bermudagrass putting greens.

An experimental method to investigate the water-based suppression of smoldering peat fire

Smoldering wildfire in peatlands is one of the largest and most persistent fire phenomena on Earth, which contributes importantly to global carbon emissions. However, very few studies are available on how to extinguish these smoldering wildfires. Herein, we develop an experimental method to explore the effectiveness of the water-based suppression on smoldering peat fire, and the proposed method can also be used to simulate fire suppression by rain. The low-temperature drying process avoids the variation of hydrophobicity of peat soil. The validation shows that the proposed approach can provide a wide range of water-spray intensities with time variation, and two examples of successful suppression of smoldering peat fire and flaming wood crib fire were presented.•The design of small-scale combustion reactor for peat can mimic the smoldering peat fire in the field.•The effectiveness of water-based fire suppression technologies on peat fire are explored in the lab.•The proposed method can evaluate the effect of rain and weather on suppressing the smoldering wildfire.

Tillage system influences hydrophobicity but not water repellency of a clay loam soil in southwestern Ontario

A 21 yr field study comparing zone tillage (ZT), no-tillage (NT), and moldboard plow tillage (MP) was used to elucidate tillage effects on soil hydrophobicity (SH) and soil water repellency index (RI) in a cool, humid clay loam soil in southwestern Ontario. The SH was 38% (P ≤ 0.05) greater for ZT and NT than MP, and it was similar between crop row (0.34) and crop inter-row (0.37) for ZT. The RI values were not different among tillage systems, or between the crop row versus crop inter-row positions under the three tillage systems.

A critical contribution on understanding the mechanism and implication of peat irreversible drying

The term irreversible drying is known as a condition when peat soil material is dry and cannot be re-wet after an intensive drying. This condition is a result of peat soil hydrophobicity that occurs when a contact angle between peat soil particles and water is greater than 90° and is always understood to be associated with water content. However, in South Kalimantan, there was a phenomenon of irreversible drying but soil water content was still around field capacity and there was a visible coating substance on the particle surface. The purposes of this study were 1) to clarify the cause of irreversible drying in this location and 2) to show a possible effect of rock phosphate addition on the hydrophobicity’s disappearance. A hydrophobic peat soil sample was taken from the location that is cultivated for oil palm. Field observation was conducted on the peat soil that had been amended by rock phosphate. The peat soil hydrophobicity was identified by the Water Drop Penetration Time method and the surface coating substance was observed using SEM-EDS. The WDPT result shows that the peat soil was in hydrophobic condition, but the water content was still around field capacity. The results from SEM-EDS indicate that the coating substance was found as sulfate salts. The rock phosphate that had been added in the field shows a positive effect on the disappearance of the peat irreversible drying. However, the mechanism of soil properties change due to rock phosphate cannot be confirmed yet and need further investigation.

Behavior of imidazolinone herbicide enantiomers in earthworm-soil microcosms: Degradation and bioaccumulation

Imidazolinone herbicides are a group of chiral herbicides that are widely used to control weeds in crops. Despite their wide use, few studies on the behavior of enantiomers in terrestrial systems have been reported. In this study, the bioaccumulation of imazamox, imazapic, and imazethapyr enantiomers in earthworm and their degradation in soils were assessed using earthworm-soil microcosms. The bioaccumulation of the three herbicides in earthworm was not significantly enantioselective. Imazamox and imazethapyr did not significant stereoselective degradation in soil (p > 0.05), while the enantioselectivity of the degradation of imazapic was significant (p < 0.05). Furthermore, biota to soil accumulation factor (BSAF) values were also calculated for three herbicides. Relationships between BSAF values and organic matter content of soil and log KOW of herbicides were investigated. The BSAFs values were negatively correlated with the log KOW of herbicides, and were positively correlated with organic matter content of soil in earthworm-soil microcosms. These relationships indicated that chemical hydrophobicity (Kow) and organic matter content of soil were good predictors to estimate the bioavailability of imidazolinone herbicides to earthworm.

Diagnosis of soil hydrophobicity linked to pig slurry use in a calcareous soil

Pig slurry fertilization in dryland agriculture of semiarid areas is a matter of concern because of the increasing intensity of livestock farming. Slurry is a nutrient source but if it triggers soil water repellency (SWR), this could constrain its application over the surface in the crop cycle. In SWR tests, choice of a suitable drying soil temperature is a key point, as temperature affects its expression. Its determination must also be easily integrated with the different standard analytical procedures in laboratories. In this study we evaluated the persistence and the severity of the SWR in undisturbed soil samples dried at 40 °C. Soil samples came from a long-term fertilization experiment where five slurry treatments plus a control were implemented. Soil samples were taken seven times during a 51 days (d) period, starting 4 d before slurry application and up to 47 d after. The maximum recorded SWR persistence and severity was classified as &lt;em&gt;moderate&lt;/em&gt; and &lt;em&gt;severe&lt;/em&gt;, respectively. As soil dried at 40 °C was able to express hydrophobicity after pig slurry fertilization, the SWR tests can be easily included in the framework of routine procedures for soil sample analysis where this effluent has been applied. Further research is needed in slurry rainfed fertilized areas to evaluate SWR variability (annual and between cropping seasons) and its additional impacts in these agricultural systems.

Digging up the dirt: Quantifying the effects on soil of a translocated ecosystem engineer

AbstractDigging mammals are often considered ecosystem engineers, as they affect important properties of soils and in turn nutrient exchange, vegetation dynamics and habitat quality. Returning such species, and their functions, to areas from where they have been extirpated could help restore degraded landscapes and is increasingly being trialled as a conservation tool. Studies examining the effects of digging mammals have largely been from arid and semi‐arid environments, with little known about their impacts and importance in mesic systems. To address this knowledge gap, we investigated the ecological role of a recently introduced population of eastern barred bandicoots (Perameles gunnii) on Churchill Island, Victoria, south‐eastern Australia, from which all digging mammals have been lost. We quantified the annual rate of soil turnover by estimating the number of foraging pits bandicoots created in 100‐m2 plots over a 24‐h period. Foraging pit counts could not be completed in each season, and the overall turnover estimate assumes that autumn/winter months represent turnover rates for the entire year; however, this is likely to fluctuate between seasons. Ten fresh and ten old pits were compared to paired undug control sites to quantify the effect soil disturbance had on soil hydrophobicity, moisture content and soil strength. Plots contained between zero and 64 new foraging pits each day. We estimated that an individual eastern barred bandicoot digs ~487 (95% CI = 416–526) small foraging pits per night, displacing ~13.15 kg (95% CI = 11.2–14.2 kg) of soil, equating to ~400 kg (95% CI = 341–431 kg) of soil in a winter month. Foraging pits were associated with decreased soil compaction and increased soil moisture along the foraging pit profile. Eastern barred bandicoots likely play an important role in ecosystems through their effects on soil, which adds to an increasing body of knowledge suggesting restoration of ecosystems, via the return of ecosystem engineers and their functions, holds much promise for conserving biodiversity and ecological function.

Membrane Enhanced Bioaccessibility Extraction (MEBE) of hydrophobic soil pollutants – Using a semipermeable membrane for separating desorption medium and acceptor solvent

Bioaccessibility extractions are increasingly applied to measure the fraction of pollutants in soil, sediment and biochar, which can be released under environmentally or physiologically relevant conditions. However, the bioaccessibility of hydrophobic organic chemicals (HOCs) can be markedly underestimated when the sink capacity of the extraction medium is insufficient. Here, a novel method called “Membrane Enhanced Bioaccessibility Extraction” (MEBE) applies a semipermeable membrane to physically separate an aqueous desorption medium that sets the desorption conditions from an organic medium that serves as acceptor phase and infinite sink. The specific MEBE method combines HOC (1) desorption into a 2-hydroxypropyl-β-cyclodextrin solution, (2) transfer through a low-density polyethylene (LDPE) membrane and (3) release into ethanol, serving as analytical acceptor phase. The surface to volume ratio within the LDPE membrane is maximized for rapid depletion of desorbed molecules, and the capacity ratio between the acceptor phase and the environmental sample is maximized to achieve infinite sink conditions. Several experiments were conducted for developing, optimizing and pre-testing the method, which was then applied to four soils polluted with polycyclic aromatic hydrocarbons. MEBE minimized sample preparation and yielded a solvent extract readily analyzable by HPLC. This study focused on the proof-of-principle testing of the MEBE concept, which now can be extended and applied to other samples and desorption media.

Assessing Relation of Soil Hydrophobicity and Soil Water Content and Determining Threshold Moisture of Organic Soil Samples

Assessing Relation of Soil Hydrophobicity and Soil Water Content and Determining Threshold Moisture of Organic Soil Samples

Influence of crop residues and nitrogen fertilizer on soil water repellency and soil hydrophobicity under long-term no-till

Crop residues and N fertilizer under no-till may increase soil water repellency (SWR) and soil hydrophobicity, but few studies have examined these two treatment factors and their interaction. A laboratory study was conducted using a long-term (since 1999) field experiment on a clay loam soil to determine the effect of three crop residues and two N fertilizer levels on SWR and soil hydrophobicity under no-till within the Dark Brown soil zone of the semi-arid Canadian prairies. The three residue treatments were residues removed from soil (Rx0), residues returned to soil (Rx1), and residues supplemented to soil (Rx2). The two fertilizer N treatments were 0 (N0) and 45 kg N ha−1 (N1). Surface (0–10 cm) soil samples were taken in the spring of 2017 after 17 yr. Laboratory measurements were conducted on air-dried and sieved (&lt;2 mm) soil to determine SWR using the repellency index method (RI), soil organic C, hydrophobic CH and hydrophilic CO functional groups, and soil hydrophobicity (CH/CO ratio). Mean RI values ranged from 2.19 to 2.75, indicating subcritical (RI &gt; 1.95) SWR. Similar (P &gt; 0.05) RI values were found for the three residue and two N fertilizer treatments, but the trend was for greater RI with increased residue addition (by 12%–26%) and N fertilizer (by 8%). Soil hydrophobicity was significantly greater by 47%–82% for straw returned or supplemented than straw removed treatments, and by 33% for fertilized than unfertilized treatments. Overall, greater residues and N fertilizer had no effect on SWR, but significantly increased soil hydrophobicity.

Linking hydrophobicity of biochar to the water repellency and water holding capacity of biochar-amended soil

Biochar addition to soil may change the hydrophobicity of amended soil and influence soil hydraulic properties. Soil hydrophobicity, i.e. soil water repellency (SWR) can interrupt water infiltration and form preferential flow leading to a potential risk of soil erosion or groundwater pollution. Up to date, the effect of different biochars on soil hydrophobicity remains unclear and the association of SWR with soil hydraulic properties is still unknown. To link the biochar hydrophobicity to SWR and soil water holding capacity (WHC), the surface structure and chemical composition of 27 biochars with different feedstocks and pyrolysis temperatures were characterized, and the SWR and soil WHC of biochar-added soil were investigated. Carboxylic groups on the biochar surface, surface area and pore volume were mostly influenced by pyrolysis temperature, which suggested the dominant factor determining the severity of biochar hydrophobicity was pyrolysis temperature. Hydrophilic soil became hydrophobic after biochar amendment. A higher addition rate led to a stronger SWR of hydrophilic soil. Biochar addition increased soil WHC of hydrophilic soil with low total organic carbon (TOC) content. Biochar did not have significant influence on SWR and soil WHC of hydrophobic soil with high TOC content. It implied that the influence of biochar on SWR and soil hydraulic properties mainly depended on soil original hydrophobicity and TOC content. Therefore, the properties of biochar and influence on soil hydrophobicity and hydraulic properties should be considered before processing biochar application.