Content Gradient Research Articles

Distribution of Bacterial Communities in Petroleum-Contaminated Soils from the Dagang Oilfield, China

Diversity in bacterial communities was investigated along a petroleum hydrocarbon content gradient (0–0.4043 g/g) in surface (5–10 cm) and subsurface (35–40 cm) petroleum-contaminated soil samples from the Dagang Oilfield, China. Using 16S rRNA Illumina high-throughput sequencing technology and several statistical methods, the bacterial diversity of the soil was studied. Subsequently, the environmental parameters were measured to analyze its relationship with the community variation. Nonmetric multidimensional scaling and analysis of similarities indicated a significant difference in the structure of the bacterial community between the nonpetroleum-contaminated surface and subsurface soils, but no differences were observed in different depths of petroleum-contaminated soil. Meanwhile, many significant correlations were obtained between diversity in soil bacterial community and physicochemical properties. Total petroleum hydrocarbon, total organic carbon, and total nitrogen were the three important factors that had the greatest impacts on the bacterial community distribution in the long-term petroleum-contaminated soils. Our research has provided references for the bacterial community distribution along a petroleum gradient in both surface and subsurface petroleum-contaminated soils of oilfield areas.

Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities

Abstract. The relation between the occurrence of ionospheric irregularities and the spatial gradient of total electron content (TEC) derived from two closely located stations (ASAB: 4.34∘ N, 114.39∘ E and DEBK: 3.71∘ N, 109.34∘ E, geomagnetic), located within the equatorial region, over Ethiopia, during the postsunset hours was investigated. In this study, the Global Positioning System (GPS)-derived TEC during the year 2014 obtained from the two stations were employed to investigate the relationship between the gradient of TEC and occurrence of ionospheric irregularities. The spatial gradient of TEC (ΔTEC∕Δlong) and its standard deviation over 15 min, σ(ΔTEC∕Δlong), were used in this study. The rate of change of TEC-derived indices (ROTI, ROTIave) were also utilized. Our results revealed that most of the maximum enhancement and reduction values in ΔTEC∕Δlong are noticeable during the time period between 19:00 and 24:00 LT. In some cases, the peak values in the spatial gradient of TEC are also observed during daytime and postmidnight hours. The intensity level of σ(ΔTEC∕Δlong) observed after postsunset show similar trends with ROTIave, and was stronger (weaker) during equinoctial (solstice) months. The observed enhancement of σ(ΔTEC∕Δlong) in the equinoctial season shows an equinoctial asymmetry where the March equinox was greater than the September equinox. During the postsunset period, the relation between the spatial gradient of TEC obtained from two closely located Global Navigation Satellite System (GNSS) receivers and the equatorial electric field (EEF) was observed. The variation in the gradient of TEC and ROTIave observed during the evening time period show similar trends with EEF with a delay of about 1–2 h between them. The relationship between σ(ΔTEC∕Δlong) and ROTIave correlate linearly with correlation coefficient of C=0.7975 and C=0.7915 over ASAB and DEBK, respectively. The majority of the maximum enhancement and reduction in the spatial gradient of TEC observed during the evening time period may be associated with ionospheric irregularities or equatorial plasma bubbles. In addition to latitudinal gradients, the longitudinal gradient of TEC has contributed significantly to the TEC fluctuations.

Visualized tracing of capillary absorption process in cementitious material based on X ray computed tomography

Moisture is one of the major deterioration factors of concrete. In this study, the capillary absorption process, which is one of the major transportation mechanism in cement paste, is non-destructively investigated by using X-ray computed tomography (XCT). A novel image processing procedure is proposed to correct the XCT image artifacts and calibrate the results of different measurements. The proposed image processing procedure allows for 3D visualization of the absorption process and additional information can be obtained, including the height of the water absorption front and the water content gradient.

Hydrogeological research in the Tuyajto Lake at the Flamingo National Reserve (Atacama, Chile)

The Tuyajto Lake is a saline lake located in the Andean Altiplano of northern Chile, at the foot of the volcano of the same name. It is fed by springs located on its eastern and northern boundaries. These springs discharge groundwater from a volcanic aquifer. Arid conditions dominate in the area, with average precipitation less than 200 mm/year. The tritium content in some groundwater samples shows the contribution of modern recharge to the total groundwater flow. Recharge occurs by infiltration of snowmelt in the austral winter months and to a lesser extent by short but intense precipitation events during the summer. The vertical gradients of rainfall isotopic content (δ18O, δ2H) and precipitation points to the recharge zone of the springs being located at the northern area of the lake, above 4,900 m a.s.l. along the slopes of the Tuyajto volcano, whereas recharge to the springs discharging on the eastern area of the lake originates in the adjacent basins of Pampa Colorada and Pampa Las Tecas at altitudes between 4,400 and 4,700 m a.s.l. The water of these springs may contain measurable tritium. The chemical composition of groundwater is the result of meteoric water evaporation processes, high temperature water-rock interaction and dissolution of buried old salt flat deposits. The groundwater flow is shallow, due to the presence of a regional low permeability ignimbrite formation that precludes the formation of deep convective groundwater flow cells due to the high density of brines. At a local scale, the Tuyajto lake behaves as a flow-through system with respect to the regional groundwater flow. The persistence of the springs is essential for the existence of the brine sheet and maintaining the ecological conditions for the waterfowl.

Environmental factors determining distribution and activity of anammox bacteria in minerotrophic fen soils.

In contrast to the pervasive occurrence of denitrification in soils, anammox (anaerobic ammonium oxidation) is a spatially restricted process that depends on specific ecological conditions. To identify the factors that constrain the distribution and activity of anammox bacteria in terrestrial environments, we investigated four different soil types along a catena with opposing ecological gradients of nitrogen and water content, from an amended pasture to an ombrotrophic bog. Anammox was detected by polymerase chain reaction (PCR) and quantitative PCR (qPCR) only in the nitrophilic wet meadow and the minerotrophic fen, in soil sections remaining water-saturated for most of the year and whose interstitial water contained inorganic nitrogen. Contrastingly, aerobic ammonia oxidizing microorganisms were present in all examined samples and outnumbered anammox bacteria usually by at least one order of magnitude. 16S rRNA gene sequencing revealed a relatively high diversity of anammox bacteria with one Ca. Brocadia cluster. Three additional clusters could not be affiliated to known anammox genera, but have been previously detected in other soil systems. Soil incubations using 15N-labeled substrates revealed that anammox processes contributed about <2% to total N2 formation, leaving nitrification and denitrification as the dominant N-removal mechanism in these soils that represent important buffer zones between agricultural land and ombrotrophic peat bogs.

Changes in spatiotemporal protein and amino acid gradients in wheat caryopsis after N-topdressing

Wheat grain nitrogen content displays large variations within different pearling fractions of grains because of radial gradients in the protein content. We identified how spatiotemporal mechanisms regulate this. The protein gradients emerged clearly at 19 days after anthesis, with the highest N content in aleurone and seed coat, followed by outer endosperm, whereas the lowest was in middle and inner endosperm. Laser microdissection, qRT-PCR and LC–MS were used to dissect tissue from aleurone, outer endosperm, middle endosperm, inner endosperm and transfer cells, measure gene expression and levels of free and protein-bound amino acids, respectively. The results showed that different FAA transportation pathways worked in parallel during grain filling stage while the grain protein gradient did not follow spatial expression of storage proteins. Additionally, two nitrogen (N) topdressing timings were conducted, either at the emergence of top third leaf (standard timing) or top first leaf (delayed timing), finding that delayed N topdressing enhanced both amino acids supply and protein synthesis capacity. The results provide insight into protein synthesis and amino acid transport pathways in endosperm and suggest targets for the enhancement of specialty pearled wheat with higher quality.

Modeling and experimentation of continuous and intermittent drying of rough rice grains

Rice (Oryza sativa L.) is one of the most produced and consumed cereals in the world, being characterized as the main food of more than half of the world population, since it is source of energy, protein, vitamins and minerals. Freshly harvested rice from the field generally has a high moisture content to be stored safely and, therefore, a suitable drying process needs to be conducted to decrease the physical-chemical activity of the product and inhibit the associated microbial activities. In this work, experiments were carried out on the intermittent drying of rice grains, in order to evaluate the effects of different drying air temperatures (40, 50, 60 and 70 °C) and tempering times (30, 60, 120, 180 and 240 min). Intermittent drying was simulated by means of a new liquid diffusion model based on a prolate spheroid geometry. To validate the model, the solution was fitted to the experimental data for the drying air temperatures of 40 and 70 °C and tempering periods ranging from 0 to 180 min. The results show that, for all experiments of intermittent drying of rough rice, the effective operating time decreased compared to the continuous drying. In addition, intermittent drying produces lower temperature on the grain surface, which minimizes the thermal damages caused to the product during the process. Numerical simulations provide information on moisture distribution inside the rice grain during the periods of interruption in hot air application. After 15 min of drying at temperatures of 40 and 70 °C, followed by a 60-min pause at room temperature, it is possible to respectively reduce about 72 and 68% of the moisture content gradients inside the rice grain. With tempering of 180 min, it is possible to eliminate almost all moisture content gradients for the drying at 70 °C.

The development of a national approach to monitoring estuarine health based on multivariate analysis.

New Zealand has a complex coastal environment spanning a large latitudinal gradient and three water masses. Here we assess whether multivariate analyses of benthic macrofaunal community composition can be a sensitive approach to assessing relative estuarine health across the country, negating the need for regional indices and reducing reliance on reference sites. Community data were used in separate canonical analyses of principal coordinates to create multivariate models of community responses to gradients in mud content and heavy metal contamination. Both models performed well (R2 = 0.81, 0.71), and were unaffected by regional and estuarine typology differences. The models demonstrate a sensitive and standardized approach to assessing estuarine health that allowed separation of the two stressors. This approach could be applied to other stressors, countries or regions.

Quantitative Assessment of State-Dependent Atmospheric Motion Vector Uncertainties

AbstractThis study examines the error characteristics of atmospheric motion vectors (AMVs) obtained by tracking the movement of water vapor features. A high-resolution numerical simulation of a dynamic weather event is used as a baseline, and AMVs tracked from retrieved water vapor fields are compared with the “true” winds produced by the model. The sensitivity of AMV uncertainty to time interval, AMV tracking window size, water vapor content, horizontal gradient, and wind structure is examined. AMVs are derived from the model water vapor field at a specific height and also from water vapor fields vertically blurred using smoothing functions consistent with high-spectral-resolution infrared (IR) and high-frequency microwave (MW) water vapor sounders. Uncertainties in water vapor AMVs are state dependent and are largest for regions with small water vapor content and small water vapor spatial gradient and in places where the flow runs parallel to contours of constant water vapor content. Smoothing of water vapor consistent with IR and MW retrievals does not increase AMV uncertainty; however, the yield of AMVs from IR sounders is much lower than from MW sounders because of the inability of IR sounders to retrieve water vapor below clouds. The yield and error are similar for AMVs in the lower and upper troposphere, even though the water vapor content in the upper troposphere is much smaller. The results have implications for the design of new observing systems, as well as the specification of errors when AMVs are ingested in data assimilation systems.

Investigation of Ce3+ Mobility in NR211 Under RH Gradients

A proton exchange membrane fuel cell (PEMFC) is an attractive candidate for use in transportation and stationary applications as a clean energy source. A key component of a PEMFC is the polymeric ionomer membrane that serves as a proton conductor and prevents reactant gas crossover and electrical shorting. A widely used class of polymeric ionomers are perfluorinated sulfonic acid (PFSA) type ionomers because of their overall superior chemical and mechanical properties. The primary product of an operating fuel cell is water, but there are also small quantities of hydroxyl radical (•OH) and hydrogen peroxide (H2O2) produced from chemical and electrochemical reactions. These species react with non-fluorocarbon atoms or the sulfonic acid moiety to degrade the polymeric ionomer. To mitigate the chemical degradation of the polymeric ionomer, redox active cations such as Ce3+ and Mn2+ can be incorporated in membrane electrode assemblies (MEAs). These cations react at kinetically sufficient rates with •OH to form water. The resulting oxidized cation is subsequently reduced by H2O2 to complete the redox cycle. Within the polymeric ionomer, these cations associate (ion pair) with negatively charged sulfonate (SO3 -) groups. At the same time, cation complexation of the SO3 - groups modulates the local water content (l = nH2O/SO3 -) in the membrane. During fuel cell operation over a period of ten to 100 hours, cations are observed to diffuse on a centimeter length scale. The redistribution of cations can impact the fuel cell performance and mitigation of chemical degradation reactions. The movement of cations within an MEA is dictated by water content (l), water content gradients (Dl), and potential gradients. Therefore, the optimization of fuel cell performance and durability requires understanding how these factors impact cation movement. In this presentation, we will report isotropic diffusion coefficients of Ce3+ and Co2+ within a NR211 membrane over an array of uniform temperature and relative humidity values. The cation concentrations were monitored using FTIR, x-ray fluorescence, and UV-vis spectroscopies. The derived diffusion coefficients from these data show a strong dependence on relative humidity and temperature. These mobility rates are also consistent with redistribution of cations in operating fuel cells. In addition, cation movement under RH gradients will be presented. In this work, a dual-RH chamber apparatus was employed to study cation mobility rates over a range of RH chamber values and temperatures. For example, uniformly Ce3+-doped NR211 membranes clearly exhibit cation migration from the high to the low RH chamber (Figure 1a) and the mobility of cations in the low RH chamber is greatly reduced. Much additional experimentation with Ce3+ patch-doped NR211 strips (Figure 1b) has been conducted to elucidate the influence of water gradients on the rate and extent of cation mobility. Finally, a 1-D in-plane Ce3+ transport model that was developed from these data will be discussed. Figure 1

Darboux transformation: new identities

This letter reports some new identities for multisoliton potentials that are based on the explicit representation provided by the Darboux matrix. These identities can be used to compute the complex gradient of the energy content of the tail of the profile with respect to the discrete eigenvalues and the norming constants. The associated derivatives are well defined in the framework of the so-called Wirtinger calculus which can aid a complex variable based optimization procedure in order to generate multisolitonic signals with desired effective temporal and spectral width.

Soil microaggregate size composition and organic matter distribution as affected by clay content

Aggregation assembles different size mixtures of soil particles into a larger architecture. Such mixtures impede resolving which particles build aggregates and how these control the accumulation of soil organic matter (OM). Here we present an approach to differentiate the size distributions of soil fractions in the size range of microaggregates (<250 μm) from their dispersible particle-size distribution using dynamic image analysis. This approach enabled us to differentiate the magnitude and preferential size ranges of aggregates and non-aggregated particles. Wet sieving was used to isolate free microaggregate-sized fractions. Larger soil structures >250 μm were sonicated to isolate occluded size fractions <250 μm. To investigate the impact of soil texture, we analyzed topsoil samples of an arable site on Cambisol soils with a gradient in clay content of 16–37% and organic carbon concentrations of 10–15 g kg−1. Our results demonstrate how soil texture governs aggregate size distributions: most water-stable microaggregates were found to be of approximately 30 μm diameter, independent of the clay content gradient. High-clay soils contain more water-stable macroaggregates (>250 μm) and larger microaggregates in the 50–180 μm size range. The low-clay soils, on the other hand, contained more non-aggregated sand-sized particles >100 μm which probably hampered the buildup of larger aggregates. The size distribution of particles <100 μm in size fractions <250 μm showed a similar prevailing soil texture pattern, with approximately 24% clay, 59% silt, and 17% sand-sized particles at all clay contents. In contrast to the prevailing texture pattern along the clay content gradient, 4% more clay-sized particles helped build up water-stable macroaggregates. In the low-clay soils, the aggregates were smaller and the size fractions <53 μm had higher OM concentrations. This indicates that the low-clay soils held most of their OM in smaller microaggregates. Such arrangement of OM in smaller microaggregates demonstrates that soil texture may control OM stabilization mostly indirectly via the distribution of OM in different aggregate fractions. The occlusion of microaggregates in larger structures led to lower alkyl:O/N-alkyl ratios in 13C nuclear magnetic resonance (NMR) spectroscopy, indicating increased preservation.

Nanoscale oxygen defect gradients in UO2+x surfaces

Oxygen defects govern the behavior of a range of materials spanning catalysis, quantum computing, and nuclear energy. Understanding and controlling these defects is particularly important for the safe use, storage, and disposal of actinide oxides in the nuclear fuel cycle, since their oxidation state influences fuel lifetimes, stability, and the contamination of groundwater. However, poorly understood nanoscale fluctuations in these systems can lead to significant deviations from bulk oxidation behavior. Here we describe the use of aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy to resolve changes in the local oxygen defect environment in [Formula: see text] surfaces. We observe large image contrast and spectral changes that reflect the presence of sizable gradients in interstitial oxygen content at the nanoscale, which we quantify through first-principles calculations and image simulations. These findings reveal an unprecedented level of excess oxygen incorporated in a complex near-surface spatial distribution, offering additional insight into defect formation pathways and kinetics during [Formula: see text] surface oxidation.

Improved Passivation Effect Due to Controlled Smoothing of the CdTe-HgCdTe Interface Gradient by Thermal Annealing

HgCdTe films grown by liquid phase epitaxy were passivated with CdTe grown by molecular beam epitaxy. A series of annealing tests with different temperatures and durations were then carried out in order to reach a two-fold goal: to smooth the gradients in Hg and Cd content across the HgCdTe film-passivation interface, and to create a Hg vacancy concentration of ∼ 1–2 × 1016 cm−3. We want the composition gradient to prevent minority carrier electrons from reaching the actual interface, as this may contain recombination centers that trap the electrons. Four different temperature–time combinations were tried for the first part of the annealing procedure (the smoothing of gradients), while they were all followed by a Hg vacancy procedure of 250°C for 18–24 h. Then some samples were cleaved, and energy-dispersive x-ray spectroscopy (EDS) line profiles were recorded on the cross sections to monitor the composition gradients. We could clearly see differences between the profiles from samples with the higher-temperature annealing, the lower-temperature annealing and no annealing. Secondary ion mass spectroscopy profiles on two samples verified the EDS results. On another subset of similar samples, planar diodes were processed and resistance-area (RA) values determined. The current–voltage (I–V) curves from the high-temperature annealed samples seemed dominated by leakage current and did generally not display diode characteristics. This could be explained by their EDS profiles, which showed a lot of Hg in the entire passivation layer. The EDS profiles from the three low-temperature annealing procedures were very similar, but planar diode I–V curves revealed diodes of varying quality, and their RA values were used to differentiate among them. The optimal annealing procedure was 300°C for 4 h, followed by 250°C for 24 h.

Hierarchical superhydrophobic surfaces for oil–water separation via a gradient of ammonia content controlling of dopamine oxidative self‐polymerization

ABSTRACTSuperhydrophobic three‐dimensional porous materials have been considering as one of the most promising candidate absorbents for removal and collection of oil spills or organic contaminants from water. In this work, we report a novel and straightforward method for construction of hierarchical superhydrophobic surfaces on the commercial melamine sponge by controlling of the dopamine oxidative selfpolymerization via a gradient of ammonia content. The surface roughness of the sponge was enhanced by the deposited polydopamine coatings whose surfaces exhibited different morphologies at solutions of varied ethanol‐ammonia ratios. Thereafter the low‐surface free energy moieties were decorated on the surfaces by utilizing a secondary modification platform of polydopamine. Correspondingly, the obtained superhydrophobic melamine sponge achieved a water contact angle of 162.6° ± 1. Furthermore, the superhydrophobic sponge exhibited excellent absorption performances and extraordinary recyclabilities toward a variety of oils and organic solvents. These findings presented in this study offer an effective and versatile approach for oil spills and organic solvents containment removal and environmental remediation in more fundamental and practical fields. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48044.

Characteristics of the liquid and vapor migration of coarse-grained soil in an open-system under constant-temperature freezing

Liquid and vapor migration is the key factor in evaluating the frost heaving properties of coarse-grained soil (CGS) in the high-speed railway (HSR) subgrade in cold regions. A fluorescein tracer was applied to investigate the liquid and vapor migration characteristics of CGS during constant-temperature freezing tests. In addition, the effects of the initial water content on the liquid and vapor migration properties were studied in this paper. The results show that the vapor migration is the dominant factor that causes the water redistribution of CGS in the freezing process. The vapor migration exists both in the supply of the external water sources and internally in the CGS. Water mainly migrates upward in the form of vapor under the effect of a water content gradient and a temperature gradient. The amount of liquid and vapor coupling migration in CGS decreases with the increase in initial water content, followed by a lower amount of external water migration, particularly vapor migration, and a lower height of the upward migration of the liquid. Although the vapor migrates across the freezing front and continually moves upward, the degree of vapor migration will gradually decline with a certain impact time domain and zone.

Structural and optical study of Zn-doped As2Se3 thin films: Evidence for photoinduced formation of ZnSe nanocrystallites

Amorphous Zn-doped As2Se3 films with a nominal zinc content x up to 10 at.% were prepared by thermal evaporation. Their structure is characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoemission spectroscopy (XPS), and Raman spectroscopy. The AFM data show a considerable increase of the film surface roughness for films with x &amp;gt; 5 at.%. A strong gradient of the Zn content decreasing into the film depth is confirmed by the EDX and XPS data. Heavily Zn-doped (above 7 at.%) As2Se3 films reveal photostructural changes in the course of the Raman measurements. New Raman features are attributed to TO and LO vibrations of ZnSe nanocrystallites formed in the film under laser illumination. Depending on the laser wavelength and power density, the ZnSe nanocrystallites can experience tensile strain in the film due to a non-thermal photoplastic effect in the As2Se3 film resulting in a partial removal of the material from the laser spot. The tensile strain value, estimated from the TO and LO phonon frequency shift, is shown to reach up to 2.9 GPa.

Capability of the Invasive Tree Prosopis glandulosa Torr. to Remediate Soil Treated with Sewage Sludge

Sewage sludge improves agricultural soil and plant growth, but there are hazards associated with its use, including high metal(loid) contents. An experimental study was conducted under greenhouse conditions to examine the effects of sewage sludge on growth of the invasive tree Prosopis glandulosa, as well as to determine its phytoremediation capacity. Plants were established and grown for seven months along a gradient of sewage sludge content. Plant traits, soil properties, and plant and soil concentrations of N, P, K, Cd, Pb, Cu, Ni, Zn, Cr, Co, As, and Fe were recorded. The addition of sewage sludge led to a significant decrease in soil pH, and Ni, Co, and As concentrations, as well as an increase in soil organic matter and the concentrations of N, P, Cu, Zn, and Cr. Increasing sewage sludge content in the growth medium raised the total uptake of most metals by P. glandulosa plants due to higher biomass accumulation (taller plants with more leaves) and higher metal concentrations in the plant tissues. P. glandulosa concentrated more Cd, Pb, Cu, Zn, and Fe in its below-ground biomass (BGB) than in its above-ground biomass (AGB). P. glandulosa concentrated Ni, Co, and As in both BGB and AGB. P. glandulosa has potential as a biotool for the phytoremediation of sewage sludges and sewage-amended soils in arid and semi-arid environments, with a potential accumulation capability for As in plant leaves.

Evaluation of factors affecting gully headcut location using summary statistics and the maximum entropy model: Golestan Province, NE Iran

Gully erosion is an important soil degradation process, which under climate changes is projected to increase. Therefore, better understating of factors controlling gully erosion and prediction of gully headcuts' (GHs) location is still highly relevant. This study aimed to examine the spatial distribution of GHs and to assess the importance of pedological (i.e. aggregate stability, organic matter, bulk density, silt, clay, and sand content) and topographical factors (i.e. altitude, slope length, gradient, and aspect) using summary statistics and the maximum entropy (MaxEnt) model. The study was conducted in the loess-covered region of NE Iran. The highly precise data of 287 GHs locations were obtained by extensive fieldwork and the interpretation of UAV images. The spatial distribution of GHs was evaluated by univariate pair correlation function and O-ring statistics. The spatial effect of GHs density controlling factors was assessed by the cumulative density correlation function Cm,K(r). Variable importance was analyzed using the MaxEnt model, which was also for the susceptibility modelling of GHs. The results of univariate tests showed the aggregated distribution of GHs. The Cm,K(r) analyses indicated that the areas characterized by higher values of bulk density, aggregate stability, and organic matter content have lower GHs density, whereas the areas with high silt content and higher slope gradient have higher GHs density. According to the MaxEnt, there is no one single factor responsible for GHs location, but rather the combination of topographical and pedological factors with the predominance of slope gradient (0.86) and silt content (0.57). The MaxEnt modelling of GHs susceptibility has revealed that the best accuracy (0.958) is given when all pedological and topographical factors are used in the model. The susceptibility maps prepared in the study can be used for soil conversation and land use planning and, consequently, for sustainable development in the region.

Internal fluctuations in green roof substrate moisture content during storm events: Monitored data and model simulations

Understanding how the moisture content in a green roof substrate varies during a storm event is essential for accurately modelling runoff detention. In this paper, a green roof test bed installed with moisture probes at three depths was used to understand how moisture content varies during storms. Detailed studies were conducted on five selected storm events. Physical characterisation tests and field-data based calibrations were performed to acquire the model parameters. Two alternative detention models, based on Reservoir Routing and Richard’s Equation, were validated against the measured green roof runoff and temporary moisture storage data. Once the moisture content exceeds local field capacity, its response at different depths occurs simultaneously during storms, although the recorded data indicate a vertical gradient in the absolute values of local field capacity. Both Reservoir Routing and Richard’s Equation can provide reasonable estimations of the runoff and the vertical moisture content profiles, although Richard’s Equation exhibited stronger vertical water content gradients than were observed in practise. The vertical water content profile is not sensitive to the soil water release curve, although the hydraulic conductivity function influences both the vertical water content profile and runoff rate. The modelled results are highly sensitive to the bottom boundary condition, with a constant suction head boundary condition providing a more suitable option than a free drainage boundary condition or a seepage boundary condition.