Water-filled Porosity Research Articles

Study of soil heterotrophic respiration as a function of soil moisture under different land covers

The relationship between soil heterotrophic respiration (Rh) and soil moisture has been often studied using disturbed soil samples and simple gravimetric and volumetric soil moisture indicators. The objective of this study was to investigate the relationship between Rh and soil moisture in terms of water-filled porosity (WFP), matric potential (Ψm), and relative soil gas diffusivity (Dp/Do) using undisturbed soil cores obtained under different land covers. Soil CO2 efflux, WFP, and Ψm were measured in undisturbed soil samples (250 cm3) collected in the 0–5 cm soil layer (without any vegetation or living roots) under laboratory conditions by combining a CO2 gas analyzer, a scale, and precision mini-tensiometers. For each site and land cover, we also measured soil chemical properties, soil physical properties, and soil microbial composition using phospholipid fatty acid analysis. Grassland soils had the largest total microbial biomass (6275 ng g−1), followed by soils from riparian (5327 ng g−1), and cropland (2745 ng g−1) sites. Bacteria were the dominant group representing 46% (SD = 5%) of the total microbial biomass across all sites and land covers. Maximum Rh was 1.88 (SD = 0.40) μmol CO2 m−2 s−1 in grassland, 1.64 (SD = 0.82) μmol CO2 m−2 s−1 in riparian, and 0.94 (SD = 0.56) μmol CO2 m−2 s−1 in cropland soils. Considering all land cover and soil types, our observations revealed that peak Rh occurred at mean WFP = 0.81 ,Ψm = −6 kPa, and Dp/Do = 0.003. Thus, we recommend avoiding the traditional field capacity definition of −33 kPa for representing peak microbial activity. Water-filled porosity was a more consistent predictor of Rh than Ψm or Dp/Do across soils with contrasting organic matter content, total microbial biomass, soil texture, and soil structure.

The Effect of Salt Concentration on Dielectric Permittivity and Interfacial Polarization in Carbonate Rocks with Complex Pore Structure

Summary Broadband dielectric dispersion measurements are attractive options for the assessment of water-filled porosity. Dielectric permittivity is influenced by salinity as well as other rock/fluid properties. However, the effect of salinity on Maxwell-Wagner polarization (i.e., interfacial polarization) and dielectric permittivity in rock samples with complex pore structures requires further investigation. The objectives of this work are (a) to perform frequency-domain dielectric permittivity numerical simulations on 3D pore-scale rock samples at different salt concentration levels, (b) to quantify the effect of salinity on dielectric permittivity and interfacial polarization in the frequency range between 20 MHz and 5 GHz, and (c) to quantify the critical frequency (i.e., the frequency at which the relative permittivity becomes frequency-independent). We first perform pore-scale frequency domain dielectric permittivity simulations in fully water-saturated carbonate samples with complex pore structures to obtain the complex dielectric permittivity in the frequency range of 0.01–5 GHz and at different salinity levels. Next, we numerically create partially water/hydrocarbon-saturated water-wet samples and perform simulations at different salinity and water saturation levels to investigate the combined effect of salinity and water saturation on dielectric permittivity. Finally, we investigate how reliable conventional mixing models, such as the complex refractive index model (CRIM) and Hanai-Bruggeman (HB), are in the assessment of water saturation at different salinity levels. We used 3D pore-scale rock samples with complex pore structures from Austin Chalk, Estaillades Limestone, and Happy Spraberry formations. The increase in salinity from 2 to 50 parts per thousand (PPT) resulted in the relative permittivity to increase by 18% at 20 MHz. Similarly, an increase in salinity from 2 PPT to 50 PPT resulted in electrical conductivity to increase by 15 times at 20 MHz. However, at 5 GHz, the difference between the relative permittivity of the samples at different salinities was negligible. We demonstrated that the critical frequency was above 1 GHz. Thus, if complex dielectric permittivity at 1 GHz is being used, an accurate salinity assumption is required in the interpretation of conventional dielectric mixture models in carbonate formations. Finally, we observed 52% and 42% average relative errors in water saturation quantification when applying CRIM and HB models at all the frequencies of interest, respectively. The results also indicated that conventional models should not be used in the presence of uncertainty in salinity at lower frequencies. The results of this work quantified the frequency at which the water-filled pore volume rather than the Maxwell-Wagner polarization controls the relative permittivity of rock samples saturated with a wide range of brine salinity. Moreover, the results demonstrated that the relative permittivity of the rock samples with complex pore structures may still be significantly affected by the interfacial polarization even at 1 GHz. Moreover, the results suggested that the conventional mixture methods cannot reliably take into account the salt concentration of formation water, and this can lead to significant errors in reserves assessment.

Dielectric dispersion model including polarization response of a shape distribution

Formation evaluation based on the complex dielectric dispersion in the megahertz to gigahertz frequency range has become a useful method for obtaining formation properties with the development of several logging tools. Such an evaluation relies on fitting the measured dielectric signals to a dielectric dispersion model and inverting for model parameters directly associated with certain formation petrophysical properties: the water-filled porosity, the brine salinity, and a water-phase tortuosity exponent. Hence, a model that can faithfully describe the dielectric dispersion governed by those formation properties is of importance for such a practice. By incorporating the polarization response of grains with a distribution of shapes, we have improved upon a widely accepted dielectric dispersion model, the bimodal model. To efficiently approximate the overall polarization response of ensembles of grains with continuous shape distributions, we establish two approaches that use a finite number of grain shapes: a Padé approximation and samplings with a Gauss quadrature rule. The latter method provides greater flexibility in what type of shape distribution can be introduced and how they are introduced. By adopting a specific class of shape distributions sampled with a Gauss quadrature rule, a new dielectric dispersion model for brine-saturated rocks is developed using a differential effective medium approach. The new model has the same number of model parameters and should have similar use cases, clay-free clastic and carbonate formations without complex pore structures, as those of the bimodal model. By fitting our model to available core measurements, the new model better describes the dielectric dispersion of brine-saturated rocks over a broader frequency range in comparison to the bimodal model, while giving good inverted petrophysical parameters. Based on the scaling behavior of the Maxwell-Wagner polarization, the new model would be more adequate for describing the dielectric dispersion of rocks saturated with higher salinity brine.

Effects of revetments on soil ecosystems in the urban river-riparian interface

SummaryBy altering material and energy exchange between river and riparian, the city revetments have an unknown impact on the service function of river-riparian interface (RRI) ecosystems. This study analyzes the differences in natural, permeable (PR), and impervious revetment (IR). We found that the water-filled porosity of revetment increased from 20% to 100%, which coincided with an increase in soil potassium, air-filled porosity, the surface soil of moisture and organic matter (SOM), and a decrease in soil nitrogen, phosphorus nutrients, and in the middle and deep soil SOM. The changes affected the abundance of dominant bacterial and fungi genera. Compared with the PR, surface soil moisture, pH, and underground biomass were lower in IR surface soils, while surface soil SOM and middle soil moisture were higher. This research provides a development direction and theoretical basis for future urban planning and environmental governance.

Evaluation of the DNDCv.CAN model for simulating greenhouse gas emissions under crop rotations that include winter cover crops

Context Process-based modelling studies can help inform conservation practices for mitigating soil surface CO2 and N2O fluxes. Aims We evaluated the ability of the DeNitrification-DeComposition (DNDC) model to predict field-measured soil surface CO2 and N2O emissions in crop rotations managed with cover crop (CC) and without cover crop (NC) under the 27-year no-till field experiment in South Dakota, USA. Methods Emissions were measured in a 2-year corn–soybean and a 4-year corn–soybean–oat–winter wheat rotation. The model was calibrated with 2-year NC treatment and evaluated against three treatments (2-year CC, 4-year NC and 4-year CC) during the growing season of corn (2017) and soybean (2018). Key results Across all treatments, the model simulated soil temperature (MBE, −0.73–0.29°C; RMSE, 1.47–4.03°C; NSE, 0.54–0.90; d, 0.89–0.98; R2, 0.64–0.93) and moisture [water-filled porosity (wfps)] (MBE, 0.03–0.06 wfps; RMSE, 0.09–40.13 wfps; NSE, −0.24–0.49; d, 0.78–0.87; R2, 0.45–0.69) that agreed well with field measurements. Predicted daily soil CO2 fluxes (kg C ha−1) provided ‘good’ agreement with MBE (range −0.58−4.67), RMSE (range 2.10−7.36), d (range 0.68–0.93), NSE (range −0.92–0.79), and R2 (range 0.49–0.85). Statistics showed ‘poor’ agreement between the simulated and measured daily N2O emissions because peak emissions events in the measured data were less than predicted. Cumulative CO2 and N2O emissions and crop yields were well estimated by the model. Conclusions DNDCv.CAN simulated the impacts of diverse crop rotations and cover crops on soil moisture, temperature and greenhouse gas emissions in the humid south-east of USA. Implications Nitrogen transformation routines and effect of rainfall interception on soil water content need further investigation to address the variations in daily N2O emissions.

Effects of different nitrogen application rates on soil water stable aggregates and N2O emission in winter wheat field.

Excessive nitrogen application would deteriorate soil structure and increase greenhouse gas emission. We set up six treatments, i.e., N0, N120, N180, N240, N300and N360(nitrogen application rates of 0, 120, 180, 240, 300 and 360 kg·hm-2, all straws returned into the field in situ) in the nitrogen fertilizer experimental site to investigate the effects of different nitrogen application rates on soil N2O emission, soil water-filled porosity (WFPS), soil temperature, nitrate and ammonium contents, composition and stability of water stable aggregates in winter wheat filed in 2018-2020. The results showed that there was a significant positive correlation between soil N2O emission and nitrogen application rate. There was no correlation between WFPS and nitrogen application rate. Soil temperature in the 0-10 cm layer decreased significantly with the increases of nitrogen application rates. There was a significant positive correlation between nitrate and ammonium contents and nitrogen application rate. With the increases of nitrogen application rates, the content of water stable aggregates with diameter >2 mm decreased, while that of water-stable aggregates with diameter <0.5 mm increased. The particle size of soil water-stable aggregates also decreased gradually. There was a significant negative correlation between nitrogen application rate with mean weight diameter (MWD) and geometric mean diameter, while no correlation with fractal dimension. The fitting equation between MWD and N2O emission flux was y=3928.3e-2.171x (R2=0.55, P<0.001), indicating that N2O emission increased markedly as MWD decreasing. The increases in nitrogen application rate reduced soil temperature in the 0-10 cm layer, increased nitrate and ammonium contents, decreased the average particle size of soil water stable aggregates, and the stability of soil aggregates, and increased soil N2O emission.

Two-dimensional analytical solution for subsurface volatile organic compounds vapor diffusion from a point source in layered unsaturated zone

Although migration of subsurface volatile organic compounds (VOCs) from contaminant sources in unsaturated soil widely exists, the related analytical models are quite limited. A two-dimensional analytical solution is hence developed to simulate vapor diffusion from the subsurface contaminant source in the layered unsaturated zone. The contaminant source is simplified as a point source leaking at a constant rate. The influences of several important factors, including thickness of stagnant air layer, depth of groundwater table, source characteristics and soil layering characteristics, on vapor migration in subsurface soil are comprehensively investigated by the present model. Soil type does not affect the normalized vapor concentration profile for homogeneous soil, which is not valid for layered soil. The width and effective diffusivity of the upward diffusion pathway and downward diffusion pathway are favorable indexes to evaluate the intensity of subsurface vapor horizontal diffusion. The single-layer capillary fringe assumption overestimates the vapor plume, the assumption can give acceptable result for coarse soil while it is recommended to divide the soil into several layers based on the water-filled porosity profile for fine soil.

Winter cereal rye cover crop decreased nitrous oxide emissions during early spring

AbstractDespite differences between the cover crop growth and decomposition phases, few greenhouse gas (GHG) studies have separated these phases from each other. This study's hypothesis was that a living cover crop reduces soil inorganic N concentrations and soil water, thereby reducing N2O emissions. We quantified the effects of a fall‐planted living cereal rye (Secale cereale L.) cover crop (2017, 2018, 2019) on the following spring's soil temperature, soil water, water‐filled porosity (WFP), inorganic N, and GHG (N2O‐N and CO2–C) emissions and compared these measurements to bare soil. The experimental design was a randomized complete block, where years were treated as blocks. Rye was fall planted in 2017, 2018, and 2019, but mostly emerged the following spring. The GHG emissions were near‐continuously measured from early spring through June. Rye biomass was 1,049, 428, and 2,647 kg ha–1 in 2018, 2019, and 2020, respectively. Compared to the bare soil, rye reduced WFP in the surface 5 cm by 29, 15, and 26% in 2018, 2019, and 2020 and reduced soil NO3–N in surface 30 cm by 53% in 2019 (p = .04) and 65% in 2020 (p = .07), respectively. Rye changed the N2O and CO2 frequency emission signatures. It also reduced N2O emissions by 66% but did not influence CO2–C emissions during the period prior to corn (Zea mays L.) emergence (VE). After VE, rye and bare soils N2O emissions were similar. These results suggest that nitrous oxide (N2O‐N) sampling protocols must account for early season impacts of the living cover.

Microbial activity in peat-reduced plant growing media: Identifying influential growing medium constituents and physicochemical properties using fractional factorial design of experiments

The development of peat-reduced plant growing media for horticulture is needed to tackle sustainability concerns related to the peat production process. Alternative growing media constituents with unique physicochemical properties, like coir pith, wood fiber, compost, and inorganic materials are currently used. However, little is known about the impact of these materials on microbial activity. Because microbial communities play an important role in plant growth and development, the impact of various growing media constituents on microbial activity was analyzed using two-level fractional factorial statistical design of experiments. The results showed that growing media composition greatly affected microbial activity. White peat (+2.4% CO2) and composted bark (+1.5% CO2) significantly promoted microbial activity over black peat and green waste compost respectively. In contrast, the organic materials coir pith and wood fiber, as well as the inorganic materials perlite and sand, had little effect on microbial activity. Physicochemical analysis of the different growing media mixtures revealed that the water-filled porosity (WFP) was the most important parameter driving microbial growth, increasing microbial activity (+2.1% CO2) at 62.95% WFP compared to 82.95% WFP. Our results are instrumental for developing novel organic growing media with distinct microbial features to move towards a low peat sustainable horticulture.

Transformation of the reabsorption characteristics of lignite treated by low and high temperature drying process

The reabsorption characteristics of the lignite treated by low and high temperature drying process were addressed in the paper. The information about the moisture form, functional groups, effective water-filled porosities and equilibrium moisture content of the lignite before and after the drying process was investigated using Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and a self-made reabsorption device, respectively. The results show that the low drying temperature (140, 190, 230 °C, 10 min, N2) has little impact on the effective water-filled porosities of the resulted samples, whereas it has a great influence on the main oxygen-containing functional groups, which amount firstly decreases and then increases with the drying temperature increasing. In the case of the lignite samples dried under high-temperature (600, 700, 800 °C, 30 s, N2), the amount of the effective water-filled porosity of the sample decreases and the amount of oxygen-containing functional groups increases as the temperature increasing. The reabsorption capability of the high temperature dried sample is much lower than that of the sample treated under low drying temperature. The reabsorption characteristics of the low-temperature dried samples are affected by the amount of the oxygen-containing functional groups, while the effective water-filled porosity is main factor for the lignite samples derived from high temperature drying process. Moreover, the work gives a good evidence that the high-temperature drying process is an effective choose for lignite upgrading.

Thermal conductive properties of solid-liquid-gas three-phase unsaturated concrete

In order to study the thermal conductivity of unsaturated concrete, 8 groups of concrete samples with different porosity and water content were prepared. For comparative analysis, the porosity of samples by adding air entraining agents with different mass fractions, and the water-filled porosity is controlled by weight and humidity method. The actual porosity, water-filled porosity and gas-filled porosity of the specimens were measured by nuclear magnetic resonance technology (NMR), and the thermal conductivity is synchronously test in the corresponding state. Based on the experimental data, it is verified that the dispersion-continuous thermal conductivity model is feasible to determine the thermal conductivity of unsaturated concrete. Combining the calculated results with the test results, we obtain the variation of thermal conductivity with porosity and gas-liquid filling of pores. Furthermore, a two-dimensional mesoscopic model of porous media was established to analyze the mechanism of the three phases of solid, liquid and gas in the heat transfer process. The results show that both porosity and water content have great influence on the thermal conductivity of concrete. Thermal conductivity not only decreases with the increase of porosity, but also increases nonlinearly with the increase of water-bearing porosity at the same porosity. Compared with the elemental materials, the pore makes the distribution of temperature field change greatly. For three-phase unsaturated concrete, the connectivity of pores and the difference of solid-liquid-gas thermal conductivity will also cause temperature distortion in local areas.

Comparison of different dielectric models to calculate water saturation and estimate textural parameters in partially saturated cores

Accurate estimation of water saturation is central in predicting capillary pressure and relative permeability, under special core analysis in the laboratory. We have explored the use of dielectric measurements at different frequencies to estimate water saturation. In addition to water saturation, dielectric measurements are sensitive to the distribution of water and oil in a porous system, reflected by the apparent cementation factor [Formula: see text], which describes the water phase tortuosity. We have performed an experimental study to benchmark water saturation from dielectric measurements on eight carbonate cores and estimated their cementation exponent [Formula: see text] and saturation exponent [Formula: see text] in Archie’s equation from dielectric data. All cores went through a series of drainage/imbibition steps, creating varying saturations of brine/fluorocarbon. Fluorocarbon was chosen because it is invisible to proton nuclear magnetic resonance (NMR). Therefore,NMR porosity represents only the water-filled porosity and can be used to benchmark dielectric water-filled porosity. Three dielectric models were used for the comparison of the dielectric water-filled porosity with the one from NMR, i.e., the complex refractive index model (CRIM), bimodal model, and Stroud-Milton-De (SMD) model, and very good agreement of 1.5 porosity units on average is found. Despite its simplicity, CRIM predicted well the water-filled porosity in this experiment. However, it cannot provide information about the texture, which is captured by bimodal and SMD models. We also estimated [Formula: see text] and [Formula: see text] based on [Formula: see text] found from bimodal and SMD models, and good agreement with [Formula: see text] from resistivity data was shown. This is the first time to our knowledge that such a rich set of dielectric and NMR measurements was acquired at different saturation stages in a surface laboratory. This study is useful in benchmarking the water saturation from dielectrics, comparing different dielectric models, and demonstrating feasibility of estimating textural parameters.

Green waste compost and vermicompost as peat substitutes in growing media for geranium ( Pelargonium zonale L.) and calendula ( Calendula officinalis L.)

Abstract This research evaluated green waste compost (GWC) and green waste vermicompost (GWV) as peat substitutes in growing media used for the production of geranium (Pelargonium zonale L.) and calendula (Calendula officinalis L.). Five growing media were prepared: 100% Peat (P), 50% Peat + 50% GWC (PC), 100% GWC (C), 50% Peat + 50% GWV (PV), and 100% GWV (V). Geranium and calendula seedlings were transplanted into each medium and were grown under commercial nursery conditions for 6 months, i.e., until they attained commercial size. The higher percentage of GWC and GWV in the growing medium could increase bulk density and air space; decrease total pore space and water-filled porosity; and increase pH, electrical conductivity, and macro- and microelement contents. The heavy metal contents of all growing media were within safe ranges. Particle-size distribution and fertility were superior in the vermicompost-based media than in the compost-based media. Geranium growth was reduced in media containing GWC (C and PC). Calendula growth in compost-based growing media was similar to or greater than growth in pure peat. Geranium and calendula growth and flowering were superior in all vermicompost-based media (PV and V) than in the control medium (P). These results indicate that GWV is better than GVC as a partial substitute for peat in the cultivation of geranium and calendula.

Measurements of complex resistivity spectrum for formation evaluation

Low resistivity reservoirs, which are important oil reservoirs with considerable productivity, cannot be easily identified through traditional electrical logging methods. In this paper, we introduced a new logging method for effective identification of low resistivity reservoirs. The complex resistivity spectrum of sandstone layers can be obtained using this method. This paper presents the electrode array for measurements in boreholes, and the relationships between the complex resistivity spectrum and petrophysical properties. A numerical simulation was performed to study the detection characteristics of this logging tool and field tests were conducted to verify the feasibility of this method. The results show that variations in water-filled porosity obtained from this tool agree well with the actual values. Finally, water saturation can be obtained for oil reservoirs. This logging method provides a more effective approach than existing methods for the characterization of low resistivity reservoirs.

Litter Type and Number of Flocks Affect Sex Hormones in Broiler Litter

Broiler litter contains 17β-estradiol, estrone, and testosterone, which can contaminate surface waters when surface applied to grasslands and no-till fields. The objective of this study was to evaluate the effects of litter type (full or cake cleanout), litter treatment (none or sodium bisulfate), and number of flocks raised on the litter (1-5) on sex hormone concentrations. Our results showed that in untreated broiler litter, cake cleanout had greater concentrations of 17β-estradiol, estrone, and testosterone than full cleanout, whereas in litter treated with sodium bisulfate, only the concentration of 17β-estradiol was greater in cake than in full cleanout. The concentrations of 17β-estradiol and estrone in untreated broiler litter increased as the number of flocks increased from one to three, with the largest increase observed for estrone in cake cleanout. We also sampled three broiler houses in brooding and nonbrooding sections during the growout period. We found no differences in hormone concentrations between sections of each house, but changes in hormone concentrations during growout varied depending on broiler litter water content. Water contents corresponding to ∼60% water-filled porosity favored a decrease in hormone concentrations with time, whereas a water-filled porosity of 44% was associated with increases in hormone concentration, probably due to slow decomposition rates. Our results suggest that cake cleanout of untreated litter, as well as all cleanouts from houses that have raised several flocks on the same bedding, may be good targets for treatments that can reduce hormone concentrations before the litter is surface applied to fields.

Ratio of CO2 and O2 as index for categorising soil biological activity in sugarcane areas under contrasting straw management regimes

This study was developed in a sugarcane area under contrasting management regimes defined by mechanical green harvesting (GH) and burning harvesting (BH) to test the hypotheses that the ratio of carbon dioxide (CO2) and oxygen (O2), known as the apparent respiratory quotient (ARQ), can be used to categorise soil biological activity. The study aimed to (i) examine the profile and relationship between the CO2 flux (FCO2) and the O2 flux (FO2) in a sugarcane area under mechanical harvesting with straw burning (BH) and mechanical harvesting with maintenance of straw (GH), considering soil moisture; (ii) and suggest the use of ARQ as an index for categorising the biological activity of soils. Our results showed consistently lower FCO2 for soil moisture in the range of 6.0–8.6% for both management regimes. The soil moisture increments triggered a decrease in FO2 and an increase in FCO2 and ARQ. The FCO2 and FO2 were positively correlated under BH. The BH yielded a cumulative CO2 emission of 53.68% higher than for GH. Overall, our findings revealed that soil moisture affected the O2 uptake and CO2 emission profile of soil, limiting O2 uptake and increasing CO2 releases for water-filled porosity below 70%. The GH management system, which incorporates sugarcane residues into the superficial layer of the soil, can help protect against soil erosion. The ARQ can be used as an index to categorise biological activity in soil, where ARQ values close to 1 can be considered a reflection of aerobic activity with balance between CO2 production and O2 consumption.

Effect of Water Salinity and Water–Filled Pore Volume on High–Frequency Dielectric Measurements in Porous Media

Summary High-frequency dielectric measurements have been attractive candidates for assessment of water-filled porosity in porous media. In the presence of saline water, the water molecules lose their orientation freedom partially because of hydration with ions and make these measurements sensitive to water salinity, which makes the interpretation of the dielectric-permittivity measurements challenging. The effects of water salinity on the real and the imaginary parts of dielectric permittivity have not yet been quantitatively studied in high-frequency (e.g., greater than 1 GHz) measurements. We measured dielectric permittivity of brine at frequencies ranging from 1 MHz to 3 GHz at room temperature and pressure conditions, where water salinity varies between 0 and 160 kiloparts per million (kppm). We also measured the dielectric permittivity of rock samples with different brine saturations. Our experimental results confirmed that there exists a critical frequency above which water salinity does not affect the real part of the dielectric constant, and such critical frequency increases as water-filled porosity and water salinity increase. At high frequencies where the real part of the dielectric constant is independent of the frequency, there exists a critical water-filled porosity below which water salinity has negligible effect on the real part of the dielectric constant. However, when water-filled porosity is higher than this critical value, the real part of the dielectric constant slightly decreases by increasing water salinity. Further, the results showed that at frequencies greater than the critical frequency, there is a critical water salinity below which the imaginary part of the dielectric constant increases as the water salinity increases, whereas the imaginary part of the dielectric constant decreases if the water salinity exceeds the critical value. The quantitative results on the effect of water salinity on dielectric measurements can potentially improve interpretation of dielectric-permittivity measurements for reliable assessment of water-filled porosity and hydrocarbon saturation.

Gas hydrate saturation and distribution in the Kumano Forearc Basin of the Nankai Trough

The Kumano Forearc Basin is located to the south-east of the Kii Peninsula, Japan, overlying the accretionary prism in the Nankai Trough. The presence of gas hydrate in submarine sediments of the forearc basin has resulted in the widespread occurrence of bottom simulating reflectors (BSRs) on seismic profiles, and has caused distinct anomalies in logging data in the region. We estimated the in situ gas hydrate saturation from logging data by using three methods: effective rock physics models, Archie’s equation, and empirical relationships between acoustic impedance (AI) and water-filled porosity. The results derived from rock physics models demonstrate that gas hydrates are attached to the grain surfaces of the rock matrix and are not floating in pore space. By applying the empirical relationships to the AI distribution derived from model-based AI inversion of the three-dimensional (3D) seismic data, we mapped the spatial distribution of hydrate saturation within the Kumano Basin and characterised locally concentrated gas hydrates. Based on the results, we propose two different mechanisms of free gas supply to explain the process of gas hydrate formation in the basin: (1) migration along inclined strata that dip landwards, and (2) migration through the faults or cracks generated by intensive tectonic movements of the accretionary prism. The dipping strata with relatively low AI in the forearc basin could indicate the presence of hydrate formation due to gas migration along the dipping strata. However, high hydrate concentration is observed at fault zones with high pore pressures, thus the second mechanism likely plays an important role in the genesis of gas hydrates in the Kumano Basin. Therefore, the tectonic activities in the accretionary wedge significantly influence the hydrate saturation and distribution in the Kumano Forearc Basin.

Biochar Reduced Nitrous Oxide and Carbon Dioxide Emissions from Soil with Different Water and Temperature Cycles

Interactions among biochar, respiration, nitrification, and soils can result in biochar increasing, decreasing, or not impacting greenhouse gas (GHG) emissions. This experiment determined the impact of water‐filled porosity (WFP) and corn (Zea mays L.) stover biochar on CO2 and N2O emissions in May (spring) and August (summer). The May experiment contained two N rates [0 and 224 kg Ca(NO3)2–N ha−1], whereas the August had three N rates [0, 224 kg Ca(NO3)2–N ha−1, and 224 kg (NH4)2SO4–N ha−1]. The average temperatures in the May and Augusts 2014 experiments were 14 and 24°C, respectively. Biochar reduced CO2–C emissions in the high WFP Ca(NO3)2 treatment in the May and August experiments 15.4 and 16.3 kg ha−1, respectively. Associated with the CO2–C decrease was a 15.7% reduction in the soil solution dissolved organic C. In addition, N2O–N and CO2–C emissions were not correlated in the May Ca(NO3)2 ha−1 treatment, whereas in the August experiment, N2O–N and CO2–C emissions were correlated (r2 = 0.98, P < 0.01). In August, biochar increased the apparent nitrification from 16 to 25 kg NH4–N (ha × d)−1 in the low WFP (NH4)2SO4 treatment, and it did not influence the nitrification rate in the high WFP (NH4)2SO4 treatment. In general, N2O–N emissions increased with WFP and N rate and were reduced 21.7% by biochar. The findings suggest that multiple mechanisms contributed to N2O emissions and seasonal differences in soil temperature could result in biochar having a mixed impact on GHG emissions.Core Ideas Biochar reduces CO2 gas emission from soil in high soil temperature. Biochar reduces N2O gas emission from soil in high soil temperature. Biochar reduces N2O gas emission from high water‐filled porosity condition.

Estimating permeability of cement paste using pore characteristics obtained from DEM-based modelling

Although an earlier developed numerical methodology for permeability estimation of cement pastes can provide satisfactory results in comparison with experiments, it would be of engineering interest to find a simpler way to perform the same task. This method referred to by “the shorter approach” is presented in this paper. In the approach, water permeability is only correlated to the water-filled porosity of the specimen. A mathematical model is proposed to approximately calculate the water permeability using the water-filled porosity as the only input parameter. The confidence limit is found to yield an appropriate level of reliability. To better understand the proposed mathematical relationship, pore throat size and connectivity of the capillary pores are separately shown as a function of the water-filled porosity. Their respective and successive impacts on permeability is illustrated in this way.