Pore Water Content Research Articles

Heavy metals profiles in a groundwater system at a solid waste disposal site, Taiping, Perak

This paper presents the distribution of heavy metals in a groundwater system at a solid waste disposal site in Taiping, Perak. In this study several boreholes were constructed within the solid waste disposal site. Soil samples were collected from the alluvial deposits at 1 m intervals between 6 and 30 m depths from 6 boreholes using a down-hole hammer. The pore water content of the samples and the ground water was extracted in order to determine the concentrations of heavy metals, such as lead (Pb), manganese (Mn), chromium (Cr), iron (Fe), zinc (Zn) and cadmium, (Cd) using the Inductively Couple Plasma Spectrometer (ICP-MS). From the profiling results, the penetration of heavy metals into the groundwater system was obtained. A profile of heavy metal concentrations in the pore water of the core samples at several boreholes within the study area, and heavy metals concentration in groundwater under different conditions were obtained. Some of the heavy metals concentration such as Pb, Mn, Zn and Fe were high. These high concentrations exceed the maximum permissible concentration as specified in the Drinking Water Standard. Based on contour diagrams, the heavy metals can be detected down to 25 m depth towards the southeast of the landfill and appear to be localized.

Complex interaction of subglacial hydrology and deforming bed processes and its implications for ice marginal stability: the example of the Middle Pleistocene British Ice Sheet from eastern England

Subglacial drainage is known to have a profound influence on glacier and ice sheet stability. Many scientists consider that such processes acted to cause abrupt climatic shifts in the North Atlantic region during Termination 1, and believe that meltwater-induced instabilities in the modern-day Greenland and Antarctic ice sheets could have similar climatic impacts in the future. Understanding the role played by porewater content and/or pressure, coupled with its temporal and spatial distribution within the subglacial bed, appear to be critical factors. These act to control the rheology and style of deformation within the subglacial deforming bed, and in-turn, the amount and distribution of ‘stick-slip’ at the ice-bed interface which facilitates ice motion. Within this paper, we present a model based upon sedimentological and structural evidence from Middle Pleistocene glacial deposits in Eastern England, which illustrate the symbiotic relationship between subglacial deforming bed processes, subglacial drainage within a pressurised channel system, and ice advance. The model shows the development of large-scale subglacial folds and thrusts within a subglacial melange that relate to temporal changes in porewater content and/or pressure within the subglacial bed. These acted to control the development and stability of subglacial drainage beneath the margins of the British Ice Sheet, ultimately leading to an increase in the efficiency of subglacial drainage and the subsequent collapse of the subglacial shear zone. This potentially slowed or even stopped ice advance leading to the part-collapse of the ice margin.

Predicting the film and lens water volume between soil particles using particle size distribution data

Summary We develop four conceptual approaches to quantify the volume of water lenses between soil particles (ei) and adsorbed water films (δi) coating soil particles based on soil Particle Size Distribution (PSD) data. Method 1 is based on expression of the ei as matric suction independent pendular rings and method 2 is based on expression of the ei as function of matric suction. Methods 3 and 4 are based on the coupling of δi estimated with van der Waals and electrostatic forces, with ei estimated with methods 1 and 2 respectively. We show that the filling angle of the lens water is independent of surface tension but increases with the porosity. The four methods are applied to predict effects of ei and δi on Soil Moisture Characteristics (SMC) in eighty soil samples selected from UNSODA database. The total component of the ei in soil water content ranged from 0.0111 (L3 L−3) to 0.1604 (L3 L−3), with the average of 0.0703 (L3 L−3) for method 1 and from 0.0082 (L3 L−3) to 0.0523 (L3 L−3), with the average of 0.0237 (L3 L−3) for method 2. The component of δi is less than 0.0121 of each pore water content. Results showed that for methods 1 and 2, the component of the ei in the soil water content was partially relevant for the prediction of SMC, especially in dry range. Moreover, the accuracy of the method 1 was slightly greater than that of the method 2. We attribute the methods error to the roughness of soil particles, high surface energy content of clay particles and, to the simplified pore geometric concepts that does not effectively reflect the pore geometry. We conclude that the main advantage of the present approaches is developing two different methods for estimation of the volume of the lens water by using only the PSD data and bulk density which are measured easily.

Absorption and frequency shift of GPR signals in sandy and silty soils: empirical relations between quality factor Q, complex permittivity and clay and water contents

ABSTRACTThe arrival time, shape and amplitude of a reflected GPR wavelet depend mainly on the real and imaginary parts of dielectrical permittivity and electrical conductivity. All these parameters are strongly affected by the water and clay content of soils. From a comparison of the amplitude and shape of the direct and reflected wavelets the quality factor can be determined independently as an additional soil parameter. To investigate the relationships between the influencing factors, we conducted high‐frequency GPR reflection measurements on soil samples with varying clay and water contents. The factor, derived from the spectral ratio method, is found to be between 5–15 for our samples that range from about 5–90% in sand content, 5–65% in silt content, 3–63% in clay content and 0–37% in pore water content. A multivariate non‐linear empirical function linking water and clay content to agrees well with the observations. We found that the ratio of the real and imaginary parts of the dielectric permittivity depends basically on the clay content. Therefore, it may become possible to determine the clay content of soils in situ from a combination of GPR and conductivity measurements. The values determined from spectral ratios are confirmed by synthetic radargrams and agree with the observed decrease of the central frequency of GPR reflections caused by absorption.

Mobilization and Transport of Naturally Occurring Enterococci in Beach Sands Subject to Transient Infiltration of Seawater

This study explores the transport of enterococci (ENT) from naturally contaminated beach sands to the groundwater table via infiltrating seawater using field, laboratory, and modeling experiments. ENT were readily mobilized and transported through the unsaturated zone during infiltration events in both the field and laboratory column experiments. Detachment mechanisms were investigated using a modified version of HYDRUS-1D. Three models for detachment kinetics were tested. Detachment kinetics that are first order with respect to the rate of change in the water content and attached surface bacterial concentrations were found to provide a best fit between predicted and observed data. From these experimental and model results we conclude that detachment mechanisms associated with the rapid increases in pore water content such as air-water interface scouring and thin film expansion are likely drivers of ENT mobilization in the investigated system. These findings suggest that through-beach transport of ENT may be an important pathway through which ENT from beach sands are transported to beach groundwater where they may be discharged to coastal waters via submarine groundwater discharge.

In situ soil cementation with ureolytic bacteria by surface percolation

The possibility of using microbiological processes to improve the mechanical properties of soil by undisturbed in situ application has gained attention over recent years. This paper describes a new variation of in situ soil reinforcement technology based on microbially induced carbonate precipitation (MICP), which involves both the hydrolysis of urea by soil bacteria enzyme and calcium carbonate precipitation in the presence of dissolved calcium ions. In contrast to other previously published approaches, the current work uses surface percolation for in situ placement of bacteria and cementation solution. Bacteria could be immobilised over the full length of a 1m column by surface percolation. To accomplish this it was necessary to percolate alternate solutions containing either bacteria or fixation solution containing calcium ions.The biologically triggered cementation resulted in homogeneous cementation over the entire length of the 1-m sand column. The efficiency of calcite crystals to form strength was found to be related to the pore water content of the continuously drained column with less water content enabling more efficient strength formation. Scanning electron microscopy supported the idea that lower water contents lead to selective positioning of crystals at the bridging points between sand grains. These findings imply that the cost of MICP technology can be reduced by optimising the conditions for effective crystals precipitation. This is expected to make this technology more readily acceptable for large scale applications.

Vibrational dynamics of water confined in mesoporous silica under low temperature

The Raman vibrational spectra of water inside mesoporous silicate are measured in a temperature range of 100 T 303 K. It is found that the Raman spectrum of confined water becomes more different from that of bulk water with the decrease of water content in pores. For samples with high water content in pore, the main peak position of the Raman spectrum of water changes abruptly in a narrow temperature range. However, when water content decreases down to 20%, the red shift of the main peak of the Raman spectrum is continuous with temperature decreasing. At the same time, its temperature-dependence is the same as that of bulk amorphous ice.

Biodegradable dextran based microgels: a study on network associated water diffusion and enzymatic degradation

Sustained drug delivery represents a major challenge in nanomedicine. Solutions to the many requirements posed by this field are not easy to address using a unique delivery vehicle. In recent years, our goal has been to implement such requirements in a single device by manipulating the structural and functional features of “soft” biocompatible drug delivery platforms. In this paper we describe a set of biocompatible drug delivery materials, with controlled structure and dimension, which are both biodegradable in a time frame of interest and designed as drug vectors for therapeutic approaches. These microdevices were obtained using ultrasound assisted “water-in-water” emulsification. The resulting material was a spherical shaped microgel with controlled pore size and water content. The dynamic behaviour of water in these matrixes showed a remarkable supercooling effect, an effect which was more pronounced for those microgels with smaller mesh sizes. The biodegradability of the microgel was monitored by observing the enzymatic breakdown of the material both as a whole, i.e. by observing a large number of microgel particles, and by focussing on single particles. A complex degradation pattern was observed, with the particles first increasing their size followed by a complete structural demolition. The time required to fully degrade a microgel can be tuned by varying the relative enzyme content and/or the degree of crosslinking of the network.

Contribution of logging tools to understanding helium porewater data across the Mesozoic sequence of the East of the Paris Basin

Helium concentration measurements made on water and rock samples collected at various depths along a 2000 m depth borehole drilled in the eastern part of the Paris basin and reaching the Triassic conglomerates were used to establish a vertical profile of dissolved helium concentration throughout the entire Mesozoic sedimentary pile. Wireline logging tools were used to measure rock density, porosity and U and Th contents every 15 cm in the various formations. Samples from the deepest Muschelkalk and Buntsandstein show a very good agreement between measured and calculated 4He porewater contents. Shallower levels show lower and lower 4He concentrations compared to calculated values when going upwards. The data set obtained by wireline logging measurements was used as inputs for numerical simulations of 1D He production/diffusion throughout the 2000 m profile. Several assumptions regarding the transport properties in the various sedimentary layers were tested and all were found to yield fairly good agreement between modeled and measured He concentrations. There is no need to invoke either a transient regime or a deep crustal He flux in this “quiet” (seismically inactive) part of the Paris basin. Moreover, the modeling results suggest that the Keuper massive halite level associated with the upper Muschelkalk pre-evaporitic series efficiently isolates the overlying layers from any input from deeper formations in the Meuse/Haute Marne area.

Molecular Dynamics Simulation of Water Influence on Local Structure of Nanoconfined Polyamide-6,6

Our recently developed molecular dynamics simulation method for simulating fluids confined in nanometric pores [Eslami et al. J. Chem. Phys.2008, 129, 194702] is employed to simulate nanoconfined polyamide-6,6+water in contact with graphene monolayers. In this work, a number of dry and wet polymer samples, containing 3 and 6 wt % water at 350 K, confined in pores of different sizes as well as the bulk polymer samples are simulated. It is shown that both water and polymer molecules form organized layers beside the surfaces. The effect of nanoconfinement on the hydrogen bonding in the polymer+water system is studied in detail. It is shown that addition of water to the polymer replaces a fraction of looser amide-amide hydrogen bonds with amide-water ones. The distribution of hydrogen bond lengths shows that both the polymer and water form shorter length hydrogen bonds in the confined region compared to the bulk system. The number of hydrogen bonds between polymer and water molecules is shown to depend on the pore size and on the water content. In small pores, water molecules are forced by the surfaces into the polymer layers and form strong hydrogen bonds with the amide groups, a process that increases the water solubility of the polymer in small pores. Increasing the water content in larger pores increases the number of hydrogen bonds between water molecules and causes the formation of big clusters in the central region of the pore. In simulations of to 50 ns, it is shown that such big clusters grow with of time, and hence, phase separate out from the mixture.

Residual nonclathrated water in sediments in equilibrium with gas hydrate

The method for experimental study of equilibrium for “pore water in sediment–hydrate-forming gas–bulk gas hydrate” system was developed at temperatures below and above 0 °C, and at different pressures. The gas pressure may be above the pressure for the three-phase equilibrium for “ice–gas–bulk gas hydrate.” The method is based on measuring the equilibrium water content in an initially air-dried sediment plate that has been placed into close contact with an ice plate under isothermal conditions and appropriate pressure by hydrate-forming gas. This equilibrium pore water content (the minimal possible amount of water in the sediments at conditions under consideration) can be defined as nonclathrated water by analogy to unfrozen water, which is widely used in geocryology science. The amount of nonclathrated water in the sediment depends on temperature, sediment type, kind of hydrate-forming gas, and gas pressure. The method was tested for nonclathrated water content measurements in kaolinite clay and different sand–clay mixtures (consisting of quartz sand with kaolinite or montmorillonite clay particles) in equilibrium with methane hydrate and CO 2 hydrate. In our opinion the experimental study of the nonclathrated water is important because it demonstrates the essential influence of this component on the thermophysical and mechanical properties of hydrate-containing sediments. ► We study equilibrium (nonclathrated) water in gas hydrate contained sediments. ► We developed experimental technique of nonclathrated water determination. ► This water in sediments sharply falls with increase of gas-forming pressure. ► Nonclathrated water in sediments increases with the increase of temperature.

Experimental study of radon production and transport in an analogue for the Martian regolith

The suggestion that radon could be used as a radioactive tracer of regolith-atmosphere exchanges and as a proxy for subsurface water on Mars, as well as its indirect detection in the Martian atmosphere by the rover Opportunity, have raised the need for a better characterization of its production process and transport efficiency in the Martian soil. More specifically, a proper estimation of radon exhalation rate on Mars requires its emanation factor and diffusion length to be determined. The dependence of the emanation factor as a function of pore water content (at 267 and 293 K) and the dependence of the adsorption coefficient on temperature, specific surface area and nature of the carrier gas (He, He + CO 2) have been measured on a Martian soil analogue (Hawaiian palagonitized volcanic ash, JSC Mars-1), whose radiometric analysis has been performed. An estimation of radon diffusion lengths on Mars is provided and is used to derive a global average emanation factor (2–6.5%) that accounts for the exhalation rate inferred from the 210Po surface concentration detected on Martian dust and from the 214Bi signal measured by the Mars Odyssey Gamma Ray Spectrometer. It is found to be much larger than emanation factors characterizing lunar samples, but lower than the emanation factor of the palagonite samples obtained under dry conditions. This result probably reflects different degrees of aqueous alteration and could indicate that the emanation factor is also affected by the current presence of pore water in the Martian soil. The rationale of the “radon method” as a technique to probe subsurface water on Mars, and its sensitivity to soil parameters are discussed. These experimental data are useful to perform more detailed studies of radon transport in the Martian atmosphere using Global Climate Models and to interpret neutron and gamma data from Mars Odyssey Gamma Ray Spectrometer.

Sediment penetration depths of epi- and infaunal ostracods from Lake Geneva (Switzerland)

Many (palaeo-)environmental parameters can be deduced from ecological and chemical analyses of ostracods. However, the specific ecology of each taxon has a great impact on its reaction to changing environmental conditions. As a consequence, each taxon records these changes differently. The mean penetration depth (MPD) and relative individual abundances have been documented along sediment depth profiles for the dominant sub-littoral to profundal species of ostracods in western Lake Geneva, Switzerland, and this data can be used to estimate their preferential habitat in terms of sediment depths. Isocypris beauchampi, Limnocytherina sanctipatricii, Cypria ophtalmica forma lacustris at 13-m water depths, Limnocythere inopinata, and a winter generation of Herpetocypris reptans have the shallowest habitat preferences at the study sites (MPDs of 0.45, 0.48, 0.49, 0.60, and 0.81 cm, respectively). These results suggest that these populations may be regarded as being preferentially epifaunal forms. Populations of Cytherissa lacustris (MPDs of 0.61, 0.73, and 0.82 cm at 13-, 33-, and 70-m water depths, respectively), Cypria ophtalmica forma lacustris at 70 m (MPD = 0.96 cm), Fabaeformiscandona caudata (MPD = 0.99 cm), and a summer generation of Herpetocypris reptans (MPD = 1.03 cm) were identified as being infaunal. Candona neglecta is the species that was found the deepest in the sediment of Lake Geneva, with MPDs of 0.65, 1.22, and 1.30 cm at 13-, 33-, and 70-m water depths, respectively. Information on the sediment texture and oxygen concentrations inferred from the analyses of sediment pore water suggest that the oxygen content of the sediment pore water is not the only dominant parameter controlling the differences in ostracod sediment penetration depths observed among the different sites, but that they might also be influenced by the sediment ‘softness,’ which itself depends on grain size, water content, and the abundance of organic matter in sediment.

Use of electrical conductivity to analyze depositional environments: Example of a Holocene delta sequence on the Nobi Plain, central Japan

The usefulness of electrical conductivity (EC) of stirred Holocene deltaic sediments from three cores from the Nobi Plain, Japan, was assessed as a proxy for marine transgression and regression. Lack of correlation of EC with mud content for the sediments with >20% mud suggested that permeability was a negligible factor. Marine deposits showed high EC (>0.9 mS/cm), terrestrial deposits low EC (<0.4 mS/cm), and brackish deposits intermediate. Because it was positively correlated with the percentage of marine diatom species, EC in inner-bay deposits primarily reflected salinity. In the YM core (the youngest of the three cores), EC of the inner-bay deposits was weakly positively correlated with clay content, which controls pore water content. EC of inner-bay clayey deposits was generally higher in YM than in KZN, suggesting that the lower EC in older clayey sediments results from compaction. These findings suggest that the EC values of fine sediments initially record salinity but may decrease gradually over time under the influence of compaction. Thus, to reconstruct the original salinity, the effects of compaction and of grain size distribution—and especially clay content—should be evaluated.

Effects of structural and compositional factors on soil electromagnetic properties

Electromagnetic properties of clay soils can be affected by many factors, including clay mineralogy, clay percentage, flocculation of clay particles, pore fluid salt concentration, anisotropy, and water content. The influences of these factors on soil dielectric permittivity and electrical conductivity are analysed using a theoretical model developed for clay minerals and the modified Maxwell-Garnett mixing formula. The analysis shows that, at frequencies higher than 50 MHz, the real permittivity of an isotropic soil is affected primarily by water content, clay percentage and clay mineralogy and, to a lesser extent, by pore fluid salt concentration and flocculation. Three theoretical correlations are established for saturated isotropic clay–water and sand–water mixtures: (1) correlation between volumetric water content and the real permittivity at 1 GHz, (2) correlation between volumetric water content and the dielectric dispersion magnitude from 50 MHz to 1 GHz, and (3) correlation between volumetric water content and the effective electrical conductivity at 20 MHz. These correlations are validated by measured data for saturated sand, kaolinite, bentonite and mixtures of bentonite and silica flour. A new method to determine volumetric water content and specific surface area from electromagnetic measurements is proposed.

Pore-Water Morphological Transitions in Polymer Electrolyte of a Fuel Cell

We show a criticality of three water morphological transitions on pore-water transport and proton conductivity in Nafion of a polymer electrolyte membrane fuel cell, addressing its pore-size distribution and the Schröder paradox. The first transition leads to the onset of proton conductivity; the second allows for the onset of the capillary percolation channels and proton conductivity jump at a low water content . Using this as immobile saturation, the predicted water distribution and cell performance are in reasonable agreement with the available experiments. The third (the paradox, postulating further capillary advancing) bounds the maximum water content on the cathode side of Nafion, which is also supported by the proposed adsorption isobar (thermodynamic equilibrium limit). These transitions appear in the available pore-size experiments which show capillary percolation channel sizes. In addition, the optimal Nafion pore-water content is between the second and third transitions.

Heavy metal (Cu, Zn, Cd and Pb) partitioning and bioaccessibility in uncontaminated and long-term contaminated soils

We investigated the pore-water content and speciation of copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in a range of uncontaminated and long-term contaminated soils in order to establish their potential bioaccessibility to soil biota, plants and humans. Among the samples, soil pH (0.01 M CaCl 2) ranged from 4.9 to 8.2. The total metal content of the uncontaminated soils ranged from 3.8 to 93.8 mg Cu kg −1, 10.3 to 95 mg kg −1 Zn, 0.1 to 1.8 mg Cd kg −1 and 5.2 to 183 mg kg −1 Pb, while metal content in the contaminated soils ranged from 104 to 6841 mg Cu kg −1, 312 to 39,000 mg kg −1 Zn, 6 to 302 mg Cd kg −1 and 609 to 12,000 mg kg −1 Pb. Our analysis of pore-water found the Cu concentrations to be much higher in contaminated soils than in uncontaminated soils, with the distribution coefficients ( K d) correlating significantly with the log of dissolved organic carbon concentrations. Despite the high total metal content of the contaminated soil, Zn, Cd and Pb were not generally found at elevated levels in the pore-water with the exception of a single contaminated soil. A long period of ageing and soil weathering may have led to a substantial reduction in heavy metal concentrations in the pore-water of contaminated soils. On the other hand, Pb bioaccessibility was found to be comparatively high in Pb contaminated soils, where it tended to exceed the total Pb values by more than 80%. We conclude that, despite the extensive ageing of some contaminated soils, the bioaccessibility of Pb remains relatively high.

Changes in Internal Phosphorus Loading and Fish Population as Possible Causes of Water Quality Decline in a Shallow, Biomanipulated Lake

AbstractImpacts of internal nutrient loading and the role of biota in phosphorus (P) dynamics were studied in a shallow, hypertrophic, biomanipulated lake. Reduced fish stock resulted in clearing water and the development of a dense submerged vegetation by 2005. However, an abrupt shift occurred in 2007, seven years after the fish manipulation. Simultaneously, water quality deteriorated which became obvious in elevated chlorophyll‐a concentration in lake water, associated with increased biomass of fish and decay of a previously extended macrophyte cover. There were no significant differences in lake water P concentrations between the two periods (2005–2006 and 2007); however, peaks of different P forms were markedly higher in 2007 than in 2005–2006. At the same time, P content of sediment pore water declined considerably in 2007. Our mesocosm experiment, carried out in the manipulated lake, emphasize the positive role of the dominant fish species (roach) in P regeneration. We suggest that fish manipulation should be carried out every 5 year to maintain clear water conditions permanent, until the total removal of redundant nutrients accumulated in the lake ecosystem. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Nitrogen Fluxes of a Slope Mire in the German Harz Mountains

Nitrogen (N) fluxes of a slope mire in the German Harz Mountains were monitored to study the effect of increased N deposition on the N retention of the mire. In addition, the N content of mire pore water beneath different plant species was analyzed to assess N retention ability of plants. Atmospheric N deposition at the study site was 4.9 ± 0.4 g N m−2 year−1 averaged for the study period of 2002 and 2003, with forest stand deposition being the largest share. Discharge was the main output pathway of N with a rate of 1.9 ± 0.3 g N m−2 year−1. The mire showed a high N retention rate of 67%. Short-term N accumulation rate was 3.9 g N m−2 year−1. Differences in mire pore water N concentration under different vegetation cover indicate a lower N retention ability for ombrotrophic Sphagnum plants.

The influence of colloid formation in a granite groundwater bentonite porewater mixing zone on radionuclide speciation

In the context of deep geological storage of high level nuclear waste the repository will be designed as multiple barrier system including bentonite as buffer/backfill material and the host rock formation as geological barrier. The engineered barrier (bentonite) will be in contact with the host rock formation and consequently it can be expected that bentonite porewater will mix with formation groundwater. We simulate in this study the mixing of Grimsel groundwater (glacial melt water) with synthetic Febex porewater (assuming already saturated state) in a batch-type study and investigate the formation of colloids by laser-induced breakdown detection (LIBD) and SEM-EDX as well as the changes in radionuclide (U, Th, Eu) speciation via ultrafiltration or via time-resolved laser fluorescence spectroscopy (TRLFS) analysis in the case of Cm(III). Based on PHREEQC saturation index (SI) calculations a precipitation of calcite might be expected at low Febex porewater (FPW) content (< 20%), fluorite precipitation at FPW contents < 60% and gibbsite precipitation at FPW contents above 10%. The colloids generated in the mixing zone aggregate when the synthetic FPW content exceeds 10%. LIBD analysis of the time-dependent colloid generation/aggregation revealed a low concentration of colloids to be stable with an estimated plateau value around 100–200 ppt and an average colloid diameter around 30 nm after 140 days reaction time at FPW admixture > 10%. SEM/EDX mostly identifies Al/Si containing colloidal phases and some sulfates could be found under certain admixture ratios. TRLFS studies show that the Cm speciation is strongly influenced by colloid formation in all solutions. In the Febex pore water/GGW mixing zone with high groundwater contents (> 80%) colloids are newly formed and Cm is almost quantitatively associated with most likely polysilicilic acid colloids.