The effects of humic substances on the transport of radionuclides: Recent improvements in the prediction of behaviour and the understanding of mechanisms     

Nick D. Bryan  Liam Abrahamsen  Nick Evans  Peter Warwick  Gunnar Buckau  Liping Weng  Willem H. Van Riemsdijk 《Applied Geochemistry》2012

Some recent developments made during the European Union 6th Framework Integrated Project FUNMIG in the understanding and prediction of behaviour in ternary systems of radionuclides, humic substances and mineral surfaces are described. These developments are placed in the context of the existing literature. The aim is to describe the current understanding of humic substance mediated radionuclide transport as it may be applied to calculations in support of Radiological Performance Assessment. Some improvements in experimental techniques that provide the raw data to calibrate metal ion binding models are explained. The various metal ion binding models that are available are described and contrasted, before the recent development of ternary system models, in particular the Ligand Charge Distribution model that can predict metal ion and humic substance behaviour in ternary systems. The kinetic effects in ternary systems are described along with the models that are used to describe them. Finally, the remaining challenges in making predictions of radionuclide transport for the Radiological Performance Assessment of radioactive waste repositories are discussed.  相似文献   

Debris dispersal modeling for the great Sumatra Tsunamis on Banda Aceh and surrounding waters     

Gegar Prasetya  Kerry Black  Willem de Lange  Jose Borrero  Terry Healy 《Natural Hazards》2012,60(3):1167-1188

The Great Sumatra Tsunami on 26 December 2004 generated large amounts of debris and waste throughout the affected coastal region in the Indian Ocean. In Banda Aceh—Indonesia, the tsunami flows were observed carrying a thick muddy sludge that mixed with all kinds of debris from the destroyed buildings, bridges and culverts, vehicles, fallen trees, and other flotsam. This waste and debris was mostly deposited inland, but traveled both onshore and offshore. Numerical dispersal modeling is carried out to simulate the transport of debris and waste produced by the tsunamis during the event. The model solves the Lagrangian form of the transport/dispersion equations using novel particle tracking techniques. Model results show that understanding the pathway and distribution of the suspended materials and flotsam caused by tsunamis is important for a proper hazards mitigation plan and waste management action, and to minimize serious long-term adverse environmental and natural resources consequences.  相似文献   

In situ study of the $$ R\overline{3} c \to R\overline{3} m $$ orientational disorder in calcite     

Sytle M. Antao  Ishmael Hassan  Willem H. Mulder  Peter L. Lee  Brian H. Toby 《Physics and Chemistry of Minerals》2009,36(3):159-169

The temperature dependences of the crystal structure and intensities of the (113) and (211) reflections in calcite, CaCO₃, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. Calcite transforms from to at about T _c = 1,240 K. A CO₃ group occupies, statistically, two positions with equal frequency in the disordered phase, but with unequal frequency in the partially ordered phase. One position for the CO₃ group is rotated by 180° with respect to the other. The unequal occupancy of the two orientations in the partially ordered phase is obtained directly from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x − 1. The a cell parameter shows a negative thermal expansion at low T, followed by a plateau region at higher T, then a steeper contraction towards T _c, where the CO₃ groups disorder in a rapid process. Using a modified Bragg–Williams model, fits were obtained for the order parameter S, and for the intensities of the (113) and (211) reflections. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

A surface structural model for ferrihydrite I: Sites related to primary charge, molar mass, and mass density     

Tjisse Hiemstra  Willem H. Van Riemsdijk 《Geochimica et cosmochimica acta》2009,73(15):4423-455

A multisite surface complexation (MUSIC) model for ferrihydrite (Fh) has been developed. The surface structure and composition of Fh nanoparticles are described in relation to ion binding and surface charge development. The site densities of the various reactive surface groups, the molar mass, the mass density, the specific surface area, and the particle size are quantified. As derived theoretically, molecular mass and mass density of nanoparticles will depend on the types of surface groups and the corresponding site densities and will vary with particle size and surface area because of a relatively large contribution of the surface groups in comparison to the mineral core of nanoparticles. The nano-sized (∼2.6 nm) particles of freshly prepared 2-line Fh as a whole have an increased molar mass of M ∼ 101 ± 2 g/mol Fe, a reduced mass density of ∼3.5 ± 0.1 g/cm³, both relatively to the mineral core. The specific surface area is ∼650 m²/g. Six-line Fh (5-6 nm) has a molar mass of M ∼ 94 ± 2 g/mol, a mass density of ∼3.9 ± 0.1 g/cm³, and a surface area of ∼280 ± 30 m²/g. Data analysis shows that the mineral core of Fh has an average chemical composition very close to FeOOH with M ∼ 89 g/mol. The mineral core has a mass density around ∼4.15 ± 0.1 g/cm³, which is between that of feroxyhyte, goethite, and lepidocrocite. These results can be used to constrain structural models for Fh. Singly-coordinated surface groups dominate the surface of ferrihydrite (∼6.0 ± 0.5 nm⁻²). These groups can be present in two structural configurations. In pairs, the groups either form the edge of a single Fe-octahedron (∼2.5 nm⁻²) or are present at a single corner (∼3.5 nm⁻²) of two adjacent Fe octahedra. These configurations can form bidentate surface complexes by edge- and double-corner sharing, respectively, and may therefore respond differently to the binding of ions such as uranyl, carbonate, arsenite, phosphate, and others. The relatively low PZC of ferrihydrite can be rationalized based on the estimated proton affinity constant for singly-coordinated surface groups. Nanoparticles have an enhanced surface charge. The charging behavior of Fh nanoparticles can be described satisfactory using the capacitance of a spherical Stern layer condenser in combination with a diffuse double layer for flat plates.  相似文献   

Using a Cloud to Replenish Parched Groundwater Modeling Efforts     

Randall J. Hunt  Joseph Luchette  Willem A. Schreuder  James O. Rumbaugh  John Doherty  Matthew J. Tonkin  Douglas B. Rumbaugh 《Ground water》2010,48(3):360-365

Groundwater models can be improved by introduction of additional parameter flexibility and simultaneous use of soft-knowledge. However, these sophisticated approaches have high computational requirements. Cloud computing provides unprecedented access to computing power via the Internet to facilitate the use of these techniques. A modeler can create, launch, and terminate “virtual” computers as needed, paying by the hour, and save machine images for future use. Such cost-effective and flexible computing power empowers groundwater modelers to routinely perform model calibration and uncertainty analysis in ways not previously possible.  相似文献   

Intersecting views of gully erosion in South Africa     

George Olivier  Marco J. Van De Wiel  Willem P. De Clercq 《地球表面变化过程与地形》2023,48(1):119-142

Gully erosion is an environmental problem recognized as one of the worst land degradation processes worldwide. Insight into regional gully perturbations is required to combat the serious on- and off-site impacts of gullying on a catchment management scale. In response, we intersect different perspectives on gully erosion-specific views in South Africa (SA), a country that exhibits various physiographic properties and spans 1.22 million km². While the debate surrounding gully origin continues, there is consensus that anthropogenic activities are a major contemporary driver. The anthropogenic impact caused gullying to transcend climatic, geomorphic, and land-use boundaries, although it becomes more prominent in central to eastern SA. Soil erodibility plays a crucial role in what extent of gully erosion severity is attained from human impact, contributing to the east–west imbalance of erosion in SA. Soil erosion rates from gullying and badlands are limited but suggest that it ranges between 30 and 123 t ha⁻¹ yr⁻¹ in the more prominent areas. These soil loss rates are comparable to global rates where gullying is concerned; moreover, they are up to four orders of magnitude higher than the estimated baseline erosion rate. On a national scale, the complexity of gullying is evident from the different temporal timings of (re)activation or stabilizing and different evolution rates. Continued efforts are required to understand the intricate interplay of human activities, climate, and preconditions determining soil erodibility. In SA, more medium- to long-term studies are required to understand better how changing control factors affect gully evolution. More research is needed to implement and appraise mitigation measures, especially using indigenous knowledge. Establishing (semi)-automated mapping procedures would aid in gully monitoring and assessing the effectiveness of implemented mitigation measures. More urgently, the expected changes in climate and land-use necessitate further research on how environmental change affects short-term gully erosion dynamics.  相似文献   

On the surface composition of Io     

Willem Wamsteker  Roger L. Kroes  James A. Fountain 《Icarus》1974,23(3):417-424

The wavelength dependence of the reflectivity of Io indicates the presence of two materials on the surface of this satellite of Jupiter. These materials are sulfur and an unspecified material (R₁) which shows a wavelength dependence of its reflectivity for 0.3 μm < λ < 1.0 μm similar to the non-H₂O frost spectrum of the rings of Saturn. A 60/40 admixture of these two spectra matches the observed reflection spectrum of Io from 0.3μm–3 μm, if the spectrum of R₁ is featureless for λ > 1 μm. Sulfur will give rise to a posteclipse brightening. The variation with wavelength of the temperature dependence of the reflectivity of sulfur will allow an observational confirmation of the presence of sulfur on Io. The material R₁ should show a large geometrical albedo. The translucency of sulfur is consistent with the polarization-phase curve to Io. The material R₁ is also required to be translucent. The thermal conductivity of a cooled sulfur powder under vacuum was measured and found to agree with the value determined for the upper layer of Io from observations at 10 μm. It is shown that this agreement is not necessarily meaningful.  相似文献   

On the oxidation and burial of organic carbon in sediments of the Iberian margin and Nazaré Canyon (NE Atlantic)     

Eric Epping  Claar van der Zee  Karline Soetaert  Willem Helder 《Progress in Oceanography》2002,52(2-4)

As a contribution to the EC-OMEX-II program, sediment carbon and nitrogen budgets are presented for the Iberian Margin (northeastern Atlantic). The budgets for degradable organic carbon and associated nitrogen were calculated from sediment and pore water properties, using a steady-state version of a numerical coupled diagenetic model, OMEXDIA. Data were collected throughout the major upwelling period along five transects, four of which were located on the open margin and one positioned in a major submarine canyon, the Nazaré Canyon.A comparison of in situ oxygen profiles measured with monocathodic microelectrodes and with Clark type microelectrodes showed that monocathodic electrodes overestimate the oxygen concentration gradient near the sediment–water interface. This artifact probably results from the loss in sensitivity of the monocathodic microelectrode during profiling. Shipboard time course measurements with Clark type electrodes demonstrated transient conditions upon sediment retrieval on deck and indicated enhanced rates of oxygen consumption in the surface sediment, presumably as a result of lysis or exudation of oxidisable substrates by infauna. As a result, oxygen fluxes calculated from shipboard oxygen profiles overestimated in situ fluxes by up to a factor of 5 for water depths >1000 m.The sediments from the canyon and from a depositional area on the shelf were enriched in organic carbon (3–4.5 wt%) relative to the open margin stations (0.5–2 wt%) and showed C/N ratios exceeding Redfield stoichiometry for marine organic matter, indicating there was deposition of organic carbon of terrestrial origin in these areas. The oxidation of organic carbon on the open margin declined from ˜11 gCm⁻²y⁻¹ on the shelf to 2 gCm⁻²y⁻¹ at 5000 m water depth, and was dominated by aerobic oxidation. The reactivity of the degradable organic carbon at the time of deposition was <2.5 y⁻¹ on the shelf, and declined to <0.5 y⁻¹ offshore. The burial of refractory organic carbon at the stations along the open margin transects also declined with increasing water depth from ˜5 gCm⁻²y⁻¹ on the shelf to <1 gCm⁻²y⁻¹ at 2000 m depth, whereas the burial of particulate inorganic carbon declined from ˜20 gCm⁻²y⁻¹ to <5 gCm⁻²y⁻¹. A comparison of the estimated total organic carbon deposition and predicted delivery for the shelf suggest that 58 to 165 gCm⁻²y⁻¹ is oxidized in the water column, laterally advected, or focused into one of the canyons.Anaerobic oxidation, denitrification and, therefore, total oxidation of organic carbon was enhanced within the canyon relative to the open margin. Total organic carbon oxidation decreased with water depth from 22 gCm⁻²y⁻¹ at the head of the canyon to 3 gCm⁻²y⁻¹ over its fan. The reactivity of the organic carbon deposited in the canyon was lower than those of the shelf stations, suggesting that the canyon is being enriched in older, laterally advected organic matter. The burial of refractory organic carbon in sediments from the Nazaré Canyon was considerably higher than in the sediments from the open margin; it also decreased with depth from 20 gCm⁻²y⁻¹ at 343 m to ˜2.5 gCm⁻²y⁻¹ at 4298 m water depth. The burial of particulate inorganic carbon was slightly lower than that of refractory organic carbon.The burial of refractory organic carbon and the deposition of degradable organic carbon were both positively correlated with the sedimentation rates for the Iberian Margin, and indicated burial efficiencies were 0.6 to 48%. A single trend for burial efficiency versus sedimentation rate for both the canyon and the open margin indicates that the sedimentation rate was the master variable for the geographical distribution of organic carbon oxidation and carbon preservation on the NW Iberian Margin.  相似文献   

The R{\overline{3}} c \to R{\overline{3}} m transition in nitratine, NaNO3, and implications for calcite, CaCO3     

Sytle M. Antao  Ishmael Hassan  Willem H. Mulder  Peter L. Lee 《Physics and Chemistry of Minerals》2008,35(10):545-557

The temperature dependences of the crystal structure and superstructure intensities in sodium nitrate, mineral name nitratine, NaNO₃, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction. Nitratine transforms from $R{\overline{3}} c\;\hbox{to}\;R{\overline{3}} m$ at T _c = 552(1) K. A NO₃ group occupies, statistically, two positions with equal frequency in the disordered $R{\overline{3}} m$ phase, but with unequal frequency in the partially ordered $R{\overline{3}} c$ phase. One position for the NO₃ group is rotated by 60° or 180° with respect to the other. The occupancy of the two orientations in the $R{\overline{3}} c$ phase is obtained from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x ? 1, where S is 0 at T _c and 1 at 0 K. The NO₃ groups rotate in a rapid process from about 541 to T _c, where the a axis contracts. Using a modified Bragg–Williams model, a good fit was obtained for the normalized intensities (that is, normalized, NI^1/2) for the (113) and (211) reflections in $R{\overline{3}} c\hbox {\,NaNO}_{3},$ and indicates a second-order transition. Using the same model, a reasonable fit was obtained for the order parameter, S, and also supports a second-order transition.  相似文献   

Variation in curve numbers derived from plot runoff data for New South Wales (Australia)     

Hongxia Cao  R. Willem Vervoort  Seth M. Dabney 《水文研究》2011,25(24):3774-3789

The curve number method is a simple one parameter (the curve number) rainfall runoff model. While its theoretical underpinning has been questioned it remains a powerful hydrological tool in the absence of detailed data and is therefore used extensively in hydrological models. This study aims to characterize the variation in maximum retention values (S), which underlie curve numbers, for a range of agricultural treatments across a large spatial area in New South Wales (NSW), Australia. The data used for the analysis spans several decades of rainfall runoff observations. A range of different derivation methods result in variation in mean and variance of S. In particular, methods that emphasize the larger storms result in greater S and thus lower runoff. For larger spatial scales, emphasis on larger storms gives more reliable estimates of S. Systematic variation in S arises from variations in treatment, pre‐runoff soil moisture, rainfall depth, and variations in cover. On the basis of the analysis, a table of curve number values for different land uses found in NSW is presented. The resulting distributions of S and curve numbers provide guidance for rainfall runoff modelling studies in the agricultural important areas of NSW. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献