bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adjusted Fick's law for gas diffusion in soils contaminated with petroleum hydrocarbons
Authors: Van De Steene J. , Verplancke H. 
Published: September 2005

SummaryIn bioremediation, hydrocarbon biodegradation rates can be estimated from measured O2 and CO2 profiles in situ. Although Fick's law is typically used in calculating the respiration rates, its theoretical base is weak. We propose an adjusted Fick's law with a correction term for the advective flux. We evaluated the applicability of this model to simulate gas diffusion associated with passive degradation of petroleum hydrocarbons in a biopile by comparing the results of this model with the results of Fick's law and the Stefan–Maxwell equations. The deviations from the use of Fick's law depended strongly on the consumption rate of oxygen, the respiration quotient, the mineralization quotient and the volatility of the hydrocarbon. In the whole range of calculated CO2 concentration versus depth profiles, production rates of CO2 could be estimated by Fick's law with a maximum deviation of 6%. For the consumption rate of O2 the maximum deviation is 19%. However, when we used the adjusted Fick's law, the deviations from the results obtained with the Stefan–Maxwell equations were much smaller. The deviations amounted up to only 4%, when the respiration rate r was 1.5 or a hydrocarbon with volatility similar to benzene was present. If the presence of a hydrocarbon was neglected in the calculations, the deviations of the adjusted Fick's law from the results obtained with the Stefan–Maxwell equations were substantial for a hydrocarbon with volatility similar to benzene or toluene.
Mobility of Cd and Zn in polluted and unpolluted Spodosols
Authors: Degryse F. , Smolders E. 
Published: September 2005

SummaryLeaching of Cd and Zn in polluted acid, well‐drained soils is a critical pathway for groundwater pollution. Models predicting future groundwater contamination with these metals have rarely been validated at the field scale. Spodosol profiles (pH 3.2–4.5) were sampled in an unpolluted (reference) field and in a field contaminated with Cd and Zn through atmospheric deposition near a zinc smelter. Average metal concentrations in the upper horizons were 0.2 mg Cd kg−1 and 9 mg Zn kg−1 in the unpolluted field, and 0.8 mg Cd kg−1 and 71 mg Zn kg−1 in the contaminated field. Isotopic dilution was used to measure the labile concentration of Cd and Zn, and the metal transport was modelled using measured sorption parameters that describe the distribution between the labile metal pool (instead of the total metal pool) and the solution phase obtained by centrifugation. Solutions were also collected by wick samplers in two polluted and one unpolluted profile at a depth of 70 cm. Concentrations in these solutions were in the order of 15 µg Cd litre−1 and 0.8 mg Zn litre−1 for the polluted profiles, and 1 µg Cd litre−1 and 0.04 mg Zn litre−1 for the unpolluted profile. The concentrations in these solutions agreed well with those in soil solutions obtained by centrifugation, which supported the use of the local equilibrium assumption (LEA). Present‐day Cd profiles in the polluted field were calculated with the LEA, based on the emission history of the nearby smelter and taking spatial variability into account. Observed and predicted depth profiles agreed reasonably well, but total Cd concentrations in the topsoil were generally underestimated by the model. This may be attributed to the presence of non‐labile Cd in the atmospheric deposition, which was not accounted for in the retrospective modelling. The large concentrations of non‐labile Zn in the topsoil of the polluted field were also indicative that metals in the atmospheric deposition were (partly) in a sparingly soluble form, and that release of these non‐labile metals is a slow process. The presence of non‐labile metals should be taken into account when evaluating metal mobility or predicting their transport.
Estimating organic carbon in the soils of Europe for policy support
Authors: Jones R. J. A. , Hiederer R. , Rusco E. , Montanarella L. 
Published: September 2005

SummaryThe estimation of soil carbon content is of pressing concern for soil protection and in mitigation strategies for global warming. This paper describes the methodology developed and the results obtained in a study aimed at estimating organic carbon contents (%) in topsoils across Europe. The information presented in map form provides policy‐makers with estimates of current topsoil organic carbon contents for developing strategies for soil protection at regional level. Such baseline data are also of importance in global change modelling and may be used to estimate regional differences in soil organic carbon (SOC) stocks and projected changes therein, as required for example under the Kyoto Protocol to the United Nations Framework Convention on Climate Change, after having taken into account regional differences in bulk density.The study uses a novel approach combining a rule‐based system with detailed thematic spatial data layers to arrive at a much‐improved result over either method, using advanced methods for spatial data processing. The rule‐based system is provided by the pedo‐transfer rules, which were developed for use with the European Soil Database. The strong effects of vegetation and land use on SOC have been taken into account in the calculations, and the influence of temperature on organic carbon contents has been considered in the form of a heuristic function. Processing of all thematic data was performed on harmonized spatial data layers in raster format with a 1 km × 1 km grid spacing. This resolution is regarded as appropriate for planning effective soil protection measures at the European level. The approach is thought to be transferable to other regions of the world that are facing similar questions, provided adequate data are available for these regions. However, there will always be an element of uncertainty in estimating or determining the spatial distribution of organic carbon contents of soils.
Sources of trace metals in Ferralsols in New Caledonia
Authors: Becquer T. , Quantin C. , Rotte‐Capet S. , Ghanbaja J. , Mustin C. , Herbillon A. J. 
Published: September 2005

SummaryOne third of New Caledonia is occupied by soils deriving from ultrabasic rocks anomalously rich in trace metals such as Cr, Ni, Mn and Co. The location of the metals present in three samples from a toposequence of Ferralsols was studied by combining selective dissolutions (CaCl2, Cu(NO3)2, hydroxylamine, dithionite–citrate–bicarbonate), examinations with a transmission electron microscope (TEM) equipped with an EDAX device, and X‐ray diffraction and infrared spectroscopy. The behaviour of the metals during dissolution was found to depend on both the type of metal and the location of the samples in the toposequence. In the lowland soil samples derived from transported materials, about 50% of total Mn and Co and a small fraction (< 1%) of total Ni were dissolved in the hydroxylamine reagent. By TEM, the manganese oxide minerals present in one of the lowland samples were found to have chemical compositions similar to those of lithiophorite–asbolane mixed layers identified previously in the subsurface horizons of the laterites capping the landscape where the toposequence occurs. Whatever the location of samples, goethite, i.e. the major constituent of these soils, was found to be the scavenger of the largest proportions of Ni and of about 40% of total Cr. However, this mineral was present as two distinct morphological facies, and each of them had a statistically different chemical composition. The small needle‐shaped goethite, which was abundant in the lowland soils only, was richer in Ni and Si and poorer in Al than the larger acicular one. Our data show that the potential mobility of trace metals in these soils is likely to be controlled by the most soluble phases identified, i.e. the Co‐rich Mn oxides and the Ni‐rich needle‐shaped goethites.
Concentrations of Ag, In, Sn, Sb and Bi, and their chemical fractionation in typical soils in Japan
Authors: Hou H. , Takamatsu T. , Koshikawa M. K. , Hosomi M. 
Published: September 2005

SummaryWe determined concentrations of Ag, In, Sn, Sb and Bi, and fractionated them by sequential extraction procedures, in five Japanese soils: Andosol‐1 (grassland), Andosol‐2 (forest), Cambisol (forest), Fluvisol (vegetable garden) and Regosol (forest). Average concentrations of Ag, In, Sn, Sb and Bi were 0.17 ± 0.08, 0.081 ± 0.019, 2.2 ± 0.5, 0.83 ± 0.32 and 0.32 ± 0.12 mg kg−1, respectively. Average distributions of the chemical fractions (omitting those with an abundance < 5%) were: Ag, residual (60%) > H2O2‐extractable, organically bound (H2O2‐Org) (18%) > metal–organic complex‐bound (Me‐Org) (10%) > amorphous metal oxide‐bound (am‐MeOx) (8.3%); In, residual (61%) > H2O2‐Org (12%) > Me‐Org (8.7%) ≥ crystalline Fe oxide‐bound (cr‐FeOx) (8.2%) > am‐MeOx (7.4%); Sn, residual (40%) > Me‐Org (19%) > carbonate‐bound (12%) > cr‐FeOx (9.0%) > H2O2‐Org (7.8%) > am‐MeOx (6.9%); Sb, residual (34%) > Me‐Org (18%) > am‐MeOx (16%) > cr‐FeOx (8.9%) ≥ H2O2‐Org (8.7%) > easily reducible metal oxide‐bound (re‐MeOx) (6.8%) > carbonate‐bound (6.1%); Bi, am‐MeOx (26%) ≥ H2O2‐Org (26%) > Me‐Org (19%) > residual (17%) > cr‐FeOx (12%). Proportions of the mobilizable (exchangeable + carbonate‐bound + Me‐Org + re‐MeOx) metal fractions were in the order Sn ≥ Sb > Bi > Ag ? In, and Cambisol > Andosol‐2 > Regosol > Andosol‐1 > Fluvisol. The proportions were predicted by multiple regression equations including pH, surface area, C contents, cation exchange capacity and clay content of the soils as independent variables (R2 > 0.96,P< 0.02).
Water repellence and soil aggregate dynamics in a loamy grassland soil as affected by texture
Authors: De Gryze S. , Jassogne L. , Bossuyt H. , Six J. , Merckx R. 
Published: September 2005

SummaryIt has been hypothesized that aggregate stability is partly caused by subcritical (i.e. mild) water repellence. We conducted both a field study at a pasture site and an incubation experiment in the laboratory to characterize the relationship between aggregate dynamics and water repellence. In the field study, we investigated 53 samples from a natural texture gradient for water repellence and aggregation. In the 3‐week incubation experiment, we added wheat straw to crushed soil material from five of the 53 soils representative of the texture gradient (a sandy loam, two loams, a silt loam and a clay loam), and followed changes in aggregate formation and water repellence. Although there was a dramatic increase (P < 0.0001) in aggregation in all the soils during incubation (the mean weight diameter increased from about 300 μm to at least 900 μm), we observed a concomitant increase in water repellence only in the clay loam soil (P = 0.0003). We found no significant correlations between water repellence and aggregation (n = 53, P > 0.05) in the field. Whereas correlation between aggregate formation and texture was weak in the incubation experiment, we found a significant correlation between aggregation and textural parameters in the field. The amount of large macro‐aggregates (> 2000 μm) was positively correlated with clay content (n = 53, r = 0.53, P < 0.001), and negatively with sand content (n = 53, r = −0.46, P < 0.001). These results indicate that (i) microbially induced water repellence might only become apparent when enough easily decomposable substrate is available, (ii) soil texture affects aggregate stabilization rather than aggregate formation, and (iii) aggregate formation is not necessarily associated with an increase in water repellence.
Free radicals, antioxidants, and soil organic matter recalcitrance
Authors: Rimmer D. L. 
Published: September 2005

SummaryHighly reactive, and potentially damaging, free radicals are readily generated in our oxygen‐rich environment, and are ubiquitous in biological systems. However, plants and animals have evolved protection against them with a range of antioxidant molecules, such as vitamins C and E, many of which are phenolic compounds. These stop the destructive chain reaction of free radical formation by being transformed into unreactive, stable free radicals. The biodegradation of food involves oxidation by free radicals, and is retarded by antioxidants. Similarly, the biodegradation of plant residues in soils involves free radicals; so the questions arise: (i) do soils have antioxidants, and (ii) what function might they have? The evidence suggests that they probably do have antioxidants. First, plant and animal remains added to soils will contain antioxidants. These are likely to persist for a time, particularly tannins, which are polyphenolic compounds with known antioxidant properties and which are relatively resistant to degradation. Second, studies using electron spin resonance spectroscopy have shown that humic materials contain stable semiquinone free radicals, and that their concentration increases as humification progresses. These semiquinone species are most likely to be derived from the reaction of phenolic compounds with reactive radicals. If this is the case, the phenolics are acting as antioxidants, because they are scavenging the reactive free radicals and terminating the oxidative chain reaction responsible for soil organic matter (SOM) degradation. Thus the soil's antioxidant capacity could control the rate of breakdown of organic matter in the more labile pools and could provide a chemical mechanism for the recalcitrance of SOM. Current available evidence for the nature of the recalcitrant pool in SOM is discussed in the light of this hypothesis, and the experimental approaches necessary for testing it are outlined.
Tracing sediment dynamics and sources in eroding rills with rare earth elements
Authors: Lei T. W. , Zhang Q. W. , Zhao J. , Nearing M. A. 
Published: September 2005

SummaryEroding rills evolve morphologically in time and space. Most current studies on rill erosion use spatially averaged soil erosion data, providing little information on soil erosion dynamics. A method is proposed to use rare earth elements (REEs) to trace sediment distribution in eroding rills. Laboratory flume simulation experiments were conducted at three flow rates (2, 4 and 8 litres minute−1) and five slope gradients (5, 10, 15, 20 and 25°) with three replicates of each treatment. The rills, of 8 m length, were subdivided into 10 equal segments of 0.8 m length and 0.1 m width, with a different REE applied to each segment. We derived computational formulae for estimating the distribution of eroded amounts along the rills. The actual erosion distribution along rills was then estimated with the data from the experiments. The precision of the REEs for tracing rill erosion was analysed. The results showed that sediment concentration increased with rill length, but the increased rate (the slope of the curve) flattened gradually. Sediment yields increased with slope gradients and flow rates, but the slope gradients had a greater effect on sediment concentration than flow rates, and greater flow rates caused more rill erosion and soil loss under the same slope gradient. The results also demonstrated the feasibility of using REEs to trace the dynamic processes of rill erosion.
A simplified parametric model to describe the magnitude and geometry of soil shrinkage
Authors: Cornelis W. M. , Corluy J. , Medina H. , Hartmann R. , Van Meirvenne M. , Ruiz M. E. 
Published: September 2005

SummaryAssessing the magnitude and geometry of soil shrinkage is indispensable for sound use and management of swelling and shrinking soils for agriculture and engineering. We have explored a simplified parametric model for the soil shrinkage characteristic curve, which is a measure for the magnitude of soil shrinkage, and tested it against experimental data for a Vertisol and a Lixisol under sugar cane in the Havana province, Cuba. We then applied the model to determine soil consistency limits, including the shrinkage, plastic and structural limits, using the model's third and fourth derivative. We further demonstrated how the model can be used to assess the geometry of shrinkage in terms of the relative crack area and the relative surface subsidence. Excellent matches were obtained between the observations and the fitted model. The shrinkage and structural limits corresponded to distinct changes in the soil shrinkage characteristic curve and were as such considered to be correctly estimated. The accuracy of the estimated plastic limit could, however, not been verified, since data were lacking. Linear regressions with R2 > 0.88 were established relating the shrinkage and plastic limits to the soil's COLE index and the cation exchange capacity. The model could be easily applied to determine the crack area and the surface subsidence. We finally demonstrated how a geometry factor rs plays a crucial role in determining the shrinkage geometry, particularly for rs values ranging from 1 to 3.
The role of mineral and organic components in phenanthrene and dibenzofuran sorption by soil
Authors: Celis R. , De Jonge H. , De Jonge L. W. , Real M. , Hermosín M. C. , Cornejo J. 
Published: September 2005

SummaryImproved predictions of sorption of hydrophobic organic compounds (HOCs) in soil require a better knowledge of the relative contribution of inorganic and organic soil constituents to the sorption process. In this paper, sorption of a three‐ring polycyclic aromatic hydrocarbon (phenanthrene) and a three‐ring heterocyclic–aromatic compound (dibenzofuran) by six agricultural soils, their clay‐size fractions, and a series of single, binary, and ternary model sorbents was evaluated to elucidate the relative role of soil mineral and organic components in the retention of these two model HOCs. The sorption coefficients for phenanthrene and dibenzofuran on purified soil organic materials (Kd = 821–9080 litre kg−1) were two orders of magnitude greater than those measured on mineral model sorbents (Kd = 0–114 litre kg−1). This, along with the strong correlation between sorption and the organic C content of the soil clay fractions (r = 0.99,P< 0.01), indicated a primary role of soil organic matter in the retention of both compounds. However, weak relationships between phenanthrene and dibenzofuran sorption coefficients and the organic C content of the bulk soils and variability ofKocvalues among soils, clay fractions, and model sorbents (1340–21020 litre kg−1C for phenanthrene and 1685–7620 litre kg−1C for dibenzofuran) showed that sorption was not predictable exclusively from the organic C content of the materials. Organic matter heterogeneity and domain blockage arising from organic matter–clay interactions and associated pH shifts were identified as the most likely causes of the different organic C‐normalized sorption capacities of the soils. A direct contribution from minerals to the sorption of phenanthrene and dibenzofuran by the soils studied was likely to be small. Our results suggested that suitable descriptors for the extent of organic matter–mineral interactions would help to improve currentKoc‐based sorption predictions and subsequently the assessment of risk associated with the presence of HOCs in soil.
Sorption regulates the fate of the amino acids lysine and leucine in soil aggregates
Authors: Vieublé Gonod L. , Jones D. L. , Chenu C. 
Published: September 2005

SummaryAmino acids are substrates widely present in soils either in a free or a polymeric state and represent a large input of organic nitrogen into most terrestrial ecosystems. However, their behaviour in soil remains poorly understood. The aim of this study was to assess critically the impact of sorption on the mineralization of two contrastingly charged amino acids, lysine and leucine, in different‐sized, real soil aggregates. In a first experiment, we assessed the spatial variability of amino acid mineralization in aggregates of different sizes. After 1 day of incubation coefficients of variation of leucine mineralization were 33% in aggregates of 2–3 mm, 15% in aggregates of 3–5 mm and 14% in aggregates of 5–7 mm diameter. Coefficients of variation of lysine mineralization were, after 1 day of incubation, 24% in aggregates of 2–3 mm, 26% in aggregates of 3–5 mm and 24% in aggregates of 5–7 mm diameter. Compared with other substrates, this variability is small and could be due to the presence of degrading microorganisms in all aggregates. We also studied the activity of such microorganisms by following the evolution with time of 14C‐amino acids in different compartments within aggregates 3–5 mm diameter (mineralized 14C, microbial biomass 14C, 14C in soil solution and residual 14C in soil). The microorganisms that degrade amino acids were able to assimilate substrates in soil solution immediately and used them preferentially for their growth and not solely for their energy production. For lysine, intense competition between adsorption and assimilation by microorganisms occurred from the start of the incubation period and persisted with time. Our results clearly show that sorption may retard biodegradation of amino acids in soil.
Monitoring organic matter dynamics in soil profiles by ‘Rock‐Eval pyrolysis’: bulk characterization and quantification of degradation
Authors: Sebag D. , Disnar J. R. , Guillet B. , Di Giovanni C. , Verrecchia E. P. , Durand A. 
Published: September 2005

SummaryRock‐Eval pyrolysis was designed for petroleum exploration to determine the type and quality of organic matter in rock samples. Nevertheless, this technique can be used for bulk characterization of the immature organic matter in soil samples and recent sediments. We studied 76 samples from seven soil classes and showed that their pyrograms can be described by a combination of four elementary Gaussian components: F1, F2, F3 and F4. These four components are related to major classes of organic constituents differing in origin and their resistance to pyrolysis: labile biological constituents (F1), resistant biological constituents (F2), immature non‐biotic constituents (F3) and a mature refractory fraction (F4). We discriminated the relative contributions of these components and used them to derive two indices: (i) to quantify the relative contributions of labile and resistant biological constituents and (ii) to quantify the degradation stage of the soil organic matter. The practical applications are illustrated via the influence of vegetal cover on soil organic matter dynamics and peat development in a Holocene sedimentary sequence, but we suggest that the approach is of much wider application.