Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    In-situ measurement of free trace metal concentrations in a flooded paddy soil using the Donnan Membrane Technique
    Pan, Y. ; Koopmans, G.F. ; Bonten, L.T.C. ; Song, J. ; Luo, Y. ; Temminghoff, E.J.M. ; Comans, R.N.J. - \ 2015
    Geoderma 241-242 (2015). - ISSN 0016-7061 - p. 59 - 67.
    dissolved organic-matter - ray-absorption spectroscopy - copper redox transformation - reduced sulfur groups - ion activity model - sandy soil - humic substances - natural-waters - higher-plants - heavy-metals
    The field Donnan Membrane Technique (DMT) has been used successfully to measure in-situ free trace metal concentrations in surface waters. However, it has not been applied previously in submerged soil systems including flooded paddy rice fields.Wetested this technique in a columnexperimentwith a flooded paddy soil contaminated with trace metals and compared the DMT measurements with predictions from a geochemical speciation model. Flooding led to a strong gradient in the redox potential (Eh) along the soil column, and the pH and concentrations ofMn, Fe, and dissolved organic carbon increased with decreasing Eh. Total dissolved tracemetal concentrations decreased from the overlying water layer to the soil layers, which might be ascribed to the elevated pH outweighing the effect of the increased DOC concentrations under anaerobic conditions. Also, free trace metal concentrations were lower in the soil solution of the upper and bottom soil layers than in the overlying water layer, largely due to the increased pH under anaerobic conditions. The DMT measurements and model predictions were similar in the aerobic water layer, except for Pb. In both anaerobic soil layers, however, Cu and Pb were poorly predicted. The applied geochemical modeling approach, which is frequently being used and performswell under aerobic conditions, does not fully capture all the chemical processes occurring under anaerobic conditions. Overall, the field DMT proved to be a useful tool for the in-situ measurement of free trace metal concentrations in flooded paddy soils.
    The use of assemblage models to describe trace element partitioning, speciation, and fate: a review
    Groenenberg, J.E. ; Lofts, S. - \ 2014
    Environmental Toxicology and Chemistry 33 (2014)10. - ISSN 0730-7268 - p. 2181 - 2196.
    dissolved organic-matter - metal-ion binding - oxide-water interface - nica-donnan model - electrical double-layer - upland uk catchment - long-term chemistry - savanna river site - humic substances - cation-binding
    The fate of trace elements in soils, sediments, and surface waters is largely determined by their binding to reactive components, of which organic matter, metal oxides, and clays are considered most important. Assemblage models, combining separate mechanistic complexation models for each of the reactive components, can be used to predict the solid-solution partitioning and speciation of trace elements in natural environments. In the present review, the authors provide a short overview of advanced ion-binding models for organic matter and oxides and of their application to artificial and natural assemblages. Modeling of artificial assemblages of mineral components and organic matter indicates that the interactions between organic and mineral components are important for trace element binding, particularly for oxyanions. The modeling of solid-solution partitioning in natural systems is generally adequate for metal cations but less so for oxyanions, probably because of the neglect of organic matter-oxide interactions in most assemblage models. The characterization of natural assemblages in terms of their components (active organic matter, reactive oxide surface) is key to successful model applications. Improved methods for characterization of reactive components in situ will enhance the applicability of assemblage models. Collection of compositional data for soil and water archetypes, or the development of relationships to estimate compositions from geospatially available data, will further facilitate assemblage model use for predictive purposes. Environ Toxicol Chem 2014;33:2181-2196. (c) 2014 SETAC
    Adsorption of levofloxacin onto goethite: Effects of pH, calcium and phosphate
    Qin, X.P. ; Liu, F. ; Wang, G.C. ; Weng, L. ; Li, L. - \ 2014
    Colloids and Surfaces. B: Biointerfaces 116 (2014). - ISSN 0927-7765 - p. 591 - 596.
    fluoroquinolone antibacterial agents - water interface - ciprofloxacin removal - antibiotic ofloxacin - humic substances - iron-oxides - sorption - complexation - tetracycline - speciation
    Adsorption of levofloxacin (LEV), one of the extensively used antibiotics, onto goethite was investigated using batch experiments. The adsorption of LEV on goethite was pH-dependent. A maximum adsorption was reached at pH 6. Above or below pH 6, the adsorption decreased. In the presence of calcium (Ca2+), a decrease in adsorption was observed, due to probably formation of Ca2+-LEV complexes in solutions. Phosphate also showed a significant inhibition on LEV adsorption over a pH range of 3-10. Phosphate competed with LEV for binding sites on the surface of goethite, and the electrostatic competition between LEV and phosphate on goethite surface might be another reason for the decrease in adsorption. These results indicated that Ca2+ and phosphate have a great influence on the distribution of LEV in soils and waters, which will eventually affect its antibacterial activity in the environment. (C) 2013 Elsevier B.V. All rights reserved.
    Enhanced Input of Terrestrial Particulate Organic Matter Reduces the Resilience of the Clear-Water State of Shallow Lakes: A Model Study
    Lischke, B. ; Hilt, S. ; Janse, J.H. ; Kuiper, J.J. ; Mehner, T. ; Mooij, W.M. ; Gaedke, U. - \ 2014
    Ecosystems 17 (2014)4. - ISSN 1432-9840 - p. 616 - 626.
    climate-change - food webs - humic substances - resource use - fresh-water - loch ness - land-use - carbon - ecosystem - phosphorus
    The amount of terrestrial particulate organic matter (t-POM) entering lakes is predicted to increase as a result of climate change. This may especially alter the structure and functioning of ecosystems in small, shallow lakes which can rapidly shift from a clear-water, macrophyte-dominated into a turbid, phytoplankton-dominated state. We used the integrative ecosystem model PCLake to predict how rising t-POM inputs affect the resilience of the clear-water state. PCLake links a pelagic and benthic food chain with abiotic components by a number of direct and indirect effects. We focused on three pathways (zoobenthos, zooplankton, light availability) by which elevated t-POM inputs (with and without additional nutrients) may modify the critical nutrient loading thresholds at which a clear-water lake becomes turbid and vice versa. Our model results show that (1) increased zoobenthos biomass due to the enhanced food availability results in more benthivorous fish which reduce light availability due to bioturbation, (2) zooplankton biomass does not change, but suspended t-POM reduces the consumption of autochthonous particulate organic matter which increases the turbidity, and (3) the suspended t-POM reduces the light availability for submerged macrophytes. Therefore, light availability is the key process that is indirectly or directly changed by t-POM input. This strikingly resembles the deteriorating effect of terrestrial dissolved organic matter on the light climate of lakes. In all scenarios, the resilience of the clear-water state is reduced thus making the turbid state more likely at a given nutrient loading. Therefore, our study suggests that rising t-POM input can add to the effects of climate warming making reductions in nutrient loadings even more urgent.
    Holocene vegetation and fire dynamics in central-eastern Brazil: Molecular records from the Pau de Fruta peatland
    Schellekens, J. ; Horak-Terra, I. ; Buurman, P. ; Silva, A.C. ; Vidal-Torrado, P. - \ 2014
    Organic Geochemistry 77 (2014). - ISSN 0146-6380 - p. 32 - 42.
    soil organic-matter - chromatography-mass-spectrometry - pyrolysis-gc-ms - humic substances - minas-gerais - isotopic composition - ombrotrophic peat - lignin - serra - plant
    Tropical climate dynamics play a major role in the global climate system. Precipitation patterns in the Serra do Espinhaço Meridional (Minas Gerais, Brazil) are influenced by both the South Atlantic Convergence Zone (SACZ) and the Inter Tropical Convergence Zone (ITCZ). This makes the area important for the interpretation of climate dynamics. The composition of the Holocene Pau de Fruta peat deposit was analysed using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Molecular records agreed well with d13C and d15N stable isotopes, C content and mineral content, and pollen records. Changes in peatland plant species composition and fire occurrence indicated several wet and dry periods for the Pau de Fruta peatland during the Holocene; from the beginning of the Holocene to 7400 cal yr BP (phase I; dry and cold), from 7400 to 4200 cal yr BP (phase II; wet and warm), from 4200 to 1000 cal yr BP (phase III; dry and warm), from 1000 to 400 cal yrBP (phase IV; wet and warm) and from 400 cal yr BP to the present (V). The hydrological shifts showed a chronology comparable with that described in other palaeoclimatic studies for central-eastern Brazil, indicating that local conditions agree with regional ones. Analytical Py of the peat deposit provided a multi-proxy record via the identification of specific markers for both peatland plants (vegetation) and charred material (fire), whereas the general chemistry provided information on the degree of decomposition of the organic matter. Molecular chemistry of the peat core sampled at high resolution provided insight into peatland C dynamics, which is important for the interpretation of C sequestration in tropical peatlands. Molecular aspects accurately reflected local environmental change. The general agreement of Py data with pollen and inorganic chemistry supports the use of the molecular approach, because it provides local proxy indicators for peatlands, avoiding a mixture of local and regional signals.
    Dynamics of soil dissolved organic carbon pools reveal both hydrophobic and hydrophilic compounds sustain microbial respiration
    Straathof, A.L. ; Chincarini, R. ; Comans, R.N.J. ; Hoffland, E. - \ 2014
    Soil Biology and Biochemistry 79 (2014). - ISSN 0038-0717 - p. 109 - 116.
    agricultural soils - humic substances - matter fractions - biodegradation - components - absorbency
    The quality of dissolved organic carbon (DOC) released from soil organic amendments may influence soil microbial activity and the quality of the soil's DOC pools. Measurements of total DOC are often considered in relation to microbial activity levels but here we propose that quantification of DOC fractions is a more informative alternative. In a laboratory incubation, soil received DOC that was extracted from three organic matter sources: fresh compost, mature compost, and a mixture of the two. Soil microbial respiration (CO2 emission), and concentrations of hydrophobic (humic acids (HA), fulvic acids (FA) and neutrals (HoN)) and hydrophilic (Hi) DOC fractions were measured throughout the 35 d incubation. The A254 specific UV absorption of total and HA DOC were measured at the start and end of the incubation as an indicator of aromaticity. Microbial respiration rates were highest in soils amended with fresh compost DOC, which had a higher proportion of Hi compounds. Concentration of Hi was significantly and positively correlated with soil respiration, explaining 24% more variation than total DOC. Humic acid concentrations significantly decreased over 35 d, including a 33% reduction in HA from an unamended control soil. Compost treated soils' HA pools increased in aromaticity, suggesting preferential mineralization of the least aromatic HA molecules. A decrease in SUVA254 values in other HA pools may be the result of HA degradation in the absence of low-aromatic HA. Our observation of depletion of hydrophobic compounds from the HA fraction provides evidence that humic substances can be a relatively reactive pool, which can provide, together with hydrophilic compounds, a readily available C source to the microbial community.
    Multi-face modeling to predict free zinc ion concentrations in low-zinc soils
    Duffner, A. ; Weng, L. ; Hoffland, E. ; Zee, S.E.A.T.M. van der - \ 2014
    Environmental Science and Technology 48 (2014)10. - ISSN 0013-936X - p. 5700 - 5708.
    donnan membrane technique - organic-matter - heavy-metals - contaminated soils - isotopic exchange - humic substances - trace-metals - sandy soil - adsorption - speciation
    Multi-surface models are widely used to assess the potential ecotoxicological risk in metal-contaminated soils. Their accuracy in predicting metal speciation in soils with low metal levels was not yet tested. Now highly sensitive analytical techniques are available to experimentally validate such models at low concentration levels. The objective of this study was to test the accuracy of a multi-surface model to predict the Zn2+ concentration and to improve our understanding of Zn bioavailability in low-Zn soils. High-Zn soils were included as controls. Model parameters were determined independently on the basis of earlier peer-reviewed publications. Model output was validated against free Zn2+ concentrations determined with the soil column Donnan membrane technique in a range of soils varying in potentially available Zn, organic matter, clay silicate, and iron (hydr)oxide contents and pH. Deviations between predicted Zn2+ concentrations and experimentally determined values over the whole Zn concentration range were less or equal to the experimental standard error, except for one low-Zn soil. The Zn2+ concentration was mainly controlled by adsorption, where organic matter was predicted to be the dominant soil sorbent. The predicted Zn2+ concentration depends more sensitively upon changes of the reactive Zn pool (application of 0.6, 1.2, 2.4, and 3.6 mg of Zn kg–1 of soil) and organic matter content (±0.2 and 0.4%) than pH changes (±0.5 and 1 pH unit).
    Speciation of heavy metals in River Rhine
    Vega, F.A. ; Weng, L. - \ 2013
    Water Research 47 (2013)1. - ISSN 0043-1354 - p. 363 - 372.
    donnan membrane technique - field-flow fractionation - dissolved organic-matter - fresh-waters - trace-metals - chemical speciation - humic substances - model parameters - surface waters - natural-waters
    Chemical speciation of Zn, Cu, Ni, Cd and Pb in River Rhine was studied by measuring free ion concentration and distribution in nanoparticles, and by comparing the measurement with speciation modeling. Concentrations of free metal ions were determined in situ using Donnan Membrane Technique (DMT). The percentage of free over total (filtered) metal concentration is 52%, 33%, 2.6%, 0.48% and 0.12% for respectively Zn, Cd, Ni, Pb and Cu, i.e. the degree of metal complexation in the river is the lowest for Zn and the highest for Cu. Metals in 1–300 nm particles were analyzed using Asymmetric Flow Field Flow Fractionation (AsF-FFF), but the overall recovery is quite low. The nano-sized Cu detected is mainly associated with DOM of 1–5 nm, whereas Pb and Zn are dominantly associated with particles of iron hydroxides and clay of larger size (30–100 nm). Free ion concentrations calculated with the speciation modeling are in good agreement with the measurements, except for Pb. Based on the model, DOM-bound is the most important complexed form for Cu and Cd, whereas formation of (bi)carbonate and EDTA complexes are more important for Ni and Zn. Adsorption of Pb to DOM is probably overestimated by the model, whereas Pb adsorption to iron hydroxides is underestimated.
    Arsenate and phosphate adsorption in relation to oxides composition in soils: LCD modelling
    Cui, Y. ; Weng, L. - \ 2013
    Environmental Science and Technology 47 (2013)13. - ISSN 0013-936X - p. 7269 - 7276.
    charge-distribution - humic substances - competitive adsorption - ion adsorption - heavy-metals - speciation - parameters - minerals - sorption - binding
    The pH dependent solid-solution distribution of arsenate and phosphate in five Dutch agricultural soil samples was measured in the pH range 4–8, and the results were interpreted using the LCD (ligand and charge distribution) adsorption modeling. The pH dependency is similar for both oxyanions, with a minimum soluble concentration observed around pH 6–8. This pH dependency can be successfully described with the LCD model and it is attributed mainly to the synergistic effects from Ca adsorption. The solubility of phosphate is much lower than that of arsenate. This big difference cannot be sufficiently explained by the reduction of small amount of As(V) into As(III), neither by slow desorption/adsorption. The difference between phosphate and arsenate in their solid-solution distribution becomes larger with the increase of aluminum (hydr)oxides (Al-oxides) contribution to the total amount of metal (Al and Fe) (hydr)oxides. The influence of Al-oxides is much larger than its relative amount extracted from the soils. When Al-oxides account for >40% of the soil oxides, the whole adsorbents behave apparently similarly to that of pure Al-oxides. These results indicated that surface coating and substitution may have modified significantly oxyanion adsorption to Fe-oxides in soils, and how to account for this complexity is a challenge for geochemical modeling.
    Soil organic matter: chemistry and physical characteristics and analytical methods. A review
    Branco de Freitas Maia, C.M. ; Novotny, E.H. ; Francischinelli Rittl, T. ; Bermingham Hayes, M.H. - \ 2013
    Current Organic Chemistry 17 (2013)24. - ISSN 1385-2728 - p. 2985 - 2990.
    nuclear-magnetic-resonance - black carbon - humic substances - reflectance spectroscopy - light fraction - amazon region - sediments - acids - charcoal - forest
    Soil organic matter (SOM) holds a prominent place among the many indicators that are studied in relation to soil function. Different viewpoints are reflected in characterizing SOM, depending on the study procedures used, or the focus of the researchers. There are many possibilities for the isolation and fractionation of SOM and this has led to a plurality of interpretations and conclusions. Transformations to organic materials that lead to the more recalcitrant components of SOM are outlined, and the associations which these materials can have in the soil environment, and aspects of their compositions are referred to. A review is given of the organic matter pools in soils, of their functions, and of the controls which they have in soil systems. A succinct review is given of physical fractionation procedures for SOM. This approach is highly relevant, though rarely used in modern studies of SOM. The merits and demerits of wet oxidation procedures, relative to dry combustion for determining soil organic carbon contents are discussed, and reference is made to the emerging chemometric techniques based on the use of Near (NIR) and Mid (MIR) infrared spectroscopy.
    Organic geochemistry of Amynteo lignite deposit, northern Greece: a Multi-analytical approach
    Iordanidis, A. ; Schwarzbauer, J. ; Georgakopoulos, A. ; Lagen, B. van - \ 2012
    Geochemistry international 50 (2012)2. - ISSN 0016-7029 - p. 159 - 178.
    maritza-east lignite - c-13 cp/mas nmr - rich mine soils - bituminous coal - brown-coal - ftir spectroscopy - humic substances - new-zealand - crude oils - py-gc/ms
    Several lignite samples were collected from boreholes of the Amynteo opencast lignite mine, northern Greece. Organic geochemical characteristics were investigated with the help of various analytical techniques, comprising Gas Chromatography (GC) and Gas-chromatography-Mass Spectrometry (GC-MS), Fourier Transform Infrared Spectroscopy (FTIR), solid-state Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopy, petrographical measurements as well as determination of bulk parameters. In the low rank (Rr = 0.21%) Amynteo lignites, huminite is the most abundant maceral group, inertinite has relatively low percentages and liptinite concentrations are rather high. Carbon Preference Index (CPI) reveals the predominance of odd-numbered, long-chained aliphatic hydro-carbons, which is related to a higher terrestrial plant input. The Pr/Ph ratio suggests that reducing conditions were persistent during peatification. Gymnosperm biomarkers such as isoprimarane, abietane, phyllocladane and sandaracopimarane, as well as angiosperm indicators (lupane) and hopanoid compounds with bacterial origin were identified. Analyses of the aromatic fractions revealed the presence of naphthalene, alkyl benzenes and phenols, pyrene, cadalene, cadinane, fluoranthene and dibenzofurane. Based on the FTIR analysis, aliphatic and oxygen containing structures were prevailed over the aromatic moieties. The intensity of the mineral bands was preferentially increased in the FTIR spectra of insoluble material. According to NMR analysis, the aliphatic carbons (0-50 ppm) have higher proportions comparing to aromatic carbons (100-160 ppm). The aromaticity fraction is low (fa = 0.32), as expected for these low rank coals. The presence of free organic radicals and Fe3+ and Mn2+ paramagnetic ions was revealed by EPR. In summary, the combined application of complementary analytical techniques allowed a deep inside into the geochemical characteristics of Amynteo lignites.
    Factors Controlling Phosphate Interaction with Iron Oxides
    Weng, L.P. ; Riemsdijk, W.H. van; Hiemstra, T. - \ 2012
    Journal of Environmental Quality 41 (2012)3. - ISSN 0047-2425 - p. 628 - 635.
    surface structural approach - donnan model parameters - charge-distribution - ion adsorption - humic substances - water interface - phosphorus loss - organic-matter - fulvic-acid - by-products
    Factors such as pH, solution ion composition, and the presence of natural organic matter (NOM) play a crucial role in the effectiveness of phosphorous adsorption by iron oxides. The interplay between these factors shows a complicated pattern and can sometimes lead to controversial results. With the help of mechanistic modeling and adsorption experiments, the net macroscopic effect of single and combined factors can be better understood and predicted. In the present work, the relative importance of the above-mentioned factors in the adsorption of phosphate was analyzed using modeling and comparison between the model prediction and experimental data. The results show that, under normal soil conditions, pH, concentration of Ca, and the presence of NOM are the most important factors that control adsorption of phosphate to iron oxides. The presence of Ca not only enhances the amount of phosphate adsorbed but also changes the pH dependency of the adsorption. An increase of dissolved organic carbon from 0.5 to 50 mg L-1 can lead to a >50% decrease in the amount of phosphate adsorbed. Silicic acid may decrease phosphate adsorption, but this effect is only important at a very low phosphate concentration, in particular at high pH.
    Effect of Soil Parameters on the Kinetics of the Displacement of Fe from FeEDDHA Chelates by Cu
    Schenkeveld, W.D.C. ; Reichwein, A.M. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2012
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 116 (2012)25. - ISSN 1089-5639 - p. 6582 - 6589.
    metal-edta complexes - donnan model parameters - strategy i plants - humic substances - ion adsorption - calcareous soil - cucumber plants - water interface - organic-matter - acid o,p-eddha
    In soil application, o,o-FeEDDHA (iron (3+) ethylene diamine-N,N'-bis(2-hydroxy phenyl acetic acid) complex) is the active ingredient of FeEDDHA chelate-based Fe fertilizers. The effectiveness of o,o-FeEDDHA is potentially compromised by the displacement of Fe from FeEDDHA by Cu. The actual impact of Cu competition is codetermined by the kinetics of the displacement reaction. In this study, the influence of soil parameters on the displacement kinetics has been examined in goethite suspensions. The displacement reaction predominantly takes place on the reactive surface rather than in solution. The rate at which the o,o-FeEDDHA concentration declined depended on the available reactive surface area, the Cu loading, and the FeEDDHA loading. Soil factors reducing FeEDDHA adsorption (high ionic strength, humic acid adsorption onto the goethite surface, and monovalent instead of divalent cations in the electrolyte) decreased the displacement rate. For meso o,o-FeEDDHA, the displacement rate equation was derived, which is first order in FeEDDHA loading and half order in Cu loading. For soil conditions, the equation can be simplified to an exponential decay function in meso o,o-FeEDDHA solution concentration.
    Evaluation of the performance and limitations of empirical partition-relations and process based multisurface models to predict trace element solubility in soils
    Groenenberg, J.E. ; Dijkstra, J.J. ; Bonten, L.T.C. ; Vries, W. de; Comans, R.N.J. - \ 2012
    Environmental Pollution 166 (2012). - ISSN 0269-7491 - p. 98 - 107.
    metal-ion binding - natural organic-matter - humic substances - heavy-metals - contaminated soils - complexation models - agricultural soils - assemblage model - cation-binding - zn
    Here we evaluate the performance and limitations of two frequently used model-types to predict trace element solubility in soils: regression based “partition-relations” and thermodynamically based “multisurface models”, for a large set of elements. For this purpose partition-relations were derived for As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Se, V, Zn. The multi-surface model included aqueous speciation, mineral equilibria, sorption to organic matter, Fe/Al-(hydr)oxides and clay. Both approaches were evaluated by their application to independent data for a wide variety of conditions. We conclude that Freundlich-based partition-relations are robust predictors for most cations and can be used for independent soils, but within the environmental conditions of the data used for their derivation. The multisurface model is shown to be able to successfully predict solution concentrations over a wide range of conditions. Predicted trends for oxy-anions agree well for both approaches but with larger (random) deviations than for cations.
    Electric relaxation processes in chemodynamics of aqueous metal complexes: From simple ligands to soft nanoparticulate complexants
    Leeuwen, H.P. van; Buffle, J. ; Town, R.M. - \ 2012
    Langmuir 28 (2012)1. - ISSN 0743-7463 - p. 227 - 234.
    dynamic speciation - physicochemical parameters - humic substances - particles - dispersions - coagulation - compilation - binding - flux
    The chemodynamics of metal complexes with nanoparticulate complexants can differ significantly from that for simple ligands. The spatial confinement of charged sites and binding sites to the nanoparticulate body impacts on the time scales of various steps in the overall complex formation process. The greater the charge carried by the nanoparticle, the longer it takes to set up the counterion distribution equilibrium with the medium. A z+ metal ion (z > 1) in a 1:1 background electrolyte will accumulate in the counterionic atmosphere around negatively charged simple ions, as well as within/around the body of a soft nanoparticle with negative structural charge. The rate of accumulation is often governed by diffusion and proceeds until Boltzmann partition equilibrium between the charged entity and the ions in the medium is attained. The electrostatic accumulation proceeds simultaneously with outer-sphere and inner-sphere complex formation. The rate of the eventual inner-sphere complex formation is generally controlled by the rate constant of dehydration of the metal ion, kw. For common transition metal ions with moderate to fast dehydration rates, e.g., Cu2+, Pb2+, and Cd2+, it is shown that the ionic equilibration with the medium may be the slower step and thus rate-limiting in their overall complexation with nanoparticles
    Carbon replacement and stability changes in short-term silvo-pastoralo experiments in Colombian Amazonia
    Mosquera Vidal, O. ; Buurman, P. ; Ramirez, B.L. ; Amezquita, M.C. - \ 2012
    Geoderma 170 (2012). - ISSN 0016-7061 - p. 56 - 63.
    soil organic-matter - humic substances - delta-c-13 - dynamics - storage - tropics
    There is little information on the effects of land use change on soil Carbon stocks in Colombian Amazonia. Such information would be needed to assess the impact of this area on the global C cycle and the sustainability of agricultural systems that are replacing native forest. The aim of this study was to evaluate soil carbon stocks and changes after the clearing of the native forest, the establishment of pastures and the reclamation of the degraded pasture, in Caquetá, Colombia. We compared the contents of Total C, Oxidizable C and Non-Oxidizable (stable) C in four different land use systems, namely Monoculture (Brachiaria grassland), Association (Brachiaria + Arachis pintoi), Forage Bank (a mixture of forage tree species), and Natural Regeneration of the pasture in both a flat area and a sloping one. The Degraded Pasture was the reference. Results showed that in the sloping area all treatments have higher Total Carbon stocks than the Degraded Pasture, while three of the treatments significantly increased the stocks of Non-Oxidizable C. In the flat landscape, only the Association significantly increased Total C stocks. Plowing and fertilization cause significant increases in Oxidizable carbon and decreases in Non-Oxidizable carbon. This effect needs further research, as C stability will influence equilibrium stocks. In the sloping area, improved pastures and fodder bank rapidly increased Total Carbon contents and stocks, with increases as large as10 ton.ha-1 yr-1. In the Traditional Fodder Bank, which showed the largest increase, this is partially due to the application of organic manure. Surprisingly, also C stocks under Natural Regeneration were significantly higher than under the original Degraded Grassland. This increase was fully due to Non-Oxidizable Carbon, which is difficult to explain. Stable isotope analysis indicated that under improved grassland, especially Brachiaria monoculture, up to 40% of the original C in the upper 10 cm was replaced in 3.3 years.
    Strategies in the application of the Donnan membrane technique.
    Weng, L.P. ; Vega, F.A. ; Riemsdijk, W.H. van - \ 2011
    Environmental Chemistry 8 (2011)5. - ISSN 1448-2517 - p. 466 - 474.
    metal-ion concentrations - soil solution - chemical speciation - organic-matter - heavy-metals - sandy soil - dynamic speciation - humic substances - model parameters - trace-metals
    e Donnan membrane technique (DMT) can be applied to measure free ion concentrations both in laboratory and in situ in the field. In designing DMT experiments, different strategies can be taken, depending on whether accumulation is needed. (1) When the free ion concentration is above the detection limit of the analytical technique (e.g. ICP-MS), no accumulation is needed and no ligand is added to the acceptor. Measurement can be based on the Donnan membrane equilibrium. (2) When an accumulation of less than 500 times is needed, an appropriate amount of ligand can be added to the acceptor and measurement can be based on the Donnan membrane equilibrium. (3) When an accumulation factor of larger than 500 times is needed, a relatively large amount of ligand is added to the acceptor and measurement can be based on the transport kinetics. In this paper, several issues in designing the DMT experiments are discussed: choice of DMT cell, measurement strategies and ligands and possible implication of slow dissociation of metal complexes in the sample solution (lability issue). The objective of this paper is to give better guidance in the application of DMT for measuring free ion concentrations in both synthetic and natural samples.
    Competitive and synergistic effects in pH dependent phosphate adsorption in soils: LCD modeling
    Weng, L.P. ; Vega, F.A. ; Riemsdijk, W.H. van - \ 2011
    Environmental Science and Technology 45 (2011)19. - ISSN 0013-936X - p. 8420 - 8428.
    induced chemical-changes - humic substances - charge-distribution - solution interface - ion adsorption - goethite - surface - phosphorus - binding - parameters
    The pH dependency of soluble phosphate in soil was measured for six agricultural soils over a pH range of 3–10. A mechanistic model, the LCD (ligand charge distribution) model, was used to simulate this change, which considers phosphate adsorption to metal (hydr)oxides in soils under the influence of natural organic matter (NOM) and polyvalent cations (Ca2+, Al3+, and Fe3+). For all soils except one, the description in the normal pH range 5–8 is good. For some soils at more extreme pH values (for low P-loading soils at low pH and for high P-loading soils at high pH), the model over predicts soluble P. The calculation shows that adsorption is the major mechanism controlling phosphate solubility in soils, except at high pH in high P-loading soils where precipitation of calcium phosphate may take place. NOM and polyvalent cations have a very strong effect on the concentration level of P. The pattern of pH dependency of soluble P in soils differs greatly from the pH effects on phosphate adsorption to synthetic metal (hydr)oxides in a monocomponent system. According to the LCD model, the pH dependency in soil is mainly caused by the synergistic effects of Ca2+ adsorption to oxides. Adsorption of Al3+ to NOM adsorbed plays an important role only at a pH <4.5. Presence of NOM coating strongly competes with phosphate for the adsorption and is an important factor to consider in modeling phosphate adsorption in natural samples
    Transfer functions for solid solution partitioning of cadmium for Australian soils
    Vries, W. de; Mc Laughlin, M.J. ; Groenenberg, J.E. - \ 2011
    Environmental Pollution 159 (2011)12. - ISSN 0269-7491 - p. 3583 - 3594.
    metal-ion activities - contaminated soils - humic substances - organic-matter - heavy-metals - surface waters - fresh-waters - pore-water - copper - speciation
    To assess transport and ecotoxicological risks of metals, such as cadmium (Cd) in soils, models are needed for partitioning and speciation. We derived regression-based “partition-relations” based on adsorption and desorption experiments for main Australian soil types. First, batch adsorption experiments were carried out over a realistic range of dissolved Cd concentrations in agricultural soils in Australia. Results showed linear sorption relationships, implying the adequacy of using Kd values to describe partitioning. Desorption measurements were then carried out to assess in-situ Kd values and relate these to soil properties The best transfer functions for solid–solution partitioning were found for Kd values relating total dissolved Cd concentration to total soil Cd concentrations, accounting for the variation in pH, SOM contents and DOC concentrations. Model predictions compared well with measurements of an independent data set, but there was a tendency to underestimate dissolved Cd concentrations of highly polluted soils.
    Effect of vermicompost on the growth and production of amashito pepper, interactions with earthworms and rhizobacteria
    Huerta, E. ; Vidal, O. ; Jarquin, A. ; Geissen, V. ; Gomez, R. - \ 2010
    Compost Science & Utilization 18 (2010)4. - ISSN 1065-657X - p. 282 - 288.
    plant-growth - humic substances - nitrogen mineralization - pig manure - take-all - soil - greenhouse - casts - decomposition - lumbricus
    Increasing yield is one of the goals in the tropics. Traditional farming is replaced in many cases by agroindustrial production which often leads to environmental pollution due to the marked use of pesticides and fertilizers. In Tabasco, Amashito pepper (Capsicum annum var. glabriusculcum) is cultivated in the traditional way in backyards or cocoa fields with no chemical inputs. The germination of these kind of peppers is difficult to achieve, since wild peppers seeds have a large range of dormancy. Plant-growth-promoting rhizobacteria (PGPRs) are used as inoculants for biofertilization, phytostimulation and biocontrol. Soil fauna has an important function in regulating rhizosphere microbial processes and therefore significantly affects plant growth. Earthworms produce indirect effects through changes in the environment of the roots or via interactions with organisms that affect root growth and production. Our aim was to study the effects of different fresh organic matter, earthworms (P. corethrurus, oligochaeta) and rhizobacteria (A. brasiliensis) on plant growth, and yield production of amashito pepper (Capsicum annuum var. glabriusculum). We established a three factorial outdoors mesocosms experiment. We tested the effects of 3 substrates (dry cocoa husks (C), Panicum sp grass-cocoa husks vermicompost (V), cocoa husks with cow manure (CC) (type of germination substrate, factor 1), the presence (E) and absence of P. corethrurus (WE) (earthworm, factor 2) and the absence (WB) or presence (B) of A. brasiliensis (rizobacteria, factor 3). After 173 days, fruit production was significantly more in plants raised in vermicompost. Vermicompost significantly enhanced the highest weight (23.4g), height (26.7 cm) and production of leaves per plant (20.6 leaves per plant). Further studies are required in order to understand the interactions between vermicompost, plants, earthworms and rhizobacteria.
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