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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Comparative analysis of biofilm formation by Bacillus cereus reference strains and undomesticated food isolates and the effect of free iron
    Hayrapetyan, H. ; Muller, L.K. ; Tempelaars, M.H. ; Abee, T. ; Nierop Groot, M.N. - \ 2015
    International Journal of Food Microbiology 200 (2015). - ISSN 0168-1605 - p. 72 - 79.
    pseudomonas-aeruginosa - stainless-steel - processing environments - twitching motility - adhesion - surface - attachment - contamination - typhimurium - sporulation
    Biofilm formation of Bacillus cereus reference strains ATCC 14579 and ATCC 10987 and 21 undomesticated food isolates was studied on polystyrene and stainless steel as contact surfaces. For all strains, the biofilm forming capacity was significantly enhanced when in contact with stainless steel (SS) as a surface as compared to polystyrene (PS). For a selection of strains, the total CFU and spore counts in biofilms were determined and showed a good correlation between CFU counts and total biomass of these biofilms. Sporulation was favoured in the biofilm over the planktonic state. To substantiate whether iron availability could affect B. cereus biofilm formation, the free iron availability was varied in BHI by either the addition of FeCl3 or by depletion of iron with the scavenger 2,2-Bipyridine. Addition of iron resulted in increased air-liquid interface biofilm on polystyrene but not on SS for strain ATCC 10987, while the presence of Bipyridine reduced biofilm formation for both materials. Biofilm formation was restored when excess FeCl3 was added in combination with the scavenger. Further validation of the iron effect for all 23 strains in microtiter plate showed that fourteen strains (including ATCC10987) formed a biofilm on PS. For eight of these strains biofilm formation was enhanced in the presence of added iron and for eleven strains it was reduced when free iron was scavenged. Our results show that stainless steel as a contact material provides more favourable conditions for B. cereus biofilm formation and maturation compared to polystyrene. This effect could possibly be linked to iron availability as we show that free iron availability affects B. cereus biofilm formation.
    Coalescence, cracking, and crack healing in drying dispersion
    Kooij, H.M. van der; Kool, R.H.M. de; Gucht, J. van der; Sprakel, J.H.B. - \ 2015
    Langmuir 31 (2015)15. - ISSN 0743-7463 - p. 4419 - 4428.
    latex film formation - glass-transition temperature - polymer diffusion - deformation - polystyrene - interfaces - coatings - surface - modes - bulk
    The formation of a uniform film from a polymer dispersion is a complex phenomenon involving the interplay of many processes: evaporation and resulting fluid flows through confined geometries, particle packing and deformation, coalescence, and cracking. Understanding this multidimensional problem has proven challenging, precluding a clear understanding of film formation to date. This is especially true for drying dispersion droplets, where the particular geometry introduces additional complexity such as lateral flow toward the droplet periphery. We study the drying of these droplets using a simplified approach in which we systematically vary a single parameter: the glass transition temperature (Tg) of the polymer. We combine optical with scanning electron microscopy to elucidate these processes from the macroscopic down to the single-particle level, both qualitatively and quantitatively, over times ranging from seconds to days. Our results indicate that the polymer Tg has a marked influence on the time evolution of particle deformation and coalescence, giving rise to a distinct and sudden cracking transition. Moreover, in cracked droplets it affects the frequently overlooked time scale of crack healing, giving rise to a second transition from self-healing to permanently cracked droplets. These findings are in line with the classical Routh–Russel model for film formation yet extend its scope from particle-level dynamics to long-range polymer flow.
    Theory of brushes formed by psi-shaped macromolecules at solid-liquid interfaces
    Zhulina, E.B. ; Leermakers, F.A.M. ; Borisov, O.V. - \ 2015
    Langmuir 31 (2015)23. - ISSN 0743-7463 - p. 6514 - 6522.
    starlike polymer brushes - dendronized polymers - gold nanoparticles - good solvent - surface - polysaccharides - adsorption - dendrimers - coatings
    We present a theoretical analysis targeted to describe the structural properties of brushes formed by ¿-shaped macromolecules tethered by terminal segment of stem to planar surface while exposing multiple free branches to the surrounding solution. We use an analytical self-consistent field approach based on the strong stretching approximation, and the assumption of Gaussian elasticity for linear chain fragments of the tethered macromolecules. The effect of weak and strong polydispersity of branches is analyzed. In the case of weakly polydisperse macromolecules, variations in length of branches lead to a more uniform polymer density distribution with slight increase in the brush thickness compared to the case of monodisperse chains with the same degree of polymerization. We demonstrate that in contrast to linear chains, strong polydispersity of ¿-shaped macromolecules does not necessarily lead to strong perturbations in polymer density distribution. In particular, mixed brushes of the so-called “mirror” dendrons (in which number of stem monomers in one component coincides with number of monomers in a branch of the other component, and vice versa) give rise to a unified polymer density distribution with shape independent of the brush composition. The predictions of analytical theory are systematically compared to the results of numerical self-consistent field modeling based on the Scheutjens–Fleer approach
    Langmuir monolayers of non-ionic polymers: Equilibrium of metastability? Case study of PEO and its PPO-PEO diblock copolymers
    Deschenes, L. ; Saint-Germain, F. ; Lyklema, J. - \ 2015
    Journal of Colloid and Interface Science 449 (2015). - ISSN 0021-9797 - p. 494 - 505.
    air-water-interface - poly(ethylene oxide) monolayers - interacting chain molecules - air/water interface - scaling description - statistical-theory - block-copolymers - liquid-films - surface - layers
    Stability and reorganization in Langmuir films of PEO in PEO homopolymers and PPO–PEO block copolymers were investigated using film balance measurements. The apparent fractional losses of EO segments transferred into the subphase resulting from successive compression–expansion cycles have been estimated. The apparent loss is mainly Gmax, Mn and time-dependent. At surface concentrations G ¿ 0.32 mg/m2, PEO films are in equilibrium. For 0.32 ¿ G ¿ 0.7 mg/m2, the losses remain modest. Further compression leads to densification of the monolayer, requiring the interplay of thermodynamics and kinetic factors In the plateau regime, the loss is higher and constant for 1 ¿ Gmax ¿ 2 mg/m2 upon maintaining the achieved surface area for 15 min. Similar losses were obtained for PEO homopolymers of high Mn and PPO353–PEO2295. It suggests that the PEO remains anchored in a metastable state at the air–water interface at surface concentration well above the onset of the plateau. Additional losses are incurred for PEO homopolymers for monolayers kept compressed in the plateau for 2 h. For the interpretation of these phenomena a combination of elements from self-consistent field theory and scaling is desirable with as a trend an increasing contribution of the latter with increasing surface concentration.
    Short- to mid-term impact of conservation agriculture on yield variability of upland rice: evidence from farmer's fields in Madagascar
    Bruelle, G. ; Naudin, K. ; Scopel, E. ; Domas, R. ; Rabeharisoa, L. ; Tittonell, P.A. - \ 2015
    Experimental Agriculture 51 (2015)1. - ISSN 0014-4797 - p. 66 - 84.
    cropping systems - tillage systems - maize productivity - soil - erosion - africa - degradation - nigeria - surface - runoff
    Family farming in the tropics suffers from low crop productivity mainly due to a combination of poor soil fertility, low investment capacity, and a variable climate. The Lake Alaotra region of Madagascar is no exception and rainfed production is particularly hard hit. To evaluate the agronomic benefits of conservation agriculture (CA) in a region of erratic rainfall, we analysed four years of yield, management and climatic data from 3803 upland rice fields cultivated by farmers and monitored by researchers. Fields located on rainfed lowlands and hillsides were cultivated with sole rice using conventional tillage (Cv) or rice sown with no-tillage on dead organic mulch and rotated with other cereal/legume combinations (CA) from 2006 to 2011. A first global comparison across seasons, locations and years of adoption showed significantly higher average yields under CA, with no change in variance (on lowland: 2.6 ± 0.9 t ha–1 Cv, 2.8 ± 0.9 t ha–1 CA; on hillside: 2.1 ± 0.8 t ha–1 Cv, 2.4 ± 0.8 t ha–1 CA). Grouping fields according to the number of years under CA (first to fourth) revealed that CA gradually increased average yields and reduced the coefficient of variation in the short and mid-term (on lowland: +0.2 t ha–1 and –6% coefficient of variation; on hillside: +0.7 t ha–1 and –13% coefficient of variation, over four to six years of successive CA cropping). The average yield increase under CA was not associated with an increase in mineral fertiliser use, as farmers used the same amounts of fertilisers (or none) under Cv and CA. The comparison Cv versus CA also highlighted a major benefit of CA regarding climate: it widened the window of possible sowing dates. A classification and regression tree analysis of the entire dataset revealed that rice yield was more affected by agro-environmental factors than management factors (fertilisation, Cv or CA), and extreme climate variability such as the severe drought of 2007–2008 could not be offset by CA. The hypothesis of yield penalties during the first years of implementation of CA cannot be verified with the evidence presented in this study.
    Assessment of evaporative water loss from Dutch cities
    Jacobs, C.M.J. ; Elbers, J.A. ; Brolsma, R. ; Hartogensis, O.K. ; Moors, E.J. ; Rodríguez-CarreteroMárquez, M.T. ; Hove, B. van - \ 2015
    Building and Environment 83 (2015). - ISSN 0360-1323 - p. 27 - 38.
    klimaatverandering - temperatuur - stedelijke gebieden - evaporatie - waterbudget - rotterdam - veluwe - climatic change - temperature - urban areas - evaporation - water budget - rotterdam - veluwe - urban heat-island - energy-balance - large-aperture - evapotranspiration - exchange - surface - scintillometers - requirements - environments - manchester
    Reliable estimates of evaporative water loss are required to assess the urban water budget in support of division of water resources among various needs, including heat mitigation measures in cities relying on evaporative cooling. We report on urban evaporative water loss from Arnhem and Rotterdam in the Netherlands, using eddy covariance, scintillometer and sapflow observations. Evaporation is assessed at daily to seasonal and annual timescale. For the summer half-year (April–September), observations from Arnhem and Rotterdam are consistent regarding magnitude and variability of evaporation that typically varies between 0.5 and 1.0 mm of evaporation per day. The mean daily evaporative cooling rate was 20–25 Wm-2, 11–14% of the average incoming solar radiation. Evaporation by trees related to sapflow was found to be a small term on the water budget at the city or neighbourhood scale. However, locally the contribution may be significant, given observed maxima of daily sap flows up to 170 l per tree. In Arnhem, evaporation is strongly linked with precipitation, possibly owing to building style. During the summer season, 60% of the precipitation evaporated again. In Rotterdam, the link between evaporation and precipitation is much weaker. An analysis of meteorological observations shows that estimation of urban evaporation from routine weather data using the concept of reference evaporation would be a particularly challenging task. City-scale evaporation may not scale with reference evaporation and the urban fabric results in strong microweather variability. Observations like the ones presented here can be used to evaluate and improve methods for routine urban evaporation estimates.
    Identification of the structural basis of thermal lability of a virus provides a rationale for improved vaccines
    Rincón, V. ; Rodriguez-Huete, A. ; Lopez-Arguello, S. ; Ibarra-Molero, B. ; Sanchez-Ruiz, J.M. ; Harmsen, M.M. ; Mateu, M.G. - \ 2014
    Structure 22 (2014)11. - ISSN 0969-2126 - p. 1560 - 1570.
    mouth-disease virus - charge-charge interactions - empty capsids - insect cells - guinea-pigs - stability - protein - design - particles - surface
    Virus stability and dynamics play critical roles during infection. Some viruses, including foot-and-mouth disease virus (FMDV), are surprisingly prone to thermal dissociation outside the cell. The structural bases and functional implications of this distinctive trait were essentially unknown. This study (1) uncovers the structural determinants of FMDV thermolability, (2) investigates the relationship between virus thermolability and infectivity, and (3) provides a structure-based rationale for engineering thermostable virus particles to develop improved vaccines and nanocontainers. The results reveal that negatively charged residues close to protein-protein interfaces exert electrostatic repulsions between capsid subunits and mediate the sensitivity of the virion to thermal dissociation, even at neutral pH. Based on these results, a series of fully infectious virions of increased thermostability were engineered by individually removing different carboxylates involved in intersubunit repulsions. The implications for virus biology and the design of thermostable vaccines are discussed.
    Functional derivatives applied to error propagation of uncertainties in topography to large-aperture scintillometer-derived heat fluxes
    Gruber, M.A. ; Fochesatto, G.J. ; Hartogensis, O.K. ; Lysy, M. - \ 2014
    Atmospheric Measurement Techniques 7 (2014). - ISSN 1867-1381 - p. 2361 - 2371.
    structure parameter - refractive-index - effective height - surface
    Scintillometer measurements allow for estimations of the refractive index structure parameter Cn2 over large areas in the atmospheric surface layer. Turbulent fluxes of heat and momentum are inferred through coupled sets of equations derived from the Monin–Obukhov similarity hypothesis. One-dimensional sensitivity functions have been produced that relate the sensitivity of heat fluxes to uncertainties in single values of beam height over flat terrain. However, real field sites include variable topography. We develop here, using functional derivatives, the first analysis of the sensitivity of scintillometer-derived sensible heat fluxes to uncertainties in spatially distributed topographic measurements. Sensitivity is shown to be concentrated in areas near the center of the beam path and where the underlying topography is closest to the beam height. Relative uncertainty contributions to the sensible heat flux from uncertainties in topography can reach 20% of the heat flux in some cases. Uncertainty may be greatly reduced by focusing accurate topographic measurements in these specific areas. A new two-dimensional variable terrain sensitivity function is developed for quantitative error analysis. This function is compared with the previous one-dimensional sensitivity function for the same measurement strategy over flat terrain. Additionally, a new method of solution to the set of coupled equations is produced that eliminates computational error.
    Shear rheology of hydrophobic adsorption layers at oil/water interfaces and data interpretation in terms of a viscoelastic thixotropic model
    Radulova, G.M. ; Danov, K.D. ; Kralchevsky, P.A. ; Petkov, J.T. ; Stoyanov, S.D. - \ 2014
    Soft Matter 10 (2014)31. - ISSN 1744-683X - p. 5777 - 5786.
    oil-water interface - dependent relaxation-times - class-ii hydrophobin - protein hfbii - hexadecane/water interface - flexible proteins - bubble stability - beta-casein - surface - monolayers
    Here, we investigate the surface shear rheology of class II HFBII hydrophobin layers at the oil/water interface. Experiments in two different dynamic regimes, at a fixed rate of strain and oscillations, have been carried out with a rotational rheometer. The rheological data obtained in both regimes comply with the same viscoelastic thixotropic model, which is used to determine the surface shear elasticity and viscosity, Esh and ¿sh. Their values for HFBII at oil/water interfaces are somewhat lower than those at the air/water interface. Moreover, Esh and ¿sh depend on the nature of oil, being smaller for hexadecane in comparison with soybean-oil. It is remarkable that Esh is independent of the rate of strain in the whole investigated range of shear rates. For oil/water interfaces, Esh and ¿sh determined for HFBII layers are considerably greater than for other proteins, like lysozyme and ß-casein. It is confirmed that the hydrophobin forms the most rigid surface layers among all investigated proteins not only for the air/water, but also for the oil/water interface. The wide applicability of the used viscoelastic thixotropic model is confirmed by analyzing data for adsorption layers at oil/water interfaces from lysozyme and ß-casein – both native and cross-linked by enzyme, as well as for films from asphaltene. This model turns out to be a versatile tool for determining the surface shear elasticity and viscosity, Esh and ¿sh, from experimental data for the surface storage and loss moduli, G' and G''.
    Characterization of colloidal Fe from soils using field-flow fractionation and Fe K-edge X-ray absorption spectroscopy
    Regelink, I.C. ; Voegelin, A. ; Weng, L. ; Koopmans, G.F. ; Comans, R.N.J. - \ 2014
    Environmental Science and Technology 48 (2014)8. - ISSN 0013-936X - p. 4307 - 4316.
    iron-oxide nanoparticles - natural organic-matter - acid forest soils - exafs spectroscopy - mineral nanoparticles - trace-metals - speciation - surface - ferrihydrite - associations
    Colloids may facilitate the transport of trace elements and nutrients like phosphate in soil. In this study, we characterized soil colloids (
    Genomic Characterization of Non-Mucus Adherent Derivatives of Lactobacillus rhamnosus GG Reveals Genes Affecting Pilus Biogenesis
    Rasinkangas, P. ; Reunanen, J. ; Douillard, F.P. ; Ritari, J. ; Uotinen, V. ; Palva, A. ; Vos, W.M. de - \ 2014
    Applied and Environmental Microbiology 80 (2014)22. - ISSN 0099-2240 - p. 7001 - 7009.
    intestinal epithelial-cells - placebo-controlled trial - gram-positive bacteria - functional-analysis - atopic disease - strain gg - adhesion - probiotics - surface - prevention
    Lactobacillus rhamnosus GG is one of the best-characterized lactic acid bacteria and can be considered a probiotic paradigm. Comparative and functional genome analysis showed that L. rhamnosus GG harbors a genomic island including the spaCBA-srtC1 gene cluster, encoding the cell surface-decorating host-interacting pili. Here, induced mutagenesis was used to study pilus biogenesis in L. rhamnosus GG. A combination of two powerful approaches, mutation selection and next-generation sequencing, was applied to L. rhamnosus GG for the selection of pilus-deficient mutants from an enriched population. The isolated mutants were first screened by immuno-dot blot analysis using antiserum against pilin proteins. Relevant mutants were selected, and the lack of pili was confirmed by immunoelectron microscopy. The pilosotype of 10 mutant strains was further characterized by analyzing pilin expression using Western blot, dot blot, and immunofluorescence methods. A mucus binding assay showed that the mutants did not adhere to porcine intestinal mucus. Comparative genome sequence analysis using the Illumina MiSeq platform allowed us to determine the nature of the mutations in the obtained pilus-deficient derivatives. Three major classes of mutants with unique genotypes were observed: class I, with mutations in the srtC1 gene; class II, with a deletion containing the spaCBA-srtC1 gene cluster; and class III, with mutations in the spaA gene. Only a limited number of collateral mutations were observed, and one of the pilus-deficient derivatives with a deficient srtC1 gene contained 24 other mutations. This strain, PB12, can be considered a candidate for human trials addressing the impact of the absence of pili.
    Live imaging of baculovirus infection of midgut epithelium cells: a functional assay of per os infectivity factors (PIFs)
    Mu, J.F. ; Lent, J.W.M. van; Smagghe, G. ; Wang, Q. ; Chen Xinwen, ; Vlak, J.M. ; Oers, M.M. van - \ 2014
    Journal of General Virology 95 (2014)Pt 1. - ISSN 0022-1317 - p. 2531 - 2539.
    occlusion-derived virus - heliothis-virescens larvae - nucleopolyhedrovirus - binding - complex - replication - proteins - surface - genes - p74
    The occlusion-derived viruses (ODVs) of baculoviruses are responsible for oral infection of insect hosts, whereas budded viruses (BVs) are responsible for the systemic infection within the host. The ODV membrane proteins play crucial roles in mediating virus entry into midgut epithelium cells to initiate infection and are important factors in host range determination. For Autographa californica multiple nucleopolyhedrovirus (AcMNPV), seven conserved ODV membrane proteins have been shown to be essential for oral infectivity and are called per os infectivity factors (PIFs). Information on the function of the individual PIF proteins in virus entry is limited, partly due to the lack of a good in vitro system for monitoring ODV entry. Here, we constructed a baculovirus with an enhanced green fluorescent protein (EGFP) fused to the nucleocapsid to monitor the entry of virus into primary midgut epithelium cells ex vivo by confocal fluorescence microscopy. The EGFP-labeled virus showed the same BV virulence and ODV infectivity as wild type virus. The ability to bind and enter host cells was then visualized for wild type AcMNPVs and viruses with mutations in P74 (PIF0), PIF1 or PIF2, showing that P74 is required for ODV binding, while PIF1 and PIF2 play important roles in entry of ODV after binding to midgut cells. This is the first live imaging of ODV entry into midgut cells and complements the genetic and biochemical evidence for the role of PIFs in the oral infection process.
    Solid phase microextraction speciation analysis of triclosan in aqueous mediacontaining sorbing nanoparticles
    Zielinska, K. - \ 2014
    Environmental Chemistry 11 (2014)1. - ISSN 1448-2517 - p. 72 - 76.
    nd-spme - samples - water - adsorption - products - binding - surface
    Solid phase microextraction (SPME) is applied in the speciation analysis of the hydrophobic compound triclosan in an aqueous medium containing sorbing SiO2 nanoparticles (NPs). It is found that these NPs, as well as their complexes with triclosan, partition between the bulk medium and the solid phase poly(dimethylsiloxane) (PDMS). Furthermore, they appear to aggregate at the PDMS–water interface. The total triclosan concentration in the solid phase thus includes both the free and the NP-bound forms. Proper computation of the analyte concentration in the sample medium requires (i) consideration of the speciation of triclosan inside the solid phase and (ii) elimination of the effects of aggregation of NP complexes at the solid phase–bulk medium interface. Possible solutions include application of a protective membrane with pore size smaller than the NP diameter. This allows measurement of the free triclosan concentration, albeit at the cost of longer accumulation times and loss of kinetic information on the triclosan–NP complex.
    Intercomparison of Methods for the Simultaneous Estimation of Zero-Plane Displacement and Aerodynamic Roughness Length from Single-Level Eddy-Covariance Data
    Graf, A. ; Boer, A. van de; Moene, A.F. ; Vereecken, H. - \ 2014
    Boundary-Layer Meteorology 151 (2014)2. - ISSN 0006-8314 - p. 373 - 387.
    frequency-response corrections - atmospheric boundary-layer - sonic anemometer data - tall vegetation - sensible-heat - surface - parameters - height - flux - temperature
    We applied three approaches to estimate the zero-plane displacement d through the aerodynamic measurement height z (with z = zm - d and zm being the measurement height above the surface), and the aerodynamic roughness length z0, from single-level eddy covariance data. Two approaches (one iterative and one regression-based) were based on the universal function in the logarithmic wind profile and yielded an inherently simultaneous estimation of both d and z0. The third approach was based on flux–variance similarity, where estimation of d and consecutive estimation of z0 are independent steps. Each approach was further divided into two methods differing either with respect to the solution technique (profile approaches) or with respect to the variable (variance of vertical wind and temperature, respectively). All methods were applied to measurements above a large, growing wheat field where a uniform canopy height and its frequent monitoring provided plausibility limits for the resulting estimates of time-variant d and z0. After applying, for each approach, a specific data filtering that accounted for the range of conditions (e.g. stability) for which it is valid, five of the six methods were able to describe the temporal changes of roughness parameters associated with crop growth and harvest, and four of them agreed on d to within 0.3 m most of the time. Application of the same methods to measurements with a more heterogeneous footprint consisting of fully-grown sugarbeet and a varying contribution of adjacent harvested fields exhibited a plausible dependence of the roughness parameters on the sugarbeet fraction. It also revealed that the methods producing the largest outliers can differ between site conditions and stability. We therefore conclude that when determining d for canopies with unknown properties from single-level measurements, as is increasingly done, it is important to compare the results of a number of methods rather than rely on a single one. An ensemble average or median of the results, possibly after elimination of methods that produce outliers, can help to yield more robust estimates. The estimates of z0 were almost exclusively physically plausible, although d was considered unknown and estimated simultaneously with the methods and results described above
    Net terrestrial CO2 exchange over China during 2001-2010 estimated with an ensemble data assimilation system for atmospheric CO 2
    Zhang, H.F. ; Chen, B.Z. ; Laan-Luijkx, I.T. van der; Peters, W. ; Chen, J. ; Xu, G. ; Yan, J.W. ; Zhou, X. ; Fukuyama, Y. ; Tans, P.P. - \ 2014
    Journal of Geophysical Research: Atmospheres 119 (2014)6. - ISSN 2169-897X - p. 3500 - 3515.
    carbon-dioxide exchange - flux inversion - north-america - ecosystems - sinks - transport - surface - temperature - forests - trends
    In this paper we present an estimate of net ecosystem CO2 exchange over China for the years 2001–2010 using the CarbonTracker Data Assimilation System for CO2 (CTDAS). Additional Chinese and Asian CO2 observations are used in CTDAS to improve our estimate. We found that the combined terrestrial ecosystems in China absorbed about -0.33 Pg C yr-1 during 2001–2010. The uncertainty on Chinese terrestrial carbon exchange estimates as derived from a set of sensitivity experiments suggests a range of -0.29 to -0.64 Pg C yr-1. This total Chinese terrestrial CO2 sink is attributed to the three major biomes (forests, croplands, and grass/shrublands) with estimated CO2 fluxes of -0.12 Pg C yr-1 (range from -0.09 to -0.19 Pg C yr-1), -0.12 Pg C yr-1 (range from -0.09 to -0.26 Pg C yr-1), and -0.09 Pg C yr-1 (range from -0.09 to -0.17 Pg C yr-1), respectively. The peak-to-peak amplitude of interannual variability of the Chinese terrestrial ecosystem carbon flux is 0.21 Pg C yr-1 (~64% of mean annual average), with the smallest CO2 sink (-0.19 Pg C yr-1) in 2003 and the largest CO2 sink (-0.40 Pg C yr-1) in 2007. We stress that our estimate of terrestrial ecosystem CO2 uptake based on inverse modeling strongly depends on a limited number of atmospheric CO2 observations used. More observations in China specifically and in Asia in general are needed to improve the accuracy of terrestrial carbon budgeting for this region
    Process-based modelling of a headwater catchment in semi-arid conditions: the influence of macropore flow
    Schaik, N.L.M.B. ; Bronstert, A. ; Jong, S.M. ; Jetten, V.G. ; Dam, J.C. van; Ritsema, C.J. ; Schnabel, S. - \ 2014
    Hydrological Processes 28 (2014)24. - ISSN 0885-6087 - p. 5805 - 5816.
    runoff generation - dehesas - uncertainty - management - hydrology - surface - spain
    Subsurface stormflow is thought to occur mainly in humid environments with steep terrains. However, in semi-arid areas, preferential flow through macropores can also result in a significant contribution of subsurface stormflow to catchment runoff for varying catchment conditions. Most hydrological models neglect this important subsurface preferential flow. Here, we use the process-oriented hydrological model Hillflow-3D, which includes a macropore flow approach, to simulate rainfall-runoff in the semi-arid Parapuños catchment in Spain, where macropore flow was observed in previous research. The model was extended for this study to account for sorptivity under very dry soil conditions. The results of the model simulations with and without macropore flow are compared. Both model versions give reasonable results for average rainfall situations, although the approach with the macropore concept provides slightly better results. The model results for scenarios of extreme rainfall events (>13.3¿mm¿30¿min-1) however show large differences between the versions with and without macropores. These model results compared with measured rainfall-runoff data show that the model with the macropore concept is better. Our conclusion is that preferential flow is important in controlling surface runoff in case of specific, high intensity rainfall events. Therefore, preferential flow processes must be included in hydrological models where we know that preferential flow occurs. Hydrological process models with a less detailed process description may fit observed average events reasonably well but can result in erroneous predictions for more extreme events.
    Geogenic and agricultural controls on the geochemical composition of European agricultural soils
    Saaltink, R. ; Griffioen, J. ; Mol, G. ; Birke, M. - \ 2014
    Journal of Soils and Sediments 14 (2014)1. - ISSN 1439-0108 - p. 121 - 137.
    robust factor-analysis - element concentrations - isotope composition - continental-crust - fertilizers - surface - impact - loess - extraction - metals
    Purpose Concern about the environmental impact of agriculture caused by intensification is growing as large amounts of nutrients and contaminants are introduced into the environment. The aim of this paper is to identify the geogenic and agricultural controls on the elemental composition of European, grazing and agricultural soils. Materials and methods Robust factor analysis was applied to data series for Al, B, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Se, Sr, U, Zn (ICP-MS) and SiO2, K2O, Na2O, Fe2O3, Al2O3 (XRF) based on the European GEMAS dataset. In addition, the following general soil properties were included: clay content, pH, chemical index of alteration (CIA), loss on ignition (LOI), cation exchange capacity (CEC), total organic carbon (TOC) and total carbon and total sulfur. Furthermore, this dataset was coupled to a dataset containing information of historic P2O5 fertilization across Europe. Also, a mass balance was carried out for Cd, Cu and Zn to determine if concentrations of these elements found in the soils have their origin in historic P2O5 fertilization. Results and discussion Seven geogenic factors and one agricultural factor were found of which four prominent ones (all geogenic): chemical weathering, reactive iron-aluminum oxide minerals, clay minerals and carbonate minerals. Results for grazing and agricultural soils were near identical, which further proofs the prominence of geogenic controls on the elemental composition. When the cumulative amount of P2O5 fertilization was considered, no extra agriculture-related factors became visible. The mass balance confirms these observations.
    PLEASE: a simple model to determine P losses by leaching
    Schoumans, O.F. ; Salm, C. van der; Groenendijk, P. - \ 2013
    Soil Use and Management 29 (2013). - ISSN 0266-0032 - p. 138 - 146.
    relating soil-phosphorus - phosphate-sorption - water-quality - united-states - runoff - eutrophication - netherlands - kinetics - surface - management
    Non-point phosphorus (P) loss from agricultural land to streams is caused mainly by overland flow and leaching. In many countries P-index methods are used to identify areas at risk of P loss to streams. In flat areas with shallow groundwater levels, where losses by leaching are important, these index methods have their limitations as leaching is often not described in detail. This study presents a simple model to predict P loss by leaching at the field scale. This model called Phosphorus LEAching from Soils to the Environment (PLEASE) is based on the well-known kinetics of P in soils and lateral water flux from soils to surface waters. PLEASE was applied using readily available information to a small catchment; and a sensitivity analysis and comparison with two soil P indicators were carried out (soil P test and the phosphate saturation degree). The model predicted a total P load of 4187kg P in the Schuitenbeek catchment. The result was also a predicted P discharge at the catchment outlet of 2973kg P corrected by independent assessment of P retention in streams in the catchment (29%). This is comparable to the measured outflow (2770kg P). The calculated P losses by leaching are highly sensitive to the soil Langmuir parameters, which means that it is important to determine the adsorption isotherm to obtain reliable estimated losses. The PLEASE approach has particular value compared to other soil P indicators for estimating actual P losses by leaching from agricultural land to surface water. These results suggest that PLEASE is a promising method for quantifying differences in P loss by leaching between fields within a catchment.
    Coalescence kinetics of oil-in-water emulsions studied with microfluidics
    Krebs, T. ; Schroen, C.G.P.H. ; Boom, R.M. - \ 2013
    Fuel 106 (2013). - ISSN 0016-2361 - p. 327 - 334.
    2-dimensional linear flow - equal-sized drops - on-a-chip - break-up - viscosity - droplets - dispersions - bubbles - systems - surface
    We report the results of experiments on the coalescence dynamics in flowing oil-in-water emulsions using an integrated microfluidic device. The microfluidic circuit permits direct observation of shear-induced collisions and coalescence events between emulsion droplets. Three mineral oils with a range of viscosities 8–70 mPa s and five silicone oils with a range of viscosities 6–100 mPa s were chosen as dispersed phase. Pure water was used as continuous phase. Trajectory analysis of colliding droplet pairs allows evaluation of the film drainage profile and coalescence time. From the coalescence times obtained for ten thousands of droplet pairs we calculate coalescence time distributions for the different emulsions. For all systems, the coalescence time decreases with increasing capillary number and increases with increasing dispersed phase viscosity. Scaling relations for the coalescence time are derived and compared with theoretical predictions. The potential of the procedure as a diagnostic tool for the prediction of emulsion stability in oil/water separation is discussed, as well as alternative applications of the microfluidic circuits.
    Quantifying the transport of subcloud layer reactants by shallow cimulus clouds over the Amazon
    Ouwersloot, H.G. ; Vilà-Guerau De Arellano, J. ; Stratum, B.J.H. van; Krol, M.C. ; Lelieveld, J. - \ 2013
    Journal of Geophysical Research: Atmospheres 118 (2013)23. - ISSN 2169-897X - p. 13041 - 13059.
    large-eddy simulation - topped mixed layers - convective boundary-layer - diurnal cycle - surface - land - fluxes - model - chemistry - campaign
    We investigate the vertical transport of atmospheric chemical reactants from the subcloud layer to the cumulus cloud layer driven by shallow convection over the Amazon during the dry season. The dynamical and chemical assumptions needed for mesoscale and global chemistry transport model parametrizations are systematically analyzed using a Large Eddy Simulation model. We quantify the mass flux transport contribution to the temporal evolution of reactants. Isoprene, a key atmospheric compound over the tropical rain forest, decreases by 8.5% h-1 on average and 15% h-1 at maximum due to mass¿flux¿induced removal. We apply mass flux parametrizations for the transport of chemical reactants and obtain satisfactory agreement with numerically resolved transport, except for some reactants like O3, NO, and NO2. The latter is caused by the local partitioning of reactants, influenced by UV radiation extinction by clouds and small¿scale variability of ambient atmospheric compounds. By considering the longer¿lived NOx (NO + NO2), the transport is well represented by the parametrization. Finally, by considering heterogeneous surface exchange conditions, it is demonstrated that the parametrizations are sensitive to boundary conditions due to changes in the boundary layer dynamics.
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