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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    Het gemeenschappelijk landbouwbeleid naar 2020
    Jongeneel, R.A. - \ 2012
    ESB Economisch Statistische Berichten 97 (2012)4639. - ISSN 0013-0583 - p. 430 - 433.
    gemeenschappelijk landbouwbeleid - eu regelingen - financieel landbouwbeleid - overheidsbestedingen - herverdeling - financiële ondersteuning - cap - eu regulations - agricultural financial policy - public expenditure - redistribution - financial support
    Het gemeenschappelijk landbouwbeleid verkeert op dit moment in een aanpassingsproces. Recente hervormingsvoorstellen impliceren ontkoppelde betalingen aan boeren naar meer gerichte betalingen. Dat kan de effectiviteit van het beleid ten goede komen, maar dan zou wel een ambitieuzere agenda nodig zijn. Het politieke debat focust meer op herverdelingseffecten dan op (kosten)effectiviteit.
    Binnen EU blijft herverdeling beperkt
    Jongeneel, R.A. - \ 2012
    Kennis Online 9 (2012)maart. - p. 10 - 10.
    gemeenschappelijk landbouwbeleid - subsidies - financieel landbouwbeleid - herverdeling - cap - subsidies - agricultural financial policy - redistribution
    Als de laatste voorstellen van de Europese Commissie voor het Gemeenschappelijk Landbouwbeleid (GLB) worden uitgevoerd, gaan de oude lidstaten, waaronder Nederland, minder landbouwsubsidie ontvangen en de nieuwe lidstaten iets meer. Maar de herverdeling blijft beperkt.
    Effecten herverdeling soms fors
    Jongeneel, R.A. - \ 2012
    Kennis Online 9 (2012)maart. - p. 9 - 9.
    gemeenschappelijk landbouwbeleid - financieel landbouwbeleid - subsidies - reductie - herverdeling - vleeskalveren - fabrieksaardappelen - cap - agricultural financial policy - subsidies - reduction - redistribution - veal calves - starch potatoes
    De vleeskalversector en zetmeelaardappelboeren zijn het meest gevoelig voor de voorgestelde veranderingen in het systeem van toeslagen van het GLB. Ze lopen het risico tienduizenden euro’s per bedrijf per jaar minder te ontvangen, een ongekende achteruitgang.
    Comparing landscape evolution models with quantitative field data at the millennial time scale in the Belgian loess belt
    Temme, A.J.A.M. ; Peeters, I. ; Buis, E. ; Veldkamp, A. ; Govers, G. - \ 2011
    Earth Surface Processes and Landforms 36 (2011)10. - ISSN 0197-9337 - p. 1300 - 1312.
    soil-erosion - land-use - hillslope evolution - dem resolution - redistribution - tillage - topography - deposition - catchment - water
    This study compares three landscape evolution models and their ability to correctly simulate measured 2500¿year landscape evolution in two small catchments in the Belgian loess belt. WATEM LT and LAPSUS both model tillage and water erosion and deposition and have detachment-limited descriptions for water erosion and deposition. Equations in LAPSUS are more mechanistic than those in WATEM LT. WATEM LTT resembles WATEM LT, but is a transport-limited model. All three models are DEM-based. Calibration and validation simulations were performed forward in time on (1D) transects for four spatial resolutions, and backward in time for (2D) catchments at 20¿m resolution. For transects, model outputs were compared with discretized observations of transect shape. For catchments, outputs were compared with point observations of palaeo-altitude, averaged over landscape element classes. For transects, the three models performed well, resulting in model efficiency factors of 0.92 to 0.99 for calibration and 0.62 to 0.96 for validation. However, for catchments, simulations showed that the transport-limited WATEM LTT model could not realistically simulate long-term landscape evolution. Performance of WATEM LT and LAPSUS at catchment scale was similar to that on transects, although LAPSUS has problems with backward calculation. Tests demonstrate that a transport-limited approach cannot be used to model long-term landscape evolution in the Belgian loess belt, which is in agreement with theoretical and empirical understanding of soil erosion processes in this environment. The difference in performance between transport-limited and detachment-limited models is clear only when the models are evaluated in a 2D catchment. The lack of such distinction when models were applied in a 1D transect highlights the importance of evaluating landscape evolution models in a 2D setting so that effects of flow convergence/divergence can be accounted for. Copyright © 2011 John Wiley & Sons, Ltd
    Changes in soil nutrients, vegetation structure and herbaceous biomass in response to grazing in a semi-arid savanna of Ethiopia
    Tessema, Z.K. ; Boer, W.F. de; Baars, R.M.T. ; Prins, H.H.T. - \ 2011
    Journal of Arid Environments 75 (2011)7. - ISSN 0140-1963 - p. 662 - 670.
    middle awash valley - african savanna - south-africa - long-term - nitrogen - redistribution - grasslands - mineralization - phosphorus - rangelands
    The effect of grazing was studied on vegetation structure, herbaceous biomass, basal and bare ground covers, together with soil nutrient concentrations in two locations in an Ethiopian semi-arid savanna. The lightly grazed sites had significantly higher herbaceous diversity, total abundance, basal cover and aboveground biomass, and a lower percentage of bare ground compared with the heavy grazed sites. Grazing pressure had no effect on the density and number of woody species as well as on the proportion of encroaching woody species. The light grazing sites had higher organic carbon, phosphorus and exchangeable bases, and therefore a higher pH and higher electrical conductance, indicating an improved soil nutrient status compared with heavy grazing sites, mainly attributed to the higher basal cover and standing biomass at light grazed sites, and the export of nutrients through grazing and dung collection from the heavily grazed sites. There were significantly higher soil nutrients, species diversity, aboveground biomass and basal cover in the light grazing sites compared with heavy grazing sites. We concluded that changes in herbaceous vegetation, standing biomass and soil compositions are caused by interactions between grazing, soil and vegetation, and these interactions determine the transitions of semi-arid savannas.
    Bread crispness and morphology can be controlled by proving conditions
    Primo Martin, C. ; Dalen, G. van; Meinders, M.B.J. ; Don, A. ; Hamer, R.H. ; Vliet, T. van - \ 2010
    Food Research International 43 (2010)1. - ISSN 0963-9969 - p. 207 - 217.
    water activity - moisture migration - mechanical-properties - food-products - cereal foods - solid food - crust - gluten - crumb - redistribution
    Bread crust crispness is lost when water migrates from crumb to crust during storage. To what extent water migration is influenced by morphology is not known. Therefore, the effect of crispy rolls morphology on crust crispness was studied. Crispy rolls were prepared at three proving volumes: 300 mL (short proving), 500 mL (control) and 800 mL (long proving). X-ray microtomography was used to characterize morphology. Water transport from crumb to crust was determined. Short proved crispy rolls showed lower rate of crust water uptake while longer proved rolls showed faster uptake during cooling down. Sensory analysis revealed higher crispness for short proved crispy rolls after the same storage time at low RH. We hypothesize that shorter proved crispy rolls with finer crumb morphology, more closed structure, smaller gas cells with less gas cells interconnections and a thicker crust have a significant positive effect on water uptake kinetics and crispness retention.
    Landbouwsubsidies voor natuur en landschap: economische effecten op melkveehouderij
    Helming, J.F.M. ; Schrijver, R.A.M. - \ 2008
    Agri-monitor 2008 (2008)juni. - ISSN 1383-6455 - 2
    gemeenschappelijk landbouwbeleid - subsidies - herverdeling - economische impact - melkveehouderij - melkveebedrijven - inkomen van landbouwers - cap - subsidies - redistribution - economic impact - dairy farming - dairy farms - farmers' income
    In de Health Check van het GLB wordt gesproken over een verdere korting van de inkomenstoeslagen ten gunste van plattelandsontwikkeling en milieu, natuur en landschap. Het sectorinkomen van de melkveehouderij zou door deze herverdeling tot 2020 met zo’n 6% kunnen dalen.
    Redistribution of velocity and bed-shear stress in straight and curved open channels by means of a bubble screen: laboratory experiments
    Blanckaert, K. ; Buschman, F.A. ; Schielen, R. ; Wijbenga, J.H.A. - \ 2008
    Journal of Hydraulic Engineering 134 (2008)2. - ISSN 0733-9429 - p. 184 - 195.
    waterbouwkunde - kanalen, klein - hydrodynamica - waterstroming - buigen - herverdeling - snelheid - turbulentie - laboratoriumproeven - hydraulic engineering - channels - hydrodynamics - water flow - bending - redistribution - velocity - turbulence - laboratory tests - submerged vanes - secondary flows - alternate bars - topography - bends - rivers
    Open-channel beds show variations in the transverse direction due to the interaction between downstream flow, cross-stream flow, and bed topography, which may reduce the navigable width or endanger the foundations of structures. The reported preliminary laboratory study shows that a bubble screen can generate cross-stream circulation that redistributes velocities and hence, would modify the topography. In straight flow, the bubble-generated cross-stream circulation cell covers a spanwise extent of about four times the water depth and has maximum transverse velocities of about 0.2 ms¿1. In sharply curved flow, it is slightly weaker and narrower with a spanwise extent of about three times the flow depth. It shifts the counter-rotating curvature-induced cross-stream circulation cell in the inwards direction. Maximum bubble-generated cross-stream circulation velocities are of a similar order of magnitude to typical curvature-induced cross-stream circulation velocities in natural open-channel bends. The bubble screen technique is adjustable, reversible, and ecologically favorable. Detailed data on the 3D flow field in open-channel bends is provided, which can be useful for validation of numerical models
    Is soil erosion in olive groves as bad as often claimed?
    Fleskens, L. ; Stroosnijder, L. - \ 2007
    Geoderma 141 (2007)3-4. - ISSN 0016-7061 - p. 260 - 271.
    rock-fragment cover - southern spain - land-use - hydraulic conductivity - management - runoff - tillage - redistribution - infiltration - simulation
    Alarming erosion rates have been reported in olive groves on sloping and mountainous land with some regional averages supposedly as high as 40-100 ton ha(-1) yr(-1). These figures are based on empirical models that apply a simple multiplication of adverse environmental factors such as steep slopes, erodible soils and low vegetation cover. We present experimental data from rainfall simulations, runoff plot studies and field assessment of erosion symptoms that challenge the alarmist view. We suggest seven factors be taken into account, to achieve more realistic estimates of erosion: 1) increased surface roughness from tillage increases infiltration; 2) a cover of rock fragments protects the soil and reduces the slope effect on erosion; 3) grove undergrowth reduces sediment losses; 4) slope irregularities created by long term erosion allow runoff to infiltrate locally; 5) vegetative strips hamper rill and gully formation; 6) erosion mainly results from infrequent high intensity rainfall events, and 7) upscaling of experimental results leads to overestimation of erosion. These factors act and/or interact at different scales; although each pertains to a certain scale of analysis only and affects erosion processes differently, taken together the factors provide an argument for indicating more precisely when, where and for whom erosion constitutes a problem. A literature review (of various types of assessments) yielded erosion rates with upper and lower limits differing more than a factor of 10 000. In some individual experiments, differences between treatments (tillage versus non-tillage or vegetative strips) were still a hundredfold-frequently to the disadvantage of tillage operations. The results of our own experiments are also presented. In some runoff plots (7.5 x 15 in, previously tilled) the soil loss after cumulative rainfall of 104 mm was 17.3 g m(-2) for non-tilled against 8.5 g m(-2) for tilled conditions (P <0.05); in another runoff plot experiment (10x22 in, previously under a cover crop) tillage initially led to higher soil loss, but differences rapidly disappeared. Field rainfall simulations on soils with plant cover had significantly less soil loss than those without plant cover (recently tilled) (61 g m(-2) versus 218 g m-2, P <0.001); runoff, however, was not significantly different. In consecutive rainfall simulations on soil with or without in situ rock fragments, the runoff, runoff coefficients and p soil loss were significantly lower (P <0.01) in the case with rock fragments. On non-uniform slopes, runoff and soil loss were spatially different, and tillage led to variable responses, depending on location. Combining the findings from our individual experiments, we conclude that tillage applied judiciously in selected locations of a grove might reduce erosion. Localised erosion may still be controlled at field level by vegetative strips. Our results suggest that average soil erosion rates are unlikely to surpass 10 ton ha(-1) yr(-1), which is nevertheless still more than the soil renewal by weathering (about I ton ha(-1) yr(-1)). Any recommendations for improved soil management should ideally be tested at the appropriate scale and should capture the climatic (rainfall) conditions under which they are intended to mitigate soil erosion problems. (c) 2007 Elsevier B.V All rights reserved.
    The effects of erosional and management history on soil organic carbon stores in ephemeral wetlands of hummocky agricultural landscapes
    Bedard-Haughn, A. ; Jongbloed, F. ; Akkennan, J. ; Uijl, A. ; Jong, E. de; Yates, T. ; Pennock, D. - \ 2006
    Geoderma 135 (2006). - ISSN 0016-7061 - p. 296 - 306.
    landform segmentation procedures - morainal landscape - saskatchewan - cultivation - deposition - storage - impact - redistribution - vegetation - canada
    Carbon sequestration by agricultural soils has been widely promoted as a means of mitigating greenhouse gas emissions. In many regions agricultural fields are just one component of a complex landscape matrix and understanding the interactions between agricultural fields and other landscape components such as wetlands is crucial for comprehensive, whole-landscape accounting of soil organic carbon (SOC) change. Our objective was to assess the effects of management and erosional history on SOC storage in wetlands of a typical hummocky agricultural landscape in southern Saskatchewan. Wetlands were classed into three land management groups: native wetlands (i.e., within a native landscape), and uncultivated and cultivated wetlands within an agricultural landscape. Detailed topographic surveys were used to develop a digital elevation model of the sites and landform segmentation algorithms were used to delineate the topographic data into landform elements. SOC density to 45 cm was assessed at seven uncultivated wetlands, seven cultivated wetlands, and twelve native wetlands. Mean SOC density decreased from 175.1 mg ha¿ 1 to 30 cm (equivalent mass depth) for the native wetlands to 168.6 mg ha¿ 1 for the uncultivated wetlands and 87.2 mg ha¿ 1 for the cultivated wetlands in the agricultural field. The SOC density of sediment depositional fans in the uncultivated wetlands is high but the total SOC stored in the fans is low due to their small area. The uncultivated wetlands occupy only 11% of the site but account for approximately 23% of SOC stores. Re-establishing permanent vegetation in the cultivated wetlands could provide maximum C sequestration with minimum energy inputs and a minimum loss of productive acreage but the overall consequences for the gas emissions would have to be carefully assessed.
    Modelling landslide dynamics in forested landscapes
    Claessens, L.F.G. - \ 2005
    Wageningen University. Promotor(en): Tom Veldkamp, co-promotor(en): Jeroen Schoorl. - Wageningen : s.n. - ISBN 9789085041450 - 143
    aardverschuivingen - landschap - landschapsecologie - modellen - herverdeling - bossen - erosie - geologie - geomorfologie - vegetatie - digitaal terreinmodel - nieuw-zeeland - landslides - landscape - landscape ecology - models - redistribution - forests - erosion - geology - geomorphology - vegetation - digital elevation model - new zealand
    The research resulting in this thesis covers the geological, geomorphological and landscape ecology related themes of the project 'Podzolisation under Kauri (Agathis australis): for better or worse?' supported by theNetherlands Organisation for Scientific Research (NWO). The general objective of this thesis is to investigate landscape, soil and vegetation dynamics in theWaitakereRangesRegionalParkon the North Island of New Zealand, where also all the fieldwork was carried out. The main core of the thesis consists of the development of a dynamic landscape process model to simulate soil redistribution by shallow landsliding. Resulting spatial patterns of erosion and deposition, changes in landslide susceptibility over time and the relation of spatially explicit landscape attributes with vegetation patterns are further explored.

    ·Chapter 1 is a general introduction elaborating on the geology, climate and socio-economic setting of the study area and explains the main objectives and research questions. The contents and overall structure of the thesis are also illustrated. Following this introductory chapter, the thesis is composed of 5 chapters based on scientific papers published in or submitted to peer reviewed journals.

    ·Chapter 2 deals with the general tectonic setting of the study area. Quaternary coastal and fluvial terrace morphology and chronology are explored to reconstruct the tectonic history of the south-west coast of the Northland region inNew Zealand. This chapter is situated on the geological timescale (1.8 Ma BP till present) and places the subsequent chapters dealing with the landscape process model and its applications, acting on a timescale of years to decades, in a broader spatio-temporal perspective. Field surveys and the analysis of aerial photography yield an inventory of 13 fluvial and 12 marine terrace levels. Due to poor exposure of clear field evidence in the form of e.g. wave-cut platforms or distinct river sediments, planar landscape morphology forms the main criterion for terrace remnant identification. Based on the record of terrace height spacings, sparse tephra age control and correlation with global paleoclimatic records, an attempt is made to reconstruct the regional Quaternary uplift rates. Because no hard chronostratigraphic marker is present within the fluvial terrace sequence, fluvial terrace levels are linked to the marine sequence by using the mean uplift rates calculated from the marine terraces (0.35 mm yr -1 from 0- 0.1 Ma and 0.26 mm yr -1 from 0.1-0.3 Ma). Both sets of terraces are then correlated with oxygen isotope fluctuations and the astronomically tuned timescale from ODP Site 677 and the Vostok ice core paleoclimatic records. Oldest marine and fluvial terrace levels are estimated 1.21 Ma and 0.242 Ma respectively. Although there seems to be some form of controversy about the uplift history and especially the preservation of terraces in the study area, a general regional uplift, superimposed on glacio-eustatic sea-level changes, is substantiated as the only possible mechanism leading to the maintenance of a considerable relief and active denudation processes inland.

    ·Chapter 3 deals with the development and application of the LAPSUS-LS landscape process model. The model is constructed as a component of the LAPSUS modelling framework ( L andsc A pe P roces S modelling at m U lti dimensions and scale S ; -LS:L and S lide,refers to the process specific model component). LAPSUS-LS delineates the location of shallow landslide initiation sites and simulates the effects on spatial patterns of soil redistribution and resulting landslide hazard for a large watershed within the study area. Processes that need to be incorporated in the model are reviewed followed by the proposed modelling framework. The model predicts the spatial pattern of landslide susceptibility within the simulated catchment and subsequently applies a spatial algorithm for the redistribution of failed material on the basis of a scenario of triggering rainfall events, relative landslide hazard and trajectories with runout criteria for failed slope material. The model forms a spatially explicit method to address the effects of shallow landslide erosion and sedimentation because digital elevation data are adapted between timesteps and on- and off-site effects over the years can be simulated in this way. By visualisation of the modelling results in a GIS environment, the shifting pattern of upslope and downslope (in)stability, triggering of new landslides and the resulting slope retreat by soil material redistribution due to former mass movements is simulated and assessed.

    ·Chapter 4 zooms in on a more theoretical aspect of the LAPSUS-LS model and evaluates digital elevation model (DEM) resolution effects on model results. The focus is on influences of grid size on landslide soil redistribution quantities and resulting spatial patterns and feedback mechanisms. Distributions of slope, specific catchment area and relative hazard for shallow landsliding are analysed for four different DEM resolutions (grid sizes of 10, 25, 50 and 100 m) for a 12 km 2 study catchment in theWaitakereRanges. The effect of DEM resolution proves to be especially pronounced for the boundary conditions determining a valid landslide hazard calculation. For coarse resolutions, the smoothing effect results in a larger area becoming classified as unconditionally stable or unstable. Simple empirical soil redistribution algorithms are applied for scenarios in which all sites with a certain landslide hazard fail and generate debris flow. The lower initial number of failing cells but also the inclusion of slope (limit) in those algorithms becomes apparent with coarser resolutions. For finer resolutions, much larger amounts of soil redistribution are found, which is attributed to the more detailed landscape representation. Looking at spatial patterns of landslide erosion and sedimentation, the size of the area affected by these processes also increases with finer resolutions. In general, landslide erosion occupies larger parts of the area than deposition, although the total amounts of soil material eroded and deposited are the same. Analysis of feedback mechanisms between soil failures over time shows that finer resolutions show higher percentages of the area with an increased or decreased landslide hazard. When the extent of sites with lower and higher hazards are compared, finer grid sizes and higher landslide hazard threshold scenarios tend to increase the total extent of areas becoming more stable relative to the less stable ones. It is concluded that extreme care should be taken when quantifying landslide basin sediment yield by applying simple soil redistribution formulas to DEMs with different resolutions. Rather, quantities should be interpreted as relative amounts. For studying shallow landsliding over a longer timeframe, the 'perfect' DEM resolution may not exist, because no resolution can possibly represent the dimensions of all different slope failures scattered in space and time. It is emphasised that the choice of DEM resolution, possibly restricted by data availability in the first place, should always be adapted to the context of a particular type of analysis.

    ·Chapter 5 and 6 describe two distinct applications of the LAPSUS-LS model: in Chapter 5 , a sediment record is used, in combination with the LAPSUS-LS model, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of theWaitakereRivercatchment and the history of the Te Henga wetland at the outlet. Sediment stratigraphy and chronology are interpreted by radiocarbon dating, foraminiferal analysis, andprovisionaltephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, the LAPSUS-LS modelisapplied to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide soil redistribution componentisadded to determine sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumesarecalculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga wetland during the last c. 1000 years. Their magnitude can be expressed by a range of critical rainfall thresholds representing a LAPSUS-LS scenario.

    ·Chapter 6 is a more ecologically focused application of the model and links digital terrain analysis and landslide modelling with the spatial distribution of mature kauri trees. The use of topographical attributes for the analysis of the spatial distribution and ecological cycle of kauri ( Agathis australis ), a canopy emergent conifer tree from northernNew Zealand, is studied. Several primary and secondary topographic attributes are derived from a DEM for theWaitakereRivercatchment and the contribution of these variables in explaining presence or absence of mature kauri is assessed with logistic regression and Receiver Operating Characteristic (ROC) plots. The topographically based landslide hazard index calculated with the LAPSUS-LS model appears to be very useful in explaining the occurrence and ecological dynamics of kauri. It is shown that the combination of topographic -, soil physical - and hydrological parameters in the calculation of this single landslide hazard index, performs better in explaining presence of mature kauri than using topographic attributes calculated from the DEM properties alone. Moreover, this example demonstrates the possibilities of using terrain attributes for representing geomorphological processes and disturbance mechanisms, often indispensable in explaining a species' ecological cycle and forest stand dynamics. The results of this analysis support the 'temporal stand replacement model', involving disturbance as a dominant ecological process in forest regeneration, as an interpretation of the community dynamics of kauri. Furthermore, a certain threshold maturity stage, in which trees become able to stabilise landslide prone sites and postpone a possible disturbance by this process, together with great longevity are seen as major factors making kauri a 'landscape engineer'.

    ·Synthesising, Chapter 7 reflects on the most important conclusions from the research resulting in this thesis and discusses the achievement of the main objectives and answers to the research questions postulated in Chapter 1. Three general themes are put forward covering the previous chapters. Finally some ideas for future research are suggested.

    Three-phase flow analysis of dense nonaqueous phase liquid infiltration in horizontally layered porous media
    Wipfler, E.L. ; Dijke, M.I.J. van; Zee, S.E.A.T.M. van der - \ 2004
    Water Resources Research 40 (2004). - ISSN 0043-1397 - p. W10101 - W10101.
    infiltratie - grondwater - waterkwaliteit - hydrologie - poreus medium - grondwaterstroming - bodemwaterbeweging - infiltration - groundwater - water quality - hydrology - porous media - groundwater flow - soil water movement - capillary forces - redistribution
    We considered dense nonaqueous phase liquid (DNAPL) infiltration into a water-unsaturated porous medium that consists of two horizontal layers, of which the top layer has a lower intrinsic permeability than the bottom layer. DNAPL is the intermediate-wetting fluid with respect to the wetting water and the nonwetting air. The layer interface forms a barrier to DNAPL flow, which causes the DNAPL to spread out horizontally just above the interface. An analytical approximation has been developed to estimate the DNAPL pressure and saturation and the horizontal extension of the DNAPL above the layer interface at steady state for low water saturations. The analytical approximation shows that the DNAPL infiltration is determined by five dimensionless numbers: the heterogeneity factor ¿, the capillary pressure parameter ¿, the gravity number N g , the ratio of the capillary and gravity numbers N c /N g , and the critical DNAPL pressure P o c . Its predictions were compared with the results of a numerical three-phase flow simulator for a number of parameter combinations. For most of these combinations the analytical approximation predicts the DNAPL pressure and saturation profiles at the interface adequately. Using the analytical approximation, we carried out a sensitivity study with respect to the maximum horizontal extension of the plume. The extension of the plumes appears to be highly sensitive to variation of the dimensionless numbers P o c , ¿ and ¿
    The 137Cs technique applied to steep Mediterranean slopes (Part I): the effects of lithology, slope morphology and land use
    Schoorl, J.M. ; Boix Fayos, C. ; Meijer, R.J. de; Graaff, E.R. van der; Veldkamp, A. - \ 2004
    Catena 57 (2004)1. - ISSN 0341-8162 - p. 15 - 34.
    soil-erosion rates - cesium-137 measurements - natural radionuclides - drainage-basin - redistribution - saskatchewan - indicators - landscape - tillage - canada
    Concentrations in the soil of anthropogenic and natural radionuclides have been investigated in order to assess the applicability of the Cs-137 technique in an area of typical Mediterranean steep slopes. This technique can be used to estimate net soil redistribution rates but its potential in areas with shallow and stony soils on hard rock lithology have not been evaluated so far. In this research, the validity of using this technique in stony shallow soils at very steep slopes is discussed together with the relations between radionuclide concentrations and other soil properties, lithology, slope morphology and land use in a Mediterranean environment. Both natural Potassium-40 (4 K), Uranium-238 (U-238), Thorium-232 (Th-212) and anthropogenic Caesium-137 (Cs-137) radionuclides have been determined in samples taken along slope transects on uncultivated serpentinite soils and cultivated gneiss soils. In addition to the radionuclide concentrations, parameters such as slope position, slope angle, aspect, soil depth, surface stone cover, moss, litter, vegetation cover, soil crust, stone content and bulk density have been quantified. All the natural radionuclides K-40, U-238, Th-232 show significantly higher concentrations in the gneiss than in the serpentinite soils, opposed to the Cs-137 concentration, which is found significantly higher in the serpentinite soils probably because of the difference in clay mineralogy. The exponential decreasing depth distribution of Cs-137 and its homogeneous spatial distribution emphasise the applicability of the Cs-137 technique in this ecosystem. Lithology determines the concentration of natural and anthropogenic radionuclides. Land use determines the relations between Cs-137 concentration/inventory and some soil characteristics. Higher Cs-137 concentration and inventory are associated with higher percentages of vegetation cover, higher percentage of stones in the soil and higher values of soil bulk density in cultivated gneiss soils. Slope morphology and land use influence the soil redistribution at slope, scale. The gneiss slopes show a zonation of four to five areas of differential erosion/accumulation processes corresponding with more regular slopes and soil redistribution due to water erosion and to tillage translocation and erosion. The serpentinites, as an example of a more unstable slope type, show more erosion areas with less accumulation downslope and soil redistribution due to water erosion. (C) 2003 Elsevier B.V. All rights reserved.
    The 137Cs technique applied to steep Mediterranean slopes (Part II): landscape evolution and model calibration
    Schoorl, J.M. ; Boix Fayos, C. ; Meijer, R.J. de; Graaff, E.R. van der; Veldkamp, A. - \ 2004
    Catena 57 (2004)1. - ISSN 0341-8162 - p. 35 - 54.
    soil-erosion rates - cesium-137 measurements - tillage erosion - loess plateau - land-use - redistribution - spain - translocation - patterns - runoff
    Over the past years the Caesium-137 (Cs-137) technique has been successfully applied in numerous environments all over the world. This technique is using the worldwide distribution of the anthropogenic Cs-137 radionuclide and its redistribution associated with soil particles as an effective estimation of net soil-loss rates. In contrast to numerous studies on deep, often cultivated, clay soils with gentle to intermediate slopes, typical Mediterranean shallow stony soils on steep slopes have received less attention. In this paper, the landscape evolution over the past 37 years has been evaluated using the Cs-137 technique for two lithological different areas under contrasting land use in the Alora case study area (Malaga, Spain). In soils on gneiss and serpentinite bedrock several transects have been selected on steep slopes up to 35 with mean soil depths from 37 cm for gneiss to 24 em for serpentinite. Estimating net soil redistribution rates from radionuclide distributions depends on the calculation of the local area reference inventory and the used calibration technique. Several methods have been tested and final results were found to differ considerably. After careful parameter selection, the resulting net soil redistribution estimates for the different transects have been compared with simulations of a simple landscape evolution model, resulting in different possible scenarios of erosional response. Total net soil-loss for the study area range from 2.3 +/- 0.25 to 69.1 +/- 7.8 t ha(-1) year(-1) for serpentinite and gneiss slopes, respectively. Differences in total slope sediment budgets as well as differences along the transeets reveal influences of landscape representation and land use. In this case the impact of soil translocation by tillage and resulting erosion rates are far more important than possible parent material induced differences. However, comparing the two sampled areas not only net rates but spatial patterns as well reveal important differences in distribution over the landscape of net erosion and net sedimentation zones. (C) 2003 Elsevier B.V. All rights reserved.
    Beheer natuurgrasland met melkvee
    Haan, M.H.A. de - \ 2002
    Lelystad : Praktijkonderzoek Veehouderij (PraktijkRapport. Rundvee, paarden, schapen, geiten / Praktijkonderzoek Veehouderij 6) - 33
    melkvee - rundvee - graslandbeheer - weiden - natuurlijke graslanden - economische impact - economische evaluatie - inkomen van landbouwers - ruwvoer (roughage) - herverdeling - betalingsbasis - kosten - dairy cattle - cattle - grassland management - pastures - natural grasslands - economic impact - economic evaluation - farmers' income - roughage - redistribution - payment basis - costs
    In dit project is getracht verschillende oppervlakten natuurgrasland in de bedrijfsvoering van een gangbaar melkveebedrijf op te nemen en het extra ruwvoer binnen het bedrijf te verwerken. Hiertoe zijn de kosten en opbrengsten integraal doorgerekend en toebedeeld aan het areaal natuurgrasland.
    Oscillations in the redistribution of the growth substance naphthylacetic acid after phototropic induction
    Haan, I. de - \ 1969
    Wageningen : [s.n.] (Publication / Centre for plant physiological research no. 77) - 11
    naa - metabolisme - herverdeling - fototropie - sapstroom - zea mays - maïs - naa - metabolism - redistribution - phototropism - sap flow - zea mays - maize
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