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  • Vanderborght, J.  (61)
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  • 1
    Language: English
    In: Pest management science, March 2011, Vol.67(3), pp.294-306
    Description: For the registration of pesticides in the European Union, model simulations for worst-case scenarios are used to demonstrate that leaching concentrations to groundwater do not exceed a critical threshold. A worst-case scenario is a combination of soil and climate properties for which predicted leaching concentrations are higher than a certain percentile of the spatial concentration distribution within a region. The derivation of scenarios is complicated by uncertainty about soil and pesticide fate parameters. As the ranking of climate and soil property combinations according to predicted leaching concentrations is different for different pesticides, the worst-case scenario for one pesticide may misrepresent the worst case for another pesticide, which leads to 'scenario uncertainty'. Pesticide fate parameter uncertainty led to higher concentrations in the higher percentiles of spatial concentration distributions, especially for distributions in smaller and more homogeneous regions. The effect of pesticide fate parameter uncertainty on the spatial concentration distribution was small when compared with the uncertainty of local concentration predictions and with the scenario uncertainty. Uncertainty in pesticide fate parameters and scenario uncertainty can be accounted for using higher percentiles of spatial concentration distributions and considering a range of pesticides for the scenario selection.
    Keywords: Computer Simulation ; Pesticides -- Analysis ; Soil Pollutants -- Analysis
    E-ISSN: 1526-4998
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  • 2
    In: Nature, 2016, Vol.536(7617), p.E1
    Description: In their study, Evaristo et al.1 collected an extensive data set on the basis of which they statistically determined the isotopic compositions of the plant water source (δ 18Ointersect and δ 2Hintersect, called respectively δ 18Ointercept and δ 2Hintercept in their paper) as the x and y coordinates in (δ 18O, δ 2H) space of the intersection between the local meteoric water line (LMWL) and the plant xylem water 'evaporation line' (EL) for a range of climates and vegetation types.
    Keywords: Isotopes ; Groundwater ; Groundwater Recharge ; Stream Flow ; Precipitation ; Botany ; Flowers & Plants;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 3
    Language: English
    In: Plant and Soil, 2014, Vol.384(1), pp.93-112
    Description: Aims A simulation model to demonstrate that soil water potential can regulate transpiration, by influencing leaf water potential and/or inducing root production of chemical signals that are transported to the leaves. Methods Signalling impacts on the relationship between soil water potential and transpiration were simulated by coupling a 3D model for water flow in soil, into and through roots (Javaux et al. 2008) with a model for xylem transport of chemicals (produced as a function of local root water potential). Stomatal conductance was regulated by simulated leaf water potential (H) and/or foliar chemical signal concentrations (C; H+C). Split-root experiments were simulated by varying transpiration demands and irrigation placement. Results While regulation of stomatal conductance by chemical transport was unstable and oscillatory, simulated transpiration over time and root water uptake from the two soil compartments were similar for both H and H+C regulation. Increased stomatal sensitivity more strongly decreased transpiration, and decreased threshold root water potential (below which a chemical signal is produced) delayed transpiration reduction. Conclusions Although simulations with H+C regulation qualitatively reproduced transpiration of plants exposed to partial rootzone drying (PRD), long-term effects seemed negligible. Moreover, most transpiration responses to PRD could be explained by hydraulic signalling alone. Keywords Soil-root modeling * R-SWMS * Hormonal Signaling * Stomatal conductance * Partial rootzone drying
    Keywords: Soil-root modelling ; R-SWMS ; Hormonal signalling ; Stomatal conductance ; Partial rootzone drying
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 4
    Language: English
    In: Water Research, 01 March 2014, Vol.50, pp.294-306
    Description: Atrazine was banned in Germany in 1991 due to findings of atrazine concentrations in ground- and drinking waters exceeding threshold values. Monitoring of atrazine concentrations in the groundwater since then provides information about the resilience of the groundwater quality to changing agricultural practices. In this study, we present results of a monitoring campaign of atrazine concentrations in the Zwischenscholle aquifer. This phreatic aquifer is exposed to intensive agricultural land use and susceptible to contaminants due to a shallow water table. In total 60 observation wells (OWs) have been monitored since 1991, of which 15 are sampled monthly today. Descriptive statistics of monitoring data were derived using the “regression on order statistics” (ROS) data censoring approach, estimating values for nondetects. The monitoring data shows that even 20 years after the ban of atrazine, the groundwater concentrations of sampled OWs remain on a level close to the threshold value of 0.1 μg l without any considerable decrease. The spatial distribution of atrazine concentrations is highly heterogeneous with OWs exhibiting permanently concentrations above the regulatory threshold on the one hand and OWs were concentrations are mostly below the limit of quantification (LOQ) on the other hand. A deethylatrazine-to-atrazine ratio (DAR) was used to distinguish between diffuse – and point-source contamination, with a global mean value of 0.84 indicating mainly diffuse contamination. Principle Component Analysis (PCA) of the monitoring dataset demonstrated relationships between the metabolite desisopropylatrazine, which was found to be exclusively associated with the parent compound simazine but not with atrazine, and between deethylatrazine, atrazine, nitrate, and the specific electrical conductivity. These parameters indicate agricultural impacts on groundwater quality. The findings presented in this study point at the difficulty to estimate mean concentrations of contamination for entire aquifers and to evaluate groundwater quality based on average parameters. However, analytical data of monthly sampled single observation wells provide adequate information to characterize local contamination and evolutionary trends of pollutant concentration.
    Keywords: Atrazine ; Groundwater Monitoring ; DAR ; Nondetects ; Data Censoring ; Principle Component Analysis ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 5
    Language: English
    In: Plant and soil, 2015, Vol.394(1), pp.109-126
    Description: AIMS: Stomata can close to avoid cavitation under decreased soil water availability. This closure can be triggered by hydraulic (‘H’) and/or chemical signals (‘C’, ‘H + C’). By combining plant hydraulic relations with a model for stomatal conductance, including chemical signalling, our aim was to derive direct relations that link soil water availability, expressed as fraction of roots in dry soil (fdᵣy), to transpiration reduction. METHODS: We used the mechanistic soil-root water flow model R-SWMS to verify this relation. Virtual split root experiments were simulated, comparing horizontal and vertical splits with varying fdᵣy and different strengths of stomatal regulation by chemical and hydraulic signals. RESULTS: Transpiration reduction predicted by the direct relations was in good agreement with numerical simulations. For small enough potential transpiration and large enough root hydraulic conductivity and stomatal sensitivity to chemical signalling isohydric plant behaviour originates from H + C control whereas anisohydric behaviour emerges from C control. For C control the relation between transpiration reduction and fdᵣy becomes independent of transpiration rate whereas H + C control results in stronger reduction for higher transpiration rates. CONCLUSION: Direct relations that link effective soil water potential and leaf water potential can describe different stomatal control resulting in contrasting behaviour. ; p. 109-126.
    Keywords: Plant Available Water ; Root Hydraulic Conductivity ; Stomata ; Leaf Water Potential ; Stomatal Conductance ; Roots ; Water Flow ; Mathematical Models ; Stomatal Movement ; Leaves ; Soil Water Potential
    ISSN: 0032-079X
    E-ISSN: 15735036
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  • 6
    Language: English
    In: Plant and Soil, 2017, Vol.415(1), pp.99-116
    Description: Background and aims The use of standard dynamic root architecture models to simulate root growth in soil containing macropores failed to reproduce experimentally observed root growth patterns. We thus developed a new, more mechanistic model approach for the simulation of root growth in structured soil. Methods In our alternative modelling approach, we distinguish between, firstly, the driving force for root growth, which is determined by the orientation of the previous root segment and the influence of gravitropism and, secondly, soil mechanical resistance to root growth. The latter is expressed by its inverse, soil mechanical conductance, and treated similarly to hydraulic conductivity in Darcy's law. At the presence of macropores, soil mechanical conductance is anisotropic, which leads to a difference between the direction of the driving force and the direction of the root tip movement. Results The model was tested using data from the literature, at pot scale, at macropore scale, and in a series of simulations where sensitivity to gravity and macropore orientation was evaluated. Conclusions Qualitative and quantitative comparisons between simulated and experimentally observed root systems showed good agreement, suggesting that the drawn analogy between soil water flow and root growth is a useful one.
    Keywords: Macropores ; Root architecture model ; Root growth direction ; R-SWMS
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 7
    Language: English
    In: Journal of Hydrology, May 2015, Vol.524, pp.680-695
    Description: Spatially highly resolved mapping of aquifer heterogeneities is critical for the accurate prediction of groundwater flow and contaminant transport. Here, we demonstrate the value of using full-waveform inversion of crosshole ground penetrating radar (GPR) data for aquifer characterization. We analyze field data from the Krauthausen test site, where crosshole GPR data were acquired along a transect of 20 m length and 10 m depth. Densely spaced cone penetration tests (CPT), located close to the GPR transect, were used to validate and interpret the tomographic images obtained from GPR. A strong correlation was observed between CPT porosity logs and porosity estimates derived from GPR using the Complex Refractive Index Model (CRIM). A less pronounced correlation was observed between electrical conductivity data derived from GPR and CPT. Cluster analysis of the GPR data defined three different subsurface facies, which were found to correspond to sediments with different grain size and porosity. In conclusion, our study suggests that full-waveform inversion of crosshole GPR data followed by cluster analysis is an applicable approach to identify hydrogeological facies in alluvial aquifers and to map their architecture and connectivity. Such facies maps provide valuable information about the subsurface heterogeneity and can be used to construct geologically realistic subsurface models for numerical flow and transport prediction.
    Keywords: Heterogeneity ; Aquifer Characterization ; Geophysical Methods ; Ground Penetrating Radar ; Full-Waveform Inversion ; Cone Penetration Tests ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 8
    Language: English
    In: Plant and Soil, 2019, Vol.439(1), pp.273-292
    Description: Background and aims Although modelling of water and nutrient uptake by root systems has advanced considerably in recent years, steep local gradients of nutrient concentration near the root-soil interface in the rhizosphere are still a central challenge for accurate simulation of water and nutrient uptake...
    Keywords: Water uptake ; Nutrient uptake ; Root system architecture ; Root soil modelling ; Multiscale ; Root system scale ; Single root scale ; Rhizosphere
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 9
    Language: English
    In: Vadose Zone Journal, 2016, Vol.15(7), p.0
    Description: A dynamic tension-controlled bottom boundary of lysimeters allows observing water and matter fluxes in lysimeters that are close to natural field conditions, as pressure heads at the lysimeter bottom are adjusted to measured pressure heads at the same depth in the surrounding field. However lysimeters are often transferred from their sampling location for practical reasons or to study, for example, the effect of climate change on soil functions. This transfer can be accompanied by a change aboveground but also in subsurface conditions that are used to control the bottom boundary and that may affect the soil water balance of lysimeters. This issue is also relevant for lysimeter stations which use a tension-controlled bottom boundary and are not directly installed near the site of excavation. The potential impact of different bottom boundary conditions on the water balance of lysimeters that were transferred in a climate impact experiment (SOILCan) was investigated exemplarily by a numerical study. Results showed that by using nonappropriate pressure heads, which were measured in soil profiles with a different texture and water table depth than the profile where the lysimeter was taken from, had partially large impacts on soil water fluxes, especially when the water table was located within a specific critical range. Different climate conditions between sampling and installation site were buffered by the soil and did not show a strong influence on the bottom boundary control of lysimeters when the groundwater table depth was assumed to remain constant. Considering a change in groundwater table depths due to changing climate tempered the effects of climate change on the soil water balance terms. In general, results demonstrate the importance of a proper control of the lysimeters bottom boundary conditions in studies that investigate the influence of climate change on soil functions and ecosystem variables by transferring lysimeter along climate gradients.
    Keywords: Water Balance ; Climate Change ; Soils ; Water Table ; Climate Change ; Climates ; Pressure Head ; Water Depth ; Boundaries ; Lysimeters ; Sampling ; Soil Water ; Groundwater ; Methods and Instruments ; General ; Bl, Bad Lauchstaedt ; Dd, Dedelow ; Eta, Evapotranspiration ; Etp, Potential Evapotranspiration ; Lai, Leaf Area Index ; Sb, Sauerbach ; Se, Selhausen;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 10
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(4), p.0
    Description: The process description of plant transpiration and soil water uptake in macroscopic root water uptake models is often based on simplifying assumptions that no longer reflect, or even contradict, the current status of knowledge in plant biology. The sink term in the Richards equation for root water uptake generally comprises four terms: (i) a root resistance function, (ii) a soil resistance function, (iii) a stress function, and (iv) a compensation function. Here we propose to use a detailed three-dimensional model, which integrates current knowledge of soil and root water flow equations, to deduct a one-dimensional effective behavior at the plant scale and to propose improvements for the four functions used in the macroscopic sink term. We show that (i) root hydraulic resistance may be well defined by the root length density but only for homogeneous lateral conductances and no limiting xylem conductance--in other cases a new function depending on the root hydraulic architecture should be used; (ii) soil resistance cannot be neglected, in particular in the rhizosphere where specific processes may occur that alter the soil hydraulic properties and therefore affect uptake; (iii) stress and compensation are two different processes, which should not be linked explicitly; (iv) there is a need for a clear definition of compensatory root water uptake independent of water stress; (v) stress functions should be defined as a maximal actual transpiration in function of an integrated root-soil interface water head rather than in terms of local bulk water heads; and (vi) nonlinearity in the stress function is expected to arise if root hydraulic resistances depend on soil matric head or when it is defined as a function of the bulk soil water head.
    Keywords: Soils ; Biogenic Processes ; Critical Review ; Darcy'S Law ; Equations ; Mathematical Models ; Models ; Movement ; One-Dimensional Models ; Processes ; Review ; Rhizosphere ; Roots ; Scale Factor ; Soils ; Solute Transport ; Three-Dimensional Models ; Transport ; Unsaturated Zone ; Water;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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