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  • 1
    Article
    Article
    Language: English
    In: Vadose Zone Journal, 2016, Vol.15(2), p.0
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 2
    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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  • 3
    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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  • 4
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(3), p.0
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 5
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(2), p.0
    Description: In this paper we reviewed the use of microwave remote sensing methods for characterizing crop canopies and vegetation water stress related phenomena. Our analysis includes both active and passive systems that are ground-based, airborne, or spaceborne. Most of the published results that have examined crop canopy characterization and water stress have used active microwave systems. In general, quantifying the effect of dynamic vegetation properties, and water stress related processes in particular, on the measured microwave signals can still benefit from improved models and more observational data. Integrated data sets providing information on both soil status and plant status are lacking, which has hampered the development and validation of mathematical models. There is a need to link three-dimensional functional, structural crop models with radiative transfer models to better understand the effect of environmental and related physiological processes on microwave signals and to better quantify the impact of water stress on microwave signals. Such modeling approaches should incorporate both passive and active microwave methods. Studies that combine different sensor technologies that cover the full spectral range from optical to microwave have the potential to move forward our knowledge of the status of crop canopies and particularly water related stress phenomena. Assimilation of remotely sensed properties, such as backscattering coefficient or brightness temperature, in terms of estimating biophysical crop properties using mathematical models is also an unexplored avenue.
    Keywords: Hydrogeology ; Applied Geophysics ; Agriculture ; Biomass ; Characterization ; Dielectric Properties ; Humidity ; Land Use ; Leaves ; Mathematical Methods ; Mathematical Models ; Microwave Methods ; Moisture ; Properties ; Remote Sensing ; Saturation ; Soils ; Stemflow ; Stress ; Surface Water ; Vegetation ; Winds;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 6
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(2), p.0
    Description: We investigated the eff ects of a drying front that emerges below an evaporating soil surface on the far-field ground-penetrating radar (GPR) data. First, we performed an analysis of the width of the drying front in soils with 12 diff erent textures by using an analytical model. Then, we numerically simulated vertical soil moisture profiles that develop during evaporation for the soil textures. We performed the simulations using a Richards flow model that considers only liquid water flow and a model that considers coupled water, vapor, and heat flows. The GPR signals were then generated from the simulated soil water content profiles taking into account the frequency dependency of apparent electrical conductivity and dielectric permitivity. The analytical approach indicated that the width of the drying front at the end of Stage I of the evaporation was larger in silty soils than in other soil textures and smaller in sandy soils. We also demonstrated that the analytical estimate of the width of the drying front can be considered as a proxy for the impact that a drying front could have on far-field GPR data. The numerical simulations led to the conclusion that vapor transport in soil resulted in S-shaped soil moisture profiles, which clearly influenced the GPR data. As a result, vapor flow needs to be considered when GPR data are interpreted in a coupled inversion approach. Moreover, the impact of vapor flow on the GPR data was larger for silty than for sandy soils. These effects on the GPR data provide promising perspectives regarding the use of radars for evaporation monitoring.
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 7
    Language: English
    In: Vadose Zone Journal, 2014, Vol.13(7), p.0
    Description: Natural fine colloids and nanoparticles have the potential to encapsulate and bind nutrients. Their size and composition is therefore relevant to understand the transport of essential nutrients like phosphorus in an aquatic ecosystem. The aim of this study was to characterize fine colloidal and nanoparticulate bound P of distinct hydromorphological areas in stream water from a forested test site in a small headwater catchment. Asymmetric flow field flow fractionation coupled online to inductively coupled plasma mass spectrometry was applied for size-resolved detection of P, Fe, and Al in the fractions. Online P detection was a challenge due to the low concentrations (in this study down to 0.1 mu g/L) in many natural waters. Additionally, the "dissolved" organic matter (DOM) content was derived from the online UV signal. The colloidal P occurred in two size fractions (2-20 and 21-300 nm), which constituted up to 100% of the total river P discharge depending on hydromorphology. For the small size fraction, variations in P concentrations correlated with Al variations; in addition, a high Fe presence in both fractions was accompanied by high P concentrations. Moreover, DOM was detected with P in the presence of Fe and Al, suggesting that Fe and Al are carriers of P and associated with organic matter. The developed methodology enables the inputs and source regions of fine colloidal and nanoparticulate fractions within a small river of a headwater catchment to be traced and conceptually defined for the first time.
    Keywords: Hydrogeology ; Hydrochemistry ; Aluminum ; Aquatic Environment ; Aqueous Solutions ; Carbon ; Central Europe ; Colloidal Materials ; Concentration ; Ecosystems ; Eifel National Park ; Europe ; Forests ; Germany ; Ground Water ; Hydromorphology ; Icp Mass Spectra ; Iron ; Mass Spectra ; Measurement ; Metals ; Nanoparticles ; North Rhine-Westphalia Germany ; Organic Compounds ; Phosphorus ; Provenance ; Recharge ; Ruhr ; Soil Solutions ; Soils ; Solute Transport ; Solutes ; Spatial Distribution ; Spectra ; Streams ; Surface Water ; Tereno ; Terrestrial Environment ; Terrestrial Environmental Observatories ; Transport ; Unsaturated Zone ; Wustebach;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 8
    Language: English
    In: Vadose Zone Journal, 01 February 2018, Vol.17(1)
    Description: The spatiotemporal distribution of root water uptake (RWU) depends on the dynamics of the root distribution and compensatory uptake from wetter regions in the root zone. This work aimed to parameterize three RWU models with different representations of compensation: the Feddes–Jarvis model...
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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  • 9
    Language: English
    In: Vadose Zone Journal, 2018, Vol.17(1), p.0
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 10
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(3), p.0
    Description: In this study, we developed spectrotransfer functions (STFs) that relate soil hydraulic properties (SHPs) to spectral reflectance values to estimate hydraulic parameters of the Mualem-van Genuchten (MvG) model. We investigated the general potential of airborne as well as space-borne remote sensors to retrieve MvG hydraulic parameters of a bare soil agricultural field. Based on the ASD full spectrum (Scenario I), simple spectral signatures were generated mimicking the hyperspectral EnMAP sensor (Scenario II), and the multispectral Sentinel-2 sensor (Scenario III). A stepwise multiple linear regression method was used for each scenario to derive STFs. We further tested laboratory- and soil-map-based HYPRES and Rosetta pedotransfer functions (PTFs) to parameterize MvG parameters and thus provide soil water characteristics and hydraulic conductivity functions in the region. The best results were obtained for Scenarios I and II, with similar R (super 2) values for shape parameters alpha * and n and the lognormal saturated hydraulic conductivity (K (sub s) *). The R (super 2) values were highest for K (sub s) * in Scenarios I and II (0.58 and 0.57, respectively). The R (super 2) values for alpha * and n were 0.30 and 0.34 in Scenario I and 0.39 and 0.31 in Scenario II, respectively. In all scenarios, the lowest R (super 2) values were obtained for saturated water content (theta (sub s) ), with values around 0.10 for Scenarios I and II and almost zero in Scenario III. Compared with HYPRES and Rosetta PTFs, the spectral approach performed reasonably well in terms of predicting soil water retention characteristics and unsaturated hydraulic conductivity. These findings suggest that spectral reflectance data provide a promising indirect and quick method for large-scale parameter estimation.
    Keywords: Applied Geophysics ; Soils ; Arid Environment ; Asia ; Cores ; Electrical Conductivity ; Experimental Studies ; Hydrodynamics ; Hydrology ; Hyperspectral Analysis ; Imagery ; Infrared Spectra ; Iran ; Laboratory Studies ; Middle East ; Mualem-An Genuchten Model ; Near-Infrared Spectra ; Northwestern Iran ; Optical Spectra ; Pedotransfer Functions ; Reflectance ; Regression Analysis ; Remote Sensing ; Saturation ; Sefidrood Basin ; Short-Wave Infrared Spectra ; Soils ; Spectra ; Spectrotransfer Functions ; Statistical Analysis ; Terrestrial Environment ; Unsaturated Zone ; Watersheds ; Zanjanrood Basin;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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