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  • 1
    Language: English
    In: Vadose Zone Journal, 01 October 2018, Vol.17(1)
    Description: Evaporation—a key process for water exchange between soil and atmosphere—is controlled by convective and diffusive surface fluxes that determine the functional time dependence of the evaporation rate (). Recent studies demonstrated that only a pore-scale surface flux model can capture the correct () curve. These studies also showed that a realistic estimate of the hydraulically connected region (HCR) of the pore-size distribution (PSD) is crucial for coupling surface flux to internal water flux. Since previous studies were often based on natural sands and glass beads, the main focus of our study was to test these conclusions for real soils. Therefore, we investigated the evaporation process within undisturbed soil columns of a sandy soil and loamy sand and measured the hydraulic functions via HYPROP experiments (a system to measure hydraulic properties using the evaporation method). Based on the isolated pore evaporation (IPE) model using a discretized form of the PSD, we developed a continuous IPE model and applied it to our experiments. Because the PSD plays a central role in the IPE model, we determined the PSD of the loamy sand soil via X-ray microtomography (μCT) for pores 〉19 μm. The consistency of the experimental data, i.e., (i) the retention curve for deriving the HCR of the pore size distribution, (ii) the unsaturated hydraulic conductivity for calculating the characteristic lengths of the evaporation process, and (iii) the high accuracy of the mass loss data strongly support the HYPROP method for this kind of complex evaporation experiment. The continuous IPE model describes the characteristic Stage 1 behavior well (functional form of the evaporation rate and length of Stage 1) for both soil types if a realistic HCR estimate is used that (i) is derived from a characteristic length analysis estimating the lower boundary of the HCR and (ii) the upper range of the HCR is based on the true PSD derived from μCT data.
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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  • 2
    Language: English
    In: Geoderma, 1 June 2018, Vol.319, pp.132-141
    Description: Irrigation with treated waste water (TWW) is a common practice in agriculture, mainly in arid and semiarid areas as it provides a sustainable water resource available at all-season in general and at freshwater shortage in particular. However, TWW still contains abundant organic material which is known to decrease soil wettability, which in turn may promote flow instabilities that lead to the formation of preferential flow paths. We investigate the impact of long-term TWW irrigation on water wettability and infiltration into undisturbed soil cores from two commercially used orchards in Israel. Changes of water content during infiltration were quantitatively analysed by X-ray radiography. One orchard (sandy clay loam) had been irrigated with TWW for more than thirty years. In the other orchard (loamy sand) irrigation had been changed from freshwater to TWW in 2008 and switched back in some experimental plots to freshwater in 2012. Undisturbed soil cores were taken at the end of the dry and the rainy season to investigate the seasonal effect on water repellency and on infiltration dynamics in the laboratory. The irrigation experiments were done on field moist samples. A test series with different initial water contents was run to detect the influence on water movement at different wettabilities. In this study we show that the infiltration front stability is dependent on the history of waste water irrigation at the respective site and on the initial water content. •A new method to quantify water infiltrating undisturbed soil cores was used.•Infiltration front pattern is influenced by water repellency.•Effect is dependent on initial water content and repellency characteristics.•Treated waste water irrigation reduced water storage capacity about 27%.
    Keywords: Soil Water Repellency ; Treated Waste Water Irrigation ; Unstable Flow ; Preferential Flow ; Water Infiltration ; X-Ray Analysis
    ISSN: 0016-7061
    E-ISSN: 18726259
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  • 3
    Language: English
    In: Vadose Zone Journal, 01 March 2018, Vol.17(1)
    Description: X-ray radiography is a suitable approach to study water dynamics in undisturbed soil. However, beam hardening impairs the deduction of soil moisture changes from X-ray attenuation, especially when studying infiltration of water into cylindrical soil columns. We developed a calibration protocol to correct for beam hardening effects that enables the quantitative determination of changing average water content in two-dimensional projections. The method works for a broad range of materials and is easy to implement. Moreover, we studied the drift of X-ray attenuation values due to the detector latency and eliminated its contribution to the quantitative analysis. Finally we could visualize the dynamics of infiltrating water into undisturbed cylindrical soil samples.
    Keywords: Agriculture
    ISSN: 1539-1663
    E-ISSN: 1539-1663
    Source: Directory of Open Access Journals (DOAJ)
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  • 4
    Language: English
    In: Geoderma, 1 January 2019, Vol.333, pp.90-98
    Description: Secondary treated wastewater, a commonly used water resource in agriculture in (semi-)arid areas, often contains salts, sodium, and organic matter which may affect soil structure and hydraulic properties. The main objective of this study was to jointly analyse the effects of long-term irrigation with treated wastewater on physicochemical soil characteristics, soil structure, and soil water dynamics in undisturbed soils. X-ray microtomography was used to determine changes in macro-porosity (〉 19 μm), pore size distribution, and pore connectivity of a sandy clay loam and a loamy sand. Differences in the pore network among soils irrigated with treated wastewater, fresh water that replaced treated wastewater, and non-irrigated control plots could be explained by changes in textural composition, soil physicochemical parameters, and hydraulic properties. In this study we showed that irrigation led to the development of a connected macro-pore network, independent of the studied water quality. The leaching of silt and clay particles in the sandy soil due to treated wastewater irrigation resulted in an increase of pores 〈 130 μm. While this change in texture reduced water retention, the unsaturated hydraulic conductivity was diminished by physicochemical alteration, i.e. induced water repellency and clay mineral swelling. Overall, the fine textured sandy clay loam was much more resistant to soil alteration by treated wastewater irrigation than the loamy sand. •Irrigation facilitates the development of a connected macro-pore network.•TWW induced clay loss of a loamy sand, but did not affect soil carbon content.•SAR and water repellency reduced unsaturated hydraulic conductivity.•Loss of clay minerals reduced soil water retention.•Sandy clay loam was highly resistant towards physicochemical soil alteration.
    Keywords: Soil Structure ; Treated Wastewater Irrigation ; Clay Dispersion ; Unsaturated Hydraulic Conductivity ; Soil Water Retention ; X-Ray Microtomography
    ISSN: 0016-7061
    E-ISSN: 18726259
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  • 5
    Language: English
    In: Science of the Total Environment
    Description: Riverbank filtration is a natural process that may ensure the cleaning of surface water for producing drinking water. For silver nanoparticles (AgNP), physico-chemical interaction with sediment surfaces is one major retention mechanism. However, the effect of flow velocity and the importance of biological retention, such as AgNP attachment to biomass, are not well understood, yet.We investigated AgNP (c = 0.6 mg L−1) transport at different spatial and temporal scales in pristine and previously pond water-aged sediment columns. Transport of AgNP under near-natural conditions was studied in a long-term riverbank filtration experiment over the course of one month with changing flow scenarios (i.e. transport at 0.7 m d−1, stagnation, and remobilization at 1.7 m d−1). To elucidate retention processes, we conducted small-scale lab column experiments at low (0.2 m d−1) and high (0.7 m d−1) flow rate using pristine and aged sediments.Overall, AgNP accumulated in the upper centimeters of the sediment both in lab and outdoor experiments. In the lab study, retention of AgNP by attachment to biological components was very effective under high and low flow rate with nearly complete NP accumulation in the upper 2 mm. When organic material was absent, abiotic filtration mechanisms led to NP retention in the upper 5 to 7 cm of the column. In the long-term study, AgNP were transported up to a depth of 25 cm. For the pristine sediment in the lab study and the outdoor experiments only erratic particle breakthrough was detected in a depth of 15 cm.We conclude that physico-chemical interactions of AgNP with sediment surfaces are efficient in retaining AgNP. The presence of organic material provides additional retention sites which increase the filtration capacity of the system. Nevertheless, erratic breakthrough events might transport NP into deeper sediment layers. Unlabelled Image •Outdoor & lab study: NP transport in absence and presence of biological components•Biological components highly increase NP retention, independent of flow velocity.•High NP retention under low flow velocity (〈1 m d−1) in lab and outdoor columns•Experiment duration and flow rate increase NP mobility in near-natural systems.•Strong NP attachment to biological components in riverbank filtration systems
    Keywords: Nanomaterial ; Long-Term Experiment ; Water-Saturated Transport ; Near-Natural Condition ; Biological Retention ; Mechanical Filtration
    ISSN: 0048-9697
    Source: ScienceDirect (Elsevier B.V.)
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