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  • 2018  (17)
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  • 2018  (17)
  • 1
    Language: English
    In: Nature, 22 February 2018, Vol.554(7693), pp.423
    Keywords: Soil ; Plant Roots -- Chemistry
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 2
    Language: English
    In: Science of the Total Environment, 15 December 2018, Vol.645, pp.192-204
    Description: Riverbank filtration systems are important structures that ensure the cleaning of infiltrating surface water for drinking water production. In our study, we investigated the potential risk for a breakthrough of environmentally aged silver nanoparticles (Ag NP) through these systems. Additionally, we identified factors leading to the remobilization of Ag NP accumulated in surficial sediment layers in order to gain insights into remobilization mechanisms. We conducted column experiments with Ag NP in an outdoor pilot plant consisting of water-saturated sediment columns mimicking a riverbank filtration system. The NP had previously been aged in river water, soil extract, and ultrapure water, respectively. We investigated the depth-dependent breakthrough and retention of NP. In subsequent batch experiments, we studied the processes responsible for a remobilization of Ag NP retained in the upper 10 cm of the sediments, induced by ionic strength reduction, natural organic matter (NOM), and mechanical forces. We determined the amount of remobilized Ag by ICP-MS and differentiated between particulate and ionic Ag after remobilization using GFAAS. The presence of Ag-containing heteroaggregates was investigated by combining filtration with single-particle ICP-MS. Single and erratic Ag breakthrough events were mainly found in 30 cm depth and Ag NP were accumulated in the upper 20 cm of the columns. Soil-aged Ag NP showed the lowest retention of only 54%. Remobilization was induced by the reduction of ionic strength and the presence of NOM in combination with mechanical forces. The presence of calcium in the aging- as well as the remobilizing media reduced the remobilization potential. Silver NP were mainly remobilized as heteroaggregates with natural colloids, while dissolution played a minor role. Our study indicates that the breakthrough potential of Ag NP in riverbank filtration systems is generally low, but the aging in soil increases their mobility. Remobilization processes are associated to co-mobilization with natural colloids.
    Keywords: Heteroaggregation ; Nanoparticle Transformation ; Breakthrough ; Mobility ; Reversibility ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 3
    Language: English
    In: Geoderma, 01 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.
    Keywords: Soil Water Repellency ; Treated Waste Water Irrigation ; Unstable Flow ; Preferential Flow ; Water Infiltration ; X-Ray Analysis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 4
    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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  • 5
    In: Water Resources Research, November 2018, Vol.54(11), pp.9033-9044
    Description: Structural hierarchy is a fundamental characteristic of natural porous media. Yet it provokes one of the grand challenges for the modeling of fluid flow and transport since pore‐scale structures and continuum‐scale domains often coincide independent of the observation scale. Common approaches to represent structural hierarchy build, for example, on a multidomain continuum for transport or on the coupling of the Stokes equations with Darcy's law for fluid flow. These approaches, however, are computationally expensive or introduce empirical parameters that are difficult to derive with independent observations. We present an efficient model for fluid flow based on Darcy's law and the law of Hagen‐Poiseuille that is parameterized based on the explicit pore space morphology obtained, for example, by X‐ray μ‐CT and inherently permits the coupling of pore‐scale and continuum‐scale domain. We used the resulting flow field to predict the transport of solutes via particle tracking across the different domains. Compared to experimental breakthrough data from laboratory‐scale columns with hierarchically structured porosity built from solid glass beads and microporous glass pellets, an excellent agreement was achieved without any calibration. Furthermore, we present different test scenarios to compare the flow fields resulting from the Stokes‐Brinkman equations and our approach to comprehensively illustrate its advantages and limitations. In this way, we could show a striking efficiency and accuracy of our approach that qualifies as general alternative for the modeling of fluid flow and transport in hierarchical porous media, for example, fractured rock or karstic aquifers. A model for the simulation of pore‐scale and continuum‐scale flow in hierarchically structured porous media is developed Explicit pore space morphology obtained by image analysis of X‐ray micro‐CT images is used for parameterization Predictions of solute breakthrough obtained by particle tracking perfectly match observations
    Keywords: Darcy'S Law ; Particle Tracking ; Column Experiments ; X‐Ray Μ‐Ct ; Pore Space Morphology ; Image Analysis
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 6
    In: Ecohydrology, September 2018, Vol.11(6), pp.n/a-n/a
    Description: By applying the newly developed flow cell (FC) concept, this study investigated the impact of small‐scale spatial variations (millimetre to centimetre) in organic matter (OM) composition (diffusive reflectance infrared Fourier transform spectroscopy), biological activity (zymography), and wettability (contact angle [CA]) on transport processes (tracer experiments, radiography). Experiments were conducted in five undisturbed soil slices (millimetre apart), consisting of a sandy matrix with an embedded loamy band. In the loamy band increased enzyme activities and OM (10 mm apart) were found compared with the sand matrix, with no interrelations although spatial autocorrelation ranges were up to 7 cm. CAs were increased (0–110°) above the loamy band and were negatively correlated with acid phosphatase. Missing correlations were probably attributed to texture variations between soil slices. A general correlation between CA and C content (bulk) were confirmed. Variability in texture and hydraulic properties led to the formation of heterogeneous flow patterns and probably to heterogeneously distributed interfacial properties. The new FC concept allows process evaluation on the millimetre scale to analyse spatial relations, that is, between small‐scale textural changes on transport processes and biological responses. The concept has been proved as a versatile tool to analyse spatial distribution of biological and interfacial soil properties in conjunction with the analysis of complex micro‐hydraulic processes for undisturbed soil samples. The concept may be improved by additional nondestructive imaging methods, which is especially challenging for the detection of small‐scale textural changes.
    Keywords: Drift Spectroscopy ; Extracellular Enzyme Activity ; Flow Cell ; Soil Water Repellency ; Transport Processes ; Undisturbed Soil ; X‐Ray Radiography
    ISSN: 1936-0584
    E-ISSN: 1936-0592
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  • 7
    In: Land Degradation & Development, September 2018, Vol.29(9), pp.3112-3126
    Description: Bioeconomy strategies have been adopted in many countries around the world. Their sustainable implementation requires a management of soils that maintains soil functions and avoids land degradation. Only then, ecosystem services can be maintained and resources used efficiently. We present an analytical framework for impact assessment that links policy and technology driving forces for soil management decisions to soil processes, soil functional changes, and their impacts on ecosystem services and resource use efficiency, both being targets that have been set by society and are anchored in bioeconomy policy strategies and sustainable development goals. Although the resource use efficiency concept has a long‐term tradition, most studies of agricultural management do not address the role of soils in their efficiency assessment. The concept of ecosystem services has received increasing attention over the last years; however, its link to soil functions and soil management practices is still not well established. This study is the first to conceptually link the socioeconomic processes of external drivers for soil management with the natural processes of soil functions and connect them back to impacts on the social system. Application of the framework helps strengthen the science‐policy interface and to systemically assess and compare the opportunities and threats of soil management practices from the perspective of goals set by society at different spatial and temporal scales. Insights gained in this way can be applied in stakeholder decision‐making processes and used to inform the design of governance instruments aimed at sustainable soil management within a bioeconomy.
    Keywords: Bioeconomy ; Ecosystem Services ; Impact Assessment ; Resource Use Efficiency ; Soil Management Practices ; Sustainable Development Goals
    ISSN: 1085-3278
    E-ISSN: 1099-145X
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  • 8
    Language: English
    In: Soil & Tillage Research, January 2018, Vol.175, pp.205-216
    Description: In recent years, there has been an increased application of conservation-oriented tillage techniques, where instead of being turned the soil is only loosened or not tilled at all. Strip tillage, a special form of conservation tillage, results in small-scale structural differences, since tillage is performed only within the seed row, while the soil between seed rows is not tilled. However, tillage always impacts upon physical soil properties and processes. A combined application of conventional soil mechanical methods and X-ray computed tomography (X-ray CT) is employed here in order to investigate small-scale structural differences in a chernozem (texture 0–30 cm: silt loam) located in central Germany under strip tillage (within and between seed rows) compared to no tillage and mulch tillage. Apart from recording changes over time (years: 2012, 2014, 2015) to dry bulk density and saturated conductivity at soil depths 2–8 and 12–18 cm, stress-strain tests were conducted to map mechanical behaviour for a load range of 5–550 kPa at a soil depth of 12–18 cm (year 2015). Mechanical precompression stress was determined from the stress-dry bulk density curves. In addition, computed tomography scans were created followed by quantitative image analysis of the morphometric parameters mean macropore diameter, macroporosity, connectivity and anisotropy of the same soil samples. For strip tillage between seed rows and no tillage, a significant increase in dry bulk density was observed over time compared to strip tillage within the seed row and mulch tillage. This was more pronounced at a soil depth of 2–8 cm than at 12–18 cm. Despite higher dry bulk density, strip tillage between the seed row displayed also an increasing saturated conductivity compared to strip tillage within the seed row and mulch tillage. The computed tomography scans showed that the macropores became more compressed and soil aggregates were pushed together as mechanical stress increased, with the aggregate arrangement being transformed down into a coherent soil mass. The soil mechanical and morphometric parameters supported each other in terms of what they revealed about the mechanical properties of the soil structures. For instance, in the strip tillage between seed rows and no tillage treatments, the lack of soil tillage not only resulted in higher dry bulk densities, but also higher aggregate densities, mechanical precompression stress values, mean macropore diameters as well as lower macroporosity and connectivity values compared to mulch tillage and strip tillage within the seed row. The computed tomography parameters are therefore highly suitable for providing Supplementary information about the compaction process. Overall, this study showed that strip tillage combines the advantages of no tillage and a deeper, soil conservation-oriented primary tillage because, on a small scale, it creates two distinct soil structures which are beneficial in terms of optimal plant growth as well as mechanical resistance by driving over the soil.
    Keywords: Pre-Compression Stress ; Dry Bulk Density ; Aggregate Density ; Image Analysis ; Soil Compaction ; Agriculture
    ISSN: 0167-1987
    E-ISSN: 1879-3444
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  • 9
    Language: English
    In: Geoderma, 01 September 2018, Vol.325, pp.37-48
    Description: Organic particles including microorganisms are a significant fraction of the mobile organic matter (MOM) pool that contributes to initial pedogenesis. Still, the dynamics and the interplay of the multitude of processes that control the mobilization, transport, and retention of MOM are vastly unclear. We studied this interplay using an ‘artificial soil’ as model for a young, unstructured soil with defined initial composition employing a novel two-layer column experiment. The upstream layer was composed of a mixture of well-defined mineral phases, a sterile organic matter source and a diverse, natural microbial inoculant mimicking an organic-rich topsoil. The downstream layer, mimicking the subsoil, was composed of the mineral phases, only. Columns were run under water-unsaturated flow conditions with multiple flow interruptions to reflect natural flow regimes and to detect possible non-equilibrium processes. Pore system changes caused by flow were inspected by scanning electron microscopy and computed micro-tomography. MOM-related physicochemical effluent parameters and bacterial community diversity and abundance were assessed by molecular analysis of the effluent and the solid phase obtained after the long-term irrigation experiment (75 d). Tomographic data showed homogeneous packing of the fine-grained media (sandy loam). During flow, the initially single-grain structured artificial soil showed no connected macropores. In total, 6% of the initial top layer organic matter was mobile. The release and transport of particulate (1.2%) and dissolved organic matter (4.8%) including bacteria were controlled by non-equilibrium conditions. Bacterial cells were released and selectively transported to downstream layer resulting in a depth-dependent and selective establishment of bacterial communities in the previously sterile artificial soil. This study underlines the importance of bacterial transport from the surface or topsoil for colonization and maturation of downstream compartments. This initial colonization of pristine surfaces is the major step in forming biogeochemical interfaces - the prominent locations of intensive biological activity and element turnover that seem to play a major role for the functioning of soil.
    Keywords: Mobile Organic Matter ; Unsaturated Two-Layer Column Experiment ; Experimental Pedogenesis ; Artificial Soil ; Computed Micro-Tomography ; Molecular Analysis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 10
    Language: English
    In: Frontiers in Environmental Science, 01 April 2018, Vol.6
    Description: Soil-borne nitrous oxide (N2O) emissions have a high spatial and temporal variability which is commonly attributed to the occurrence of hotspots and hot moments for microbial activity in aggregated soil. Yet there is only limited information about the biophysical processes that regulate the production and consumption of N2O on microscopic scales in undisturbed soil. In this study, we introduce an experimental framework relying on simplified porous media that circumvents some of the complexities occuring in natural soils while fully accounting for physical constraints believed to control microbial activity in general and denitrification in particular. We used this framework to explore the impact of aggregate size and external oxygen concentration on the kinetics of O2 consumption, as well as CO2 and N2O production. Model aggregates of different sizes (3.5 vs. 7 mm diameter) composed of porous, sintered glass were saturated with a defined growth medium containing roughly 109 cells ml−1 of the facultative anaerobic, nosZ-deficient denitrifier Agrobacterium tumefaciens with N2O as final denitrification product and incubated at five different oxygen levels (0–13 vol-%). We demonstrate that the onset of denitrification depends on the amount of external oxygen and the size of aggregates. Smaller aggregates were better supplied with oxygen due to a larger surface-to-volume ratio, which resulted in faster growth and an earlier onset of denitrification. In larger aggregates, the onset of denitrification was more gradual, but with comparably higher N2O production rates once the anoxic aggregate centers were fully developed. The normalized electron flow from the reduced carbon substrate to N-oxyanions (edenit-/etotal- ratio) could be solely described as a function of initial oxygen concentration in the headspace with a simple, hyperbolic model, for which the two empirical parameters changed with aggregate size in a consistent way. These findings confirm the important role of soil structure on N2O emissions from denitrification by shaping the spatial patterns of microbial activity and anoxia in aggregated soil. Our dataset may serve as a benchmark for constraining or validating spatially explicit, biophysical models of denitrification in aggregated soil.
    Keywords: Greenhouse Gas Emissions ; Denitrification Kinetics ; Microbial Hotspots ; Microsites ; Anoxic Aggregate Centers ; Agrobacterium Tumefaciens ; Environmental Sciences
    E-ISSN: 2296-665X
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