Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • General
Type of Medium
Language
Year
  • 1
    Language: English
    In: Ecological Modelling, 24 February 2015, Vol.298, pp.1-3
    Keywords: Environmental Sciences ; Ecology
    ISSN: 0304-3800
    E-ISSN: 1872-7026
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(5), p.0
    Description: The guest editors introduce the seven contributions to the special issue on processes in capillary fringes, with a focus on the complex interaction of biological, chemical, and physical processes in this environemnt. Processes in capillary fringes (CFs) have a complex nature due to the interactions between the solid, liquid, and gaseous environments. Despite a considerable body of literature on CFs coming from different disciplines, the ongoing processes and their complex interactions are yet only partially understood.
    Keywords: Soils ; Solids ; Vadose Water ; Methods and Instruments ; General;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    In: Water Resources Research, May 2014, Vol.50(5), pp.4514-4529
    Description: A major difficulty in modeling multiphase flow in porous media is the emergence of trapped phases. Our experiments demonstrate that gas can be trapped in either single‐pores, multipores, or in large connected networks. These large connected clusters can comprise up to eight grain volumes and can contain up to 50% of the whole trapped gas volume. About 85% of the gas volume is trapped by gas clusters. This variety of possible trapped gas clusters of different shape and volume will lead to a better process understanding of bubble‐mediated mass transfer. Since multipore gas bubbles are in contact with the solid surface through ultrathin adsorbed water films the interfacial area between trapped gas clusters and intergranular capillary water is only about 80% of the total gas surface. We could derive a significant (R = 0.98) linear relationship between the gas‐water‐interface and gas saturation. We found no systematic dependency of the front velocity of the invading water phase in the velocity range from 0.1 to 0.6 cm/min corresponding to capillary numbers from 2 × 10 to 10. Our experimental results indicate that the capillary trapping mechanism is controlled by the local pore structure and local connectivity and not by thermodynamics, i.e., by the minimum of the , at least in the considered velocity range. Consistent with this physical picture is our finding that the trapping frequency (= bubble‐size distribution) reflects the pore size distribution for the whole range of pore radii, i.e., the capillary trapping process is determined by statistics and not by thermodynamics. No systematic dependency of trapping efficiency on capillary number Majority of trapped gas bubbles (85%) are multipore trapped Trapping of gas clusters is determined by statistics and not by thermodynamics
    Keywords: Gas Clusters ; Capillary Trapping ; Interfacial Area
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(5), p.0
    Description: We used X-ray computed microtomography to study gas trapping in a fluctuating water table. Our results show that capillary forces control trapping and phase distribution in dynamic capillary fringes. In porous media, the nonwetting phase is trapped on water saturation due to capillary forces acting in a heterogeneous porous structure. Within the capillary fringe, the gas phase is trapped and released along with the fluctuation of the water table, creating a highly active zone for biological transformations and mass transport. We conducted column experiments to observe and quantify the magnitude and structure of the trapped gas phase at the pore scale using computed microtomography. Different grain size distributions of glass beads were used to study the effect of the pore structure on trapping at various capillary numbers. Viscous forces were found to have negligible impact on phase trapping compared with capillary and buoyancy forces. Residual gas saturations ranged from 0.5 to 10%, while residual saturation increased with decreasing grain size. The gas phase was trapped by snap-off in single pores but also in pore clusters, while this single-pore trapping was dominant for grains larger than 1 mm in diameter. Gas surface area was found to increase linearly with increasing gas volume and with decreasing grain size.
    Keywords: Grain Size ; Water Table ; Mass Transport ; Buoyancy ; Pores ; Porous Media ; Particle Size ; Water Table ; Saturation ; Vadose Water ; Fluctuations ; Trapping ; Buoyancy ; Methods and Instruments ; General;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    In: Water Resources Research, November 2015, Vol.51(11), pp.9094-9111
    Description: We study the impact of pore structure and surface roughness on capillary trapping of nonwetting gas phase during imbibition with water for capillary numbers between 10 and 5 × 10, within glass beads, natural sands, glass beads monolayers, and 2‐D micromodels. The materials exhibit different roughness of the pore‐solid interface. We found that glass beads and natural sands, which exhibit nearly the same grain size distribution, pore size distribution, and connectivity, showed a significant difference of the trapped gas phase of about 15%. This difference can be explained by the microstructure of the pore‐solid interface. Based on the visualization of the trapping dynamics within glass beads monolayers and 2‐D micromodels, we could show that bypass trapping controls the trapping process in glass beads monolayers, while snap‐off trapping controls the trapping process in 2‐D micromodels. We conclude that these different trapping processes are the reason for the different trapping efficiency, when comparing glass beads packs with natural sand packs. Moreover, for small capillary numbers of 10, we found that the cluster size distribution of trapped gas clusters of all 2‐D and 3‐D porous media can be described by a universal power law behavior predicted from percolation theory. This cannot be expected a priori for 2‐D porous media, because bicontinuity of the two bulk phases is violated. Obviously, bicontinuity holds for the thin‐film water phase and the bulk gas phase. The snap‐off trapping process leads to ordinary bond percolation in front of the advancing bulk water phase and is the reason for the observed universal power law behavior in 2‐D micromodels with rough surfaces. Surface roughness controls capillary trapping efficiency The transition‐zone model can be applied to 2‐D micromodels with rough surfaces The 2‐D and 3‐D porous media belong all to the same universality class
    Keywords: Surface Roughness ; Precursor Thin‐Film Flow ; Snap‐Off Trapping ; Universal Power Law ; Ordinary Bond Percolation
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: Journal of Soils and Sediments, 10/2015, Vol.15(10), pp.2155-2173
    Description: Issue Title: Advances in Sediment Fingerprinting Purpose Water reservoirs around the world suffer from accelerated sediment loads and, consequently, contamination. Notably, in water-scarce regions such as Jordan, this poses a threat to an important water source, and identifying the sediment sources is an important task. Thus, a sediment fingerprinting study in the Wadi Al-Arab catchment of northern Jordan was implemented with special attention directed to the development of suitable correction factors necessary to improve the comparability of source and sink sediments. The selection of seven conservative elements for the sediment fingerprinting was made, with specific attention directed to the chemical environment of the reservoir. Materials and methods Thirty-six samples from six different surface and subsurface sources and 38 sink samples from the Wadi Al-Arab reservoir were collected. In total, 27 organic and inorganic elements as well as radionuclides were analysed. Two vertical physicochemical water profiles provided information on the pH and Eh conditions and common element concentrations. The stepwise multiple regression analysis model (SMRAM) was developed to explore parameters that influence the element concentrations and their interrelations, and to calculate an element-specific correction factor. The standard selection procedure was expanded by the comparison of water and sink sediment element concentrations, a literature review concerning the pH and Eh conditions and, in selected cases, a correlation analysis. Results and discussion The combination of Al, Cr, Mn, Fe, ^sup 232^Th, ^sup 228^Th and ^sup 137^Cs provided the best source discrimination, and based on Monte Carlo simulations, the mixing model revealed the existence of three major sediment source areas. These are as follows: (i) olive orchards on slopes, which delivered 59±8 % of the sediments in the sink; (ii) cultivated fields on plateau and saddle positions contributed 11±9 %; and (iii) slopes with natural vegetation used for grazing contributed 29±15 % of the deposited sediment. With a mean residual error of 1.04 %, the sum of the source concentrations differs only slightly from sink concentrations and proves that the model is reliable. Conclusions The SMRAM model revealed that the different inorganic (total inorganic carbon, TIC) and organic (total organic carbon, TOC) carbon contents and the clay/sand content influence the element concentrations of the sediment samples. Due to the carbonatic environment, it was mainly necessary to correct for TIC. Applying an expanded literature review regarding the chemical environment under investigation, in addition to the standard mass conservation and Kruskal-Wallis test, prevented possible non-conservative elements from entering the discriminant analysis.
    Keywords: Sediment Transport ; Reservoirs ; Grain Size ; Soil Erosion ; Correction Factors ; Grain Size Selectivity ; Jordan ; Soil Erosion ; Stepwise Multiple Regression;
    ISSN: 1439-0108
    E-ISSN: 1614-7480
    Source: Springer (via CrossRef)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    In: Journal of Contaminant Hydrology, December 2016, Vol.195, pp.31-39
    Description: Engineered nanoparticles released into soils may be coated with humic substances, potentially modifying their surface properties. Due to their amphiphilic nature, humic coating is expected to affect interaction of nanoparticle at the air-water interface. In this study, we explored the roles of the air-water interface and solid-water interface as potential sites for nanoparticle attachment and the importance of hydrophobic interactions for nanoparticle attachment at the air-water interface. By exposing Ag nanoparticles to soil solution extracted from the upper soil horizon of a floodplain soil, the mobility of the resulting “soil-aged” Ag nanoparticles was investigated and compared with the mobility of citrate-coated Ag nanoparticles as investigated in an earlier study. The mobility was determined as a function of hydrologic conditions and solution chemistry using column breakthrough curves and numerical modeling. Specifically, we compared the mobility of both types of nanoparticles for different unsaturated flow conditions and for pH = 5 and pH = 9. The soil-aged Ag NP were less mobile at pH = 5 than at pH = 9 due to lower electrostatic repulsion at pH = 5 for both types of interfaces. Moreover, the physical flow field at different water contents modified the impact of chemical forces at the solid-water interface. An extended Derjaguin-Landau-Verwey-Overbeek (eDLVO) model did not provide satisfactory explanation of the observed transport phenomena unlike for the citrate-coated case. For instance, the eDLVO model assuming sphere-plate geometry predicts a high energy barrier (〉 90 ) for the solid-water interface, indicating that nanoparticle attachment is less likely. Furthermore, retardation through reversible sorption at the air-water interface was probably less relevant for soil-aged nanoparticles than for citrate-coated nanoparticles. An additional cation bridging mechanism and straining within the flow field may have enhanced nanoparticle retention at the solid-water interface. The results indicate that the mobility of engineered Ag nanoparticles is sensitive to solution chemistry, especially pH and the concentration of multivalent cations, and to the unsaturated flow conditions influencing particle interaction at biogeochemical interfaces.
    Keywords: Unsaturated Transport ; Water Dynamics ; Cation Bridging ; Amphiphilic ; Edlvo ; Engineering ; Environmental Sciences ; Geography
    ISSN: 0169-7722
    E-ISSN: 1873-6009
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    In: Soil Science, 2014, Vol.179(6), pp.273-283
    Description: ABSTRACT: Soil aggregates are useful indicators of soil structure and stability, and the impact on physical and mechanical aggregate properties is critical for the sustainable use of organic amendments in agricultural soil. In this work, we evaluated the short-term soil quality effects of applying biochar (0–10 kg m), in combination with swine manure (2.1 and 4.2 kg m), to a no-till maize (Zea mays L.) cropping system on a sandy loam soil in Denmark. Topsoil (0–20 cm) aggregates were analyzed for clay dispersibility, aggregate stability, tensile strength (TS), and specific rupture energy (SRE) using end-over-end shaking, a Yoder-type wet-sieving method, and an unconfined compression test in soil samples collected 7 and 19 months after final biochar application. The highest rates of biochar and swine manure application resulted in the highest aggregate stability and lowest clay dispersibility. Applying both amendments systematically increased TS and SRE for large aggregates (4–8 and 8–16 mm) but not for small aggregates (1–2 and 2–4 mm). Increased biochar application also decreased the friability index of soil aggregates. Based on X-ray visualization, it was found that aggregates containing larger amounts of biochar particles had higher TS and SRE probably because of bonding effects. Based on the improved soil aggregate properties, we suggest that biochar can be effective for increasing and sustaining overall soil quality, for example, related to minimizing the soil erosion potential.
    Keywords: Denmark ; Corn ; Soil Sciences ; Sustainable Development ; Organic Farming ; Tensile Strength ; Clay ; Soil Erosion Control;
    ISSN: 0038-075X
    E-ISSN: 15389243
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    In: Water Resources Research, March 2007, Vol.43(3), pp.n/a-n/a
    Description: Large‐scale models of transient flow processes in the unsaturated zone require, in general, upscaling of the flow problem in order to capture the impact of heterogeneities on a small scale, which cannot be resolved by the model. Effective parameters for the upscaled models are often derived from second‐order stochastic properties of the parameter fields. Such properties are good quantifications for parameter fields, which are multi‐Gaussian. However, the structure of soil does rarely resemble these kinds of fields. The non‐multi‐Gaussian field properties can lead to strong discrepancies between predictions of upscaled models and the averaged real flow process. In particular, the connected paths of parameter ranges of the medium are important features, which are usually not taken into account in stochastic approaches. They are determined here by the Euler number of one‐cut indicator fields. Methods to predict effective parameters are needed that incorporate this type of information. We discuss different simple and fast approaches for estimating the effective parameter for upscaled models of slow transient flow processes in the unsaturated zone, where connected paths of the material may be taken into account. Upscaled models are derived with the assumption of capillary equilibrium. The effective parameters are calculated using effective media approaches. We also discuss the limits of the applicability of these methods.
    Keywords: Richards Equation ; Unsaturated Flow ; Upscaling
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages