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
  • Elsevier (CrossRef)  (92)
Type of Medium
Language
Year
  • 1
    Language: English
    In: Water Research, 01 May 2013, Vol.47(7), pp.2572-2582
    Description: Saturated sand-packed column experiments were conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized silver nanoparticles (AgNPs). The normalized concentration in breakthrough curves (BTCs) of AgNPs increased with a decrease in solution ionic strength (IS), and an increase in water velocity, sand grain size, and input concentration ( ). In contrast to conventional filtration theory, retention profiles (RPs) for AgNPs exhibited uniform, nonmonotonic, or hyperexponential shapes that were sensitive to physicochemical conditions. The experimental BTCs and RPs with uniform or hyperexponential shape were well described using a numerical model that considers time- and depth-dependent retention. The simulated maximum retained concentration on the solid phase ( ) and the retention rate coefficient ( ) increased with IS and as the grain size and/or decreased. The RPs were more hyperexponential in finer textured sand and at lower because of their higher values of . Conversely, RPs were nonmonotonic or uniform at higher and in coarser sand that had lower values of , and tended to exhibit higher peak concentrations in the RPs at lower velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when was approaching filled conditions. Nonmonotonic RPs had peak concentrations at greater distances in the presence of excess amounts of surfactant, suggesting that competition between AgNPs and surfactant diminished close to the column inlet. The sensitivity of the nonmonotonic RPs to IS and velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary minimum. However, elimination of the secondary minimum only produced recovery of a small portion (〈10%) of the retained AgNPs. These results imply that AgNPs were largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity. ► The presence of surfactant affected the shape of the retention profiles (RPs). ► RPs transitioned from hyperexponential, to nonmonotonic, and then to uniform. ► Nanoparticles mainly irreversibly interacted with microscopic heterogeneity.
    Keywords: Stabilized Silver Nanoparticles ; Saturated Porous Media ; Time- and Depth-Dependent Retention ; Surfactant ; Competitive Attachment ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Journal of Hydrology, October 2015, Vol.529, pp.1754-1767
    Description: Soil moisture plays a key role in the water and energy balance in soil, vegetation and atmosphere systems. According to Wood et al. (2011) there is a grand need to increase global-scale hyper-resolution water–energy–biogeochemistry land surface modelling capabilities. These modelling capabilities should also recognize epistemic uncertainties, as well as the nonlinearity and hysteresis in its dynamics. Unfortunately, it is not clear how to parameterize hydrological processes as a function of scale, and how to test deterministic models with regard to epistemic uncertainties. In this study, high resolution long-term simulations were conducted in the highly instrumented TERENO hydrological observatory of the Wüstebach catchment. Soil hydraulic parameters were derived using inverse modelling with the Hydrus-1D model using the global optimization scheme SCE-UA and soil moisture data from a wireless soil moisture sensor network. The estimated parameters were then used for 3D simulations of water transport using the integrated parallel simulation platform ParFlow-CLM. The simulated soil moisture dynamics, as well as evapotranspiration (ET) and runoff, were compared with long-term field observations to illustrate how well the model was able to reproduce the water budget dynamics. We investigated different anisotropies of hydraulic conductivity to analyze how fast lateral flow processes above the underlying bedrock affect the simulation results. For a detail investigation of the model results we applied the empirical orthogonal function (EOF) and wavelet coherence methods. The EOF analysis of temporal–spatial patterns of simulated and observed soil moisture revealed that introduction of heterogeneity in the soil porosity effectively improves estimates of soil moisture patterns. Our wavelet coherence analysis indicates that wet and dry seasons have significant effect on temporal correlation between observed and simulated soil moisture and ET. Our study demonstrates the usefulness of the EOF and wavelet coherence methods for a more in-depth validation of spatially highly resolved hydrological 3D models.
    Keywords: 3d Hydrological Simulation ; Soil Moisture ; Eof Analysis ; Wavelet Coherence Analysis ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: English
    In: Journal of Hydrology, October 2015, Vol.529, pp.872-889
    Description: Many attempts have been made to characterize particle size distribution (PSD) curves using different mathematical models, which are primarily used as a basis for estimating soil hydraulic properties. The principle step in using soil PSD to predict soil hydraulic properties is determining an accurate and continuous curve for PSD. So far, the characteristics of the PSD models, their fitting accuracy, and the effects of their parameters on the shape and position of PSD curves have not been investigated. In this study all developed PSD models, their characteristics, behavior of their parameters, and their fitting capability to the UNSODA database soil samples were investigated. Results showed that beerkan estimation of soil transfer (BEST), two and three parameter Weibull, Rosin and Rammler (1 and 2), unimodal and bimodal Fredlund, and van Genuchten models were flexible over the entire range of soil PSD. Correspondingly, the BEST, two and three parameter Weibull, Rosin and Rammler (1 and 2), hyperbolic and offset renormalized log-normal models possessed a high fitting capability over the entire range of PSD. The few parameters of the BEST, Rosin and Rammler (1 and 2), and two parameter Weibull models provides ease of use in soil physics and mechanics research. Thus, they are seemingly fit with acceptable accuracy in predicting the PSD curve. Although the fractal models have physical and mathematical basis, they do not have the adequate flexibility to contribute a description of the PSD curve. Different aspects of the PSD models should be considered in selecting a model to describe a soil PSD.
    Keywords: Fitting ; Mathematical Psd Models ; Models Parameters ; Particle Size Distribution ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Water Research, 2010, Vol.44(4), pp.1288-1296
    Description: A study was conducted to understand the role of cell concentration and metabolic state in the transport and deposition behaviour of with and without substrate addition. Column experiments using the short-pulse technique (pulse was equivalent to 0.028 pore volume) were performed in quartz sand operating under saturated conditions. For comparison, experiments with microspheres and inactive (killed) bacteria were also conducted. The effluent concentrations, the retained particle concentrations and the cell shape were determined by fluorescent microscopy. For the transport of metabolically-active without substrate addition a bimodal breakthrough curve was observed, which could be explained by the different breakthrough behaviour of the rod-shaped and coccoidal cells of . The 70:30 rod/coccoid ratio in the influent drastically changed during the transport and it was about 20:80 in the effluent and in the quartz sand packing. It was assumed that the active rod-shaped cells were subjected to shrinkage into coccoidal cells. The change from active rod-shaped cells to coccoidal cells could be explained by oxygen deficiency which occurs in column experiments under saturated conditions. Also the substrate addition led to two consecutive breakthrough peaks and to more bacteria being retained in the column. In general, the presence of substrate made the assumed stress effects more pronounced. In comparison to microspheres and inactive (killed) bacteria, the transport of metabolically-active bacteria with and without substrate addition is affected by differences in physiological state between rod-shaped and the formed stress-resistant coccoidal cells of .
    Keywords: Bacteria Transport ; Colloid Deposition ; Cell Morphology ; Physiological State ; Pseudomonas Fluorescens ; Oxygen Stress ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Water Research, 01 February 2013, Vol.47(2), pp.933-944
    Description: Water-saturated column experiments were conducted to investigate the effect of input concentration ( ) and sand grain size on the transport and retention of low concentrations (1, 0.01, and 0.005 mg L ) of functionalized C-labeled multi-walled carbon nanotubes (MWCNT) under repulsive electrostatic conditions that were unfavorable for attachment. The breakthrough curves (BTCs) for MWCNT typically did not reach a plateau, but had an asymmetric shape that slowly increased during breakthrough. The retention profiles (RPs) were not exponential with distance, but rather exhibited a hyper-exponential shape with greater retention near the column inlet. The collected BTCs and RPs were simulated using a numerical model that accounted for both time- and depth-dependent blocking functions on the retention coefficient. For a given , the depth-dependent retention coefficient and the maximum solid phase concentration of MWCNT were both found to increase with decreasing grain size. These trends reflect greater MWCNT retention rates and a greater number of retention locations in the finer textured sand. The fraction of the injected MWCNT mass that was recovered in the effluent increased and the RPs became less hyper-exponential in shape with higher due to enhanced blocking/filling of retention locations. This concentration dependency of MWCNT transport increased with smaller grain size because of the effect of pore structure and MWCNT shape on MWCNT retention. In particular, MWCNT have a high aspect ratio and we hypothesize that solid phase MWCNT may create a porous network with enhanced ability to retain particles in smaller grain sized sand, especially at higher . Results demonstrate that model simulations of MWCNT transport and fate need to accurately account for observed behavior of both BTCs and RPs. ► Breakthrough curves and retention profiles were measured and numerically modeled. ► We used very low (0.005–1 mg L ) input concentrations of carbon nanotubes (CNTs). ► Breakthrough of CNTs increased with increasing input concentration and grain size. ► Data were simulated well using time- and depth-dependent retention coefficients. ► Model predictions indicate the transport of CNTs to distances greater than 12 cm.
    Keywords: Carbon Nanotubes ; Column Experiments ; Quartz Sand ; Breakthrough Curves ; Retention Profiles ; Transport Modeling ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: Chemosphere, 2011, Vol.84(4), pp.409-414
    Description: ► The sorption of a branched nonylphenol isomer (NP111) on humic acids was investigated by a dialysis technique. ► Humic acids were characterized by solid-state C DP/MAS NMR spectroscopy. ► A relationship between the organic carbon-normalized sorption coefficients of NP111 and the aliphaticity of humic acids was established. By using dialysis equilibrium experiments, the sorption of a branched nonylphenol isomer [4-(1-ethyl-1,3-dimethylpentyl)-phenol] (NP111) on various humic acids (HAs) isolated from river sediments and two reference HAs was studied. The HAs were characterized by solid-state C direct polarization/magic angle spinning nuclear magnetic resonance ( C DP/MAS NMR) spectroscopy. Sorption isotherms of NP111 on HAs were described by a linear model. The organic carbon-normalized sorption coefficient ( ) ranged from 2.3 × 10 to 1.5 × 10 L kg . Interestingly, a clear correlation between value and alkyl C content was observed, indicating that the aliphaticity of HAs markedly dominates the sorption of NP111. These new mechanistic insights about the NP111 sorption indicate that the fate of nonylphenols in soil or sediment depends not only on the content of HA, but also on its structural composition.
    Keywords: Branched Nonylphenol ; Sorption ; Humic Acids ; NMR ; Aliphaticity ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Language: English
    In: Journal of Hydrology, 2011, Vol.399(3), pp.410-421
    Description: ► Top soil moisture observations for estimation of hydraulic parameters. ► Simultaneous update of model states (soil moisture) and hydraulic parameters. ► SIR-PF for propagation of non-Gaussian distributions through a nonlinear model. ► Estimation of hydr. parameters driven by non linearity between SM and pressure head. In a synthetic study we explore the potential of using surface soil moisture measurements obtained from different satellite platforms to retrieve soil moisture profiles and soil hydraulic properties using a sequential data assimilation procedure and a 1D mechanistic soil water model. Four different homogeneous soil types were investigated including loamy sand, loam, silt, and clayey soils. The forcing data including precipitation and potential evapotranspiration were taken from the meteorological station of Aachen (Germany). With the aid of the forward model run, a synthetic data set was designed and observations were generated. The virtual top soil moisture observations were then assimilated to update the states and hydraulic parameters of the model by means of a particle filtering data assimilation method. Our analyses include the effect of assimilation strategy, measurement frequency, accuracy in surface soil moisture measurements, and soils differing in textural and hydraulic properties. With this approach we were able to assess the value of periodic spaceborne observations of top soil moisture for soil moisture profile estimation and identify the adequate conditions (e.g. temporal resolution and measurement accuracy) for remotely sensed soil moisture data assimilation. Updating of both hydraulic parameters and state variables allowed better predictions of top soil moisture contents as compared with updating of states only. An important conclusion is that the assimilation of remotely-sensed top soil moisture for soil hydraulic parameter estimation generates a bias depending on the soil type. Results indicate that the ability of a data assimilation system to correct the soil moisture state and estimate hydraulic parameters is driven by the non linearity between soil moisture and pressure head.
    Keywords: Soil Moisture ; Data Assimilation ; Particle Filter ; Sequential Importance Resampling ; Hydrus-1d ; Smos ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: Water Research, 01 February 2017, Vol.109, pp.358-366
    Description: Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L ) of functionalized C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca in comparison to K , and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca in comparison to K . Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K displaced Ca ) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that 〉23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca than K . These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs.
    Keywords: Multi-Walled Carbon Nanotubes ; Soil ; Breakthrough Curves ; Retention Profiles ; Cation Exchange ; Soil Fractionation ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Language: English
    In: Soil Biology and Biochemistry, May 2015, Vol.84, pp.107-115
    Description: Despite the fact that microbial nitrification and denitrification are considered the major soil N O emission sources, especially from agricultural soils, several abiotic reactions involving the nitrification intermediate hydroxylamine (NH OH) have been identified leading to N O emissions, but are being neglected in most current studies. Here, we studied N O formation from NH OH in cropland, grassland, and forest soils in laboratory incubation experiments. Incubations were conducted with and without the addition of NH OH to non-sterile and sterile soil samples. N O evolution was quantified with gas chromatography and further analyzed with online laser absorption spectroscopy. Additionally, the isotopic signature of the produced N O (δ N, δ O, and N site preference) was analyzed with isotope ratio mass spectrometry. While the forest soil samples showed hardly any N O evolution upon the addition of NH OH, immediate and very large formation of N O was observed in the cropland soil, also in sterilized samples. Correlation analysis revealed soil parameters that might explain the variability of NH OH-induced N O production to be: soil pH, C/N ratio, and Mn content. Our results suggest a coupled biotic–abiotic production of N O during nitrification, e.g. due to leakage of the nitrification intermediate NH OH with subsequent reaction with the soil matrix.
    Keywords: Coupled Biotic–Abiotic Process ; Nitrification ; Intermediate ; N2o ; Nh2oh ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
    Source: ScienceDirect Journals (Elsevier)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    In: Journal of Hydrology, May 2016, Vol.536, pp.365-375
    Description: In distributed hydrological modelling one often faces the problem that input data need to be aggregated to match the model resolution. However, aggregated data may be too coarse for the parametrization of the processes represented. This dilemma can be circumvented by the adjustment of certain model parameters. For instance, the reduction of local hydraulic gradients due to spatial aggregation can be partially compensated by increasing soil hydraulic conductivity. In this study, we employed the information entropy concept for the scale dependent parameterization of soil hydraulic conductivity. The loss of information content of terrain curvature as consequence of spatial aggregation was used to determine an amplification factor for soil hydraulic conductivity to compensate the resulting retardation of water flow. To test the usefulness of this approach, continuous 3D hydrological simulations were conducted with different spatial resolutions in the highly instrumented Wüstebach catchment, Germany. Our results indicated that the introduction of an amplification factor can effectively improve model performances both in terms of soil moisture and runoff simulation. However, comparing simulated soil moisture pattern with observation indicated that uniform application of an amplification factor can lead to local overcorrection of soil hydraulic conductivity. This problem could be circumvented by applying the amplification factor only to model grid cells that suffer from high information loss. To this end, we tested two schemes to define appropriate location-specific correction factors. Both schemes led to improved model performance both in terms of soil water content and runoff simulation. Thus, we anticipate that our proposed scaling approach is useful for the application of next-generation hyper-resolution global land surface models.
    Keywords: Scale Dependent Parameterization ; 3d Hydrological Modelling ; Topographical Information Content ; Soil Hydraulic Conductivity ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    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