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  • MEDLINE/PubMed (NLM)  (66)
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  • 1
    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
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  • 2
    In: Nature, 2016, Vol.536(7617), p.E1
    Description: In their study, Evaristo et al.1 collected an extensive data set on the basis of which they statistically determined the isotopic compositions of the plant water source (δ 18Ointersect and δ 2Hintersect, called respectively δ 18Ointercept and δ 2Hintercept in their paper) as the x and y coordinates in (δ 18O, δ 2H) space of the intersection between the local meteoric water line (LMWL) and the plant xylem water 'evaporation line' (EL) for a range of climates and vegetation types.
    Keywords: Isotopes ; Groundwater ; Groundwater Recharge ; Stream Flow ; Precipitation ; Botany ; Flowers & Plants;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 3
    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
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  • 4
    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
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  • 5
    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
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  • 6
    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
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  • 7
    In: Global Change Biology, March 2017, Vol.23(3), pp.1338-1352
    Description: Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer‐reviewed papers and conducted a meta‐analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil (12%) and soil total N (210%), although it decreased soil (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil NO fluxes as well as hydrological and fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen () flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta‐analysis. Overall, this meta‐analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro‐ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro‐ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized.
    Keywords: Costal Ecosystem ; Denitrification ; Dissimilatory Nitrate Reduction To Ammonium Dnra ; Nitrogen Cycle ; Salinity Intrusion ; Sea‐Level Rise ; Soil Salinization
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 8
    Language: English
    In: Water Research, 01 March 2014, Vol.50, pp.294-306
    Description: Atrazine was banned in Germany in 1991 due to findings of atrazine concentrations in ground- and drinking waters exceeding threshold values. Monitoring of atrazine concentrations in the groundwater since then provides information about the resilience of the groundwater quality to changing agricultural practices. In this study, we present results of a monitoring campaign of atrazine concentrations in the Zwischenscholle aquifer. This phreatic aquifer is exposed to intensive agricultural land use and susceptible to contaminants due to a shallow water table. In total 60 observation wells (OWs) have been monitored since 1991, of which 15 are sampled monthly today. Descriptive statistics of monitoring data were derived using the “regression on order statistics” (ROS) data censoring approach, estimating values for nondetects. The monitoring data shows that even 20 years after the ban of atrazine, the groundwater concentrations of sampled OWs remain on a level close to the threshold value of 0.1 μg l without any considerable decrease. The spatial distribution of atrazine concentrations is highly heterogeneous with OWs exhibiting permanently concentrations above the regulatory threshold on the one hand and OWs were concentrations are mostly below the limit of quantification (LOQ) on the other hand. A deethylatrazine-to-atrazine ratio (DAR) was used to distinguish between diffuse – and point-source contamination, with a global mean value of 0.84 indicating mainly diffuse contamination. Principle Component Analysis (PCA) of the monitoring dataset demonstrated relationships between the metabolite desisopropylatrazine, which was found to be exclusively associated with the parent compound simazine but not with atrazine, and between deethylatrazine, atrazine, nitrate, and the specific electrical conductivity. These parameters indicate agricultural impacts on groundwater quality. The findings presented in this study point at the difficulty to estimate mean concentrations of contamination for entire aquifers and to evaluate groundwater quality based on average parameters. However, analytical data of monthly sampled single observation wells provide adequate information to characterize local contamination and evolutionary trends of pollutant concentration.
    Keywords: Atrazine ; Groundwater Monitoring ; DAR ; Nondetects ; Data Censoring ; Principle Component Analysis ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 9
    Language: English
    In: Science of the Total Environment, 01 May 2018, Vol.622-623, pp.954-973
    Description: Terrestrial environmental systems are characterised by numerous feedback links between their different compartments. However, scientific research is organized into disciplines that focus on processes within the respective compartments rather than on interdisciplinary links. Major feedback mechanisms between compartments might therefore have been systematically overlooked so far. Without identifying these gaps, initiatives on future comprehensive environmental monitoring schemes and experimental platforms might fail. We performed a comprehensive overview of feedbacks between compartments currently represented in environmental sciences and explores to what degree missing links have already been acknowledged in the literature. We focused on process models as they can be regarded as repositories of scientific knowledge that compile findings of numerous single studies. In total, 118 simulation models from 23 model types were analysed. Missing processes linking different environmental compartments were identified based on a meta-review of 346 published reviews, model intercomparison studies, and model descriptions. Eight disciplines of environmental sciences were considered and 396 linking processes were identified and ascribed to the physical, chemical or biological domain. There were significant differences between model types and scientific disciplines regarding implemented interdisciplinary links. The most wide-spread interdisciplinary links were between physical processes in meteorology, hydrology and soil science that drive or set the boundary conditions for other processes (e.g., ecological processes). In contrast, most chemical and biological processes were restricted to links within the same compartment. Integration of multiple environmental compartments and interdisciplinary knowledge was scarce in most model types. There was a strong bias of suggested future research foci and model extensions towards reinforcing existing interdisciplinary knowledge rather than to open up new interdisciplinary pathways. No clear pattern across disciplines exists with respect to suggested future research efforts. There is no evidence that environmental research would clearly converge towards more integrated approaches or towards an overarching environmental systems theory.
    Keywords: Review ; Interdisciplinary Links ; Integrated Environmental Modelling ; Research Needs ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 10
    In: Global Change Biology, October 2017, Vol.23(10), pp.4068-4083
    Description: Animal manure application as organic fertilizer does not only sustain agricultural productivity and increase soil organic carbon () stocks, but also affects soil nitrogen cycling and nitrous oxide (NO) emissions. However, given that the sign and magnitude of manure effects on soil NO emissions is uncertain, the net climatic impact of manure application in arable land is unknown. Here, we performed a global meta‐analysis using field experimental data published in peer‐reviewed journals prior to December 2015. In this meta‐analysis, we quantified the responses of NO emissions to manure application relative to synthetic N fertilizer application from individual studies and analyzed manure characteristics, experimental duration, climate, and soil properties as explanatory factors. Manure application significantly increased NO emissions by an average 32.7% (95% confidence interval: 5.1–58.2%) compared to application of synthetic N fertilizer alone. The significant stimulation of NO emissions occurred following cattle and poultry manure applications, subsurface manure application, and raw manure application. Furthermore, the significant stimulatory effects on NO emissions were also observed for warm temperate climate, acid soils ( 〈 6.5), and soil texture classes of sandy loam and clay loam. Average direct NO emission factors (s) of 1.87% and 0.24% were estimated for upland soils and rice paddy soils receiving manure application, respectively. Although manure application increased stocks, our study suggested that the benefit of increasing stocks as sinks could be largely offset by stimulation of soil NO emissions and aggravated by emissions if, particularly for rice paddy soils, the stimulation of emissions by manure application was taken into account. The uncertain manure effects on NO emissions constrain evaluation of the net climatic impact of manure application in arable lands. A global meta‐analysis was performed to quantify the overall responses of NO emissions to manure application relative to synthetic N fertilizer in agricultural soils. Manure application on average significantly increased NO emissions by 32.7% as compared to synthetic N fertilizer alone, and the sign and magnitude of NO emissions were dependent on manure characteristics, climate, and soil properties. The benefit of C sequestration could be largely offset by stimulation of soil NO emissions and aggravated by CH emissions if, particularly for rice paddy soils, the stimulation of CH emissions by manure application was taken into account.
    Keywords: Animal Manure ; Emission Factor ; Greenhouse Gas Balance ; Manure Characteristics ; Meta‐Analysis ; Nitrous Oxide ; Soil Ph ; Soil Texture
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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