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  • Darnault, Christophe  (8)
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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 04 April 2017, Vol.114(14), pp.E2802-E2803
    Description: In their recent article, Coyte et al. (1) use an innovative combination of microfluidic experiments, mechanistic models, and game theory to study the impact of physical microenvironments on the activity of bacteria in porous media. The authors find that hydrodynamics can profoundly affect...
    Keywords: Biological Evolution ; Environment
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(6), pp.2037-2048
    Description: When the Soil Science Society of America was created, 75 yr ago, the USA was suffering from major dust storms, causing the loss of enormous amounts of topsoil as well as human lives. These catastrophic events reminded public officials that soils are essential to society's well-being. The Soil Conservation Service was founded and farmers were encouraged to implement erosion mitigation practices. Still, many questions about soil processes remained poorly understood and controversial. In this article, we argue that the current status of soils worldwide parallels that in the USA at the beginning of the 20th century. Dust bowls and large-scale soil degradation occur over vast regions in a number of countries. Perhaps more so even than in the past, soils currently have the potential to affect populations critically in several other ways as well, from their effect on global climate change, to the toxicity of brownfield soils in urban settings. Even though our collective understanding of soil processes has experienced significant advances since 1936, many basic questions still remain unanswered, for example whether or not a switch to no-till agriculture promotes C sequestration in soils, or how to account for microscale heterogeneity in the modeling of soil organic matter transformation. Given the enormity of the challenges raised by our (ab)uses of soils, one may consider that if we do not address them rapidly, and in the process heed the example of U.S. public officials in the 1930s who took swift action, humanity may not get a chance to explore other frontiers of science in the future. From this perspective, insistence on the fact that soils are critical to life on earth, and indeed to the survival of humans, may again stimulate interest in soils among the public, generate support for soil research, and attract new generations of students to study soils. ; p. 2037-2048.
    Keywords: Dust Storms ; Students ; Carbon Sequestration ; Topsoil ; Urban Soils ; Society ; No-Tillage ; Soil Organic Matter ; Humans ; Climate Change ; Models ; Farmers ; Soil Degradation ; Toxicity ; Soil Conservation
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 3
    Language: English
    In: Journal of Soils and Sediments, 2015, Vol.15(3), pp.634-647
    Description: Byline: Burcu UyuAur (1), Chunyan Li (2), Philippe C. Baveye (3), Christophe J. G. Darnault (2) Keywords: Geochemistry; Precipitation; Sorption; Two-site and mobile-immobile transport models; Uranyl silicates; Vadose zone Abstract: Purpose Uranium contamination of subsurface environments was once thought to be an isolated occurrence, mostly at production sites. But recent evidence has shown that the presence of uranium in phosphate fertilizers has caused massive amounts of this element to be released worldwide. Concerns are related to uranium movement to groundwater supplies and its significant toxicological risks to human populations. Information is direly needed on how geochemical processes control uranium transport in the vadose zone. Materials and methods Laboratory experiments were performed to investigate the effects of the pH of the soil solution on the reactive transport of uranium(VI) in the vadose zone. The uranium solution was prepared by dilution of a 10.sup.-3 M stock solution of uranium perchlorate, (UO.sub.2(ClO.sub.4).sub.2), with DI water. Two U(VI) solutions were prepared at concentrations of 2x10.sup.-6 M at pH 6 and 11 and were percolated under steady-state conditions through columns filled with sand. The convective-dispersion equation (CDE) was used to analyze the tracer and uranium breakthrough curves resulting from the column experiments. The program CXTFIT was used to estimate the transport parameters of equilibrium and nonequilibrium (i.e., two-site and mobile-immobile) models applied to the experimental data. Results and discussion Comparison of U(VI) breakthrough behavior at pH 6 with that of a nonreactive tracer indicated that U(VI) transport was significantly retarded, and about 52 % of the added U(VI) adsorbed to the quartz sand, likely in the cationic forms U[O.sub.2]OH.sup.+ and UO .sub.2 .sup.2+ . The adsorption was reversible upon the addition of deionized water. At pH 11, the U(VI) breakthrough curve increased gradually and reached a plateau value C/C .sub.0 oscillating between 72 and 82 %. Upon reaction, Si was released from the dissolution of quartz sand, which allowed the possible transport of U(VI) following precipitation of a U(VI) containing solid, such as uranyl-silicate minerals, or sorption of U(VI) onto silica colloids. Two-site and mobile-immobile (MIM) models suggested an influence of either rate-limited mass transfer processes or immobile/mobile water partitioning in U(VI) reactive transport. Conclusions The reactive transport of U(VI) governed by adsorption-desorption processes, precipitation, and complexation reactions in which kinetic behaviors are controlled by pH, solution chemistry, and heterogeneous flow regime impacts the mobility of U(VI). The column transport experiments indicated that under geochemical conditions and vadoze zone processes (preferential flow) that favor the mobility of U(VI), dissolved- and colloidal-phase associations of U(VI) may be transported rapidly and in high concentrations from the soil surface to the groundwater. Author Affiliation: (1) Tubitak Marmara Research Center, P.K. 21 41470, Gebze, Kocaeli, Turkey (2) Department of Environmental Engineering and Earth Sciences, L.G. Rich Environmental Laboratory, Clemson University, 342 Computer Court, Anderson, SC, 29625, USA (3) Laboratory of Soil and Water Engineering, Department of Civil and Environmental Engineering, Rensselaer Polytechnic University, 319 Materials Research Center, 110 Eighth St., Troy, NY, 12180, USA Article History: Registration Date: 31/10/2014 Received Date: 19/05/2014 Accepted Date: 31/10/2014 Online Date: 20/11/2014 Article note: Responsible Editor: Dong-Mei Zhou
    Keywords: Geochemistry ; Precipitation ; Sorption ; Two-site and mobile-immobile transport models ; Uranyl silicates ; Vadose zone
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 4
    Language: English
    In: Frontiers in Environmental Science, 01 June 2017, Vol.5
    Description: Groundwater contamination by oocysts of the waterborne pathogen Cryptosporidium parvum is a significant cause of animal and human disease worldwide. Although research has been undertaken in the past to determine how specific physical and chemical properties of soils affect the risk of groundwater contamination by C. parvum, there is as yet no clear conclusion concerning the range of mobility of C. parvum that one should expect in field soils. In this context, the key objective of this research was to determine the magnitude of C. parvum transport in a number of soils, under conditions in which fast and preferential transport has been successfully prevented. C. parvum oocysts were applied at the surface of different soils and subjected to artificial rainfall. Apparently for the first time, quantitative PCR was used to detect and enumerate oocysts in the soil columns and in the leachates. The transport of oocysts by infiltrating water, and the considerable retention of oocysts in soil was demonstrated for all soils, although differences in the degree of transport were observed with soils of different types. More oocysts were found in leachates from sandy loam soils than in leachates from loamy sand soils and the retention of oocysts in different soils did not significantly differ. The interaction of various processes of the hydrologic system and biogeochemical mechanisms contributed to the transport of oocysts through the soil matrix. Results suggest that the interplay of clay, organic matter, and Ca2+ facilitates and mediates the transfer of organic matter from mineral surfaces to oocysts surface, resulting in the enhanced breakthrough of oocysts through matrices of sandy loam soils compared to those of loamy sand soils. Although the number of occysts that penetrate the soil matrix account for only a small percentage of initial inputs, they still pose a significant threat to human health, especially in groundwater systems with a water table not too distant from the soil surface. The results of the research demonstrate a critical need for the simultaneous study of the interaction of various processes affecting oocysts transport in the subsurface, and for its expansion into complex systems, in order to obtain a coherent picture of the behavior of C. parvum oocysts in soils.
    Keywords: Cryptosporidium ; Microorganisms ; Groundwater ; Soil Transport ; Qpcr ; Environmental Sciences
    E-ISSN: 2296-665X
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  • 5
    Language: English
    In: Frontiers in Microbiology, 01 August 2018, Vol.9
    Description: Over the last 60 years, soil microbiologists have accumulated a wealth of experimental data showing that the bulk, macroscopic parameters (e.g., granulometry, pH, soil organic matter, and biomass contents) commonly used to characterize soils provide insufficient information to describe quantitatively the activity of soil microorganisms and some of its outcomes, like the emission of greenhouse gasses. Clearly, new, more appropriate macroscopic parameters are needed, which reflect better the spatial heterogeneity of soils at the microscale (i.e., the pore scale) that is commensurate with the habitat of many microorganisms. For a long time, spectroscopic and microscopic tools were lacking to quantify processes at that scale, but major technological advances over the last 15 years have made suitable equipment available to researchers. In this context, the objective of the present article is to review progress achieved to date in the significant research program that has ensued. This program can be rationalized as a sequence of steps, namely the quantification and modeling of the physical-, (bio)chemical-, and microbiological properties of soils, the integration of these different perspectives into a unified theory, its upscaling to the macroscopic scale, and, eventually, the development of new approaches to measure macroscopic soil characteristics. At this stage, significant progress has been achieved on the physical front, and to a lesser extent on the (bio)chemical one as well, both in terms of experiments and modeling. With regard to the microbial aspects, although a lot of work has been devoted to the modeling of bacterial and fungal activity in soils at the pore scale, the appropriateness of model assumptions cannot be readily assessed because of the scarcity of relevant experimental data. For significant progress to be made, it is crucial to make sure that research on the microbial components of soil systems does not keep lagging behind the work on the physical and (bio)chemical characteristics. Concerning the subsequent steps in the program, very little integration of the various disciplinary perspectives has occurred so far, and, as a result, researchers have not yet been able to tackle the scaling up to the macroscopic level. Many challenges, some of them daunting, remain on the path ahead. Fortunately, a number of these challenges may be resolved by brand new measuring equipment that will become commercially available in the very near future.
    Keywords: Soil Microbiology ; Biodiversity ; Upscaling ; Tomography ; X-Ray Computed ; Nanosims Imaging ; Biology
    E-ISSN: 1664-302X
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  • 6
    Language: English
    In: Vadose Zone Journal, 2004, Vol.3(1), p.262
    Description: As a result of Cryptosporidium parvum in drinking water, several outbreaks of cryptosporidiosis have occurred in the last 10 yr. Although it is generally believed that movement of pathogens through the soil is minimal, recent research has shown that appreciable numbers of C. parvum oocysts may be transported via preferential or fingered flow to groundwater. The objective of the present research was to further investigate and model the transport of oocysts through preferential flow paths in the vadose zone under a "worst-case" scenario. This was studied by adding calves feces containing C. parvum oocysts with a Cl- tracer to undisturbed silt loam columns and disturbed sand columns during a simulated steady-state rain. The sand columns exhibited preferential flow in the form of fingers whereas macropore flow occurred in the undisturbed cores. In the columns with fingered flow, oocysts and Cl were transported rapidly with the same velocity through the columns. Although only 14 to 86% of the amount applied, the number of oocysts transported across the columns was several orders of magnitude above an infective dose. The macropore columns had only a very limited breakthrough of oocysts, which appeared several pore volumes after the Cl broke through initially. A simulation model for the transport of oocysts via preferential flow was developed on the basis of an existing preferential flow model for nonadsorbing solutes, with addition of a first-order sink term for adsorbance of the C. parvum to the air-water-solid (AWS) interfaces, and with velocity and dispersivity parameters derived from Cl- transport. The breakthrough of C. parvum oocysts could be described realistically for the sand columns. However, the model could not describe oocyst transport in the columns with macropores. ; Includes references
    Keywords: Soil Transport Processes ; Sand ; Vadose Zone ; Soil Pollution ; Mathematical Models ; Simulation Models ; Silt Loam Soils ; Preferential Flow ; Oocysts ; Feces ; Calves ; Cryptosporidium Parvum;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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  • 7
    Language: English
    In: Vadose Zone Journal, 2004, Vol.3(2), p.736
    Description: As a result of Cryptosporidium parvum in drinking water, several outbreaks of cryptosporidiosis have occurred in the last 10 yr. Although it is generally believed that movement of pathogens through the soil is minimal, recent research has shown that appreciable numbers of C. parvum oocysts may be transported via preferential or fingered flow to groundwater. The objective of the present research was to further investigate and model the transport of oocysts through preferential flow paths in the vadose zone under a "worst-case" scenario. This was studied by adding calves feces containing C. parvum oocysts with a Cl- tracer to undisturbed silt loam columns and disturbed sand columns during a simulated steady-state rain. The sand columns exhibited preferential flow in the form of fingers whereas macropore flow occurred in the undisturbed cores. In the columns with fingered flow, oocysts and Cl were transported rapidly with the same velocity through the columns. Although only 14 to 86% of the amount applied, the number of oocysts transported across the columns was several orders of magnitude above an infective dose. The macropore columns had only a very limited breakthrough of oocysts, which appeared several pore volumes after the Cl broke through initially. A simulation model for the transport of oocysts via preferential flow was developed on the basis of an existing preferential flow model for nonadsorbing solutes, with addition of a first-order sink term for
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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  • 8
    Language: English
    In: Water environment research : a research publication of the Water Environment Federation, 2003, Vol.75(2), pp.113-20
    Description: When oocysts of the protozoan Cryptosporidium parvum contaminate drinking water supplies, they can cause outbreaks of Cryptosporidiosis, a common waterborne disease. Of the different pathways by which oocysts can wind up in drinking water, one has received little attention to date; that is, because soils are often considered to be perfect filters, the transport of oocysts through the subsoil to groundwater is generally ignored. To evaluate the significance of this pathway, a series of laboratory experiments investigated subsurface transport of oocysts. Experiment 1 was carried out in a vertical 18-cm-long column filled either with glass beads or silica sand, under conditions known to foster fingered flow. Experiment 2 involved undisturbed, macroporous soil columns subjected to macropore flow. Experiment 3 aimed to study the lateral flow on an undisturbed soil block. The columns and soil samples were subjected to artificial rainfall and were allowed to reach steady state. At that point, feces of contaminated calves were applied at the surface along with a known amount of potassium chloride to serve as a tracer, and rainfall was continued at the same rate. The breakthrough of oocysts and chloride, monitored in the effluent, demonstrate the importance of preferential flow on the transport of oocysts. Compared with chloride, peak oocyst concentrations were not appreciably delayed and, in some cases, occurred even before the chloride peak. Recovery rates for oocysts were low, ranging from 0.1 to 10.4% of the oocysts originally applied on the columns. However, the numbers of oocysts present in the effluents were still orders of magnitude higher than 10 oocysts, the infectious dose considered by the U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, to be sufficient to cause Cryptosporidiosis in healthy adults. These results suggest that the transport of oocysts in the subsurface via preferential flow may create a significant risk of groundwater contamination in some situations.
    Keywords: Cryptosporidium Parvum ; Oocysts
    ISSN: 1061-4303
    E-ISSN: 15547531
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