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  • 1
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    Significant mixed layer nitrification in a natural iron-fertilized bloom of the Southern Ocean (2015)
    Wiley
    Details
    Publication Date: 2015-10-22
    Description: Nitrification, the microbially mediated oxidation of ammonium into nitrate, is generally expected to be low in the Southern Ocean mixed layer. This paradigm assumes that nitrate is mainly provided through vertical mixing and assimilated during the vegetative season, supporting the concept that nitrate uptake is equivalent to the new primary production (i.e., primary production which is potentially available for export). Here we show, that nitrification is significant (~40 to 80% of the seasonal nitrate uptake) in the naturally iron-fertilized bloom over the southeast Kerguelen Plateau. Hence, a large fraction of the nitrate-based primary production is regenerated, instead of being exported. It appears that nitrate assimilation (light-dependent) and nitrification (partly light-inhibited) are spatially separated between the upper and lower parts, respectively, of the deep surface mixed layers. These deep mixed layers, extending well below the euphotic layer, allow nitrifiers to compete with phytoplankton for the assimilation of ammonium. The high contributions of nitrification to nitrate uptake are in agreement with both low export efficiency (i.e., the percentage of primary production that is exported) and low seasonal nitrate drawdown despite high nitrate assimilation.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Revisiting carbon flux through the ocean's twilight zone (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-04-28
    Description: The oceanic biological pump drives sequestration of carbon dioxide in the deep sea via sinking particles. Rapid biological consumption and remineralization of carbon in the "twilight zone" (depths between the euphotic zone and 1000 meters) reduce the efficiency of sequestration. By using neutrally buoyant sediment traps to sample this chronically understudied realm, we measured a transfer efficiency of sinking particulate organic carbon between 150 and 500 meters of 20 and 50% at two contrasting sites. This large variability in transfer efficiency is poorly represented in biogeochemical models. If applied globally, this is equivalent to a difference in carbon sequestration of more than 3 petagrams of carbon per year.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Buesseler, Ken O -- Lamborg, Carl H -- Boyd, Philip W -- Lam, Phoebe J -- Trull, Thomas W -- Bidigare, Robert R -- Bishop, James K B -- Casciotti, Karen L -- Dehairs, Frank -- Elskens, Marc -- Honda, Makio -- Karl, David M -- Siegel, David A -- Silver, Mary W -- Steinberg, Deborah K -- Valdes, Jim -- Van Mooy, Benjamin -- Wilson, Stephanie -- New York, N.Y. -- Science. 2007 Apr 27;316(5824):567-70.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA. kbuesseler@whoi.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17463282" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Carbon/metabolism ; Carbon Dioxide ; Copepoda/physiology ; *Ecosystem ; Food Chain ; Geologic Sediments/chemistry ; Hydrogen-Ion Concentration ; Pacific Ocean ; Phytoplankton/physiology ; *Seawater/chemistry ; Zooplankton/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    A Discontinuous Finite Element suspended sediment transport model for water quality assessments in river networks (2017)
    Wiley
    Details
    Publication Date: 2017-02-19
    Description: Suspended sediment plays an important role in the distribution and transport of many pollutants (such as radionuclides) in rivers. Pollutants may adsorb on fine suspended particles (e.g. clay) and spread according to the suspended sediment movement. Hence, the simulation of the suspended sediment mechanism is indispensable for realistic transport modelling. This paper presents and tests a simple mathematical model for predicting the suspended sediment transport in river networks. The model is based on the van Rijn suspended load formula and the advection-diffusion equation with a source/sink term that represents the erosion/deposition fluxes. The transport equation is solved numerically with the Discontinuous Finite Element method. The model evaluation was performed in two steps, firstly by comparing model simulations with the measured suspended sediment concentrations in the Grote Nete - Molse Nete River in Belgium, and secondly by a model inter-comparison with the sediment transport model NST MIKE 11. The simulations reflect the measurements with a Nash-Sutcliffe model efficiency of 0.6, while the efficiency between the proposed model and the NST MIKE 11 simulations is 0.96. Both evaluations indicate that the proposed sediment transport model, that is sufficiently simple to be practical, is providing realistic results.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 4
    Electronic Resource
    Electronic Resource
    Description of a Mossbauer spectrometer using a piezoelectric bar
    Amsterdam : Elsevier
    Nuclear Instruments and Methods 81 (1970), S. 211-213 
    Details
    ISSN: 0029-554X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0029-554X(70)90636-1
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Improved electronic control unit for a motor type beam scanner
    Amsterdam : Elsevier
    Nuclear Instruments and Methods 93 (1971), S. 391-393 
    Details
    ISSN: 0029-554X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0029-554X(71)90498-8
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  • 6
    Electronic Resource
    Electronic Resource
    Geochemical processes in muddy and sandy tidal flat sediments (1991)
    Springer
    Geo-marine letters 11 (1991), S. 188-193 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Different approaches, such as element analyses of the bulk sediment and of the fine sediment fraction (〈63 μm), sequential extraction techniques, correlation coefficient, and enrichment factor calculations, clearly demonstrate the differences in geochemical behavior of a muddy and a sandy sediment on the same tidal flat in the Scheldt estuary (Belgium). The geochemical processes in combination with the relatively large transport mobility of dissolved compounds due to the tidal action in the sediment, created compound specific vertical distribution profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02431011
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  • 7
    Electronic Resource
    Electronic Resource
    Microbial activity in sandy and muddy estuarine sediments (1991)
    Springer
    Geo-marine letters 11 (1991), S. 194-198 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Striking differences were observed in the use of the electron acceptors involved in the degradation of organic matter by heterotrophic bacterial activity between a muddy and a sandy sediment on the same tidal flat of the Scheldt estuary. These bio-reduction reactions could have a quite different effect on the cycling of trace metals in the sediment as suggested by the results of the mobilization experiments. Trace metal speciation can be described as a function of the redox potential, in view of the fact that the latter is related to the heterotrophic bacterial activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02431012
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  • 8
    Electronic Resource
    Electronic Resource
    Geochemistry of mercury in an intertidal flat of the Scheldt estuary (1993)
    Springer
    Aquatic ecology 27 (1993), S. 267-277 
    Details
    ISSN: 1573-5125
    Keywords: Estuarine sediments ; mercury ; methylmercury ; methylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sediments were sampled on the ‘Groot Buitenschoor’, an intertidal flat located at about 60 km from the Scheldt's river mouth. Hg concentrations ranged from 30 to 1756 ng g−1. The concentrations were strongly correlated with fine grain fraction, organic matter content and sulphide concentrations. Incubation experiments were performed in order to determine the potential methylation rate of Hg as well as biotic and abiotic factors influencing this transformation. About 1 to 2% of the added inorganic Hg is converted into methylmercury. This conversion rate points to the same equilibrium ratio as was observed in natural sediments, indicating an equilibrium between methylation and demethylation reactions in the sediments. Incubation of a sterilised sediment sample significantly decreased the methylation rate, but the methylmercury concentrations observed are still ten times higher than the natural (unspiked) sediment. This result could be due to a chemical (non-enzymatic) methylation of mercury. Sulphate reducing bacteria are the main species responsible for the methylation of Hg at this site. Addition of Na2MoO4, a specific inhibitor of sulphate reducing bacteria, decreased the methylation rate to the abiotic level (sterilised sediment). High sulphate reduction rates, however, lead to lower methylation rates. Increased formation of sulphides due to microbial sulphate reduction leads to enhanced HgS formation and this reaction competes with the methylation process. HgS is in fact the major product formed by the reaction of sulphate reducing bacteria with Hg species. About 50% of the Hg spiked to the sediments is transformed into HgS during the incubation experiments, and that compound is practically unavailable for methylation in contrast to other bound forms of Hg.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02334790
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  • 9
    Electronic Resource
    Electronic Resource
    The behaviour of copper and zinc in the Scheldt estuary (1993)
    Springer
    Aquatic ecology 27 (1993), S. 279-286 
    Details
    ISSN: 1573-5125
    Keywords: particulate and dissolved Cu and Zn ; Scheldt estuary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The behaviour of copper and zinc in the Scheldt estuary, both in the particulate and the dissolved phase, is discussed for the period 1982–1983. The longitudinal particulate copper and zinc profiles fall below the dilution line, which is attributed to mixing and mobilization processes. In the dissolved phase both metals show a production region in the end member of the estuary, for copper a pronounced mid estuarine maximum is observed. Study of the metal speciation suggested that organic ligands might keep heavy metals in solution, especially in area of intensive production, and promote the subsequent export of these metals downstream the estuary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02334791
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  • 10
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    Description of a Mössbauer spectrometer using a piezoelectric bar (1970)
    Elsevier
    Details
    Publication Date: 1970-05-01
    Print ISSN: 0029-554X
    Electronic ISSN: 1878-3759
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Physics
    Published by Elsevier
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