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  • 1
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    Dissolved and particulate reactive nitrogen in the Elbe River/NW Europe: a 2-year N-isotope study (2010)
    Copernicus
    Details
    Publication Date: 2010-10-19
    Description: Rivers collect and transport reactive nitrogen to coastal seas as nitrate, ammonium, dissolved organic nitrogen (DON), or particulate nitrogen. DON is an important component of reactive nitrogen in rivers and is suspected to contribute to coastal eutrophication, but little is known about seasonality of DON loads and turnover within rivers. We measured the concentrations and the isotope ratios 15N/14N of combined DON+NH4+ (δ15DON+NH4+), nitrate (δ15N−NO3−) and particulate nitrogen (δ15PN) in the non-tidal Elbe River (SE North Sea, NW Europe) over a period of 2 years (June 2005 to December 2007) at monthly resolution. Combined DON+NH4+ concentrations ranged from 22 to 75 μM and comprised nearly 23% of total dissolved nitrogen in the Elbe River in annual mean; PN and nitrate concentrations ranged from 11 to 127 μM, and 33 to 422 μM, respectively. Combined PN and DON+NH4+ concentrations were, to a first approximation, inversely correlated to nitrate concentrations. δ15DON+NH4+, which varied between from 0.8‰ to 11.5‰, changed in parallel to δ15PN (range 6 to 10‰), and both were anti-correlated to δ15N−NO3− (range 6 to 23‰). Seasonal patterns of DON+NH4+ concentrations and δ15DON+NH4+ diverge from those expected from biological DON+NH4+ production in the river alone and suggest that the elution of organic fertilisers significantly affects the DON+NH4+ pool in the Elbe River.
    Print ISSN: 1810-6277
    Electronic ISSN: 1810-6285
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
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    Nitrogen isotope dynamics and fractionation during sedimentary denitrification in Boknis Eck, Baltic Sea (2013)
    Copernicus
    Details
    Publication Date: 2013-01-10
    Description: The global marine nitrogen cycle is constrained by nitrogen fixation as a source of reactive nitrogen, and denitrification or anammox on the sink side. These processes with their respective isotope effects set the marine nitrate 15N-isotope value (δ15N) to a relatively constant average of 5‰. This value can be used to better assess the magnitude of these sources and sink terms, but the underlying assumption is that sedimentary denitrification and anammox, processes responsible for approximately one third of global nitrogen removal, have little to no isotope effect on nitrate in the water column. We investigated the isotope fractionation in sediment incubations, measuring net denitrification and nitrogen and oxygen stable isotope fractionation in surface sediments from the coastal Baltic Sea (Boknis Eck, Northern Germany), a site with seasonal hypoxia and dynamic nitrogen turnover. We found tremendously high denitrification rates, and regardless of current paradigms assuming little fractionation during sediment denitrification, we measured fractionation factors of 18.9‰ for nitrogen and 15.8‰ for oxygen in nitrate. While the input of nitrate to the water column remains speculative, these results challenge the current view of fractionation during sedimentary denitrification and imply that nitrogen budget calculations may need to consider this variability, as both preferential uptake of light nitrate and release of the remaining heavy fraction can significantly alter water column nitrate isotope vales at the sediment-water interface.
    Print ISSN: 1810-6277
    Electronic ISSN: 1810-6285
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
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    Nitrogen turnover in a tidal flat sediment: assimilation and dissimilation by bacteria and benthic microalgae (2012)
    Copernicus
    Details
    Publication Date: 2012-06-14
    Description: In a short-term (24 h) 15N-labeling experiment, we investigated reactive nitrogen cycling in a tidal flat sediment, focusing on the relative importance of assimilatory versus dissimilatory processes and the role of benthic microalgae therein. 15N-labeled ammonium and nitrate were added separately to homogenized sediment, and 15N was subsequently traced into sediment and dissolved inorganic nitrogen (DIN) pools. Integration of results in a N-cycle model allowed us to quantify rates for the major assimilatory and dissimilatory processes in the sediment. Overall, results indicate that the balance between assimilation and dissimilation in this tidal mudflat was mainly dependent on the nitrogen source. Nitrate was utilized almost exclusively dissimilatory via denitrification, whereas ammonium was rapidly assimilated, with about a quarter of this assimilation due to benthic microalgae (BMA). Benthic microalgae significantly affect assimilation of ammonium, because in the absence of BMA activity the sediments turns from a net ammonium sink to a net source. Nitrification rates were initially very high, but declined rapidly suggesting that nitrification rates are low in undisturbed sediments, and that in a dynamic environment like tidal flats, intense and fast nitrification/denitrification of ammonium is common. The driving mechanisms for assimilation or dissimilation accordingly appear to be ruled to a large extent by external physical forcing, with the entire system being capable of rapid shifts following environmental changes.
    Print ISSN: 1810-6277
    Electronic ISSN: 1810-6285
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 4
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    Amino acid composition and δ15N of suspended matter in the Arabian Sea (2013)
    Copernicus
    Details
    Publication Date: 2013-08-12
    Description: Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid composition and stable nitrogen isotopic ratios of suspended matter sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to investigate organic matter degradation/modification during passage through the water column. We found that amino acid (AA) composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of suspended matter in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations is dominated by fine material that has a long residence time and organic matter that is resistant to degradation. Whereas SPM in areas of high primary productivity is essentially derived from fresh plankton and thus has a strong imprint of the subsurface nitrate source, SPM at oligotrophic stations and at subthermocline depths appears to exchange amino acids with the DOC pool influencing also the δ15N values.
    Print ISSN: 1810-6277
    Electronic ISSN: 1810-6285
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 5
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    Nitrogen isotope dynamics and fractionation during sedimentary denitrification in Boknis Eck, Baltic Sea (2013)
    Copernicus
    Details
    Publication Date: 2013-05-07
    Description: The global marine nitrogen cycle is constrained by nitrogen fixation as a source of reactive nitrogen, and denitrification or anammox on the sink side. These processes with their respective isotope effects set the marine nitrate 15N-isotope value (δ15N) to a relatively constant average of 5‰. This value can be used to better assess the magnitude of these sources and sink terms, but the underlying assumption is that sedimentary denitrification and anammox, processes responsible for approximately one-third of global nitrogen removal, have little to no isotope effect on nitrate in the water column. We investigated the isotope fractionation in sediment incubations, measuring net denitrification and nitrogen and oxygen stable isotope fractionation in surface sediments from the coastal Baltic Sea (Boknis Eck, northern Germany), a site with seasonal hypoxia and dynamic nitrogen turnover. Sediment denitrification was fast, and regardless of current paradigms assuming little fractionation during sediment denitrification, we measured fractionation factors of 18.9‰ for nitrogen and 15.8‰ for oxygen in nitrate. While the input of nitrate to the water column remains speculative, these results challenge the current view of fractionation during sedimentary denitrification and imply that nitrogen budget calculations may need to consider this variability, as both preferential uptake of light nitrate and release of the remaining heavy fraction can significantly alter water column nitrate isotope values at the sediment–water interface.
    Print ISSN: 1726-4170
    Electronic ISSN: 1726-4189
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 6
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    Balance of assimilative and dissimilative nitrogen processes in a diatom-rich tidal flat sediment (2012)
    Copernicus
    Details
    Publication Date: 2012-10-22
    Description: Tidal flat sediments are subject to repetitive mixing and resuspension events. In a short-term (24 h) 15N-labelling experiment, we investigated reactive nitrogen cycling in a tidal flat sediment following an experimentally induced resuspension event. We focused on (a) the relative importance of assimilatory versus dissimilatory processes and (b) the role of benthic microalgae therein. 15N-labelled substrate was added to homogenized sediment, and 15N was subsequently traced into sediment and dissolved inorganic nitrogen (DIN) pools. Integration of results in a N-cycle model allowed us to quantify the proportion of major assimilatory and dissimilatory processes in the sediment. Upon sediment disturbance, rates of dissimilatory processes like nitrification and denitrification were very high, but declined rapidly towards a steady state. Once this was reached, the balance between assimilation and dissimilation in this tidal mudflat was mainly dependent on the nitrogen source: nitrate was utilized almost exclusively dissimilatory via denitrification, whereas ammonium was rapidly assimilated, with about a quarter of this assimilation due to benthic microalgae (BMA). Benthic microalgae significantly affected the nitrogen recycling balance in sediments, because in the absence of BMA activity the recovering sediment turned from a net ammonium sink to a net source. The driving mechanisms for assimilation or dissimilation accordingly appear to be ruled to a large extent by external physical forcing, with the entire system being capable of rapid shifts following environmental changes. Assimilatory pathways gain importance under stable conditions, with a substantial contribution of BMA to total assimilation.
    Print ISSN: 1726-4170
    Electronic ISSN: 1726-4189
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
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    Amino acid composition and δ15N of suspended matter in the Arabian Sea: implications for organic matter sources and degradation (2013)
    Copernicus
    Details
    Publication Date: 2013-11-27
    Description: Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid (AA) composition and stable nitrogen isotopic ratios of suspended matter (SPM) sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to understand organic matter degradation/modification during passage through the water column. We found that AA composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of SPM in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations is dominated by fine material that has a long residence time and organic matter that is resistant to degradation. SPM in areas of high primary productivity is essentially derived from fresh plankton and thus has a strong imprint of the subsurface nitrate source, whereas SPM at oligotrophic stations and at subthermocline depths appears to exchange amino acids and nitrogen isotopes with the dissolved organic carbon (DOC) pool influencing also the δ15N values.
    Print ISSN: 1726-4170
    Electronic ISSN: 1726-4189
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 8
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    Dissolved and particulate reactive nitrogen in the Elbe River/NW Europe: a 2-yr N-isotope study (2011)
    Copernicus
    Details
    Publication Date: 2011-12-01
    Description: Rivers collect and transport reactive nitrogen to coastal seas as nitrate, ammonium, dissolved organic nitrogen (DON), or particulate nitrogen. DON is an important component of reactive nitrogen in rivers and is suspected to contribute to coastal eutrophication, but little is known about seasonality of DON loads and turnover within rivers. We measured the concentrations and the isotope ratios 15N/14N of combined DON + NH4+ (δ15DON + NH4+), nitrate (δ15N − NO3−) and particulate nitrogen (δ15PN) in the non-tidal Elbe River (SE North Sea, NW Europe) over a period of 2 yr (June 2005 to December 2007) at monthly resolution. Combined DON + NH4+ concentrations ranged from 22 to 75 μM and comprised nearly 23% of total dissolved nitrogen in the Elbe River in annual mean; PN and nitrate concentrations ranged from 11 to 127 μM, and 33 to 422 μM, respectively. Combined PN and DON + NH4+ concentrations were, to a first approximation, inversely correlated to nitrate concentrations. δ15DON + NH4+, which varied between from 0.8‰ to 11.5‰, changed in parallel to δ15PN (range 6 to 10‰), and both were anti-correlated to δ15N − NO3− (range 6 to 23‰). Seasonal patterns of DON + NH4+ concentrations and δ15DON + NH4+ diverge from those expected from biological DON + NH4+ production in the river alone and suggest that the elution of organic fertilisers significantly affects the DON + NH4+ pool in the Elbe River.
    Print ISSN: 1726-4170
    Electronic ISSN: 1726-4189
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 9
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    Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates (2017)
    Inter-Research
    Details
    Publication Date: 2017-12-13
    Print ISSN: 0948-3055
    Electronic ISSN: 1616-1564
    Topics: Biology
    Published by Inter-Research
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  • 10
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    N2 fluxes in sediments of the Elbe Estuary and adjacent coastal zones (2013)
    Inter-Research
    Details
    Publication Date: 2013-11-20
    Print ISSN: 0171-8630
    Electronic ISSN: 1616-1599
    Topics: Biology
    Published by Inter-Research
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