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  • 1
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    High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary (2017)
    Frontiers
    In:  Frontiers in Marine Science, 4 . Art.Nr. 162.
    Details
    Publication Date: 2020-02-06
    Description: Nitrous oxide (N2O) is one of the most important greenhouse gases and a major sink for stratospheric ozone. Estuaries are sites of intense biological production and N2O emissions. We aimed to identify hot spots of N2O production and potential pathways contributing to N2O concentrations in the surface water of the tidal Elbe estuary. During two research cruises in April and June 2015, surface water N2O concentrations were measured along the salinity gradient of the Elbe estuary by using a laser-based on-line analyzer coupled to an equilibrator. Based on these high-resolution N2O profiles, N2O saturations, and fluxes across the surface water/atmosphere interface were calculated. Additional measurements of DIN concentrations, oxygen concentration, and salinity were performed. Highest N2O concentrations were determined in the Hamburg port region reaching maximum values of 32.3 nM in April 2015 and 52.2 nM in June 2015. These results identify the Hamburg port region as a significant hot spot of N2O production, where linear correlations of AOU-N2Oxs indicate nitrification as an important contributor to N2O production in the freshwater part. However, in the region with lowest oxygen saturation, sediment denitrification obviously affected water column N2O saturation. The average N2O saturation over the entire estuary was 201% (SD: ±94%), with an average estuarine N2O flux density of 48 μmol m−2 d−1 and an overall emission of 0.18 Gg N2O y−1. In comparison to previous studies, our data indicate that N2O production pathways over the whole estuarine freshwater part have changed from predominant denitrification in the 1980s toward significant production from nitrification in the present estuary. Despite a significant reduction in N2O saturation compared to the 1980s, N2O concentrations nowadays remain on a high level, comparable to the mid-90s, although a steady decrease of DIN inputs occurred over the last decades. Hence, the Elbe estuary still remains an important source of N2O to the atmosphere.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3389/fmars.2017.00162
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates (2017)
    Inter Research
    In:  Aquatic Microbial Ecology, 80 (3). pp. 289-300.
    Details
    Publication Date: 2020-02-06
    Description: Nitrification, the step-wise oxidation of ammonium to nitrite and nitrate, is important in the marine environment because it produces nitrate, the most abundant marine dissolved inorganic nitrogen (DIN) component and N-source for phytoplankton and microbes. This study focused on the second step of nitrification, which is carried out by a distinct group of organisms, nitrite-oxidizing bacteria (NOB). The growth of NOB is characterized by nitrite oxidation kinetics, which we investigated for 4 pure cultures of marine NOB (Nitrospina watsonii 347, Nitrospira sp. Ecomares 2.1, Nitrococcus mobilis 231, and Nitrobacter sp. 311). We further compared the kinetics to those of non-marine species because substrate concentrations in marine environments are comparatively low, which likely influences kinetics and highlights the importance of this study. We also determined the isotope effect during nitrite oxidation of a pure culture of Nitrospina (Nitrospina watsonii 347) belonging to one of the most abundant marine NOB genera, and for a Nitrospira strain (Nitrospira sp. Ecomares 2.1). The enzyme kinetics of nitrite oxidation, described by Michaelis-Menten kinetics, of 4 marine genera are rather narrow and fall in the low end of half-saturation constant (Km) values reported so far, which span over 3 orders of magnitude between 9 and 〉1000 µM NO2-. Nitrospina has the lowest Km (19 µM NO2-), followed by Nitrobacter (28 µM NO2-), Nitrospira (54 µM NO2-), and Nitrococcus (120 µM NO2-). The isotope effects during nitrite oxidation by Nitrospina watsonii 347 and Nitrospira sp. Ecomares 2.1 were 9.7 ± 0.8 and 10.2 ± 0.9‰, respectively. This confirms the inverse isotope effect of NOB described in other studies; however, it is at the lower end of reported isotope effects. We speculate that differences in isotope effects reflect distinct nitrite oxidoreductase (NXR) enzyme orientations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/ame01859
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  • 3
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    Nitrogen cycling in sediments on the NW African margin inferred from N and O isotopes in benthic chambers (2022)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Benthic nitrogen cycling in the Mauritanian upwelling region (NW Africa) was studied in June 2014 from the shelf to the upper slope where minimum bottom water O 2 concentrations of 25 µM were recorded. Benthic incubation chambers were deployed at 9 stations to measure fluxes of O 2 , dissolved inorganic carbon (DIC) and nutrients (NO 3 - , NO 2 - , NH 4 + , PO 4 3- , H 4 SiO 4 ) along with the N and O isotopic composition of nitrate (δ 15 N-NO 3 - and δ 18 O-NO 3 - ) and ammonium (δ 15 N-NH 4 + ). O 2 and DIC fluxes were similar to those measured during a previous campaign in 2011 whereas NH 4 + and PO 4 3- fluxes on the shelf were 2 – 3 times higher and possibly linked to a long-term decline in bottom water O 2 concentrations. The mean isotopic fractionation of NO 3 - uptake on the margin, inferred from the loss of NO 3 - inside the chambers, was 1.5 ± 0.4 ‰ for 15/14 N ( 15 ϵ app ) and 2.0 ± 0.5 ‰ for 18/16 O ( 18 ϵ app ). The mean 18 ϵ app : 15 ϵ app ratio on the shelf (〈 100 m) was 2.1 ± 0.3, and higher than the value of 1 expected for microbial NO 3 - reduction. The 15 ϵ app are similar to previously reported isotope effects for NO 3 - respiration in marine sediments but lower than determined in 2011 at a same site on the shelf. The sediments were also a source of 15 N-enriched NH 4 + (9.0 ± 0.7 ‰). A numerical model tuned to the benthic flux data and that specifically accounts for the efflux of 15 N-enriched NH 4 + from the seafloor, predicted a net benthic isotope effect of N loss ( 15 ϵ sed ) of 3.6 ‰; far above the more widely considered value of ~0‰. This result is further evidence that the assumption of a universally low or negligible benthic N isotope effect is not applicable to oxygen-deficient settings. The model further suggests that 18 ϵ app : 15 ϵ app trajectories > 1 in the benthic chambers are most likely due to aerobic ammonium oxidation and nitrite oxidation in surface sediments rather than anammox, in agreement with published observations in the water column of oxygen deficient regions.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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  • 4
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    Seasonal variability of nitrous oxide concentrations and emissions in a temperate estuary (2023)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Nitrous oxide (N2O) is a greenhouse gas, with a global warming potential 298 times that of carbon dioxide. Estuaries can be sources of N2O, but their emission estimates have significant uncertainties due to limited data availability and high spatiotemporal variability. We investigated the spatial and seasonal variability of dissolved N2O and its emissions along the Elbe Estuary (Germany), a well-mixed temperate estuary with high nutrient loading from agriculture. During nine research cruises performed between 2017 and 2022, we measured dissolved N2O concentrations, as well as dissolved nutrient and oxygen concentrations along the estuary, and calculated N2O saturations, flux densities, and emissions. We found that the estuary was a year-round source of N2O, with the highest emissions in winter when dissolved inorganic nitrogen (DIN) loads and wind speeds are high. However, in spring and summer, N2O saturations and emissions did not decrease alongside lower riverine nitrogen loads, suggesting that estuarine in situ N2O production is an important source of N2O. We identified two hotspot areas of N2O production: the Port of Hamburg, a major port region, and the mesohaline estuary near the maximum turbidity zone (MTZ). N2O production was fueled by the decomposition of riverine organic matter in the Hamburg Port and by marine organic matter in the MTZ. A comparison with previous measurements in the Elbe Estuary revealed that N2O saturation did not decrease alongside the decrease in DIN concentrations after a significant improvement of water quality in the 1990s that allowed for phytoplankton growth to re-establish in the river and estuary. The overarching control of phytoplankton growth on organic matter and, subsequently, on N2O production highlights the fact that eutrophication and elevated agricultural nutrient input can increase N2O emissions in estuaries.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
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  • 5
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    The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean (2022)
    Nature Research
    Details
    Publication Date: 2022-10-14
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marshall, T., Granger, J., Casciotti, K. L., Dahnke, K., Emeis, K.-C., Marconi, D., McIlvin, M. R., Noble, A. E., Saito, M. A., Sigman, D. M., & Fawcett, S. E. The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean. Communications Earth & Environment, 3(1), (2022): 151, https://doi.org/10.1038/s43247-022-00474-x.
    Description: Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the ocean’s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate estimates vary five-fold, with models attributing most dinitrogen fixation to the western basin. From hydrographic properties and nitrate isotope ratios, we show that the Angola Gyre in the eastern tropical South Atlantic supports the fixation of 1.4–5.4 Tg N.a−1, 28-108% of the existing (highly uncertain) estimates for the basin. Our observations contradict model diagnoses, revealing a substantial input of newly-fixed nitrogen to the tropical eastern basin and no dinitrogen fixation west of 7.5˚W. We propose that dinitrogen fixation in the South Atlantic occurs in hotspots controlled by the overlapping biogeography of excess phosphorus relative to nitrogen and bioavailable iron from margin sediments. Similar conditions may promote dinitrogen fixation in analogous ocean regions. Our analysis suggests that local iron availability causes the phosphorus-driven coupling of oceanic dinitrogen fixation to nitrogen loss to vary on a regional basis.
    Description: This work was supported by the South African National Research Foundation (114673 and 130826 to T.M., 115335, 116142 and 129320 to S.E.F.); the US National Science Foundation (CAREER award, OCE-1554474 to J.G., OCE-1736652 to D.M.S. and K.L.C., OCE-05-26277 to K.L.C.); the German Federal Agency for Education and Research (DAAD-SPACES 57371082 to T.M.); the Royal Society (FLAIR fellowship to S.E.F.); and the University of Cape Town (T.M., J.G., S.E.F.). The authors also recognize the support of the South African Department of Science and Innovation’s Biogeochemistry Research Infrastructure Platform (BIOGRIP).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Nitrogen isotopic inventory of the Lena River Delta (2022)
    In:  EPIC3EGU General Assembly 2022, Vienna, Austria, 2022-05-23-2022-05-27Nitrogen isotopic inventory of the Lena River Delta 
    Details
    Publication Date: 2022-10-04
    Description: Permafrost-affected soils around the Arctic Ocean contain a large reservoir of organic matter including nitrogen, which partly reach the river after thawing, degradation and erosion of permafrost. After mobilization, reactive remineralised nitrogen is either used for primary production, microbial processing or is simply transported to coastal waters. With analyzing the natural abundance of the stable isotope composition in different form of nitrogen components, we aim to unravel the balance of transport and biological nitrogen turnover processes like remineralization or nitrification and in consequent the fate of the nitrogen. We have analyzed soil, suspended matter and dissolved inorganic and organic nitrogen for their contents and 15N stable isotope composition to create a baseline for a nitrogen inventory of the Lena River Delta in 2019/2020. We used samples from two transect cruises through the delta in March and August 2019, a monitoring program at Samoylov Island in the central delta (2019/2020), and different soil type samples from Samoylov and Kurunghak Island. Our aim was to determine nitrogen sources, sinks and transformation processes during transport in river and delta. Our data shows that in winter the nitrogen transported from the delta to the Laptev Sea were dominated by dissolved organic nitrogen (DON) and nitrate, which occur in similar amounts of approx. 10 µmol/L. The load of nitrate, during the transect cruise, increased slightly in the delta, while we observed no changes to the isotope values of DON and nitrate indicating a lack of biological activity in the winter season and the lateral transport from soils was the likely source. In summer, nitrogen was mainly transported as DON and particulate nitrogen in the suspended matter and nitrate was mainly below 1µmol/L. The nitrogen stable isotope values of the different nitrogen components ranges between 0.5 and 4.5‰, and were subsequently enriched from the soils via suspended particulate matter (SPM)/sediment and DON to nitrate. These light values indicate soil nitrogen mainly originates from atmospheric nitrogen fixation. During transport and remineralization, biogeochemical recycling via nitrification and assimilation by phytoplankton led to an isotopic enrichment in summer. In the coastal waters of the Laptev Sea, the exported river waters are slowly mixed with marine nitrate containing waters from the Arctic Ocean, and a part of the riverine organic nitrogen is buried in the sediments. Our data provides a baseline for isoscape analysis and can be used as an endmember signal for modeling approaches.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 7
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    Nitrogen isotopic inventory of the Lena River Delta (2022)
    In:  EPIC3
    Details
    Publication Date: 2023-04-18
    Description: Permafrost-affected soils around the Arctic Ocean contain a large reservoir of organic matter including nitrogen, which partly reach the river after thawing, degradation and erosion of permafrost. After mobilization, reactive remineralised nitrogen is either used for primary production, microbial processing or is simply transported to coastal waters. We have analyzed soil, suspended matter and dissolved inorganic and organic nitrogen for their contents and 15N stable isotope composition to create a baseline for a nitrogen inventory of the Lena River Delta in 2019/2020. We used samples from two transect cruises through the delta in March and August 2019, a monitoring program at Samoylov Island in the central delta (2019/2020), and different soil type samples from Samoylov Island. Our data shows that the nitrogen transported from the delta to the Laptev Sea were dominated by dissolved organic nitrogen (DON) and nitrate, which occur in similar amounts of approx. 10 μmol/L. DON was available during the whole year. Nitrate showed a clear seasonal pattern: increase from late summer until the spring flood, during summer the nitrate concentration are close to zero. During the spring flood the nitrogen concentration are higher with up to 100 μmol/L. The nitrogen stable isotope values of the different nitrogen components ranges mainly between 0.5 and 4.5‰, and were subsequently enriched from the soils via suspended particulate matter (SPM)/sediment and DON to nitrate. During the spring flood, the stable isotope signature of nitrate suggested a strong source of atmospheric deposition. The 15N values are depleted with appox. -8‰ and the 18O values are enriched up to 60‰. Our data provides a baseline for isoscape analysis and can be used as an endmember signal for modeling approaches.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 8
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    Permafrost land-ocean interactions: fluxes, transport processes and degradation pathways (2023)
    In:  EPIC3
    Details
    Publication Date: 2023-07-11
    Description: Permafrost-affected soils around the Arctic Ocean contain a large reservoir of organic matter including nitrogen, which partly reaches the riverine system after thawing, degradation and erosion of permafrost. After mobilization, reactive nitrogen in form of dissolved organic nitrogen (DON) ordissolved inorganic nitrogen (DIN: ammonium and nitrate) is either used for primary production, microbial turnover and/or is transported to coastal waters where it serves as a key source of nutrition for the marine food web. In this study, we have followed the nitrogen released from permafrost soil via the Lena River into the Laptev Sea and used the natural abundance of 15N stable isotopes to identify sources, sinks and processes. Therefore, we have investigated different soil. We present a comprehensive data set from two transect cruises (03/08 2019) through the delta, and the outcome of a monitoring program (2018 - 2021) at Samoylov Island in the central delta. High-frequency monitoring and cruise data shows that the nitrogen transported from the river to the Laptev Sea was dominated by DON and nitrate, which occurred in similar amounts of approx. 10 μmol L–1 in the river water. The nitrate concentration decreased during the early summer and increased from late summer throughout the winter until the spring flood. During the spring flood, the nitrogen concentration was up to ten times higher. Thus, spring floods transport approx. 20 % of the annual load of reactive nitrogen into the Laptev Sea just at the onset of the growing season. The nitrogen stable isotope values of the different nitrogen components ranged mainly between 0.5 and 4.5‰, and were subsequently enriched from the permafrost soils via suspended particulate matter/sediment and DON to nitrate, which indicate an oligotrophic ecosystem. Using a Bayesian mixing model, the stable isotope signature of nitrate suggested a strong source of atmospheric deposition during the spring flood. During the rest of the year, soils are the main source of the reactive nitrogen, which is transported to the marine realm.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 9
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    Nitrous oxide (N2O) measurements in the surface water of the Elbe Estuary in 2015 (2017)
    PANGAEA
    In:  Supplement to: Brase, Lisa; Bange, Hermann Werner; Lendt, Ralf; Sanders, Tina; Dähnke, Kirstin (2017): High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary. Frontiers in Marine Science, 4, https://doi.org/10.3389/fmars.2017.00162
    Details
    Publication Date: 2023-07-06
    Description: Nitrous oxide (N2O) is one of the most important greenhouse gases and a major sink for stratospheric ozone. Estuaries are sites of intense biological production and N2O emissions. We aimed to identify hot spots of N2O production and potential pathways contributing to N2O concentrations in the surface water of the tidal Elbe estuary. During two research cruises in April and June 2015, surface water N2O concentrations were measured along the salinity gradient of the Elbe estuary by using a laser-based on-line analyzer coupled to an equilibrator. Based on these high-resolution N2O profiles, N2O saturations, and fluxes across the surface water/atmosphere interface were calculated. Additional measurements of DIN concentrations, oxygen concentration, and salinity were performed. Highest N2O concentrations were determined in the Hamburg port region reaching maximum values of 32.3 nM in April 2015 and 52.2 nM in June 2015. These results identify the Hamburg port region as a significant hot spot of N2O production, where linear correlations of AOU-N2Oxs indicate nitrification as an important contributor to N2O production in the freshwater part. However, in the region with lowest oxygen saturation, sediment denitrification obviously affected water column N2O saturation. The average N2O saturation over the entire estuary was 201% (SD: ±94%), with an average estuarine N2O flux density of 48 ?mol m-2 d-1 and an overall emission of 0.18 Gg N2O y-1. In comparison to previous studies, our data indicate that N2O production pathways over the whole estuarine freshwater part have changed from predominant denitrification in the 1980s toward significant production from nitrification in the present estuary. Despite a significant reduction in N2O saturation compared to the 1980s, N2O concentrations nowadays remain on a high level, comparable to the mid-90s, although a steady decrease of DIN inputs occurred over the last decades. Hence, the Elbe estuary still remains an important source of N2O to the atmosphere.
    Keywords: Ammonium; Continuous flow analyser (AA3, Seal Analytics, Germany); Date/Time of event; DEPTH, water; Elbe Estuary; Event label; FerryBox system; Helmholtz-Zentrum Geesthacht, Institute of Coastal Research; HZG; Latitude of event; Longitude of event; LP201504; LP201504_Stat_1_1; LP201504_Stat_1_10; LP201504_Stat_1_11; LP201504_Stat_1_12; LP201504_Stat_1_13; LP201504_Stat_1_14; LP201504_Stat_1_15; LP201504_Stat_1_16; LP201504_Stat_1_17; LP201504_Stat_1_18; LP201504_Stat_1_19; LP201504_Stat_1_2; LP201504_Stat_1_3; LP201504_Stat_1_4; LP201504_Stat_1_5; LP201504_Stat_1_6; LP201504_Stat_1_7; LP201504_Stat_1_8; LP201504_Stat_1_9; LP201504_Stat_10_1; LP201504_Stat_10_10; LP201504_Stat_10_11; LP201504_Stat_10_12; LP201504_Stat_10_13; LP201504_Stat_10_14; LP201504_Stat_10_15; LP201504_Stat_10_16; LP201504_Stat_10_17; LP201504_Stat_10_18; LP201504_Stat_10_19; LP201504_Stat_10_2; LP201504_Stat_10_20; LP201504_Stat_10_3; LP201504_Stat_10_4; LP201504_Stat_10_5; LP201504_Stat_10_6; LP201504_Stat_10_7; LP201504_Stat_10_8; LP201504_Stat_10_9; LP201504_Stat_11_1; LP201504_Stat_11_10; LP201504_Stat_11_11; LP201504_Stat_11_12; LP201504_Stat_11_13; LP201504_Stat_11_14; LP201504_Stat_11_15; LP201504_Stat_11_16; LP201504_Stat_11_17; LP201504_Stat_11_18; LP201504_Stat_11_19; LP201504_Stat_11_2; LP201504_Stat_11_20; LP201504_Stat_11_3; LP201504_Stat_11_4; LP201504_Stat_11_5; LP201504_Stat_11_6; LP201504_Stat_11_7; LP201504_Stat_11_8; LP201504_Stat_11_9; LP201504_Stat_12_1; LP201504_Stat_12_10; LP201504_Stat_12_2; LP201504_Stat_12_3; LP201504_Stat_12_4; LP201504_Stat_12_5; LP201504_Stat_12_6; LP201504_Stat_12_7; LP201504_Stat_12_8; LP201504_Stat_12_9; LP201504_Stat_13_1; LP201504_Stat_13_10; LP201504_Stat_13_11; LP201504_Stat_13_12; LP201504_Stat_13_13; LP201504_Stat_13_14; LP201504_Stat_13_15; LP201504_Stat_13_2; LP201504_Stat_13_3; LP201504_Stat_13_4; LP201504_Stat_13_5; LP201504_Stat_13_6; LP201504_Stat_13_7; LP201504_Stat_13_8; LP201504_Stat_13_9; LP201504_Stat_14_1; LP201504_Stat_14_2; LP201504_Stat_14_3; LP201504_Stat_14_4; LP201504_Stat_14_5; LP201504_Stat_14_6; LP201504_Stat_15_1; LP201504_Stat_15_2; LP201504_Stat_15_3; LP201504_Stat_15_4; LP201504_Stat_17_1; LP201504_Stat_17_10; LP201504_Stat_17_11; LP201504_Stat_17_12; LP201504_Stat_17_13; LP201504_Stat_17_14; LP201504_Stat_17_15; LP201504_Stat_17_16; LP201504_Stat_17_17; LP201504_Stat_17_2; LP201504_Stat_17_3; LP201504_Stat_17_4; LP201504_Stat_17_5; LP201504_Stat_17_6; LP201504_Stat_17_7; LP201504_Stat_17_8; LP201504_Stat_17_9; LP201504_Stat_18_1; LP201504_Stat_18_2; LP201504_Stat_18_3; LP201504_Stat_19_1; LP201504_Stat_19_10; LP201504_Stat_19_11; LP201504_Stat_19_12; LP201504_Stat_19_13; LP201504_Stat_19_14; LP201504_Stat_19_15; LP201504_Stat_19_16; LP201504_Stat_19_2; LP201504_Stat_19_3; LP201504_Stat_19_4; LP201504_Stat_19_5; LP201504_Stat_19_6; LP201504_Stat_19_7; LP201504_Stat_19_8; LP201504_Stat_19_9; LP201504_Stat_2_1; LP201504_Stat_2_10; LP201504_Stat_2_11; LP201504_Stat_2_12; LP201504_Stat_2_13; LP201504_Stat_2_14; LP201504_Stat_2_15; 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    Type: Dataset
    Format: text/tab-separated-values, 3585 data points
    Location Call Number Limitation Availability
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    DATA PANGAEA
  • 10
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    Nitrite consumption and associated isotope changes during a river flood event in the Elbe river (2016)
    PANGAEA
    In:  Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research | Supplement to: Jacob, Juliane; Sanders, Tina; Dähnke, Kirstin (2016): Nitrification and Nitrite Isotope Fractionation as a Case Study in a major European River. Biogeosciences, 13(19), 5649-5659, https://doi.org/10.5194/bg-13-5649-2016
    Details
    Publication Date: 2023-07-11
    Description: In oceans, estuaries, and rivers, nitrification is an important nitrate source, and stable isotopes of nitrate are often used to investigate recycling processes (e.g. remineralisation, nitrification) in the water column. Nitrification is a two-step process, where ammonia is oxidised via nitrite to nitrate. Nitrite usually does not accumulate in natural environments, which makes it difficult to study the single isotope effect of ammonia oxidation or nitrite oxidation in natural systems. However, during an exceptional flood in the Elbe River in June 2013, we found a unique co-occurrence of ammonium, nitrite, and nitrate in the water column, returning towards normal summer conditions within 1 week. Over the course of the flood, we analysed the evolution of d15N-[NH4]+ and d15N-[NO2]- in the Elbe River. In concert with changes in suspended particulate matter (SPM) and d15N SPM, as well as nitrate concentration, d15N-NO3 - and d18O-[NO3] -, we calculated apparent isotope effects during net nitrite and nitrate consumption. During the flood event, 〉 97 % of total reactive nitrogen was nitrate, which was leached from the catchment area and appeared to be subject to assimilation. Ammonium and nitrite concentrations increased to 3.4 and 4.4 µmol/l, respectively, likely due to remineralisation, nitrification, and denitrification in the water column. d15N-[NH4]+ values increased up to 12 per mil, and d15N-[NO2]- ranged from -8.0 to -14.2 per mil. Based on this, we calculated an apparent isotope effect 15-epsilon of -10.0 ± 0.1 per mil during net nitrite consumption, as well as an isotope effect 15-epsilon of -4.0 ± 0.1 per mil and 18-epsilon of -5.3 ± 0.1 per mil during net nitrate consumption. On the basis of the observed nitrite isotope changes, we evaluated different nitrite uptake processes in a simple box model. We found that a regime of combined riparian denitrification and 22 to 36 % nitrification fits best with measured data for the nitrite concentration decrease and isotope increase.
    Keywords: Ammonium; Carbon, total, particulate; Carbon/Nitrogen ratio; Colorimetric; DATE/TIME; DEPTH, water; Element analyser, Thermo Finnigan flash EA 1112; FerryBox system; Fluorescence determination; Geesthacht weir, Germany; Gravimetric analysis (GF/F filtered); GW2011-2016_Stat_1; Mass spectrometer Finnigan MAT 252; Mass spectrometer ThermoFisher Delta V; Nitrate; Nitrite; Nitrogen, inorganic, dissolved; Nitrogen, total, particulate; Oxygen; pH; Phosphate; Salinity; Sample ID; Seal QuAAtro SFA Analyzer, Seal Analytical, 800 TM; Silicate; Suspended particulate matter; Temperature, water; Water sample; WS; δ15N, ammonium; δ15N, nitrate; δ15N, nitrite; δ15N, total particulate nitrogen; δ18O, nitrate
    Type: Dataset
    Format: text/tab-separated-values, 443 data points
    Location Call Number Limitation Availability
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    DATA PANGAEA
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