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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-295
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-295
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 07 Aug 2019

Submitted as: research article | 07 Aug 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Spatial variations in sedimentary N-transformation rates in the North Sea (German Bight)

Alexander Bratek1,2, Justus van Beusekom1,3, Andreas Neumann1, Tina Sanders1, Jana Friedrich1, Kay-Christian Emeis1,2, and Kirstin Dähnke1 Alexander Bratek et al.
  • 1Helmholtz-Zentrum Geesthacht, Institute for Coastal Research, Geesthacht, Germany
  • 2University of Hamburg, Center for Earth System Research and Sustainability, Institute for Geology, Hamburg, Germany
  • 3University of Hamburg, Center for Earth System Research and Sustainability, Institute for Hydrobiology and Fisheries, Hamburg, Germany

Abstract. In this study, we investigate the role of sedimentary N cycling in the Southern North Sea. We present a budget of ammonification, nitrification and sedimentary NO3 consumption/denitrification in contrasting sediment types of the German Bight (Southern North Sea), including novel net ammonification rates. Dissolved inorganic nitrogen concentration (nitrate, nitrite and ammonium) in the water column showed low levels between 0.2 to 3.2 µmol L−1. We incubated sediment cores with labeled nitrate and ammonium to calculate net and gross N transformation rates. The results show that impermeable sediments are the main site of ammonification (on average 10.2 ± 1.2 mmol m−2 d−1) and that they are an important source for primary producers in the water column, contributing ~ 17 to 61 % of reactive nitrogen in the water column. Ammonification and oxygen penetration depth are the main drivers of sedimentary nitrification. One third of freshly produced nitrate in impermeable sediment and two-thirds in permeable sediment were reduced to N2. The semi-permeable and permeable sediments are responsible for ~ 80 % of the total benthic N2 production rates (~ 890 t N d−1) in the southern North Sea. We conclude that impermeable sediments are important sources of reactive N and that semi-permeable and permeable sediments are the main sinks of reactive N, counteracting eutrophication in the southern North Sea (German Bight).

Alexander Bratek et al.
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Alexander Bratek et al.
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The following paper highlight the importance of benthic nitrogen (N) transformation rates in different sediment types in the southern North Sea as a source of fixed nitrogen for primary producers and also as a sink of fixed nitrogen. Sedimentary ammonification contributung ~ 17 to 61 % of reactive nitrogen in the water column, whereas semi-permeable and permeable sediments are responsible for ~ 80 % of the total benthic N2 production rates in the southern North Sea (~ 890 t N d−1).
The following paper highlight the importance of benthic nitrogen (N) transformation rates in...
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