06 Dec 2022
 | 06 Dec 2022
Status: this preprint is currently under review for the journal BG.

Alkalinity and nitrate dynamics reveal dominance of anammox in a hyper-turbid estuary

Mona Norbisrath, Andreas Neumann, Kirstin Dähnke, Tina Sanders, Andreas Schöl, Justus E. E. van Beusekom, and Helmuth Thomas

Abstract. Total alkalinity (TA) regulates the oceanic storage capacity of atmospheric CO2. TA is produced along two general pathways, weathering reactions and anaerobic respiration of organic matter, e.g., by denitrification, the anaerobic reduction of nitrate (NO3-) to elemental nitrogen (N2). Anammox, is another anaerobic pathway, yields N2 as its terminal product via comproportionation of ammonium (NH4+) and nitrite (NO2-); this is, however, without release of alkalinity as a byproduct. In order to investigate these two nitrate / nitrite respiration pathways and their resulting impact on TA generation, we sampled the highly turbid estuary of the Ems River, discharging into the North Sea in June 2020. We sampled a transect from the Wadden Sea to the upper tidal estuary, five vertical profiles during ebb tide, and fluid mud for incubation experiments in the hyper-turbid tidal river. The data reveal a strong increase of TA and DIC in the tidal river, where stable nitrate isotopes indicate water column denitrification as the dominant pathway. In the fluid mud of the tidal river, the TA data imply only low denitrification rates, with the majority of the N2 being produced by anammox (> 90 %). The relative abundances of anammox and denitrification, respectively, thus exert a major control on the CO2 storage capacity of adjacent coastal waters.

Mona Norbisrath et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-226', Anonymous Referee #1, 01 Jan 2023
    • AC1: 'Reply on RC1', Mona Norbisrath, 18 Feb 2023
  • RC2: 'Comment on bg-2022-226', Anonymous Referee #2, 07 Jan 2023
    • AC2: 'Reply on RC2', Mona Norbisrath, 13 Mar 2023

Mona Norbisrath et al.

Mona Norbisrath et al.


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Short summary
Total alkalinity (TA) is the oceanic capacity to store CO2. Estuaries can be a source for TA, by producing it by e.g., anaerobic metabolic pathways like denitrification (reduction of NO3- to N2), a major nitrogen (N) sink. Another important N sink is anammox, which transformes NH4+ with NO2- into N2. By combining TA and N2 production, we identified a TA source, denitrification occurring in the water column, and suggest anammox as the dominant N2 producer in the bottom layers of the Ems Estuary.