Denitrification and DNRA at the Baltic Sea oxic–anoxic interface: Substrate spectrum and kinetics

Research output: Contribution to journalArticle


The dependence of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) on different electron donors was tested in the nitrate-containing layer immediately below the oxic–anoxic interface (OAI) at three stations in the central anoxic basins of the Baltic Sea. Additionally, pathways and rates of fixed nitrogen transformation were investigated with 15N incubation techniques without addition of donors. Denitrification and anammox were always detected, but denitrification rates were higher than anammox rates. DNRA occurred at two sites and rates were two orders of magnitude lower than denitrification rates. Separate additions of dissolved organic carbon and sulfide stimulated rates without time lag indicating that both organotrophic and lithotrophic bacterial populations were simultaneously active and that they could carry out denitrification or DNRA. Manganese addition stimulated denitrification and DNRA at one station, but it is not clear whether this was due to a direct or indirect effect. Ammonium oxidation to nitrite was detected on one occasion. During denitrification, the production of nitrous oxide (N2O) was as important as dinitrogen (N2) production. A high ratio of N2O to N2 production at one site may be due to copper limitation, which inhibits the last denitrification step. These data demonstrate the coexistence of a range of oxidative and reductive nitrogen cycling processes at the Baltic OAI and suggest that the dominant electron donor supporting denitrification and DNRA is organic matter. Organotrophic denitrification is more important for nitrogen budgets than previously thought, but the large temporal variability in rates calls for long-term seasonal studies.


  • Stefano Bonaglia
  • Isabell Klawonn
  • Loreto De Brabandere
  • Barbara Deutsch
  • Bo Thamdrup
  • Volker Brüchert
External organisations
  • Stockholm University
  • Vrije Universiteit Brussel (VUB)
  • University of Southern Denmark
  • Leibniz Institute of Freshwater Ecology and Inland Fisheries
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Oceanography, Hydrology, Water Resources
Original languageEnglish
Pages (from-to)1900-1915
Number of pages16
JournalLimnology and Oceanography
Issue number5
Publication statusPublished - 2016 Sep 1
Publication categoryResearch