BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-7-3259-2010 Denitrification in sediments as a major nitrogen sink in the Baltic Sea: an extrapolation using sediment characteristics Deutsch B. 1 3 Forster S. 2 Wilhelm M. 1 Dippner J. W. 1 Voss M. 1 Leibniz Institute for Baltic Sea Research-Warnemünde, Seestrasse 15, 18119 Rostock, Germany University of Rostock, Albert Einstein Str. 3, 18059 Rostock, Germany now at: Department of Applied Environmental Science, Stockholm University, Sweden 21 10 2010 7 10 3259 3271 Copyright: © 2010 B. Deutsch et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/7/3259/2010/bg-7-3259-2010.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/7/3259/2010/bg-7-3259-2010.pdf

Rates of denitrification in sediments were measured with the isotope pairing technique at different sites in the southern and central Baltic Sea. The rates varied between 0.5 μmol N m<sup>−2</sup> h<sup>−1</sup> in sands and 28.7 μmol N m<sup>−2</sup> h<sup>−1</sup> in muddy sediments and showed a good correlation to the organic carbon contents of the surface sediments. N-removal rates via sedimentary denitrification were estimated for the entire Baltic Sea calculating sediment specific denitrification rates and interpolating them to the whole Baltic Sea area. Another approach was carried out by using the relationship between the organic carbon content and the rate of denitrification. The N-removal by denitrification in sediments varied between 426–652 kt N a<sup>−1</sup>, which is around 48–73% of the external N inputs delivered via rivers, coastal point sources, and atmospheric deposition. Moreover, an expansion of the anoxic bottom areas was considered under the assumption of a rising oxycline from 100 to 80 m water depth. This leads to an increase of the area with anoxic conditions and an overall decrease in sedimentary denitrification by 14%. Overall, we show here that this type of data extrapolation is a powerful tool to estimate the nitrogen losses for a whole coastal sea and may be applicable to other coastal regions and enclosed seas.

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