, Volume 117, Issue 2–3, pp 455–472 | Cite as

On the importance of quantifying bioavailable nitrogen instead of total nitrogen

  • Linda Jørgensen
  • Stiig MarkagerEmail author
  • Marie Maar


Monitored and modeled data provided the basis for the establishment of two nitrogen (N) budgets covering the Kattegat-Belt Sea area in the period 2000–2009: one for total nitrogen (TN) and one for bioavailable nitrogen (Nbio). Our results show a significant difference between the two budgets, and we argue that Nbio is more important than TN for our understanding of the sources causing marine eutrophication. Consequently, an optimal strategy for abatement of eutrophication aims at minimizing Nbio rather than TN. The TN budget shows that advection from the adjacent seas is the dominant source of N to the Kattegat-Belt Sea area. The loadings from land and atmosphere only account for 14 and 9 % of the TN loadings, respectively. However, when the bioavailability of the different N sources is taken into account, the supply from land and atmosphere becomes relatively more important, now accounting for 21 and 16 %, respectively (37 % in total). The ecological relevance of land and atmosphere loadings is most likely even larger since a fraction of the input from the Skagerrak is exported again before it can support primary production. Water action plans have reduced the direct loadings of TN from land and atmosphere by about 35 % since the 1980s. The contributions from land and atmosphere accounted for 47 % of the Nbio loadings in the 1980s. Hence, loadings from land and atmosphere have only decreased by 10 % points since the 1980s: from 47 to 37 %. The largest sink of TN in the study areas is advection to the adjacent seas (71 %) whereas denitrification and burial only accounts for 17 and 11 %, respectively.


Nitrogen budget Eutrophication Nitrogen Dissolved organic nitrogen Bioavailability 



The authors wish to thank Aarhus University, Department of Bioscience, the Swedish University of Agricultural Sciences, the Baltic Nest Institute, DHI, the Helsinki Commission (HELCOM) and the Danish AgriFish Agency for delivering data for this study. We would also like to thank Cordula Göke for help with GIS calculations and Helle Knudsen-Leerbeck, Michael Olesen, Jesper Andersen and Ciarán Murray for critically reviewing the manuscript. This work was funded by The Danish Council for Strategic Research to the project IMAGE (Integrated Management of Agriculture, Fishery, Environment and Economy, grant no. 09-067259). We also thank two anonymous reviewers and the editor for valuable comments that helped improve the budgets and the manuscript.


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Authors and Affiliations

  1. 1.Department of BioscienceAarhus UniversityRoskildeDenmark
  2. 2.Marine Biological SectionUniversity of CopenhagenHelsingørDenmark

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