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River biogeochemistry and source identification of nitrate by means of isotopic tracers in the Baltic Sea catchments
1Baltic Sea Research Institute, Seestr. 15, 18119 Rostock, Germany
2Stockholm University, Department of System Ecology, 10691 Stockholm, Sweden
3Stockholm University, Department of Applied Environmental Science, 10691 Stockholm, Sweden
4Finnish Environment Institute, P.O. Box 140, 00251 Helsinki, Finnland
5Sea Fisheries Institute, Kollataja 1, 81–332 Gdynia, Poland
6Ruhr Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany
Abstract. Nitrate input to a river is largely controlled by land use in its catchment. We compared the information carried by the isotopic signatures of nitrate in 12 Baltic rivers, in relation to the vegetation cover of their catchments. We found isotope values in nitrate ranging from −2 to 14 for δ15N and 8 to 25 per mil for δ18O. Seasonal signals were evident in all rivers. The annual variability of riverine isotope signatures is presented in detail for one Nordic, the Kemijoki, and two southern rivers, Vistula and Oder. Nordic rivers with relatively pristine vegetation in its catchments show not only low δ15N values and high δ18O-NO3− but also lower annual variability than rivers draining densely populated land. Seasonal signals could be found in all of the rivers. We used load weighted nitrate isotope data and data from the three major sources (farmland/sewage, atmospheric deposition and from runoff of pristine soils) to theoretically estimate the shares of nitrate from these sources. The results agree well with same estimates derived from a Global Land Cover data base. The comparison with an emission model (EM) reveals good agreements for intensively used catchments and rather bad ones for pristine catchments. Advantages and limitations of the tested model types are discussed.
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Citation: Voss, M., Deutsch, B., Elmgren, R., Humborg, C., Kuuppo, P., Pastuszak, M., Rolff, C., and Schulte, U.: River biogeochemistry and source identification of nitrate by means of isotopic tracers in the Baltic Sea catchments, Biogeosciences Discuss., 3, 475-511, 2006. Bibtex EndNote Reference Manager
