HESS Hydrology and Earth System Sciences HESS Hydrol. Earth Syst. Sci. 1607-7938 Copernicus Publications Göttingen, Germany 10.5194/hess-11-1593-2007 Riverine transport of biogenic elements to the Baltic Sea – past and possible future perspectives Humborg C. 1 4 Mörth C.-M. 2 4 Sundbom M. 1 Wulff F. 3 4 Dept. of Applied Environmental Science, Stockholm University, 10691 Stockholm, Sweden Dept. of Geology & Geochemistry, Stockholm University, 10691 Stockholm, Sweden Dept. of Systems Ecology, Stockholm University, 10691 Stockholm, Sweden Baltic Nest Institute, Stockholm University, 10691 Stockholm, Sweden 26 09 2007 11 5 1593 1607 Copyright: © 2007 C. Humborg et al. 2007 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/ This article is available from https://hess.copernicus.org/articles/11/1593/2007/hess-11-1593-2007.html The full text article is available as a PDF file from https://hess.copernicus.org/articles/11/1593/2007/hess-11-1593-2007.pdf

The paper reviews critical processes for the land-sea fluxes of biogenic elements (C, N, P, Si) in the Baltic Sea catchment and discusses possible future scenarios as a consequence of improved sewage treatment, agricultural practices and increased hydropower demand (for N, P and Si) and of global warming, i.e., changes in hydrological patterns (for C). These most significant drivers will not only change the total amount of nutrient inputs and fluxes of organic and inorganic forms of carbon to the Baltic Sea, their ratio (C:N:P:Si) will alter as well with consequences for phytoplankton species composition in the Baltic Sea. In summary, we propose that N fluxes may increase due to higher livestock densities in those countries recently acceded to the EU, whereas P and Si fluxes may decrease due to an improved sewage treatment in these new EU member states and with further damming and still eutrophic states of many lakes in the entire Baltic Sea catchment. This might eventually decrease cyanobacteria blooms in the Baltic but increase the potential for other nuisance blooms. Dinoflagellates could eventually substitute diatoms that even today grow below their optimal growth conditions due to low Si concentrations in some regions of the Baltic Sea. C fluxes will probably increase from the boreal part of the Baltic Sea catchment due to the expected higher temperatures and heavier rainfall. However, it is not clear whether dissolved organic carbon and alkalinity, which have opposite feedbacks to global warming, will increase in similar amounts, because the spring flow peak will be smoothed out in time due to higher temperatures that cause less snow cover and deeper soil infiltration.

 References Algesten, G., Sobek, S., Bergstrom, A. K., Agren, A., Tranvik, L. J., and Jansson, M.: Role of lakes for organic carbon cycling in the boreal zone, Global Change Biol., 10, 141–147, 2004. Berner, E. K. and Berner, R. A.: Global Environment: Water, Air and Geochemical Cycles, Prentice Hall, 1995. Boyer, E. W., Hornberger, G. M., Bencala, K. E., and McKnight, D.: Overview of a simple model describing variation of dissolved organic carbon in an upland catchment, Ecol. Model., 86, 183–188, 1996. Boyer, E. W., Goodale, C. L., Jaworski, N. A., and Howarth, R. W.: Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the northeastern USA, Biogeochemistry, 57, 137–169, 2002. Campling, P., Terres, J. M., Walle, S. V., Van Orshoven, J., and Crouzet, P.: Estimation of nitrogen balances from agriculture for EU-15: spatialisation of estimates to river basins using the CORINE Land Cover, Phys. Chem. Earth, 30, 25–34, 2005. Egge, J. K. and Aksnes, D. L.: Silicate as Regulating Nutrient in Phytoplankton Competition, Mar. Ecol.-Prog. Ser., 83, 281–289, 1992. Eriksson, H., Pastuszak, M., Löfgren, S., Mörth, C.-M., and Humborg, C.: Nitrogen budgets of the Polish agriculature 1960-2000: implications for riverine nitrogen loads to the Baltic Sea from transitional countries, Biogeochemistry, 85, 153–168, 2007. Evans, C. D., Freeman, C., Monteith, D. T., Reynolds, B., and Fenner, N.: Climate change – Terrestrial export of organic carbon – Reply, Nature, 415, 862–862, 2002. Evans, C. D., Chapman, P. J., Clark, J. M., Monteith, D. T., and Cresser, M. S.: Alternative explanations for rising dissolved organic carbon export from organic soils, Global Change Biol., 12, 2044–2053, 2006. Freeman, C., Evans, C. D., Monteith, D. T., Reynolds, B., and Fenner, N.: Export of organic carbon from peat soils, Nature, 412, 785–785, 2001. Gorham, E.: Northern Peatlands – Role in the Carbon-Cycle and Probable Responses to Climatic Warming, Ecol. Appl., 1, 182–195, 1991. Graham, L. P.: Climate change effects on river flow to the Baltic Sea, Ambio, 33, 235–241, 2004. Grant, R., Nielsen, K., and Waagepetersen, J.: Reducing nitrogen loading of inland and marine waters – Evaluation of Danish policy measures to reduce nitrogen loss from farmland, Ambio, 35, 117–123, 2006. Haith, D. A. and Shoemaker, L. L.: Generalized Watershed Loading Functions for Stream-Flow Nutrients, Water Resour. Bull., 23, 471–478, 1987. Hannerz, F. and Destouni, G.: Spatial characterization of the Baltic Sea Drainage Basin and its unmonitored catchments, Ambio, 35, 214–219, 2006. HELCOM: The fourth Baltic Sea pollution load compilation (PLC-4), Baltic Sea Environment Proceedings, Baltic Sea Environment Proceedings, 93, 133 pp., 2004. Hinzman, L. D., Bettez, N. D., Bolton, W. R., Chapin, F. S., Dyurgerov, M. B., Fastie, C. L., Griffith, B., Hollister, R. D., Hope, A., Huntington, H. P., Jensen, A. M., Jia, G. J., Jorgenson, T., Kane, D. L., Klein, D. R., Kofinas, G., Lynch, A. H., Lloyd, A. H., McGuire, A. D., Nelson, F. E., Oechel, W. C., Osterkamp, T. E., Racine, C. H., Romanovsky, V. E., Stone, R. S., Stow, D. A., Sturm, M., Tweedie, C. E., Vourlitis, G. L., Walker, M. D., Walker, D. A., Webber, P. J., Welker, J. M., Winker, K., and Yoshikawa, K.: Evidence and implications of recent climate change in northern Alaska and other arctic regions, Climatic Change, 72, 251–298, 2005. Howarth, R. W., Billen, G., Swaney, B., Townsend, A., Jaworski, N., Lajtha, K., Downing, J. A., Elmgren, R., Caraco, N., Jordan, T., Berendse, F., Freney, J., Kudeyarov, V., Murdoch, P., and Zhu Zhao, L.: Regional nitrogen budgets and riverine N & P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences, Biogeochemistry, 35, 75–139, 1996. Humborg, C., Smedberg, E., Mörth, C.-M., Rahm, L., and Danielsson, A.: Dissolved silica dynamics in boreal and arctic rivers: vegetation control over temperature?, in: The Silicon Cycle, edited by: Ittekkot, V., Unger, D., Humborg, C., and Tac An, N., Washington DC, Island Press, 53–69, 2006a. Humborg, C., Conley, D. J., Rahm, L., Wulff, F., Cociasu, A., and Ittekkot, V.: Silicon retention in river basins: Far-reaching effects on biogeochemistry and aquatic food webs in coastal marine environments, Ambio, 29, 45–50, 2000. Humborg, C., Pastuszak, M., Aigars, J., Siegmund, H., Mörth, C. M., and Ittekkot, V.: Decreased silica land-sea fluxes through damming in the Baltic Sea catchment – significance of particle trapping and hydrological alterations, Biogeochemistry, 77, 265–281, 2006b. Humborg, C., Blomqvist, S., Avsan, E., Bergensund, Y., Smedberg, E., Brink, J., and Mörth, C. M.: Hydrological alterations with river damming in northern Sweden: Implications for weathering and river biogeochemistry, Global Biogeochem. Cy., 16, GB1039, https://doi.org/10.1029/2000GB001369, 2002. Humborg, C., Smedberg, E., Blomqvist, S., Mörth, C. M., Brink, J., Rahm, L., Danielsson, A., and Sahlberg, J.: Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land-sea fluxes, Limnol. Oceanogr., 49, 1871–1883, 2004. Iital, A., Stålnacke, P., Deelstra, J., Loigu, E., and Pihlak, M.: Effects of large-scale changes in emissions on nutrient concentrations in Estonian rivers in the Lake Peipsi drainage basin, J. Hydrol., 304, 261–273, 2005. Johansson, S., Bonsdorff, E., and Wulff, F.: The MARE Research Program 1999–2006 – Reflections on program management, Ambio, 36, 119–122, 2007. Johnes, P. J., Moss, B., and Phillips, G. L.: The determination of water quality by land use, livestock numbers and population data – testing of a model for use in conservation and water quality management, Freshw. Biol., 36, 451–473, 1996. Kronvang, B., Jeppesen, E., Conley, D. J., Sondergaard, M., Larsen, S. E., Ovesen, N. B., and Carstensen, J.: Nutrient pressures and ecological responses to nutrient loading reductions in Danish streams, lakes and coastal waters, J. Hydrol., 304, 274–288, 2005. Lasaga, A.: Kinetic Theory in Earth Sciences, Princton University Press, 1998. Lehner, B., Czisch, G., and Vassolo, S.: The impact of global change on the hydropower potential of Europe: a model-based analysis, Energy Policy, 33, 839–855, 2005. Löfgren, S., Gustafson, A., Steineck, S., and Stålnacke, P.: Agricultural development and nutrient flows in the Baltic states and Sweden after 1988, Ambio, 28, 320–327, 1999. Meybeck, M.: Pathways of major elements from land to ocean through rivers, in: River Inputs to Ocean Systems, edited by: Martin, J.-M., Burton, J. D., and Eisma, D., UNEP IOC SCOR United Nations, 18–30, 1979. Mörth, C.-M., Humborg, C., Eriksson, E., Danielsson, A., Medina, R., Löfgren, S., Swaney, D. P., and Rahm, L.: Modeling riverine nutrient transport of the Baltic Sea-A large scale approach, Ambio, 36, 124–133, 2007. Nixon, S. W.: Coastal Marine Eutrophication – a Definition, Social Causes, and Future Concerns, Ophelia, 41, 199–219, 1995. Oenema, O., Boers, P. C. M., van Eerdt, M. M., Fraters, B., van der Meer, H. G., Roest, C. W. J., Schroder, J. J., and Willems, W. J.: Leaching of nitrate from agriculture to groundwater: the effect of policies and measures in the Netherlands, Environ. Pollut., 102, 471–478, 1998. Peterson, B. J., Holmes, R. M., McClelland, J. W., Vörösmarty, C. J., Lammers, R. B., Shiklomanov, A. I., Shiklomanov, I. A., and Rahmstorf, S.: Increasing river discharge to the Arctic Ocean, Science, 298, 2171–2173, 2002. Rukhovets, L. A., Astrakhantsev, G. P., Menshutkin, V. V., Minina, T. R., Petrova, N. A., and Poloskov, V. N.: Development of Lake Ladoga ecosystem models: modeling of the phytoplankton succession in the eutrophication process. I, Ecol. Model., 165, 49–77, 2003. Sandberg, J., Andersson, A., Johansson, S., and Wikner, J.: Pelagic food web structure and carbon budget in the northern Baltic Sea: potential importance of terrigenous carbon, Mar. Ecol.-Prog. Ser., 268, 13–29, 2004. Sapek, A.: The Effects of Agriculture on Water Quality: A Polish Perspective, in: Center for Agricultural and Rural Development, Iowa State University, p 22, 1997. Schelske, C. L., Stoermer, E. F., Conley, D. J., Robbins, J. A., and Glover, R. M.: Early eutrophication in the lower Great Lakes: New evidence from biogenic silica in sediments, Science, 222, 320–322, 1983. Schernewski, G. and Neumann, T.: The trophic state of the Baltic Sea a century ago: a model simulation study, J. Mar. Syst., 53, 109–124, 2005. Smedberg, E., Mörth, C. M., Swaney, D. P., and Humborg, C.: Modeling hydrology and silicon-carbon interactions in taiga and tundra biomes from a landscape perspective: Implications for global warming feedbacks, Global Biogeochem. Cy., 20, GB2014, https://doi.org/10.1029/2005GB002567, 2006. Sobek, S., Tranvik, L. J., and Cole, J. J.: Temperature independence of carbon dioxide supersaturation in global lakes, Global Biogeochem. Cy., 19, GB2003, https://doi.org/10.1029/2005GB002567, 2006. Stålnacke, P., Grimvall, A., Sundblad, K., and Wilander, A.: Trends in nitrogen transport in Swedish rivers, Environ. Monit. Assess., 59, 47–72, 1999a. Stålnacke, P., Grimvall, A., Sundblad, K., and Tonderski, A.: Estimation of riverine loads of nitrogen and phosphorus to the Baltic Sea, 1970–1993, Environ. Monit. Assess., 58, 173–200, 1999b. Stålnacke, P., Grimvall, A., Libiseller, C., Laznik, A., and Kokorite, I.: Trends in nutrient concentrations in Latvian rivers and the response to the dramatic change in agriculture, J. Hydrol., 283, 184–205, 2003. Tranvik, L. J. and Jansson, M.: Climate change – Terrestrial export of organic carbon, Nature, 415, 861–862, 2002. Treguer, P., Nelson, D. M., van Bennekom, A. J., Demaster, D. J., Leynaert, A., and Queguiner, B.: The silica balance in the world ocean – a reestimate, Science, 268, 375–379, 1995. Vagstad, N., Stålnacke, P., Andersen, H. E., Deelstra, J., Jansons, V., Kyllmar, K., Loigu, E., Rekolainen, S., and Tumas, R.: Regional variations in diffuse nitrogen losses from agriculture in the Nordic and Baltic regions, Hydrol. Earth Syst. Sci., 8, 651–662, 2004. Vahtera, E., Conley, D. J., Gustafsson, B. G., Kuosa, H., Pitkanen, H., Savchuk, O. P., Tamminen, T., Viitasalo, M., Voss, M., Wasmund, N., and Wulff, F.: Internal ecosystem feedbacks enhance nitrogen-fixing cyanobacteria blooms and complicate management in the Baltic Sea, Ambio, 36, 186–194, 2007. Walker, D. A., Auerbach, N. A., Bockheim, J. G., Chapin, F. S., Eugster, W., King, J. Y., McFadden, J. P., Michaelson, G. J., Nelson, F. E., Oechel, W. C., Ping, C. L., Reeburg, W. S., Regli, S., Shiklomanov, N. I., and Vourlitis, G. L.: Energy and trace-gas fluxes across a soil pH boundary in the arctic, Nature, 394, 469–472, 1998. Weyhenmeyer, G. A., Meili, M., and Livingstone, D. M.: Nonlinear temperature response of lake ice breakup, Geophys. Res. Lett., 31, LO7203, https://doi.org/10.1029/2004GLO19530, 2004. Winsor, P., Rodhe, J., and Omstedt, A.: Baltic Sea ocean climate: an analysis of 100 yr of hydrographic data with focus on the freshwater budget, Climate Res., 18, 5–15, 2001. Witek, Z., Humborg, C., Savchuk, O., Grelowski, A., and Lysiak-Pastuszak, E.: Nitrogen and phosphorus budgets of the Gulf of Gdansk (Baltic Sea), Estuar. Coast. Shelf Sci., 57, 239–248, 2003. Wulff, F., Savchuk, O., Sokolov, A., Humborg, C., and Mörth, C.-M.: Management options and effects on a marine ecosystem: Assessing the future of the Baltic., Ambio, 36, 243–249, 2007. Zessner, M. and Lindtner, S.: Estimations of municipal point source pollution in the context of river basin management, Water Sci. Technol., 52, 175–182, 2005.