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Riverine transport of biogenic elements to the Baltic Sea – past and possible future perspectives

Author(s): C. Humborg | C.-M. Mörth | M. Sundbom | F. Wulff

Journal: Hydrology and Earth System Sciences Discussions
ISSN 1812-2108

Volume: 4;
Issue: 3;
Start page: 1095;
Date: 2007;
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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, increased hydropower demand and global warming, i.e., changes in hydrological patterns. 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 will increase due to higher live stock densities in those countries recently acceded to the EU, whereas P and Si fluxes will decrease due to an increase in 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 will be substituting 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 both dissolved organic carbon and alkalinity, that have opposite feedbacks to global warming will increase in similar amounts, since the spring flow peak will be smoothed out in time due to higher temperatures that cause less snow cover and deeper soil infiltration.

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