The Baltic Sea a century ago - a reconstruction from model simulations, verified by observations

Pre-industrial trophic conditions in the Baltic Sea were simulated with SANBALTS (Simple As Necessary BAltic Long-Term large Scale) model. External nutrient inputs to the major basins of the Baltic Sea a century ago were reconstructed from various literature and data sources. The reconstructed input of total nitrogen was less than a half and that of total phosphorus was about a third of their contemporary values. The simulated pre-industrial conditions are validated by comparison to actual historical data on the water transparency, oxygen concentration, primary production, and net sediment accumulation. The pre-industrial trophic state could have been more phosphorus limited than today because simulated basin-wide annual averages of dissolved inorganic phosphorus concentrations of 0.06-0.3 mu M P are about 40-80% of their present day values, while dissolved inorganic nitrogen concentrations of 2-4 mu M N are almost the same as today or even slightly higher. (C) 2008 Elsevier B.V. All rights reserved.