On the response of the Baltic proper to changes of the total phosphorus supply

Using a time-dependent phosphorus (P) budget model for the Baltic proper, describing sources and sinks at the external borders of the water column, one may compute the e-folding time T of the adjustment of the winter surface water P concentration c (1) to abruptly changed total P supply. The restoration time TR = 3T is introduced as a practical measure of the time it takes to achieve 95% of the change of c (1) towards the final, equilibrium, state c (1e). The P budget model, including an internal source emanating from deep anoxic bottoms, also shows that c (1e) is proportional to the total P supply to the water column. About 70% of present time total P supply to the Baltic proper comes from deep anoxic bottoms. If deep bottoms were kept oxygenated, this internal P supply would be turned off and the equilibrium concentration c(1e) would be reduced by about 70%. This should imply that the Baltic proper may be restored to a state determined by the external P supplies from land-based and oceanic sources. According to the model, restoration would take 10-15 years. Thereafter most of the equipment used for oxygenation may be shut off since also the deepwater oxygen demand by decomposition of fresh organic matter, would have decreased by about 70% implying that the deepwater would be kept oxic by the natural vertical circulation. The model presented in this paper provides a new science-based solution of the eutrophication problem of the Baltic proper, which is of great interest from a management point of view.