Baltic eutrophication

The external supply (source) of phosphorus (P) to the Baltic has been halved since the middle of the 1980s. In spite of this, the phosphorus content in the water column of the Baltic has continued to increase, which has led to increasing areas of anoxic bottoms and increasing blooms of cyanobacteria.

The eutrophication of the Baltic may be removed quickly by man-made oxygenation of the anoxic deepwater. Oxygenation can be done at low cost because there is a huge renewable oxygen reservoir in the so-called winter water, usually residing between 30 and 50 m depth, that each winter is cooled and saturated with oxygen.

As a first step toward oxygenation of the whole Baltic proper one should build an array of pumps for the Bornholm Basin, where pumping winter water (1000 m³/s) down into the deepwater would keep the deepwater oxygenated. However, before that one has to complete an environmental impact study (EIS).

The main weakness with the oxygenation method to remove the eutrophication of the Baltic is that it is unbelievably cheap and effective. It is hard for people to understand that this huge old problem can be solved so easily and at such a low cost.