Estimated nutrient load from waste waters originating from ships in the Baltic Sea area

Maritime transport in the Baltic Sea area, and especially in the Gulf of Finland, has changed significantly over the last decade. The new oil terminals in Russia and the economic boom in the Baltic States have resulted in remarkable rise in maritime traffic, mainly tankers and cargo ships. At the same time, the vulnerable nature of the Baltic Sea and the ever-increasing eutrophication has made it necessary to reduce the nutrient load. The purpose of this study was to estimate the nutrient load from waste waters originating from ships in the Baltic Sea area. The study also includes information about the maritime traffic, waste water management and legislation. The nutrient load originating from pleasure craft was not included in the study. The estimated nutrient load from ship-generated sewage was calculated, assuming there is no waste water treatment onboard and all waste waters are discharged into the sea. The ship-borne nitrogen load represents approximately 0.05% of the total nitrogen load, and the phosphorus load represents approximately 0.5% of the total phosphorus load both into the Baltic Sea and into the Gulf of Finland. The nutrient load from ships' exhaust gases contributes to 6% of the total atmospheric deposition of nitrogen. The main nutrient load into the Baltic Sea is derived from water-borne inputs and atmospheric deposition. On the basis of the calculations and references, the nutrient load originating from ships is rather small, but not negligible due to the sensitivity of the Baltic Sea marine environment. The nutrient load is concentrated along the shipping routes and is immediately available for uptake by, e.g., blue green algae, adding to the severe eutrophication of the Baltic Sea. The nutrient load from ships is much easier to reduce, when compared to the atmospheric emissions or nutrient inputs from land-based sources, by ordering ships to discharge the sewage into the sewer network ashore or by installing waste water purification systems onboard. In the future, it is likely that limits will be set for the concentration of nitrogen and phosphorus in ships' waste waters.