Agriculture is a large source of nutrients to the Baltic Sea. Only about half of the nutrients in fertiliser and manure are converted to harvested crops. Nutrient use efficiency must improve.
Human inputs of nitrogen and phosphorus to the Baltic Sea are responsible for the eutrophication that is apparent in algal blooms, reduced water clarity, changes in species composition, and reduced oxygen concentrations in bottom waters.
The Baltic Sea is particularly sensitive to eutrophication because of limited exchange of water with the North Sea. Together, these environmental stressors limit opportunities for people to enjoy the sea.
Agriculture is the single largest source of new nutrients to the Baltic Sea, contributing about half of total waterborne nitrogen and phosphorus inputs. A major portion of mineral fertiliser and livestock feed which is imported to the catchment is transformed into manure; however, the nutrients in manure are often not used efficiently in crop production.
This inefficiency can result in the accumulation of nutrients in agricultural soils and increase the risk of losses to lakes, streams, and the Baltic Sea. There is potential to reduce these nutrient losses by improving manure management and replacing imported mineral fertilizers with manure.
Reducing the import of livestock feed and the number of animals in regions with high densities can also reduce agricultural nutrient surpluses.
This policy brief presents research regarding agricultural nutrient flows for the whole Baltic Sea catchment in the context of eutrophication.
The State of the Baltic Sea
Progress has been made in reducing nutrient inputs to the Baltic Sea. Since 1995, nitrogen inputs have decreased by 17 % and phosphorus by 20 %.
After nutrient inputs are reduced, it will take time before there are noticeable improvements. Although the eutrophication status of most parts of the Baltic Sea is still poor, improvement is seen in some areas, such as the Gulf of Finland, Kattegat, and Danish Straights.
It took decades for the sea to become eutrophic and it will take decades for it to recover. However, reducing nutrient leakage on land will not only benefit the sea, but also lakes, rivers and groundwater.