A new study estimates that 45 percent of waterborne phosphorus to the Baltic Sea is from legacy sources; 14 percent is from rapidly transported sources, 8 percent is sewage from coastal cities. The remaining 33 percent is from natural, background sources. Illustration: Elsa Wikander/Azote



Over the past century, countries around the Baltic Sea have applied more than 44 million tons of mineral phosphorus fertilisers to agricultural soils. Throughout the years, farmers been advised to apply large amounts of mineral fertiliser and manure to increase crop yields. As a result, more fertiliser has been applied than has been removed with harvested crops, and this has led to the accumulation of phosphorus in soils. A more balanced fertilisation is recommended nowadays, but there are still areas with large surpluses.

For the Baltic Sea catchment as a whole, the amount of phosphorus that has accumulated in agricultural soils is the same order of magnitude as three decades of crop nutrient needs. Phosphorus from human sewage wastewater has also accumulated on land. In the early days of flush toilets, wastewater was untreated or poorly treated and disposed of in nearby surface waters. Some phosphorus from this wastewater likely remains in the sediments of rivers and lakes that flow to the Baltic Sea.

The legacy can be described as too much of a good thing, because while phosphorus is critical for all life, it can leak to water bodies and have an unintended fertilising effect that contributes to eutrophication. Even if no more phosphorus is applied to land, legacy phosphorus will continue to leak for decades to downstream lakes and coastal areas where it can cause environmental problems.

Recommendations for concrete action

• Limit phosphorus fertilisation by setting maximum application rates or maximum surpluses. Account for current phosphorus status in crop soils.

• Increase the proportion of locally produced feed in animal husbandry, as stated in the EU strategy for the promotion of protein crops, in order to reduce phosphorus imports.

• Improve the use efficiency of manure in agriculture by, for example, supporting farm extension on nutrient management, including soil-nutrient mapping.

• Allocate funding to implement measures that reduce the transport phosphorus that escapes from crop land, such as buffer strips and sedimentation ponds. But to be effective, these measures must be adapted to local conditions. Within the Common Agricultural Policy, this could be achieved by reducing income support (Pillar I) and increase payments for public goods, for instance via the Rural Development Programme (Pillar II).

• Facilitate the development and trade of recycled fertilisers.

• Expand current zones that are deemed as environmentally sensitive or vulnerable to nutrient losses to include livestock density limits.

• All countries around the Baltic Sea should urgently comply with the EU Urban Waste Water Directive. The directive needs to be reviewed and sharpened.



Michelle McCrackin

Limnologist, Baltic Sea Centre
+46 (0)8 16 17 78, 



Read and download

Policy Brief: Phosphorus in the catchment (479 Kb)  (pdf)