The accumulated pool of phosphorus on land receives much less attention than the pool in the Baltic Sea, despite being substantially larger and the ultimate source to the sea.
Actions taken to reduce the internal load will not address the causes of eutrophication. Instead, actions must focus on improving both nutrient use efficiency in agriculture and sewage treatment.
Eutrophication constitutes the greatest threat to the Baltic Sea ecosystem, affecting marine animals, plants, and habitats and limiting opportunities for people to enjoy the sea. How to address eutrophication is a hot topic in the debate in many countries around the Baltic Sea.
Lately, phosphorus released from the pool in the Baltic Sea ecosystem – the internal load – has been brought forward as the main cause of eutrophication. Some argue that the magnitude of recycling from this accumulated stock is so huge that actions on land will not have any effect. Others go further and suggest different geo-engineering actions as the best way to save the Baltic Sea ecosystem.
Unfortunately, the ongoing debate on how to best address eutrophication in relation to internal load is characterised by a number of misconceptions. The most common one is to refer to internal load as a new source of phosphorus to the Baltic Sea. It is not.
The ultimate source of phosphorus to the Baltic Sea comes from the pool of phosphorus on land. This is called the external load.