Europe's discharge of nitrogen and phosphorus calculated

Agriculture discharges the most nitrogen into Europe's coastal seas. Discharges of phosphorus come from treatment works to a larger extent, although in some areas agriculture and forestry are responsible for large discharges. This is shown by a study carried out by scientists at SMHI.

For the first time scientists have carried out a complete calculation of the amount of nitrogen and phosphorus transported daily by watercourses and from coastal areas to the seas around Europe, and which sources they originate from. The calculation takes into account that a certain percentage of the nutrient salts nitrogen and phosphorus is delayed, converted and to some extent remains in watercourses and lakes.

Nutrient salts play an important role in the eutrophication of watercourses and maritime environments.

“It's important to know where the discharges come from in order to improve the water quality in the coastal seas and, in the long term, reduce algal bloom in vulnerable areas to which the discharges are led by sea currents,” says Chantal Donnelly, a hydrology scientist at SMHI.

Agriculture a major source

The results show that agriculture accounts for the largest discharges of nitrogen, with artificial fertilizers and soil cultivation being contributing factors. Only in the two areas which flow into the Arctic Ocean and the Celtic Sea did forestry and point sources respectively have a larger impact, but the levels here are very low. The total discharge in these areas is far lower than in other parts of Europe.
 

Total amount and division of sources of nitrogen discharges from land to the seas around Europe.
Total amount and division of sources of nitrogen discharges from land to the seas around Europe. A = Agriculture, F = Forestry, PS = Point sources (such as treatment works and industrial operations), RH = Rural Households, Other.
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Phosphorus comes from treatment works to a larger extent and they are considered point sources. But here too agriculture is a major contributor in large parts of Europe.

“The division between sources for Europe closely resembles that for Sweden. But natural treatment when nutrient salts are delayed, converted and to some extent remain in watercourses and lakes is lower in Europe than in Sweden because there are fewer lakes on the continent,” says Niclas Hjerdt, head of marketing for hydrology and water management at SMHI.
 

Total mängd fosfor (ton/år) samt källfördelning
Total amount and division of sources of phosphorus discharges from land to the seas around Europe. A = Agriculture, F = Forestry, PS = Point sources (such as treatment works and industrial operations), RH = Rural Households, Other.
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Water treatment important for total amounts

The results also show that the total amounts of discharged nitrogen and phosphorus vary across Europe.

“The countries around the Baltic Sea have been treating the water for a long time, and this means that discharges of phosphorus in particular are lower than for the Black Sea. Improved treatment around, for example, the Black Sea would have a major impact,” says Donnelly.

The calculation for the whole of Europe is made using dynamic modelling and is an initial basis which will be gradually improved in new versions of the model. It should also be supplemented with more detailed studies into which measures can be introduced to reduce discharges.

The calculation of nitrogen and phosphorus from agriculture, forestry, point sources and rural households to Europe's coastal seas has been carried out with E-HYPE. E-HYPE is SMHI's model for calculating and simulating water flows in Europe and to Europe's coasts.

SMHI carries out daily calculations of water flows and the transport of nutrients in drainage areas across Europe and to seas near the European coasts. The calculations are currently used by oceanographers in Europe in sea models.