Causes of eutrophication

The atmospheric deposition of nitrogen compounds in Europe is due, in roughly equal parts, to emissions of nitrogen oxides and ammonia.

Nitrogen oxides are always produced during combustion. Emissions from land-based sources in Europe have fallen from 23 million tonnes a year in 1980 to 13 million tonnes a year in 2010, a reduction of 44 per cent. About half the emissions in Europe come from the transport sector, and most the rest from combustion plants. In the case of nitrogen oxides a large part of the emission reduction from land-based sources has been offset by rising emissions at sea. Ship emissions around Europe increased from 2.4 to 4.0 million tonnes between 1980 and 2010.

The main source of ammonia emissions is agriculture. The amount of ammonia that evaporates depends primarily on how the manure is handled during storage and spreading. According to statistics, emissions have fallen by 34 per cent between 1990 and 2010, from 7.6 to 5.0 million tonnes per year.

Due to long-range transport by winds, the problems are largely unrestricted by national borders, especially in the case of nitrogen oxides and their transformation products.

The atmospheric deposition of nitrogen compounds in Europe is greatest in the Netherlands, Belgium, France, southern England, northern Germany, and northern Italy.

The reason why the situation is worst in areas with intensive agriculture is that a relatively large proportion of nitrogen from ammonia, 90 per cent of which comes from livestock farming, is deposited relatively close to the source of emissions.

Note that it is not just airborne nitrogen that ends up in nature. In many environments nitrogen is also added in the form of fertilizer. Large amounts are spread on fields, and sometimes also on natural grazing land, which leads to impoverishment of the natural flora. Fertilizer is also spread on forest land to increase forestry yield. In addition to direct deposition, nitrogen also reaches the sea through leaching from the land and discharges from wastewater treatment plants and individual households.