Indicator: Eutrophication of the North Sea/Baltic Sea by nitrogen

A graph shows the change in concentration of total nitrogen in all the main rivers which enter the North Sea and Baltic Sea in Germany. A distinction is made between the North Sea and the Baltic Sea. The concentration value is given as the moving average of the flows of the past 5 years in milligrams per litre.Click to enlarge
Outflow-weighted mean of the total nitrogen concentration of the North Sea and Baltic Sea inlets
Source: German Environment Agency according to the Federal States and River Basin Communities Figure as PDF

Table of Contents

 

At a glance

  • To achieve the objectives for the protection of the marine environment, Germany has committed to comply with maximum concentrations of nitrogen at estuaries.
  • These target concentrations in the North Sea and Baltic Sea are only slightly exceeded on average by all rivers, but some rivers still have very high concentrations.
  • In order to fulfil the objectives, it is necessary that each river achieves the target.
  • In order to achieve further reductions in nitrogen concentrations in the rivers, measures need to be taken, especially in agriculture.
 

Environmental importance

Coastal and transitional waters of the German North Sea and Baltic Sea fail to achieve “good ecological status”. The main cause of this are the excessive nutrient loads of nitrogen and phosphorous (eutrophication). The negative effects of eutrophication are described by the indicator ‘Ecological status of transitional and coastal waters’.

Nutrients are carried into the sea mainly via rivers. This indicator considers the concentration of nitrogen in the rivers entering the North Sea and the Baltic Sea in Germany and in the Rhine border river (the Oder is excluded). These concentrations can fluctuate significantly depending on the weather, because in years with plentiful precipitation more nitrogen is leached out of the soils. In terms of the nutrient phosphorous, it can be assumed that the achievement of the guideline values that have been set for rivers is sufficient for the achievement of good status of the coastal and marine waters (cf. ‘River eutrophication by phosphorus’).

 

Assessing the development

In order to achieve the EU Water Framework Directive (WFD, 2000/60/EG) and the EU Marine Strategy Framework Directive (MSFD, 2008/56/EG), the German Surface Waters Ordinance sets management target values for the rivers running into the North Sea and Baltic Sea (OGewV 2016, in German only): 2.6 milligrammes of total nitrogen per litre (mg/l) for rivers flowing into the Baltic Sea and 2.8 mg/l for those flowing into the North Sea. These target values were also adopted for the German Sustainable Development Strategy (BReg 2016).

Average nitrogen concentrations have decreased since the start of monitoring, mainly due to improvements in wastewater treatment. However, concentrations have stagnated in recent years. While the average of all rivers (3.0 mg/l in the Baltic Sea and 2.9 mg/l in the North Sea) is approaching the target value, the concentrations of individual rivers are still well above or even below the target value. The Baltic inflows have higher maximum concentrations than the North Sea inflows. The minimum concentrations of the North Sea and Baltic Sea inflows are already below the limit values.

The main responsibility for achieving these target values lies with the Federal States. The federal government provides the legal framework through the Fertiliser Ordinance and the Waste Water Ordinance, and the Länder implement these ordinances and monitor compliance with them. Measures to reduce the input of nutrients are being taken as part of the implementation of the WFD. Currently most pollution comes from agriculture. The amendment to the German Fertiliser Application Ordinance will lead to a reduction in this pollution in the medium term (cf. ‘Agricultural nitrogen surplus‘ indicator). It is likely that additional measures will be needed in agriculture in order to achieve the target values.

 

Methodology

The Federal States where the rivers flow into the North and Baltic Seas maintain measuring stations at the estuaries. The nitrogen concentration of each of the flowing waters is measured at these stations at least once a month. These measured values, averaged over a period of a year, are used as the basis for the indicator. In order to compensate for annual weather-related fluctuations, the indicator is calculated as the moving average of the last 5 years and the individual flows are weighted on the basis of their outflow. In addition, the maximum and minimum concentrations were calculated as moving averages for the last 5 years.

More detailed information: 'Flusseinträge und direkte Einträge in die Nordsee' and 'Flusseinträge und direkte Einträge in die Ostsee' (in German only).