Indicator: River eutrophication by phosphorus

• Too high phosphorus concentrations are measured at more than half of all river measurement stations in Germany.
• The share has declined by around one third since the beginning of the 1980s. Extreme levels of pollution are very rare nowadays.
• Aim of the Sustainability Strategy is to meet the requirements for good status for phosphorous in all water bodies by 2030 at the latest.
• This requires a change in fertiliser practices in agriculture. Also, very small sewage treatment plants need to remove phosphorus in accordance with current technology.

The majority of Germany's water bodies are not in a good status (cf. indicators of the ecological status of rivers, lakes and seas). The overfertilization of water bodies (eutrophication) with phosphorus is one of the biggest problems because it triggers excessive growth of algae and aquatic plants. When these die, they are decomposed by microorganisms. In the process, a lot of oxygen is consumed. Oxygen deficits in water bodies have a negative effect on fish and other aquatic organisms; in extreme situations, it can lead to the death of fish. To avoid overfertilization, the load of phosphorus in particular must be reduced. The map service “Nutrients and Salts” shows assessments for approx. 250 measuring points in German rivers (in German only).

In the early 1980s, excessive phosphorus concentrations were measured at almost 90 % of sampling sites. Since 2018 this share has remained slightly below 60 %. However, if the poorer quality classes are considered, then a further improvement can be seen. Overall, the share of sampling sites where the requirement for phosphorus was exceeded has decreased. This improvement is mainly the result of introducing phosphate-free washing powders and phosphate precipitation in the larger sewage treatment plants.

There are currently shortages in the supply of precipitants (e.g. aluminum salts), which are used to remove phosphorus from sewage in wastewater treatment plants. If these chemicals are not available in sufficient quantities for wastewater treatment, this results in an increase in phosphorus concentrations in the water.

According to the European Water Framework Directive (EU Directive 2000/60/EC), all water bodies must achieve a good ecological status by 2027. In Germany almost two thirds of water bodies have concentrations of phosphorus which are too high to meet this requirement. In order to remedy this, the fertiliser ordinance is intended to induce agriculture to apply less liquid manure nor mineral fertilisers containing phosphorus to soils sufficiently supplied with phosphorus. In eutrophic areas, the requirements can be made stricter. Impact monitoring will show whether this is sufficient. Also, the waste water regulation should be changed in such a way that small purification plants remove phosphorus after the state-of-the-art. This is already happening in the bigger plants. According to Objective 6.1.a of the German Sustainable Development Strategy, the guideline values for phosphorus should be complied with by 2030 at the latest.

The Federal States send measurements to the German Environment Agency from approximately 250 representative sampling sites. For classification in a water quality class, the mean value of the phosphorus concentration is compared with the concentration which should not be exceeded for good ecological status in the respective water type (orientation value). Details are regulated in annex 7 to the Ordinance on the Protection of Surface Water (OGewV 2016). They range between 0.1 and 0.15 milligrams per litre of phosphorus (0.3 mg/l for one type), depending on the watercourse type; and 0.045 mg/l in transitional waters. The indicator gives the share of measuring sites that do not comply with these guideline values.