Indicator: River eutrophication by phosphorus

A graph shows the measuring points that do not comply with the orientation values for phosphorus for the years 1982 to 2019. These are divided into quality classes depending on the level of exceedance. The proportion without exceedances has increased. The proportion of medium and severe exceedances (QC IV) has fallen sharply.Click to enlarge
Sampling sites which exceed the requirement for good status for total phosphorus in rivers
Source: German Environment Agency from data provided by the German Working Group on water issues of the Federal States and the Federal Government Figure as PDF

Table of Contents

 

At a glance

  • Too high phosphorus concentrations are measured at more than half of all river measurement stations.
  • The share has declined by around one third since the beginning of the 1980s. Very high levels of pollution are very rare nowadays.
  • The Federal Government's aim 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, small sewage treatment plants also need to remove phosphorus in accordance with current technology.
 

Environmental importance

The term ‘eutrophic’ comes from Greek (eu trophos) and means ‘well fed’. Eutrophication is caused by human activities which lead to an accumulation of nutrients in previously nutrient-poor water bodies. Algae and aquatic plants fertilised in this way can then grow excessively and deprive other plant species of light and, when they die, many microorganisms and animals of the oxygen they need to survive.

The majority of Germany's water bodies are not in a good status (cf. indicators of the ecological status of rivers, lakes and seas). In addition to nitrate pollution, nutrient overload is one of the biggest problems. To avoid this, phosphorus levels must be reduced: According to Liebig's "Minimum Law", the growth of organisms is restricted above all by the scarcest resource. For algae and aquatic plants, this is phosphorus in most waters.

 

Assessing the development

At the beginning of the 1980s excessive phosphorus concentrations were measured at almost 90 % of sampling sites. 2019 this share was around 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 decreased. This improvement is mainly the result of introducing phosphate-free washing powders and phosphate precipitation in the larger sewage treatment plants.

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 (DüV 2017) 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 (BReg 2016).

 

Methodology

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. The indicator gives the share of measuring sites that do not comply with these guideline values.