Indicator: River eutrophication by total phosphorus

• Too high total phosphorus concentrations are measured at more than half of all river sampling sites in Germany.
• The share of high total phosphorus concentrations has declined by around one third since the beginning of the 1980s. Extreme levels of pollution are rare nowadays.
• The aim of the sustainability strategy is to reduce total phosphorus concentrations in all water bodies by 2030 at the latest to such an extent that good status (quality class II) is achieved.
• This requires a change in fertilisation practices in agriculture. Also, small sewage treatment plants need to remove phosphorus using state-of-the-art 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 phosphorus input into water bodies is one of the biggest problems because it triggers excessive growth of algae and aquatic plants (eutrophication). When they die, they are decomposed by microorganisms. In this process, a lot of oxygen is consumed. Oxygen deficits in water bodies have a negative effect on fish and other aquatic organisms; under extreme situations, fish die-offs may occur. To prevent eutrophication, the main priority is to reduce phosphorus pollution. The map service “Nutrients and Salts” shows phosphorus concentrations for around 250 sampling sites in German rivers.

In the early 1980s, excessive phosphorus concentrations were measured at almost 90 % of sampling sites. Since 2018 this share has remained slightly below 60 %. Major improvements can be seen across the different quality classes: overall, the proportion of more heavily polluted water bodies has declined. This improvement has been driven primarily by the introduction of phosphate-free detergents and the expansion of third treatment stage including phosphate precipitation in larger sewage treatment plants since the 1990s.

The requirements for reducing phosphorus concentrations in water bodies are diverse: According to the European Water Framework Directive (EU Directive 2000/60/EC), all water bodies must achieve good ecological status by 2027. The Fertiliser Ordinance stipulates that less fertiliser must be applied to soils with high phosphorus levels. The Waste Water Ordinance stipulates that even small sewage treatment plants must remove phosphorus from waste water using state-of-the-art technology. In accordance with Objective 6.1.a of the German Government’s Sustainability Strategy, the phosphorus limits must be met by 2030 at the latest.

The Federal States submit measurement data from around 250 representative sampling sites to the German Environment Agency. For the classification of a water body into a water quality class, the average of the measured phosphorus concentrations is compared with the value that must not be exceeded for good ecological status (Surface Water Ordinance, 2016). Depending on the type of water bodies, these values range between 0.1 and 0.15 mg/l phosphorus (for one type 0.3 mg/l) and 0.045 mg/l in transitional waters. The indicator represents the proportion of sampling sties that do not comply with these values.