Plankton are mostly microscopic small organisms floating in the water. In big rivers, plankton is an important part of the ecosystem. The major share of aquatic vegetation here consists of single-celled algae, the so-called phytoplankton. If they strongly develop, they lead to the well-known eutrophication and impact the water quality.

An excessive development of plankton algae indicates too high nutrient contents in Rhine water. Such „eutrophication“ may in particular develop in the downstream section of the Rhine or in Lake IJssel.
In a river such as the Rhine the development of plant plankton is not only influenced by nutrient content, but even stronger by flow velocity and other physical and hydrodynamic factors.
Since 1990 and within the “Rhine” and “Rhine 2020” Action Programmes of the International Commission for the Protection of the Rhine (ICPR), the phytoplankton of the Rhine is regularly being sampled along the entire course of the river.
With the inventory in 2006/2007, the programme has for the first time been adapted to the requirements of Annex V of the EU Water Framework Directive (WFD) and been extended to a 6 years cycle.

In 2012, the phytoplankton biomass proved to be slightly above that during the monitoring programmes in 2000 and 2006/2007. Considering the long-term trend and compared to the 1980s, the phytoplankton biomass however remains on a low level. This long-term trend correlates to reduced nutrient concentrations and phytoplankton input from Lake Constance and is presumably to a certain extent also caused by filtration activities of immigrated mussels.

This biological quality component is extensively discussed in the ICPR report no. 224, “The Phytoplankton of the Rhine in 2012”.

Did you know ...

that plant plankton is the basis for all life in water?

It is also known as phytoplankton and, in the Rhine, mainly consists of diatoms and cyanobacteria.

It serves as nutrition for zooplankton. In the Rhine, this zooplankton mainly consists of protozoans and rotatorias; in the Delta Rhine, copepods such as water flea and Cyclops also occur.