Monitoring nutrient pollution in European rivers, lakes and groundwater

Impact of nutrients in freshwater 

Large inputs of nutrients to water bodies can lead to eutrophication, a process where increased nutrient concentration gives increased algal growth, including potentially harmful algal blooms, and the subsequent bacterial decomposition of algal biomass causes oxygen depletion. Eutrophication can cause substantial environmental degradation, including loss of aquatic biodiversity (reduction in ecological status) and negative impacts on the use of water for human consumption and recreation. The main sources of nutrient pollution are domestic and industrial waste water and fertilizer runoff from agricultural land.  

Nutrients monitoring data in European waters

Several policies aim at protecting water from pollution realted to excessive concentrations of nutrients: The Water Framework Directive (WFD) and its daughter directive the Groundwater Directive (GWD), Drinking Water Directive (DWD), the Nitrates Directive, the Urban Waste Water Treatment Directive, the Industrial Emissions Directive, the Convention on Long-range Transboundary Air Pollution and the National Emission Ceilings Directive. Reducing nutrient pollution from agriculture is an important aspect of the Common Agricultural Policy and the European Green Deal, including the ‘Farm to Fork’ Strategy, the Biodiversity Strategy and the Zero Pollution Action Plan. 

EEA countries can submit detailed monitoring data via the Water Information System for Europe – State of the Environment (WISE SoE) data flow to the EEA. Up to 38 countries have contributed data on rivers, lakes, and groundwater to the Waterbase - Water Quality ICM. This data collection includes concentrations of chemicals and nutries. Through harmonising data collection and reporting, Waterbase -Water Quality ICM can be used to support transparent assessment, highlights areas in need of improvement, and tracks the progress of water policies.

Thresholds used to assess exceedances

It is not possible to set thresholds for nutrient concentrations with respect to ecological effects that apply to all surface waters. ‘Good ecological status’ as defined in the WFD, means that the water body shows low levels of distortion resulting from human activity. However, the level at which this occurs varies between water body types, e.g. depending on geology, climate zone, size. For instance, surface waters can be naturally nutrient poor or nutrient rich, and the species will be adapted to this. See Kelly et al. (2022) for an overview of thresholds applied across water types and countries. For use of groundwater and surface water as drinking water, the GWD and DWD list a maximum allowable concentration of 50 mg NO3/l (11.3 mg NO3-N/l), but this applies to individual samples, not average concentrations as presented here. All in all, this is why concentration classes are defined by frequency distribution rather than linking to specific policies. Furthermore, this is why it is not possible to say when concentrations are low enough when analysing aggregated time series. 

The graphics shown on this page apply a similar methodology to that developed for the EEA indicator for Nutrients in freshwater in Europe. This indicator evaluates changes over time, through time series and trend analysis based on water chemistry data from water bodies with acceptable frequency of observations over time. The time series and trend analysis results are aggregated across water bodies within countries and across Europe. In addition, the indicator quantifies the spatial variability in present nutrient concentration, based on assigning water bodies to concentration classes. A detailed description of the methodology, including quality checking and modelling of water body time series is provided in "Methodology, oxygen consuming substances and nutrients indicators”.