NAPSEA: joining forces to improve water quality from source to sea
How can we effectively reduce nutrient pollution in rivers and coastal seas, while accounting for climate change and complex governance structures? That question was at the heart of the NAPSEA project, which was completed in September 2025. NAPSEA focused on improving water quality in river basins and downstream marine ecosystems in Germany and the Netherlands, with particular attention to nitrogen and phosphorus loads and their impacts on the Wadden Sea.
Why nutrient reduction mattersThe Wadden Sea is the largest unbroken tidal flats system in the world and an ecosystem of high ecological and societal value. It is strongly influenced by major rivers such as the Rhine and the Elbe, whose catchments extend across large parts of Germany and the Netherlands. Nutrient inputs from upstream activities can lead to eutrophication, affecting biodiversity and ecosystem functioning. Although European policies such as the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD) provide a shared framework for water quality management, their implementation remains challenging—especially in transboundary river basins and under changing climatic conditions. An integrated source‑to‑sea approachNAPSEA applied an integrated source‑to‑sea perspective, connecting inland and marine water systems and combining three complementary perspectives:
This approach made it possible to link measures at the source (such as agriculture and wastewater treatment) to ecological effects in downstream lakes, estuaries, and coastal waters.  From technical indicators to visible ecological recoveryOne of the key challenges identified in the project is that water quality objectives are not always consistent across policy frameworks and countries. Moreover, existing indicators can be highly technical and difficult to communicate beyond expert audiences. NAPSEA therefore explored ecosystem‑based objectives that are more tangible and meaningful, such as:
These habitats are highly valued for their biodiversity and clearly show the benefits of reducing nutrient pollution. What do the models show?Using models that describe nutrient transport from source to sea, NAPSEA assessed different nutrient reduction scenarios for the Rhine, Elbe and Hunze catchments under moderate climate change conditions towards 2050. The results show that:
Governance and social acceptanceEven where policy frameworks are aligned at European level, NAPSEA found that implementation and monitoring are often fragmented at local and regional levels, with many actors involved. The project highlights the importance of strengthening cooperation between inland and marine water management and across national borders. NAPSEA also assessed the social acceptance of nutrient reduction measures, such as buffer strips, reduced livestock intensity and stricter fertilisation management. Both citizens and farmers recognise the risks of eutrophication, particularly for biodiversity and future generations. Farmers emphasised the importance of:
These insights underline the need for policies that are not only effective, but also socially feasible. About the projectNAPSEA ran for three years and was funded by Horizon Europe. The project was coordinated by Deltares and carried out by a consortium of Dutch, German and Austrian partners, including competent authorities from both countries. By combining scientific modelling, ecological assessment, governance analysis and stakeholder perspectives, NAPSEA provides valuable insights into how nutrient pollution can be addressed more coherently—from source to sea. |
