The effectiveness of nitrogen and phosphorus load reduction measures from source to sea, considering the effects of climate change

Project Information

NAPSEA

Grant agreement ID: 101060418

DOI

10.3030/101060418

Project closed

EC signature date 25 May 2022

Start date 1 October 2022

End date 30 September 2025

Funded under

• Food, Bioeconomy Natural Resources, Agriculture and Environment

Total cost

€ 1 999 721,25

EU contribution

€ 1 999 721,25

Coordinated by

STICHTING DELTARES
Netherlands

Periodic Reporting for period 2 - NAPSEA (The effectiveness of nitrogen and phosphorus load reduction measures from source to sea, considering the effects of climate change)

Reporting period: 2024-04-01 to 2025-09-30

Summary of the context and overall objectives of the project

A wide range of measures adopted since the late 1970s to combat eutrophication e.g. in the frameworks of OSPAR and the EU (among others WFD and MSFD) resulted in a substantial reduction of nutrient emissions and in healthier ecosystems in the North Sea and the adjacent Wadden Sea. Nevertheless, eutrophication targets in many affected inland and marine waters are not reached. Further progress—particularly for diffuse sources in regional inland waters—requires more complex and costly interventions, and the pace of nutrient reductions is slowing down. At the same time, societal fatigue around nitrogen-related issues (in particular related to agriculture) has grown, and the topic has become increasingly politicized. This makes it more challenging to maintain momentum for additional measures.

The NAPSEA project aimed at supporting national and local authorities in selecting effective nutrient load reduction measures and policies and in gaining societal support for their implementation. The project’s geographical scope covered the catchment of the Wadden Sea, with case studies for the Rhine, Elbe and Hunze catchments and the Wadden Sea itself. NAPSEA proposed an integrated approach to address nutrient pollution from source to sea, combining three complementary perspectives: governance and social acceptance, nutrient pathways and measures and ecosystem health, as illustrated in Figure 1:
1. For the perspective of ecosystem health, we analysed currently used indicators as well as their thresholds and explored the development of additional more comprehensive indicators—moving beyond the current targets for chlorophyll-a. The aim was to better reflect the benefits of nutrient reduction measures for ecosystem functioning and resilience.
2. The perspective of pathways and measures quantified nutrient emission sources and their pathways to the Wadden Sea with models, to assess how nutrient loads are affected by various scenarios of nutrient reduction measures and climate change.
3. The governance and social acceptance and acceptability perspectives assessed the coherence of the relevant policy frameworks across scales and the public and farmer support for nutrient reduction measures.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Governance and Policy
- Developed a framework to assess the feasibility of existing nutrient reduction strategies for the Wadden Sea, aligned with the EU zero-pollution goal (50% nutrient loss reduction).
- Assessed social acceptance of agricultural nutrient reduction measures among farmers and citizens in Germany and the Netherlands.
- Provided recommendations to improve coherence in current nutrient reduction strategies for the Wadden Sea.

Measures and Pathways
- Created a dataset and a calibrated modelling framework to test scenario effectiveness.
- Developed and calibrated catchment models for the Rhine and Elbe basins to simulate historical nitrogen and phosphorus trends, including terrestrial and instream retention.
- Defined socially acceptable scenarios focusing on source control and retention, covering both waterborne and airborne nutrient pathways.
- Implemented scenarios in Rhine, Elbe, and Hunze catchments, reporting on nutrient concentrations and exports.
- Transferred modelled results from demonstrator basins to other basins contributing to Wadden Sea nutrient loads.

Ecological Health
- Reviewed existing indicators, effects, and nutrient targets from OSPAR, WFD, and MSFD.
- Established Safe Ecological Limits for the Wadden Sea based on seagrass and phytoplankton data; compared required reductions across Rhine, Elbe, and Hunze case studies.
- Found that planned measures nearly meet reduction targets, but additional actions are needed. Emphasized the importance of reducing both nitrogen and phosphorus to avoid rising N/P ratios and considered climate change impacts.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

IMPACT
The NAPSEA project aims to make an impact on healthy & resilient water and subsurface systems, in particular on the path towards zero pollution and healthy environments from source to sea (Figure 2), ultimately leading to cleaner and restored aquatic (eco-)systems within the EU and associated countries.

OUTCOME
- Technical: developing, implementing and monitoring techniques, (nature based) solutions, interventions and strategies
- Regulation: contribute to government's drafting policy and plans by integral systems-approaches to water and subsurface management 
- Political: providing the knowledge and information for evidence-based, timely and contextualized political decision-making on environmental management measures and investments

OUTPUT/ACTIVITIES
- Technical:
- Advanced understanding of points source, diffuse sources and various environmental factors influencing the pathway of nutrients from source to sea
- Developed a calibrated catchment model on nutrient transport from source to sea, allowing us to quantify measures to reduce nutrient inputs
- Regulation/political:
- Proposed scenarios (set of potential reduction measures) focusing on nutrient flux elements.
- Drafted an overview of current indicators, primarily chlorophyll levels (comparable across frameworks and borders)

Figure 1. Schematic overview of interconnected activities in the NAPSEA project

Figure 2. Impact scheme