
NAPSEA
N and P from Source to Sea
October 2022 - September 2025
Context
The central aims of the NAPSEA project are to support of authorities in selecting effective measures for nutrient load reduction. NAPSEA uses an integrated approach to address nutrient pollution from source to sea, combining three complementary perspectives: governance, nutrient pathways & measures and ecosystem health.
Our group at the UFZ is, with our partners at the UBA (Federal Environment Agency) responsible for the work package "Nutrient pathways & measures".
Project goals
Our work in NAPSEA aims to:
(i) Provide a data base on past nutrient inputs and outputs in the Elbe and Rhine basin and the Hunze catchment.
(ii) Calibrate the water quality models mQM (multiscale water quality model for nitrogen, Nguyen et al. 2022) and CnANDY (Coupled Complex Algal-Nutrient Dynamics for phosphorous, Yang et al. 2021) to past observed concentrations and loads.
(iii) Use the calibrated models to project water quality response to different scenarios of nutrient load reduction measures and climate change effects.
Methodology
Our applied models are both based on the fundamental principle of travel times shaping retention and dynamics of exported nutrients. In the case of mQM the model is able to capture multi-year subsurface travel times between nitrogen inputs on the land and nitrogen exports from the catchments. In the case of CnANDY the model captures the travel time of P-species in the river network and the competition of benthic and pelagic algae for light and nutrients.
Both model utilize our rich databasis on nutrient diffuse and point sources (Buettner 2020, Batool et al., 2022, Sarrazin et al., 2024) and on observational water quality data (QUADICA, Ebeling et al., 2022).
Results
Our model setup allows a view into the history of nutrient inputs and exports from Elbe and Rhine basin into the Wadden sea and a look to the future of nutrient exports under climate change. The example presented here keeps the nitrogen inputs from diffuse and point sources constant after the year 2022 but applies a climate change scenario unter RCP4.5.

Project partners
The project is led by Deltares. The Helmholtz Centre for Environmental Research leads the work package on nutrient pathways and measures with collaboration with UBA and hereon.
Helmholtz Centre for Environmental Research - UFZ
Department of Hydrogeology (Andreas Musolff, with contributions by José L. J. Ledesma, Rohini Kumar, Tam Nguyen, Pia Ebeling, Niklas Heinemann, Alexander Hubig, Dietrich Borchardt, and Norbert Kamjunke)
Federal Environmental Agency (UBA)
Andreas Gericke, Wera Leujak
Helmholtz-Centre hereon
Justus van Beusekom
Funding
NAPSEA is funded by the European Union

Contact
PI: Andreas Musolff (UFZ) - andreas.musolff@ufz.de
Co-PI: José L. J. Ledesma (UFZ and MNCN-CSIC) - jose.ledesma@ufz.de
References
- Batool, M., Sarrazin, F. J., Attinger, S., Basu, N. B., Van Meter, K., & Kumar, R. (2022). Long-term annual soil nitrogen surplus across Europe (1850-2019). Scientific Data, 9(1), ARTN 612. https://doi.org/10.1038/s41597-022-01693-9
Buettner, O. (2020). DE-WWTP - data collection of wastewater treatment plants of Germany (status 2015, metadata). https://doi.org/10.4211/hs.712c1df62aca4ef29688242eeab7940c
- Ebeling, P., Kumar, R., Lutz, S. R., Nguyen, T., Sarrazin, F., Weber, M., Buttner, O., Attinger, S., & Musolff, A. (2022). QUADICA: water QUAlity, Discharge and Catchment Attributes for large-sample studies in Germany. Earth System Science Data, 14(8), 3715-3741. https://doi.org/10.5194/essd-14-3715-2022
- Nguyen, T. V., Sarrazin, F. J., Ebeling, P., Musolff, A., Fleckenstein, J. H., & Kumar, R. (2022). Toward Understanding of Long-Term Nitrogen Transport and Retention Dynamics Across German Catchments. Geophysical Research Letters, 49(24). https://doi.org/ARTN e2022GL100278
10.1029/2022GL100278 - Sarrazin, F. J., Attinger, S., & Kumar, R. (2024). Gridded dataset of nitrogen and phosphorus point sources from wastewater in Germany (1950-2019). Earth System Science Data, 16(10), 4673-4708. https://doi.org/10.5194/essd-16-4673-2024
- Yang, S., Bertuzzo, E., Büttner, O., Borchardt, D., & Rao, P. S. C. (2021). Emergent spatial patterns of competing benthic and pelagic algae in a river network: A parsimonious basin-scale modeling analysis. Water Research, 193. https://doi.org/10.1016/j.watres.2021.116887