To what extent does nitrogen in wastewater effluent contribute to stream water quality deterioration in Germany?

Over the past seven decades, Germany has undergone transformative changes in wastewater management, largely driven by technological advancements, policy interventions, and the introduction of European Union (EU) directives targeting wastewater treatment plants (WWTPs). Simultaneously, the country has experienced profound societal transformations, notably the political and economic divergence between East and West Germany and shifts in population density, which further influenced WWTP infrastructure and management practices. This study focuses on nitrogen in effluent from WWTPs, which directly discharge into rivers, often having an immediate and localized impact. Understanding the spatial and temporal evolution of nitrogen in wastewater effluent contribution to stream water quality deterioration is essential for designing sustainable water management strategies. To this end, we combined data-driven analysis and modeling approaches, making use of recently published datasets on diffuse nitrogen sources (Batool et al., 2022), nitrogen point sources (Sarrazin et al., 2024), and a state-of-the-art water quality model (Nguyen et al., 2022). We applied the model across various German catchments with diverse agriculture and wastewater amount and treatment development from 1950 to 2020. Our results reveal a noticeable decrease in N effluents from WWTPs, leading to a decline in N contribution to instream nitrogen in the last decades. However, this declining pattern and trend varied across West and East Germany. Our study enables the identification of hot spots, helping spatially targeted management.

 

References

Batool et al., (2022). https://doi.org/10.1038/s41597-022-01693-9

Nguyen et al. (2022). https://doi.org/10.1029/2022GL100278

Sarrazin, et al. (2024). https://doi.org/10.5194/essd-16-4673-2024, 2024