Towards understanding the dynamics of phosphorus legacy across German river basins

Excessive phosphorus (P) drives eutrophication in surface waters, contaminates groundwater, threatening aquatic ecosystems and drinking water quality. Legacy P from past agricultural and urban inputs has shown to create nutrient reservoirs that continue to fuel contemporary P pollution. Different forms of P, such as total phosphorus (TP) and soluble reactive phosphorus (SRP), may show distinct behavior. While SRP is critical because of its bioavailability, TP determines the overall P load in the system including P already incorporated into biomass. Understanding the long-term dynamics of TP and SRP, along with legacy sources and landscape filtering, is essential for managing water quality and reducing environmental impacts.

Using a long-term database of point and diffuse P sources (Batool et al., 2024; Sarrazin et al., 2024) and observational riverine TP and SRP concentrations (Ebeling et al., 2022), we analyzed the retention and export dynamics of P across more than 100 river catchments in Germany over the period 1950–2019. Our analysis focuses on the lag-time behavior between P inputs to the catchments and outputs by river water, incorporating effective transport time distributions (TTDs) to characterize landscape filtering processes. We employed various TTD models, ranging from log-normal to more flexible gamma distributions, and compared key characteristics such as mean, median, and mode of transport times across catchments. Our findings reveal a substantial decline in P point and diffuse sources across German landscapes over the past 70 years, which has not been matched by equivalent reductions in riverine P concentrations. In this presentation, we will discuss the spatial variability of TTs between P input and output, highlighting differences in legacy effects and contrasting contributions from point and diffuse sources in shaping the P dynamics of German river systems.

References:

Batool, M., Sarrazin, F. J., and Kumar, R.: Century Long Reconstruction of Gridded Phosphorus Surplus Across Europe (1850–2019), Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2024-294, in review (accepted), 2024.

Ebeling, P., Kumar, R., Lutz, S. R., Nguyen, T., Sarrazin, F., Weber, M., Büttner, 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.

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.