Post-drought nitrate mobilization in German catchments
- 1Helmholtz Centre for Environmental Research - UFZ, Catchment Hydrology, Germany
- 2Helmholtz Centre for Environmental Research - UFZ, Department of Hydrogeology, Leipzig, Germany
- 3School of Architecture, Civil and Environmental Engineering, EPFL, Lausanne, Switzerland
- 4Mountain Hydrology and Mass Movements, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland
- 5WSL Institute for Snow and Avalanche Research (SLF), Davos Dorf, Switzerland
Nitrate excess in rivers is caused by anthropogenic nitrogen sources, such as agriculture and wastewater. Diffuse sources stemming from agricultural fertilization can remain in the soil for long periods of time as a legacy and are mobilized through hydrological pathways that connect sources with rivers. Previous studies show that drought periods can increase nitrogen stored in the soil due to lower nitrate transport to streams and less nitrate uptake by plants due to dry conditions. This accumulation of nitrogen during drought and its subsequent transport under wet conditions during the post-drought period can result in high nitrate concentrations in rivers.
In our study, we analyze the nitrate response of 190 German rivers during hydrological post-drought conditions from 1978 to 2019. We define droughts as periods with more than 30 consecutive days of discharge deficit using a variable threshold method and post-droughts as 100-day periods following the termination of a drought. We particularly focus on post-drought periods in the winter season that display the most pronounced concentration anomalies. Our results show that during the winter post-drought period, 66% of the catchments export higher nitrate concentrations compared to non-drought conditions, with 19% of the catchments exporting significantly higher nitrate concentrations (Kruskal-Wallis test, p-value<0.05). Catchments that exhibit a significant increase in nitrate concentrations during winter post-drought periods tend to be characterized by higher annual precipitation and shallower aquifers, indicating that fast hydrological transport could be a key factor in the winter post-drought delivery of nitrate excess. A projected increase in the frequency of severe droughts due to climate change could lead to more frequent post-drought episodes with high nitrate concentrations in the future. Understanding the main drivers of post-drought transport of nitrate across catchments is crucial for focusing management efforts efficiently.
How to cite: Saavedra, F., Musolff, A., Von Freiberg, J., Merz, R., Knoll, K., Müller, C., Brunner, M., and Tarasova, L.: Post-drought nitrate mobilization in German catchments , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7069, https://doi.org/10.5194/egusphere-egu23-7069, 2023.
