Drought Affects Export Patterns Across Different Solutes

The severe 2018 drought affected water quantity and quality across Europe. While the consequences for water quantity have received substantial attention, the effects on water quality are intricate and require careful analysis. Nevertheless, understanding these impacts is crucial because the scarcity of water resources elevates the importance of their quality.

Here, we conducted a comprehensive analysis of a high-frequency dataset (hourly) encompassing stream water chemistry across various solutes, including nutrients, heavy metals, and other ions, in the pre-alpine Erlenbach catchment (0.7 km², Switzerland). We used concentration-discharge (C-Q) relationships to detect the drought impacts on solute export patterns at the catchment outlet. The month of July 2018, characterized by the highest annual average temperature, experienced the most pronounced drought conditions. During this period, all solute concentrations exhibited a notable divergence in export patterns compared to the same month in other years with normal conditions (July 2017, 2019, 2020). In August, when conditions returned to normal, some solute concentrations also reverted to typical patterns, while others continued to deviate. These observations suggest a drought-induced alteration in solute mobilization, hydrologic transport, and retention, accompanied by potential solute-source-specific memory effects.

The extensive and unique dataset documenting stream water chemistry in the Erlenbach catchment provides valuable insights into the processes shaping water quality during drought. If this knowledge can be extrapolated to other catchments, it may offer a foundation for safeguarding our precious freshwater resources in the face of an increasing risk for the occurrence of severe and prolonged droughts.