High-resolution monitoring of the Günz River: Assessing water quality risks for managed aquifer recharge

Abstract. Adapting to hydrological extremes through managed aquifer recharge using river water as a source requires a profound understanding of the quantity and quality dynamics of the river. While quantitative data with high temporal resolution is available at numerous gauging stations, qualitative data for many catchment areas is generally sparse or not available at all. In this work, a combination of risk-based watershed screening, continuous on-site monitoring, and laboratory analyses was carried out to improve this understanding of river quality dynamics. For on-site monitoring, a cost-efficient and reliable monitoring kit was developed to generate time-resolved data, which proved essential for capturing hydrochemical dynamics and can serve as a decision-support tool, reducing the parameter set required for quality control. It was installed at the Günz River in the southwest of Bavaria, Germany. The water quality measurements were combined with the risks arising from this rural watershed, where wastewater treatment plants and agriculture were the primary pollution sources. The contamination state improved during events with high water levels due to dilution, except for very few trace substances washed out from the topsoil. From a technical point of view, turbidity was defined as the most urgent parameter to consider in the water treatment before reuse due to particle-associated contaminant transport and the risk of clogging. The results demonstrated that the Günz River would be a suitable source for managed aquifer recharge with particle removal as a pre-treatment step. By linking identified watershed risks to river water quality, this study highlights the importance of understanding catchment processes for effective water management. The insights of this study contribute to optimizing high-resolution monitoring, advancing managed aquifer recharge implementation, and enhancing water resource resilience in similar catchments.