Multiparameter approach to evaluate spatiotemporal hydrochemical variations at different scales: Improved understanding of the deep Brilon karst system

$\textbf{Study region}$
The Brilon karst system (Germany), crucial for the drinking water supply of the region.

$\textbf{Study focus}$
The study provides the first comprehensive evaluation of hydrochemical data from the karst system. To cover both spring and catchment scale, sampling sites include springs, drinking water wells, groundwater monitoring wells, and surface streams. In addition to publicly available data, six sampling campaigns were realized over an annual cycle. Physicochemical data, major ions, trace elements, and rare-earth elements were evaluated using ion ratios, multivariate statistics, seasonal and long-term trends to develop a hydrogeological conceptual model.

$\textbf{New hydrological insights for the region}$
Results show strong spatial variations at spring and catchment scale, while seasonal variations are low. The karst system is predominantly controlled by deeper groundwater, which is characterized by higher Na$^+$ and Cl$^-$ concentrations, and enriched with the trace elements Li, Rb, Sr, Cs, U, Ba, and Ti. Ion ratios of 0.86 for Na$^+$/Cl$^-$ and 45.9 for Na$^+$/K$^+$ show that the deeper karst groundwater is related to the dissolution of evaporites. ... mehrA waste water influenced sinking stream has a Na$^+$/Cl$^-$ ratio of 1 related to the application of road salt. It is further characterized by higher NO$^{3-}$ and K$^+$ concentrations, and shows a positive gadolinium anomaly. At drinking water abstraction sites, long-term trends show significantly increasing Na$^+$ and Cl$^-$ concentrations, while NO$^{3-}$ concentrations are decreasing or stable.