Story continued: The Lagged Rejuvenation Phenomenon at the Krycklan catchment - 49 new samples reveal groundwater flow patterns and hydrological connectivity 

Abstract

<p>The distribution of groundwater ages in aquifers is a key indicator for flow processes, solute transport and biogeochemical reactions. A lagged rejuvenation of groundwater ages has been observed at a 0.47 km<sup>2</sup> subcatchment of the Krycklan catchment in 2017<sup>1</sup>. Chlorofluorocarbons (CFCs) were measured in 9 wells at different depths located close to the stream and revealed an overall representative age stratification for the subcatchment. Immediately below the water table at 1-2 meters depth, groundwater was already 30 years old. This lag in rejuvenation was successfully modeled on the assumption that it was caused by seepage flow of groundwater in the subsurface discharge zone that evolves along the interface between two soil types with different hydraulic permeability. The comparison of the observed groundwater age stratification with a simple analytical approximation shows that the lag in rejuvenation is an indicator for the extent of the subsurface discharge zone and the vertical gradient for the overall aquifer recharge.</p><p>To test this hypothesis a second sampling campaign in 2021 was performed. CFCs were measured in 49 sampling locations at different depths and distances to the stream within the subcatchment and neighboring subcatchment.  CFC-based groundwater ages show the extent of the subsurface discharge zone and reveal groundwater flow patterns. This study provides further information on the hydrological connectivity of groundwater in the hydrological cycle. </p><p> </p><p>