Groundwater Age and Mixing Patterns in the Deep Subsurface of a High-Energy Beach
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The subsurface of sandy beaches under high energy conditions function as effective biogeochemical reactors where waterbodies of varying physico-chemical properties mix and reactions alter solute fluxes across the land-sea continuum. Groundwater residence times are fundamental to understanding groundwater flow and transport regimes and to interpret (bio)geochemical data. This study investigates groundwater residence times and mixing patterns in a high-energy deep sandy beach aquifer on Spiekeroog Island, Germany. To this end we used a combination of environmental tracers including apparent ³H-3He ages, electrical conductivity, temperature, and dissolved silica concentrations. Results show residence times of weeks to decades in the deep subsurface and allow delineating zones where different endmembers prevail and modulate the solute composition.