A multidisciplinary approach to characterizing coastal alluvial aquifers to improve understanding of seawater intrusion and submarine groundwater discharge

Coastal aquifers are affected by seawater intrusion (SWI), which causes their salinization, and yield submarine groundwater discharge (SGD), feeds marine ecosystems. Characterizing dynamics in coastal is fundamental for understanding both processes interaction. In order to gain insights into SWI SGD, we developed a 100 m-scale experimental field site located alluvial aquifer at the mouth of an ephemeral stream on Maresme coastline (Barcelona, Spain). Given complexity dynamism occurring therein, coupled can be achieved combining methods approaches across different hydrogeological disciplines. this study, conduct detailed characterization based four pillars hydrogeology: geology (lithological description core samples analyses), geophysics (downhole cross-hole measurements), hydraulics (pumping tidal response tests) hydrochemistry (major minor elements, together with stable Ra isotopes). Each discipline contributed aquifer: (1) geological revealed that consists fluvial sediments, organized fining upwards sequences alternating layers gravel, sand silt; (2) helped identifying silt continuity, play segmenting role hydrodynamics; (3) tests, specifically evidenced loading, rather than hydraulic connection sea, drives response; (4) surprising high reactivity, as most ions reflect some reaction, beyond expected cation exchange. The summary aquifer, initially looked like homogeneous unconfined 22 m thick, effectively behaves multi-aquifer reactive system freshwater discharging beneath saltwater several depths. fact thin caused such significant impact opens new paths study management (the possibility transient pumping resources) ecology (expect diffuse discharge).