Seawater intrusion into groundwater aquifer through a coastal lake - complex interaction characterised by water isotopes 2H and 18O

The present study investigates the complex interactions among surface waters, groundwaters and a coastal lake in northeastern Greece, using their stable isotopic composition (δ¹⁸O, δ²H) in combination with hydrogeological and hydrochemical data. Seasonal and spatial trends of water isotopes were studied and revealed that all water bodies in the study area interact. It was also shown that the aquifer's increased salinity is not due to fossil water from past geological periods, but is attributed to brackish lake water intrusion into the aquifer induced by the extensive groundwater pumping for irrigation purposes. Quantification of the contribution of the lake to the aquifer was achieved using the simple dilution formula. The isotopic signatures of the seawater and the groundwaters are considerably different, so there is a very little possibility of direct seawater intrusion into the aquifer.