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Sampling of springs, for which the mean elevation of recharge could be estimated, provided an estimate of −0.44‰ 100 m−1 for the groundwater altitude effect on the δ18O value in Eastern Macedonia and −0.21‰ in Thrace. A slight difference in both the slope and the intercept of the lines expressing the regression of elevation against δ18O values in the continental part of Thrace and the island of Thassos, is also observed. As case studies, the isotopic composition of surface water and groundwater was used to investigate the mechanism of recharge of groundwater in the areas of Lekani Mountains and Thassos Island. As a result, the contribution of water leaking from the river Nestos to the recharge of the springs of Paradissos, near to the river bed, Kastro Filippon and Aghios Athanassios, at a distance of over 25 km from the river bed, as well as of the aquifers tapped by boreholes in the plain between Kastro Filippon and Aghios Athanassios, was indicated. The estimate is 54 ± 12% for the contribution of the river water to the spring yield, in the case of Aghios Athanassios, and 43 ± 10% in the case of the springs of Paradissos. As another result, the hydraulic connection between the marbles of Profitis Ilias and the marbles and dolomites of Potamia series, in the case of Thassos Island, was confirmed. Finally, the extent of the carbonate rocks and the amount of precipitation effective in recharge to the main springs, as well as to the aquifers tapped by boreholes in the different plains of the areas under investigation were estimated. |
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