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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.

The isotopic composition of surface water and groundwater was used to investigate the mechanism of recharge of groundwater in the Axios River plain in northern Greece. Sampling of springs, for which the mean elevation of recharge could be estimated, in the Paikon Mountains provided an estimate of −0.28‰ per 100 m for the altitude effect. The δ18O estimated for the recharge of the Neogene formation between the river valley and the Paikon Mountains agreed with many of the sampled locations. However, in the southwestern part of the area there is an indication of a contribution from the limestone formation of the Paikon Mountains. The stable isotopic composition of shallow groundwater close to the river indicates contributions from the river. Deeper groundwater farther away from the river also contains a proportion of infiltrated river water. Some of the boreholes close to the river have chlorinities ranging up to about 6000 mg 1−1. The stable isotopic and chemical data indicate that the salinity is due to varying proportions of sea water, infiltrated river water and local recharge. The isotopic composition of Aravissos Spring water suggests that the spring is recharged by the upper series of the semi-metamorphic Paikon zone (dolomitic limestones, spilites-keratophyres and Gropi series; the mean altitude of recharge computed for the area so defined is 867 m and its potential annual yield, i.e. the amount of annual precipitation effective in recharge in this area, is 43.6 ± 10 × 106 m3). This suggests that the actual annually exploited quantity of the spring water for the water supply of Thessaloniki (about 44 × 106 m3) is at the limit of the corresponding potential yield.

Variations in the isotopic composition of water were used to define the mechanism of recharge of the Assopos riverplain and the Kalamos Attikis coastal brackish karst springs. The plain is mainly recharged by local rain water, while the karst springs are fed by the Parnis mountain system, the mean recharge altitude being estimated in the order of 870 m. The apparent velocity and the underground pathway of the water feeding the springs were deduced and the most convenient sites for the drilling of production wells for recovery of the spring water before salinization were sited. As a result, 73,000 m3 of water are now pumped per day and used as additional potable water for the Athens area, comprizing about one-sixth of the mean daily consumption.

Deuterium and oxygen-18 data have been used to identify the origin of recharge to a coastal complex of springs and also aquifers developed for supplying water to Aghios Nikolaos, Crete. Tritium data have been used to estimate the age of groundwater at different sampling locations. The results of this study indicate that the Almyros Aghios Nikolaos springs are recharged mainly from the part of the Gavrovo-Tripolitza limestones forming the mountains of Selena, Katharo Tsivi and Lassithiotika, while the part of the same limestones forming the mountainous area of Mavro Dassos provides recharge to the northern part of the Aghios Nikolaos plateau. The total surfaces of these areas, their corresponding potential annual recharges, as well as the flow velocity of the water recharging the springs of Almyros Aghios Nikolaos during the last few kilometers of its way are estimated.

An earlier hypothesis of a rapid equilibrium between complexes, formed in an organic mixture between bromine activated by isomeric transition and the two organic constituents of the mixture, is now extended to explain the effect of change of concentration of elemental bromine in the mixture. A general scheme of reactions is proposed, from which linear equations are derived describing the change in retention and yields of the different products with changes in the mole fractions of the various components of a ternary mixture, containing elemental bromine and two organic liquids. These equations, in simpler forms, are first applied to the two binary mixtures of elemental bromine and each of the two organic liquids to determine the various parameters needed for the quantitative analysis of the results obtained with the respective ternary mixtures. Agreement between theory and experiment is confirmed (a) by the linearity of the various experimental plots based on the above equations, and (b) by the internal consistency of the proposed scheme, as judged from the agreement between the values of the same parameters determined from different equations and different mixtures. It is probable that analogous schemes apply to other nuclear transformations.