Abstract In this chapter, we analyse the influence of the Carpathian Mountains on the variability of stable isotopes in precipitation by employing a combination of observed and model data. Overall, the mean value of the stable isotopes in precipitation over the Carpathian Mountains, based on observational data, was −9.8‰ for δ 18 O and −68.6‰ for δ 2 H. The local meteoric line, using all samples from the study sites, was δ 2 H = 7.65 × δ 18 O + 5.82. The simulated δ 18 O, based on the ECHAM5-wiso isotopes enable model, showed good agreement with the observed isotopic data. By comparing all the monthly values of the observed isotopic data from all analysed stations and the corresponding model data, a correlation coefficient of 0.76 ( n = 455, p < 0.001) was obtained. The spatial distribution of the simulated δ 18 O values in precipitation had the lowest values over the Romanian Carpathian Mountains and the highest values over the extra-Carpathian area, with the maximum in southeastern Romania. This pattern was strongly influenced by the Carpathian Mountains orography. Using the simulated δ 18 O data, we show that the spatial distribution of the δ 18 O values increases with temperature and decreases with altitude and latitude (−0.5‰ for δ 18 O per degree of latitude). The continental gradient is characterized by a polynomial trend of the second degree in the form of a large-open ‘U’ shape, and the general pattern of the δ 18 O values follows the spatial distribution of the Carpathian Mountains.

Abstract To investigate the influence of local climate and transboundary circulation of moisture on the stable isotope of precipitation in Ramnicu Valcea, Romania, monthly values of δ 2 H, δ 18 O, deuterium excess (d excess ), temperature, relative humidity and precipitation were determined between January 2012 and December 2018. Monthly analysis showed differences in d excess varying between 24.2‰ (October 2015) and −23.7‰ (July 2013) with a multi-annual average of 6.1 ± 5.9‰, suggesting an Atlantic origin of moisture with episodic Mediterranean transport. Also a significant correlation between the North Atlantic Oscillation on the local temperature during winter season was noticed. The local meteoric water line (LMWL) for the entire period showed slope and intercept values similar to those for neighbouring localities with the same altitude. When the analysis was extended to summer (April–October) and winter (November–March) seasons, the LMWL slope and intercept were different, reflecting the summer–winter difference in temperatures and air circulation. The monthly values of all parameters formed equal-spaced time series whose detailed analysis confirmed at p < 0.01 that δ 2 H, δ 18 O, temperature and relative humidity show a well-evidenced one-year periodicity. In contrast, precipitation and d excess seasonality were almost unrecognizable, most probably owing to the reduced number of observations.

Abstract A groundwater geochemistry study was carried out on 24 samples collected from different springs and wells situated in a plateau area at an elevation of 200–300 m in the Mehedinţi County, southwestern Romania. The study was motivated by the fact that springs have represented the only source of potable water in the region, only recently completed by tens of metres-deep well drillings. Spring distributions and geological data reveal the presence of a multilayered system situated in the Lower Quaternary deposits. The mean δ 18 O and δ D values of groundwater, −9.8 and −67.8‰, respectively, reflect the yearly weighted mean of the isotopic composition of precipitation, demonstrating locally derived recharge. The Piper ternary diagrams indicate that the dominant hydrochemical type is HCO 3 − –Ca 2+ –Mg 2+ with transition towards higher SO 4 2− and Mg 2+ contents to the deeper aquifer. The anions vary from HCO 3 − with transition to no dominant type and with Cl − contents higher for the shallower aquifer. The sequence of abundance of cations is generally Ca 2+ > Mg 2+ > K + > Na + and