Factors controlling variation of δ2H and δ18O in precipitation in Southern Bohemia, Central Europe

Abstract

The effects of local climate parameters, seasonality and sources of air masses on the stable water isotopes [hydrogen (δ²H) and oxygen (δ¹⁸O)] in precipitation were investigated along an altitudinal gradient (381–1118 m a.s.l.) in southern Bohemia, Central Europe, from December 2021 to November 2023. The relationship between the observed δ²H and δ¹⁸O values was consistent with the Global Meteoric Water Line. The isotopic composition of precipitation changed with increasing altitude by −6.5 and −1.2‰ km⁻¹ for δ²H and δ¹⁸O, respectively. The δ values differed between seasons, with the values being most enriched in summer and most depleted in winter. An analysis of the air mass trajectories using the Hybrid Single-Particle Lagrangian Integrated Trajectory Model showed that the main sources of precipitation were the North Atlantic (from 44% in spring to 70% in fall and winter), the Arctic Ocean (from 15% in summer to 38% in spring) and the Mediterranean Sea (from 12% in winter to 34% in summer). Throughout the study period, average δ values differed significantly between air masses (p < 0.05) and along the altitudinal gradient, with the most enriched values (from −56 to −37‰ for δ²H and from −8.2 to −5.5‰ for δ¹⁸O) and the most depleted values (from −91 to −84‰ for δ²H and from −12.7 to −12.0‰ for δ¹⁸O) occurring in the Mediterranean and Arctic air masses, respectively. However, for individual daily samples, strong correlations occurred between the δ values and air temperature (the strongest), humidity, precipitation, time of sunshine and solar radiation, while the influence of air mass directions was not significant. A stepwise regression analysis showed that most of the variation in daily δ values (43–48% and 47–52% of δ²H and δ¹⁸O, respectively) was explained by the combination of air temperature and humidity, precipitation amount, and season.