Preliminary Results of the Water Isotope Study in the Vardar River Basin, Macedonia

Modern scientific research approaches to studying the hydrological cycle of water in nature, in addition to the mathematical modeling of hydrological–hydraulic processes that have expanded in recent years, increasingly include isotope hydrology on a global scale. This paper presents the preliminary results of research in the Vardar River basin. The research is in the field of isotope hydrology with the analysis of stable isotopes of hydrogen (δ2H) and oxygen (δ18O) in precipitation (P), surface water (SW) and groundwater (GW). For this purpose, a network for taking water samples in the Vardar River basin has been established. The isotopic composition of precipitation shows a relatively wide variability, with δ2H values ranging from −83.7‰ to −12.4‰ and δ18O values from −11.65‰ to −2.99‰. In contrast, groundwater samples exhibit a considerably narrower isotopic range, with δ18O values between −10.98‰ and −10.1‰ and δ2H values between −73.3‰ and −68.1‰. Surface water samples show δ18O values ranging from −10.7‰ to −9.11‰ and δ2H values from −70.6‰ to −61.6‰. The results of the study show that the waters in the Vardar River basin are predominantly of meteoric origin, with their isotopic composition being strongly influenced by climatic factors and altitude, varying from approximately 1400 m and 2000 m a.s.l. The study confirms that precipitation is the primary source of both surface and groundwater. Evaporation is the dominant process that modifies isotopic signatures during rainfall, surface runoff and groundwater recharge. Due to good fit and nearly parallel meteoric lines observed in the three different locations, preliminary LMWLs and RMWL were estimated. A similar isotopic composition of surface water (SW) and groundwater (GW) in some locations indicates the presence of a direct and active hydrological connection between these water bodies, which need to be investigated in more detail in future research. However, one of the groundwater sampling locations suggest more depleted isotopic composition, which is probably related to different recharge altitudes, but also possibly very interesting relationship between Vardar River, alluvial aquifers and karst aquifer in the Žeden massif.