Distribution of H and O stable isotopes in the surface waters of the Sava River, the major tributary of the Danube River.

Highlights • Spatiotemporal variability in stable H and O isotope composition in surface water was observed in the Sava River Basin (SRB). • δ 18O temporal variations of surface waters follow the pattern of precipitation with lower seasonal amplitude. • Mean residence time in river surface waters was estimated to be <2 years. • Complexity of spatial patterns of δ 18O in precipitation over SRB was described by latitude, longitude and altitude. • Precipitation controls spatial variation of δ 18O values in surface water across the SRB. Abstract The presented paper describes spatial and temporal variations in extended stable isotope datasets of hydrogen and oxygen (δ 2H and δ 18O) in the Sava River water that were used to estimate the mean residence time (MRT) of stream water using an exponential flow model. The re-examining MRT was <2 years in the Slovenian part of the Sava River and was in a good agreement with previous estimates and with the MRT estimated in the Sava River at Ostružnica near Belgrade, Serbia. A MRT >2.2 years was observed in the Danube River at Vinča also near Belgrade. The spatial distribution of δ 18O in precipitation over the Sava River Basin (SRB) was mapped based on the long-term weighted mean annual δ 18O values and established relationship with various geographical controls (latitude, longitude and altitude). The modelled δ 18O values in precipitation agree with the measured values in the surface river water at different locations indicating that the spatial variation in the isotopic composition of precipitation is the dominant factor controlling surface water isotope ratios over the SRB. [ABSTRACT FROM AUTHOR]