A 50 Years’ Isotope Record of the Danube River Water and Its Relevance for Hydrological, Climatological and Environmental Research

The isotope record of the Danube River water at Vienna station probably is the longest dataset of a large river worldwide: 3H record since 1963, stable isotopes 2H and 18O records since 1968. From the 2H-18O relation (“deuterium excess”) can be concluded that the isotopic composition in the Danube River water reflects mainly the isotopic relations in the precipitation in the catchment area with some delay due to the residence time of the precipitation water in the catchment. It allows drawing hydro-meteorological conclusions on a larger scale based on a relatively small number of measurements. The stable isotope time series shows significant changes on a decadal scale. Since 1952, the 3H content in the precipitation and the Danube River water has been dominated by the 3H releases of nuclear weapon tests. From this 3H record a mean residence time of about three years of precipitation water in the Danube River catchment upstream of Vienna can be calculated (mainly base flow). A similar value can be found by using the climatologic signal of the stable isotope time series. Since about 1995 short-term 3H elevations owing to releases from nuclear power plants have been detected. In order to obtain an isotopic database for the entire Danube River Basin, the Danube River water sampling at Tulcea (delta region) was carried out in 2009.