Environmental Isotope Ratios of River Water in the Danube Basin

The objectives of the Danube study were documentation of existing data and completion of long term data sets (2H, 3H, 18O), continuation of monthly sampling of river water, investigation of short term influences, and preliminary interpretation of long term isotope records of river water with respect to hydrological processes, meteorological conditions and environmental changes. Furthermore, this report includes the complete 3H and 18O data set for the Danube at Vienna (1963-2005) and a summary of the results from the Joint Danube Survey 2 (2007). δ18O values of JDS2 river water samples ranged from -13.1 per mille (Inn, alpine river) up to -6.4 per mille (River Sio, evap oration influence). The δ18O value of the Danube increased from -10.8 per mille after the confluence of the Inn River with the upper Danube up to -9.6 per mille at the mouth, with a major change after the inflow of Tisa and Sava. The isotopic composition of river water in the Danube Basin is mainly governed by the isotopic composition of precipitation in the catchment area, while evaporation effects play only a minor role. Short term and long term isotope signals from precipitation are thus transmitted through the whole catchment. Tritium concentrations in most parts of the Danube river system lay around 10 TU during the JDS2 period and reflected the actual 3H content of precipitation in Central Europe, but 3H values up to 40 TU in the Danube and up to 250 TU in some tributaries are clear evi dence for discontinuous releases of 3H from local sources (nuclear power plants) into the rivers. (author)