Investigation of sediment transport in the Austrian part of the Danube using environmental isotopes

During the last 30 years eight hydroelectric power plants have been constructed along the Austrian part of the Danube; as a consequence sediment transport and deposition have changed considerably. Thick piles of fine sediments have accumulated in the uppermost of the chain of reservoirs (Aschach) from 1964 onward. The task of this preliminary study is to investigate which information on sedimentation and sediment transport can be obtained using environmental isotope methods. The tritium content and the stable isotope ratios of the pore water were measured. Chemical constituents and radionuclides (7Be, 90Sr, 137Cs) were investigated in several size fractions of the sediments. Preliminary results obtained from measuring the 3H content of the pore water indicate that the latter is mainly the original Danube water entrapped during sedimentation. Apart from the 3H peak in the 1960s, a second smaller peak was detected, corresponding to precipitation with high 3H content in the Austrian Alps in May 1974. Up to April 1986 the 137Cs content of the sediments decreased from its maximum in 1963. Measurements on post-Chernobyl samples taken from all reservoirs in October 1986 show an increase in 137Cs concentration of about two orders of magnitude. There is a more or less continuous decrease in 7Be content along the chain of reservoirs, possibly due to different sedimentation rates of redistribution. (author). 6 refs, 9 figs, 2 tabs