Implications of slow deep water renewal of Lake Koenigssee derived from combined tritium-3helium measurements

Two vertical tritium and 3helium profiles from December 1980 and September 1981 taken at a station near the deepest point of Lake Koenigssee are presented. The tritium profiles indicate that water inflow by rivers is concentrated at shallow depth. The deep water renewal rate by inflowing rivers during winter 80/81 deduced from tritium data is 10%, which corresponds to a water turnover time of 10 years. The tritium - 3helium-age, i.e. the gas residence time in the deep water is around 5 years. The deep water net oxygen consumption rate, that is based on the T - 3He-age, amounts 0.07 mg/l/month. 3Helium gas exchange rates of 0.2 m/d during winter 80/81 and 0.02 m/d during summer 1981 are calculated from the data. From the September 81 profile a vertical eddy diffusion coefficient for tritium, 3helium and temperature of 0.03 +- 0.01 cm2/sec is derived for the depth range between 6 m and 21 m, i.e. directly below the thermocline. (orig.)