|Autoren des Beitrags|
|Titel des Beitrags||Long term Cs-137 time dependences in water and different fish species of a small eutrophic lake|
|Titel veröffentlicht in ...||Book of abstracts of the 4th International Conference on Radioecology and Environmental Radioactivity (ICRER)||Erscheinungsjahr||2017||Publikations-Art||Kongressschrift / Tagungsband||Name der Konferenz/Veranstaltung||4th International Conference on Radioecology and Environmental Radioactivity (ICRER)|
Lake Vorsee, a glacially formed small and shallow eutrophic lake, is situated in Southern Germany, about 25 km north of Lake Constance. With a surface area of 0.084 km2, a mean water depth of only 0.9 m and a swampy catchment of 1.15 km2, it is a type of lake which can be found quite often in the prealpine area and typically it is intensely used for fishing. Even decades after the 137Cs fallout considerable amounts of 137Cs are still transported from the catchment area into the lake, and the 137Cs activity concentration in the lake water and the transfer into fish is relatively high compared to many other lakes (Pröhl et al., 2006).
Materials and methods
Samples of several hundred liters of water (adsorbed in hexacyanoferrate) and suspended matter (collected on blue ribbon paper filters, SchleicherSchuell) were taken with a Large Volume Water Sampler (Midiya-System). The 137Cs activity concentration was determined gamma-spectrometrically by HPGe-detectors. The concentration of the competing ions K+ and NH4+ was determined by ion chromatography. 137Cs in fish samples with a length up to 15 cm was measured without head and gills, for larger fishes only muscle tissue was used.
Radioecological situation in catchment area and lake
The vertical distribution of 137Cs in soil profiles taken at 4 positions of the catchment area described by the analytical solution of the simple diffusion-convection differential equation with single pulse input results in a convection speed of activity v = (0.16 ± 0.08) cm/a and an effective diffusion DE= (1.22 ± 1.32) cm2/a. This means that most of the inventory is still in the top 20 cm of the soil.
The 137Cs soil-inventory determined at 9 different positions in the catchment area amounts to (28.7 ± 6.9) kBq/m2. By far, most of the inventory of this lake system is still in the soil of the catchment area.
The vertical 137Cs distribution in 7 sediment cores from different positions in the lake is measured and modelled also by a convectiondiffusion model but with fixation and redissolution of 137Cs in the sediment. Average parameters are a very low bulk density of around 0.032 g/cm3, a sedimentation rate Rs = (0.03 ±0.01) g/(cm2 a), a distribution coefficient of the exchangeable 137Cs Kdex = (530 ±139) L/kg, and a bio-turbation Dbio = (4.3 ± 3.5) cm2/a at the surface which decreases to Dbio = 0 at a depth of 1 m. The bio-turbation is necessary to describe the broad Cs-maximum which cannot be separated into distinct Chernobyl and NWT derived Cs-peaks. The inventory in sediments is the second largest in the lake system after the inventory in the soil in the catchment area.
Time dependences of 137Cs activity concentration in lake water and fish
Time dependences of 137Cs activity concentration in lake water and fish can be well described by a simple compartment model based on the Aquascope model (J. Smith; 2000, 2002, 2005). In this model run-off into the lake, outflow, sedimentation, radioactive decay as well as uptake and excretion by fish is taken into account. Data for 137Cs activity concentration in water (n=250) and fish (n=627) is available from 1986 to 2016.
The seasonal cycling of the 137Cs activity concentration in the lake water and the correlation of the activity concentration with different influencing factors e.g. K+-, NH4+-concentration, pH and O2-concentration will be discussed.
Estimations on uptake and loss rate parameters as well as ecological half-lives for fish species from different trophic levels will be presented (Pike, Esox lucius; n=153; Small whiting, Cyprinidae, n=400; Eel and Catfish, Anguilla anguilla and Silurus glanis, n=67).
Pröhl G., Ehlken S., Fiedler I., Kirchner G., Klemt E., Zibold G. 2006. Ecological half-lives of 90Sr and 137Cs in terrestrial and aquatic ecosystems. J. Environ. Radioact. 91: 4172.
Smith J.T., Kudelsky A.V., Ryabov I.N., Hadderingh R.H. 2000. Radiocaesium concentration factors of Chernobyl-contaminated fish: a study of the influence of potassium, and blind testing of a previously developed model. J. Environ. Radioact. 48: 145-164.
Smith J.T., Kudelsky A.V., Ryabov I.N., Daire S.E., Boyer L., Blust R.J., Fernandez J.A., Hadderingh R.H., Voitsekhovitch O.V. 2002. Uptake and elimination of radiocaesium in fish and the size effect. J. Environ. Radioact. 62: 359-369.
Smith J.T., Bulgakov A.A., Comans R.N.J., Konoplev A.V., Kudelsky A.V., Madruga M.J., Ryabov I.N., Voitsekhovitch O.V., Zibold G. 2005. The AQUASCOPE simplified model for predicting 89,90Sr, 131I and 134,137Cs in surface waters after a large-scale radioactive fallout. Health Physics. 89: 624-644.
Bachelorstudiengang Physikalische Technik
Masterstudiengang Umwelt- und Verfahrenstechnik
Fakultät Technologie und Management
Institut für Angewandte Forschung (IAF)
Schwerpunkt Energie und Umwelt (IAF)
Masterstudiengang Umwelt- und Verfahrenstechnik - Intranet
Bachelorstudiengang Energie- und Umwelttechnik - Intranet
Dr. rer. nat.
Verbundprojekt TransAqua: Transfer von Radionukliden in Aquatischen Ökosystemen; Teilprojekt I