Some considerations concerning 137Cs vertical profile in the Danube Delta: Matita Lake core

By using γ-ray spectrometry and x-ray diffraction, the vertical profile of 137Cs specific activity as well as the mineralogical composition of a set of cores collected from the Danube Delta-Matita Lake was investigated; the observed profiles are typical for an undisturbed site. An overlapping of the 1963 nuclear tests and 1986 Chernobylderived 137Cs specific activity peak was observed. From the experimental profiles, two different values for the mixing rate, D, have been determined: D1 = 1.81 × 10−8 cm2 s−1 for the upper 10-cm layer and D2 = 6.20 × 10−8 cm2 s−1 for the next 10–30-cm layer. These values correspond to different bioturbation regimes. The sedimentation rate has been determined as R = 0.15 ± 0.05 g cm−2 year−1. The total cesium inventory is 3.596 ± 0.090 kBq m−2, a value approximately equal to the sum of the nuclear tests and Chernobyl fallout.