Knowledge of sedimentation rates in lakes is
required to understand and quantify the geochemical processes involved
in scavenging and remobilization of contaminants at the Sediment-Water
Interface (SWI). The well-known 210Pb excess (210Pbex) method cannot be used for quantifying sedimentation rates in uranium-enriched catchments, as large amounts of 210Pb produced by weathering and human activities may dilute the atmospheric 210Pb. As an alternative dating method in these cases, we propose an original method based on 232Th decay series nuclides.
study focuses on an artificial lake located in a granitic catchment
downstream from a former uranium mine site. The exponential decay of 228Ra excess (228Raex) with depth in two long cores yields sedimentation rates of 2.4 and 5.2 cm yr−1 respectively. These sedimentation rates lead to the attribution of the 137Cs activity peak observed at depth to the Chernobyl fallout event of 1986. The 228Raex method was also applied to two short cores which did not display the 137Cs peak, and mean sedimentation rates of 2.1 and 4.0 cm y−1 were deduced. The proposed method may replace the classical radiochronological methods (210Pbex, 137Cs) to determine sedimentation rates in granitic catchments.