Со-60 as a time marker to date sediment layers and estimate sediment transport distances during the 2006 flood event on the Yenisei River

Abstract

The study of bottom sediments collected from the Yenisei River downstream of the Mining-and-Chemical Combine (MCC) conducted from 2006 to 2016 revealed increased concentrations of 60Co, which was present in dispersed form and in the form of radioactive microparticles, in the upper core layers. The increase in 60Co activity concentration occurred when the 2006 extreme flood on the Yenisei washed away the radionuclide-containing soil from the riverbank at the MCC. The 137Cs/60Co ratio in the upper layers of bottom sediments after the 2006 flood varied between 0.2 and 1.5 and differed considerably from the 137Cs/60Co ratio in the upper sediment layers before the flood (2.5–6.0). Because of the increased concentrations of 60Co, especially in the form of microparticles, in some sediment layers, 60Co was used as a time marker (2006) enabling calculation of sedimentation rates and radionuclide sediment chronology. The 137Cs sediment chronology calculated using 60Co showed that the major 137Cs peak was dated to the most extreme flood on the Yenisei, which occurred in 1966. Those calculations confirmed the appropriateness of using 60Co as a time marker. Our findings suggest that during the 2006 flood, 60Co was washed away from the MCC area to the Yenisei and transported as a component of suspended particles as far as 245 km downstream of the MCC.