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CESIUM-137 AS AN INSTRUMENT FOR DETERMINING THE SEDIMENTATION RATES IN THE LAKES OF THE BLACK SEA DRAINAGE BASIN

Yury Fedorov

Abstract

Cesium-137 is a long-lived technogenic radionuclide. The study of its distribution in the environment is important either from ecological point of view or as it may be used as a marker for sediment core dating. Lakes are excellent objects for the application of these approaches. A scientific expedition was carried out in order to extract and to study sediment cores from the beds of Lake Maly Liman, Lake Abrau, Lake Maly Utrish (Municipality of Novorossiysk, Region of Krasnodar), and Lake Bolshoi Tambukan (at the border of Stavropol Region and Kabardino-Balkar Republic). In Lake Abrau, the specific activity of 137Cs is detected within the upper sediment layer 30 cm thick with two distinct peaks. In the deeper layers, there is no any 137Cs specific activity. In Lake Maly Liman, 137Cs is concentrated in the upper sediment layer 20 to 25 cm thick. In the Utrish Lake it is detected in all the sediment layers. In the sediment core of Lake Bolshoi Tambukan almost all the Cesium-137 is concentrated in the upper layer 15 cm thick with only one distinct peak. In the superficial layer of bottom sediments of all the considered lakes the 137Cs specific activity is lower than at 7 to 15 cm of sediment core depth. That indicates the decrease in the 137Cs intake in the recent years. In general, the 137Cs specific activity in the sediment cores of the lakes is lower than in the Sea of Azov. The upper peak of the 137Cs specific activity is related to the Chernobyl accident of 1986, and the second peak was formed by the global radioactive fallout due to numerous tests of thermonuclear weapons in the atmosphere in the end of 1950s and beginning of 1960s. According to the sediment core depths of the first peak of 137Cs specific activity, the sedimentation rates in Lake Bolshoi Tambukan, Lake Maly Liman, Lake Abrau, and Lake Maly Utrish are estimated respectively at 3.6, 4.2, 4.2, and 6.0 mm a year. The sediment core depths of the second peak of 137Cs related to the global radioactive fallout gives the estimate of about 7.4 mm per year for Lake Maly Utrish and 3.7 mm a year for Lake Maly Liman and Lake Abrau.

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DOI resolver: doi.org/10.5593/sgem2017/51/s20.025

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