Factors Forming the Spatial Distribution ofNatural and Man-Made Radionuclides in the Bottom Sediments of the Kamyshovaya Bay, Sevastopol

Purpose. The purpose of the article is to reveal the features of spatial distribution of the radionuclide (210Pbex, 226Ra, 137Cs and 40K) contents in the bottom sediments of the Kamyshovaya Bay and to identify the factors determining them. Methods and Results. The paper presents the results of measurements of the concentrations of 210Pbex, 226Ra, 137Cs and 40K in nine samples of the surface (0-5 cm) layer and in two columns of bottom sediments collected in the Kamyshovaya Bay in July 2021. The activity of 210Pbex, 226Ra, 137Cs and 40K in the samples was determined using a low-background gamma spectrometer with a well-type NaI(Tl) scintillation detector. Estimates of the relationship between the activity of the radionuclides under consideration in the bottom sediments with the sediment granulometric composition and the organic carbon content are given. The rate of sedimentation and the flux of matter and radionuclides to the bottom sediments were quantitatively assessed. Conclusions. Spatial variability of the concentrations of radionuclides under consideration reveals a general tendency towards increase of their values from the northern part of the bay to its southern one. The results of the analysis indicate that the spatial variability of radionuclide content in the surface sediment samples and their vertical distribution in the two columns are explained by the changes in particle size distribution and in sedimentation rates, as well as by presence of the storm water and domestic wastewater sources in the bay southern part. Based on the results of the correlation analysis, the process of water purification in the area under study was assumed to result from the adsorption of radionuclides and organic matter by a fine-grained material that was followed by sedimentation of this material in bottom sediments. The average values of the sedimentation rate and the matter flux to bottom sediments were 0.43 cm/year and 2976 g/(m2 center dot year), respectively. The flux of radionuclides to the bottom sediments was 53.0 Bq/(m2 center dot year) for 137Cs, 690.5 Bq/(m2 center dot year) for 40K, 58.0 Bq/(m2 center dot year) for 226Ra and 79.5 Bq/ (m2 center dot year) for 210Pbex.