Natural radionuclides and cesium-137 in soils and bottom sediments Of the Khanka lake

The paper describes the radionuclide composition of soils of the territories around the Khanka Lake and the bottom sediments of the lake and the Spasovka River flowing into the Khanka Lake. The questions of distribution and spatial variability of natural (238U, 232Th, 40K) and artificial (137Cs) radionuclides are discussed. Recently the economic activities in the lake basin have acquired particular importance, as the territory fell under the state program “Far Eastern hectare”. So the article emphasizes the importance of studying geo-ecological problems and pollution of the natural environment, as well as the need to take measures to address them. The paper provides a detailed characteristic of soil composition and properties in the vicinity of the Khanka Lake and identifies the conditions of the radial migration of radionuclides. Plains with excessive moisturing and water-retaining horizon are favorable for peat formation (peat horizon can reach 50 cm), which promotes radionuclide migration to deeper horizons. Clay sod-podzolic and podzolic-brown soils of clayey and loamy granulometric composition are formed on higher elevation territories, which on the contrary prevents the migration of radionuclides down the profile. The average content of organic components in soils was found to be 4 %. The mineralogical composition of some samples demonstrates the presence of potassium and sodium feldspars, accompanied by calcium langbeinite gypsum phases in the upper layers, indicating the use of salt sulfate mineral fertilizers. The proportion of organic matter in bottom sediments was 2–3 %. Background levels of radionuclides in the vicinity of the lake are 18–177 Bq/m2 for 137Cs; 500–1800 Bq/m2 for 238U и 323Th; 1300–11000 Bq/m2 for 40K. There are no signs of the influence of radiation catastrophes on the study area. Intensive leaching of т40K from the lake catchment by river runoff was detected. The lowest content of 40K stocks was found in soils and river bottom sediments (up to 1–10 kBq/m2) and the highest in lake sediments (8–20 kBq/m2).