ИСТИНА

There are several high level 137Cs anomaly zones detected in the deposits of the SW part of the Kara Sea. These anomaly zones were formed in the Ob’ and the Enisey river estuaries due to the geochemical “river-sea” boarder barrier. Level of radiocaesium specific activity reaches 120Bq*kg-1 in the deposits from these zones. Radiochemical enterprises occur in the both river basins. Their activity results in caesium-137 transfer into the river net. Vast area is contaminated by 137Cs after nuclear weapons in Semipalatinsk test-site and Kyshtym disaster in the Ob’ river basin. Moreover, caesium comes to the Ob’ and the Enisey river basins with global atmospheric fallout. The inflow of global fallout caesium-137 to the catchments is 660kCi (320 kCi including radioactive decay) that is 4 times higher than 137Cs emission due to Fukushima disaster. Therefore, these river basins as any other huge catchment are an important sources of radioactive contamination of the Arctic Ocean. The aim of our research is to study behavior of global fallout caesium-137 in the landscapes of the Ob and the Enisey river basins. We studied caesium-137 behavior on the example of first order catchments in taiga, wetland, forest-steppe, steppe, and semi-arid landscapes. Geographic information system (GIS) was made. The tenth-order catchments (n=154, Horton coding system) shape 20-groups due to topsoil properties controlling cesium mobility. Eleven first-order basins, characterized 7 groups of tenth order catchments, were studied. And 700 bulk-core soil samples were collected in 2011-2013. Caesium runoff is calculated for 3 first-order river basins in taiga and forest-steppe landscapes. Storage of global fallout caesium-137 declines from undisturbing taiga first-order river basin (90% of cumulative fallout including radioactive decay)> arable steppe and fores-steppe (70 – 75%)> undisturbing wetland (60%). Caesium-137 transfer is high in arable lands or acid soils with considerable among of dissolve organic matter. And 137Cs accumulates in slightly alkaline soils with mull in topsoil. The data obtained show that global fallout cesium-137 runoff from undisturbing humid first-order river basins (n=1) is less than 0.5 Ci*km-1. Runoff from arable semi-humid first-order river basins (n=2) varies from 3 to 35 Ci*km-1. According to GIS, internal flow areas occur 23% of the Ob’ river basin total area and accumulate whole 137Cs. Humid and semi-humid river basins cover 40% and 8% of study area, respectively. We assume these basins yield as the main contribution in 137Cs runoff from the Ob’ river basin. Thus global fallout caesium-137 runoff is 0.9-6.1 kCi including radioactive decay (0.5-3.4% of total storage) from the Ob’ river basin to the Kara sea. Comparable among of caesium-137 could enter to the Kara sea due to liquid radioactive wastes by the nuclear plants located in the Ob’ and the Enisey river basins. As a result, global fallout caesium-137 runoff from the background landscapes of the Ob’ and the Enisey river basins plays an important role in radioactive contamination of the Kara sea. Conducted research results proved to estimate yield of radiochemical plants to radioactive contamination of the Arctic Ocean.