ИСТИНА

Nine great rivers discharge into the Arctic Ocean and transfer fallout 137Cs from their watersheds. The highest concentration measured in the bottom sediments in the estuaries of the Yenisei and Ob Rivers. One of these anomaly zones formed in the Ob’ estuary due to the geochemical river-sea boarder barrier. The main sources of radioactive cesium in the Ob’ River basin are liquid radioactive wastes from plant association “Mayak” (300 – 3200 curie for 1958 – 2004) and runoff of global fallout 137Cs. The goal of our research is to calculate runoff of global fallout 137Cs from the Ob’ estuary macroarena. It includes the Ob’ river basin (83% of macroarena total area) and smaller river basins flowing in the Ob’ estuary. Geographic information system (GIS) is made. The tenth-order river basins (n=154, Horton coding system) shape 20 groups due to topsoil properties controlling cesium mobility. Six first order tributary river basins, characterized five groups of tenth order tributary river basins, were studied, and 600 bulk core soil samples were collected in 2011 and 2012. The data obtained show that global fallout cesium-137 runoff from undisturbing humid first order tributary river basins (n=4) is less than 0.5Ci*km-1. Runoff from arable semi-humid first order tributary river basins (n=2) varies from 3 to 35Ci*km-1. According to GIS, internal flow areas occur 23% of the macroarena 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 the main contribution in 137Cs runoff from the macroarena. Global fallout 137Cs runoff summarized is 350 – 8400 curie (0,1 – 2,2 % of total storage in the Ob’ estuary macroarena) from humid and semi-humid river basins.