The sediment budget and migration of 137Cs in Chernobyl affected area: 30 years of investigations in the Plava River basin, Tula region

Abstract

The Plava River basin (Tula region) is considered the most polluted with Chernobyl fallout region in Russian Federation. Detailed studies of sediment redistribution and migration of 137Cs produced by Chernobyl were conducted in the basin. The article provides an overview of results from various studies conducted during the last 30 years estimating the rate of erosion and sediment redistribution based on different methodology including 137Cs. Sediment budgets for different parts of the fluvial network were developed based on estimated rates of erosion and accumulation of sediments within the Plava River basin for the post-Chernobyl period. It has been established that eroded from agricultural fields sediments accumulate on the slopes of interfluves (38.4%) and in the bottoms of dry valleys (2738%). Part of the sediment delivered by slope runoff and temporary watercourses from the slopes of the interfluves to the bottoms of river valleys was redeposited on river floodplains (1011%), and the remaining part (13.124.7%) passed into the river sediment load. The value of basin contribution of sediments to the Plava River sediment runoff is somewhat overestimated due to the specifics of the erosion models used to calculate soil erosion from arable land. It has been established that for the period of more than 25 years since the Chernobyl accident, 5% of 137Cs deposits were lost due to soil erosion (less than 0.2% annually). According to evaluated sediment budget, only a quarter of mobilized material leaves basin as a sediment yield. Thus, only about 1% of the initial 137Cs fallout was removed from the Plava basin. The perspective directions for research on sediment redistribution in the plain river basins located in the temperate zone using 137Cs as a technogenic tracer are outlined.