ИСТИНА

It is well-known that floodplain sediments deposited during overbank floods has been used to reconstruct past changes in sediment sources, to provide information on changing sediment fluxes and to evaluate the antropogenic influence on the river basin. This presentation reports the use of sediment cores collected from the River Niida floodplains to provide information on evaluation of human impact on sediment and sediment-associated pollutants redistribution and river environment in River Nitta basin affected by radionuclide contamination in the NE part of Honshu Island in Japan after Fukushima Dai-ichi NPP accident in 2011. Detailed study of 137Cs vertical distributions curves in floodplain soils were carried out at different levels of the floodplain to 7 sections, located across the River Niida fluvial network. The River Niida drains a mountainous region with mostly forested slopes in the upper and middle parts of basin and piedmont plain near the Pacific Ocean in the lower part of basin. Wide valley bottoms of the upper part of the basin are mainly used as paddy fields. After radionuclide contamination of upper part of the basin, all rice fields were abandoned and the recent work carried out on decontamination. The lower part of the basin is still being used in agriculture. In the upper part of the basin river streams were canalized, and the earthen levees were built along the streams in the lower part of the basin. Floodplain deposition rates are significantly controlled by human influence and may explain the local impact of natural and anthropogenic factors on the environment of the river. Finally it is discussed the differences of human activity impact on the river environment between the River Niida and the River Plava, located in the Chernobyl contamination zone.