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VERTICAL AND LATERAL MIGRATION OF FUKUSHIMA-DERIVED RADIOCESIUM WITHIN NIIDA RIVER CATCHMENTтезисы доклада
- Авторы: KONOPLEV A., GOLOSOV V., WAKIYAMA Y., NANBA K., ONDA Y., TAKASE T.
- Сборник: THE SECOND INTERNATIONAL YOUNG SCIENTISTS FORUM ON SOIL AND WATER CONSERVATION AND ICCE SYMPOSIUM 2018 «Climate Change Impacts on Sediment Dynamics: Measurement, Modelling and Management» PROGRAMME BOOK
- Тезисы
- Год издания: 2018
- Место издания: Moscow
- Аннотация: INTRODUCTION Processes of vertical and lateral migration lead to gradual reduction in contamination of catchment soil, particularly its top layer. This, in turn, results in a gradual decrease of radiocesium activity concentrations in the surface runoff and river water, in both dissolved and particulate forms. The purpose of this research is to study the dynamics of Fukushima-derived radiocesium in undisturbed soils and floodplain deposits exposed to erosion and sedimentation during floods. METHODS Seven cross-sections for sampling and sediment traps installation were selected on the Niida River floodplain. One cross-section characterized the headwaters of the Hiso River basin upstream of its most polluted part (site N7). Three cross-sections integrate the 137Cs concentration in sediments delivered from headwaters of the main uplands rivers (Upper Niida, Iitoi and Hiso, sites N4, N5 and N6 respectively). Two cross-sections are in lower reaches of the Niida River (sites N1 and N2). Site N3 was selected for integration of 137Cs concentration in sediments transported from both the Iitoi and the Upper Niida Rivers at the boundary between headwaters uplands and mid-basin rangelands (Konoplev et al., 2018). Fig. 1 demonstrates dynamics of 137Cs vertical distribution in the upper 30-cm layer of soil/sediments at four selected observation sites on the Niida River floodplain. CONCLUSIONS Combined observations of radiocesium vertical distribution in soil and sediment deposition on artificial lawn-grass mats on the Niida River floodplain allowed us to estimate both annual mean sediment accumulation rates and maximum sedimentation rates corresponding to an extreme flood event during Tropical Storm Etau, 6-11 September 2015. Dose rates were reduced considerably for floodplain sections with high sedimentation because the top soil layer with high radionuclide contamination was eroded and/or buried under cleaner fresh sediments produced mostly due to bank erosion and sediments movements. Sediment deposition for downstream section of Niida river floodplain reached 20 cm after the event, and for upstream section in the area of confluence of Hiso river with basic Niida river – up to 40 cm. Extreme flood events during typhoons result in fast and efficient natural attenuation. Generally, due to higher precipitation, steeper slopes, higher temperatures and higher biological activities in soils, selfpurification and natural attenuation of radioactive contamination in Fukushima associated with vertical and lateral radionuclide migration is essentially faster than in Chernobyl. Accounting for soil erosion and sediment accumulation within river catchment and in particular, river floodplain, is key for predicting redistribution of radioactive contamination after the FDNPP accident on the contaminated territories, as well as for decision making about remediation and clean-up of contaminated territories.
- Добавил в систему: Голосов Валентин Николаевич