Spectrocolorimetric, geochemical and radiocesium properties of source material and sediment collected after the 2019 typhoons in Fukushima coastal rivers (Japan)

Spectrocolorimetric properties analysed with a portable diffuse reflectance spectrophotometer (Konica Minolta CM-700d) and geochemical contents obtained with an energy dispersive X-ray fluorescence spectrometer (ED-XRF Epsilon 4) were analysed in potential source material that may supply sediment to coastal rivers draining the main Fukushima radioactive pollution plume (Japan). Three potential source materials (n=57) were considered (cropland soils ready for cultivation after the completion of the local decontamination programme; forest soils and subsurface material originating from landslides and channel bank collapse). Recent sediment lag deposits (mud drapes deposited on channel-bed sand; n=24) were collected along the main rivers draining the Mano and Niida catchments (Fukushima Prefecture, Japan) on the 29th and 30th of October 2019 after the 2019 typhoon season including typhoon Hagibis. In addition to spectrolorimetric and geochemical properties, radiocesium (Cs-137) concentrations were analysed by gamma spectrometry using Germanium Hyperpure detectors in all source and sediment samples (n=81).

本研究针对可为承接日本福岛主要放射性污染羽流的沿海河流输送沉积物的潜在源物质，开展了相关指标分析：采用便携式漫反射分光光度计（portable diffuse reflectance spectrophotometer，Konica Minolta CM-700d）测定其分光色度特性，采用能量色散X射线荧光光谱仪（energy dispersive X-ray fluorescence spectrometer，ED-XRF Epsilon 4）测定其地球化学成分。本次研究共选取三类潜在源物质（样本量n=57）：当地去污计划完成后可供耕作的农田土壤、由滑坡与河道岸坡坍塌形成的森林土壤及地下物质。2019年10月29日至30日，在2019年包含海贝思台风（typhoon Hagibis）的台风季结束后，研究团队沿流经日本福岛县真野与新井田流域的主要河流，采集了24份近期沉积物滞后堆积体——即沉积于河床沙体之上的泥质覆盖层。除上述分光色度与地球化学指标外，所有源物质与沉积物样本（总样本量n=81）均采用高纯锗探测器伽马能谱分析法（gamma spectrometry using Germanium Hyperpure detectors）检测了放射性铯（radiocesium，Cs-137）的浓度。