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In the context of elevated concerns related to nuclear accidents and warfare, the lessons learnt from the Fukushima Daiichi Nuclear Power Plant accident in 2011 are important. In particular, Japanese authorities implemented an ambitious decontamination program to reduce the air dose rate in order to facilitate the return of the local inhabitants to previously evacuated areas. This approach contrasts the strategy adopted in Chernobyl, where the most contaminated areas remain off limits. Nonetheless, the effectiveness of the Japanese decontamination strategy on the dispersion of radioactive contaminant fluxes across mountainous landscapes exposed to typhoons has not been quantified. Based on the unique combination of river monitoring and modeling in a catchment representative of the most impacted area in Japan, we demonstrate that decontamination of 16% of the catchment area resulted in a decrease of 17% of sediment-bound radioactive fluxes in rivers. Decontamination operations were therefore relatively effective, although they could only be conducted in a small part of the area due to the dominance of steep forested slopes. In fact, 67% of the initial radiocesium contamination was calculated to remain stored in forested landscapes, which may contribute to future downstream radiocesium dispersion during erosive events. Given that only a limited proportion of the initial population had returned in 2019 (~30%), it raises the question as to whether decontaminating a small percentage of the contaminated area was worth the effort, the price, and the amount of waste generated? [ABSTRACT FROM AUTHOR]

The 20 km2 Galabre catchment belongs to the French network of critical zone observatories (OZCAR; Gaillardet et al., Vadose Zone Journal, 2018, 17(1), 1–24). It is representative of the sedimentary lithology and meteorological forcing found in Mediterranean and mountainous areas. Due to the presence of highly erodible and sloping badlands on various lithologies, the site was instrumented in 2007 to understand the dynamics of suspended sediments (SS) in such areas. Two meteorological stations including measurements of air temperature, wind speed and direction, air moisture, rainfall intensity, raindrop size and velocity distribution were installed both in the upper and lower part of the catchment. At the catchment outlet, a gauging station records the water level, temperature and turbidity (10 min time‐step). Stream water samples are collected automatically to estimate SS concentration‐turbidity relationships, allowing quantification of SS fluxes with known uncertainty. The sediment samples are further characterized by measuring their particle size distributions and by applying a low‐cost sediment fingerprinting approach using spectrocolorimetric tracers. Thus, the contributions of badlands located on different lithologies to total SS flux are quantified at a high temporal resolution, providing the opportunity to better analyse the links between meteorological forcing variability and watershed hydrosedimentary response. The set of measurements was extended to the dissolved phase in 2017. Both stream water electrical conductivity and major ion concentrations are measured each week and every 3 h during storm events. This extension of measurements to the dissolved phase will allow progress in understanding both the origin of the water during the events and the partitioning between particulate and dissolved fluxes of solutes in the critical zone. All data sets are available at https://doi.osug.fr/public/DRAIXBLEONE_GAL/index.html. [ABSTRACT FROM AUTHOR]

• Two contrasting years of monitoring of an agricultural tile-drained catchment. • Water and suspended particle transfers displayed high temporal variability. • Two transfer pathways to tile drains were observed. • Suspended particle dynamics in tile drains may be controlled by sediment storage and exhaustion. Soil erosion, runoff and sediment connectivity are strongly impacted by anthropogenic features in lowland agricultural catchments. Among these landscape features, the role played by tile drainage on water and sediment transfers and hillslope-to-river connectivity in drained catchments remains poorly understood. This study quantified water and sediment transfers in a tile drained catchment of central France by combining high frequency rainfall, discharge and sediment concentration measurements at the outlet of a set of 10 tile drained plots (34 ha) and at the medium-sized (120 km2) catchment scale. Over the monitoring period, including a dry and a wet year compared to average conditions (one year with 112% of the mean annual rainfall and one year with 64% of the mean annual rainfall), 36 rainfall-flood events were recorded and analyzed. The high frequency analysis of water and sediment transfers in tile-drained plots showed a high seasonal variability and the occurrence of two transfer pathways in the soil column including the slow drainage of saturated soils and the occurrence of preferential flow pathways through the soil column. Indeed, 13 of the 36 recorded flood events showed hydrographs with two components, reflecting these two pathways: slow transfers in the soil columns and fast transfers through soil macropores and/or cracks. Indeed, at the beginning of the flood event, a high-magnitude peak overlaid on the hydrograph. On average, this fast peak contributed 15% of the water and sediment fluxes. The sediment dynamics in tile drains was suggested to depend on sediment storage and exhaustion processes occurring in the tile drain network. [ABSTRACT FROM AUTHOR]

Agricultural drainage increases hydrological connectivity between fields and receiving environments. Tile drains and drainage ditches are the main drainage types studied at the field scale. They can be associated with temporary surface drains to improve the removal of surface water. Combining surface drains with tile drains is likely to modify surface runoff and soil water dynamics. The behaviour of tile-drained fields has been studied at the event scale, but few studies have been conducted over a full hydrological year, and no studies have quantified water volumes in a field combining surface and tile drainage. So quantifications of water partition between surface drainage, tile drainage and soil water are needed to understand the hydrological behaviour of a field combining surface and tile drains. Moreover, at the event scale, few studies showed macropores can contribute to tile drain runoff but the partition between preferential flow and matrix flow is still unclear. It needs to be study depending on several parameters as soil type, soil water content or agricultural practice for a better understanding. In this study, high temporal resolution quantification of surface runoff and tile drainage was conducted for two full hydrological years to study hydrological functioning of the field using the water balance for a drained field. Soil water pathways were studied under dry and saturated soil conditions, tracing water by measuring stable isotope (18O and 2H) concentrations in rainwater, soil water, and surface and tile runoff. Runoff quantification showed that surface drainage and tile drainage respectively transferred 44% and 20% of annual effective rainfall. However, water balance showed that, at the annual scale, 65% of infiltrating water was not captured by tile drains. At the event scale, water tracing showed a season variation in macropores contribution depending on soil hydric state. Under dry conditions, rainwater was directly transferred to tile drains, likely through macropores. On saturated soil, pre-event soil water content provided most of the water flowing out from the tile drain, but rainfall can contribute up to 25% of the water flowing out from the tile drains. Combining water balance and water trancing allowed to propose a conceptual model for surface and tile drainage hydrological functioning at the event scale. • High temporal resolution monitoring of surface and tile drain runoffs. • Two years water balance of a field combining surface and tile drains. • Around 65% of infiltrating water is not intercepted by tile drains. • Macropore contribution to tile drain flow depends on soil hydric state. [ABSTRACT FROM AUTHOR]

The geochemical distribution of U and associated major and trace elements (As, Li, Pb, Sr, Zn) was studied at the former Rophin U mine (Puy-de-Dôme, France). Three zones of contrasting radiological settings were identified and sampled: a background area (<200 nSv·h−1), a streambed flowing downstream of the former mine (radiation level between 200 and 800 nSv·h−1) and a wetland soil (>1000 nSv·h−1). Sediment and water samples were collected both in a streambed located in the background area and in the streambed downslope the former mining area, and a soil sample was collected in the wetland downslope. Using both sequential and selective chemical extractions, and quantifying also the chemical reservoirs of As, Li, Pb, Sr, and Zn, it could be concluded that, in the streams, U was mainly bounded to primary ore minerals (phosphates) that were transported through particulate transport. It was also bound, to a lower extent, to clays, Mn oxyhydroxides and organic matter, certainly due to the sorption of aqueous U originating from partial dissolution or leaching of primary ore materials. Ore minerals remaining stable in the stream sediments were certainly included in a quartz matrix and hence were not in accessible for dissolution. In the wetland soil, selective extractions evidenced that U was about evenly distributed between humid/fulvic acids and organic matter unaffected by NH 4 OH 1M. [Display omitted] • Investigation of the radiological and geochemical settings downstream a former U mine. • In streams, U migration dictated by interplay between sorption of aqueous U and particulate transport. • In stream sediments, U primarily bound to ore material and to lesser extent clay, Fe/Mn hydroxides, and organic matter. • In a wetland soil, U bound to humic/fulvic acids and possibly lignin, clue for U uptake by plants. [ABSTRACT FROM AUTHOR]

Abstract: Selenium 79 is a beta emitter produced from 235U fission and is one of the long half-life radionuclides of interest in nuclear waste disposal problematic because of its potential migration capacity to the surface environment. Measurement of 79Se is particularly difficult due to its low activity in waste matrices (about 10−3 Bqg−1). A radiochemical procedure based on ion exchange separations was already described in a previous paper. This work presents different applications of the radiochemical separation to waste samples and an improvement of this procedure, including a selective extraction of selenium as diethylselenium in an organic solvent followed by a re-extraction in aqueous medium. This additional step allows the decontamination factor to be increased with the aim of counting 79Se by liquid scintillation counting. [Copyright &y& Elsevier]