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Sediment connectivity characterizes the physical transfer of sediment through different geomorphic compartments in catchments due to sediment detachment, transport and deposition. Quantifying and modelling sediment connectivity is therefore a key prerequisite to improving our understanding of the dispersion of particle‐borne contaminants, especially in catchments exposed to highly erosive climates. The objective of this study is to provide novel insights into typhoon impacts on sediment connectivity from hillslopes to rivers. The dispersion of particle‐bound caesium‐137 (137Cs) was investigated in two coastal catchments draining the main contamination plume from the Fukushima Daiichi Nuclear Power Plant accident. Five sampling campaigns were carried out from November 2011 to November 2015, after each typhoon season. The spatial and temporal evolution of 137Cs contamination was investigated through the calculation of 137Cs enrichment ratios in sediment relative to nearby soils. Rainfall erosivity (EI30) associated with the main typhoons that occurred prior to each sampling campaign were computed, mapped, and finally used to improve a topographic‐based index of connectivity. From 2011 to 2015, mean contamination levels in Mano and Niida catchments decreased from 11.9 kBq kg−1 to 3.3 kBq kg−1 and from 34.1 kBq kg−1 to 8.0 kBq kg−1, respectively. Regional mean EI30 ranged from 262 MJ mm ha−1 h−1 for typhoon Jelawat (in 2012) to 1695 MJ mm ha−1 h−1 for typhoon Roke (in 2011). Typhoons Roke (2011) and Etau (2015) showed the highest connectivity from contaminated sources to the rivers, and induced a significant export of sediment to the ocean. In 2013 a slight increase in 137Cs levels in river sediments occurred, likely resulting from initial decontamination works and the occurrence of two consecutive typhoons. Importantly, this research provides new insights into the connectivity of the main sources of sediments contaminated with radiocaesium in Fukushima Prefecture and their temporal evolution, which will help with ongoing decontamination efforts. Copyright © 2016 John Wiley & Sons, Ltd.

Soil erosion rates in cultivated areas have intensified during the last decades leading to both on and off-site problems for farmers and rural communities. Furthermore, soil redistribution processes play an important role in sediment and carbon storage within, and exports from, cultivated catchments. This study focuses on the impact of land consolidation and changes in landscape structure on medium term soil erosion and landscape morphology within a 3.7-ha field in France. The area was consolidated in 1967 and we used the 137 Cstechnique to quantify soil erosion for the period (1954-2009). We measured the 137 Cs *revised manuscript Click here to download Manuscript: CATENA755_revision_bw.doc Click here to view linked References

Abstract. The Fukushima Daiichi nuclear power plant (FD-NPP) accident in March 2011 resulted in the fallout of significant quantities of radiocesium over the Fukushima region. After reaching the soil surface, radiocesium is quickly bound to fine soil particles. Thereafter, rainfall and snowmelt run-off events transfer particle-bound radiocesium downstream. Characterizing the precipitation regime of the fallout-impacted region is thus important for understanding post-deposition radiocesium dynamics. Accordingly, 10 min (1995Accordingly, 10 min ( -2015 and daily precipitation data from 42 meteorological stations within a 100 km radius of the FDNPP were analyzed. Monthly rainfall erosivity maps were developed to depict the spatial heterogeneity of rainfall erosivity for catchments entirely contained within this radius. The mean average precipitation in the region surrounding the FDNPP is 1420 mm yr −1 (SD 235) with a mean rainfall erosivity of 3696 MJ mm ha −1 h −1 yr −1 (SD 1327). Tropical cyclones contribute 22 % of the precipitation (422 mm yr −1 ) and 40 % of the rainfall erosivity (1462 MJ mm ha −1 h −1 yr −1 (SD 637)). The majority of precipitation (60 %) and rainfall erosivity (82 %) occurs between June and October. At a regional scale, rainfall erosivity increases from the north to the south during July and August, the most erosive months. For the remainder of the year, this gradient occurs mostly from northwest to southeast. Relief features strongly influence the spatial distribution of rainfall erosivity at a smaller scale, with the coastal plains and coastal mountain range having greater rainfall erosivity than the inland Abukuma River valley. Understanding these patterns, particularly their spatial and temporal (both inter-and intraannual) variation, is important for contextualizing soil and particle-bound radiocesium transfers in the Fukushima region. Moreover, understanding the impact of tropical cyclones will be important for managing sediment and sediment-bound contaminant transfers in regions impacted by these events.

Macaire. Classification and mapping of anthropogenic landforms on cultivated hillslopes using DEMs and soil thickness data -Example from the SW Parisian Basin, France. Geomorphology, Elsevier, 2011Elsevier, , 135 (1-2), pp.8-20. 10.1016Elsevier, /j.geomorph.2011 Classification and mapping of anthropogenic landforms on cultivated hillslopes using DEMs and soil thickness data -Example from the SW Parisian Basin, France AbstractThis study focuses on linear anthropogenic landforms of decametric width on cultivated hillslopes and their relations to soil thickness variability. The 16 ha study area shows a rolling topography supported by Cretaceous chalk of the SW Parisian Basin, France. Two types of landforms were identified: lynchets, similar to those described as soil terraces occurring on downslope field parts in other contexts, and undulations, linear, convex landforms that cut across fields. Accurate DEM construction and a detailed soil thickness survey were performed all over the study area. Soil samples were classified considering their location on specific types of anthropogenic landforms. The Classification Tree (CT) method was applied to assess whether lynchets and undulations can be discriminated through morphometric attributes (slope, curvature, profile curvature and planform curvature) and soil thickness (CT soil ) or through morphometric attributes only (CT topo ). The CT application establishes predictive classification models to map the spatial distribution of lynchets and undulations over the whole study area. The validation results of the CT soil and CT topo applications show model efficiencies of 83% and 67%, respectively. Both models performed well for lynchets. Errors arise mainly from difficulties in unequivocally discriminating gently convex undulations and undifferentiated surfaces, especially when soil thickness is not accounted for. Mean values of soil thickness are 1.08, 0.62 and 0.45 m in lynchets, undulations and undifferentiated areas, respectively. The general shape of the thickened soil is characteristic to each type of anthropogenic landform. Multi-temporal mapping of field border networks shows that undulations are linked to borders that were removed during the latest land consolidation. Lynchets are associated with current field borders. Lynchets and undulations, which cover 39% of the study area, define topographic indicators of human-induced soil accumulations. The method involves perspectives for efficiently mapping and quantifying the anthropogenically modified spatial variability of soil thickness on agricultural hillsides.

Summer typhoons and spring snowmelt led to the riverine spread of continental Fukushima fallout to the coastal plains of Northeastern Japan and the Pacific Ocean. Four fieldwork campaigns based on measurement of radioactive dose rates in fine riverine sediment that has recently deposited on channel bed-sand were conducted between November 2011 and May 2013 to document the spread of fallout by rivers. After a progressive decrease in the fresh riverine sediment doses rates between 2011 and early spring in 2013, a fifth campaign conducted in November 2013 showed that they started to increase again after the occurrence of violent typhoons. We show that this increase in dose rates was mostly due to remobilization of contaminated material that was temporarily stored in river channels or, more importantly, in dam reservoirs of the region during the typhoons. In addition, supply of particles from freshly eroded soils in autumn 2013 was the most important in areas where decontamination works are under progress. Our results underline the need to monitor the impact of decontamination works and dam releases in the region, as they may provide a continuous source of radioactive contamination to the coastal plains and the Pacific Ocean during the coming years.

Measurement of radioactive dose rates in fine sediment that has recently deposited on channel bed-sand provides a solution to address the lack of continuous river monitoring in Fukushima Prefecture after Fukushima Dai-ichi nuclear power plant (FDNPP) accident. We show that coastal rivers of Eastern Fukushima Prefecture were rapidly supplied with sediment contaminated by radionuclides originating from inland mountain ranges, and that this contaminated material was partly exported by typhoons to the coastal plains as soon as by November 2011. This export was amplified during snowmelt and typhoons in 2012. In 2013, contamination levels measured in sediment found in the upper parts of the catchments were almost systematically lower than the ones measured in nearby soils, whereas their contamination was higher in the coastal plains. We thereby suggest that storage of contaminated sediment in reservoirs and in coastal sections of the river channels now represents the most crucial issue.

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident led to important releases of radionuclides into the environment, and trace levels of plutonium (Pu) were detected in northeastern Japan. However, measurements of Pu isotopic atom and activity ratios are required to differentiate between the contributions of global nuclear test fallout and FDNPP emissions. In this study, we used a double-focusing sector field ICP-MS to measure Pu atom and activity ratios in recently deposited sediment along rivers draining the most contaminated part of the inland radioactive plume. Results showed that plutonium isotopes (i.e., (239)Pu, (240)Pu, (241)Pu, and (242)Pu) were detected in all samples, although in extremely low concentrations. The (241)Pu/(239)Pu atom ratios measured in sediment deposits (0.0017-0.0884) were significantly higher than the corresponding values attributed to the global fallout (0.00113 ± 0.00008 on average for the Northern Hemisphere between 31°-71° N: Kelley, J. M.; Bond, L. A.; Beasley, T. M. Global distribution of Pu isotopes and (237)Np. Sci. Total. Env. 1999, 237/238, 483-500). The results indicated the presence of Pu from FDNPP, in slight excess compared to the Pu background from global fallout that represented up to ca. 60% of Pu in the analyzed samples. These results demonstrate that this radionuclide has been transported relatively long distances (∼45 km) from FDNPP and been deposited in rivers representing a potential source of Pu to the ocean. In future, the high (241)Pu/(239)Pu atom ratio of the Fukushima accident sourced-Pu should be measured to quantify the supply of continental-originating material from Fukushima Prefecture to the Pacific Ocean.