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Sediment that has deposited after the flood generated by the 2019 typhoon (referred to as Flood Sediment, FS) was collected along two rivers in eastern Fukushima Prefecture, Japan to determine the total and exchangeable radiocesium ($^{137}\mathrm{Cs}$), and acid-extractable potassium (K) contents. Then, these FS parameters were compared with those of decontaminated soils (DS) in nearby agricultural fields to discuss the potential transfer risk of $^{137}\mathrm{Cs}$ from rivers to nearby remediated soils. While FS had about four times higher total $^{137}\mathrm{Cs}$ content, it showed a three-times lower exchangeable $^{137}\mathrm{Cs}$ content than DS. Furthermore, acid-extractable K referred to as non-exchangeable K (Nex-K) content was high enough to restrict $^{137}\mathrm{Cs}$ transfer from soil to crops for both FS and DS. From these comparisons, we concluded that deposition of FS onto DS may not increase the transfer of $^{137}\mathrm{Cs}$ from soil to crops.

The Fukushima nuclear accident in March 2011 generated a 3000 km$^{2}$ plume of soils heavily contaminated with $^{137}$Cs. Decontamination was completed early in 2019. Typhoon Hagibis was the first extreme event that occurred in the region after decontamination. Its impact on sediment sources and sediment $^{137}$Cs contamination was investigated through the application of a sediment fingerprinting procedure using spectrocolorimetry and geochemical properties. Sediment deposits ($n=24$) were collected in the Mano and Niida River catchments after the 2019 typhoons, and their signature was compared to that of potential sources (e.g., cropland, forests, and subsurface; $n=57$). Results demonstrate the dominance of cropland as the main source of sediment (mean: 54%) followed by forests (41%) with much lower contributions of subsurface material (5%). Overall, $^{137}$Cs concentrations in sediment were on average 84%–93% lower than the levels recorded after the accident in 2011, which demonstrates the effectiveness of cropland decontamination.

Past nuclear weapons testing (NWT) and nuclear power plant (NPP) accidents have resulted in the ubiquitous deposition of radionuclides in the environment. While radionuclide contamination of the environment is associated with concerning health risks, these fallout radionuclides (FRNs) are considered the privileged markers ("golden spikes") of the Anthropocene stratigraphic layers. Their deposition in the 1950s coincided with the "Great Acceleration", which is characterized by large-scale shifts in the Earth's systems, including increased land-use change and soil degradation. Among the FRNs deposited globally, 137Cs has been the most commonly used to assess soil erosion and/or the chronology of sediment deposition, and 239+240Pu is an emerging soil erosion tracer and chronological marker increasingly used due to a number of advantages. We compiled 137Cs and 239+240Pu data published from undisturbed (so called "reference") soils in the Equatorial and Southern Hemisphere regions to build a database under the AVATAR Project ("A reVised dATing framework for quantifying geomorphological processes during the Anthropocene"). Using this database, named the AVATAR-Soils Database, we determined the distributions of 137Cs and 239+240Pu inventories in Equatorial and Southern Hemisphere soils, along with the relative contributions of different fallout nuclear weapon sources by analysing their isotopic ratios. Additionally, we demonstrated how the database can be used to identify the environmental factors that influence the distributions of 137Cs and 239+240Pu in reference soils by applying a machine-learning algorithm. Our metanalysis revealed that high 137Cs and 239+240Pu inventories were recorded near the equator and within the 20–40° S latitudinal bands, which coincide with the location of multiple NWT. The 240Pu/239Pu atomic ratios suggest that sources other than the global fallout (primarily from US and USSR weapon testing with a 240Pu/239Pu atomic ratio of ~ 0.18) contributed to the reference inventories in the Southern Hemisphere. These additional sources have been relatively neglected so far. On average, the French fallout contributed ~20 % to the reference soil 239+240Pu inventories in South America and up to 70 % in French Polynesia. In contrast, the British fallout contributed ~27 % to the reference soil 239+240Pu inventories in the rest of Oceania. Our machine-learning algorithm identified precipitation of the coldest quarter, longitude, and latitude as the strongest predictors of 137Cs inventory. For 239+240Pu inventory, mean diurnal temperature range, temperature annual range, and precipitation of the driest quarter were the strongest predictors. Altogether, these findings demonstrate the potential of the AVATAR-Soils Database as resource for improving our understanding of the distribution and sources of 137Cs and 239+240Pu in Equatorial and Southern Hemisphere soils and refining their application as tools in various Earth Science research. The AVATAR-Soils Database may be accessed at https://doi.org/10.5281/zenodo.14008220 (Dicen et al., 2024). [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) has revolutionized ecological research, particularly for biodiversity assessment in various environments, most notably aquatic media. Environmental DNA analysis allows for non‐invasive and rapid species detection across multiple taxonomic groups within a single sample, making it especially useful for identifying rare or invasive species. Due to dynamic hydrological processes, eDNA samples from running waters may represent biodiversity from broad contributing areas, which is convenient from a biomonitoring perspective but also challenging, as hydrological knowledge is required for meaningful biological interpretation. Hydrologists could also benefit from eDNA to address unsolved questions, particularly concerning water movement through catchments. While naturally occurring abiotic tracers have advanced our understanding of water age distribution in catchments, for example, current geochemical tracers cannot fully elucidate the timing and flow paths of water through landscapes. Conversely, biological tracers, owing to their immense diversity and interactions with the environment, could offer more detailed information on the sources and flow paths of water to the stream. The informational capacity of eDNA as a tracer, however, is determined by the ability to interpret the complex biological heterogeneity at a study site, which arguably requires both biological and hydrological expertise. As eDNA data has become increasingly available as part of biomonitoring campaigns, we argue that accompanying eDNA surveys with hydrological observations could enhance our understanding of both biological and hydrological processes; we identify opportunities, challenges, and needs for further interdisciplinary collaboration; and we highlight eDNA's potential as a bridge between hydrology and biology, which could foster both domains. This article is categorized under:Science of Water > Hydrological ProcessesScience of Water > MethodsWater and Life > Nature of Freshwater Ecosystems [ABSTRACT FROM AUTHOR]

Andosols are the soil type that potentially has the highest radiocesium (RCs) transfer risk due to their deficiency in micaceous minerals (micas) that can strongly retain RCs in their interlayer sites. However, an exogeneous source of micas as a component of Asian dust may have contributed largely to increase the RCs retention ability for Andosols in Tohoku Region, Japan. We investigated 29 pasture soils with andic soil properties that were collected at various places across this region to clarify the provenance of micas whether they originated from Asian dust or local lithological materials. Mica content in bulk size fraction (<2.0 mm) positively and strongly correlated with the factor related to felsic elemental composition obtained by principal component analysis (r = 0.90, p < 0.01). Fine micas in the <20 µm fraction (Mica<20 µm) accounted for a large fraction (72 ± 16%) of the total mica contents and positively correlated with the content of fine quartz derived from Asian dust (Qzad_<20 µm) (r = 0.86, p < 0.01), which were distinguished from fine quartz derived from igneous bedrock materials (Qzig_<20 µm) by using the δ18O values for quartz isolated from the <20 µm fraction. Furthermore, Mica<20 µm correlated positively with radiocesium interception potential (RIP) of this fraction. These results for the first time demonstrated the importance of Asian-dust-derived micas relative to those from another local sources on the RCs retention abilities in Andosols in Tohoku, Japan. [ABSTRACT FROM AUTHOR]

Grain crops have expanded at the expense of native grasslands in South America's Pampa biome in recent decades, thereby, increasing the sediment delivery to the river systems. This study aimed to evaluate the impact of land use change on sediment source contributions in the Ibirapuitã catchment (5942 km2), Southern Brazil. For this purpose, a sediment fingerprinting approach was developed based on organic matter composition, ultraviolet–visible reflectance, and fallout radionuclide activities as potential tracers. Four main sediment sources were investigated: croplands (n = 36), native grasslands (n = 31), unpaved roads (n = 31), and subsurface sources (n = 34). Tracers were selected following a three‐step procedure: conservative range test, Kruskal–Wallis H‐test, and linear discriminant function analysis (LDA). Selected tracers were introduced into a mass balance mixing model to estimate the source contributions to in‐stream sediment. The seven tracers selected by the LDA were able to explain 91% of the variance and correctly classify 83% of the source samples. Despite covering less than 10% of the catchment surface area, croplands that replaced the native grasslands supplied the primary sediment source (33%) to the main outlet, followed by subsurface sources (27%). In contrast, native grasslands covering 80% of the surface area provided only 17% of sediment to the river network. These findings confirm that soil erosion processes are accelerating in response to the recent land use changes in the region. To prevent soil loss and sediment delivery to the river systems, land use conversion from native grasslands into croplands should be associated with the implementation of appropriate land conservation practices, such as runoff control, no‐tillage system, and crop rotation. [ABSTRACT FROM AUTHOR]