Application of bomb- and Chernobyl-derived radiocaesium for reconstructing changes in erosion rates and sediment fluxes from croplands in areas of European Russia with different levels of Chernobyl fallout

Temporal trajectories of artificial radiocaesium 137Cs in French rivers over the nuclear era reconstructed from sediment cores

137Cs is a long-lived man-made radionuclide introduced in the environment worldwide at the early beginning of the nuclear Era during atmospheric nuclear testing's followed by the civil use of nuclear energy. Atmospheric fallout deposition of this major artificial radionuclide was reconstructed at the scale of French large river basins since 1945, and trajectories in French nuclearized rivers were established using sediment coring. Our results show that 137Cs contents in sediments of the studied rivers display a large spatial and temporal variability in response to the various anthropogenic pressures exerted on their catchment. The Loire, Rhone, and Rhine rivers were the most affected by atmospheric fallout from the global deposition from nuclear tests. Rhine and Rhone also received significant fallout from the Chernobyl accident in 1986 and recorded significant 137Cs concentrations in their sediments over the 1970-1985 period due to the regulatory releases from the nuclear industries. The Meuse River was notably impacted in the early 1970s by industrial releases. In contrast, the Seine River display the lowest 137Cs concentrations regardless of the period. All the rivers responded similarly over time to atmospheric fallout on their catchment, underlying a rather homogeneous resilience capacity of these river systems to this source of contamination.

Changes in the Regime of Erosive Precipitation on the European Part of Russia for the Period 1966–2020

The objective of this work is to analyze the spatial-temporal features of the trends in the frequency and amount of erosion-hazardous precipitation in the European part of Russia (EPR) for the period 1966–2020, as a reflection of the influence of climatic changes on surface runoff from the cultivated slopes during the warm season. One hundred and fifty-nine EPR weather stations were selected for analysis based on the length of the time series and the amount of missing data. Several characteristics of erosion-hazardous precipitation were considered: the number of days with a daily precipitation of more than 12.7 mm, the number of days with a daily precipitation of 12.7 to 40 mm, the number of days with a daily precipitation of more than 40 mm, the maximum one-day precipitation. In general, it can be stated that even within the southern taiga, mixed forests, and forest-steppe ecoregion (broad-leaved forests), within which a positive increase in the frequency of erosion-hazardous precipitation was detected, there was no significant increase in the rate of washout and linear washout, which is primarily due to a more significant reduction of slope runoff and soil washout during spring snowmelt. Precipitation, the daily amount of which is more than 40 mm, as well as the maximum daily amount of precipitation, show an upward trend in the western contact zone of mixed forests and forest-steppe, on the Black Sea coast, as well as in the northern foothills of the Caucasus, where their contribution to erosion processes is likely to increase against the decrease in the number of days with precipitation of a 12.7–40 mm daily amount.

The anthropogenic fallout radionuclides in soils of Mount Khuko (the Western Caucasus) and their application for determination of sediment redistribution

The purposes of this study are to determine the content and origin of anthropogenic fallout radionuclides (FRN) in soils of Mount Khuko, located in the western sector of the Caucasus Mountains and to assess the possibility to use them for evaluation of sediment redistribution for the alpine grasslands,. The field study was carried out in August 2019 near the top of Mount Khuko, located in the western part of the main Caucasus Mountain Ridge. Integral and incremental soil samples were collected from the different morphological units of the studied area. The content of ¹³⁷Cs and ²⁴¹Am in soil samples was evaluated using laboratory gamma-spectrometry. A part of samples was selected for Pu isotopes extraction and then alpha-spectrometric analysis. It was established that the ¹³⁷Cs contamination of soils in the studied area has at least two sources of origin. The first source is the ¹³⁷Cs bomb-derived fallout after the bomb tests in 1950-60th, which is widespread across the globe. The second source is ¹³⁷Cs Chernobyl-derived fallout High random variability (Cv = 25-42%) was found within reference sites, located at the undisturbed areas on the local flat interfluves due to high variability of soil characteristics (grain size, density, organic matter content etc.). However minimum spatial variability (range 12,2-14,3 kBq/m²) was identified for the mean value of ¹³⁷Cs inventories for all 5 reference sites located in the different parts of the studied area. It is difficult to separate individual peaks of the bomb-derived and Chernobyl-derived ¹³⁷Cs falloutin sediment sinks with low sedimentation rates. Application ^239,240Pu as an additional chronological marker allows to identify the origin of above mention peaks in the soils of alpine grasslands and of dry lake bottom.

On the ordered nature of redistribution of technogenic elements in undisturbed elementary landscape-geochemical systems of the temperate zone on the example of the Chernobyl 137Cs fallout

The study is aimed at identifying patterns in distribution of pollutants in the elementary landscape-geochemical systems (ELGS) of the temperate zone. The study used ¹³⁷Cs as a tracer, which allows a highly detailed analysis of the nature of the heterogeneity of secondary migration in the toposequence: summit-slope-closing depression, treated as the elementary landscape-geochemical system. The study site was located in the Bryansk region in the Chernobyl abandoned area with an initial level of ¹³⁷Cs contamination exceeding 1480 kBq/m² (40 Ci/km²). An original technique of repeated ¹³⁷Cs measurements along cross-sections accompanied by topographic survey and soil cores sampling has been applied. The obtained results showed a complete absence of constant increase of ¹³⁷Cs concentration downslope but revealed a steady regular variability of ¹³⁷Cs activity of a cyclical type. Given uniformity of the initial ¹³⁷Cs fallout within a small-sized plot, variation of ¹³⁷Cs due to its secondary distribution in ELGS was 2-2.7-fold according to field gamma-spectrometry data which corresponded to the radionuclide contamination density of the top 20-cm layer of the soil containing 96-99% of the total radionuclide amount (correlation between the parameters equaled to r0.01 = 0.782, n = 20). A specifically regular structure obviously formed under the set of radionuclide water migration processes seems to be inherent in all systems of the studied type. The results obtained are believed to be of both theoretical and practical importance, since they can contribute to making decisions on the precise monitoring of zones of technogenic accumulation, as well as solving fundamental problems of soil formation and its restoration after technogenic pollution.

Reconstruction of time changes in radiocesium concentrations in the river of the Fukushima Dai-ichi NPP contaminated area based on its depth distribution in dam reservoir's bottom sediments

Radionuclide depth distribution in bottom sediments in deep-water zones of dam reservoirs, where no sediment mixing occurs, can be used to reconstruct time changes in particulate activity concentrations of radionuclides strongly bound to bottom sediments. This approach was used to analyze the ¹³⁷Cs concentration profile in a bottom sediment core collected from Ogaki dam reservoir on the Ukedo River in the Fukushima Dai-ichi nuclear power plant contaminated zone in October 2019. The derived ¹³⁷Cs particulate concentrations provided a basis for estimating the dissolved concentration and its temporal trend in the Ukedo River, using the mean value of the apparent ¹³⁷Cs distribution coefficient. The reconstructed particulate and dissolved ¹³⁷Cs concentrations and their temporal trends are consistent with monitoring data. The annual mean particulate and dissolved ¹³⁷Cs wash-off ratios were also calculated for the period of eight years after the accident. Interestingly, the particulate ¹³⁷Cs wash-off ratios for the Ukedo River at Ogaki dam were found to be similar to those for the Pripyat River at Chernobyl in the same time period after the accident, while the dissolved ¹³⁷Cs wash-off ratios in the Ukedo River were an order of magnitude lower than the corresponding values in the Pripyat River. Both the particulate and dissolved ¹³⁷Cs wash-off ratios in the Ukedo River declined faster during the first eight years after the FDNPP accident than predicted by the diffusional model, most likely, due to greater natural attenuation and, to some extent, remediation measures implemented on the catchments in Fukushima.

Using reservoir sediment deposits to determine the longer-term fate of chernobyl-derived 137Cs fallout in the fluvial system

Vast areas of Europe were contaminated by the fallout of ¹³⁷Cs and other radionuclides, as a result of the Chernobyl accident in 1986. The post-fallout redistribution of Chernobyl-derived ¹³⁷Cs was associated with erosion and sediment transport processes within the fluvial system. Bottom sediments from lakes and reservoirs can provide a valuable source of information regarding the post-fallout redistribution and fate of ¹³⁷Cs released by the Chernobyl accident. A detailed investigation of sediment-associated ¹³⁷Cs in the bottom sediments of a reservoir in a Chernobyl-affected area in Central Russia has been undertaken. A new approach, based on the vertical distribution of ¹³⁷Cs activity concentrations in the reservoir bottom sediment makes it possible to separate the initially deposited bottom sediment, where the ¹³⁷Cs activity reflects the direct fallout of Chernobyl-derived ¹³⁷Cs to the reservoir surface and its subsequent incorporation into sediment deposited immediately after the accident, from the sediment mobilized from the catchment deposited subsequently. The deposits representing direct fallout from the atmosphere was termed the "Chernobyl peak". Its shape can be described by a diffusion equation and it can be distinguished from the remaining catchment-derived ¹³⁷Cs associated with sediment accumulated with sediments during the post-Chernobyl period. The ¹³⁷Cs depth distribution above the "Chernobyl peak" was used to provide a record of changes in the concentration of sediment-associated ¹³⁷Cs transported from the upstream catchment during the post-Chernobyl period. It was found that the ¹³⁷Cs activity concentration in the sediment deposited in the reservoir progressively decreased during the 30-year period after the accident due to a reduction in the contribution of sediment eroded from the arable land in the catchment. This reflects a reduction in both the area of cultivated land area and the reduced incidence of surface runoff from the slopes during spring snowmelt due to climate warming.

Detailed study of post-Chernobyl Cs-137 redistribution in the soils of a small agricultural catchment (Tula region, Russia)

A detailed study of ¹³⁷Cs redistribution was conducted within a small agricultural catchment in the highly contaminated Plavsk radioactive hotspot in the Tula region of Central Russia, 32 years after the Chernobyl nuclear power plant (NPP) accident, which occurred on April 26, 1986. Although more than three decades have passed since the Chernobyl NPP incident, ¹³⁷Cs contamination is high. The ¹³⁷Cs inventory varies from 67 to 306 kBq·m^-2, which is 2-6 times higher than the radiation safety standard; however, the soils remain suitable for crop cultivation. The initial ¹³⁷Cs fallout within the Plavsk radioactive hotspot was extremely heterogeneous, with a trend of decreasing ¹³⁷Cs inventories from the NW to the SE directions within the studied territory. Contemporary ¹³⁷Cs inventories are also very heterogeneous in the studied catchment. However, the trend of the initial ¹³⁷Cs fallout does not appear in the contemporary ¹³⁷Cs inventories on the slopes. Two methods of interpolation (expert-visual and automatic) were used to calculate the ¹³⁷Cs budget, revealing high similarity in their ¹³⁷Cs loss estimates; however, a large discrepancy was observed in their ¹³⁷Cs gain estimates. A detailed analysis of ¹³⁷Cs redistribution revealed the importance of hollows and "plow ramparts" (positive topographic forms on the boundaries of cultivated fields) in the transport and deposition of sediments. A quarter of the total ¹³⁷Cs gain was deposited within the arable land, whereas a quarter was deposited within the non-plowing sides of the dry valley; the other half was deposited in the valley bottom. About 7-8 × 10⁶ kBq of the ¹³⁷Cs inventory flowed out of the catchment area, which was only about 2% of the ¹³⁷Cs fallout after the Chernobyl NPP accident. About 89% of the total ¹³⁷Cs reserve is concentrated in the top (0-25 cm) layer of soils, regardless of land use or location within the catchment.

Near real-time soil erosion mapping through mobile gamma-ray spectroscopy

Soil erosion has been associated with various negative environmental impacts foremost of which is the potential pressure it could impose on global food security. The poor conditions of our agricultural soil can be attributed to years of unsustainable farming practices occurring throughout history that has placed significant pressure on the environment. Moreover, climate change scenarios indicate further intensification which is likely making prediction and assessment of erosion processes critical for long term agricultural sustainability. This study demonstrates the potential of mobile gamma-ray spectrometry with large volume NaI(Tl) detectors to identify, at high spatial resolution, changes in ¹³⁷Cs soil concentration within the ploughed layer of soil and enabling the soil erosion processes to be quantified. This technique represents a significant advantage over conventional spatially-isolated point measurements such as soil sampling as it offers real time mapping at the field scale. However, spectral signal derived from measurements in the field are highly dependent on the calibration procedure used and are particularly sensitive to source-detector changes such as the presence of a vehicle, ground curvature and soil moisture content. Conventional calibration procedures tend to not consider these potential sources of uncertainty potentially leaving the system vulnerable to systematic uncertainties, especially when 137Cs concentrations are low. This study used Monte Carlo simulations to investigate such changes utilising additional information including a high-resolution digital terrain model. The method was demonstrated on a ploughed site in Scotland, revealing a mixture of tillage and water erosion patterns supported by soil core data. Findings showed that the sites topography had relatively little effect (<10%) on calculated erosion rates, but moisture content could be the determining factor, albeit very difficult to measure reliably throughout a survey.