Pu Activity Research Articles

Distinctive distribution and migration of global fallout plutonium isotopes in an alpine lake and its implications for sediment dating

This work investigated plutonium (Pu) isotopes in sediment cores collected from an alpine lake (Lake Heinongpo with 3779 m above sea level) in Southwestern China. 240Pu/239Pu atom ratios in all sediment samples showed the typical global fallout values of ∼0.18 without any influences from other Pu contaminant sources. 239+240Pu activities with surface and subsurface maximums followed by exponential decline with sediment depth were respectively observed in the two sediment cores. The distinctive depth distributions of 239,240Pu in the lake sediments was attributed to the very slow sediment deposition rate due to the lack of terrestrial sediment input, while the alpine snowmelt input was the primary source of Pu in the lake sediments in addition to the direct atmospheric deposition. The total Pu inventory was estimated to be 56.3 ± 1.4 and 63.9 ± 0.8 Bq/m2 respectively in the two sediment cores. The generally higher Pu inventory in the Lake Heinongpo compared with other reported lakes in similar latitude should be mainly attributed to their different Pu input passages. The advection-diffusion equation was further applied to evaluate the downward migration of Pu isotopes in the sediment cores and predict the future evolution of Pu distribution in the sediment cores. The fitted results indicated that the diffusion effect controlled the downward migration of Pu in the sediments, but this diffusive migration will not prevent the peak of global fallout Pu in undisturbed sediment cores from being a valuable time marker for sediment dating.

Vertical distribution of Pu in forest soil in Qinghai-Tibet Plateau

The 239+240Pu and 137Cs activities and 240Pu/239Pu atom ratios in surface soil and soil core collected from Qinghai-Tibet Plateau were investigated. The maximum of 239+240Pu and 137Cs activity concentrations in five soil cores were found in upper layers and have a same trend: the maximum followed by exponential decline. The 240Pu/239Pu atom ratio ranged from 0.160 ± 0.009 to 0.212 ± 0.012, clarified that the plutonium mainly came from the global fallout and the contribution of Lop Nor test sites was negligible. In addition, the vertical profiles of radionuclides (210Pb, 238U, 232Th, 226Ra, 40K) have been studied and a high correlation has been found between them. The correlations of Pu between organic matter (OM) and heavy metals were also studied. Person Correlation Coefficients revealed Pu had significant positive correlations with organic matter and Cd, Cu, Co, Zn, but negative correlation with Tl. The results have important implication for further understanding of the sources, records and environmental impacts of global and regional nuclear activities, which expanded the database of Pu activity level and atom ratio in Chinese soil and established a foundation for future environmental risk assessment.

Plutonium and americium in the deep Black Sea bottom sediments

The new data on 239+240Pu, 238Pu, 241Pu, 241Am vertical distribution in the deep western Black Sea sediments was analyzed. The sediment dating, obtained by means of 238Pu/239+240Pu activity ratio vertical distribution, suggested the upper 3 cm layer of sediments to be formed during 27 years after the Chernobyl accident and the deeper layers to be formed earlier in pre-Chernobyl time (before 1986). The whole data set on profiles of radionuclides studied was shown to reflect the history of their input into the basin and elimination of these radionuclides from the water column. Analysis of inventories of plutonium alpha-emitting nuclides ensured a more significant contribution of Chernobyl fallout into the present total 238Pu inventory than into 239+240Pu one. The 241Am inventory after-deposition enhancement due to 241Pu decay was estimated at 74% in pre-Chernobyl sediment layer and the general contribution of 241Pu support in the total 241Am inventory in situ enhancement was estimated at 49%.

Source, Spatial Distribution and Migration of <sup>239+240</sup>Pu in Chinese Soils

The source, spatial distribution, typical vertical distribution and migration of 239+240 Pu in Chinese 647 surface soils and 66 soil cores are investigated in this study. To provide a complete spatial distribution of 239+240 Pu in Chinese surface soil, an overall pattern of and mechanism for 239+240 Pu migration in Chinese core soil, we summarize and analyze the 239+240 Pu surface and vertical distributions in literature. Comprehensive statistical analysis suggests four typical distributions in Chinese soil cores. It is found that the 239+240 Pu vertical distribution is closely related to the soil type and the 239+240 Pu migration. The result indicates that global fallout is the major source of 239+240 Pu in Chinese soils, with the average 240 Pu/ 239 Pu atom ratios around 0.18. Abnormally low 240 Pu/ 239 Pu ratios are detected in Jiuquan region and northern Xinjiang province in Northwest China, which can be attributed to nuclear weapons tests. To further investigate the migration behaviors of 239+240 Pu in soil cores in China, we apply the Convection Dispersion Equation (CDE) model and find that 239+240 Pu apparent convection velocities ranges from 0.00032±0.00031 cm/a to 0.473±0.083 cm/a. As shown in four typical vertical 239+240 Pu activity distribution soil cores, the deepened 239+240 Pu activity maximum value position implies a fast 239+240 Pu migration rate or apparent convection velocity. This study for the first time suggests a significant linear correlation ( R 2 =0.847) between depth of 239+240 Pu maximum value (cm) and apparent convection velocity (v, cm/a), and we speculate that v usually does not exceed 0.5 cm/a. A significant linear correlation is also identified between apparent dispersion coefficient (D, cm 2 /a) and v 2 in Chinese soil cores.

A Comparative Analysis of Different Outlier Detection Techniques in Cognitive Radio Networks with Malicious Users

In a cognitive radio (CR), opportunistic secondary users (SUs) periodically sense the primary user’s (PU’s) existence in the network. Spectrum sensing of a single SU is not precise due to wireless channels and hidden terminal issues. One promising solution is cooperative spectrum sensing (CSS) that allows multiple SUs’ cooperation to sense the PU’s activity. In CSS, the misdetection of the PU signal by the SU causes system inefficiency that increases the interference to the system. This paper introduces a new category of a malicious user (MU), i.e., a lazy malicious user (LMU) with two operating modes such as an awakened mode and sleeping mode. In the awakened mode, the LMU reports accurately the PU activity like other normal cooperative users, while in the sleeping mode, it randomly reports abnormal sensing data similar to an always yes malicious user (AYMU) or always no malicious user (ANMU). In this paper, statistical analysis is carried out to detect the behavior of different abnormal users and mitigate their harmful effects. Results are collected for the different hard combination schemes in the presence of the LMU and opposite categories of malicious users (OMUs). Simulation results collected for the error probability, detection probability, and false alarm at different levels of the signal-to-noise ratios (SNRs) and various contributions of the LMUs and OMUs confirmed that out of the many outlier detection tests, the median test performs better in MU detection by producing minimum error probability results in the CSS. The results are further compared by keeping minimum SNR values with the mean test, quartile test, Grubbs test, and generalized extreme studentized deviate (GESD) test. Similarly, performance gain of the median test is examined further separately in the AND, OR, and voting schemes that show minimum error probability results of the proposed test as compared with all other outlier detection tests in discarding abnormal sensing reports.

Transuranic nuclides Pu, Am and Cm isotopes, and 90Sr in seafloor sediments off the Fukushima Daiichi Nuclear Power Plant during the period from 2012 to 2019

The 238Pu, 239+240Pu, 241Am, 242Cm, 243+244Cm and 90Sr concentrations in seafloor surface sediments collected at three sampling stations off the Fukushima Daiichi Nuclear Power Plant (FDNPP) site during the period from 2012 to 2019 were determined to elucidate the impacts of the FDNPP accident onto their concentrations in coastal sediments and to discuss the sources of the measured radionuclides. The 239+240Pu, 241Pu and 241Am concentrations and 240Pu/239Pu atom ratios in a sediment core were also determined to allow comparison of their inventories between this study and previously reported values and to identify the Pu sources. The 238Pu, 239+240Pu, 241Am and 90Sr concentrations showed no remarkable temporal variations; no significant increases in concentrations after the FDNPP accident were observed; these concentrations were comfortably within the previously reported concentration range; and no detectable 242Cm and 243+244Cm amounts were observed in surface sediments. The observed 238Pu/239+240Pu activity ratios were approximately two orders of magnitudes lower than those for the damaged FDNPP reactor core inventories and the observed values in terrestrial samples after the accident. The 239+240Pu, 241Pu and 241Am inventories in the sediment core were 389 ± 5, 503 ± 33 and 214 ± 3 Bq m−2, respectively. The 239+240Pu inventory was about an order of magnitude greater than the expected cumulative deposition density of global fallout from atmospheric nuclear weapons testing due to an enhanced scavenging effect. The 240Pu/239Pu atom ratios in the sediment core ranged from 0.239 to 0.246 with a mean value of 0.242 ± 0.002; these ratios were clearly greater than the mean global fallout ratio of 0.18. The results for 238Pu/239+240Pu activity ratios and 240Pu/239Pu atom ratios reflected a mixture of global fallout and Pacific Proving Grounds (PPG) close-in fallout Pu rather than Fukushima accident-derived Pu. The sediment column inventory for 239+240Pu originating from the PPG close-in fallout was calculated as 166 Bq m−2, which corresponded to 43% of the total inventory. A significant amount of the PPG-derived Pu has been transported by ocean currents and then preferentially scavenged in the coastal waters of Japan.

Activity concentration of plutonium isotopes in bottom sediments and water in Crimean salt lakes

The 238,239+240Pu activity concentrations in sediments and in water in the Crimean salt lakes were studied. Activity ratio of 238Pu/239+240Pu in depth profiles of sediments was used to estimate the contribution of two main sources of man-made plutonium to the Pu sediment inventory. The most part of the plutonium was of global origin. Concentration factor of the plutonium isotopes in sediments, radiocapacity factor of the lake, the type of biogeochemical behavior of plutonium in these reservoirs and the sediment inventory of 238,239+240Pu in the lakes were evaluated.

Deep Learning-Based Spectrum Sensing in Cognitive Radio: A CNN-LSTM Approach

For most existing spectrum sensing detectors, the design of their test statistics relies on certain signal-noise model assumptions and hence, their detection performance heavily depends on the accuracy of the assumed models. Therefore, recently, much attention in the research of spectrum sensing is focused on deep learning which is free from model assumptions. Note that, in deep learning, the convolutional neural networks (CNNs) and the long-short term memory (LSTM) networks have the powerful capabilities in extracting spatial and temporal features of the input, respectively. In this letter, we propose a CNN-LSTM detector which first uses the CNN to extract the energy-correlation features from the covariance matrices generated by the sensing data, then the series of energy-correlation features corresponding to multiple sensing periods are input into the LSTM so that the PU activity pattern can be learned. The purpose of learning PU activity pattern is to further promote the detection probability. With sufficient simulations, the superiority of the CNN-LSTM detector is proven in scenarios with and without noise uncertainty.

Применение концептуальной модели зональности хронического действия мощностей доз ионизирующих излучений на объекты биосферы Г. Г. Поликарпова в прикладной гидробиологии

В работе кратко рассмотрена эволюция подхода к оценке воздействия ионизирующей радиации на живые организмы. На примере черноморских гидробионтов показана возможность применения концептуальной радиохемоэкологической модели зональности действия хронического облучения ионизирующих излучений в природе Г. Г. Поликарпова для оценки уровня экологического воздействия ионизирующего излучения от техногенных радиоизотопов на водную биоту. Эта модель может служить в прикладной гидробиологии основой комплексного подхода к оценке экологического состояния водной биоты и его прогноза для широкого диапазона концентраций активности 239,240Pu в морской воде. Подчёркивается необходимость совместного применения биогеохимического и эквидозиметрического показателей поведения радиоизотопов в водоёме. В частности, для прогнозных дозиметрических оценок важно учитывать количественные характеристики концентрирующей способности черноморских гидробионтов и тип биогеохимического поведения радиоэлемента, отражающие особенности биогеохимической миграции плутония в морской экосистеме.

Future migration: Key environmental indicators of Pu accumulation in terrestrial sediments of Queensland, Australia

Plutonium (Pu) interactions in the environment are highly complex. Site-specific variables play an integral role in determining the chemical and physical form of Pu, and its migration, bioavailability, and immobility. This paper aims to identify the key variables that can be used to highlight regions of radioecological sensitivity and guide remediation strategies in Australia. Plutonium is present in the Australian environment as a result of global fallout and the British nuclear testing program of 1952–1958 in central and west Australia (Maralinga and Montebello islands). We report the first systematic measurements of 239+240Pu and 238Pu activity concentrations in distal (≥1000 km from test sites) catchment outlet sediments from Queensland, Australia. The average 239+240Pu activity concentration was 0.29 mBq.g −1 (n = 73 samples) with a maximum of 4.88 mBq.g −1.238Pu/239+240Pu isotope ratios identified a large range (0.02–0.29 (RSD: 74%)) which is congruent with the heterogeneous nuclear material used for the British nuclear testing programme at Maralinga and Montebello Islands. The use of a modified PCA relying on non-linear distance correlation (dCorr) provided broader insight into the impact of environmental variables on the transport and migration of Pu in this soil system. Primary key environmental indicators of Pu presence were determined to be actinide/lanthanide/heavier transition metals, elevation, electrical conductivity (EC), CaO, SiO2, SO3, landform, geomorphology, land use, and climate explaining 81.7% of the variance of the system. Overall this highlighted that trace level Pu accumulations are associated with the coarse, refractive components of Australian soils, and are more likely regulated by the climate of the region and overall soil type.

Distribution of Pu isotopes and 210Pb in the Bohai Sea and Yellow Sea: Implications for provenance and transportation

Particle-reactive radionuclides are useful for tracing sediment dynamics in marginal seas. We collected a suite of surface sediment samples in May 2014 from the Bohai Sea (BS) and Northern Yellow Sea (NYS) to observe the spatial distribution of Plutonium (Pu) isotopes and 210Pb activities. 239+240Pu activities ranged from 0.001 to 0.288 and 0.040–0.269 Bq kg−1 in BS and NYS surface sediments, respectively. 210Pbex shows a significant correlation with 239+240Pu (r = 0.84, p < 0.01) that suggested these two nuclides were scavenged to the same grade. 240Pu/239Pu atom ratios in BS (0.173–0.256) and NYS (0.196–0.275) were slightly higher than the global fallout value of 0.18 and lower than the Pacific Proving Ground (PPG) value of 0.36, indicating that some fraction of Pu originating from the PPG was capable of being transported to the BS and NYS. Mass balance results showed that 41% of 239+240Pu (8.9 × 109 Bq yr−1) and 18% of 210Pb (2.4 × 1012 Bq yr−1) in the NYS originated in the oceanic input. In the BS, 63% of 210Pb originated from atmospheric deposition and 84% of 239+240Pu originated from riverine input. Using Pu and 210Pb as tracers, we estimate that (1.8–2.6) × 108 t yr−1 and (3.6–3.8) × 108 t yr−1 of sedimentary particles could be transported from the BS to the NYS and from the NYS to the Southern Yellow Sea, respectively. Furthermore, the 226Ra/238U activity ratio distribution suggested that sedimentary particles derived from the Yellow River could be transported to the middle of the BS and coastal areas of the NYS.

Plutonium in Southern Yellow Sea sediments and its implications for the quantification of oceanic-derived mercury and zinc

The spatial distributions of mercury (Hg) and zinc (Zn) concentration and the isotopic composition of plutonium (Pu) were investigated in surface sediments and sediment cores collected from the Southern Yellow Sea (SYS) during May 2014. The variation of the 240Pu/239Pu atom ratio (0.18–0.31) in the surface sediments of the SYS clearly indicated a signal of close-in fallout input from the Pacific Proving Ground (PPG). The buried 239+240Pu in the sediment of the SYS was estimated to be (4.7 ± 0.5) × 1010 Bq y−1 during the period from 2011 to 2014, of which ∼33% (1.5 × 1010 Bq y−1) was derived from the PPG by long-range transport via ocean currents (e.g., the North Equatorial Current and Kuroshio Current). The concentrations of Hg and Zn varied from 0.003 to 0.067 mg kg−1 and from 43.9 to 137 mg kg−1, respectively, and exhibited positive correlations with the 239+240Pu activity both in the surface sediments (0–1 cm) and upper layers (7 cm) of the sediment cores. Therefore, by using Pu as a tracer, we estimated that the oceanic input contributed 2.0 tons y−1 of Hg and 1.0 × 103 tons y−1 of Zn to the SYS sediments between 2011 and 2014, which accounted for 33% and 3% of total buried Hg and Zn, respectively. These findings indicate that environmental pollution control should also consider the oceanic contribution of some pollutants. The results of the present work help to elucidate the biogeochemical cycling of trace metals in marginal seas, and are helpful for managing environmental pollution in marine environments.

Insights into the Pu isotopic composition (239Pu, 240Pu, and 241Pu) and 236U in marshland samples from Madagascar

This work provides new insights into the presence of 239Pu, 240Pu, 241Pu, and 236U in the Southern Hemisphere through the study of peat bog cores from marshlands in Madagascar (19°S). 210Pb, 238Pu and 239+240Pu activities were characterized by alpha spectrometry in previous studies. Here, Pu from alpha-spectrometry discs corresponding to 10 peat-bog cores (85 samples) was reassessed for the aim of completing its isotopic composition (239Pu, 240Pu, and 241Pu) by Accelerator Mass Spectrometry. In addition, 236U was studied in a single core exhibiting unusually low 240Pu/239Pu ratios. Integrated 240Pu/239Pu atom ratios in the single cores ranged above and below the (0–30°S) fallout average ratio, 0.173 ± 0.027, from 0.126 ± 0.003 to 0.206 ± 0.002, without a regional pattern, thereby demonstrating the heterogeneous distribution of the 239Pu and 240Pu signal. However, such a variability was not observed for 241Pu/239Pu, ranging from (6 ± 1) · 10−4 to (11 ± 1) · 10−4 and consistently below the (0–30°S) fallout ratio of (9.7 ± 0.3) · 10−4 (2012). The integrated 236U/239Pu atom ratio in the studied core, 0.147 ± 0.005, was also significantly lower than the values reported for the global fallout in the Northern Hemisphere, in the 0.20–0.23 range. Our results point out to stratospheric fallout as the main source of both 236U and 241Pu at the studied site, whereas 239Pu and 240Pu signals show the influence of tropospheric fallout from the low-yield tests conducted in Australia (1952–1958) by United Kingdom and in French Polynesia (1966–1975) by France despite the long relative distances (i.e. about 15,000 and 8500 km). It was also demonstrated that a representative number of samples is necessary in order to assess Pu contamination and its various origins in a specific region in the Southern Hemisphere due to the heterogeneous distribution, and results based on single sample analysis should be interpreted with caution.

Uranium and plutonium isotopes and their environmental implications in surface sediments from the Yangtze River catchment and estuary

The U-series and Pu isotope signatures in the environment have emerged as important tools for promoting geochemical studies. To enhance the understanding of U and Pu sources and behaviours in river systems, this study examined 234U, 235U, 236U, 238U and 239Pu, 240Pu isotopes in surface sediments collected from the Yangtze River catchment and estuary in China, for the first time. The 234U, 235U, 238U and 236U concentrations were measured in the range of 8.29–20.6 Bq/kg, 0.352–0.789 Bq/kg, 7.39–16.4 Bq/kg and (3.05–21.1) × 107 atoms/g. Additionally, the 236U/238U, 234U/238U and 235U/238U atom ratios were in the range of (1.43–6.85) × 10−8, (6.08–7.01) × 10−5 and (7.49–8.08) × 10−3 respectively. For all samples, the 239+240Pu activity concentrations ranged from 0.01 to 3.40 Bq/kg. In the Yangtze River catchment, 240Pu/239Pu atom ratios presented typical global fallout values (0.168–0.201); while in the Yangtze River estuary, higher values of 0.216–0.264 located between global fallout and PPG (Pacific Proving Grounds) close-in fallout values. From west to east, the 234U, 235U, 236U and 238U activities generally exhibited decreasing trend from the upstream parts of the river to the estuary. The values of 236U concentrations and 236U/238U, 240Pu/239Pu, 236U/239Pu atom ratios located in the range of global fallout level in environmental samples from other regions, therefore, it may be concluded that 236U in surface sediments of the Yangtze River catchment and estuary are mainly derived from global fallout.

Radionuclides in the environment around the uranium mines in Guangxi, China

Uranium and plutonium are both poisonous radioactive elements, which are very harmful to human health and environment. Therefore, it is of great significance to study the distribution of 238U concentration and 239+240Pu activity in the uranium mine surrounding soils. We have collected some surface soil sediments within 2 km of two uranium mines and a solid waste management center in Guangxi Province. The 238U concentration in these study areas is in the range of 1.44–83.91 mg/g, and the 238U concentration in the A uranium mine surrounding surface soils is higher than that in the B uranium mine and the solid waste management center. While the B uranium mine and the solid waster management center don't pollute the surrounding soils because the 238U concentrations in their surrounding soils are similar to the average 238U concentration in the soil. The 239+240Pu activities in soil samples collected around the two uranium mines and the solid waste management center are close ranged from 0.06 mBq/g to 0.51 mBq/g. Moreover, the 240Pu/239Pu atom ratios in our study samples are ranged from 0.15 to 0.23, which indicate the Pu may come from the global fallout. In addition, we study heavy metals in our collected samples, only heavy metal Tl has weak positive correlations with 238U concentrations and 239+240Pu activities. And there is a weak positive correlation between 238U concentrations and 239+240Pu activities.

Reference materials for quality assurance of environmental plutonium analysis

Reference materials (RMs) are very important for method development and validation. In order to quickly and reliably select the suitable RM for validating the determination of plutonium (Pu), we reviewed the RMs of Pu and prepared extensive Pu datasets in this study. After data treatment and a series of statistical analyses, we obtained the statistical values of 238−241Pu activity and Pu isotopic ratio for RMs. The statistical value of 239+240Pu activity is consistent with the certified value, indicating these measured values are highly reliable. We anticipate that, after further independent work at different laboratories, the statistical values of the Pu isotopic ratios are very important to validate analysis methods and calibrate the mass bias for environmental Pu analysis.

Double Threshold Weighted Energy Detection for Asynchronous PU Activities in the Presence of Noise Uncertainty

Cognitive Heterogeneous Network (CHN) is a network that provides heterogeneous services on a cognitive radio basis. The existence of such heterogeneous services introduces a syndrome of concurrent problems. Handling each problem separately may result in more consequences. This paper aims to mitigate the combined effects of noise uncertainty and asynchronous primary user occurrence within the sensing interval of the secondary user in cognitive heterogeneous network. The paper proposes a double threshold energy detection method based on unequal scale sampling criteria. An analytic formula is deduced for both thresholds employing the power scaling criteria. Simulation results show a complete agreement with the performance expectations in terms of increased probability of detection while keeping the false alarm probability within the required limits, which is guaranteed by plotting the ROC curves. Moreover, an optimal threshold is formulated to minimize the overall detection errors, that led to further enhancements in performance as illustrated also via simulations.

Distribution and Source Identification of Pu in River Basins in Southern China.

The 239+240Pu activities and 240Pu/239Pu atom ratios in surface sediments from the major river basins in southern China were analyzed to investigate the distribution and source of Pu. We clarified that the 239+240Pu activities in these river basins were very similar, however, only the 239+240Pu activities in the Jinjiang Basin were generally higher than other samples. Because of river transport function, the distribution of 239+240Pu activities in these river basins presented an increasing trend from the upstream region to the estuary. According to the 240Pu/239Pu atom ratios, the Pu source in the inner river basins might be from global fallout, and the Pu in river estuaries might be from the global fallout and the Pacific Proving Grounds (PPG) in the Marshall Islands. Using a mass balance of the Pu model, we quantified in the Pearl River Estuary and the Pu contribution from the Pearl River Basin to Pu inventory was 13 ± 5%. These data not only filled in a knowledge gap of Pu in these river basins but also served as background data for Pu contamination from a nuclear reactor. Also, there are several planned and operating nuclear power plants in these river basins and these data could provide some indications for dealing with nuclear accidents in different parts of river basins in the future. In this study, we also analyzed some factors that would affect the distribution of 239+240Pu activities; however, only total organic carbon (TOC) content and the heavy metal As had a positive correlation with the 239+240Pu activity.

Characteristic of Pu from urban wetland and lacustrine sediments in Suzhou Industrial Park, China

In this study, plutonium activity concentrations in the urban wetlands and lacustrine sediment of Suzhou Industrial Park (SIP) are studied for the first time. Results show 239+240Pu activity concentrations in the wetland surface soils of SIP range from 0.035 to 0.426 mBq/g and the 240Pu/239Pu atom ratio ranges from 0.171±0.024 to 0.226±0.049. Judging from the atom ratio of 240Pu/239Pu, the main source of Pu in the wetland is global fallout. The correlations of Pu between organic matter and heavy metals are also studied. The correlation coefficients show Pu has significant positive correlations with Cu, Sn and Pb but negative correlation with As. Unlike distributions of Pu in other places, Pu in SIP has weak correlation with organic matter content. A sediment core from Lake Yangcheng is also analyzed to investigate the historical record of Pu deposition. The atom ratios of each layer in the sediment core indicate the area is mainly influenced by global fallout. Using Pu as a discrete-time maker, the deposition rate in Lake Yangcheng is 0.396±0.019 cm/yr. The calculated inventory of 239+240Pu is 58.5 Bq/m2, which is in the range of inventories of the corresponding latitudes according to UNSCEAR.

Soil denudation rates in an old‐growth mountain temperate forest driven by tree uprooting dynamics, Central Europe

AbstractTree uprooting may distinctly affect landscape dynamics and slope denudation. Little is known, however, about the corresponding soil redistribution rates (erosion and accumulation) on either a long‐term (millennia;10Be) or a short‐term (decades;239+240Pu) scale. We determined these rates in a well‐investigated forest reserve (Zofinsky primeval forest, Czech Republic) using complementary techniques: nuclides in soils and tors to derive short‐ to long‐term rates and monitoring data (43 years) of repeated tree censuses using tree uprooting data. Temporal trends of soil erosion rates were obtained by dating the timing of exhumation (10Be) of tors. The average long‐term denudation rates were about 30–40 t km−2yr−1. It seems that these rates varied over time with probably a maximum during the Pleistocene/Holocene transition (58–91 t km−2yr−1).239+240Pu activities in the soils identified soil redistribution rates of 50 to &gt;100 t km−2yr−1for the last decades and agree with results from the tree uprooting monitoring (&lt;92 t km−2yr−1). In‐situ10Be in soils gave similar denudation rates (58–76 t km−2yr−1). Meteoric10Be provided a mean residence time of a soil particle of 33–100 ka supporting the measured average long‐term erosion rates. Soil aggregates indicated stable physical conditions meaning that soil mass redistribution occurs only sporadically. It seems that the main driving factors of denudation changed over time. An erosion peak at the Pleistocene/Holocene transition (climate change) seems likely but needs further proof. Over the last few millennia, tree uprooting seems the main driver of soil erosion.