137Cs Peak Research Articles

The environmental consequences of rapid urbanization in central Florida reconstructed with high resolution 241Am and 210Pb dating in lake sediments

Throughout the 20th century, Florida was one of the fastest growing states in the US, putting unique environmental stress on the region. Accurately dated lake sediments can provide invaluable records of environmental change that extend beyond monitoring records. Here, we analyze profiles of americium-241 (241Am), cesium-137 (137Cs), lead (Pb), zinc (Zn), and uranium-series radionuclides in Lake Bonny in Lakeland, Florida. The 241Am peak is sharp in the sediment profile, while the 137Cs peak is broader and spread evenly across two layers. The measured 137Cs inventory of ~448Bq/m2 is less than half of the expected inventory from atmospheric deposition (accounting for decay since deposition), indicating significant losses. The reliability of 137Cs as a chronological tool can be complicated in environments with low quantities of 2:1 clays and low available potassium (K), characteristic of Florida and the U.S. southeast. Using a piecewise constant rate of supply 210Pb model verified by 241Am, we reconstruct sedimentation and chemical change in this lake. Highest sedimentation rates in the lake occur during decades of peak population growth in the mid-20th century. Uranium (U) and radium-226 (226Ra) inputs to the lake reach a maximum in the 1960s, consistent with expansion of local phosphate mines and elevated groundwater pumping during that time in response to drought conditions. Total Pb in the sedimentary record captures the rise and fall of the use of leaded gasoline, but Zn inputs to the lake remain nearly two orders of magnitude above background levels in the last decade. Our high-resolution chronology of the lake reveals regional impacts on water and lake quality in central Florida during a period of rapid population growth.

Investigation of natural radionuclides and radiation shielding potential of some commonly used building materials in Northwestern Nigeria

This study assessed the gamma-ray shielding potential of clay, sand, gypsum and kaolin commonly used as a building material in Northwestern, Nigeria. The radiological status of the samples was first evaluated by determining the activity concentrations of 238U, 232Th and 40K using NaI (Tl) detector after which elemental composition and mass density were determined using Neutron Activation Analytical Technique. After which the mass attenuation coefficients (MAC), linear attenuation coefficients (LAC), half value layer (HVL), tenth value layer (TVL), and effective atomic number (Zeff) were determined experimentally and theoretically using standard point sources of 137Cs and 60Co photon peaks (0.662 and 1.332, 1.173) MeV and Py-MLBUF software. The activity concentrations were found to range from 51 to 59 Bq kg−1 with a mean value of 59 Bq kg−1 for 238U, 24 to 27 Bq kg−1 with a mean value of 29 Bq kg−1 for 232Th, and 219 to 247 Bq kg−1 with a mean value of 247 Bq kg−1 for 40K which were about within the world recommended values of 33, 45 and 420 Bq kg−1 respectively. The results of the elemental compositions show that Si, Al, K, Fe, and Ba in clay and sand samples have concentrations in the range of 36.83–78.48%, 1.92–26.05%, 6.33–21.96%, 2.39–19.09%, and 0.09–1.44%, respectively, while in kaolin and gypsum, results revealed that Si, Al, K, Fe, and Ca range between 0.34 and 65.52%, 1.14–35.82%, 0.00–12.12%, 0.00–5.77%, and 0.00–96.6%, respectively. However, the concentrations of other elements such as Mg, Ti, Mn, Zn, Na, and Ba varied significantly with the samples. The results showed that clay has an average density of 1.96 g/cm3, sand has 2.32 g/cm3, kaolin has 2.63 g/cm3, and gypsum has the highest density with a value of 2.66 g/cm3 compared to other samples. During the measurements, a thallium-activated sodium-iodide NaI (TI) detector was used. A narrow beam transmission geometry condition was adopted for the measurements to ensure minimal scattered radiation. Absorption and attenuation of gamma beams as a function of sample thickness against gamma energy generally exhibit an increasing gamma ray behaviour as the sample thickness increases from 1 to 3 cm. The results showed that the gypsum, kaolin, sand, and clay were capable of attenuating 63.5%, 61.5%, 58.4%, and 44.2 of gamma-ray photons of energy 0.662 MeV at 3 cm thickness %, respectively, and 40.6%, 32.9%, 30.6%, and 27.3% of gamma energy 1.332 MeV at 3 cm thickness, respectively. The results showed that MAC, LAC, and Zeff of all the samples decreased with an increase in photon energy, while those of HVL and TVL increased. The experimental results for all the gamma-ray shielding parameters were found to be in good agreement with the theoretical values obtained using Py-MLBUF. The results have shown that all the samples have similar photon attenuation behaviours; however, gypsum has the best shielding potential than kaolin and this is attributed due to its highest density value.

Anthropogenic activities mediate stratification and stability of microbial communities in freshwater sediments

BackgroundFreshwater sediment microbes are crucial decomposers that play a key role in regulating biogeochemical cycles and greenhouse gas emissions. They often exhibit a highly ordered structure along depth profiles. This stratification not only reflects redox effects but also provides valuable insights into historical transitions, as sediments serve as important archives for tracing environmental history. The Anthropocene, a candidate geological epoch, has recently garnered significant attention. However, the human impact on sediment zonation under the cover of natural redox niches remains poorly understood. Dam construction stands as one of the most far-reaching anthropogenic modifications of aquatic ecosystems. Here we attempted to identify the ecological imprint of damming on freshwater sediment microbiome.ResultsWe conducted a year-round survey on the sediment profiles of Lake Chaohu, a large shallow lake in China. Through depth-discrete shotgun metagenomics, metataxonomics, and geophysiochemical analyses, we unveiled a unique prokaryotic hierarchy shaped by the interplay of redox regime and historical damming (labeled by the 137Cs peak in AD 1963). Dam-induced initial differentiation was further amplified by nitrogen and methane metabolism, forming an abrupt transition governing nitrate–methane metabolic interaction and gaseous methane sequestration depth. Using a random forest algorithm, we identified damming-sensitive taxa that possess distinctive metabolic strategies, including energy-saving mechanisms, unique motility behavior, and deep-environment preferences. Moreover, null model analysis showed that damming altered microbial community assembly, from a selection-oriented deterministic process above to a more stochastic, dispersal-limited one below. Temporal investigation unveiled the rapid transition zone as an ecotone, characterized by high species richness, low community stability, and emergent stochasticity. Path analysis revealed the observed emergent stochasticity primarily came from the high metabolic flexibility, which potentially contributed to both ecological and statistical neutralities.ConclusionsWe delineate a picture in which dam-induced modifications in nutrient availability and sedimentation rates impact microbial metabolic activities and generate great changes in the community structure, assembly, and stability of the freshwater sediment microbiome. These findings reflect profound ecological and biogeochemical ramifications of human–Earth system interactions and help re-examine the mainstream views on the formation of sediment microbial stratification.CKW67QzkRJsDF17fMBne_jVideo

Design and manufacture of scintillation detector using CsI(Tl) crystal coupled with silicon photomultipliers

In this research, a scintillation detector was developed using the CsI(Tl) scintillator crystal coupled with a silicon photomultiplier (SiPM) to replace the photomultiplier tube (PMT), resulting in a compact and energy-efficient detector. A rectangular box-shaped CsI(Tl) scintillation crystal with dimensions of 50x25x25 mm from Kinheng and a SiPM module S13361-3050AE-08 with dimensions of 25x25 mm from Hamamatsu were selected to use. The preamplifier circuit, power supply, and temperature stabiliser have also been integrated into the detector. The characteristics of this detector were evaluated using a 137Cs standard radioactive source together with Ortec’s multichannel analyser device and Gamma Vision software for spectrum analysis. Results showed that the energy resolution for the 137Cs peak of this detector is about 8.03%, which is almost equivalent to the energy resolution of 7.87% of the Canberra detector using 76x76 mm NaI(Tl) crystal coupled to the PMT. The results of the evaluation of stability over time when the operating ambient temperature of this detector with no change showed that the energy peak position and the energy resolution for the 137Cs radioactive source are almost unchanged. The research also investigated the stability of the detector according to the operating ambient temperature. The results exhibited that the output pulse amplitude varies greatly with the ambient temperature, it decreases when the temperature increases and vice versa. Under the condition that the operating ambient temperature varies from 11oC to 50oC, the energy peak position of 137Cs changes were 1762 and 167 channels, respectively in the cases without and with adjustment of output pulse amplitude stabilisation function in power supply for SiPM. When there is a function of output pulse amplitude stabilisation, the change in peak position according to operating ambient temperature is still about 4.3 channels/oC, so further research is needed to correct the influence of ambient temperature on the operation of this detector, to provide wide applicability of scintillation detector using SiPM to replace traditional PMT in the future.

Online control of the gain drift with temperature of SiPM arrays used for the readout of LaBr3:Ce crystals

LaBr3:Ce crystals have been introduced for radiation imaging in medical physics, with photomultiplier or single SiPM readout. An R&D was pursued with 1/2″ and 1″ LaBr3:Ce crystals, from different producers, to realize compact large area detectors (up to some cm2 area) with SiPM array readout, aiming at high light yields, good energy resolution, good detector linearity and fast time response for low-energy X-rays. A natural application was found inside the FAMU project at RIKEN-RAL muon facility, that aims at a precise measure of the proton Zemach radius to solve the so-called “proton radius puzzle”, triggered by the recent measure of the proton charge radius at PSI. The goal is the detection of characteristic X-rays around 130 keV. Other applications may be foreseen in medical physics, such as PET, and gamma-ray astronomy. A limiting factor is the gain drift of SiPM arrays with temperature, that give a deterioration of the detector’s FWHM energy resolution. To solve this problem, a custom NIM module, based on CAEN A7585 digital power supply, was developed. Test results of the correction of gain drift with temperature for SiPM arrays from Advansid, Sensl, Hamamatsu will be presented. At the 137Cs peak, an energy resolution better than 3% was obtained for a typical LaBr3:Ce crystal, using Hamamatsu S13461 arrays. This compares well with best available results obtained with a PMTs.

Со-60 as a time marker to date sediment layers and estimate sediment transport distances during the 2006 flood event on the Yenisei River

The study of bottom sediments collected from the Yenisei River downstream of the Mining-and-Chemical Combine (MCC) conducted from 2006 to 2016 revealed increased concentrations of 60Co, which was present in dispersed form and in the form of radioactive microparticles, in the upper core layers. The increase in 60Co activity concentration occurred when the 2006 extreme flood on the Yenisei washed away the radionuclide-containing soil from the riverbank at the MCC. The 137Cs/60Co ratio in the upper layers of bottom sediments after the 2006 flood varied between 0.2 and 1.5 and differed considerably from the 137Cs/60Co ratio in the upper sediment layers before the flood (2.5–6.0). Because of the increased concentrations of 60Co, especially in the form of microparticles, in some sediment layers, 60Co was used as a time marker (2006) enabling calculation of sedimentation rates and radionuclide sediment chronology. The 137Cs sediment chronology calculated using 60Co showed that the major 137Cs peak was dated to the most extreme flood on the Yenisei, which occurred in 1966. Those calculations confirmed the appropriateness of using 60Co as a time marker. Our findings suggest that during the 2006 flood, 60Co was washed away from the MCC area to the Yenisei and transported as a component of suspended particles as far as 245 km downstream of the MCC.

Sedimentation rates and sediment age of the high-altitude cold desert Ramsar Wetland, the Chandratal, inferred from radionuclide (210Pb and 137Cs) technique.

In the current scenario, the pristine Himalayan Wetlands are under endangerment due to higher sedimentation rate, including siltation, reduction of ecological value, pollution, and significant anthropogenic encroachment along with advanced civilization. The more increased sedimentation reduces the depth and existing expansion of the Wetland. This study articulates the record of sedimentation in the Chandratal present in Western Himalaya, Himachal Pradesh, India, at the altitude of 4300m. The sedimentation rate of the Chandratal was calculated based on a 1-m core sample considering isotopes of 137Cs and 210Pb dating techniques. The present study based on the Constant Rate of Supply (CRS) model of 210Pb reveals that the Wetland experienced an average sedimentation rate of 1.75 ± 0.04cm/year during the last 63years observed from 1953 to 2016. The 137Cs peak method-based calculated sedimentation rate of the Chandratal is 1.6 ± 0.02cm/year representing the years for about 62years from 1954 to 2016. The Wetland's functional survival prevalence was estimated to be 420 and 459years based on 210Pb and 137Cs dating techniques, respectively. The study communicates that the magnified human interference in the catchment area of the Chandratal is accountable for the faster sedimentation in recent years.

The detection efficiency study of NaI(Tl) scintillation detector with the different numbers of SiPMs

SiPMs are generally coupled into whole columns in gamma energy spectrum measurement, but the relationship between the distribution of whole SiPM columns and the energy resolution of the measured energy spectra is rarely reported. In this work, ∅ 3 × 3 inch NaI scintillator is placed on an 8 × 8 SiPM array, and the energy resolution of the 137Cs peak at 662 keV corresponding to the γ-ray is selected as a reference. Each SiPM is switched to explore the influence of the number of SiPM arrays, distribution position, and reflective layer on the energy resolution of SiPMs. Results show that without coupling, the energy resolution is greatly improved when the number of SiPMs ranges from 4 to 32. However, after 32 slices (the area covered by SiPMs relative to the scintillator reaches 25.9%), the improvement in energy resolution and total pulse count is not obvious. In addition, the position of SiPMs relative to the scintillator does not exert much impact on the energy resolution. Results also indicate that by adding a reflective film (ESR), the energy resolution of the tested group increases by 10.38% on average. This work can provide a reference for the design and application of miniaturized SiPM gamma spectrometers.

Radiocesium in the Taiwan Strait and the Kuroshio east of Taiwan from 2018 to 2019

The release of anthropogenic radiocesium to the North Pacific Ocean (NPO) has occurred in the past 60 years. Factors controlling 137Cs (half-life, 30.2 year) and 134Cs (half-life, 2.06 year) activity concentrations in the Kuroshio east of Taiwan and the Taiwan Strait (latitude 20° N–27° N, longitude 116° E–123° E) remain unclear. This study collected seawater samples throughout this region and analyzed 134Cs and 137Cs activity concentrations between 2018 and 2019. A principal component analysis (PCA) was performed to analyze the controlling factors of radiocesium. Results of all 134Cs activity concentrations were below the detection limit (0.5 Bq m−3). Analyses of water column 137Cs profiles revealed a primary concentration peak (2.1–2.2 Bq m−3) at a depth range of 200–400 m (potential density σθ: 25.3 to 26.1 kg m−3). The PCA result suggests that this primary peak was related to density layers in the water column. A secondary 137Cs peak (1.90 Bq m−3) was observed in the near-surface waters (σθ = 18.8 to 21.4 kg m−3) and was possibly related to upwelling and river-to-sea mixing on the shelf. In the Taiwan Strait, 137Cs activity concentrations in the near-surface waters were higher in the summer than in the winter. We suggest that upwelling facilitates the vertical transport of 137Cs at the shelf break of the western NPO.

Scintillation gamma radiation sensors based on solid-state photomultipliers in wireless industrial internet networks

The article examines the principles of developing wireless networks of autonomous gamma sensors in order to create systems for spatial environmental radiation monitoring. The main task of such systems is to control the level of gamma radiation in areas where potential sources of ionizing radiation are located. An autonomous gamma-ray spectrometer is used as a measuring sensor. The authors propose to apply measuring sensors based on a silicon photomultiplier to create autonomous wireless networks of the industrial Internet for radiation monitoring. To confirm the possibility of using this class of receivers as part of gamma spectrometers, the main structural elements of the system were modeled, and the experimental model of the gamma spectrometer was prototyped. The linearity and energy resolution of the experimental sample were also investigated. To test the model for constructing a gamma spectrometer, a CsI (Tl) scintillation crystal and a Sensl Array-60035-4P photomultiplier were used. The established range of recorded energies is in the range from 121 keV to 1332 keV, the relative energy resolution for the 137Cs peak is 11.07 %, the linearity of the transfer characteristic is 99.91 %. Based on this sensor, the architecture of an automated wireless system for monitoring the spatial distribution of gamma radiation has been developed. The results of the work allow the use of radiation monitoring systems in accordance with the requirements of Industry 4.0.

Ce:LaBr3 crystals with SiPM array readout and temperature control for the FAMU experiment at RAL

Compact X-rays detectors made of 1/2′′ Ce:LaBr3 crystals of cubic shape with SiPM array readout have been developed for the FAMU experiment at RIKEN-RAL, to instrument regions of difficult access. Due to the high photon yield of Ce:LaBr3 it was possible to use a simple readout scheme based on CAEN V1730 digitizers, without a dedicated amplification stage. The drift with temperature of SiPM gain was corrected by using CAEN A7885D regulated power supply chips with temperature feedback. Energy resolutions (FWHM) around 3.5% at the 137Cs peak and around 9% at the 57Co peak were obtained.

Environmental radioactivity in a sediment core from Algiers Bay: Radioecological assessment, radiometric dating and pollution records

Abstract The sedimentary system of the Algiers Bay has been impacted in the last decades by the exponential increases in population, urbanism and industrial activities of the city of Algiers, and by episodic floods, mudflows, earthquakes and tsunamis. Activity concentrations of environmental gamma-emitters, namely 210Pb, 226Ra, 40K, 228Ra, 228Th and 137Cs, were measured in a sediment core sampled in 2015 at the central zone of this bay, at 73 m depth from the surface water. The 210Pb-based radiometric dating was challenging due to the incomplete recovery of the inventory, the absence of 137Cs peaks, and the failure of classical models. The analysis of clusters in the logarithmic plot of the excess 210Pb versus mass depth profile allowed for establishing a reliable chronology. Fluxes of excess 210Pb and sediment accumulation rates (SAR) have both varied over the last five decades. Recent SAR values are of 0.73 ± 0.21 g cm−2y−1. Major and trace elements were determined by X-Ray Fluorescence in some selected sediment slices. Moderate enrichments have been observed for Mn, Zn, Br, Rb, Sr, Y and Pb in the 0–1 cm sediment layer (when using Al as normalization element), being governed by Fe-rich carriers. The major impact is observed in the carbon content, which increased by two orders of magnitude (from their basal values) for three decades since early 70's. The dataset also allowed for a radioecological assessment in the area, performed using the ERICA software.

Using reservoir deposits to quantify the source contributions to the sediment yield in the Black Soil Region, Northeast China, based on the fingerprinting technique

Identifying patterns of sediment dynamics is an important aspect of understanding soil erosion processes and developing reasonable management strategies to address environmental problems and assess the ecological functions of soil and water conservation measures. In this study, the sediment fingerprinting technique was applied in order to quantify the relative contributions of sediment to the Hebei catchment in the black soil region of Northeast China, with the aim of determining the response of soil erosion to recent changes in land management. Within an area of approximately 28 km2, three potential sediment sources were identified based on land use types. They included cultivated topsoil, uncultivated topsoil, and gullies. A total of 69 sediment source samples were collected from potential sediment sources from 27 sampling sites for cultivated topsoil, 18 sampling sites for uncultivated topsoil, and 24 sampling sites for gullies. Six uniformly spatially distributed sediment cores were sampled from the Liudui reservoir. The Walling–Collins model was optimized using a genetic algorithm combined with the Latin hypercube sampling procedure. The results indicated that cultivated topsoil and gullies were the primary sediment provenances and that gully erosion is as important as rill and interrill erosion. According to the mean sediment contributions of the six deposited sediment cores, the sediment contribution from cultivated topsoil was 50.6%, ranging from 34.4% to 63.7%, whereas gullies contributed 42.9%, ranging from 30.1% to 57.8%. However, the sediment from uncultivated topsoil (mainly containing forest and grassland) contributed only 6.5%, with a range of 5.0% to 7.8% over the last few decades with a mean absolute fit of 0.95. This indicated that caution is needed in when using only a single core to provide results for a reservoir. Over the 1976–2016 period, rill and interrill erosion showed a general decreasing trend, whereas gully erosion showed an increasing trend. According to the sedimentation depth and time marks based on the 137Cs and D50 peak horizon and decayed vegetation layer in the six sediment cores, sedimentation rates during 1976–1998 and 1999–2016 were 1.6 cm yr−1 (14.4 kg m−2 yr−1) and 0.9 cm yr−1 (7.6 kg m−2 yr−1), respectively. For the entire time series (1976–2016), the sedimentation rate was 1.2 cm yr−1 (10.7 kg m−2 yr−1). A good correlation exists between the distance from the reservoir entrance and sediment contribution/mean annual sedimentation rate (r2 > 0.68, except uncultivated topsoil).

Long-term stability of records of fallout radionuclides in the sediments of Brotherswater, Cumbria (UK)

Results from a recent multi-core study of 137Cs and 210Pb in Brotherswater, Cumbria, are compared with those from two similar multi-core studies carried out at the same lake in 1976/1977 and 1988/1989. The purpose of this new study was to assess of the long-term stability of fallout records of these radionuclides in the sediments of Brotherswater and their reliability as tools for dating the sediments. Six cores were taken from four different areas of the lake, similar to those used in the earlier studies. Dried sediment samples from each core were analysed by gamma spectrometry for 210Pb, 226Ra, 137Cs and 241Am following a similar protocol to that used in the 1988/1989 study. The 137Cs results graphically illustrate the progressive burial of a peak in concentrations recording the 1963 fallout maximum from the atmospheric testing of nuclear weapons, and its subsequent reduction due to radioactive decay. The post-1986 cores are characterised by the appearance and burial of a second peak recording fallout from the 1986 Chernobyl accident. Identification of the 1963 137Cs peak in post-1986 cores was confirmed by the co-presence of traces of 241Am, also a product of nuclear weapons test fallout. In both the 1988/1989 study and the present study, 210Pb dates calculated using the CRS model for the most part placed 1963 and 1986 at depths very similar to those determined from the 137Cs records. The maintenance of this agreement over a period of more than two decades provides evidence of the reliability of sediment records in this lake and the validity of models used to interpret them. The 137Cs records were too indistinct and 1963 too recent to make similar comparisons in the case of the 1976/1977 cores. Agreement between 210Pb and 137Cs dates was best at sites where the net rate of supply of 210Pb to the sediment record was comparable to the atmospheric flux. Small but significant discrepancies were observed at sites where the 210Pb supply rate greatly exceeded the atmospheric flux, most probably due to additional time-dependent inputs from the catchment, or post-depositional sediment redistribution within the lake.

The approaching obsolescence of 137Cs dating of wetland soils in North America

The peak fallout in 1963 of the radionuclide 137Cs has been used to date lake, reservoir, continental shelf, and wetland sedimentary deposits. In wetlands such dating is used to project the ability of wetlands to keep pace with sea level rise and develop strategies for mitigating carbon pollution using biological carbon sequestration. Here we demonstrate that reliable 137Cs profiles are increasingly difficult to obtain from wetland soils. Among 58 soil cores recently collected from a range of wetland types and 137Cs fallout densities across the United States, 25% contain no identifiable 137Cs peaks. Less than 40% of 137Cs ages are consistent with 210Pb dating. We provide a new measure of 137Cs peak clarity (τ) for our core dataset by comparing the 50% interquartile range of data around the 137Cs peak for “ideal” cores profiles determined using 137Cs fallout data to that of observed core profiles. Our results show that overall τ is approximately 10 times greater for observed cores than ideal cores. The deterioration in the 137Cs peak has occurred due to radionuclide decay, 137Cs migration in situ, which is ubiquitous in this study, and 137Cs amendments from surface waters. Such deterioration likely extends to both Mexican and non-permafrost, Canadian wetlands. We recommend continued use of 137Cs only if the full bound of dating uncertainty for both 137Cs and an additional method such as 210Pb is propagated into estimates of wetland vertical accretion and carbon sequestration.

Evaluating Sediment Deposition Prediction by Three 137Cs Erosion Conversion Models

Core Ideas We used 34 years of measured plot erosion data for 137Cs model validation. For the first time, deposition prediction of three widely used models was evaluated. A simple proportional model appeared to perform better than mass balance models. More rigorous validation is needed in conditions including 137Cs peak fallout period. Although the 137Cs technique has been widely used to estimate soil redistribution in past decades, most 137Cs‐conversion models have not been rigorously validated. The objective of this study was to explicitly evaluate the sediment deposition components of three widely used 137Cs models using 34 yr of soil loss data from a plot (200 × 80 m). The average slope of the plot is approximately 4% in the upper section and 1% in the lower section. The primary soil (fine, mixed, thermic, Udertic or Pachic Paleustoll) is silt loam with 23% sand and 56% silt. Winter wheat (Triticum aestivum L.) was raised primarily under conventional tillage. Sediment load was measured with a pump sampler at the outlet. Bulk soil cores were taken in a 10‐m grid to estimate 137Cs inventory. The 137Cs depth profiles were measured at eight locations to determine net deposition depth. The proportional model (PM) and two mass balance models (mass balance model 1 [MBM1] and mass balance model 2 [MBM2]) were evaluated. The measured average deposition depth in the depositional area of the lower section was 5.83 cm, and the predicted deposition depths in the area were 4.12, 2.02, and 1.64 cm for PM, MBM1, and MBM2. The results indicated that the simple PM appeared to predict deposition depths better than the two sophisticated mass balance models under the study conditions. However, the true capability of the two mass balance models needs to be further evaluated under more complex conditions that include the critical period of 137Cs peak fallout in the 1950s and 1960s.

High resolution lake sediment record reveals self‐organized criticality in erosion processes regulated by internal feedbacks

AbstractReconstruction of high‐frequency erosion variability beyond the instrumental record requires well‐dated, high‐resolution proxies from sediment archives. We used computed tomography (CT) scans of finely laminated silt layers from a lake‐sediment record in southwest Oregon to quantify the magnitude of natural landscape erosion events over the last 2000 years in order to compare with palaeorecords of climate, forest fire, and seismic triggers. Sedimentation rates were modeled from an age–depth relationship fit through five 14C dates and the 1964 AD 137Cs peak in which deposition time (yr mm‐1) varied inversely with the proportion of silt sediment measured by the CT profile. This model resulted in pseudo‐annual estimates of silt deposition for the last 2000 years. Silt accumulation during the past 80 years was strongly correlated with river‐discharge at annual and decadal scales, revealing that erosion was highly responsive to precipitation during the logging era (1930–present). Before logging the frequency–magnitude relationship displayed a power‐law distribution that is characteristic of complex feedbacks and self‐regulating mechanisms. The 100‐year and 10‐year erosion magnitude estimated in a 99‐year moving window varied by 1.7 and 1.0 orders of magnitude, respectively. Decadal erosion magnitude was only moderately positively correlated with a summer temperature reconstruction over the period 900–1900 AD. Magnitude of the seven largest events was similar to the cumulative silt accumulation anomaly, suggesting these events ‘returned the system’ to the long‐term mean rate. Instead, the occurrence of most erosion events was related to fire (silt layers preceded by high charcoal concentration) and earthquakes (the seven thickest layers often match paleo‐earthquake dates). Our data show how internal (i.e. sediment production) and external processes (natural fires or more stochastic events such as earthquakes) co‐determine erosion regimes at millennial time scales, and the extent to which such processes can be offset by recent large‐scale deforestation by logging. Copyright © 2018 John Wiley & Sons, Ltd.

Accumulation rates, focusing factors, and chronologies from depth profiles of 210Pb and 137Cs in sediments of the Laurentian Great Lakes

Abstract Sediment cores from 41 sites were collected from the Laurentian Great Lakes during 2010–2014, sectioned into 0.5–2.0 cm intervals, and the activities of 210Pb, 137Cs, and 226Ra were measured in the upper 25 to 40 cm of the sediment column by gamma spectrometry. Sediment mass accumulation rates (dry mass) calculated from 210Pb profiles range from 0.006 ± 0.001 to 0.59 ± 0.06 g cm−2 yr −1 and are similar to those reported in previous Great Lakes sediment studies. Sediment mass accumulation rates decreased with increasing water depth. 210Pb-based models in cores exhibiting favorable characteristics (i.e., those having the highest unsupported-210Pb activity at the sediment-water interface, exponential decrease of unsupported-210Pb with increasing depth in sediment cores, and a clear peak in 137Cs activity at some depth below the sediment-water interface) give calendar date profiles that are largely concordant with the maximum 137Cs peak activity at 1963. Sediment focusing factors derived from unsupported-210Pb inventories range from 0.09 to >5.34, and are well correlated with those derived from 137Cs inventories that range from 0.07 to 4.04, demonstrating the ubiquitous occurrence of horizontal sediment transport processes within the lakes. This more recent survey provides a Great Lakes-wide chronological framework for comparing the depositional histories and inventories of a wide variety of persistent, bioaccumulative and toxic pollutants that have been measured in the same sediment cores. This information will be useful for resolving scientific and practical issues pertaining to the environmental quality and management of contaminated sediments in the Laurentian Great Lakes ecosystem.

Palynological and Geochemical Records of Environmental Changes in a Taxodium Swamp near Lake Pontchartrain in Southern Louisiana (USA) during the Last 150 Years

Ryu, J.; Bianchette, T.A.; Liu, K.-B.; Yao, Q., and Maiti, K.D., 2018. Palynological and Geochemical Records of Environmental Changes in a Taxodium Swamp near Lake Pontchartrain in Southern Louisiana (USA) during the Last 150 Years. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 381–385. Coconut Creek (Florida), ISSN 0749-0208.The hydrological and environmental histories of estuarine wetlands in southern Louisiana are not well-documented. To better understand their local developmental processes, a 59 cm sediment core (WMA-1) was extracted from a bald cypress (Taxodium distichum) swamp located approximately 800 m west of Lake Pontchartrain. This area has been heavily influenced by human activities, and is susceptible to inundation from storm surges from Lake Pontchartrain as well as fluvial and lacustrine processes. 210Pb analysis indicates that WMA-1 has a sedimentation rate of 0.39 cm/year, consistent with the detection of a 137Cs peak at 18 cm depth. Sedimentological and geochemical analyses reveal two distinct sedimentological facies: an organic-rich dark brown peat unit from 0 to 29 cm containing low concentrations of terrestrial elements (e.g., Ti, and Fe), and a clay unit from 29 to 59 cm with elevated concentrations of most elements (e.g., Sr, Cl, Ti, Mn, and Fe). The pollen assemblage in the clay section is dominated by TCT (mainly Taxodium), but it is replaced by Salix and wetland herbaceous taxa in the overlying peat. The Taxodium swamp was present at the site at least 150 years ago, and was replaced by Salix and other bottomland hardwood trees and wetland herbs due to a decrease in water level around AD 1940. While climate may have played a role, this hydrological change was most likely caused by the significant regional human activities during the last 100 years. Two thin clay layers (at 3–5 cm, 14–19 cm) embedded in the upper peat section were likely deposited from hurricanes Isaac (2012) and Betsy (1969): two events responsible for heavy rain and significant storm-surge flooding. Our findings suggest that human activities are capable of altering local wetland hydrology and ecology, while the clay layers represent hurricane-induced floods at the site during the past century.

From floodplain to aquatic sediments: Radiogeochronological fingerprints in a sediment core from the mining impacted Sancho Reservoir (SW Spain)

The Sancho Reservoir (SW Spain) was built in 1962, about the time of maximum 137Cs fallout, and it has been affected by acid mine drainage (AMD) particularly since the mining cease in 2001. This is a unique scenario for studying the radiogeochronological fingerprints in AMD-affected sediments deposited over the former flood plain. A sediment core sampled in 2011 was analysed for bulk density, 137Cs, 239Pu, 240Pu, 210Pb, 226Ra, 228Ra, 234Th (238U) and 40K, and studied with various radiometric dating models. Bulk density revealed unsteady compaction and likely depositional events. The activity concentrations of 226Ra, 228Ra, 234Th (238U) and 40K were uniform down-core, but declining overall in the upper 0–25cm, revealing changes in provenance except for 238U, which increased in the top 10cm likely due to its supply by AMD. The AMD fingerprint was also found in the 239+240Pu/137Cs activity ratio, which increased in the top sediment layers. The 137Cs and 239+240Pu profiles show well defined peaks at the same depth, with inventories being about four times higher than the expected integrated atmospheric deposition in the area. The unsupported 210Pb (210Pbexc) showed a complex non-monotonic profile interrupted at several sections, particularly around the 137Cs peak. The whole dataset cannot be interpreted in terms of continuous sedimentation processes. Based upon correlated features in the bulk density and 210Pbexc profiles, a series of depositional events (likely linked to peaks in the rainfall records) have been identified in the core. These events date back to the period comprised since the construction of the dam until its increase in height in 1972, which likely displaced upstream the main depositional area of riverine loads, as inferred from sediment trap data. The CRS (with a reference date) and (a piecewise) CIC models have been used for complementing and discussing the chronology.