Dating of recent sediments from Lago Maggiore and Lago di Lugano (Switzerland/Italy) using 137Cs and 210Pb

Comparison of spatiotemporal burial and contamination of heavy metals in core sediments of two plateau lakes with contrasting environments: implication for anthropogenic-driven processes

Investigating the impacts of climatic factors and human activities on sedimentary records of heavy metal (HM) contamination in lakes is essential for decision-making in global environmental monitoring and assessment. Spatiotemporal distributions of grain size (GS) and HM (Al, Cr, Mn, Ni, Cu, Zn, As, and Pb) concentrations have been conducted in core sediments that are collected from two adjacent plateau fault-bound lakes in southwest China with contrasting environments, i.e., deep oligotrophic Lake Fuxian (FX) and shallow hypertrophic Lake Xingyun (XY). Results showed that the average value of d50 in FX (4.61 μm) was lower than that in XY (8.35 μm), but the average concentrations of HMs (except Cr and Mn) in XY were higher than those in FX. Heavy metal burial rates (HMBR) were mainly controlled by sediment accumulation rates (SARs) rather than HM concentrations. The correlation coefficients between GS and HM concentrations became strong as the increasing water depths were associated with a stable sedimentary environment. Time-integrated enrichment factors (EF) and source identification of HMs between FX and XY represented that Cr, Ni, and Cu originated from natural sources but Mn, Zn, As, and Pb from anthropogenic sources, respectively. Regardless of FX and XY, the transition times of HMs from natural to anthropogenic sources occurred in the mid-1960s. Comparison of qualification impacts of climatic factors and human-induced factors on increased anthropogenic HMBR by the partial least squares path modeling (PLS-PM) implied that socio-economic activities, such as population density (PD) and gross domestic product (GDP), provided higher contributors to increased anthropogenic HMBR in XY (0.23/0.71) than FX (0.11/0.18). The comparative results of this study provided new insights into environmental monitoring and management of HM contamination for adjacent lakes with contrasting environments.

Bottom sediment radioactivity of the six Caucasus lakes located in different altitude zones

Natural and artificial radioactivity of bottom sediment in the six lakes of the Western and Central Caucasus have been evaluated. It allowed to define the variation of sedimentation rate during the last 100-150 years using technogenic (¹³⁷Cs) and natural (²¹⁰Pb, ²²⁶Ra) radionuclides as a chronomarkers. The studied lakes are located in the contrasting geographic conditions, different orographic positions, and have different origin. The average annual precipitation in the area of each of the lakes has been detected to stay relatively constant during the ¹³⁷Cs fallout period, while the air temperature has markedly increased during the last decades. The detected sedimentation rates are the indirect indicator of climate change in the mountains. They are slightly decreasing owing to the increased protection of soil by vegetation cover in the lower altitude zone; in the upper zones, they are growing due to accelerated glacier retreat. The radioecological situation is estimated as normal. High levels of ¹³⁷Cs (33 kBq m^-2) and ²⁴¹Am (0.1 kBq m^-2) in bottom sediments are attributed to the region-specific geographical characteristics.

Historical evolution of polycyclic aromatic hydrocarbon pollution in Chaihe Reservoir from 1863 to 2018

Pollution from polycyclic aromatic hydrocarbons (PAHs) spreads and changes worldwide. The pollution evolution in the regional water environment evolves in response to multiple factors, requiring considerable attention. PAH heterogeneity in the sediment core from Chaihe Reservoir was investigated to indicate dynamic changes in PAH pollution levels and sources and propose recommendations for controlling PAHs. Dynamic PAH patterns showed that the overall decline in PAH pollution was in association with local anthropogenic activities, temperature, and precipitation over the period 1863-2018. Nevertheless, coal, oil, and natural gas consumptions still played significant roles in transferring PAHs to the reservoir. Meanwhile, there were dominant local origins, including grass, wood, and coal combustion. The results highlight that the joint action of natural and anthropogenic interventions mitigated PAH pollution in the reservoir. Promoting improved fuels, new energy vehicles, and cleaner energy may further lower PAH pollution.

Long-term deposition records of microplastics in a plateau lake under the influence of multiple natural and anthropogenic factors

Microplastic accumulation in the lake aquatic environment has attracted worldwide attention, but the long-term deposition characteristics and influencing factors of microplastics are not clear. Hence, we attempted to analyze the factors that influence the accumulation of microplastics during the process of natural environmental change and social development through the method of the sedimentological approach. In this investigation, the chronological sequence of sediment core was set up based on lead-210 composition to study microplastic accumulation rates in a plateau lake, Jianhu Lake. For the first time, the records of microplastic deposition were analyzed combined with multiple anthropogenic and natural factors, including 4 natural and 17 social factors to reveal the influence of natural processes and social development on microplastic abundances. The results showed that sediments were highly contaminated by microplastics, and the mean abundance of microplastics in the sediment cores of Jianhu Lake was 924 ± 427 particles/kg, and showed a gradually increasing trend from the bottom (25 to 30 cm) to surface layer (0 to 5 cm). Blue and black were the main colors of microplastics, and the average proportion of wirelike microplastics was 63 %. Additionally, the polymer type of microplastic was mainly rayon, the surface morphology of different polymer types was disparate, and various elements enriched on the surface of microplastics were also detected. In the past 70 years, the deposition rate of microplastics in Jianhu Lake maintained the trend of continuous growth, and the abundance of microplastics is projected to be 448 to 3017 and 513 to 3670 particles/kg by 2035 and 2050, respectively. What is more, there are significant correlations among multiple natural and anthropogenic factors and microplastic deposition, as well as microplastic polymer species.

High-resolution records of cesium, plutonium, americium, and uranium isotopes in sediment cores from Swiss lakes

The Aare river system in Switzerland, with two nuclear power plants on the banks of the river, and its intermediate lakes and reservoirs, provides a unique opportunity to analyze the contribution of different sources to the radioactive contamination. Sediment cores were collected from two lakes and a reservoir, all connected by the river Aare. In order to study the influence of the Chernobyl accident, one sediment core was collected from a lake in the southern part of Switzerland. The sediment cores were sliced and analyzed with gamma ray spectrometry. Plutonium, americium, and uranium were extracted radiochemically, and their concentrations were measured with a sector field ICP-MS. The uranium isotope ratios were further measured with a multi collector ICP-MS. The maximum ¹³⁷Cs activity from the Chernobyl accident and the Pu and ¹³⁷Cs activities associated to the 1963 global fallout maximum were well identified in sediments from all three lakes. High-resolution records of plutonium isotopes in the zone of the sediments corresponding to the period of maximum fallout from the atmospheric nuclear weapon testing showed distinct fingerprints, depending on the different test activities. Pu isotope ratios could be used to detect non-global fallout plutonium. The ratio ²⁴¹Am/²⁴¹Pu was used to determine the age of the plutonium. Despite of very low ²⁴¹Pu and ²⁴¹Am concentrations, the calculated plutonium production dates seemed to be reasonable for the sediment layers corresponding to the NWT tests. The calculated production date of the plutonium in the upper most 15 cm of the sediment core seemed to be younger. The reason for this could be additional non-global fallout plutonium. For the lake sediments, natural ratios for ²³⁵U/²³⁸U and enriched or depleted ratios for ²³⁴U/²³⁸U were measured, depending on the lake. A small increase of the ²³⁶U/²³⁸U ratio could be recognized for the NWT zone in all three lakes and, for Lake Lugano, a further distinct increase in the Chernobyl layer.

Response of sedimentation rate to environmental evolution in Da River Reservoir in Southwest China

Lake sediment records the evolution process of the interaction between human and nature. It is important to master the lacustrine sedimentation rate for the ecological environment assessment of catchment. A 60-cm sediment core was collected in the Da River Reservoir during 2019 to analyze radionuclides (²¹⁰Pb and ¹³⁷Cs) massic activities, grain size, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and metals (Mn, Cu, Al, and Pb) mass fractions to reconstruct the response of sedimentation rate to environmental evolution. The environmental changes in the small catchment were classified into the following three stages through cluster analysis (CA) for geochemical parameters in the sediment core: phase I (1881-1985), phase II (1987-1999), and phase III (2000-2018). The average depth sedimentation rates (ADSRs) of the three stages were 0.33, 0.90, and 1.50 cm/year, respectively. The sedimentation rates increased from the bottom to the surface layer, indicating that the exogenous inputs into the reservoir have been occurring. The sediment deposition in phase III was strongly disturbed by the environmental changes (such as warmer climate and intensified land use). Therefore, sedimentation rates showed a rapid increase. Both Pearson correlation analysis and redundancy analysis (RDA) showed that sedimentation rates were positively correlated with climatic factors, particle size, nutrients and metals mass fractions, elemental ratios, and socioeconomic parameters. Sedimentation rates show high sensitivity to anthropogenic activities and climatic change, which can be used to reconstruct the environmental evolution process at a small catchment scale.

Spatial and vertical distribution of 137Cs activity concentrations in lake sediments of Turawa Lake (Poland)

The main objective of this research was to study the spatial and vertical distribution of 137Cs activity concentrations in the bottom sediments of Turawa Lake 32 years after the Chernobyl fallout to investigate possible factors responsible for the post-fallout migration and accumulation of 137Cs in the selected reservoir. The results demonstrated a strong relationship between the increasing 137Cs and 40K activity concentrations and the decreasing grain size of sediments. Significant amounts of 137Cs were detected in the bottom sediments deposited in the deeper parts of the reservoir (especially near the dam). Therefore, this research showed that Turawa Lake can be an important trap for sediments polluted with 137Cs. Moreover, disturbed vertical distribution of 137Cs activity concentrations in the sediment columns collected from the littoral zone of this lake was observed, which is probably related to the bottom erosion intensified by wind-wave action, bioturbations, and water-level fluctuations. In the profundal zone, the vertical distribution of 137Cs activity concentrations was undisturbed, which indicates stable sedimentation conditions in this part of Turawa Lake.

Research on the geochemical background values and evolution rules of lake sediments for heavy metals and nutrients in the Eastern China Plain from 1937 to 2017

For the first time, background quality guidelines have been developed for lake sediments along the Yangtze River. Evolution Rules of watershed environment in Eastern China were analyzed in 1937-2017. These methods of ¹³⁷Cs and ²¹⁰Pb radionuclide, 75% cumulative frequency, and background method were applied to calculate the sediment geochemical backgrounds (GB). The average GB values of Cu, Zn, Cd, Pb, Cr, total carbon (TC), total nitrogen (TN) and total phosphorus (TP) are 45.14 mg/kg, 86.99 mg/kg, 0.29 mg/kg, 33.71 mg/kg, 110.90 mg/kg, 17.20 mg/g, 1.60 mg/g, and 665.78 mg/kg, respectively. The radionuclide methods indicated that the sediment rate of 34 cm corresponding to 1963 is 0.63 cm yr^-1. The risk and accumulation of the sediment metals and nutrients in Yangtze Plain were uncontaminated levels before 1960, raised since 1980, and increased significantly in 2000. The Cd, TC, and TN in lake sediment were at low to moderate pollution, and few lakes are at high pollution. Sediment background values of the plain are different from soil background values in China and Consensus-Based Sediment Quality Guidelines in Europe/America. Results of sediment quality guidelines provide an important guidance for pollution prevention, environmental management, and risk assessment, especially the formulation of environmental laws.

Heavy metals and Pb isotopes in a marine sediment core record environmental changes and anthropogenic activities in the Pearl River Delta over a century

Heavy metal accumulation in marine sediments is associated with changes in both the natural environment and human activities. This study used heavy metals and Pb isotopes in a precisely dated (by ²¹⁰Pb and ¹³⁷Cs) sediment core from the Macao Sea to reconstruct the historical changes in anthropogenic activities and the environment in the western Pearl River Estuary (PRE). The distribution of heavy metals in the sediment core could be divided into four stages (pre-1950, 1950-1976, 1976-2000, and post-2000), which corresponded to the changes in anthropogenic activities and environment of the Pearl River Delta during the past 100 years. The contribution of anthropogenic metals (Pb and Zn) in the sediments increased gradually over time. However, the concentrations, enrichment factors, and fluxes of heavy metals in the sediments all displayed a downward trend since 2010, revealing a decline in metal pollutant input due to strict emission reduction policies implemented in the last decade. The Pb isotopes in the sediments showed a similar trajectory to the heavy metals, reflecting the changes in Pb sources in the sediments at different stages. Based on a binary Pb isotope mixing model, the calculated proportions of anthropogenic and natural Pb in the sediments were 0-50.9% (mean 15.9%) and 49.1-100% (mean 84.1%), respectively, suggesting that the Pb in the PRE sediments is mainly controlled by natural sources.

Evaluating the effectiveness of soil conservation at the basin scale using floodplain sedimentary archives

Evaluation of the spatial and temporal composition of floodplain sediments and soils is critical in the creation of soil management strategies for impacted riverine catchments. The objective of this study was to determine the distribution, and to identify the sources, of particulate trace elements and fallout radionuclides in the catchment of the River Avon (SW England), where sedimentary processes had been altered by reservoir construction in the 1950s. The catchment was compartmentalized into its main functional units namely, cultivated land, pasture, woodland, wet moorland, and channel bank. Surface soils were collected in each unit, along with four strategically-placed cores, all of which were analyzed for particle size, fallout radionuclides and elemental concentrations. Sediment particle sizes and sediment accumulation rates were affected by the construction of the reservoir, specifically the distributions of silt and clay. The concentrations of fertilizer constituent Cr and P were highly correlated in the mid-catchment but were unrelated downstream due to elevated concentrations of Cr from geological deposits. Copper, As, Pb and Sn had variable down-core distributions, with pulses in concentrations due to mining inputs. The contributions of the end-member sources of particulate elements in the sedimentary mixtures were evaluated, quantitatively, using a Bayesian Mixing Model and the cultivated land was identified as a significant contributor to the mixtures, independent of space and time. The results contribute to advances in soil quality and conservation measures as components of a catchment management plan for the Avon, an approach maybe applicable to other small catchments in the UK and internationally.

Radionuclides in sediments of the Aare and Rhine river system: Fallouts, discharges, depth-age relations, mass accumulation rates and transport along the river

The Aare-Rhine river system with its four nuclear power plants on the banks of these rivers and with its intermediate lakes and reservoirs provide the unique chance to analyze the input of radioactivity into the system thereby furnishing information on the sources, to analyze the transport within the sediment and along the rivers, and to refine unsupported ²¹⁰Pb dating validated by known discharge maxima. At three locations (Lake Biel, Klingnau Reservoir, old branch of the Rhine) in the Aare and Rhine rivers system downstream of the older nuclear power plants (NPPs) Mühleberg and Beznau, the vertical distributions of ¹³⁷Cs, ²¹⁰Pb, ²¹⁴Pb, ²¹⁴Bi, ⁴⁰K, ⁷Be, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Am, and ²³⁷Np in sediment cores were determined. Depth-age relations using the excess 210 Pb were established with the raw and with the piecewise Constant Rate Supply (CRS) models. A comparison of the piecewise CRS method with the imprints of known discharges showed differences of up to two years. Besides typical ¹³⁷Cs signals (about 100 Bq∙kg^-1) from the atmospheric nuclear weapons testing (NWT) and the Chernobyl fallouts, imprints of known ¹³⁷Cs discharges (10-70 Bq∙kg^-1) from the NPPs were found in the sediments. The ²³⁷Np distributions (6-10 Bq∙kg^-1) essentially follow the ¹³⁷Cs NWT distributions. In the sediment downstream the NPP Mühleberg (Lake Biel) a²³⁹Pu distribution (<3 Bq∙kg^-1) was found, which was solely due to the NWT fallout. Downstream the NPP Beznau (Klingnau Reservoir and an old branch of the Rhine), besides the NWT distribution, also imprints of ²³⁹Pu discharges (up to 7 Bq∙kg^-1) were found within the time interval 1963 to 1986.²⁴⁰Pu/²³⁹Pu ratios revealed that the burn-up times of the nuclear fuel in the NPP (²³⁵U enrichment of 3.5%), from which the discharges stem, should be about 1 year or less. A comparison between the calculated and the measured ¹³⁷Cs/²³⁹Pu ratio revealed no large discrepancies for the Lake Biel and Rhine positions, but in the Klingnau distribution, the calculated ¹³⁷Cs/²³⁹Pu ratio is one order of magnitude larger than the measured one. The reason could be either a natural uranium research reactor as the source, or strong, short-range ²³⁹Pu precipitation after the discharge from the Beznau NPP. The largest ²³⁹Pu peak in the Rhine sediment (1968/70) corresponds to no major peak in the Klingnau sediment. For the NPP Mühleberg discharge of 1982 the ratio of the ¹³⁷Cs deposition in sediments from Lake Biel, Klingnau Reservoir and the Rhine river is about 1 : 0.5 : 2.9. For the 1977/78 ²³⁹Pu deposition the ratio is 1 : 0.02, for the Klingnau Reservoir and the Rhine sediments, respectively. These numbers indicate a long-range transport of Cs and a rather short-range transport of Pu.

serac: an R package for ShortlivEd RAdionuclide chronology of recent sediment cores

Short-lived radionuclides are measured in surface sediment to provide a geochronology for the past century. Age-depth models are produced from ²¹⁰Pb_ex activity-derived sedimentation rates and corroborated by known events, such as ¹³⁷Cs and ²⁴¹Am activities that are result of fallout from nuclear weapon tests and the Chernobyl accident. Different methods of age depth modelling using such data require expertise in lake sedimentation processes. Here, we present a package, serac, that allows the user to compute an age-depth model and generate a graph, the age-depth correspondence in a text file, and metadata, using the free open-source statistical software R. serac ensures the reproducibility of age-depth or age-mass depth models and allows testing of several ²¹⁰Pbex models (CFCS, CIC, CRS, CRS piecewise) and sedimentation hypotheses (changes in sedimentation rates, presence of instantaneous deposits, varved sedimentation, etc.). Using several case studies, including lakes and lagoon in different environments, we demonstrate the use of the program in diverse situations that may be encountered. The rising number of sediment cores in recent palaeo studies and the need to correlate them require reproducible methods. serac is a user-friendly code that enables age model computation for the past century and encourages the standardisation of outputs.

Application of Non-Destructive Techniques on a Varve Sediment Record from Vouliagmeni Coastal Lake, Eastern Gulf of Corinth, Greece

During the last few decades, X-ray attenuation systems have been established as standard techniques in geosciences and as excellent scientific tools for the analysis of sedimentary facies and structures. In the present study, we use two non-destructive and high-resolution systems (computed tomography, X-ray fluorescence) to address all sedimentological facies and structural characteristics on a 6 m long, partly laminated sediment record, from Vouliagmeni lake, located at the eastern part of the Corinth Gulf, Greece. Vouliagmeni lake is the deepest coastal lake in Greece, and its location is of great importance since it is located in one of the most tectonically active regions in the world. The chronological framework of the retrieved sediment sequence spans the last 12,000 years, with alternations of laminated and non-laminated sections. The annual accumulation of the laminated sequences was determined through the radionuclide concentration of 14 samples. Scanning tomography was performed with a medical CT scanner and a μCT scanner, aiming to compare the potentials and variations of both methods. Lamination boundaries, event layers (turbidites) and sediment deformations were distinguished through processing the extracted 3D rendered volumes, after applying ranges depending on Hounsfield (HU) values. Microscopic analysis revealed three main layer types in the varve sequences that were examined, attributing to summer/spring, autumn and winter deposits. Statistical analysis of the elemental composition, magnetic susceptibility (MS) measurements and HU values revealed three clusters/facies, reflecting climatic and in-lake hydrological changes. Cluster A emulates sedimentation during arid conditions, while Cluster B reflects humid conditions with increased precipitation and erosion. Cluster C represents sequences with homogenous Ca-rich sediment. Our proposed workflow highlights the possible correlation between the non-destructive variables that were measured, but also the variations and applications of each method and software used during this study.