Pb Flux Research Articles

Historical trends of anthropogenic metals in sediments of Jiaozhou Bay over the last century

Reconstructing heavy metal historical trends are essential for better understanding anthropogenic impact on marine ecosystems. In this work, the ecological risk and sources of Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb in Jiaozhou Bay were studied and the anthropogenic metal emissions was also quantified. The ecological risk was mainly caused by Cd, As and Cu, which presented an increasing trend with increased anthropogenic activities since the 1950s. The statistical analysis show that Cr, Mn, Ni, Cu and Zn were primarily from natural sources. Cadmium and Mn might originate from both natural and anthropogenic sources. Arsenic and Pb were sourced from agricultural activities and atmospheric precipitation, respectively. The anthropogenic flux of Cr, Mn, Ni, Cu, Zn, As, Cd and Pb were 138, 586, 63, 66, 161, 35, 0.31 and 44 mg/m2/a since the 1950s. Over 40.0% of Cu and As were quantified from anthropogenic emissions since the 1950s.

Applying of Modified Constant Rate of Supply Model to Lake Sediments in <sup>210</sup>Pb Dating and Assessment of Some Heavy Metals

In present study, Lead-210 (Polonium-210) activity concentrations were indirectly obtained by utilizing alpha spectrometry. Sediment chronology was determined by using modified CRS model. Average sediment accumulation rates are 0.351, 0.324, 0.222 g cm -2 y -1 in S-1, S-2, S-3 stations respectively. With reference to atmospheric 210 Pb flux (29 mBq cm -2 y -1 ) Lake Karagol has extra outer 210 Pb input (soil erosion) from the catchment area. In terms of Enrichment Factor (EF), heavy metal concentrations are lower than the anthropogenic values. So it can be said that the elements except Au originate from the continental supply. Au has unexpectedly too high level EF value (58.22) in northern station (S-1) of the Lake Karagol. It corresponds to time interval from 2004 to nowadays. However Pollution Load Index (PLI) says different consequences from the EF values. PLI value has only baseline levels of pollutants in northern part of the Lake Karagol as it shows progressive deterioration of the site for southern part of the Lake Karagol.

Temporal evolution of lead isotope ratios and metal concentrations in sediments of the north Aegean Sea, in Turkish coast

In present research, fifteen surficial and two profile sediment samples were studied in terms of sediment chronology and pollution degree on the ground of pollution indexes such as enrichment factor (EF), contamination factor (CF), Pollution Load Index (PLI) and lead isotope ratios (206Pb/207Pb, 208Pb/206Pb). Lead-210 (polonium-210) activity concentrations were measured by utilizing alpha spectrometry. Sediment chronology was determined via modified CRS mathematical model. Average mass accumulation rates are 0.301 and 0.227 g cm−2 year−1 in Bakircay River mouth and Ayvalik offshore stations respectively. Mass accumulation rates do not display the systematic increases along the cores from bottom layers to top layers. In Bakircay River mouth station 210Pb flux is higher than the range of global atmospheric 210Pb flux value. Due to the high CF and EF values of Sr both of stations have hydrothermal features. Ayvalik offshore station has displayed Na, Cd pollution since 1945, but Na, Cd, As, Mo, Ag pollutions have existed in Bakircay River mouth station since 1983 in terms of CF and EF values. According to PLI index, Bakircay River mouth station has “starting level pollution” degree and it displayed an “acute corruption” in 1981. 206Pb/207Pb ratios range from 1.17 to 1.25, 208Pb/206Pb ratios range from 1.99 to 2.16 in study area. When 206Pb/207Pb and 208Pb/206Pb ratios are evaluated with together, it is seen that both of the stations have had the natural (geologic) sediments since 2011.

Pollution characteristics of atmospheric dustfall and heavy metals in a typical inland heavy industry city in China

Through field sampling of atmospheric dustfall in regions of Zhuzhou City, China for a period of one year, the deposition fluxes of atmospheric dustfall and five heavy metals contained inside, including Cr, As, Cd, Hg and Pb, were analyzed. Meanwhile the enrichment factor and index methods were used to analyze the pollution characteristics of heavy metals of atmospheric dustfall in Zhuzhou. The annual deposition flux of atmospheric dustfall in Zhuzhou was 50.79 g/(m2·year), while the annual deposition fluxes of Cr, As, Cd, Hg and Pb were 9.80, 59.69, 140.09, 0.87 and 1074.91 mg/(m2·year), respectively. The pollution level of atmospheric dustfall in Zhuzhou was relatively lower compared with most other cities in China, but the deposition fluxes of As, Cd, Hg and Pb in atmospheric dustfall in Zhuzhou were much higher than that in most cities and regions around the world. Cd is the typical heavy metal element in atmospheric dustfall in Zhuzhou, and both the enrichment factor and pollution index of Cd were the highest. Cd, Hg, Pb and As in atmospheric dustfall were mainly from human activities. According to the single-factor index, Nemerow index and pollution load index analyses, the atmospheric dustfall in Zhuzhou could easily cause severe heavy metal pollution to urban soil, and the most polluting element was Cd, followed by Pb, As and Hg. Only the pollution level of Cr lay in the safety region and mainly originated from natural sources.

Evolution of structure and superconductivity in Ba(Ni1−xCox)2As2

The effects of Co-substitution on Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ ($0\leq x\leq 0.251$) single crystals grown out of Pb flux are investigated via transport, magnetic, and thermodynamic measurements. BaNi$_2$As$_2$ exhibits a first order tetragonal to triclinic structural phase transition at $T_s=137 K$ upon cooling, and enters a superconducting phase below $T_c=0.7 K$. The structural phase transition is sensitive to cobalt content and is suppressed completely by $x\geq0.133$. The superconducting critical temperature, $T_c$, increases continuously with $x$, reaching a maximum of $T_c=2.3 K$ at the structural critical point $x=0.083$ and then decreases monotonically until superconductivity is no longer observable well into the tetragonal phase. In contrast to similar BaNi$_2$As$_2$ substitutional studies, which show an abrupt change in $T_c$ at the triclinic-tetragonal boundary that extends far into the tetragonal phase, Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ exhibits a dome-like phase diagram centered around the first-order critical point. Together with an anomalously large heat capacity jump $\Delta C_e/\gamma T\sim 2.2$ at optimal doping, the smooth evolution of $T_c$ in the Ba(Ni$_{1-x}$Co$_x$)$_2$As$_2$ system suggests a mechanism for pairing enhancement other than phonon softening.

Retraction: Estimation of sediment accumulation rates using naturally occuring 210Pb models and heavy metal measurements in Gülbahçe Hydrothermal Vent Zone

In this study, sediment chronology was determined by using Lead-210 (210Pb) dating models in Gulbahce Bay. Sediment cores were obtained via a gravity core sampler from hydrothermal area and also from reference point and surficial distribution of Polonium-210 (210Po) was investigated in the study area. The average surficial 210Po concentration was relatively higher in hydrothermal area than the reference point. Sedimentation rates in Core reference point (RN) displayed an increase till the 1940’s and a decrease afterwards, sedimentation rates in any core from hydrothermal area did not exhibit regular continuous increase or decrease. The 210Pb fluxes measured from core inventories are close to each other but they are a bit higher than the average mediterranean and mean atmospheric 210Pb flux values. This situation indicates that there are outer contribution to the study area apart from atmospheric precipitation of 210Pb concentration. Average enrichment factors indicating that the sediments have not been co...

Anthropogenic Signatures of Lead in the Northeast Atlantic

AbstractAnthropogenic activities have resulted in enhanced lead (Pb) emissions to the environment over the past century, mainly through the combustion of leaded gasoline. Here we present the first combined dissolved (DPb), labile (LpPb), and particulate (PPb) Pb data set from the Northeast Atlantic (Celtic Sea) since the phasing out of leaded gasoline in Europe. Concentrations of DPb in surface waters have decreased by fourfold over the last four decades. We demonstrate that anthropogenic Pb is transported from the Mediterranean Sea over long distances (>2,500 km). Benthic DPb fluxes exceeded the atmospheric Pb flux in the region, indicating the importance of sediments as a contemporary Pb source. A strong positive correlation between DPb, PPb, and LpPb indicates a dynamic equilibrium between the phases and the potential for particles to “buffer” the DPb pool. This study provides insights into Pb biogeochemical cycling and demonstrates the potential of Pb in constraining ocean circulation patterns.

Atmospheric heavy metal deposition in agro-ecosystems in China

Atmospheric deposition has become one of the main sources of heavy metals in crops in developed and industrial zones in China for the past several years. However, lack of data of the agro-ecosystems on the vast areas of China makes it difficult to assess the impacts of air pollution on the heavy metal accumulation in crops. In this study, with deposit samples from 67 sites located at different agro-ecosystems (typical, factory nearby, town nearby, roadside, and remote) of four natural regions [Huanghuai (HH), Southeast (SE), Southwest (SW) and upper-mid Yangzi River (Up-mid YR)], atmospheric heavy metal deposition in agro-ecosystems on a large scale in China was studied. The results showed that during the growing season, the deposition fluxes of Cr, Ni, As, Cd, and Pb in typical agro-ecosystems were 0.60-36.86, 0.65-25.37, 0.05-8.88, 0.12-5.81, and 0.43-35.63μgm-2day-1, respectively, which varied greatly between the four different regions. The average deposition fluxes of Cr, Ni, Cd, and Pb in the HH region, as well as the fluxes of As in the SW region, were significantly higher than those in the SE region. Heavy metal deposition rates among agro-ecosystems were very similar, except for the sites around cement factory in flat HH region. In mountainous SW region, however, deposition rates varied widely with sites nearby towns relatively higher and remote regions much lower. Higher correlation coefficients were observed between Cr, As, Pb, and Ni deposition rates, suggesting that they had similar sources. Samples from the SW and SE regions exhibited higher 207Pb/206Pb and 208Pb/206Pb ratios than those from the HH and Up-mid YR regions. Airborne Pb in SW agro-ecosystems were mainly derived from vehicle exhaust and local smelting, whereas that in the HH region from burning of northern Chinese coal.

Historical evolution of heavy metal pollution and recent records in Lake Karagöl sediment cores using 210Pb models, western Turkey

In present study, Activity concentrations of 210Pb (Polonium-210) were indirectly determined by utilizing alpha spectrometry. Sediment chronology was obtained by using 210Pb (CF; CS, CRS, CIC) models and corrected via residence time of the 210Pb in each core for Lake Karagol. Average residence times of the 210Pb is 6.5, 4.8, 5.3 months and average sedimentation rate is 0.366, 0.322, 0.237 cm year−1 in S-1, S-2, S-3 stations respectively. According to atmospheric 210Pb flux (24 mBq cm−2 year−1) and 210Po/210Pb ratio values, we determine the soil erosion in the lake catchment. The ranges of ratios in the sediment cores obtained from Lake Karagol are 1.4–1.3, 1.5–1.2, 1.3–1.1 in S-1, S-2, S-3 stations respectively. In terms of Enrichment Factor, heavy metal concentrations are lower than the antropogenic values. So we can say that the elements originate from the continental supply. In other words there is not metal pollution in the lake.

Influence of saline groundwater discharge on river water chemistry in the Athabasca oil sands region – A chloride stable isotope and mass balance approach

A chloride mass and stable isotope (δ37Cl) balance approach was employed to calculate the effect of saline groundwater discharge into the Athabasca and Clearwater rivers in the Athabasca Oil Sands Region (AOSR) in north-eastern Alberta, Canada. Saline groundwater affected by halite, carbonate, and anhydrite dissolution discharges Na-Cl type water with total dissolved solids (TDS) up to 51,700 mg/L from exposed Devonian and Cretaceous units in the river valleys in this area. In this study, nine springs discharging groundwater with a median Cl concentration of 9800 mg/L were sampled and chloride stable isotope ratios were determined, with δ37Cl values ranging from 0.2 to 1.0‰. In contrast, river waters had historical monthly median Cl concentrations between 5.9 and 49.5 mg/L and δ37Cl values between −2.2 and −1.4‰. The discharge rate of saline groundwater was calculated to be 100 ± 20 L/s into the Clearwater River and 134 ± 68 L/s into the Athabasca River. The chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions, metals, and PAHs in the Athabasca and Clearwater rivers. Overall, saline groundwater contributed less than 0.2% of river discharge, but 0.04–39% of major ion concentrations in the rivers, with highest contributions under winter low-flow conditions. In the Clearwater River, saline groundwater contributed 23–39% of average monthly Cl flux and 18–32% of average monthly Na flux. For the same major ion fluxes in the Athabasca River, saline groundwater contributed 12–18% and 6–12%, respectively. The influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible, contributing less than 1% of river fluxes of Cu, Ni, Pb, and Zn. Similarly, the influence on mass flux of PAHs in the rivers was found to be negligible (<0.03%) but quantifiable. These results provide important insights on the natural contributions of saline groundwater discharge to river chemistry in the AOSR, a necessary factor to consider when monitoring for anthropogenic effects of oil sands development on river water quality.

7Be, 210Pb and 40K depositions over 11 years in Málaga

The monthly bulk depositional fluxes of three natural radionuclides (7Be, 210Pb and 40K) were measured at a Mediterranean coastal station (Málaga) over an 11-year period from 2005 to 2015. The mean annual depositional fluxes of 7Be, 210Pb and 40K were 1215, 144 and 67 Bq m−2 year−1 respectively, showing a clear seasonal trend with minimum values recorded during summer and maximum values in winter. The rainfall regime with dry summers allows estimating the dry deposition. Assuming constant dry deposition through each year, 7Be, 210Pb and 40K would account for 12.5, 26.5 and 33% of the bulk fallout respectively which indicates that deposition for 210Pb and 40K are significantly higher than 7Be. The precipitation-normalized enrichment factor alpha used to explain seasonal variations in the depositional fluxes of radionuclides with respect the rainfall, indicates higher depositional fluxes during spring and summer than expected from the amount of rainfall. Despite their different origin, 210Pb and 7Be monthly depositional fluxes have strong correlation. The atmospheric deposition fluxes of 7Be, 210Pb and 40K were controlled mainly by the amount of rainfall (r = 0.89, 0.91 and 0.66 respectively). Moreover, principal component analysis was applied to the datasets and deposition of radionuclides and rainfall in the same component highlighting the importance of the washout mechanism. The mean depositional velocity of aerosols evaluated using 7Be and 210Pb are similar and are compared to other published values.

Weathering fluxes and sediment provenance on the SW Scottish shelf during the last deglaciation

The reconstruction of past ice sheet dynamics can inform on long-term ice stream activity, and in turn provide constraints on the response of modern ice sheets to climate change. The Hebrides Ice Stream (HIS) flowed across part of the western Scottish shelf to the shelf-break during the last glacial cycle. To investigate the deglacial dynamics of the HIS following the Last Glacial Maximum (LGM), lead (Pb) isotope records were extracted from the FeMn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of HIS during its retreat. These provide, respectively, relative timing of glacially weathered inputs to the marine environment and some source information on the eroded sediments. The FeMn oxyhydroxide fraction is dominated by pre-formed particles and shows a marked decrease from radiogenic at ~21cal ka to less radiogenic Pb isotope compositions towards 15.4–13ka. This decrease represents a reduction in the flux of subglacially-derived radiogenic Pb to the continental shelf, and it is interpreted as the result of the break-up of the ice-stream in western Scotland around that time. The Pb, Sr and Nd isotopic signatures of the detrital fraction indicate a preponderance of fine sediments originated from the NW Highlands throughout the period studied (~21 to 15cal ka BP), most likely dictated by the orientation of tidal and oceanic current directions and sediment delivery. Both fractions show inversion of the 208Pb/204Pb ratio relative to the other Pb isotope ratios. This is observed only in one core site in the detrital fraction, and extended to all cores in the FeMn oxyhydroxide fraction. This behaviour highlights the influence of ocean currents in restricting the detrital but encouraging dispersal of the FeMn oxyhydroxide signal. Periodic increased contributions from a high Th/U source, potentially the neighbouring Archaean amphibolitic Lewisian basement in the Outer Hebrides, are proposed as the source of these 208Pb/204Pb inversions. This study demonstrates how geochemical investigation on continental shelves can be used to constrain the activity and flow sources of palaeo-ice streams, and the utility of combining detrital and FeMn oxyhydroxides to determine the combined influence of the continental sources of material and their dispersal in the marine environment.

Atmospheric deposition of trace elements at urban and forest sites in central Poland – Insight into seasonal variability and sources

This paper includes the results of chemical composition of bulk deposition samples collected simultaneously at urban (Poznań city) and forest (Jeziory) sites in central Poland, between April 2013 and October 2014. Rainwater samples were analyzed for trace elements (As, Zn, Ni, Pb, Cu, Cr, Cd) and physicochemical parameters. Overall, three metals, i.e. Zn, Pb and Cu were the most abundant anthropogenic constituents of rainwater samples from both locations. In Poznań city, the rainwater concentrations of trace elements did not differ significantly between spring and summer. However, they were elevated and more variable during the cold season (fall and winter), suggesting strong contribution from local high-temperature processes related to coal combustion (commercial and residential sector). In contrast to the urban site, relatively low variability in concentrations was found for Cu, Ni, Zn at the forest site, where direct impact of emission from vehicle traffic and coal-fired combustion (power plants) was much lower. The bulk deposition fluxes of Ni, As, Pb and Zn at this site exhibited a clear trend, with higher values during the cold season (fall and winter) than in spring and summer. At the urban site, the sums of total bulk deposition fluxes of Zn, Cu, Pb, Ni, As, Cr, Cd were as follows: 8460.4, 4209.2, 2247.4, 1882.1, 606.6, 281.6 and 31.4μgm−2. In addition, during the winter season, a significantly higher deposition fluxes of Cu and Zn were observed for rain (on average 103.8 and 129.4μgm−2, respectively) as compared to snow (19.7μgCum−2 and 54.1μgZnm−2). This suggests that different deposition pattern of trace elements for rain, mixed and snow was probably the effect of several factors: precipitation type, changes in emission and favorable meteorological situation during rain events.

Recent 210Pb, 137Cs and 241Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)

Over the past 50 years, 210Pb, 137Cs and 241Am have been abundantly used in reconstructing recent sediment and peat chronologies. The study of global aerosol-climate interaction is also partially depending on our understanding of 222Rn-210Pb cycling, as radionuclides are useful aerosol tracers. However, in comparison with the Northern Hemisphere, few data are available for these radionuclides in the Southern Hemisphere, especially in the South Indian Ocean. A peat core was collected in an ombrotrophic peatland from the remote Amsterdam Island (AMS) and was analyzed for 210Pb, 137Cs and 241Am radionuclides using an underground ultra-low background gamma spectrometer. The 210Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (137Cs and 241Am) that are related to nuclear weapon tests. We compared the AMS 210Pb data with an updated 210Pb deposition database. The 210Pb flux of 98 ± 6 Bq·m−2·y−1 derived from the AMS core agrees with data from Madagascar and South Africa. The elevated flux observed at such a remote location may result from the enhanced 222Rn activity and frequent rainfall in AMS. This enhanced 222Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The 210Pb flux at AMS is higher than those derived from cores collected in coastal areas in Argentina and Chile, which are areas dominated by marine westerly winds with low 222Rn activities. We report a 137Cs inventory at AMS of 144 ± 13 Bq·m−2 (corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere.

Constraining the Spatial Extent of Marine Oil Snow Sedimentation and Flocculent Accumulation Following the Deepwater Horizon Event Using an Excess 210Pb Flux Approach.

Following the Deepwater Horizon (DWH) event in 2010, there were several lines of evidence indicating the presence of marine oil snow sedimentation and flocculent accumulation (MOSSFA). A significant amount of marine oil snow formed in the water column of the northern Gulf of Mexico (nGoM), settled rapidly, and ultimately accumulated in the sediments of the nGoM. This study utilized a commonly used radioisotope tracer (excess 210Pb, 210Pbxs) from 32 sediment cores collected from 2010 to 2013 to characterize the spatial extent of MOSSFA on the seafloor. Relative to pre-DWH conditions, an increase in 210Pbxs flux occurred in two distinct regions: (1) in the western portion of the study area on an east-northeast to west-southwest axis, stretching 230 km southwest and 140 km northeast of the DWH wellhead, and (2) in the eastern portion of the study area on a 70 km northeast to southwest axis near the DeSoto Canyon. The total sedimentary spatial extent of MOSSFA, as calculated by increased 210Pbxs flux after 2010, ranged from 12 805 to 35 425 km2. 210Pbxs flux provides a valuable tool for documenting the spatial extent of MOSSFA following DWH and will continue to aid in the determination of advective transport and ultimate depocenters of MOSSFA material.

Biogeochemistry of Lead. Its Release to the Environment and Chemical Speciation.

Lead (Pb) is a metal that is not essential for life processes and proves acutely toxic to most organisms. Compared to other metals Pb is rather immobile in the environment but still its biogeochemical cycling is greatly perturbed by human activities. In this review we present a summary of information describing the physical and chemical properties of Pb, its distribution in crustal materials, and the processes, both natural and anthropogenic, that contribute to the metal's mobilization in the biosphere. The relatively high volatility of Pb metal, low melting point, its large ionic radius, and its chemical speciation in aquatic systems contributes to its redistribution by anthropogenic and natural processes. The biogeochemical cycle of Pb is significantly altered by anthropogenic inputs. This alteration began in antiquity but accelerated during the industrial revolution, which sparked increases in both mining activities and fossil fuel combustion. Estimates of the flux of Pb to the atmosphere, its deposition and processing in soils and freshwater systems are presented. Finally, the basin scale distribution of dissolved Pb in the ocean is interpreted in light of the chemical speciation and association with inorganic and organic particulate matter. The utility of stable radiogenic Pb isotopes, as a complement to concentration data, to trace inputs to the ocean, better understand the biogeochemical cycling of Pb and track water mass circulation in the ocean is discussed. An ongoing international survey of trace elements and their isotopes in seawater will undoubtedly increase our understanding of the deposition, biogeochemical cycling and fate of this infamous toxic metal.

Contaminated sediment dynamics in peatland headwater catchments

Despite substantial research into Pb storage in peatlands, formal description of the mechanisms of contaminated sediment mobilisation is limited. This study explores the controlling factors of contaminated sediment dynamics in an eroding peatland in the Peak District National Park, UK. This study uses the Pb contamination stored near the peat’s surface as a fingerprint to trace contaminated sediment dynamics in three severely degraded headwater catchments. A field portable XRF analyser was used across a range of catchment surfaces to examine patterns of contaminant storage and release. Lead concentrations varied greatly over a small spatial scale. Erosion is exposing high concentrations of Pb on interfluve surfaces (up to 1660 μg g−1), and substantial amounts of reworked contaminated material (up to 1010 μg g−1) are stored on other catchment surfaces (gully walls and floors). A variety of factors have been shown to significantly control Pb release and storage in this environment, including wind action, aspect, and gully depth. Vegetation also plays an important role in retaining sediment-bound heavy metals within contaminated peat catchments. This study provides the first comprehensive overview of the mechanisms controlling Pb release and storage in degraded peatlands. Previous assessments of Pb fluxes may have underestimated contaminant export from severely degraded systems. Wind has also been identified as an as yet unaccounted for vector for heavy metal transport in peatland environments.

Historic and Industrial Lead within the Northwest Pacific Ocean Evidenced by Lead Isotopes in Seawater

We report the continued lead (Pb) contamination of the Northwest Pacific Ocean in 2002 and present the first comprehensive Pb isotope data set for that region. In the upper ocean, a Pb concentration maxima (64-113 pmol kg-1) extended throughout the entire North Pacific Subtropical Gyre (NPSG). We determined most of the Pb in this feature was from industrial emissions by many nations in the 1980s and 1990s, with the largest contributions from leaded gasoline emissions. In contrast, the deep water (>1000 m) Pb concentrations were lower (6-37 pmol kg-1), and constituted a mix of background (natural) Pb and anthropogenic Pb inputs from preceding decades. Deep water below the Western Subarctic Gyre (WSAG) contained more industrial Pb than below the NPSG, which was attributed to a calculated 60-fold greater flux of particulate Pb to abyssal waters near the Asian continent. Assuming Pb isotope compositions in the North Pacific Ocean were homogeneous prior to large-scale 20th century anthropogenic inputs, this evidence suggests a relatively faster change in Pb isotope ratios of North Pacific deep water below the WSAG versus the NPSG.

Variations in the transport, distribution, and budget of 210Pb in sediment over the estuarine and inner shelf areas of the East China Sea due to Changjiang catchment changes

AbstractTo investigate the impact of changes in the Changjiang catchment on the estuarine coast‐shelf sedimentary system, variations in the transport, distribution, and budget of 210Pb in the sediment of the Changjiang subaqueous delta (CSD) and the Zhejiang‐Fujian coastal mud belt (ZFCMB) system were analyzed before and after the impounding of the Three Gorges Dam (TGD). The results indicate that the 210Pbex activity in the surficial sediments of the CSD‐ZFCMB decreased significantly after 2003 and that the surficial and vertical distribution of the 210Pbex activity in the CSD changed substantially due to intensified sediment redistribution. The 210Pb contribution of the Changjiang catchment to the CSD‐ZFCMB is not negligible. Due to the trapping effect of the TGD, 76 ± 49% of the 210Pb supply from the Changjiang upstream areas was retained in the TGD, resulting in the 210Pb flux into the sea decreased substantially. Furthermore, our findings demonstrate that the cross‐shelf plume provides a major conduit for the transport of 210Pb over the East China Sea. The variation in the 210Pb budget in the sediment of the CSD‐ZFCMB also indicated that the influence of Changjiang catchment changes on the 210Pbex and supported 210Pb activities will become more significant in the future. In addition, the rate of 210Pb burial in the sediments of the ZFCMB decreased, whereas the retention index of 210Pb and the amount of 210Pb retained in the CSD increased significantly, suggesting that after 2003, the material transfer function of the CSD weakened.

Estimating Recent Sedimentation Rates Using Lead-210 in Tropical Estuarine Systems: Case Study of Volta and Pra Estuaries in Ghana, West Africa

The Volta River and its basin form about one-third of Ghana's total land area and contributes significantly to the hydrological network of the country’s river system while River Pra basin is noted for large and small scale mining activities within it. Both river systems are important for sediment delivery for beach nourishment along Ghana’s coast. This work presents the first ever estimates of the sedimentation rates at the estuaries of these rivers using 40 cm long sediment cores. Sediment accumulation rates were estimated using the 210Pb sediment dating technique which is based on alpha and gamma emitting radionuclides. The total 210Pb concentration in the sediment was measured with an alpha spectrometer while the activities of supported 210Pb and 137Cs were measured with a gamma spectrometer with high germanium n-type detector. The unsupported 210Pb was determined by subtraction of the supported from the total at each core sediment level. Irregularities in the 210Pb activity versus depth profile, indicated variation in the net sedimentation accumulation rate during the past 96 and 182 years at the Volta and Pra estuaries, respectively. From the CRS model calculations, sedimentation rates varied markedly before (1.1 gcm-2y-1) and after (0.5 gcm-2y-1) construction of the Akosombo dam resulting in about 50% drop in sedimentation rate at the Volta estuary. Sediment accumulation rates were relatively low at the Pra estuary compared to the Volta estuary. Depositional fluxes of 210Pb were 190.1 ± 15.9 Bqcm-1y-1 and 217.8 ± 11.8 Bqcm-1y-1 in Pra and Volta estuaries respectively. 137Cs profile did not show defined peaks. However, the ages and sedimentation rates were better explained using historical events and anthropogenic activities that occurred within the catchment areas, providing a better understanding of deficit in sediment budget caused by hydric erosion processes prevailing in the Ada and Keta beaches in Ghana, due to reduction of sediment input from the Volta estuary.