Lead-210 Dating Research Articles

Contributions of Organic and Mineral Matter to Vertical Accretion in Tidal Wetlands across a Chesapeake Bay Subestuary

Persistence of tidal wetlands under conditions of sea level rise depends on vertical accretion of organic and inorganic matter, which vary in their relative abundance across estuarine gradients. We examined the relative contribution of organic and inorganic matter to vertical soil accretion using lead-210 (210Pb) dating of soil cores collected in tidal wetlands spanning a tidal freshwater to brackish gradient across a Chesapeake Bay subestuary. Only 8 out of the 15 subsites had accretion rates higher than relative sea level rise for the area, with the lowest rates of accretion found in oligohaline marshes in the middle of the subestuary. The mass accumulation of organic and inorganic matter was similar and related (R2 = 0.37). However, owing to its lower density, organic matter contributed 1.5–3 times more toward vertical accretion than inorganic matter. Furthermore, water/porespace associated with organic matter accounted for 82%–94% of the total vertical accretion. These findings demonstrate the key role of organic matter in the persistence of coastal wetlands with low mineral sediment supply, particularly mid-estuary oligohaline marshes.

Reconstructing the History of Nutrient Loads and Sources in the Derwent Estuary, Tasmania, Australia, using Isotopic Fingerprinting Techniques

Carbon and nitrogen stable isotope analysis of estuarine sediment cores has proved useful for tracing nutrient sources and for assessing changes to nutrient loading through time. However, this technique has rarely been applied to estuaries in the Southern Hemisphere, despite the vulnerability of urban estuaries to excess nutrient loading and eutrophication because of mounting anthropogenic pressures. This study uses sediment core nutrient concentrations (total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP)) and stable isotope analysis (δ13C, δ15N, and δ34S) in combination with lead-210 (210Pb) dating, to reveal information about past and current nutrient loads and sources to various parts of the Derwent estuary, Tasmania, Australia. The upper estuary was found to experience periods of low dissolved oxygen levels and δ13C and δ15N values indicate that the nutrient sources to the upper estuary are predominantly riverine inputs and pulp and paper mill effluent. The middle estuary was found to have higher nutrient (TN and TP) concentrations than other Australian estuaries (Quibray Bay, Woolooware Bay, and Moreton Bay). Along the whole estuary there was a transition of predominantly terrestrial OM in upper estuary to predominantly marine OM in middle/lower estuary. However, there was a clear influence from a nitrogen source with an enriched δ15N value, likely wastewater treatment plant (WWTP) effluent. 3-endmember mixing analysis between terrestrial OM, marine OM, and WWTP effluent shows that WWTP effluent has contributed to up to 30.9% of sediment composition in the past—highlighting the significance of anthropogenic nutrient inputs, such as waste-water treatment plant effluent, to an urban estuary.

Impacts of land reclamation on tidal marsh ‘blue carbon’ stocks

Tidal marsh ecosystems are among earth's most efficient natural organic carbon (C) sinks and provide myriad ecosystem services. However, approximately half have been ‘reclaimed’ – i.e. converted to other land uses – potentially turning them into sources of greenhouse gas emissions. In this study, we applied C stock measurements and paleoanalytical techniques to sediments from reclaimed and intact tidal marshes in southeast Australia. We aimed to assess the impacts of reclamation on: 1) the magnitude of existing sediment C stocks; 2) ongoing C sequestration and storage; and 3) C quality. Differences in sediment horizon depths (indicated by Itrax-XRF scanning) and ages (indicated by lead-210 and radiocarbon dating) suggest a physical loss of sediments following reclamation, as well as slowing of sediment accumulation rates. Sediments at one meter depth were between ~2000 and ~5300 years older in reclaimed cores compared to intact marsh cores. We estimate a 70% loss of sediment C in reclaimed sites (equal to 73 Mg C ha−1), relative to stocks in intact tidal marshes during a comparable time period. Following reclamation, sediment C was characterized by coarse particulate organic matter with lower alkyl-o-alkyl ratios and higher amounts of aromatic C, suggesting a lower extent of decomposition and therefore lower likelihood of being incorporated into long-term C stocks compared to that of intact tidal marshes. We conclude that reclamation of tidal marshes can diminish C stocks that have accumulated over millennial time scales, and these losses may go undetected if additional analyses are not employed in conjunction with C stock estimates.

Radiocarbon and lead-210 age-depth model and trace elements concentration in the Wolbrom fen (S Poland)

Abstract A one-meter long peat core was taken from the peatland in Wolbrom (Silesian-Cracovian Upland, southern Poland). The analysis of the botanical composition showed that Wolbrom is a fen. Vegetation species such as Carex rostrata and Phragmites australis have been found. An age-depth model was constructed using 12 conventional radiocarbon dates and 13 lead-210 dates from the upper part of the deposit. In this work, the results of radiocarbon dating are presented. According to the model, we can estimate the age of the fen. The oldest part comes from a depth of 1.05 meter and its conventional age is 5940 ± 95 BP (modelled date 5000–4790 BC, 68.2% probability interval). The accumulation rate varies between approximately 0.53 mm·yr-1 and 6.48 mm·yr− 1. The core has been also tested for the presence of trace elements (Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) using ICP-OES. There are considerable variations in the concentrations of the tested metals – in many cases the concentration starts to rise at about 40 cm and may be connected with the human activity. This depth corresponds to the modelled age intervals 355–300 BC (17.4%) and 205–45 BC (50.7%).

Recent sedimentation rates in lakes in lower Yangtze River basin

This study attempted to quantify the lake sedimentation and its role in recording catchment soil erosion in the lower reaches of the Yangtze River basin, using cesium-137 ( 137Cs, anthropogenic) and lead-210 ( 210Pb, natural) dating. Six cores taken from five lakes, including the two largest lakes in the region (Taihu, Chaohu), were selected for understanding the change of sedimentation rates. High rates of sediment accumulation between the late 1920s and the late 1960s in the three lakes of the Qinyi-Shuiyang River basin showed good correlation with farmland change in adjacent counties, indicating enhanced human-induced soil erosion in the catchment. Chaohu Lake core to some extent also recorded catchment erosion, e.g., high flux in the late 1960s consistent with catchment disturbance. However, at Taihu Lake, sediment accumulation rates do not generally reflect catchment erosion history. Sediment accumulation rates of large shallow lakes in the lower Yangtze River basin do not accurately record soil erosion, whereas relatively small lakes may be sensitive to catchment disturbance.

Determining the History and Sources of Contaminants in Sediments in the Tamar Estuary, Tasmania, Using 210Pb Dating and Stable Pb Isotope Analyses

Environmental Context.Dating estuary sediments provides insights into the materials entering the estuary and can pinpoint when the contamination occurred. Heavy metal contamination is a known health risk but attributing it to a source can be contentious. For a sample sourced downstream of a city and a mining region, lead-210 dating and stable lead isotope analyses uncovered the sources of lead inputs. These methods quantified the extent that upstream mining activities and, for the first time, the extent that non-mining inputs (vehicles, industry) contributed to the estuary’s pollution. Abstract.210Pb dating and heavy metal analyses (Cd, Cu, Pb, Zn) have been combined to establish an historical profile of pollutant levels in sediments in the Tamar Estuary (Tasmania, Australia) over the past century. Heavy metal profiles through the core show a strong correlation with mining activities and industrialization during the past century, reflecting catchment disturbance in one of Australia’s earliest settled areas. A source apportionment of Pb in the sediment core using stable Pb isotope ratios (204Pb, 206Pb, 207Pb, 208Pb) shows that mine pollution has been contributing 10–25 mg kg–1 to Tamar Estuary sediments since the start of mining in the early 1890s, whilst non-mining inputs were not significant until post-1930 and became increasingly significant post-World War II. Since the 1950s–1960s, non-mining anthropogenic Pb inputs have become as significant as Pb from mining activities, although there does appear to be a decline in non-mining inputs during the past 20 years, which is consistent with findings elsewhere where reductions in atmospheric Pb levels have been observed and are attributed to the phasing-out of leaded gasoline. The source apportionment does, however, suggest that Pb from mine pollution at Storys and Aberfoyle Creeks continues to impact upon upper Tamar Estuary sediment quality.

Land-Ocean Systems in the Siberian Arctic, Dynamics and History

Land-Ocean Systems in the Siberian Arctic, Dynamics and History

Recent environmental changes inferred from the sediments of small lakes in Yellowstone's northern range

Recent sediments of eight small lakes in the northern winter range of Yellowstone National Park were cored to examine stratigraphic records of past changes in limnology and local environment that might be attributed to grazing and other activities of elk, bison, and other large ungulates. Cores of undisturbed sediment were analyzed at close intervals to depths covering the last 100–150 years according to chronologies established by lead-210 dating. Pollen analyses were made to show change in regional vegetation, and diatom and geochemical analyses were made to reveal possible limnological changes resulting from soil erosion and nutrient input from the lake catchments.

The calculation of lead-210 dates for McKay Lake sediments

Lead-210 dates are assigned to a sediment core retrieved from McKay Lake, Ottawa, Canada. Sediment mixing is found to have little, but discernible, influence on the age/depth profile. Consideration of mixing yields lower estimates of the derived ages, in agreement with the prediction based on a mathematical model. The inferred dates support the previous assignments based on Ambrosia horizon and the known occurrence of a catastrophic event. The procedures used in the calculation of the age profiles are fully described.

The history of airborne polycyclic aromatic hydrocarbons (PAH) and perylene as recorded in dated lake sediments

Polycyclic aromatic hydrocarbons (PAH) were analyzed in sediment cores from five small forest lakes in Finland. The catchments of the lakes were undisturbed (2 lakes) or only very slightly disturbed by human activity (3 lakes). None of the lakes had runoff delivery of PAH from their shores. Lead-210 dating of four lakes enabled the calculation of individual PAH fluxes over the past 100 to 150 yr. The sedimentary distribution of abiotic PAH in these lakes appears to be indicative of the development of combustion-generated energy production in Finland and adjacent countries. This development is reflected in an overall increase in sedimentary PAH since about 1850. After World War II the rate of accumulation of PAH continues to increase. The large variation between the PAH fluxes of different lakes indicates different trapping efficiencies and/or different preservation of the PAH compounds due to limnological differences between the lakes.

Evidence for a sedimentary siloxane horizon

Selected samples from two Puget Sound sediment cores have been analyzed for poly(organo)siloxanes(silicones). One core was 60 years old at 30-cm depth (ages by lead-210 dating) and showed no evidence for silicones there. The second, 15 years old at depth, exhibited silicones at depth. Clearly shown is evidence for a siloxane horizon in theses two cores, with the presence of the horizon directly related to the fact that silicones have been in widespread use only since World War II. All samples were analyzed by solvent extraction and diffuse reflectance Fourier transform infrared spectrometry. 10 references, 2 figures, 1 table.

Caesium-137 and lead-210 dating of recent sediments from Mondsee (Austria)

Mean annual sedimentation rates over the last 20–30 years were determined in the pre-alpine Mondsee (Upper Austria) using Cs-137 and Pb(Po)-210 profiles for sediment core dating and two natural sediment markers. Lower sedimentation rates of about 2–3 mm yr−1 were observed in the central part of the lake near the shore at 18–20 m and in the southern part at 30 m depth. Higher sedimentation rates of 4–7 mm yr−1 were found in the central part of the lake at 47 and 65 m and in the northern bay at 18 and 41 m depth. At both these sites the Pb-210 profiles were strongly disturbed in the upper zone of the sediment cores, whereas the Cs-137 pattern remained intact. The higher annual sediment accumulation rates can be explained only partly by deposition of allochthonous material discharged by the streams, enhanced eutrophication in these parts of the lake, erosion and sediment focusing by turbidity currents being also probable.

Long distance transport of anthropogenic lead as measured by lake sediments

Long-term atmospheric deposition of Pb has been measured using lake sediment cores. The average ‘whole-lake’ Pb burden was measured for several lakes in each of four regions located throughout Ontario and Quebec, Canada. Since the regions were remote to any point source of Ph, large scale variation in atmospheric transport could be studied. The results indicate that Pb deposition is highest in South-Central Ontario, where lake burdens ranged from 312 to 432 mg m−2, and that it decreases in an eastward direction into Quebec. Lowest deposition was at the site farthest north, Schefferville, Quebec, where fallout was 31 to 42 mg m−2, less than one-tenth of that previously observed in South-Central Ontario. Lead-210 dating of sediment cores from the northern site showed that input to these remote lakes has occurred over the same time period as in the southern sites.

Lead-210 dating of sediments compared with accumulation rates estimated by natural markers and measured with sediment traps

Methods to provide accurate accumulation rates for lake models are discussed. Cores were taken in 1979 in two basins of Lake Lucerne, Switzerland, and accumulation rates were calculated by using Pb-210 dating and by a natural landslide marker of 1795 in one basin (Weggis). In the other basin (Horw Bay) the sediment accumulation rates based on the lead method were compared with yearly sedimentation rates measured by sediment traps in 1969/70. At the Weggis station, the core dating yielded sediment accumulation rates of about 400 g dry wt. m−2 y−1 with the lead method, averaged over a sediment depth of 4–20 cm; accumulation was about 700 g dry wt. m−2 y−1 with the marker method, averaged over 0–33 cm. In Horw Bay, the trap method yielded about 1300 g dry wt. M−2 y−1 compared with 400–1000 g dry wt. m−2 y−1 obtained with the lead method and related to various depth intervals. The characteristic sources of error of the three methods as well as several hypotheses for these discrepancies are discussed.

Lead-210 dating of sediments compared with accumulation rates estimated by natural markers and measured with sediment traps

Methods to provide accurate accumulation rates for lake models are discussed. Cores were taken in 1979 in two basins of Lake Lucerne, Switzerland, and accumulation rates were calculated by using Pb-210 dating and by a natural landslide marker of 1795 in one basin (Weggis). In the other basin (Horw Bay) the sediment accumulation rates based on the lead method were compared with yearly sedimentation rates measured by sediment traps in 1969/70. At the Weggis station, the core dating yielded sediment accumulation rates of about 400 g dry wt. m−2 y−1 with the lead method, averaged over a sediment depth of 4–20 cm; accumulation was about 700 g dry wt. m−2 y−1 with the marker method, averaged over 0–33 cm. In Horw Bay, the trap method yielded about 1300 g dry wt. M−2 y−1 compared with 400–1000 g dry wt. m−2 y−1 obtained with the lead method and related to various depth intervals. The characteristic sources of error of the three methods as well as several hypotheses for these discrepancies are discussed.

Lead-210 dating of sediments compared with accumulation rates estimated by natural markers and measured with sediment traps

Methods to provide accurate accumulation rates for lake models are discussed. Cores were taken in 1979 in two basins of Lake Lucerne, Switzerland, and accumulation rates were calculated by using Pb-210 dating and by a natural landslide marker of 1795 in one basin (Weggis). In the other basin (Horw Bay) the sediment accumulation rates based on the lead method were compared with yearly sedimentation rates measured by sediment traps in 1969/70. At the Weggis station, the core dating yielded sediment accumulation rates of about 400 g dry wt. m−2 y−1 with the lead method, averaged over a sediment depth of 4–20 cm; accumulation was about 700 g dry wt. m−2 y−1 with the marker method, averaged over 0–33 cm. In Horw Bay, the trap method yielded about 1300 g dry wt. M−2 y−1 compared with 400–1000 g dry wt. m−2 y−1 obtained with the lead method and related to various depth intervals. The characteristic sources of error of the three methods as well as several hypotheses for these discrepancies are discussed.

Measurement of Whole Lake Sediment Accumulation and Phosphorus Retention Using Lead-210 Dating

Lead-210 dating was used to measure rates of sediment accumulation in 15 cores from Bob Lake, Ontario. The rate of accumulation was highly correlated with sample depth. This relation allowed the calculation of accumulation of sediments over the whole lake area. Phosphorus (P) retention was calculated from mean concentration of P in the sediments and the whole lake accumulation of sediment. Retention of P calculated in this way was similar to retention calculated from previously measured input and output of P.Key words: lead-210 dating, sediment accumulation, phosphorus retention

The calculation of lead-210 dates assuming a constant rate of supply of unsupported 210Pb to the sediment

The paper describes a method of calculating sediment age from 210 Pb profiles where changes in accumulation rate have affected initial 210 Pb concentration. Previously published age/depth profiles derived from 210 Pb measurements have assumed a constant initial concentration of unsupported 210 Pb per unit dry weight at each stage of accumulation, despite variations in accumulation rates. In sediments from three sites which have experienced rapid acceleration in accumulation in recent times, the assumption is not compatible with the measured unsupported 210 Pb concentrations. the alternative assumption of a constant rate of supply of unsupported 210 Pb to the sediments per unit time allows calculation of age throughout the profiles irrespective of evidence for rapidly accelerating accumulation. The methods of calculation used are outlined, illustrated and discussed in the light of evidence obtained from the sediments of Lough Erne and Lough Neagh, N. Ireland and lakes Ipea and Egari in the Highlands of Papua New Guinea. They provide a means of dating variations in accumulation rate resulting from human activity in the drainage basin. Es wird eine Methode zur Berechnung des Sedimentalters beschrieben, die auf 210 Pb-Profilen beruht, bei denen Veränderungen der Akkumulationsgeschwindigkeit die anfängliche 210 Pb-Konzentration beeinflußt haben. Frühere Alters-Tiefen-Profile aufgrund von 210 Pb-Messungen sind von konstanter Anfangskonzentration von 210 Pb im Trockengewicht in jedem Sedimentationsstadium ausgegangen, obwohl Unterschiede in den Akkumulationsraten berücksichtigt werden. In Sedimenten von den Standorten mit großer Beschleunigung der Akkumulation in jüngerer Zeit ist diese Annahme nicht mit der gemessenen 210 Pb-Zufuhr je Zeiteinheit erlaubt dagegen eine Altersberechung unabhängig von der stark beschleunigten Akkumulation. Die Berechnungsmethoden werden erläutert und diskutiert anhand der Befunde an den Sedimenten der nordirischen Lough Erne und Lough Neagh sowie der Seen Ipea und Egari im Hochland von Papua Neu Guinea. Sie stellen ein Hilfsmittel zur Datierung unterschiedlicher Sedimentationsraten in Abhängigkeit von menschlicher Aktivität in den Einzugsgebieten dar.