Sedimentation rates in the central lake constance determined with210Pb and137Cs

Sediment cores from central Lake Constance were dated with²¹⁰Pb and¹³⁷Cs. A sedimentation rate of (0.11±0.02) g·cm⁻²·y⁻¹ was determined with the²¹⁰Pb method.¹³⁷Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm⁻²·y⁻¹ and (0.08±0.01) g·cm⁻²·y⁻¹ respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the¹³⁷Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30–125 days residence times for suspended particulate matter were calculated from⁷Be measurements.     

Multiple dating of varved sediments from Lake Łazduny,northern Poland: Toward an improved chronology for the last 150 years

On two short sediment cores from Lake Łazduny (northeastern Poland) different methods for age estimation were applied including varve counting, ²¹⁰Pb, ¹³⁷Cs and OSL dating. The investigated sediment consists of finely laminated, organic-rich calcareous gyttja interrupted by a sand layer. For ²¹⁰Pb we tested the CFCS, CIC, CRS and SIT models and compared the results with the established varve chronology and the ¹³⁷Cs distribution. The total ²¹⁰Pb activity distribution is consistent between cores and shows a regular decrease with depth. However, the total inventory of unsupported ²¹⁰Pb was significantly different and indicates varying rates of sediment focusing. Our results show that all ²¹⁰Pb dating models used in this study produced different results, while the SIT model performed best in comparison with varve counts and ¹³⁷Cs peaks. The CFCS model produced a realistic age-depth trend but obtained ages were too old compared to the varve time scale. The age estimates provided by the CRS model were too old as well with an increasing offset downcore and the CIC model failed completely by producing an unrealistic chronology with age inversions. This confirms that only systematic testing of different ²¹⁰Pb dating models and routine validation using independent time markers produces reliable ²¹⁰Pb chronologies. OSL dating of two samples from the sand layer provided much too old results which indicate incomplete bleaching during deposition of the analyzed quartz grains. This multiple dating approach demonstrates the considerable potential but also potential pitfalls of dating such young sediments.     

Floodplain sedimentation rates in an alpine watershed determined by radionuclide techniques

Vertical profiles of the activities of ¹³⁷Cs and ²¹⁰Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm^?2 yr^?1 and were in good agreement with sedimentation rates calculated from the inventories of ¹³⁷Cs and ²¹⁰Pb. Sedimentation rates calculated from the position of the ¹³⁷Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of ¹³⁷Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the ¹³⁷Cs and ²¹⁰Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.     

137Cs湖泊沉积年代学方法应用的局限——以Crawford湖为例

＾１３７Ｃｓ湖泊沉积年代学方法是测定现代湖泊沉积物沉积年代和沉积速率的重要同位素年代学方法之一。对加拿大Ｃｒａｗｆｏｒｄ湖采集的沉积孔柱内＾１３７Ｃｓ垂直分布的研究发现,该方法给出时的标有明显偏差。比较＾２１０Ｐｂ和纹层等年代方法的结果,其１９６３年时标蓄积峰值所在位置明显移向表层,而作为１９５４年时标的该核素出现蓄积的层位则远早于该年沉积物蓄积层位。研究还表明,孔柱中较高的间隙水含量、缺少足以吸     

Pb-derived ages for the reconstruction of terrestrial contaminant history into the Mexican Pacific coast: Potential and limitations

²¹⁰Pb is widely used for dating recent sediments in the aquatic environment; however, our experiences working in shallow coastal environments in the Pacific coast of Mexico have demonstrated that the potential of ²¹⁰Pb for reliable historical reconstructions might be limited by the low ²¹⁰Pb atmospheric fallout, sediment mixing, abundance of coarse sediments and the lack of ¹³⁷Cs signal for ²¹⁰Pb corroboration. This work discusses the difficulties in obtaining adequate sedimentary records for geochronological reconstruction in such active and complex settings, including examples of ²¹⁰Pb geochronologies based on sediment profiles collected in two contrasting areas coastal areas (mudflats associated to coastal lagoons of Sinaloa State and the continental shelf of the Gulf of Tehuantepec), in which geochemical data was used to support the temporal frame established and the changes in sediment supply recorded in the sediment cores which were related to the development of land-based activities during the last century.     

Selected trace metals (As,Cd and Hg) distribution and contamination in the coastal wetland sediment of the northern Beibu Gulf,South China Sea

Contamination with As, Cd and Hg, their spatial and temporal distribution are reported from the coastal wetland sediments of the northern Beibu Gulf, South China Sea. The content of As, Cd, Hg and TOC in surface sediments is 8.1 ± 5.8 μg g^?1, 0.08 ± 0.14 μg g^?1, 0.034 ± 0.028 μg g^?1 and 0.45 ± 0.39%, respectively. The mean sedimentation rates are 0.93–1.37 cm year^?1 during 1920s to 2008 determined by ²¹⁰Pb and ¹³⁷Cs dating in three cores. The vertical profiles of As, Cd and Hg content in the cores retrieved from Qin and Nanliu River estuaries show increasing trends during 1985–2008 due to anthropogenic impact caused by local economic development. Locally the surface sediments have potential ecological risk of As to benthos according to the NOAA sediment quality guidelines.     

210Pb dating of a Loch Lomond sediment core by conventional and particle track methods and some geochemical observations

²¹⁰Pb dating of a short Mackereth core, from a suite characterised previously by palaeomagnetic and radiocarbon dating, has been performed using both conventional radiochemical and particle track methods. The latter involves total α and U assay using plastic detectors and untreated sediment pellets. Sedimentation rates determined by the two techniques are in good agreement (～22 mg cm^?2 y^?1), suggesting that the simpler particle track method has much to offer in routine sediment dating. The radiometric time scale is totally consistent with heavy metal profiles and the known industrial history of the surrounding area.     

Radioactivity in sediments of the Great Lakes: Post-depositional redistribution by deposit-feeding organisms

At two locations in southern Lake Huron (U.S.A.), twelve 35.5-cm diameter cores of fine-grained sediments were taken for comparison of the vertical distributions of²¹⁰Pb and falllout¹³⁷Cs with the distributions of benthic macroinvertebrates, mainly oligochaete worms (Tubificidae) and the amphipod,Pontoporeia affinis. Locations were selected on the basis of²¹⁰Pb distributions measured a year earlier which indicated contrasting depths of mixing of surface sediments. At one location the activity of²¹⁰Pb is uniform down to about 6 cm and 95% of total invertebrates occur within this zone; at the other location the zone of constant activity is only 3 cm deep but 90% of the invertebrates occur within it. Comparison of published tubificid defecation rates with sediment accumulation rates based on²¹⁰Pb shows that oligochaetes alone can account for mixing in one case while the effects of amphipods may be required in the case of shallower mixing. If mixing is represented as a diffusional process, eddy diffusion coefficients are at least 5.8 and 3.3 cm² yr^?1 at respective locations. In comparison with bioturbation, molecular diffusion is of minor importance in the post-depositional mobility of¹³⁷Cs. The necessity for introducing a diffusion coefficient varying continuously with depth is indicated by characteristics of the distribution of¹³⁷Cs. Biological reworking of near-surface sediments is an important process affecting radioactivity and chemical profiles in profundal deposits of this and probably other Great Lakes.     

Chronology of Holocene lacustrine sediments in Co Ngoin, central Tibetan Plateau

Lake sediments, in which abundant, continuous and high resolved signals are preserved, have the potential to recover the history of terrestrial environmental variation. The value of such paleo-environment signals depends firstly on tying them to accurate …     

Determining soil erosion rates on semi‐arid watersheds using radioisotope‐derived sedimentation chronology

This study investigates erosion dynamics of the past 90 years in three small semi‐arid watersheds with histories of grazing and vegetation change. Activity of ¹³⁷Cs and excess ²¹⁰Pb from 18 cores collected from sedimentation ponds were measured using a gamma spectrometer. The sediment was dated using a constant rate of supply (CRS) model. This study represents the first time that reservoir sediment accumulation rates determined from fallout isotopes have been verified by direct volumetric measurements of aggradation based on topographic surveys. Measured sedimentation in the ponds ranged between 1.9 and 2.3 cm y^?1, representing average sediment delivery rates from the watersheds of between 0.6 and 2.0 t ha^?1 y^?1. These sediment delivery rates were in agreement with those established by other methods for similar catchments in the region. Past variations in sedimentation rates were identified and correlated with recorded history of anthropogenic disturbance. ¹³⁷Cs and ²¹⁰Pb methods are suitable for use in arid environments and can complement each other to increase reliability of erosion rate estimates. The abundance of stock ponds in southwestern USA presents an opportunity to quantify historic erosion and sediment transfer dynamics in areas that have not been well studied or instrumented. Published 2016. This article is a U.S. Government work and is in the public domain in the USA     

Sedimentation in arctic proglacial lakes: Mittivakkat Glacier,south‐east Greenland

Several sediment cores were collected from two proglacial lakes in the vicinity of Mittivakkat Glacier, south‐east Greenland, in order to determine sedimentation rates, estimate sediment yields and identify the dominant sources of the lacustrine sediment. The presence of varves in the ice‐dammed Icefall Lake enabled sedimentation rates to be estimated using a combination of X‐ray photography and down‐core variations in ¹³⁷Cs activity. Sedimentation rates for individual cores ranged between 0·52 and 1·06 g cm⁻² year⁻¹, and the average sedimentation rate was estimated to be 0·79 g cm⁻² year⁻¹. Despite considerable down‐core variability in annual sedimentation rates, there is no significant trend over the period 1970 to 1994. After correcting for autochthonous organic matter content and trap efficiency, the mean fine‐grained minerogenic sediment yield from the 3·8 km² basin contributing to the lake was estimated to be 327 t km⁻² year⁻¹. Cores were also collected from the topset beds of two small deltas in Icefall Lake. The deposition of coarse‐grained sediment on the delta surface was estimated to total in excess of 15 cm over the last c. 40 years. In the larger Lake Kuutuaq, which is located about 5 km from the glacier front and for which the glacier represents a smaller proportion of the contributing catchment, sedimentation rates determined for six cores collected from the centre of the lake, based on their ¹³⁷Cs depth profiles, were estimated to range between 0·05 and 0·11 g cm⁻² year⁻¹, and the average was 0·08 g cm⁻² year⁻¹. The longer‐term (c. 100–150 years) average sedimentation rate for one of the cores, estimated from its unsupported ²¹⁰Pb profile, was 0·10–0·13 g cm⁻² year⁻¹, suggesting that sedimentation rates in this lake have been essentially constant over the last c. 100–150 years. The average fine‐grained sediment yield from the 32·4 km² catchment contributing to the lake was estimated to be 13 t km⁻² year⁻¹. The ¹³⁷Cs depth profiles for cores collected from the topset beds of the delta of Lake Kuutuaq indicate that in excess of 27 cm of coarse‐grained sediment had accumulated on the delta surface over the last approximately 40 years. Caesium‐137 concentrations associated with the most recently deposited (uppermost) fine‐grained sediment in both Icefall Lake and Lake Kuutuaq were similar to those measured in fine‐grained sediment collected from steep slopes in the immediate proglacial zone, suggesting that this material, rather than contemporary glacial debris, is the most likely source of the sediment deposited in the lakes. This finding is confirmed by the ¹³⁷Cs concentrations associated with suspended sediment collected from the Mittivakkat stream, which are very similar to those for proglacial material. Copyright © 2000 John Wiley & Sons, Ltd.     

Establishing a high-resolution surface sediment chronology with multiple dating methods – Testing 137Cs determination with Nurmijärvi clastic-biogenic varves

The uppermost 50 cm of sediments from the 23 m deep lacustrine basin of Nurmijärvi, a lake in south-central Finland, are composed of the clastic-biogenic type of varves. We use multiple dating methods to render a sediment chronology that is as precise and accurate as possible for future paleoenvironmental research on this high-fidelity sedimentary archive. The 250-year-long varve chronology contains a chronological error of ±2%, as estimated based on repeated varve counts. The varve-based chronology was verified with the vertical distribution of ¹³⁷Cs by comparing variations in the paleomagnetic relative declination of the surface sediments with instrumental observations and a calculated representation of declination features in Finland. A comparison of the sediment cesium content using two gamma counters, different sediment pretreatments, and normalization of the ¹³⁷Cs concentration with masses and accumulation rates of different sediment components revealed that the AD 1986 fallout peak from the Chernobyl accident is the dominant feature in the studied sediments, regardless of the sample pretreatment or normalizing procedure. The vertical distribution of the AD 1986 peak in sediments with clastic-biogenic varves is fairly narrow, thus providing an accurate age-depth marker for the recent deposits. However, the Nurmijärvi section also reveals a ca. 10-year-long period of catchment-to-basin ¹³⁷Cs mobilization and redeposition after the AD 1986 fallout, as well as significant downwards diffusion of the Chernobyl-derived cesium in the sediment. This study highlights the ways in which the quality of surface sediment chronology needs to be considered and secured prior to comparisons between paleoproxy records and instrumental observations.     

Use of fallout radionuclides as indicators of erosion processes

The different depth penetration characteristics of ¹³⁷Cs, ⁷Be and ²¹⁰Pb excess in undisturbed soils can be used to identify erosion processes by analysis of sediments derived from surface erosion. Caesium-137 concentrations (half-life 30 years) typically decrease to half the surface value at between 30 and 50 mm. Beryllium-7 (half-life 53 days) has half-penetration depths of between 0.7 and 10 mm, whereas ²¹⁰Pb excess (half-life 20.2 years) has half-penetration depths between 10 and 30 mm. Experiments designed to determine the applicability of these depth penetration characteristics to soil erosion studies are reported. Surface runoff was artificially generated at two locations in a grazed paddock using a rainfall simulator. Suspended sediment was extracted from runoff and analysed for natural and artificial gamma emitting radio-nuclides. Suspended sediment derived from sheet flow contained initially high values of ¹³⁷Cs, ⁷Be and ²¹⁰Pb excess. As the experiment continued ¹³⁷Cs concentrations remained high, but ⁷Be and ²¹⁰Pb excess value decreased with time. This is interpreted as indicating a change from sheet dominated erosion to rill dominated erosion. During a second experiment artificial rain was allowed to fall onto an eroded gully wall. The derived suspended sediment contained no detectable ¹³⁷Cs, ⁷Be or ²¹⁰Pb excess. Overland flow from above the gully wall was then allowed to run down the gully face and mix with the water falling directly onto the gully wall. There was no detectable change in the radionuclide signature, showing that the gully wall was the predominant source of sediment. This was tested independently by mass balance and ²²⁶Ra to ²³²Th ratios. The good correlation between ²¹⁰Pb excess and ⁷Be at this site suggests that the differential technique described here may be applicable over time-scales longer than are possible with ⁷Be. It may therefore be practical to examine catchment erosion history through analysis of ²¹⁰Pb excess and ¹³⁷Cs in sediment cores.     

210Pb et isotopes stables du plomb dans des sediments lacustres

²¹⁰Pb measurements were carried out on the sediments cores from a small south Belgian pond. In two cores, the²¹⁰Pb activity decreases exponentially with depth. Under various assumptions described in the article, the corresponding accumulation rates would be of the order of 60–100 mg/cm² of dried sediment per year.The stable lead content greatly increases from the older to the more recent sediment. This increase is accompanied by a change in isotopic composition: from the bottom to the top of the cores, the lead isotopic composition becomes progressively less radiogenic, reaching at the surface values identical to that for present atmospheric lead.     

Sedimentary processes in the inner New York Bight: Evidence from excess210Pb and239,240Pu

Particle-reactive radionuclides were determined in sediments from the inner New York Bight to trace transport and storage of fine-grained sediments and associated reactive materials. Seven sediment ? cores 20–50 cm in length were analyzed for water content, loss on ignition (LOI) and excess²¹⁰Pb; three of these were also analyzed for^239,240Pu. Excepting some depth horizons in a core from a dredge-spoil dumpsite, every sample analyzed contained excess²¹⁰Pb. Variations in the concentration of excess²¹⁰Pb with depth in the sediment at all stations correlated strongly with LOI, which apparently traces that fraction of the sediment which is active in removing reactive elements from the water column. In the cores analyzed for^239,240Pu, every sample contained finite Pu, and Pu concentrations correlated strongly with excess²¹⁰Pb.The radionuclide distributions may be simply viewed as products of steady-state sediment accumulation or of mixing. Geochemically reasonable accumulation rates are very high (0.5–2.6 g/cm² y) and could probably only be sustained by offshore transport of dumped materials. At the other extreme the relationships between excess²¹⁰Pb and LOI are compatible with rapid mixing of a²¹⁰Pb carrier phase (traced by LOI) into the pre-existing substrate with little or no actual accumulation. Other non-steady-state processes, such as sediment gravity flow, could also explain the observed distributions.Measured sediment inventories (dpm/cm²) of excess²¹⁰Pb and Pu at these stations are greatly in excess of those supportable by direct atmospheric deposition: lateral supply is required. Incorporation of sedimentary fines into the sand substrate could make the inner New York Bight an important repository of reactive materials.     

One century sedimentary record of Hg and Pb pollution in the Sagua estuary (Cuba) derived from Pb and Cs chronology

The vertical distribution of Hg and Pb were determined in a sediment core collected from the Sagua estuary (North Cuba) that receives input from the Sagua river, one of the most polluted rivers discharging into the Cuban coastal environment. Depth profiles of metal concentrations were converted to time-based profiles using the ²¹⁰Pb dating method and confirmed with the ¹³⁷Cs fallout peak. The mean mass accumulation rate was estimated to be 0.17 ± 0.04 g cm⁻² y⁻¹ (mean sediment accumulation rate 0.52 ± 0.13 cm y⁻¹) and the core bottom was estimated to date back about 130 years. The historical sedimentary record showed a strong enrichment of mercury concentrations in the past decades, caused by the incomplete treatment of industrial wastes from a chlor-alkali plant with mercury-cell technology in the Sagua river basin. Lead fluxes to sediments showed a gradual increase from the 1920s to present, which agrees with a population increase in Sagua la Grande City. Fluxes of both metals have increased the past 25 years, with values reaching a maximum of 0.5 and 3.9 μg cm⁻² y⁻¹ for Hg and Pb, respectively.     

Lake catchment based studies of erosion and denudation in the merevale catchment,Warwickshire, U.K.

Sediment yields estimated from contemporary stream monitoring of suspended sediment in the Merevale forested catchment, North Warwickshire, were compared with the sediment yield record obtained from analysis of lake sediment in the downstream reservoir. Total sediment volume and mass for nine periods since 1861 were calculated by extrapolation of synchronous levels in 54 cores, identified from magnetic susceptibility and other magnetic measurements, and by using ²¹⁰Pb and ¹³⁷Cs analysis to provide an absolute sediment chronology. Sediment yield estimated from the two methods show comparable but low (50-200 kg ha^?1 yr^?1) levels of sediment loss. While suggesting that lake sediments can be a useful means for extending the period over which contemporary monitoring exists, the study stresses the need for detailed historical records of land use and climate against which long term sediment yield records can be evaluated.     

Historic and contemporary sediment transfer in an upland Pennine catchment,UK

A sediment budget for an upland catchment–reservoir system at Burnhope Reservoir, North Pennines, UK has been developed. This provides a framework for quantifying historic and contemporary sediment yields and drainage basin response to disturbance from climate change and human activities in the recent past. Bathymetric survey, core sampling, ¹³⁷Cs dating and aerial photographs have been used to assess sediment accumulation in the reservoir. The average reservoir sedimentation rate is 1·24 cm yr^?1 (annual sediment yield 33·3 t km^?2 yr^?1 ± 10%, trap efficiency 92%). Mean annual reservoir sedimentation over the 67 year period has been estimated at 592 t ± 10%. Inputs of suspended sediment from direct catchwater streams account for 54% of sediment supply to the budget (best estimate yield of 318 t yr^?1 ± 129%), while those from actively eroding reservoir shorelines contribute 328 t yr^?1 ± 92%. Sediment yield estimates from stream monitoring and reservoir sedimentation are an order of magnitude lower than those reported from South Pennine reservoirs of comparable drainage basin area. Analysis of historical rainfall series for the catchment shows fluctuations in winter and summer rainfall patterns over the past 62 years. From 1976 to 1998 there has been a diverging trend between winter and summer rainfall, with a large increase in winter and a gradual decrease in summer totals. Periods of maximum variation occur during the summer drought events of the late 1970s, early 1980s and mid‐1990s. Analysis of the particle size of core sediments highlights abrupt increases in sand‐sized particles in the top 20 cm of the core. Based on the ¹³⁷Cs chronology, these layers were deposited from the late 1970s onwards and relate to these diverging rainfall records and rapidly fluctuating reservoir levels. This provides evidence of potential sediment reworking within the reservoir by rapid water‐level rise after drought. Copyright © 2008 John Wiley & Sons, Ltd.     

利用210Pb、137Cs和241Am计年法测算云南抚仙湖现代沉积速率

通过对云南抚仙湖沉积物柱芯样品的210Pb、137Cs和241Am测试表明,柱芯剖面上有明显的1963年和1986年137Cs蓄积峰,验证了1975年次级蓄积峰存在的可能性,这些峰形完好的蓄积峰对抚仙湖的现代沉积环境有明显的时标意义。利用137Cs计年法得到抚仙湖沉积物自1963年、1975年及1986年以来到2007年的平均沉积速率分别为0.063g/(cm2·a)、0.052g/(cm2·a)和0.039g/(cm2·a),说明了过去近五十年抚仙湖沉积速率整体上经历了一个由快到慢的过程。借助于241Am 的1963年蓄积峰可以提高137Cs计年的准确性。根据210PbCRS计年模式,计算出每个样品深度所对应的年代,与137Cs计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。通过质量深度和年代分析,抚仙湖的沉积速率变化幅度比较大,表明抚仙湖近129年来的沉积环境不稳定,可能与相应历史时期的人类活动有密切的关系。     

210pb as a chronometer and tracer,Burrinjuck Reservoir,Australia

Cores taken at Burrinjuck Reservoir in southeastern New South Wales have been dated using the first appearance of ¹³⁷Cs, charcoal/bushfire correlations, and annual grass pollen peaks. None of the main ²¹⁰Pb dating models reproduced the ‘known’ chronology. Correlation analysis shows no significant relationship between original ²¹⁰Pb (unsupp.) concentration and grain-size, sedimentation rate or loss on ignition. Differences in sediment source may explain the variations in ²¹⁰Pb. A simple provenance model has been used to interpret the ratio of original ²¹⁰Pb (unsupp.)/²²⁶Ra as a tracer of topsoils and subsoils. High ratios in the reservoir sediments probably indicate eroded topsoils and low ratios eroded subsoils.