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1.
Seven cores were collected from different sediment zones of tidal flats at Xinyanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of 137Cs and 210Pb analysis were carried out for these cores. Sediment rates of the cores and radioisotopes distribution in surface sediment in different zones of the tidal flat were calculated from the 137Cs and 210Pb activities in sediments cores. The results indicated that each tidal zone had experienced different evolution phases, hydrological dynamics in the tidal flats made the grain-size of the surface sediment change gradually. 137Cs and 210Pb activities on the superficial layer of the cores varied spatially and the reason was discussed. On tidal flats, the fluctuation of 137Cs and 210Pb activities in the cores reflected the special sedimentary characteristics. Vegetation affects the grain-size distribution and the vertical profiles of 137Cs and 210Pb in the upper depths. 137Cs and 210Pb chronology got the comparable average sediment rates on the tidal flat. The characteristics of 137Cs and 210Pb in the cores reflected various depositional dynamical environments in different tidal zones and gave information on the different evolvement phases of the tidal zones. Based on the information of grain-size distribution, texture of the cores, sediment rates and topography, the evolution lines of the tidal flat were reconstructed.  相似文献   

2.
江苏北部潮滩沉积物中~(137)Cs和~(210)pb的分布特征(英文)   总被引：1，自引：0，他引：1  
Seven cores were collected from different sediment zones of tidal flats at Xin-yanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of ~(137)Cs and ~(210)Pb analysis were carried out for these cores. Sediment rates of the cores and radioisotopes distribution in surface sediment in different zones of the tidal flat were calculated from the ~(137)Cs and ~(210)Pb activities in sediments cores. The results indicated that each tidal zone had experienced different evolution phases, hydrological dynamics in the tidal flats made the grain-size of the surface sediment change gradually. ~(137)Cs and ~(210)Pb activities on the superficial layer of the cores varied spatially and the reason was discussed. On tidal flats, the fluctuation of ~(137)Cs and ~(210)Pb activities in the cores reflected the special sedimentary characteristics. Vegetation affects the grain-size distribution and the vertical profiles of ~(137)Cs and ~(210)Pb in the upper depths. ~(137)Cs and ~(210)Pb chronology got the comparable average sediment rates on the tidal flat. The characteristics of ~(137)Cs and ~(210)Pb in the cores reflected various depositional dynamical environments in different tidal zones and gave information on the different evolvement phases of the tidal zones. Based on the information of grain-size distribution, texture of the cores, sediment rates and topography, the evolution lines of the tidal flat were reconstructed.  相似文献   

3.
Sediment cores collected from six sites in Lake Baikal as part of an extensive investigation of sediment records of recent environmental change were dated radiometrically by 210Pb. Although the results obtained were in some respects comparable to those obtained by previous 210Pb studies, there were some significant differences. Most notably, a core from abyssal depths in the centre of the middle basin appeared to record at least wo major episodes of rapid sedimentation, possibly caused by turbidity currents. All cores, including those from the North Basin, contained significant records of weapons test fallout 137Cs, though these were of little chronological value due to the long residence time of 137Cs in the water column. Models and budgets for sediment and radionuclide transport through Baikal are presented and used to help validate the 210Pb results.  相似文献   

4.
A large seabird colony of northern fulmars (Fulmarus glacialis) at Cape Vera on Devon Island in the Canadian high Arctic has been shown to act as an effective biological pump, transporting large quantities of marine-derived nutrients and contaminants to the ponds beneath their nesting sites. Previous research has shown that seabirds also have the potential to elevate radionuclide concentrations in their immediate surroundings. Here, we assess the influence of the Cape Vera seabird colony on the 210Pb budgets of six affected ponds and one control site, and discuss potential implications with respect to 210Pb dating methodologies. In general, fluxes of 210Pb at Cape Vera were similar to, or less than, those measured at other Arctic locations not influenced by seabirds. Plots of unsupported 210Pb activity versus depth showed a number of non-monotonic features in all sediment cores, necessitating the use of the constant-rate-of-supply (CRS) model to derive age-depth profiles. We conclude that seabird activity has not dramatically increased the 210Pb flux to the ponds at Cape Vera. Overall, the low flux of excess 210Pb made accurate dating problematic for some of the study cores, necessitating the use of independent dating markers (e.g., 137Cs and PCB concentrations) to verify the reliability of the chronologies.  相似文献   

5.
We examine sediment distribution patterns in seven Florida lakes and discuss implications for paleolimnological studies of shallow, subtropical lakes. The study lakes are highly productive and should exhibit thick organic sediment deposits, but organic sediments are often grossly lacking because basins are shallow, and frequent mixing, lack of stratification, and warm temperatures lead to breakdown of organic material.Organic sediment distribution patterns are highly variable. We observe three types of distribution patterns. When organic sediments are abundant, there may be (1) uniform sediment distribution. In lakes lacking organic sediments, there are (2) distribution to deeper areas if present, or (3) distribution to peripheral areas and embayments when deep waters are absent. We advocate the use of systematic mapping surveys to locate optimal coring sites for paleolimnological studies of shallow, wind-stressed lakes. Because numerous factors affect diagenesis and sediment redistribution, sediment abundance and location are not predictable. Sediment chronologies may be discontinuous and disturbed even in accumulation zones. The extent to which sedimentary records are discontinuous or disturbed is not quantifiable in any practical manner. 210Pb and 137Cs radioisotopic profiles provide qualitative evidence of the degree of stratigraphic disturbance. Total excess 210Pb inventories show that sediments are focused into depositional zones when sediment distribution is uneven. Excess 210Pb inventories are not informative about the completeness of sedimentary profiles unless small inventories suggest discontinuous sedimentation or erosional events. We present examples of disturbed and undisturbed profiles, and discuss how we use radioisotopic and geochemical evidence, and multiple cores to assess stratigraphic continuity.Journal Series No. R-04815 of the Florida Agricultural Experiment Station.  相似文献   

6.
We examine the use of two alternative techniques for assessing the redistribution volumes of sorbed 137Cs within the upper components of the fluvial network, based on the concept of catchment as a lithodynamical system. In terms of one of them, we made a substantive analysis of changes in reserves on accumulative positions where the 137Cs distribution curves showed a significant increase in radionuclide content levels. We carried out a typization o the accumulation surfaces in order to extrapolate data, obtained for a group of soil profiles, to the territory of the entire catchment and to make a direct assessment of the increases in accumulation. An alternative technique was used to assess the volumes of accumulated sediment loads on accumulative positions by analyzing the 137Cs distribution curves, and to correlate with denudation zones in the drainage area under consideration. Values of the wash-out rates for the period 1986–2012 have been obtained, which are necessary for the formation of the accumulative layer observed. We calculated the volume of 137Cs swept away during 26 years after the Chernobyl accident, based on information regarding the volumes of initial reserves in the denudation zones and a correlation between the erosion rate and a specific reduction in reserves. It is established that the technique on the basis of analyzing the wash-out zones featuring high economical efficiency can be used in assessing 137Cs migration for larger territories with relatively low labor-consuming effort.  相似文献   

7.
在广东省东南部惠州市的黄洞水库中取得沉积物柱芯,对其样品做了210Pb 和137Cs 比活度分析、粒度分析和孢粉及炭屑分析,并收集了这一水库邻近气象站的降水数据,计算了1960 年以来的年降水量、夏季（6-9 月） 降水量和24 小时暴雨量。利用上述210Pb和137Cs比活度分析结果建立了沉积物剖面的年代框架,结合孢粉浓度、炭屑浓度与降水量计算结果,对沉积剖面的粒度变化做出了解译,并初步推测1960-2009 年间水库所在流域的土壤侵蚀变化情况及其原因。研究表明,在该亚热带丘陵地区植被覆盖度较高的自然条件下,侵蚀作用对降水量波动和植被（尤其是乔木、灌木等木本植物） 覆盖度变化的响应十分灵敏,水库沉积物的粒度变化在一定程度上可以反映流域内土壤侵蚀相对强度的变化。  相似文献   

8.
210Pb geochronologies should be validated with independent tracers such as 137Cs. In the cases with constant 210Pb activity in the topmost sediments, the presence of a distinct 137Cs peak within the 210Pb plateau has been used as a definitive demonstration of acceleration (increase in the sedimentation rate in recent years) versus fast mixing. Nevertheless, some limitations can be identified in the use of semiquantitative arguments, and a global understanding of the whole 137Cs activity profile is then required. Particularly, the incomplete mixing within the top sediment zone (described through the Incomplete Mixing Zone model) can explain quantitatively and simultaneously the 137Cs peak and the flattening in the 210Pb activity profile. This is demonstrated using selected examples from literature data. Thus, measured constant 210Pb activities in the top 6 cm of a sediment core from Lake Zürich. Nevertheless, they found 7Be only in the uppermost layer, the distinct 137Cs maximum at 6 cm depth, and undisturbed varves. The fast mixing seemed then opposed to common sense. The constant rate of supply model shows acceleration and it adequately matches the position of the 1963 137Cs peak. Nevertheless it fails to explain the whole 137Cs profile when handling time series of 137Cs atmospheric deposition. Finally, it is shown how the incomplete mixing of the activity (through the pore water) over a certain mass depth at the top sediment, with a finite value of the mixing coefficient, can quantitatively explain the whole activity versus mass depth profiles of 137Cs and 210Pb, and the presence of 7Be only in the uppermost sediment layer. A further validation of these ideas is presented from other literature data.  相似文献   

9.
Low-background gamma counting: applications for210Pb dating of sediments   总被引：1，自引：0，他引：1  
Sediment cores from three lakes were dated with210Pb using a constant rate of supply (CRS) model. We used low-background gamma counting to measure naturally occurring levels of210Pb,226Ra, and137Cs in sediment samples because sample preparation is simple and non-destructive,226Ra activity provides a direct measure of supported210Pb activity for each sample analyzed, and137Cs activity may provide an independent age marker for the 1962–1963 peak in atmospheric fallout of this radionuclide. In one core supported210Pb activity was estimated equally well from226Ra activity of each sampling interval or from the mean total210Pb activity of constant activity samples at depth. Supported210Pb activity was constant with depth in this core. In a short freeze core, determining226Ra activity of every sample proved advantageous in estimating supported210Pb activity because supported210Pb activity could be estimated from210Pb measurements only at the deepest sampling interval. Supported210Pb activity estimated from226Ra activity also yielded more precise estimates of highly variable sedimentation rates. In the third core226Ra activity exceeded210Pb activity at the top of the core and varied 20 fold with depth. This high input of226Ra in disequilibrium with210Pb is attributed to recent erosion of radium-bearing materials in the drainage basin. These data invalidate the assumption that supported210Pb activity is constant in sediment cores and can be estimated from the mean total210Pb activity at depths where210Pb activity is constant. We recommend using gamma counting or another independent assay of226Ra to validate the assumption of constant supported210Pb activity in sediment cores if there is reason to expect that226Ra activity varies with depth.This is the fourth of a series of papers to be published by this journal following the 20 th anniversary of the first application of210Pb dating of lake sediments. Dr. P.G. Appleby is guest editing this series.  相似文献   

10.
Reconstructing recent limnological history often relies on lead-210 dating to accurately ascribe a chronology to a sediment profile. In Lake Okeechobee, Florida, a large, shallow subtropical lake that may experience severe mixing, multiple dating methods are required to confirm that conformable sedimentation has been preserved and that the assumptions of the 210Pb method are satisfied. This study uses stratigraphic profiles of heavy metals, 137Cs, PCBs and pollen as independent dating markers to validate the sediment chronology as determined by 210Pb for three cores from the central mud zone of the lake. Unsupported 210Pb and most dating markers show distinct concentration/depth profiles, suggesting that the sediments have not been severely mixed for at least the last 75 years. Onset and maximum activity of the radioisotope 137Cs in the cores coincides with the 210Pb-dated interval of 1945–1970. This agrees well with the known timing of atmospheric deposition of 137Cs that resulted from above-ground nuclear testing during late 1940s until 1963. Sediment core profiles of atmospherically deposited metals such as Zn and Pb, which reflect regional increases during industrialization and decreases after regulation in the 1970s, exhibit expected concentration increases and peaks coinciding within 5–15 years of the predicted 210Pb dates. Uranium, a contaminant in some phosphate fertilizers, shows large concentration increases at core depths dated to be about 1950 by 210Pb, matching the intensification of agriculture after WWII. PCBs, which are expected to peak in the early 1970s, were measured in one core, and the observed peak corresponds to a 210Pb date of about 1960. Pollen makers were unable to verify specific events, but increases in disturbance taxa and declines in native types correspond generally with the expected dates assigned by 210Pb dating. Conformity between the 210Pb defined dates and independent markers of < ±15 years confirm that Lake Okeechobee sediments do preserve a sequential and reliable stratigraphic history of the lake, useful for reconstructing past limnological conditions.  相似文献   

11.
Sediment focusing in six small lake basins is inferred from sedimentary radionuclide profiles. The activities of137Cs and9+240Pu do not decrease to zero above the sub-surface maximum but tail off gradually. Similar behavior is observed in the sediments of three lakes for134Cs and60Co, which were added only to the lake. This upward tailing is not caused by bioturbation or erosion from the watershed. Sediment focusing is the likely cause, further substantiated by inventories in deep sediments of9+240Pu and210Pb that are twice as high as expected from atmospheric fallout. Inventories in deep sediments of137Cs are in several cases lower than expected from atmospheric fallout, and cannot be explained by hydraulic flushing from the lakes, as this would require unreasonable flushing rates. The low137Cs inventories and the sedimentary profiles of the137Cs/9+240Pu ratio are consistent with137Cs removal from the water column by boundary scavenging to shallow sediments. The profiles and inventories of all three nuclides could be reproduced with a simple three box model, assuming focusing of shallow sediments (50–60% of total sediment area) to deep sediments with a rate constant of 5–10% yr–1.This is the seventh of a series of papers to be published by this journal following the 20 th anniversary of the first application of210Pb dating of lake sediment. Dr P. G. Appleby is guest editing this series.  相似文献   

12.
210Pb and 137Cs dating methods in lakes: A retrospective study   总被引：1，自引：0，他引：1  
210Pb has been used for more than two decades to provide the geochronology of annually deposited sediments and to construct pollution histories. Evidence from some lakes suggests that this radionuclide may be adequately mobile to compromise dating reliability. This study provides one test of that possibility by comparing recent measurements of 210Pb and trace metals to ones carried out more than 20 yrs in the past. 137Cs dating is used to confirm sediment accumulation rates in the recent cores. In the three Connecticut, USA, lakes studied, sediment accumulation rates changed abruptly to higher values between 40-50 yrs ago (increasing by factors of 2.2, 2.9, and 3.0). In all three lakes, rates calculated from 210Pb distributions both above and below this horizon agreed, within measurement uncertainty, in recent and older cores. Furthermore, when the older data were corrected for 20 yrs of burial, the changes in slope in 210Pb distributions occurred at the same depth in each pair of cores. The depth of sharp peaks in concentrations of trace metals also matched. In general, this evidence supports the idea that sediments in these lakes have simply been buried, without significant diagenetic remobilization of 210Pb and trace metals . Nevertheless, some important differences were also observed. For two of the three lakes, there was a significant difference in average sediment accumulation rate during the past 33 yrs as calculated from 137Cs and 210Pb in the recent cores. Most potential causes for this difference can be ruled out, and it appears that one of the two nuclides is remobilized compared to the other. There were also significant differences in the total inventories of both 210Pb and trace metals (both up to 2 ×) between recent and older cores in some cases. This may be due to dissimilar sediment focusing, since it is not known for certain whether the new cores were collected at exactly the same sites as in the past.  相似文献   

13.
Sediment cores collected from eight lakes along the western coast of Svalbard as part of a project investigating atmospheric pollution and environmental change in Arctic regions were dated radiometrically using natural (210Pb) and artificial (137Cs and 241Am) fallout radionuclides. At four sites the sedimentation rates were relatively uniform, and in consequence the 210Pb dates were relatively unambiguous. At the remaining sites there were irregularities in the 210Pb activity versus depth profiles, indicating significant variations in the net sediment accumulation rate during the past 120 years. At these sites, there were significant differences between 210Pb dates calculated using the two standard simple dating models, constant rate of supply (CRS) and constant initial concentration (CIC). In most cases, stratigraphic dates based on the 137Cs and 241Am records supported use of the CRS model, though at one site (Ossian Sarsfjellet) the CIC model appeared more appropriate. The irregularities in the 210Pb records were mainly caused by episodes of accelerated sedimentation due, for example, to inwash or slump events, though at some sites there appears to have been a systematic increase in sediment accumulation rates in recent decades. Sediment accumulation rates were generally lower at the northern sites, and higher at the more southerly locations. Mean sediment accumulation rates varied by an order of magnitude, ranging from 0.002 to 0.050 g cm−2 y−1 (0.02–0.10 cm y−1). 210Pb fluxes measured from the core inventories were mostly in the range 34–80 Bq m−2 y−1 typical of Arctic sites. Much higher values, recorded at two sites (Birgervatnet and Daltjørna), may be due to significant inputs from the catchments during spring thaw.  相似文献   

14.
There is an important volume of published information on Lac Dufault (Québec) which describes the history of metal inputs over 70 years and the changes that occurred in the lake as a result of this contamination. We used this abundant source of chronological markers to test the hypothesis that lake sediments can provide true historical records of trace metal loading from metal mining. Sediment cores were obtained from the deepest zone of the lake (19 m). The sediments were dated using 210Pb and 137Cs and they were analyzed for total elemental concentrations (Ca, Cd, Cu, Fe, P, Pb, S, Zn). Metal profiles in the sediment core preserved the distinct signatures of different mine exploitations documented in the lake watershed. In particular, the core recorded: the beginning of industrialization in 1926; increasing sedimentation rates associated with perturbations in the lake watershed; the maximum of sediment [Cu] and the contemporary exploitation of ore bodies rich in Cu; the maximum of sediment [Fe] and the contemporary production of pyrite by a mining operation; the low sediment [Cu] and [Zn] in the 1950s and the low contemporary production of these metals by mining operations; the maximum of sediment [Cd] and the contemporary production of Cd by a subsequent mining operation. Anomalies in the distribution of 214Pb activities in sediments reflected the intensity of acid mine drainage (AMD). There is good evidence that the lake resisted acidification from this AMD for the last thirty years. Overall, our results support the thesis that profiles of sedimentary Cd, Cu, Zn, Pb and Fe levels reflect the past history of metal input to Lac Dufault.  相似文献   

15.
Low‐energy gamma ray spectroscopy has been employed to estimate floodplain sedimentation rates using measurements of 210Pb in floodplain alluvium. The utility of the technique is assessed through the analysis of excess (unsupported) 210Pb profiles in three sediment cores taken from the floodplain of the Labasa River on Vanua Levu in northern Fiji. A low‐energy germanium spectrometer (LEGe) was used for the nondestructive determination of excess 210Pb in a region cultivated intensively with sugarcane. Measured average historical (c. 25 years) vertical accretion rates are between 2.2 and 4.4 cm yr?1. The findings are broadly comparable with published sedimentation rates from analyses of radionuclide profiles elsewhere in the tropical South Pacific Islands, but the rates are higher than those measured previously at the same Labasa River sites using 137Cs profiles. Accelerated soil erosion owing to cane burning and land tillage seems to be largely responsible for sediment production, although flood‐related effects such as channel accretion by coarse bedload and the emplacement of large organic debris also influence floodplain sedimentation. However, application of the 210Pb technique in Fiji (and perhaps neighbouring island countries) is found to have serious drawbacks compared to the more robust 137Cs method, owing principally to the low 210Pb concentrations in the sandy alluvial sediment tested.  相似文献   

16.
We present 137Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth. 137Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken in the deep-water zone of each lake where sediment and 137Cs focusing would be expected. At all three locations, lake sediment 7Be and unsupported 210Pb (210Pbun) inventories are not significantly lower than the local reference inventory. 137Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that monovalent cations (especially Na+ and K+) replace 137Cs on exchange sites leading to the upward migration and loss of 137Cs. Rising sea levels may therefore contribute to remobilisation and release of 137Cs to the aquatic environment from the sediments of coastal lagoons.  相似文献   

17.
Although lake sediment archives are widely used for reconstructing historical records of atmospherically delivered pollutants, the quantitative relationship between fallout levels and their record in the sediments is complex and not well known. The original input signal from the atmosphere can be significantly distorted by mediating transport processes in the catchment, through the water column and within the sediments themselves. Since these processes also affect the fallout radionuclide 210Pb commonly used to date sediments, a better understanding of their impact is also important to improving the accuracy and reliability of sediment dating. Blelham Tarn has been the subject of a number of palaeolimnological investigations using radiometric dating techniques since the early 1970s. More recently it was the site of a major study carried out within the EU Transuranics project concerning the long-term fate of fallout radionuclides in catchment/lake systems. This paper reviews the radiometric data from this study and uses the results to determine mass balances for fallout 210Pb, 137Cs and 239+240Pu in Blelham Tarn, and their spatial distribution over the bed of the lake. Atmospheric fluxes were determined by measuring concentrations in rainwater and cumulative inventories in soil cores from non-eroding sites. Sediment records in a grid of 16 cores were used to determine the spatial distribution over the bed of the lake, and net inputs from the catchment. Mass balance calculations indicate that c. 47% of 210Pb in the sediments derives from erosive inputs from the catchment. For 239+240Pu the figure rises to 61%. Reduced amounts of 137Cs in the sediments are attributed to greater losses of this radionuclide from the water column via the outflow due to its greater solubility. Inputs of radionuclides from the catchment are concentrated near one of the major input streams. Away from this part of the lake the sediment record is dominated by direct atmospheric fallout, though the detailed pattern is influenced by sediment focussing. A one parameter catchment/lake transport model is developed that incorporates the assumption that transport rates will decline with time as fallout on the catchment diffuses into the soil and becomes less available for removal. Values of the transport parameter were calculated for 210Pb and 239+240Pu and found to be comparable. The results suggest that it will take c. 11000 years to remove 50% of 239+240Pu from the catchment to the lake.  相似文献   

18.
Spheroidal carbonaceous particles (SCP) from combustion of oil and coal have been quantified in cores from top sediments of Danish shallow lakes. Chronologies were provided by 210Pb-dating supplemented by measurements of other radionuclides (137Cs, 134Cs, 241Am). All cores show indications of sediment mixing but most still retain a characteristic SCP record. Deposition rates of SCP were low until the 1920s, increased strongly after World War II, reached maximum levels around 1970 and decreased thereafter. These results were used to infer a new chronology for a sediment core from a shallow lake, from which a 210Pb chronology had previously been published.SCP inventories are positively correlated with 210Pb inventories and dry matter accumulated since 1900, suggesting that absolute SCP accumulation rates may be more influenced by sedimentary processes than by atmospheric fluxes. The concentrations of SCP in surface sediments of the six lakes do, however, correlate with regional SO2 emissions.  相似文献   

19.
The Portil lagoon is a natural freshwater reservoir located at the southwest of Spain, near the coast. In its surroundings an important tourist complex has been developed since the earlier 1970s. This has resulted in increased loads of nutrients, specially during summer months. In order to evaluate the impact from humans on the lagoon caused by anthropogenic activities, we have determined vertical profiles of excess 210Pb and 137Cs in a sediment core taken from its bottom. Vertical profile of excess 210Pb seems to indicate that the sediment core was affected by large-scale mixing processes. Nevertheless this possibility was ruled out based on the shape of the 137Cs vertical distribution after modelling the 137Cs profile considering large-scale mixing. The chronology developed from 210Pb and 137Cs has allowed us to calculate the temporal evolution of the mass sedimentation rate during the last century. This mass sedimentation rate increased in 1973: from 0.08(2) g cm-2 a-1 in the period 1900-1973 to 0.17(5) g cm-2 a-1 in the period 1973-1995. This increase could be related to land-movements in the drainage area and to permitted sewage inputs into the lagoon, both with its origin in the growing/running of the surrounding tourist complex.  相似文献   

20.
We used sediment chronology data from fourteen published studies of lake cores across much of North America and Scandinavia in order to make a large scale comparison of the different dating techniques. The uncertainty of210Pb derived dates was determined using common sediment event markers: the stable Pb rise, the137Cs rise, and theAmbrosia pollen rise. For all data combined, the 95% confidence intervals for the stable Pb rise and theAmbrosia rise, were approximately 30 years. These 95% confidence intervals are slightly higher than those derived by First-Order Error analysis performed by others on210Pb derived dates. When comparing the concordance of two210Pb models (CRS and CIC) against markers of known history, we found that the CRS model dates (constant rate of supply) had consistently better agreement than the CIC model dates (constant initial concentration). Major discrepancies between137Cs and210Pb were common, but were consistently more severe in sediments of soft water lakes pointing to an inability of sediments with low mineral content to immobilize Cs.This is the ninth of a series of papers to be published by this journal following the 20 th anniversary of the first application of210Pb dating of lake sediments, Dr. P. G. Appleby is guest editing this series.  相似文献   

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