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91.
92.
P.G. Appleby E.Y. Haworth H. Michel D.B. Short G. Laptev G.T. Piliposian 《Journal of Paleolimnology》2003,29(4):459-473
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
93.
Concentrations of P and of heavy metals (Zn, Cd, Pb, Cu) were determined in sediment cores from the Peel-Harvey Estuary in Western Australia. Two cores were extracted, each representing one of the two basins of the estuary. Sediments were dated by surplus210Pb, by137Cs and by changes in the Fe/S ratio. Increasing exports of P from the mainly agricultural catchments have resulted in more than a doubling of both total P and acid extractable inorganic P in sediments of the estuary. Accumulation of P in the estuary is less than expected for complete retention of inputs of P from the major tributaries. Historical data show that since 1950 average concentrations of dissolved inorganic P have approximately doubled in the Peel Inlet and increased by times seven in the Harvey Estuary. Increases in concentrations in surface sediments of acid extractable Zn, Cd, Pb and Cu are noticeable in the Peel Inlet, and of Zn and Cd in the Harvey Estuary. The greatest increase, relative to background, is shown by Zn. Concentrations of extractable Zn and Cd in surface sediments are similar to those estimated from average concentrations in the water column for equilibrium adsorption to organic matter in sediments. Extractable Pb is greater than estimated for equilibrium adsorption to sediments. Extractable Cu is of the order of what can be expected for equilibrium adsorption to sediments in the Peel Inlet, but is less than expected in the Harvey Estuary. 相似文献
94.
95.
本文利用放射化学分析法测定了长江口及其邻近陆架沉积物中~(226)Ra和~(210)Pb的含量。结果表明,在该海区的沉积物中,~(226)Ra含量的水平分布随经度增加而直线下降,而~(210)Pb含量的水平分布则随经度增加而直线上升,二者形成明显的同步反向分布。 相似文献
96.
Sedimentary response to Late Quaternary sea-level changes in the Romagna coastal plain (northern Italy) 总被引:5,自引:0,他引:5
Data from 17 continuously cored boreholes, 40–170 m deep, reveal the subsurface stratigraphy of the Romagna coastal plain. Sedimentological and microfaunal data allow the distinction of eight facies associations of Late Pleistocene–Holocene age, including 18 lithofacies and 16 faunal associations. Ten 14C dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky BP of the last glacio-eustatic cycle. The eight facies associations can be grouped into lowstand, transgressive and highstand systems tracts. The upper part of the lowstand systems tract consists of alluvial plain deposits. These accumulated during the Late Pleistocene when the shoreline was ≈250 km south of its present-day position. A pronounced stratigraphic hiatus (between 25 and 8·8 ky BP) is invariably recorded at the upper boundary (transgressive surface) of these Pleistocene, indurated and locally pedogenized alluvial deposits. The succeeding postglacial history is represented by a well developed transgressive–regressive cycle. Transgressive deposits, interpreted to reflect the rapid landward migration of a barrier–lagoon system, include two wedge-shaped, paralic and marine units. These thicken in opposite directions and are separated by a ravinement surface. Above the transgressive deposits, the maximum flooding surface (MFS) marks the change from a transgressive barrier–lagoon complex to a prograding, wave-dominated delta system (early Po delta). The MFS can be traced landwards, where it constitutes the base of lagoonal deposits. An aggradational to progradational stacking pattern of upper delta plain (marsh), lower delta plain (lagoon/bay), and delta front (beach ridge) deposits reflects the progressive increase in the sediment supply/accommodation ratio during the following highstand. The alluvial deposits capping the sequence accumulated by the 13th century AD, in response to an avulsion event that caused abandonment of the former Po delta lobe and the northward migration of the Po River towards its present position. 相似文献
97.
鄱阳湖现代沉积210Pb测年模式的选择和沉积速率的变化 总被引:4,自引:3,他引:1
由于受到长江和入湖河流双重影响,鄱阳湖沉积可分为南部三角洲前缘、中部开阔湖和北部入江水道三个区域。按各区特点,采用了C.J.C.和C.R.S.不同计算模式,分别得出其沉积速率为0.52、0.16和0.34cm/a。湖区不同沉积地貌单元沉积速率的差异,受物源和水动力条件的影响:水下天然堤、漫滩、堤外洼地及开阔湖沉积速率分别为0.80、0.36、0.13和0.17cm/a。此外,三角洲的迅速伸长,河道分汊或改道,流域水土流失及大型水利工程等天然和人为活动也影响到沉积速率的时空变化。 相似文献
98.
Disequilibria between 210Po and 210Pb in surface waters of the southern South China Sea and their implications 总被引:1,自引:0,他引:1
Yang Weifeng Huang Yipu Chen Min Zhang Lei Li Hongbin Liu Guangshan Qiu Yusheng 《中国科学D辑(英文版)》2006,49(1):103-112
Activities of the naturally occurring radionuclides, 210Pb and 210Po, were measured in both dissolved (<0.45 μm) and particulate (>0.45 μm) phases from surface waters of the southern South
China Sea. The average activity of particulate 210Pb, 0.23 Bq/m3 (n=23), accounted for about 12% of the total 210Pb, which corresponds with values of open oceans. Particulate 210Po, with an average activity of 0.43 Bq/m3, accounted for about 40% of the total 210Po, which was much higher than those of open and eutrophic oceans. The residence times of total 210Po and 210Pb in surface waters estimated from an irreversible steady-state model were 0.82 a and 1.16 a, respectively. The consistently
high fractionation factor calculated either by scavenging rate constants (5.42) or Kd values (6.69) suggested that a significant fractionation occurred between 210Po and 210Pb during their removal from solution to particles and that the two radionuclides had different biogeochemical cycling pathways
in the oligotrophic South China Sea. Furthermore, our results indicated that there exist different fractionation mechanisms
between 210Po and 210Pb in different marine environments: in eutrophic ocean, plankton detritus and fecal pellets are the main carrier of 210Po and 210Pb, by which 210Po and 210Pb have been scavenged and removed; while in oligotrophic ocean, microbes could become the main carrier of 210Po and fractionate 210Po and 210Pb significantly as a result of scarce plankton detritus and fecal pellets. These results suggest the use of 210Po to trace marine biogeochemical processes relating to microbial activities and the cycling of sulfur group elements (S,
Se, Te and Po). 相似文献
99.
对南沙海域表层水中溶解态(<0.45 mm)和颗粒态(>0.45 mm)210Po和210Pb进行了研究. 结果表明, 南沙海域表层水中溶解态和颗粒态210Po平均比活度分别为0.61 Bq/m3(n = 24)和0.43 Bq/m3 (n = 23). 溶解态和颗粒态210Pb 平均比活度分别为1.66 Bq/m3 (n = 24)和0.23 Bq/m3(n = 23). 颗粒态210Pb比活度约占总210Pb比活度的12%, 与开阔大洋相应值吻合; 而颗粒态210Po占总210Po的比例约40%, 明显高于开阔大洋和富营养海域. 根据稳态不可逆模型得到总210Po和210Pb的停留时间分别为0.82 和1.16 a. 清除过程中210Po和210Pb的平均分馏因子由清除速率常数法和固-液分配系数法计算分别为5.42和6.69, 揭示了210Po和210Pb从溶解相清除至颗粒相的过程中发生了明显的分馏. 进一步的研究证明了南沙海域210Po和210Pb的分馏主要由微生物控制, 与富营养海域的分馏机制不同: 在富营养海域, 浮游植物颗粒和粪粒充当210Po和210Pb清除和迁出过程的主要载体, 210Po和210Pb的分馏主要发生于浮游植物颗粒和粪粒对两核素的清除过程; 在寡营养南沙海域, 由于浮游植物颗粒和粪粒的相对贫乏, 使微生物对210Po的清除作用相对突出, 并在此过程中使210Po和210Pb产生明显的分馏效应. 这与寡营养的马尾藻海的研究结果极为相似, 进一步证实寡营养海域和富营养海域210Po生物地球化学行为和循环路径的差异. 这表明210Po可能是研究与微生物有关的海洋学过程, 尤其是研究硫族元素(S, Se, Te和Po)生物地球化学循环的有用示踪剂. 相似文献
100.
广西钦州湾海岸带孢粉组合和沉积环境演变 总被引:2,自引:1,他引:1
对广西钦州湾海岸滩涂的4个钻孔的沉积物进行孢粉分析,结合 210Pb法测得沉积速率,讨论了该地区大约150年来的沉积环境演变规律.钦州湾地区具有19世纪中-末叶较现在偏凉的区域性气候; 20世纪初期西海岸沉积物中红树林花粉Rhizophora和Aegiceras锐减,反映出红树林滩衰退的特征; 60年代和70年代,钦州湾西海岸线明显向内陆迁移,高潮滩环境向低潮滩演化; 而80年代始,东海岸线由于钦江流域来沙的迅速堆积,沉积速率较高,岸线向海推移明显,沉积物中木本植物花粉和禾本科均有所增加,这和围垦修堤的人类活动加速了低潮滩向高潮滩演化有关.钦州湾总体表现出西向扩张,东向缩减的趋势. 相似文献