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1.
210PBex沉积通量突发增大对湖泊生产力的指示--以程海为例 总被引：4，自引：0，他引：4
210Pb沉积计年的基本假设是大气沉降并经由湖水转入沉积物的210Pbex通量稳定.当沉积速率相对稳定时,沉积物中210Pbex的比活度将随沉积年代呈指数衰减.湖泊水体中的210Pbex主要随有机微粒的沉降而进入沉积物.如果湖泊水体中有机质沉积通量出现突发增大时,则可能显著地增大210Pbex被清洗而转入沉积物的通量.这种突发性清洗效应,一方面显然不符合210Pb沉积计年的基本前提; 另一方面可能指示湖泊水体初级生产力的明显变化.根据云南程海近代沉积物210Pbex垂直剖面的特殊变化,对这一问题进行讨论.沉积物柱芯于1997年6月采自程海深水湖区.137Cs比活度垂直剖面呈现出3峰特征,给出了可靠的计年结果并显示出近几十年间沉积物堆积的稳定性.而210Pbex比活度垂直剖面呈现出特异的峰值分布,并与Corg垂直剖面相似.这一现象可能与制约210Pbex转入沉积物的机制有关.程海沉积物中Horg/Corg和Corg/Norg原子比平均值分别为5.51和7.04,表明其有机质主要源于内生藻类残骸.根据沉积物有机质"沉降-降解-堆积"的3阶段特征,模拟计算出1970年以来有机碳Corg的沉积通量(F(Corg)).不同年代210Pbex的沉积通量(F(210Pbex))与F(Corg)显示出很好的同步关系.特别是1972～1974年和1986～1989年的两个时段,二者同步增大.F(Corg)的变化导致F(210Pbex)的变化; F (210Pbex)的变化在一定程度上反映出湖泊生产力的历史变化. 相似文献
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近百年来新疆博斯腾湖初级生产力的变化 总被引：2，自引：1，他引：1
本研究选择新疆博斯腾湖不同区域进行沉积岩芯采集.在210Pb、137Cs定年的基础上,利用漫反射光谱分析了湖泊沉积物中叶绿素a的含量,结合沉积速率、烧失量以及开都河的径流量记录等,探讨近百年来湖泊初级生产力的变化.结果表明:开都河的径流量变化对博斯腾湖沉积速率与生产力演化有一定影响,而人类活动干扰则是影响湖泊初级生产力演化的主要原因.1950s开始的新疆第一次大规模开垦活动导致了湖泊的沉积速率及初级生产力开始上升.沉积物的沉积速率以及叶绿素a的沉积通量在1970年左右出现最高值后下降,这与新疆的第二次大规模垦荒有关,同时,周边地区盐碱地除盐方式的改变对湖泊的生态环境变化也有很大影响.从1980s至今,由于流域内人类活动干扰增强,沉积物中的叶绿素a浓度逐渐增加,湖泊初级生产力呈上升的趋势. 相似文献
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湖泊沉积记录研究对了解流域侵蚀、揭示区域气候环境变化及人类活动影响、建立外生地球化学循环模式等均具有重要意义.放射性同位素~(210)Pb和~(137)Cs组合定年法是百年尺度湖泊沉积记录研究的首选方法,在过去几十年中得到了广泛应用,大力推动了湖泊沉积记录的高分辨率气候环境变化研究的开展.然而,如何理解和选择适用的计算模式来尽可能地提高定年准确度目前仍存在争议,这在一定程度上限制了该方法的应用.鉴于上述问题,本文基于本实验室近年来从青藏高原获取的若干支代表性湖芯的定年结果,从样品前处理、仪器及测试、数据分析及计算等全过程对~(210)Pb、~(137)Cs定年原理和方法进行了较为系统的阐述;在此基础上,提出了~(210)Pb定年样品封装原则,探讨了高纯锗γ谱仪在放射性活度测量中的影响因素,并建立了准确有效的比活度校正方法;明确指出了恒定初始浓度模式(constant initial concentration,CIC)可用于计算沉积物每层的年龄,而不是部分研究中认为的平均沉积速率,这对于深刻理解该定年模式并提供准确的定年结果具有重要的参考意义.同时,通过对比两种放射性核素的分布特征发现,相对于~(210)Pb而言,~(137)Cs更容易发生垂向迁移进而影响其时标准确性,这需引起研究者的充分重视,因此,当二者定年结果出现明显差异时,建议以~(210)Pb定年结果为准. 相似文献
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近百年来湖北太白湖沉积通量变化与流域降水量和人类活动的关系 总被引：12，自引：4，他引：8
湖泊沉积通量蕴含了流域降水量及人类活动的丰富信息.依据太白湖沉积岩芯210Pb定结果及CRS模式,建立了近百年来的沉积年代序列,对比分析了不同时期沉积通量变化与流域降水量及人类活动的关系.1900-1920、1928、1937-1942、1953-1954年沉积通量较高的四个时段,分别对应于夏季降水较多的1900-1920、1931、1938-1939、1954年,沉积通量增加主要与夏季降水量偏多,被带入湖泊的泥沙量增加有关.1958-1963年,太白湖流域上游兴建三座水库,对洪水及入湖泥沙起到了调蓄作用,自此之后,太白湖的平均沉积通量减小,降水量已不再是影响沉积通量的主导因素;1958-1970年沉积通量较高,主要是太白湖围垦导致的入湖泥沙量的增加及湖泊面积减小所致;1983-1993年沉积通量的增加则反映了农业生产方式由集体转为个体生产模式后,耕作业的快速发展所导致的水土流失的加重.研究结果证明,采用210Pb强度及CRS模式所建立的太白湖近百年来的沉积年代标尺精度较高(误差小于4年),太白湖沉积环境稳定,可采用其沉积指标进行流域及湖泊环境演化重建. 相似文献
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210Pbex沉积通量突发增大对湖泊生产力的指示 总被引：8，自引：0，他引：8
210Pb沉积计年的基本假设是大气沉降并经由湖水转入沉积物的210Pbex 通量稳定. 当沉积速率相对稳定时, 沉积物中210Pbex 的比活度将随沉积年代呈指数衰减. 湖泊水体中的210Pbex 主要随有机微粒的沉降而进入沉积物. 如果湖泊水体中有机质沉积通量出现突发增大时, 则可能显著地增大210Pbex 被清洗而转入沉积物的通量. 这种突发性清洗效应, 一方面显然不符合210Pb沉积计年的基本前提; 另一方面可能指示湖泊水体初级生产力的明显变化. 根据云南程海近代沉积物210Pbex 垂直剖面的特殊变化, 对这一问题进行讨论. 沉积物柱芯于1997年6月采自程海深水湖区. 137Cs比活度垂直剖面呈现出3峰特征, 给出了可靠的计年结果并显示出近几十年间沉积物堆积的稳定性. 而210Pbex 比活度垂直剖面呈现出特异的峰值分布, 并与Corg垂直剖面相似. 这一现象可能与制约210Pbex 转入沉积物的机制有关. 程海沉积物中Horg/Corg和Corg/Norg原子比平均值分别为5.51和7.04, 表明其有机质主要源于内生藻类残骸. 根据沉积物有机质“沉降-降解-堆积”的3阶段特征, 模拟计算出1970年以来有机碳Corg的沉积通量(F(Corg)). 不同年代210Pbex 的沉积通量(F(210Pbex ))与F(Corg)显示出很好的同步关系. 特别是1972～1974年和1986～1989年的两个时段, 二者同步增大. F(Corg)的变化导致F(210Pbex )的变化; F (210Pbex)的变化在一定程度上反映出湖泊生产力的历史变化. 相似文献
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高山湖泊吉仁错位于川西高原树线以上,受现代冰川融水补给影响.通过吉仁错沉积钻孔~(210)Pb/~(137)Cs定年和沉积枝角类和多环境代用指标分析,结合主成分分析和冗余分析等方法,高分辨率重建了近200 a来吉仁错枝角类组合和环境变化的过程.结果表明,尽管过去200 a来吉仁错枝角类组合一直以沿岸种为主,但仍经历了3个明显的变化阶段.1850 AD后,枝角类组合中Alonella nana、Chydorus sphaericus和Pleuroxus sp.的增加、以及Alona rustica和Alona guttata丰度的下降指示了水温和水体pH值的上升.1900 AD后枝角类通量的增高并不同步于组合的变化,指示了湖泊营养开始增加,这种不一致的变化分别代表了大气氮沉降和区域气候变暖的影响结果.多指标综合分析得出,过去150 a来,气候变暖和大气污染沉降通过直接和间接作用(流域冰川融水过程和植被土壤过程),较深刻地影响了湖泊物理过程(水温升高和无冰期加长)、营养过程(氮、磷营养升高)和酸碱平衡过程(碱性增强),改变了湖泊生物的生长季节,并通过促进藻类发育,最终引起了湖泊枝角类群落组合的变化和生物量的增加.1945 AD前后吉仁错枝角类与藻类群落结构和湖泊环境的同步变化,响应于持续增温背景下多环境过程的相互作用. 相似文献
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贵州红枫湖沉积物磷赋存形态及沉积历史 总被引：38，自引：4，他引：34
采集了云贵高原深水湖泊红枫湖现代沉积物未受扰动的柱状样品,通过分析不同形态沉积磷在沉积剖面上的分布特征,并结合沉积物样品柱的210Pb、137Cs年代学研究结果,揭示了红枫湖现代沉积过程中不同形态沉积磷的早期成岩改造的时间变化序列,以及沉积磷外源输入负荷的历史变化.采用Ruttenberg法分析沉积磷的地球化学赋存形态,研究表明,红枫湖沉积物中有机磷和铁结合态磷是沉积磷的主要赋存形态,分别占沉积全磷的60%和28%.沉积磷在垂直剖面上的分布特征显示,红枫湖现代沉积过程中,沉积磷在最终埋藏前可能发生非常剧烈的形态转化和再迁移,尤其是有机磷和铁结合态磷的成岩改造可能是湖泊系统磷循环质量平衡的重要方面.年代学数据同时表明,近年的人为活动导致湖泊系统(包括沉积物)磷负荷的显著增加. 相似文献
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乌梁素海大气重金属沉降入湖通量初步估算 总被引：1，自引：1，他引：0
重金属元素以大气颗粒物为载体,最终以沉降的方式进入湖泊水体,会引起湖泊的重金属污染.为调查大气沉降对乌梁素海重金属污染的贡献,于2013年7月1日至30日围绕乌梁素海进行大气沉降样品采集,分别测定Cu、Zn、Pb、Cd、Cr、Hg、As 7种重金属元素的含量,并在此基础上估算7月大气重金属沉降通量及入湖量.结果表明,乌梁素海重金属元素大气沉降通量大小依次为:ZnPbCuCrAsHgCd.结合社会调查情况及数据分析显示,大气微粒携带重金属借助风力迁移,较大的沉降通量出现在主风向的下风向区域,说明风向是影响乌梁素海大气重金属沉降通量的主要因素之一.排干输入与大气沉降方式下的乌梁素海重金属入湖量比较发现,大气沉降是除排干输入外湖泊的另一重要重金属污染源.Zn、Pb、Cu、Cr、As、Hg、Cd等重金属元素月入湖量分别为10.6、1.04、1.02、0.833、0.342、0.00514、0.00281t/月.通过估算底泥重金属增量来评价大气沉降对湖泊重金属的贡献表明,大气Hg、Zn、Pb、Cu、As、Cd、Cr等重金属沉降对湖泊贡献率分别为46.4%、44.7%、14.1%、12.0%、8.48%、4.75%、4.03%. 相似文献
11.
P. H. Santschi 《中国科学D辑(英文版)》2005,48(4)
Recent sediments in lakes and gulfs are a sensi-tive recorder of the information about environmentalchanges in the catchment areas during recent geologi-cal history. Precise determination of the ages of sedi-ments is the key to deciphering the environmental re-cords. The 210Pb dating technique and the markertechnique based on fallout radionuclide 137Cs havefound wide applications in sedimentation rate on atime scale of several tens to one hundred years, as wellas the varve chron… 相似文献
12.
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. 相似文献
13.
The GEF/UNDP/IMO/PEMSEA project identifies Manila Bay as among the marine pollution hot spots in the Seas of East Asia. 210Pb dating of its sediment can provide a historical perspective of its pollution loading. However, the validity of 210Pb dating in a complex dynamic coastal system of Manila Bay may come into question. Land-based sediment input can be high and physical and biological processes can possibly disturb the sediment layers. In this report, the 210Pb profiles of sediment cores from different parts of the bay are presented. The linear sedimentation rates are shown to be higher in the recent past and are also variable across the bay. The largest change in sedimentation rate, coincided with the occurrence of a volcanic eruption in 1991 and is shown by applying a variant of the CIC model in sedimentation rate calculations. The data suggest that 210Pb dating can be useful in estimating relative magnitudes of sedimentation rates, even in a complex dynamic coastal system like Manila Bay. 相似文献
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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. 相似文献
15.
Anthropogenic metal contamination and sapropel imprints in deep Mediterranean sediments 总被引：2，自引：0，他引：2
Angelidis MO Radakovitch O Veron A Aloupi M Heussner S Price B 《Marine pollution bulletin》2011,62(5):1041-1052
Sediment cores from the deep Balearic basin and the Cretan Sea provide evidence for the accumulation of Cd, Pd and Zn in the top few centimeters of the abyssal Mediterranean sea-bottom. In both cores, 206Pb/207Pb profiles confirm this anthropogenic impact with less radiogenic imprints toward surface sediments. The similarity between excess 210Pb accumulated in the top core and the 210Pb flux suggests that top core metal inventories reasonably reflect long-term atmospheric deposition to the open Mediterranean. Pb inventory in the western core for the past 100 years represents 20-30% of sediment coastal inventories, suggesting that long-term atmospheric deposition determined from coastal areas has to be used cautiously for mass balance calculations in the open Mediterranean. In the deeper section of both cores, Al normalized trace metal profiles suggest diagenetic remobilization of Fe, Mn, Cu and, to a lesser extent, Pb that likely corresponds to sapropel event S1. 相似文献
16.
Use of fallout radionuclides as indicators of erosion processes 总被引：1，自引：0，他引：1
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. 相似文献
17.
H. N. Erten H. R. von Gunten E. Rössler M. Sturm 《Aquatic Sciences - Research Across Boundaries》1985,47(1):5-11
210Pb- and137Cs-measurements, and varve counting have been used to date sediment cores from Lake Zurich (Switzerland). Two cores from different water depths were dated with210Pb/210Po and revealed sediment accumulation rates of (0.055±0.015) g·cm?2·y?1 and (0.09±0.03) g·cm?2·y?1, respectively. A comparable rate of (0.07±0.01) g·cm?2·y?1 has been obtained from137Cs measurements. These rates were confirmed by annual layer (varve)-counts which lead to rates of 0.07 g·cm?2·y?1. Constant210Pb activities were observed in the top 6 cm of the sediment cores. This constancy is generally explained in the literature by mixing processes caused by bioturbation and by distortion during coring operations of the uppermost water-rich fluffy sediments. However the distinct137Cs-maxima and the regular and undisturbed varve lamination of the top sediment observed in the cores of Lake Zurich contradict this assumption. In addition, measurements of7Be at the water/sediment interaces proved complete sediment core recovery and mechanically undisturbed sediments. Remobilization processes are assumed to cause the observed constant210Pb activities. Remobilization may also be the reason for an incomplete210Pb inventory in the sediments which contain only about 50% of the fallout from atmosphere. The results of the210Pb dating should therefore be considered with some care. If existent, varve counting represents the easiest and most reliable means for dating lake sediments. 相似文献
18.
The 210Pb dating method was first introduced by Goldberg (1963), and since then has been applied to study sediment from lakes, estuaries and coastal marine environments. Hundreds of studies around the world have used 210Pb as a geochronological tool in aquatic ecosystems. However little attention has been paid to the potential of this naturally occurring isotope as an environmental tracer of ecological events. Here we report three instances in which 210Pb profiles measured on undisturbed sediment cores from lakes, rivers and fjords show us the potential of 210Pb profile as a tracer of natural and anthropogenic processes. The methodology used here is a suite of techniques combining biogeochemistry (micro-electrodes), paleomagnetism (susceptibility), sediment characteristics (LOI) and visualization (SPI and X-ray) applied to the interpretation of 210Pb profiles. We measured 210Pb profiles on sediments from a river, Cruces River (Chile), which recorded a clear shift in the water chemistry caused by a pulp mill effluent to the river. Here metal mobilization and remobilization of the tracer may be the cause of the observed profile. We also measured 210Pb profiles in sediment from two fjords of Southern Chile (Pillan and Reñihue), the sudden deposition change of fresh 210Pb with depth observed could very well be the result of bioturbation but it occurred in a seafloor area deprived of bioturbators. In this case, 210Pb recorded the onset of aquaculture activities (fish farming) that took place two decades ago. Finally, 210Pb profiles measured in two lakes in the “pampa Argentina”: Epecuen and Venado showed a particular shape with depth. These profiles apparently registered a sudden depositional event with recent 210Pb material, probably related to strong shifts in precipitation and drought cycles in that part of the world. These three examples show that 210Pb profiles provide valuable information not only on geochronology, but also related to natural and anthropogenic short term processes, as shown here, but these are not always reported and well understood. 相似文献
19.
WU Yanhong WANG Sumin& HOU Xinhua . Key Laboratory of Lake Sedimentation Environment Nanjing Institute of Geography Limnology Chinese Academy of Sciences Nanjing China . Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China . Graduate University of Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2006,49(9):991-1001
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 … 相似文献