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1.
《地理学报(英文版)》2019,(10)
Wind-driven soil erosion results in land degradation, desertification, atmospheric dust, and sandstorms. The Hunshandake Sandy Land, an important part of the Two Barriers and Three Belts project, plays important roles in preventing desert and sandy land expansion and in maintaining local sustainability. Hence, assessing soil erosion and soil accumulation moduli and analyzing the dynamic changes are valuable. In this paper, Zhenglan Banner,located on the southern margin of the Hunshandake Sandy Land, was selected as the study area. The soil erosion and accumulation moduli were estimated using the ~(137)Cs and ~(210)Pb_(ex) composite tracing technique, and the dynamics of soil erosion and soil accumulation were analyzed during two periods. The results are as follows:(1) the regional ~(137)Cs reference inventory was 2123.5±163.94 Bq/m~2, and the regional ~(210)Pb_(ex) reference inventory was 8112±1787.62 Bq/m~2.(2) Based on the ~(137)Cs isotope tracing analysis, the erosion moduli ranged from –483.99 to 740.31 t·km~(-2)·a~(-1). Based on the ~(210)Pb_(ex) isotope tracing analysis, the erosion moduli ranged from –441.53 to 797.98 t·km~(-2)·a~(-1).(3) Compared with the earliest 50 years, the subsequent 50 years exhibited lower soil erosion moduli and accumulation moduli.Therefore, the activities of local sand dunes weakened, and the quality of the local ecological environment improved. The multi-isotope composite tracing technique combining the tracers ~(137)Cs and ~(210)Pb_(ex) has potential for similar soil erosion studies in arid or semiarid regions around the world. 相似文献
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为研究石笋δ~(13)C与δ~(18)O在千年尺度随时间的变化关系,通过对比贵州石将军洞SJJ-1石笋的δ~(13)C与δ~(18)O变化发现二者之间既有相似性又不完全同步。千年尺度两者之间的相似性主要由δ~(13)C与δ~(18)O共同受太阳辐射驱动的东亚季风强度变化所致。通过中国地层孢粉反演的植被空间格局变化,碳氧同位素的滞后期与太阳辐射相对于植被变化的滞后时间一致。因植被中δ~(13)C随年降水量增加具有变轻趋势,因此,两者的不同步性更大可能是太阳辐射驱动的季风强度变化与植被变化的不同步性引起。 相似文献
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采用４０Ａｒ／３９Ａｒ法和激光微区等时线方法，对南极南设得兰群岛利文斯顿岛东部产出的鲍勒斯山组火山岩重新进行了年龄测定。结果表明，４５Ｄ安山质熔岩和２６２玄武安山质熔岩的等时年龄分别为（１０５．６２±２．１１）Ｍａ和（１１１．４８±２．２３）Ｍａ，其４０Ａｒ／３９Ａｒ初始比与尼尔值相当，岩石中不含过剩氩，表明等时年龄代表岩石真正的形成年龄。脉状产出的Ａ９３５２细晶岩的４０Ａｒ／３９Ａｒ坪年龄为（９６．７±１．６）Ｍａ，计算得到等时年龄为９６．６Ｍａ，晚于熔岩喷发而形成。新的年龄数据证实了鲍勒斯山组火山岩形成于白垩纪。白垩纪火山活动曾影响了整个利文斯顿岛，在赫德半岛出露的鲍勒斯山组火山岩曾被较年轻火山岩所覆盖，构造抬升使其出露。 相似文献
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广东基督教教案的时空演变 (1584~1910) 总被引：1，自引：0，他引：1
教案是外来宗教文化与本土文化激烈冲突最为直接的反映。对广东基督教教案时空演变的研究,恰能直观地反映出基督教文化在广东文化扩散和文化适应的历史地理过程。研究从相关历史文献中提取数据,并运用GIS图形技术和数理统计方法进行分析,发现1584~`1910年期间,广东基督教教案大致经历了初生、多发、高潮、衰退四个时期。其空间分布具有不均衡的特性:珠三角自始至终是教案发生的中心,潮汕地区和粤东客家地区也先后成为教案的分布次中心地。地理集中指数的测算进一步印证了教案分布的这一结构特征。从文化传播的模式看,广东基督教教案的扩散属于墨渍式迁移扩散,但也明显带有以人口密度为主、行政区等级为次的等级扩散特征。形成这种分布与扩散的地域文化成因则在于广东对内封闭、对外开放的整体地理环境和各民系地域文化差异的共同作用。 相似文献
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本文综述了南极冰盖雪冰中SO2 -4 的来源、SO2 -4 浓度记录的时空分布特征 ,特别对nss SO2 -4 记录的火山活动事件进行了概括与总结 ,反映了近年来南极雪冰中SO2 -4 记录的最新研究进展。南极冰盖雪冰中SO2 -4 来源的综述表明南极地区雪冰中的SO2 -4 主要来源于海盐、海洋生物和火山喷发三种。很多研究表明 ,用南极冰芯中记录的nssSO2 -4 可以恢复火山活动的历史 ,虽然对同一次火山活动 ,在取自南极不同地区的冰芯中 ,其浓度和沉积通量大不一样 ,然而 ,各次火山活动引起的硫酸根离子的沉积通量相对于Tambora火山的沉积通量的百分比在不同冰芯中却经常具有可比性 ,这使得利用冰芯中nssSO2 -4 的沉积通量推算历史时期火山喷发的强度成为可能 相似文献
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在黔南峰丛洼地区林间白云岩坡地应用137Cs法研究土壤侵蚀。4个坡面采样样方的137Cs面积浓度都低于137Cs本底值浓度;表土样137Cs浓度随着坡长增加而增大,全样137Cs面积浓度的顺坡变化呈逐步下降趋势;应用137Cs农耕地侵蚀模型计算获得样点土壤侵蚀量后,加以坡长加权平均计算获得的坡长权重土壤位移量为2.045 t/(km2·a)。同时在坡脚的土壤分层剖面中的137Cs浓度峰值在土壤次表层出现,随着深度增加呈指数递减变化,属于未受耕作扰动的无侵蚀非农耕地,但表层含有相对低浓度137Cs是坡面侵蚀泥沙的搬运堆积结果,估算距1963年以来侵蚀泥沙年平均堆积厚度为0.0682~0.1364 cm/a。坡地土壤侵蚀速率远小于以往贵州喀斯特地区典型喀斯特小流域和坡地的观测结果,但坡脚泥沙堆积速率远大于坡地土壤侵蚀速率。表明季节性暴雨、坡面降雨汇流和耕作侵蚀等侵蚀作用使喀斯特坡地土壤颗粒出现微距离位移,长期则在坡脚出现显著的侵蚀泥沙堆积。 相似文献
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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
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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
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云南抚仙湖近现代沉积速率变化研究 总被引：14，自引：0，他引：14
借助GPS定位,采集了云南抚仙湖不同区域的7 个沉积物柱芯。通过对抚仙湖沉积物柱芯样品的放射性核素210Pb 和137Cs 测试分析,发现所有柱芯中均存在3 个公认的137Cs 计年时标(1954 年137Cs首次沉降、1963 年全球公认的137Cs最大沉降蓄积峰和1986 年前苏联切尔诺贝利核事故产生的137Cs 沉降蓄积峰),部分柱芯中存在20 世纪70 年代中期中国大气核试验形成的1975/1976 年次级蓄积峰,分析了该次级定年时标存在的合理性。借助210Pb CRS计年模式获得了抚仙湖过去百余年来的沉积年代,与137Cs 时标计年结果相比较存在一定偏差,对两种计年结果产生差异的可能原因进行了探讨。基于210Pb 和137Cs 计年结果,结合历史文献记载得出,自19 世纪中期以来,抚仙湖各个沉积物柱芯(FX6 除外) 的沉积速率变化规律具有相似性,大致可以划分为3 个阶段：A：自然演化阶段,B：人为扰动阶段,C：人为改造阶段。这种不稳定的沉积环境与抚仙湖地区相应历史时期的人类活动有密切关系,表明人类活动是影响短时间尺度下环境变化的主要驱动力。 相似文献
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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
15.
Highly variable sediment distribution in shallow, wind-stressed lakes: a case for sediment-mapping surveys in paleolimnological studies 总被引：1，自引：0，他引：1
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
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Yves Couillard Michel Courcelles Antonella Cattaneo Sybille Wunsam 《Journal of Paleolimnology》2004,32(2):149-162
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
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江苏王港盐沼的现代沉积速率 总被引：35，自引：0，他引：35
江苏海岸湿地总面积超过5000km^2，但围垦活动的加剧使盐沼湿地面积迅速减少；为了达到海岸防护、保滩促淤的目的，先后引种了大米草和互花米草。通过采集江苏王港潮滩盐沼湿地9处柱状样和挖取探槽剖面，以及对沉积剖面样品进行^210Pb和^137Cs测年分析，探讨了^210Pb的本底及影响^210Pb富集的因素，估算了王港盐沼湿地的现代沉积速率。王港潮滩盐沼沉积物对^210Pb的吸附作用较弱；受风暴潮、生物扰动、物源变化及实验误差等因素的影响，在^210Pbex剖面上出现了数据异常点，将这些数据点剔除后计算得到的沉积速率为33cm yr^-1，^137Cs测年显示，该地区1963年以来的平均沉积速率3．1cm yr^-1，与^210Pb法及前人研究结果相一致。根据一个典型剖面的^137Cs测年数据分析，王港潮滩盐沼的沉积过程根据地貌特征的不同可分3个阶段，大米草覆盖阶段滩面高程迅速增加，互花米草的生长提高了滩面淤积速率。 相似文献
18.
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
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P.G. Appleby 《Journal of Paleolimnology》2004,31(4):433-443
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
20.
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