南海东北部表层沉积物天然放射性核素与~(137)Cs

用HPGeγ谱仪测定了南海东北部表层沉积物中的放射性核素 .结果给出 7种核素的平均比活度分别为40 K :538Bq/kg ,2 10 Pb :1 1 6Bq/kg ,2 2 6Ra:2 7 7Bq/kg ,2 2 8Ra:4 4 9Bq/kg ,2 2 8Th :4 2 0Bq/kg ,2 38U :35 4Bq/kg和137Cs:1 1 6Bq/kg ,2 10 Pb的比活度随离岸距离增大 ,2 2 6Ra比活度随离岸距离没有明显变化 ,其余核素比活度随离岸距离减小 .与对我国近海其他海域报道的沉积物放射性核素含量相比 ,40 K和137Cs稍低于其他海域 ,其余核素为中等水平 .     

137Cs剖面的沉积信息提取——以香港贝澳湿地为例

通过建立模型,对采自香港大屿山岛贝澳湿地三个站位的沉积样品的137Cs实测剖面与模型计算剖面的比较分析,得出三个站位的沉积速率分别为0.24 cm/a、0.21 cm/a、0.34 cm/a,除P1站位外,P2、P3站位由于受到潮水的作用,表层沉积物受到侵蚀,侵蚀量分别为4.8 cm和7 cm。该结果与常用的时标方法所的结果进行了比较,P1站位由上述模型所得的结果与常用的时标方法所得的结果一致。可以看出,在稳定的沉积环境下,常用的确定时标的方法可以较准确地计算出沉积速率,而在堆积与侵蚀变化的沉积环境下,常用的确定时标的方法就存在一定的缺陷。该工作为137Cs剖面的沉积信息提取进行了有益的尝试。但上述模型中,由于采用日本东京地区的137Cs大气沉降通量记录替代香港地区的137Cs大气沉降通量记录,并没有考虑 137Cs的扩散效应,所以该模型还有待进一步的改进。     

Environmental evaluation of elemental cesium and strontium contents and their isotopic activity concentrations in different soils of La Mancha (Central Spain)

Cesium and Strontium concentrations were analyzed in eight pedogenetic soil profiles developed on different rocks from a semiarid mediterranean region: La Mancha (Central Spain). Concentration activities of ¹³⁷Cs and ⁹⁰Sr, as for some soil properties, were also measured. The results are presented in this document: Cs concentrations range between 0.4 and 18.3 mg kg⁻¹ and Sr varies widely between 11.0 and 3,384 mg kg⁻¹. Therefore, it is clear that there is a broad range of concentrations and there are also values significantly higher than the average values stated by several authors. Concentrations of long-life artificial radionuclides (¹³⁷Cs, ⁹⁰Sr) were determined in some of the same soils. The activity concentration mean values (Bq kg⁻¹) were ranging between 0.82 and 21.76 for ¹³⁷Cs and ⁹⁰Sr variations range between 6.73 and 0.35. There were no significant correlations between radionuclides and stable trace elements. The data indicate that the soils do not show significant radioactivity of these elements and therefore they do not pose a danger. By the same token, no risk of contamination by this activity was detected. Finally, spatial patterns seem to be affected by the soil type and some soil properties.     

210Pb and 137Cs measurements in the Circum Bohai Sea coastal region: sedimentation rates and implications

The representative ²¹⁰Pb and ¹³⁷Cs age-depth profiles were selected from more than 100 sites in the Circum Bohai Sea (CBS) coastal region to examine the sedimentation rates and associated environmental changes. There are three unique ²¹⁰Pb_exc distribution patterns: 1) ideal-decaying type, representing relatively constant sediment supply and quieter environmental setting; 2) wiggling type, but with approximately equivalent amplitude, representing coarser sediments and associated stronger flow current environment; and 3) episodic-eventinfluencing type, each representing typhoon storm-influenced depositional environment. Our results also show that there is a lower sedimentation rate (ca. 0.1 cm/a) in the coastal lowlands, a higher sedimentation rate (ca. 0.5–3 cm/a) in the intertidal flat and an intermediate rate of ca. 0.58 cm/a in the subtidal zone near the Huanghua Harbor. The interbedded silt layer occurring in the core sediment reveals lower ²¹⁰Pb activities, indicating a discontinuous sedimentation mostly due to typhoon events which dwarfs against ²¹⁰Pb and ¹³⁷Cs applicability. Overall, the ²¹⁰Pb and ¹³⁷Cs measurements of the present study provide physical insight into the evaluation of the coastal-marine ecological environment and associated management.     

Cs+水合结构密度泛函理论计算研究

本文用密度泛函理论在WB97XD/gen def2-tzvp基组水平上对[Cs(H2O) n] +(n=1-15)水合团簇结构的振动光谱进行了研究。研究表明,随着水分子数的增加,在气相和液相中,8配位的Cs+ 水合团簇是最稳定的;随着水分子数的增加,Cs-O键长增大,Cs+上的电荷密度减小。当水分子数大于11时,Cs-O键长和Cs+上的电荷密度变化很小。O(H2O)-O(H2O)距离、∠O(H2O)-Cs-O(H2O)°统计结果表明,15个水分子足以形成Cs+的近似饱和水合层。此外,红外光谱显示[Cs(H2O)n]+水合团簇中O-H伸缩振动随着水分子数的增加而发生变化,由此可以作为鉴别水合层位置的一种参考方法。     

放射性核素210Pb、137Cs测定巴丹吉林沙漠湖泊岩芯的年代及沉积速率

巴丹吉林沙漠发育了世界上独一无二的丘间湖泊群,100多个永久性的丘间湖泊分布于沙漠的东南部。沙漠湖泊岩芯是干旱地区重要的气候、环境档案,然而受沙漠湖泊发育极端环境的影响,岩芯测年面临很大挑战。本文选择巴丹吉林的沙漠南缘的阿尔吉林和敦德吉林进行钻探,获取无扰动岩芯,利用核素（210Pb、137Cs）进行测年,并计算其沉积速率。结果表明：（1）核素（210Pb和137Cs）测年能够获取巴丹吉林沙漠丘间现代湖泊岩芯的可靠年代。（2）岩芯Ar-1的CRS测年结果为102±8a,沉积速率分布范围为0.13 ~ 0.33cma-1,岩芯Dd-1的CRS测年结果为123±2a,沉积速率分布范围为0.18 ~ 0.70cma-1。（3）沙漠岩心沉积速率空间分布具有自沙漠腹地向边缘递增的趋势,210Pbuns-CRS平均沉积速率分布范围为 0.16 ~ 0.57cma-1 ,137Cs沉积速率分布范围为0.05 ~ 0.6 cm a-1。未来对于沉积速率空间变化的可能影响因素,如高大沙山的围限阻挡效应、137Cs的分子扩散效应以及古地震等,应进行更深入研究。     

土壤颗粒组成影响137Cs含量的初步实验结果

放射性核素¹³⁷Cs作为人类核试验的产物,以其独特的理化性质而成为研究土壤侵蚀和泥沙沉积一种良好的示踪源。在¹³⁷Cs的再分配过程中,土壤颗粒组成是影响土壤¹³⁷Cs的重要因子。一般认为,土壤中的¹³⁷Cs活度主要与粘粘含量有关,但这要取决于原生沉积物的颗粒组成。通过选取共和盆地主要的三种土壤类型,采集0~30cm的混合样品,进行入工筛分,测定不同粒径成分的¹³⁷Cs含量。初步实验表明,砂质土的¹³⁷Cs活度与平均粒径之间呈负指数关系,0.01~0.1mm组分对¹³⁷Cs含量的影响最为显著;壤质土的¹³⁷Cs活度主要与粗粉砂(0.01~0.05mm)含量有关,与137Cs活度主要与原生沉积物的颗粒特性和粒度有关.¹³⁷Cs一旦被原生沉积物颗粒吸附,在以后的土壤颗粒再分配过程中,是很难被置换掉的。     

湖泊沉积中的10Be含量变化——有助于识别第四纪古冰川的有无

20世纪50-70年代核试验产生的¹³⁷Cs尘埃,在现代冰川和非冰川湖泊沉积剖面中的深度分布存在明显差异.同理,大气宇宙射线成因的长半衰期¹⁰Be尘埃,在第四纪冰川和非冰川湖泊沉积剖面中的深度分布也应存在差异.第四纪冰川湖泊,冰期时流域内冰雪和¹⁰Be的累积量大于消融量,间冰期时冰雪和¹⁰Be的消融量大于累积量.因此,冰川湖泊冰期的¹⁰Be入湖通量小于间冰期.湖泊沉积剖面¹⁰Be浓度的波动,很可能表征流域内冰雪消融与累积的变化.非冰川湖泊,不存在冰川的累积与消融对¹⁰Be入湖通量的影响.开展第四纪冰川与非冰川湖泊沉积¹⁰Be含量变化的对比研究,有可能为破译中国东部中低山区古冰川和青藏高原大冰盖的世纪之争提供新的证据.     

Using 137Cs measurements to establish catchment sediment budgets and explore scale effects

Growing awareness of the wider environmental significance of fine sediment transport by rivers and associated sediment problems linked to sediment–water quality interactions, nutrient and contaminant transfer, and the degradation of aquatic habitats has resulted in the need for an improved understanding of the mobilization and transfer of sediment in catchments to support the development of effective sediment management strategies. The sediment budget provides a key integrating concept for assembling information on the internal functioning of a catchment in terms of its sediment dynamics by providing information on the mobilization, transfer, storage and output of sediment. One key feature of a catchment sediment budget is the relationship between the sediment yield at the catchment outlet and rates of sediment mobilization and transfer within the catchment, which is commonly represented by the sediment delivery ratio. To date, most attempts to derive estimates of this ratio have been based on a comparison of the measured sediment yield from a catchment with an estimate of the erosion occurring within the catchment, derived from an erosion prediction procedure, such as the Universal Soil Loss Equation (USLE) or its revised version, RUSLE. There is a need to obtain more direct and spatially distributed evidence of the erosion rates occurring within a catchment and to characterize the links between sediment mobilization, transfer, storage and output more explicitly. In this context, fallout radionuclides have proved particularly useful as sediment tracers. This paper reports the results of a study aimed at exploring the use of caesium‐137 (¹³⁷Cs) measurements to establish sediment budgets for three catchments of different sizes and contrasting land use located in Calabria, southern Italy. Long‐term measurements of sediment output were available for the catchments, and, by using the estimates of gross and net rates of soil loss within the catchments provided by ¹³⁷Cs measurements, it was possible to establish the key components of the sediment budget for each catchment. By documenting the sediment budgets of three catchments of different sizes, the study provides a basis for exploring the effects of scale on catchment sediment budgets and, in particular, the increasing importance of catchment storage as the size of the catchment increases. The results of this study demonstrate a reduction in the sediment delivery ratio from 98 to 2% as catchment area increases from 1·47 ha to 31·2 km². Copyright © 2010 John Wiley & Sons, Ltd.