【作者】 吴梅桂；

【导师】 杜金洲；

【作者基本信息】 华东师范大学 ， 海洋化学， 2011， 硕士

【摘要】 本文以具有颗粒活性的放射性核素为工具,其中包括7Be、137Cs、228Th.210Pb以及210po,通过了解各站位表层沉积物核素活度的分布,并对不同来源的核素活度比值进行比较,如大气来源和径流来源,结合高、中、低潮滩表层沉积物的粒度特征,对崇明东滩沉积物进行初步的物源分析,为进一步了解该区泥沙的沉积特征积累信息。主要研究结果包括：(1)沉积物粒度的时空特征：在植被、泥沙来源和水动力等多重因素的影响下,从北断面到南断面,从高潮滩到低潮滩,表层沉积物的平均粒径逐渐增大；崇明东滩各站位的沉积物样品粒度(除特别说明单位外,如Φ,均为um单位)呈现春夏小于秋冬的趋势。利用粒度分级装置对崇明东滩中断面高中低潮滩三站位的沉积物进行分级,得到A、B、C、D(从粗到细)四类粒径级别的样品,从A到D,粘土含量依次升高,粉砂含量依次降低,平均粒径依次减小,粗粒部分同一粒级的含量随离岸距离的增大而增高,细粒部分则反之。(2)核素活度的变化：7Be在春季呈现高值；137Cs的活度全年较小,137Cs和210Pbex的活度随平均粒径的变化有较显著的相关性；210Po/210Pb比值大于1,表明210po相对于210pb过剩。210po活度和：0Po/210Pb比值与样品烧失量呈现很好的相关性,说明210po易被有机物吸附。(3)核素活度与沉积物粒径的关系：表层沉积物随平均粒径增大,核素活度依次递减。对分级样品的平均粒径(①)与核素活度值做相关性分析发现,各核素活度与平均粒径(Φ)在P<0.01范围内显著相关,其中210pbex和137Cs的相关系数(R)分别为0.82和0.78,高于228Thex(0.63)和7Be(0.50)。(4)物源初探：中断面高、中、低潮滩表层沉积物的210Po/210Pb的平均值分别为1.07、1.08和1.04,与上海地区雨水的年平均值(0.22)差别很大,而接近于徐六泾悬浮颗粒物的210Po/210Pb)A.R的平均值(0.90),反映了崇明东滩表层沉积物的主要来源为陆源输送；表层沉积物中的7Be/210Pbex和137Cs/210Pbex均与徐六泾颗粒态中的核素比值接近,进一步显示出崇明东滩沉积物受陆源控制；并通过7Be/210Pbex和137Cs/210Pbex的关系图,发现高、中潮滩的陆源特征较为明显,低潮滩由于受水动力控制,陆源影响较小,但波动较大。更多还原

【Abstract】 To evaluate the source of sediment in East Chongming Tidal Flat and further more understand the deposition characteristic of sediment in the Changjiang Estuary, particle-reactive radionuclides such as 7Be, 137Cs,228Th,210Pb and 210Po were used in this article by studying the distribution of radionuclides and their activity ratios from atmospheric deposition and river input, and the grain-size of sediment from high flat to low flat were also considered. The main results are showed below:(1) The temporal and spatial distribution of sediment grain-size:Under the influence of vegetation, sediment source and hydrodynamics, the sediment grain-size in the Tidal Flat showed temporal and spatial variations. The mean size of surface sediment increased from north section to south and increased from high flat to low flat. Compared to mean size of surface sediment in autumn and winter, the mean size is much smaller in spring and summer. By using a water elutriation apparatus, sediment in the Tidal Flat was devided into 4 grades called A(the most thick), B, C and D(the most fine) according to size of the sediment particle. From A to D, the content of clay increased while the grain-size and content of silt decreased. In the same grade of sediment the thick part exhibited an offshore increasing trend, and the fine part showed a decreasing trend.(2) The activities of radionuclides:7Be had a high value in activity in spring; 137Cs had a low value in activity in the whole year and its variation with the size of sediment particle is same as 210Pb. The 210Po/210Pb ratio was greater than 1, which meant 210Po was excess. The 210Po activity and 210Po/210Pb ratio correlated well with the loss on ignition meant a highly correlation between 210Po activity and organic material content.(3) Correction analysis between grain-size and radionuclide activities: Correlation analysis between grain-size and activities were done and it showed that all the correlation were significant at the 0.01 level. The activities of radionuclides decreased as the size of surface sediment increased. The correlation coefficient of 210Pbex,137Cs,228Thex and 7Be were 0.82,0.78,0.63 and 0.50 separately.(4) The radioactivitie ratios:The average 210Po/210Pb ratio of Chongming tidal flat from high to low flat were 1.07,1.08 and 1.04 separately, which were closed to those of suspended particulate matter from XuLiuJing (0.90). The average values from atmospheric deposition of Shanghai was 0.22. The 7Be/210Pbex and 137Cs/210Pbex ratio of surface sediment were both closed to XuLiuJing. These revealed that the sediment of the Chongming tidal flat was mainly controlled by the supply of the Changjiang River. Further study on 7Be/210Pbex and 137Cs/210Pbex ratio showed that the terrial characteristic of high flat and middle flat were stronger than low flat, which had less value of nuclide ratio due to the influence of hydrodynamics.更多还原