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一、引言湖泊沉积物不仅记载着积水区域环境质量的历史变化,而且反映出沉积过程的环境条件和沉积物质的地球化学行为。瑞士Greifcn湖是一个受人为活动强烈干扰的富营养湖泊,其下层滞水带季节性缺氧。在前文中,我们已报道了该湖新近沉积物孔柱中天然散落放射性核素(~7Pe、~(210)Pb),和人为散落放射性核素(~(90)Sr、~(137)Cs、~(238,239,240)Pu)的分布;并用~(210)Pb_(ex)、核试验散落核索时标、纹理对比等计年方法,讨论了该湖现代沉积物堆积速率。当继续审议沉积物孔柱中各种放射性核素的累计值时发现:即使在同一孔柱中,不同放射性核素累计投递比率f(即一核素在沉积物孔柱中的累计值与根据大气散落记载所期望的该核素的累计沉降值之比),具有明显的差别(表1),
I. INTRODUCTION Lake sediments not only record the historical changes of the environmental quality of the sediment, but also reflect the environmental conditions of deposition and the geochemical behavior of the sediments. The Greifcn Lake in Switzerland is an eutrophic lake that is strongly disturbed by anthropogenic activities and has seasonal hypoxia in the stagnant water below it. In the previous section, we have reported the natural scattered radionuclides (~ 7Pe, ~ (210) Pb) and the artificial scattered radionuclides (~ (90) Sr, ~ , ~ (238,239,240) Pu). The dating rates of ~ (210) Pb ex, nuclear test of scattered cores, texture contrast and so on were also discussed. The deposition rate of modern sediment in the lake was discussed. When continuing to review the cumulative values of various radionuclides in sediment columns, it was found that, even in the same column, the cumulative delivery rate f for different radionuclides (ie, the cumulative value of a nuclide in the column of sediment, Atmospheric scattered record of the expected total nuclide sedimentation value ratio), there is a clear difference (Table 1),