长江口氧化还原敏感元素的早期成岩过程

通过测试长江口沉积物及间隙水中Fe、Mn、U及Mo的含量，结合早期成岩模型及地球化学热力学分析，探讨了在河口环境中影响间隙水氧化还原敏感元素(Fe、Mn、U及Mo)分布的主要因素.根据Fick第一定律，估算了Fe、Mn、U及Mo在沉积物-水界面的扩散通量.结果表明，间隙水Fe、Mn、U及Mo的含量分别介于0.8~106μmol/L、14.8~258μmol/L、1.9~14.4nmol/L及60~546nmol/L之间.在垂直剖面上，间隙水Fe、Mn峰值分别出现在约5cm或10cm的深度.早期成岩过程是影响长江口沉积物间隙水Fe、Mn分布的主要因素.吸附系数对间隙水Fe、Mn的分布也有重要的影响.吸附系数越高，间隙水Fe、Mn浓度越低.影响间隙水U分布的主要因素为Fe，而Mo与Fe、Mn之间不存在相关性.通量计算结果显示Fe、Mn、U及Mo的扩散通量分别介于3.0~10.5μmol·(m2·d)-1、35.7~439.5μmol·(m2·d)-1、-2.3~0.2nmol·(m2·d)-1及-36.0~94.6nmol·(m2·d)-1之间.沉积物中自生铀组分约占总铀的6%~67%. 

Early Diagenetic Processes of Redox Sensitive Elements in Yangtze Estuary

The major factors that govern the vertical distributions of redox sensitive elements (Fe, Mn, U and Mo) in interstitial water are studied by analyzing the measurement of concentrations of Fe, Mn, U and Mo in pore water and sediments in Yangtze estuary, combining with the early diagenesis model and geochemical thermodynamic analysis, The benthic fluxes of Fe, Mn, U and Mo have been calculated according to the Fick's first law. The results show that the concentrations of Fe, Mn, U and Mo in interstitial water in Yangtze Estuary sediments range from 0.8 to 106μmol/L, 14.8 to 258μmol/L, 1.9 to 14.4nmol/L and 60 to 546nmol/L, respectively. The maximum of interstitial Fe2+ and Mn2+ have been observed at 5cm or 10cm in the vertical profiles, respectively. The interstitial iron and manganese profiles are mainly controlled by early diagenetic processes in Yangtze Estuary sediments. Adsorption process has great effect on the distribution of interstitial Fe2+ and Mn2+. The greater the adsorption coefficients are, the less the concentrations of interstitial Fe2+ and Mn2+ are. The vertical distributions of interstitial uranium are mainly controlled by iron. However, there is no correlation between Mo and Fe or Mn. The calculated diffusive fluxes of Fe, Mn, U and Mo range from 3 to 10.5μmol·(m2·d)-1, 35.7 to 439.5μmol·(m2·d)-1, -2.3 to 0.2nmol·(m2·d)-1 and -36 to 94.6nmol·(m2·d)-1, respectively. The ratio of authigenic uranium to total uranium ranges from 6% to 67%.