2011长江中下游旱涝急转前后河口表层沉积物地球化学特征研究

Study on the geochemical characteristics of the surface sediments from the Yangtze River estuary under the 2011 sharp turn from drought to flood in middle and lower Yangtze

系统分析了2011旱涝急转前后长江口表层沉积物中常量元素、微量元素和有机碳等地球化学特征的变化及其影响因素,探讨了旱涝急转状况对河口沉积地球化学分区的影响。结果显示,洪涝期河口沉积物粒度总体有变粗的趋势,尤其是南支水道至三角洲前缘区。洪涝期含量下降的组分主要有Al2O3、K2O和Na2O等,含量增加主要有TFe2O3、CaCO3、CaO、TiO2、Mn和P等。干旱期常量元素组分与黏土的正相关性更高,但S4站的情况相反,这可能主要跟径流携带的流域物质的输入状况和该区特有的沉积动力条件有关。洪涝期大多数沉积物中微量元素的平均含量表现为不同程度增加,反映了研究区洪涝期沉积物粒度整体变粗和流域洪水导致的入海物质通量升高的影响。不同时期TOC和TN均具有较好的正相关关系,有机质C/N值指示洪涝期陆源贡献大于干旱期;但C/N值整体相对偏低,这可能跟物源贡献和微生物作用有关。洪涝期各元素变量在主因子载荷图上的分布更加分散,反映了洪涝期粒度对元素组合分布的控制作用有所减弱和径流携带流域物质的输入有所增强。基于各样品的因子得分,发现旱涝急转前后河口沉积物样品的元素地球化学分区基本一致。

The geochemical characteristics of major elements, trace elements and organic carbon and their influential factors were analyzed for the surface sediment samples from the Yangtze River estuary under a sharp turn from drought to flood in 2011 in the Yangtze River, then further to evaluate the impact of this sharp turn event on the sedimentary geochemical province. The results showed that the sediment grain-size turned to coarser in flood season, especially in the southern river mouth to the front delta. The decreased major elements in flood season were Al2O3, K2O, Na2O, whereas the increased components of TFe2O3, CaCO3, CaO, TiO2, Mn and P. The correlation between major elements and clay is more significant in the drought season, the inconsistent relationship between major component and grain-size was observed in $4 from the southern transect. This could be related to the fluvial input and specific depositional hydrodynamic setting. The trace elements in most sediment samples showed an increase during flood season, revealing the impact of coarser grain-size and increased flux of fluvial input. The correlation between TOC and TN in the drought and flood periods showed good positive relation, but with higher C/N ratios in the flood season showing higher terrigenous contributions. Even though, the lower C/N ratios should be ascribed to the source pool of organic matter, the input of soil organic matter and degradation of microorganisms. The distribution of variables on the loading plot showed more scattered in the flood season, reflecting the decreased control of grain-size on the element association and increased riverine input. Based on the sample scores, the geochemical province of the estuarine samples showed little variation during the sharp turn from drought to flood.