The composition of suspended matter from Ganges-Brahmaputra sediment dispersal system during low sediment transport season
The composition of suspended matter from Ganges-Brahmaputra sediment dispersal system during low sediment transport season
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DOI：
10.1016/s0009-2541(01)00396-5
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发表时间：
2002-04
期刊：
影响因子：
3.9
通讯作者：
J. Stummeyer;V. Marchig;W. Knabe
中科院分区：
文献类型：
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作者：
J. Stummeyer;V. Marchig;W. Knabe
在悬浮物负荷较低时（1997 年 11 月/12 月），对邻近陆架区域的水域中恒河 - 布拉马普特拉河系统供应的悬浮物进行了采样。悬浮物的绝对量范围在河口附近 >500 mg/l 和外陆架 <1 mg/l 之间。对悬浮物的化学和矿物学分析表明，其成分随着距污染源的距离而变化。成分变化基于粒度分配；石英和重矿物沉淀得更快，导致外架悬浮物中石英、稀土元素、锆、铪、铌、钽、钨、铀、钍、钇和钙的含量耗尽。成分变化的另一部分是基于悬浮物与海水的反应。氢氧化锰在悬浮物颗粒上形成涂层，并从海水中吸附元素。因此，可以在外架悬浮物中观察到 Mn、Zn、Ni、Cr、Co、Li、Cs、As、Sb、Pb、Tl 和 Cd 的富集。砷在内架上积累了两倍。连续浸出实验中的化学分配表明，砷不遵循锰和其他过渡金属的富集机制。总砷的 90% 以上与悬浮物的几乎不溶相结合（例如结晶氧化铁、残留矿物质）。为了与悬浮物进行比较，对邻近的表面沉积物进行了采样和分析。在这种沉积物中，主要相是在高悬浮负荷期间沉降的相，具有更多的石英和重矿物以及随之而来的化学成分。氧化锰和吸附的过渡金属的富集丧失；由于近海底海水中的厌氧条件，它们从沉积物中溶解并在海水中循环利用。砷存在于沉积物中几乎不溶的部分，就像悬浮物中的情况一样
Suspended matter supplied from the Ganges–Brahmaputra river system was sampled in waters of the adjacent shelf area in times of low suspended matter load (November/December 1997). The absolute amount of suspended matter ranges between >500 mg/l near the river mouth and <1 mg/l on the outer shelf. Chemical and mineralogical analyses of the suspended matter show changes in its composition with distance from the source. Compositional changes are based on grain size partitioning; quartz and heavy minerals are precipitating sooner, leaving the suspended matter from the outer shelf depleted in quartz, REE, Zr, Hf, Nb, Ta, W, U, Th, Y, and Ca. The other part of the compositional changes is based on the reaction of suspended matter with seawater. Manganese hydroxide is producing coatings on suspended matter grains, and adsorbing elements out of the seawater. As a consequence, enrichment of Mn, Zn, Ni, Cr, Co, Li, Cs, As, Sb, Pb, Tl, and Cd can be observed in the suspended matter from the outer shelf. Arsenic is accumulating on the inner shelf by a factor of 2. Chemical partitioning in sequential leaching experiments shows that arsenic does not follow the enrichment mechanism of manganese and other transition metals. More than 90% of the total arsenic is bound to nearly insoluble phases of the suspended matter (e.g., crystalline iron oxides, residual minerals). For comparison with suspended matter, adjacent surface sediments were sampled and analysed. In this sediment, the dominating phase is the one which settled down during the times of high suspended load, with more quartz and heavy minerals and consequent chemical composition. The enrichment of manganese oxide and adsorbed transition metals gets lost; because of anaerobic conditions in the bottom-near seawater, they dissolve from the sediment and get recycled in seawater. Arsenic is found in nearly insoluble parts of the sediment, as it is the case in the suspended matter