This study is focussed on understanding of molybdenum (Mo) cycling in the mesotidal to macrotidal estuary of the Ganga (Hooghly) River in India. Our investigation encompasses the composition of water and suspended particulate matter (SPM) samples collected in three separate periods (pre-monsoon: PrM, monsoon: M and post-monsoon: PoM) over two consecutive years, surface sediments, exchangeable phases of surface and suspended sediments, one sediment core, urban and industrial effluent waters and ground waters. The observed dissolved Mo concentrations in the estuary are in excess of those expected from conservative mixing of seawater and river water. The “excess” Mo values, observed in the mid-to-high salinity regions (4–27 ‰) for four out of the six study periods, are the highest in the monsoon samples. The bulk and exchangeable phase compositions are supportive of release of Mo from the Fe-Mn oxyhydroxide phases of the SPM and surface sediments in the estuary. Mass balance calculations indicate that Mo release from the SPM and surface sediments can account for up to 40 % of the median value of the “excess” Mo in the estuary. The compositions of the sediment core provide evidence for the mobilization of Mo and its release to porewater due to reductive dissolution of Fe-Mn oxyhydroxides. The tidally induced sediment resuspension likely facilitates the transport of porewater Mo to the overlying water. Mass balance calculations indicate that Mo loss from the sediment column can account for the bulk of the “excess” Mo in the estuary waters. This study further demonstrates that industrial effluents, urban waste waters and groundwaters do not constitute significant sources of dissolved Mo in the estuary.

中文翻译：

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印度恒河（胡格利）河口钼的非保守行为：溶质-颗粒相互作用和沉积物成岩作用的作用


本研究的重点是了解印度恒河（胡格利）河中到大潮汐河口的钼 （Mo） 循环。我们的调查包括连续两年在三个不同时期（季风前：PrM、季风：M 和季风后：PoM）收集的水和悬浮颗粒物 （SPM） 样本的成分、表层沉积物、表层沉积物和悬浮沉积物的可交换相、一个沉积物核心、城市和工业废水以及地下水。在河口观察到的溶解钼浓度超过了海水和河水保守混合的预期浓度。在六个研究期中的四个研究期中，在中高盐度区域 （4-27 ‰） 观察到的“过量”钼值在季风样本中最高。本体和可交换相组成支持从 SPM 的 Fe-Mn 羟基氧化物相和河口表层沉积物中释放 Mo。质量平衡计算表明，SPM 和表层沉积物中释放的 Mo 可以占河口“过量”Mo 中位数的 40%。沉积物芯的成分为 Mo 的动员及其由于 Fe-Mn 羟基氧化物的还原溶解而释放到孔隙水中提供了证据。潮汐诱导的沉积物再悬浮可能有助于将孔隙水 Mo 输送到上覆水域。质量平衡计算表明，沉积物柱中的 Mo 损失可以解释河口水域中“过量”Mo 的大部分。这项研究进一步表明，工业废水、城市废水和地下水并不构成河口溶解 Mo 的重要来源。