Previous studies have documented a weathering‐limited regime in the upper reaches of the Ganges River Basin. Chemical weathering and element mobility at six sites in the lower reaches of the Ganges‐Brahmaputra tidal floodplain of southwest Bangladesh were investigated by comparing compositions of rice paddy soils, precursor tidal channel sediments, surface waters, and extract solutions, which represent the soluble fraction of solids. Little spatial variation in water and solid compositions is observed in each season, indicating similar processes are acting to transport elements across this region. Roughly one to several decades after deposition, rice paddy soils are not significantly different in mineralogy or composition from precursor tidal channel sediments, and both are similar to the composition of average upper continental crust. Soil and sediments contain mostly stable, cation depleted minerals, and coexisting waters are saturated in those minerals. There is no detectable change in composition of tidal channel water between upstream and downstream sites. Together, these observations indicate the dominance of weathered material and weak chemical weathering in the tidal floodplain, consistent with a transport‐limited regime. Multiple lines of evidence indicate a lack of exchange equilibrium between surface waters and coexisting solids, which may be a common feature in tidal river deltas where transport‐limited regimes likely dominate.

中文翻译：

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孟加拉国恒河潮汐三角洲平原限制运输的化学风化和元素固定性的初步证据

先前的研究已记录了恒河流域上游的一种受天气限制的制度。通过比较稻田土壤，前驱潮汐河道沉积物，地表水和提取液的组成，研究了孟加拉国西南部恒河-布拉马普特拉潮汐洪泛区下游六个地点的化学风化作用和元素迁移率，这些水代表了可溶性固体。在每个季节中，观察到的水和固体成分几乎没有空间变化，这表明类似的过程正在起作用，从而在该区域内运输元素。沉积大约一到几十年后，稻田土壤的矿物学或组成与潮汐河道前体沉积物没有显着差异，并且都与平均上陆壳的组成相似。土壤和沉积物主要含有稳定的，消耗了阳离子的矿物质，并且这些矿物质中并存的水饱和。上游和下游站点之间的潮汐通道水组成没有可检测到的变化。这些观察结果共同表明，潮汐洪泛区的风化物质占主导地位，化学风化作用弱，这与交通限制制度相一致。多条证据表明，地表水和固体共存之间缺乏交换平衡，这可能是潮汐河三角洲的一个普遍特征，在这些三角洲中，交通限制机制很可能占主导地位。这些观察表明潮汐平原上风化的物质占主导地位，化学风化较弱，这与运输受限的制度相一致。多条证据表明，地表水和固体共存之间缺乏交换平衡，这可能是潮汐河三角洲的一个普遍特征，在这些三角洲中，交通限制机制很可能占主导地位。这些观察结果表明潮汐泛滥平原中风化物质占主导地位，化学风化较弱，这与运输受限制度相一致。多条证据表明，地表水和固体共存之间缺乏交换平衡，这可能是潮汐河三角洲的一个普遍特征，在这些三角洲中，交通限制机制很可能占主导地位。