泥沙作为絮凝床的证据——河流三角洲的物质负荷与冲刷负荷

IF 3.8 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
Justin A. Nghiem, Gen K. Li, Joshua P. Harringmeyer, Gerard Salter, Cédric G. Fichot, Kyle Wright, Paola Passalacqua, Michael P. Lamb
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引用次数: 0

摘要

从大陆到海洋的沉积物和有机碳的颗粒负荷主要是泥浆,但泥浆的浓度和输送速率仍然是出了名的难以预测。在河流中,泥浆被认为是作为冲积颗粒运输的,它们非常小,以至于不存在于河床中,像被动的示踪剂一样在河流中被冲刷,并且受外部输入的控制,而不是来自河床的局部沉积物夹带。然而,河流中的淡水絮凝可以将泥浆颗粒聚集成更大的颗粒,其流体动力学行为更像沙子。如果正确的话,这一发现为将泥浆输送描述为床层和水柱之间动态交换的床层物质负载颗粒打开了大门,对此存在可靠的理论。在这里,我们提出的证据表明,在淡水蜡湖三角洲(WLD)(密西西比河三角洲的一个主要支流)中,泥浆表现为絮凝床物质负荷而不是冲刷负荷。粒径-浓度-深度分布图表明,泥浆在WLD中发生絮凝。原位浊度传感器、机载高光谱成像(AVIRIS-NG)和浓度-深度剖面显示,泥浆浓度随剪切应力变化而随时间和空间变化,与床质载荷动态一致。此外,泥沙主要存在于河道河床中(体积平均泥沙含量为14%),而在三角洲岛屿的河床中占主导地位(体积平均泥沙含量为90%)。床上物质夹带理论用一种公式解释了观察到的床附近的泥浆浓度,该公式解释了床附近的絮凝体生长和致密化。总之,这些发现支持将沙和絮凝泥作为低地河流和三角洲的床质负荷的统一处理。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Evidence for Mud as Flocculated Bed-Material Load Versus Washload in a River Delta

Evidence for Mud as Flocculated Bed-Material Load Versus Washload in a River Delta

Evidence for Mud as Flocculated Bed-Material Load Versus Washload in a River Delta

Evidence for Mud as Flocculated Bed-Material Load Versus Washload in a River Delta

Evidence for Mud as Flocculated Bed-Material Load Versus Washload in a River Delta

Mud dominates the particulate load of sediment and organic carbon from continents to oceans, but mud concentration and transport rate remain notoriously difficult to predict. In rivers, mud is thought to be transported as washload—particles so small that they are absent from the riverbed, washed through the river like passive tracers, and controlled by external inputs rather than local sediment entrainment from the bed. However, freshwater flocculation in rivers can aggregate mud grains into larger particles that behave hydrodynamically more like sand. If correct, this finding opens the door to describe mud transport as bed-material load—particles in dynamic interchange between the bed and water column—for which robust theory exists. Here we present evidence that mud behaves as flocculated bed-material load rather than washload in the freshwater Wax Lake Delta (WLD), a major distributary of the Mississippi River Delta. Grain size-specific concentration-depth profiles indicate that mud is flocculated in WLD. In situ turbidity sensors, airborne hyperspectral imaging (AVIRIS-NG), and concentration-depth profiles show that mud concentration varies temporally and spatially in response to shear stress variations, consistent with bed-material load dynamics. Furthermore, mud exists in the channel bed (median 14% mud by volume) and dominates the bed on deltaic islands (median 90%). Bed-material entrainment theory explains observed near-bed mud concentrations using a formulation that accounts for floc growth and densification near the bed. Together, these findings support a unified treatment of sand and flocculated mud as bed-material load in lowland rivers and deltas.

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来源期刊
Journal of Geophysical Research: Earth Surface
Journal of Geophysical Research: Earth Surface Earth and Planetary Sciences-Earth-Surface Processes
CiteScore
6.30
自引率
10.30%
发文量
162
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