Estuaries, as connectors between land and ocean, have complex interactions of river and tidal flows that affect the transport of buoyant materials like floating plastics, oil spills, organic matter, and larvae. This study investigates surface-trapped buoyant particle transport in estuaries by using idealized and realistic numerical simulations along with a theoretical model. While river discharge and estuarine exchange flow are usually expected to export buoyant particles to the ocean over subtidal timescales, this study reveals a ubiquitous physical transport mechanism that causes retention of buoyant particles in estuaries. Tidally varying surface convergence fronts affect the aggregation of buoyant particles, and the coupling between particle aggregation and oscillatory tidal currents leads to landward transport at subtidal timescales. Landward transport and retention of buoyant particles is greater in small estuaries, while large estuaries tend to export buoyant particles to the ocean. A dimensionless width parameter incorporating the tidal radian frequency and lateral velocity distinguishes small and large estuaries at a transitional value of around 1. Additionally, higher river flow tends to shift estuaries toward seaward transport and export of buoyant particles. These findings provide insights into understanding the distribution of buoyant materials in estuaries and predicting their fate in the land–sea exchange processes.

中文翻译：

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小河口在截留浮力颗粒方面的作用


河口作为陆地和海洋的连接器，河流和潮汐流之间存在复杂的相互作用，影响漂浮塑料、石油泄漏、有机物和幼虫等浮力物质的运输。本研究通过使用理想化和现实的数值模拟以及理论模型来研究河口中表面捕获的浮力颗粒的输运。虽然通常预计河流流量和河口交换流会在潮下时间尺度上将浮力颗粒输出到海洋，但这项研究揭示了一种普遍存在的物理输送机制，导致浮力颗粒滞留在河口。潮汐变化的表面辐合锋影响浮力粒子的聚集，粒子聚集和振荡潮流之间的耦合导致潮下时间尺度的向陆地传输。在小河口，浮力颗粒向陆地的输送和滞留较多，而大河口则倾向于将浮力颗粒输送到海洋。结合潮汐弧度频率和横向速度的无量纲宽度参数以 1 左右的过渡值区分小河口和大河口。此外，较高的河流流量往往会使河口向海洋输送和输出浮力颗粒。这些发现为了解河口浮力物质的分布和预测它们在陆地-海洋交换过程中的命运提供了见解。