研究团队通过理想化和现实的数值模拟以及理论模型，研究河口表面捕获悬浮颗粒的输运。虽然河流排放和河口交换流通常会在潮下时标上向海洋输出悬浮颗粒，但本研究揭示了一种普遍存在的物理运输机制，该机制可以调节悬浮颗粒在河口的滞留。潮汐变化的地表辐合锋影响悬浮颗粒的聚集，颗粒聚集与振荡潮流之间的耦合导致潮下时标的向陆输送。
结果表明，在小河口，悬浮颗粒向陆地的迁移和滞留更大，而大河口则倾向于向海洋输出悬浮微粒。包含潮汐弧度频率和横向速度的无量纲宽度参数，在大约为1的过渡值处区分大小河口。此外，较高的河流流量会使河口向海洋迁移并输出悬浮颗粒。这些发现为理解河口悬浮物质的分布，和预测它们在陆海交换过程中的命运提供了见解。
据介绍，河口作为陆地和海洋之间的连接器，河流和潮汐流之间有着复杂的相互作用，影响着悬浮塑料、石油泄漏、有机物和幼虫等浮力物质的运输。
附：英文原文
Title: On the role of small estuaries in retaining buoyant particles
Author: Bo, Tong, Ralston, David K., Geyer, W. Rockwell, McWilliams, James C.
Issue&Volume: 2024-8-19
Abstract: 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.
DOI: 10.1073/pnas.2401498121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2401498121