Transport and settling of particles in the ocean and estuaries

海洋和河口颗粒的输送和沉降

• 批准号: RGPIN-2022-03291
• 负责人: Sutherland, Bruce
• 金额: $ 3.13万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=750913
• 关键词: Transport; settling; particles; ocean; estuaries

Of the municipal plastic waste which is released into rivers and the ocean and which is buoyant, at most 3% is observed to be floating on the ocean surface. To help predict where the missing waste is located, the proposed research aims to examine three mechanisms through which buoyant plastics are transported and ultimately settle to the river bottom or ocean floor. Recently we discovered that kaolin clay is electrically attracted to the buoyant plastic, pliolite, when in contact with salt water. Because clay is more dense than sea water, this suggests that, when plastics in a muddy river enter the ocean, the accumulation of clay on the plastics will cause them to settle predominantly in estuaries, deltas and near the coast. This proposed research stream aims to quantify the enhanced settling of plastics as it depends on the type and size of plastic, the type and relative concentration of clay, and the salinity of the water in which these particles are suspended. Most muddy rivers entering the ocean are less dense than sea water, and so they float over the surface as a so-called "hypopycnal current". Nonetheless the clay eventually descends through the water column. Although an individual particle of clay settles very slowly, when in contact with salt water, the clay together with microplastics gather into flocs that, can settle thousands of times faster than an individual particle. As these flocs accumulate at the base of the hypopycnal current, research suggests that the fluid-particle mixture becomes convectively unstable further enhancing the settling speed. This proposed research stream will use particle-resolving numerical simulations to examine clay-clay and clay-plastic flocculation with an aim to develop predictions for the enhanced settling speed. For floating plastics in the open ocean, they are dominantly transported by currents, gyre circulations and surface waves. The third proposed research stream will examine a different mechanism, whereby particles are transported by internal tides, which are similar to the surface tide except that they move due to the buoyancy between the relatively warm near-surface waters and the colder abyss. Recently we discovered that when the internal tide is generated near a coast and propagates out to sea, particles near the surface are driven back toward the coast. However, particularly in the tropics, the waves steepen and drive particles in the wave-ward direction - again toward a coast where they eventually break. This proposed research stream will develop predictions for the surface transport of plastics by steepening internal tides. Each proposed study concerningly suggests that microplastics settle predominantly in coastal waters.  This research will therefore be useful to a broad community including environmentalists, marine biologists and Fisheries and Oceans Canada, who may better assess where to find, monitor and clean up plastic pollution in such biologically productive regions.

被释放到河流和海洋且浮力的市政塑料废物中，观察到最多3％的是漂浮在海面上。为了帮助预测丢失的废物的位置，拟议的研究旨在检查三种机制，通过这些机制运输浮力，并最终定居在河底或海底。最近，我们发现高岭土被浮力的塑料Pliolite被电到电吸引，因为粘土比海水更密集，这表明，当泥泞的河中的塑料进入海洋时，塑料上粘土的积累会导致它们主要在埃斯托里亚里群岛，Deltas和海岸附近地沉降。该提出的研究流旨在量化塑料的增强沉降，因为它取决于塑料的类型和大小，粘土的类型和相对浓度以及这些颗粒所惊讶的水的盐度。大多数进入海洋的泥泞河流比海水密集，因此它们以所谓的“次频电流”的形式漂浮在地面上。但是，粘土最终通过水柱下降。尽管粘土的单个颗粒非常缓慢地沉降，但是在与盐水接触时，粘土和微塑料会聚集到泡沫中，这些粘土可以比单个粒子快数千倍。随着这些絮凝物积聚在次副群电流的底部，研究表明，流体粒子混合物变得方便地不稳定，进一步提高了设定速度。该提出的研究流将使用粒子分辨的数值模拟来检查粘土粘土和粘土塑料絮凝，旨在为增强的设置速度开发预测。为了在开阔的海洋中浮动塑料，它们主要由电流，回旋循环和表面波运输。第三个提出的研究流将检查一种不同的机制，从而通过内部潮汐运输颗粒，这与表面潮汐相似，除了它们是由于相对温暖的近地面水和较冷的深渊之间的繁殖而移动的。最近，我们发现，当内部潮汐在海岸附近产生并传播到海中时，地面附近的颗粒被驱动回海岸。但是，尤其是在热带地区，海浪沿波动方向驱动颗粒 - 再次朝着它们有时破裂的海岸。拟议的研究流将通过钢内潮汐来开发塑料表面运输的预测。每项提出的研究都涉及沿海水域中的微塑料主要定居。因此，这项研究对于包括环保主义者，海洋生物学家和渔业以及加拿大海洋在内的广泛社区将很有用，他们可以更好地评估在此类生物学生产性地区的何处，监测和清理塑料污染。